Langmuir Research Papers - Academia.edu (original) (raw)

The present study is focused on developing a nanoparticle carrier for the photosensitizer protoporphyrin IX for use in photodynamic therapy. The entrapment of protoporphyrin IX (Pp IX) in silica spheres was achieved by modification of Pp IX molecules with an organosilane reagent. The immobilized drug preserved its optical properties and the capacity to generate singlet oxygen, which was detected by a direct method from its characteristic phosphorescence decay curve at near-infrared and by a chemical method using 1,3-diphenylisobenzofuran to trap singlet oxygen. The lifetime of singlet oxygen when a suspension of Pp IX-loaded particles in acetonitrile was excited at 532 nm was determined as 52 µs, which is in good agreement with the value determined for methylene blue in acetonitrile solution under the same conditions. The Pp IX-loaded silica particles have an efficiency of singlet oxygen generation (η ∆) higher than the quantum yield of free porphyrins. This high efficiency of singlet oxygen generation was attributed to changes on the monomer-dimer equilibrium after photosentisizer immobilization.

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- Chemistry, Photochemistry, Nanoparticle, Nanoparticles

Polystyrene-b-poly(4-vinylpyridine) copolymers were quaternized with 1-bromohexane and 6-perfluorooctyl-1bromohexane. Surfaces prepared from these polymers were characterized by contact angle measurements, near-edge X-ray absorption fine structure spectroscopy and X-ray photoelectron spectroscopy. The fluorinated pyridinium surfaces showed enhanced antibacterial activity compared to their nonfluorinated counterparts. Even a polymer with a relatively low molecular weight pyridinium block showed high antimicrobial activity. The bactericidal effect was found to be related to the molecular composition and organization in the top 2-3 nm of the surface and increased with increasing hydrophilicity and pyridinium concentration of the surface.

- by Daniel Fischer and +1
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- Multidisciplinary, Block Copolymer, Escherichia coli, Antimicrobial activity
- by Hans-Peter Weikard
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- Risk Adjustment, Langmuir, sub-Saharan African Literature

Sum frequency generation (SFG) vibrational spectroscopy has been applied to investigate surface structures of an amphiphilic surface-active block copolymer (SABC) film deposited on a CaF 2 substrate, in air and in water in situ. Developed as a surface-active component of an antifouling coating for marine applications, this amphiphilic triblock copolymer contains both hydrophobic fluorinated alkyl groups as well as hydrophilic ethoxy groups. It was found that surface structures of the copolymer film in air and in water cannot be probed directly using the SFG experimental geometry we adopted because SFG signals can be contributed from the polymer/air (or polymer/water) interface as well as the buried polymer/CaF 2 substrate interface. Using polymer films with varied thicknesses, structural information about the polymer surfaces in air and in water can be deduced from the detected SFG signals. With SFG, surface restructuring of this polymer has been observed in water, especially the methyl and methylene groups change orientations upon contact with water. However, the hydrophobic fluoroalkyl group was present on the surface in both air and water, and we believe that it was held near the surface in water by its neighboring ethoxy groups.

- by Christopher Ober
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- Water, Vibrational Spectroscopy, Polymers, Vibration

The surface of a p-MoSe2 electrode has been observed in 0.05 M HNO3, in situ, by electrochemical scanning tunneling microscopy (ECSTM). Randomly oriented nanometer size spots have been observed on the surface. The STM images of the p-MoSe2 surface have been found to change with the electrode potential. That is, the nanometer size spots appeared as a dark contrast under a smaller band bending condition (0.2 V versus SCE) while the spots disappeared or further appeared as bright contrast under a larger band bending condition (0 and -0.2 V versus SCE). This is presumed to result from whether the acceptor level, within the band gap of the p-MoSe2, is occupied or not. In addition, it will depend on the electrode potential, which determines the amount of the band bending.

- by Carlos R. Cabrera
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- Multidisciplinary, Langmuir

Self-assembly of highly soluble water-stable tetramethyldisiloxane-based dimer of α,α′-dialkylquaterthiophene on the water−air interface was investigated by Langmuir, grazing incidence X-ray diffraction, and X-ray reflectivity techniques. The conditions for formation of very homogeneous crystalline monolayer Langmuir-Blodgett (LB) films of the oligomer were found. Monolayer organic field-effect transistors (OFETs) based on these LB films as a semiconducting layer showed hole mobilities up to 3 × 10 −3 cm 2 /(V s), on−off ratio of 10 5 , small hysteresis, and high long-term stability. The electrical performance of the LB films studied is close to that for the same material in the bulk or in the monolayer OFETs prepared from water vapor sensitive chlorosilyl derivatives of quaterthiophene by self-assembling from solution. These findings show high potential of disiloxane-based LB films in monolayer OFETs for large-area organic electronics.

- by Artem Bakirov
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- Multidisciplinary, Langmuir

The surface properties of a polydisperse poly(vinycaprolactam) (48 kDa) have been studied at the air/ water and hexane/water interfaces. Adsorption of the polymer at both interfaces shows substantial timedependent surface tension lowering at remarkably low concentrations in the aqueous phase. This adsorption is increased by addition of electrolyte, which also lowers the lower consolute temperature (LCT) of the polymer in solution. Adsorption is endothermic, corresponding with the approach to the LCT as the temperature is raised. Spreading of the polymer at the air/water interface from aqueous solutions is near quantitative. The surface pressure-area isotherms indicate extensive coiling in the monolayer at low pressures and looping of the polymer monolayer into the aqueous phase in the higher pressure range.

- by Brian A Pethica
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- Multidisciplinary, Langmuir

The self-assembly of the trifluoroacetate salt of the short peptide (ala) 6 -lys (A 6 K) in water has been investigated by cryo-transmission electron microscopy and small-angle X-ray scattering. For concentrations below ca. 12%, the peptide does not self-assemble but forms a molecularly dispersed solution. Above this critical concentration, however, A 6 K self-assembles into several-micrometer-long hollow nanotubes with a monodisperse crosssectional radius of 26 nm. Because the peptides carry a positive charge, the nanotubes are charge-stabilized. Because of the very large aspect ratio, the tubes form an ordered phase that presumably is nematic. (16) Knaapila, M.; Svensson, C.; Barauskas, J.; Zackrisson, M.; Nielsen, S. S.; Toft, K. N.; Vestergaard, B.; Arleth, L.; Olsson, U.; Pedersen, J. S.; Cerenius, Y.

- by Irem Nasir
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- Water, Microscopy, Small Angle X Ray Scattering, Self Assembly

Background: 1E10 monoclonal antibody is a murine anti-idiotypic antibody that mimics N-glycolyl-GM3 gangliosides. This antibody has been tested as an anti-idiotypic cancer vaccine, adjuvated in Al(OH) 3 , in several clinical trials for melanoma, breast, and lung cancer. During early clinical development this mAb was obtained in vivo from mice ascites fluid. Currently, the production process of 1E10 is being transferred from the in vivo to a bioreactor-based method.

- by Adolfo Castillo
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- Engineering, Thermodynamics, Organic Chemistry, Physical Chemistry

Lyotropic phases and their higher derivatives are known for their applications in various chemical, biotechnological, and medical fields. 1À9 They also resemble biological configurations like biomembranes, liposomes, and so forth and have important implications in their functioning. 10À17 The study concerning nanostructural parameters of lyotropic phases formed from different amphiphilic molecules is crucial in order to control the properties suitable for particular applications, as well as for understanding some of the complex biological processes for example, membrane fusion. 18À20 Amphiphilic molecules form type 1 (normal) or type 2 (inverse) phases based on their average molecular shape which can be cylindrical, conical, or wedge-like or their inverted forms 21À23 ). The mean curvature (H), which is simply a mean of two principal curvatures, is considered positive for normal micelles and negative for inverse types of micelles. Aforementioned molecular shapes then become a part of amphiphilic self-assemblies that display one-, two-, or threedimensional morphologies such as flat lamellae (lamellar phase), elongated tube (hexagonal phase), simple sphere (spherical micelles), and so forth to rather complex yet well-ordered geometries (cubic phases) and sometimes even disordered architectures (sponge phases). There are three commonly observed bicontinuous cubic phases, designated by corresponding space groups as Ia3d, Pn3m, and Im3m, which underlie G (gyroid), D (double diamond), and P (primitive) types of mathematical minimal surfaces, respectively. 26 These cubic phases mediate lamellar and hexagonal phases regarding average mean curvature values ) as well as the location in phase diagrams. The unit cell dimensions of lyotropic phases vary from ∼2.5 nm to ∼25.0 nm which themselves can be modulated by some percent by adding water or certain additives and/or by changing physical triggers such as temperature and pressure. 26 Due to their nanometer size range and adoption of intermediate properties between ordered solids and disordered liquids, the lyotropic phases are also called "liquid crystalline nanostructures". Further hierarchically ordered structures can be formed by kinetically stabilizing these nanostructures. 27À34 Amphiphilic molecules have rather diverse chemical structures and sources ranging from very complex biological molecules to simple natural and synthetic molecules including lipids and surfactants. Most common lipids have one or two C 10 -C 20 chains and one or more functional groups like ester, hydroxyl, or amino. Despite the structural simplicity, lipid molecules show fascinating polymorphism in aqueous environment. It is, therefore, possible to control the "phase" behavior and even their "nanostructural properties" by fine-tuning the chemical structure of lipid molecules. It was shown in a recent report that, by changing the

- by Chandrashekhar V Kulkarni
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- Water, Multidisciplinary, Nanostructures, Temperature

We developed strategies based on self-assembly principles to etch substrates patterned with monolayer resists with high selectivity and etch directionality. Our strategies exploit the defined composition and order of these ultrathin resists and overcome their imperfections. Defects in a monolayer can be healed by additives present in an etch bath. Alternatively, large molecules that cannot diffuse through defects can be employed as etchants. It is also possible to taper structures using the competition between etching and the side-growth of a self-assembling etch barrier, nucleating from the originally patterned monolayer. The application of these concepts lets defect-sensitive monolayers become robust and versatile resists, which should promote their acceptance and use in microtechnology.

- by A. Bietsch
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- Multidisciplinary, Langmuir

In this letter, we report the design and fabrication of different metal patterns for the realization of spatially controlled hydrophobic/hydrophilic regions with micrometer resolution. The fabrication procedure, based on a combination of lithographic techniques and wet-chemistry reactions (namely, spontaneous Galvanic displacement reactions) is reliable, undemanding, and highly versatile, allowing the achievement of precise spatial control along with the use of a wide variety of different materials. Jani, H.; Plessis, J. D.; Coloe, P. J.; Bhargava, S. K. Adv. Mater. 2008, 20, 717-723. (c) Liang, H. P.; Zhang, H. M.; Hu, J. S.; Guo, Y. G.; Wan, L. J.; Bai, C. L. Angew.

- by Loris Rizzello
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- Chemistry, Design, Water, Silicon

An atomic force microscope has been used to study the forces between a silica sphere in the colloidal size range and silica or mica flat surfaces as a function of distance of separation. At low ionic strength, independent electrokinetic measurements ( potentials) of both the spheres (by electrophoresis) and flat surfaces (by streaming potential) under the same conditions show excellent agreement with the diffuse double layer potentials derived from the force data using conventional DLVO theory. At higher ionic strength, the electrokinetically derived potentials were found to deviate from those derived from the fitted atomic force microscopy data, and a short range steric type repulsion was observed between the surfaces, the magnitude of which increased with decreasing pH.

- by Ian Larson
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- Multidisciplinary, Silica, Langmuir

In this work we discuss the oil chain length dependence of ternary DDAB microemulsions, comparing decane, dodecane, and tetradecane. With dodecane and shorter alkanes the L2 microemulsion phase extends to the oil corner, while with tetradecane the microemulsion phase forms an island in the center of the ternary phase diagram. We present new NMR self-diffusion and 14 N NMR relaxation data, where the three systems are compared at similar compositions. It is argued that the disconnection of the microemulsion phase from the oil corner with longer oils is associated with the Winsor II to Winsor III transition known from nonionic microemulsions. It follows that the tetradecane microemulsion has, in a major part, a monolayer rather than a bilayer structure.

- by Maura Monduzzi
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- Multidisciplinary, Langmuir

Microfluidic networks (µFNs) are passive (self-filling) devices incorporating microchannels for guiding minute volumes of fluids over surfaces. µFNs can be employed to localize the deposition of proteins from aqueous solutions onto substrates, for example. The walls of the channels must be hydrophilic for this purpose and should ideally resist the adsorption of proteins. We made µFNs using poly(dimethylsiloxane) (PDMS), Si/SiO2, and Au-covered Si and derivatized them with poly(ethylene glycol)s (PEGs) to fulfill both of these requirements. The grafting of the PEG molecules is optimized for either type of µFN: the networks from PDMS and silicon are derivatized using PEG-silanes and the Au-coated networks are derivatized with a thiolated PEG. Additionally, the zones of the Au-covered Si µFNs separating the channels are selectively covered with a hydrophobic thiol using microcontact printing. X-ray photoelectron spectroscopy and contact angle measurements indicate that all grafted layers have the expected chemical composition and are thin, homogeneous, and hydrophilic where desired. Finally, using fluorescently labeled antibodies we show that these µFNs are more effective for patterning, with high positional accuracy and edge resolution on PDMS substrates, than conventional O2-plasma-treated µFNs made from PDMS. Overall, our approach should help in making and using µFNs made from different materials but having similar surface properties.

- by David Juncker
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- Multidisciplinary, Polyethylene Glycol, Langmuir

Polydopamine (PDA) formed by the oxidation of dopamine is an important polymer, in particular, for coating various surfaces. It is composed of dihydroxyindole, indoledione, and dopamine units, which are assumed to be covalently linked. Although PDA has been applied in a manifold way, its structure is still under discussion. Similarities have been observed in melanins/eumelanins as naturally occurring, deeply colored polymer pigments derived from L-DOPA. Recently, an alternative structure was proposed for PDA wherein dihydroxyindoline, indolinedione, and eventually dopamine units are not covalently linked to each other but are held together by hydrogen bonding between oxygen atoms or π stacking. In this study, we show that this structural proposal is very unlikely to occur taking into account unambiguous results obtained by different analytical methods, among them 13 C CPPI MAS NMR (cross-polarization polarization−inversion magic angle spinning NMR), 1 H MAS NMR (magic angle spinning NMR), and ES-HRMS (electrospray ionization high-resolution mass spectrometry) for the first time in addition to XPS (X-ray photoelectron spectroscopy) and FTIR spectroscopy. The results give rise to a verified structural assignment of PDA wherein dihydroxyindole and indoledione units with different degrees of (un)saturation are covalently linked by C−C bonds between their benzene rings. Furthermore, proof of open-chain (dopamine) monomer units in PDA is provided. Advanced DFT calculations imply the arrangements of several PDA chains preferably by quinone−hydroquinone-type interactions in a parallel or antiparallel manner. From all of these results, a number of hypotheses published before could be experimentally supported or were found to be contradictory, thus leading to a better understanding of the PDA structure.

Nitrogen adsorption isotherms on organized mesoporous aluminas prepared by several different synthesis procedures were analyzed by means of comparative plot method using Aluminiumoxid C (Degussa) and R-alumina as reference adsorbents. To secure the high-resolution ability of this method, all the adsorption measurements were carefully performed in a relative pressure range from 10 -6 to 0.99. Although some samples of organized mesoporous alumina were treated at temperatures up to 1000°C, only the Aluminiumoxid C has proved to be suitable as a reference adsorbent. The comparative analysis of isotherms on activated aluminas has shown that this method allows the determination of very small amounts of microporosity. The standard nitrogen adsorption data for Aluminiumoxid C and R-alumina are presented in a tabulated form, which consists of 91 points for each adsorbent.

- by Jiri Rathousky
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- Multidisciplinary, Nitrogen, High Resolution, Langmuir

Squalene-based nucleolipids, including anticancer or antiviral prodrugs, gave rise to nanoparticles displaying a diversity of structures upon nanoprecipitation in water. Synchrotron small-angle X-ray scattering and cryo-TEM imaging revealed that both the nature of the nucleoside and the position of the squalene moiety relative to the nucleobase determined the self-assembly of the corresponding bioconjugates. It was found that small chemical differences resulted in major differences in the self-organization of nucleolipids when squalene was grafted onto the nucleobase whereas only lamellar phases were observed when squalene was linked to the sugar moiety. The key role of hydrogen bonds between nucleobases in the formation of the lamellar phases was suggested, in agreement with molecular simulations. These findings provide a way to fine tune the supramolecular organization of squalene-based prodrugs, with the aim of improving their pharmacological activity.

- by Claudie Bourgaux and +1
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- Molecular Dynamics Simulation, Nanoparticles, Multidisciplinary, Lipids

To determine the internal molecular arrangement of organic dye aggregates, a technique for observing the fluorescence microscope image of a solution consisting of dye aggregates in a magnetic field was developed. Using this technique, the fluorescence image of meso-tetrakis (4-sulfonatophenyl) porphine (TPPS) J-aggregates in a solution in a magnetic field of 10 T was observed. It was observed that individual rod-shaped TPPS aggregates (4-20 µm in length) were aligned parallel to the applied field. The polarized absorption spectra of the sample solution were also measured in the fields of up to 10 T. The spectra show the magnetic field dependence of the J-band intensity, reflecting the magnetic alignment of the aggregates. On the basis of the magnetic and optical properties obtained by the experiments, it was proposed that TPPS J-aggregates have a tube-like structure and are constructed from one-dimensional molecular arrays that are stacked parallel to the long axis of the tube.

- by Y. Kitahama
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- Multidisciplinary, Magnetic field, Langmuir

In a previous study, we established that the attraction between electrically charged particles attached to a water/tetradecane interface is stronger than predicted on the basis of the gravity-induced lateral capillary force. Here, our goal is to explain this effect. The investigated particles are hydrophobized glass spheres of radii between 240 and 320 μm. Their weight is large enough to deform the liquid interface. The interfacial deformation is considerably greater for charged particles because of the electrodipping force that pushes the particles toward the water phase. By independent experiments with particles placed between two electrodes, we confirmed the presence of electric charges at the particle/tetradecane interface. The theoretical analysis shows that if the distribution of these surface charges is isotropic, the meniscus produced by the particle electric field decays too fast with distance and cannot explain the experimental observations. However, if the surface-charge distribution is anisotropic, it induces a saddle-shaped deformation in the liquid interface around each particle. This deformation, which is equivalent to a capillary quadrupole, decays relatively slow. Its interference with the gravity-induced isotropic meniscus around the other particle gives rise to a longrange attractive capillary force, F ∼ 1/L 3 (L = interparticle distance). The obtained agreement between the experimental and theoretical curves, and the reasonable values of the parameters determined from the fits, indicate that the observed stronger attraction in the investigated system can be really explained as a hybrid interaction between gravity-induced "capillary charges" and electric-field-induced "capillary quadrupoles".

- by Krassimir Danov
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- Multidisciplinary, Langmuir, Electric Field

Cyclization of 2-(3-bromopropyloxy)phenoxide ion (PhBr7) in micelles is a model for SN2 reactions of nucleophilic anions at micelle-water interfaces. In this paper we report observed rate constants (kobs) in aqueous micelles of dimeric surfactants. kobs in 1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide (1) is constant in a range of concentration, then increases at high [1], suggesting a transition to a different type of aggregate. A 1 H NMR investigation confirms a phase transition at the [1] which corresponds to the reactivity change. (2S,3S)-2,3-Dimethoxy-1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide forms very large aggregates and shows a modest catalytic effect. Cyclization of 2-(12-bromododecyloxy)phenoxide ion (PhBr16) in 1 under preparative conditions yields the intramolecular cyclic product only despite a low effective molarity and a relative high substrate concentration. This result reveals the presence of a well-organized substrate-surfactant aggregate.

- by Luciana Luchetti and +1
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- Multidisciplinary, Langmuir
- by C. Calberg
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- Kinetics, Multidisciplinary, Surface Properties, Surface Active Agents

Prediction and optimization of liquid propagation rates in micropillar arrays are important for various lab-on-a-chip, biomedical, and thermal management applications. In this work, a semianalytical model based on the balance between capillary pressure and viscous resistance was developed to predict liquid propagation rates in micropillar arrays with height-to-period ratios greater than 1 and diameter-to-period ratios less than 0.57. These geometries represent the most useful regimes for practical applications requiring large propagation rates. The capillary pressure was obtained using an energy approach where the meniscus shape was predicted using Surface Evolver simulations and experimentally verified by interference microscopy. The combined viscous resistance of the pillars and the substrate was determined using Brinkman's equation with a numerically obtained permeability and corroborated with finite element simulations. The model shows excellent agreement with one-dimensional propagation experiments of deionized water in silicon micropillar arrays, highlighting the importance of accurately capturing the details of the meniscus shape and the viscous losses. Furthermore, an effective propagation coefficient was obtained through dimensionless analysis that is functionally dependent only on the micropillar geometry. The work offers design guidelines to obtain optimal liquid propagation rates on micropillar surfaces.

- by Ryan Enright
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- Scanning Electron Microscopy, Multidisciplinary, Viscosity, Theoretical Models

Alkylsilane self-assembled monolayers (SAMs) on oxide substrates are commonly used as liquid crystal (LC) alignment layers. We have studied the effects of alkyl chain length, photolytic degradation, and mechanical rubbing on polar and azimuthal LC anchoring. Both gradient surfaces (fabricated using photolytic degradation of C18 SAMs) and unirradiated SAMs composed of short alkyl chains show abrupt transitions from homeotropic to tilted alignment as a function of degradation or chain length. In both cases, the transition from homeotropic to tilted anchoring corresponds to increasing wettability of the SAM surfaces. However, there is an offset in the critical contact angle for the transition on gradient vs unirradiated SAMs, suggesting that layer thickness is more relevant than wettability for LC alignment. Mechanical rubbing can induce azimuthal alignment along the rubbing direction for alignment layers sufficiently near the homeotropic-to-planar transition. Notably, mechanical rubbing causes a small but significant shift in the homeotropic-to-tilted transition, e.g., unrubbed C5 SAMs induce homeotropic anchoring, but the same surface after rubbing induces LC pretilt.

- by Daniel Schwartz
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- Multidisciplinary, Langmuir, Self Assembled Monolayer

We simulate evaporation-driven self-assembly of colloidal crystals using an equivalent network model. Relationships between a regular hexagonally close-packed array of hard, monodisperse spheres, the associated pore space, and selectivity mechanisms for face-centered cubic microstructure propagation are described. By accounting for contact line rearrangement and evaporation at a series of exposed menisci, the equivalent network model describes creeping flow of solvent into and through a rigid colloidal crystal. Observations concerning colloidal crystal growth are interpreted in terms of the convective steering hypothesis, which posits that solvent flow into and through the pore space of the crystal may play a major role in colloidal self-assembly. Aspects of the convective steering and deposition of high-Peclet-number rigid spherical particles at a crystal boundary are inferred from spatially resolved solvent flow into the crystal. Gradients in local flow through boundary channels were predicted due to the channels' spatial distribution relative to a pinned free surface contact line. On the basis of a uniform solvent and particle flux as the criterion for stability of a particular growth plane, these network simulations suggest the stability of a declining {311} crystal interface, a symmetry plane which exclusively propagates fcc microstructure. Network simulations of alternate crystal planes suggest preferential growth front evolution to the declining {311} interface, in consistent agreement with the proposed stability mechanism for preferential fcc microstructure propagation in convective assembly.

- by Juan M . Desantos
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- Crystal Growth, Multidisciplinary, Langmuir

Silicon surface was chemically modified by covalent attachment of homologous organic molecules having different dipole moments. Surface photovoltage measurements clearly confirm that organic molecules have a profound effect on surface band bending of semiconductor. Metal-molecules-silicon junctions were constituted for molecules belonging to ethynylbenzene series using soft mercury contact. These junctions show a systematic change in the electrical charge transport with dipole moment of molecules. Parameters such as ideality factor, barrier height, and density of interface states of various junctions are estimated to understand the role of organic molecules. These studies offer the prospect to develop molecular electronics, which may find potential applications in solar cells and chemical and biological sensors.

- by Basavaraj Mulimani
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- Multidisciplinary, Langmuir

We review recent developments in our group regarding the solution-phase synthesis of one-dimensional nanostructures of metals. The synthetic approaches include solution-liquid-solid growth for nanowires of low-melting-point metals such as Pb; seed-directed growth for Ag nanowires, nanobeams, and nanobelts; kinetically controlled growth for Pt nanorods, nanowires, and multipods; and galvanic replacement for nanotubes of Au, Pt, and Pd. Both characterization and mechanistic studies are presented for each nanostructure. Finally, we highlight the electrical and plasmonic properties of these metal nanostructures and discuss their potential applications in nanoscale devices. (1) Xia, Y.; Yang, P.; Sun, Y.; Wu, Y.; Mayers, B.; Gates, B.; Yin, Y.; Kim, F.; Yan, H. Alekseeva, A. V.; Bogatyrev, V. A.; Dykman, L. A.; Khlebtsov, B. N.; Trachuk, L. A.; Melnikov, A. G.; Khlebtsov, N.

- by Jingyi Chen
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- Kinetics, Nanotechnology, Multidisciplinary, Nanowires
- by Johannes Walter
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- Multidisciplinary, Langmuir

The interaction of pyridine with acidic H-ZSM5, H-, and H-MORD zeolites and a perfluorosulfonic superacidic membrane (H-Nafion) has allowed us to study the IR spectrum of PyH + hydrogen bonded to the negative zeolite skeleton (Z -) or to CF2SO3 -groups of the membrane. In the presence of excess Py the formation of PyH + ‚‚‚Py is also detected. On H-MORD (a zeolite with higher Al content) the adsorption of Py at room temperature is limited to the external surfaces of the crystallite, owing to the blockage of channel mouths caused by the PyH + formed in high concentration. The IR spectra of hydrogen-bonded PyH + in the ν(NH‚‚‚) stretching region are strongly influenced by Fermi resonance effects with the overtones and combinations of low-frequency modes. In the H-Nafion/Py system the modification induced by the proton transfer on the internal modes of the -SO3H groups (with formation of SO3 -species) gives additional information on the proton transfer process. To complete the assignment of all the observed surface species (including the weakly adsorbed ones) the interaction of Py with silicalite (a purely siliceous zeolite with a pentasilic structure) has also been investigated.

- by Carlo Lamberti
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- Multidisciplinary, Langmuir

Illumination of TiO 2 thin films with UV light is known to induce the transformation of the surface of this material from partially hydrophobic into fully hydrophilic. The present work shows that this transformation is accompanied by other effects that may be used to control the synthesis of composite materials. For this purpose, TiO 2 and Ta 2 O 5 transparent thin films with a columnar structure and open pores were prepared by electron evaporation at glancing angles. Transparent TiO 2 thin films with micropores (i.e., pores smaller than 2 nm) prepared by plasma enhanced chemical vapor deposition (PECVD) were also used. All these films became hydrophilic upon UV illumination. Rhodamine 6G and Rhodamine 800 dyes were irreversibly adsorbed within the columns of the TiO 2 and Ta 2 O 5 thin films by immersion into a water solution of these molecules. Isolated and aggregated molecules of these two dyes were detected by visible absorption spectroscopy. The infiltration adsorption efficiency was directly correlated with the acidity of the medium, increasing at basic pHs as expected from simple considerations based on the concepts of the point of zero charge (PZC) in colloidal oxides. The infiltration experiments were repeated with columnar TiO 2 and Ta 2 O 5 thin films that were subjected to preillumination with UV light. It was found that this treatment produced a modification in the type (isolated or aggregated) and amount of dye molecules incorporated into the pores. Moreover, the selective adsorption of a given dye in preilluminated areas of the films permitted the lithographic coloring of the films. Preillumination also controls the UV induced deposition of silver on the surface of the microporous TiO 2 thin films. It was found that the size distribution of the formed silver nanoparticles was dependent on the preillumination treatment and that a well-resolved surface plasmon resonance at around 500 nm was only monitored in the preilluminated films. A model is proposed to account for the effects induced by UV preillumination on the TiO 2 and Ta 2 O 5 oxide surfaces. The possibilities of this type of light treatment for the tailored synthesis of nanocomposite thin films (i.e., dye-oxide, metal nanoparticles-oxide) are highlighted. Langmuir 2008, 24, 9460-9469

- by Ana Borras and +1
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- Multidisciplinary, Thin Film, Composite Material, Langmuir

We present a study on the hydrophobization of spin-on Silicalite-1 zeolite films through silylation with trimethylchlorosilane. Microporous and micro-mesoporous Silicalite-1 films were synthesized by spin coating of suspensions of Silicalite-1 nanozeolite crystallized for different times. Ellipsometric porosimetry with toluene and water adsorbates reveals that silylation decreases the porosity and makes the films hydrophobic. The decrease in porosity depends on the exposed surface area in the pores. Water contact angle measurements confirm the hydrophobicity. Fourier transform infrared spectroscopy reveals that the trimethylsilyl groups are chemisorbed selectively on isolated silanols and less on geminal and vicinal silanols due to steric limitations. Time-of-flight secondary-ion mass spectroscopy and in situ ellipsometry analysis of the reaction kinetics show that the silylation is a bulk process occurring in the absence of diffusion limitation. Electrical current leakage on films decreases upon silylation. Silylation with trimethylchlorosilane is shown to be an effective hydrophobization method for spin-on Silicalite-1 zeolite films.

- by F. Iacopi
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- Multidisciplinary, Langmuir

By combining quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR), the organic mass, water content, and corresponding protein film structure of fibrinogen adsorbed to acrylic polymeric substrates with varying polymer chain flexibility was investigated. Albumin and immunoglobulin G were included as reference proteins. For fibrinogen, the QCM-D model resulted in decreased adsorbed mass with increased polymer chain flexibility. This stands in contrast to the SPR model, in which the adsorbed mass increased with increased polymer chain flexibility. As the QCM-D model includes the hydrodynamically coupled water, we propose that on the nonflexible polymer significant protein conformational change with water incorporation in the protein film takes place. Fibrinogen maintained a more native conformation on the flexible polymer, probably due to polymer chain rearrangement rather than protein conformational change. In comparison with immunoglobulin G and albumin, polymer chain flexibility had only minor impact on adsorbed mass and protein structure. Understanding the adsorption and corresponding conformational change of a protein together with the mutual rearrangement of the polymer chain upon adsorption not only has implications in biomaterial science but could also increase the efficacy of molecular imprinted polymers (MIPs).

- by Hans Elwing
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- Multidisciplinary, Adsorption, Fibrinogen, Quartz

Enhancements of the molecular signals are known to occur in the mid-IR region when the molecules are in close proximity to rough metal surfaces. This phenomenon, known as surface enhanced infrared absorption (SEIRA), is complementary to surface enhanced Raman scattering (SERS) and can be used for biochemical sensing. However, designing substrates for SEIRA that are resonant in the mid-IR has

- by Janardan Kundu
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- Engineering, Analytical Chemistry, Technology, Membrane Proteins

Molecular dynamics simulations of monolayers of surfactant mixtures at the air/water interface were performed where the binary mixture was composed of sodium dodecyl sulfate (SDS) and dodecanol molecules. At the same ratio of SDS and dodecanol molecules, two monolayer mixtures were prepared. In the first monolayer, all the dodecanol molecules were placed together in the center of the simulation box, whereas in the second monolayer, those molecules were uniformly distributed in the surface area in such a way that they were far from each other. Simulations of both systems indicate that the dodecanol tails in the first monolayer are straighter and more ordered than those in the second monolayer. From the present results, we observed new insights of how the different molecules should array or distribute at the interface in real systems. Finally, studies of the interfacial water around the different surfactants were also analyzed, showing that they are closer to the polar headgroups of dodecanol than to the SDS headgroups.

- by Hector Dominguez
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- Multidisciplinary, Computer Simulation, Langmuir

Bimolecular self-assembled monolayers (SAMs) of aromatic and aliphatic chlorosilanes were self-assembled onto silica, and their characteristics were established by contact angle measurement, near-edge X-ray absorption fine structure spectroscopy, and Fourier transform infrared spectroscopy. Three aromatic constituents (phenyltrichlorosilane, benzyltrichlorosilane, and phenethyltrichlorosilane) were studied in combination with four aliphatic coadsorbates (butyltrichlorosilane, butyldimethylchlorosilane, octadecyltrichlorosilane, and octadecyldimethylchlorosilane). Our results demonstrate that whereas SAMs made of trichlorinated organosilanes are densely packed, SAMs prepared from monochlorinated species are less dense and poorly ordered. In mixed systems, trichlorinated aromatics and trichlorinated aliphatics formed SAMs with highly tunable compositions; their surfaces were compositionally homogeneous with no large-scale domain separation. The homogeneous nature of the resulting SAM was a consequence of the formation of in-plane siloxane linkages among neighboring molecules. In contrast, when mixing monochlorinated aliphatics with trichlorinated aromatics, molecular segregation occurred. Although the two shortest aromatic species did not display significant changes in orientation upon mixing with aliphatics, the aromatic species with the longest polymethylene spacer, phenethyltrichlorosilane, displayed markedly different orientation behavior in mixtures of short-and longchain aliphatics.

- by Kirill Efimenko
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- Multidisciplinary, Silica, Contact angle, Fourier transform infrared spectroscopy

A label-free biosensor based on antiapolipoprotein B 100 functionalized-aminated reduced graphene oxide interface has been fabricated for detection of low density lipoprotein (LDL or lipid) cholesterol. The aminated reduced graphene oxide (NH 2 -rGO) based electrode surface is covalently functionalized with antiapolipoprotein B 100 (AAB or lipid) using EDC/NHS coupling chemistry. The lipid−lipid interactions at the NH 2 -rGO electrode surface have been investigated using electrochemical impedance spectroscopic technique. The structural and morphological investigations of NH 2 -rGO based immunosensor have been accomplished via transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, UV−visible, and electrochemical techniques. The impedimetric response of the proposed immunosensor shows excellent sensitivity (612 Ω mg −1 dL cm −2 ), a response time of 250 s, and a low detection limit of 5 mg/dL of LDL molecules. The association, dissociation, and equilibrium rate constants for this immunoelectrode are found to be 1.66 M −1 s −1 , 0.6 s −1 , and 2.77 M −1 , respectively. The long-term stability and excellent reproducibility of the proposed immunosensor indicates a suitable platform for detection of LDL or lipid molecules. This immunosensor provides an efficient platform for analysis of the antigen−antibody interactions of lipid molecules.

- by Renu John
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- Multidisciplinary, Lipids, Graphite, Surface Properties

O conhecimento do fator capacidade de P (FCP) dos solos do Estado da Paraíba é importante para tornar mais eficiente a interpretação do teor de P disponível e a recomendação de adubação fosfatada em solos desse Estado. Os objetivos deste trabalho foram avaliar os parâmetros das isotermas de adsorção de P (Langmuir e Freundlich), por meio das técnicas de regressão não linear e de linearização, em amostras de solos do Estado da Paraíba, e verificar a correlação dos valores desses parâmetros com características químicas e físicas desses solos. Foram coletadas amostras de doze solos na camada de 0-30 cm de profundidade, sendo seis solos mais intemperizados e seis menos intemperizados, de modo a ter ampla variação de valores de características físicas e químicas de cada grupo de solos. O modelo hiperbólico da isoterma de Langmuir foi ajustado por meio da técnica de regressão não linear (região única) e por meio da técnica de linearização (região única e segunda região). Foram realizadas análises de correlação entre os valores dos parâmetros das isotermas e características do solo que refletem o FCP. Em todos os solos, o modelo ajustado por meio da técnica de regressão não linear apresentou melhor ajuste aos dados observados, em comparação ao mesmo modelo ajustado por meio da técnica de linearização. No grupo de solos mais intemperizados, os valores de capacidade máxima de adsorção de fosfato (CMAP) apresentaram correlação elevada com os valores de P remanescente (r = -0,95**), teor de oxihidróxidos de Fe (r = 0,90**) e equivalente de umidade (r = 0,88**), mas não se correlacionaram com o teor de argila (r = 0,64ns). Dentro do grupo de solos menos intemperizados, os valores de CMAP correlacionaram-se com os valores de P remanescente (r = -0,99**), equivalente de umidade (r = 0,93**) e teor de argila (r = 0,97**), mas não se correlacionaram com o teor de oxi-hidróxidos de Fe livre (r = 0,10ns).

- by Djail Santos
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- Langmuir

This paper reports the synthesis, optical, and thin-film-forming properties of a new water-soluble poly-(phenylene ethynylene) that features phosphonate solubilizing groups. The new polymer, PPE-PO3 -, is prepared by a synthetic route that involves initial preparation of a neutral analogue polymer in which the phosphonate groups are in the form of dibutyl esters. The neutral polymer is converted to the water-soluble form by cleavage of the phosphonate ester groups using (CH 3)3SiBr. PPE-PO3absorbs in the blue of the visible region and features a moderately intense fluorescence. The absorption and fluorescence of the polymer vary strongly with pH, an effect which is believed to arise because the polymer exists in a strongly aggregated form at low pH and in a relatively unaggregated state at high pH. Ultrathin multilayer films of the PPE-PO 3are deposited by the layer-by-layer (LbL) method using either the cationic polyelectrolyte poly(diallyldimethylamine) or Zr(IV) as deposition "partners". Absorption spectroscopy indicates that the average bilayer thickness of the LbL films increases as the pH of the deposition solution decreases. This effect is believed to be due in part to the fact that the R-PO 3groups are partially neutralized at low pH; however, aggregation of the polymer in solution is also believed to contribute to the increase in the amount of polymer deposited at low pH. The fluorescence of PPE-PO 3is quenched very strongly in solution by cationic electron and energy acceptors, with Stern-Volmer quenching constants of ≈10 7 M -1 . Finally, an electroluminescent device was fabricated using a 10 bilayer film consisting of PPE-PO3 -/Zr(IV). The device turns on between 5 and 6 V and exhibits a yellow-orange emission.

- by Mauricio Pinto
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- Multidisciplinary, Layer by Layer, Water soluble polymers, Langmuir

A method to quantitatively determine the spontaneity (S) of the spontaneous emulsification process using a laser diffraction particle size analysis technique is presented. The method was experimentally tested by studying the rate of increase of the specific interfacial area (cm 2 mL -1 s -1 ) and the equilibrium specific interfacial area for different systems formed by the surfactant Brij30 dissolved in linear alkyl oils (C8-C16) when brought in contact with ultrapure water. The experimental results confirmed the effectiveness of the proposed method, and they also suggest that the oil chain length of the linear alkyl oils has an important effect on the driving force of the spontaneous emulsification process in these systems. Finally, a molecular spontaneous emulsification mechanism is proposed for the systems studied.

- by Carlos Lopez Morales
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- Multidisciplinary, Langmuir

Reductive energy generated at a TiO2 photocatalyst under UV light can be stored in WO3 by coupling them together, and the stored energy can be used after dark. However, the reduction of WO3 requires cation intercalation for charge neutralization. Thus, behavior of the TiO2-WO3 composite on an ITO electrode was examined in nonelectrolytic media. When the TiO2 and WO3 were close to each other (less than 1 mm), WO3 could be reduced even in pure water or humid air (relative humidity g25%), by irradiating the composite with UV light. In dry air, WO3 was not reduced efficiently, even if the TiO2 and WO3 nanoparticles were mixed well. These results suggest that protons generated at the TiO2 surface as a result of photocatalytic oxidation of water are intercalated into WO3, and therefore ionic conductivity of the medium or the composite film surface is important. The composite film charged in air exhibited almost the same electrode potential as that of the film charged in aqueous NaCl. . Changes in the potential of an ITO electrode coated with the TiO2-WO3 composite film (type b, thin film) after irradiated with UV light (10 mW cm -2 , 1 h) in a 3 wt % aqueous solution (pH 5) or air (relative humidity, 50%).

- by Pailin Ngaotrakanwiwat
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- Multidisciplinary, Energy Storage, Langmuir

Figure 3. (a) Microscopic image (objective 20×) of a monolayer of 2.4 µm sterically stabilized PS particles. (b) Microscopic image (objective 100×) of a monolayer of 1.4 µm PS-EPMA core-shell particles transferred by the Langmuir-Schaefer technique. Corresponding diffraction images with Bertrand lens (right insert) and 2D-FFT transformation (left insert, 512 × 512 pixels) are shown.

- by Leonid Goldenberg and +1
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- Multidisciplinary, Langmuir

To clarify the structure and species of rhodamine 6G (R6G) aggregates formed in taeniolite (TN) interlayer spaces, the oriented thin films of R6G-TN hybrid materials were prepared and analyzed. XRD investigations of these films indicated that the R6G molecules were intercalated in the TN interlayers and that the TN layers were parallel to the glass plate in the thin films. Most of the intercalated R6G molecules were assumed to form various kinds of H-type aggregates in the TN interlayer spaces, since the R6G-TN hybrid films exhibited no emission spectrum by excitation at λ ) 530 nm. The peak-deconvolution results of the UV/vis absorption spectra of the hybrid films indicated that there was one kind of H-type R6G dimer in the thin film. Moreover, polarized UV/vis spectroscopy revealed the existence of high-order aggregates in addition to these dimers. The high-order aggregates, but not the dimers, were found to be aligned perpendicularly to the TN surface in the TN interlayer spaces.

- by Hideaki Itoh
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- Multidisciplinary, Thin Film, Langmuir

Three dissymmetric gemini surfactants (abbreviated as 12-s-14) in which n-dodecyldimethylammonium bromide and n-tetradecyldimethylammonium bromide are connected at the polar headgroups by a flexible -(CH2)s-spacer (s ) 2, 6, or 10) have been synthesized. The influence of the spacer length on the structural and thermal properties of 12-s-14 surfactants was investigated by means of IR and NMR spectral analysis, X-ray diffraction, thermogravimetry, differential scanning calorimetry, and polarizing optical microscopy. Geminis with s ) 2 or 10 form monolayers in which two alkyl chains are in the trans configuration, while the gemini with s ) 6 forms interdigitated bilayers with two alkyl chains in the cis configuration with respect to the spacer. All compounds exhibited a complex polymorphism and thermotropic mesomorphism from the stable crystalline form to the liquid crystalline phases of smectic type. The number of thermal phase transitions and the sequence of phases are markedly affected by the spacer length; that is, they depend on the configuration of the two alkyl chains with respect to the spacer. . The X-ray diffraction patterns of the 12-6-14 surfactant taken at different temperatures upon heating and cooling to room temperature. The temperatures are indicated.

- by Irina Pucic
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- Multidisciplinary, Phase transition, Langmuir

In 1976, B. J. Carroll derived the equation to show that a symmetric liquid droplet sitting on a thin cylindrical fiber would acquire a bell shape at equilibrium. We have extended his derivation to describe a drop located at the top end of a vertical, cylindrical fiber. By minimizing the Gibbs free energy of the drop at the fiber tip, it was found that the drop consists of two portions, a spherical cap on the fiber tip and a full, symmetrical bell located on the fiber body adjacent to the fiber tip. The experimental verification of the predicted shapes was performed using water, ethylene glycol, and Kaydol drops on nylon cylindrical fibers. Only four parameters are required to obtain agreement between the theoretical shape and the observed shape: the drop volume, the fiber radius, the surface tension of the liquid, and the Young contact angle of the liquid on a flat surface of the same composition as the fiber.

- by Stephen Michielsen
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- Water, Multidisciplinary, Composition, Fiber

Small-angle neutron scattering (SANS) was used to investigate the interparticle interactions in concentrated dispersions of colloidal silica stabilized either by steric or by electrostatic repulsive interactions. In 10 mM NaCl, an adsorbed PEO layer is required to prevent flocculation, and particles are stabilized by steric repulsions. The adsorbed layer was made invisible to neutrons by contrast matching with the aqueous continuous phase. Dispersions of the same particles at the same concentrations but in the absence of added salt and adsorbed PEO were also studied. In both cases, the SANS spectra of concentrated dispersions show a peak at low Q, which is due to interparticle interactions: a structure factor. The SANS data can be described rather well by a homogeneous spherical form factor and a structure factor based on the Hayter-Penfold/Yukawa potential model. The steric potential was compared to the electrostatic potential obtained by fitting the SANS data of the bare silica dispersions. The steric potential shows a greater dependence on the particle volume fraction, which we ascribe to the penetration and compression of the adsorbed PEO layer as the particles approach.

- by Terence Cosgrove
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- Multidisciplinary, Langmuir, Small Angle Neutron Scattering

We report the design and characterization of a microfluidic hydrogen fuel cell with a flowing sulfuric acid solution instead of a Nafion membrane as the electrolyte. We studied the effect of cell resistance, hydrogen and oxygen flow rates, and electrolyte flow rate on fuel cell performance to obtain a maximum power density of 191 mW/cm 2 . This flowing electrolyte design avoids water management issues, including cathode flooding and anode dry out. Placing a reference electrode in the outlet stream allows for independent analysis of the polarization losses on the anode and the cathode, thereby creating an elegant catalyst characterization and optimization tool.

- by Larry Markoski
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- Multidisciplinary, Langmuir

2 H NMR was used to study the nature of deuterated water in kanemite. Evidence is presented that shows that the water changes state from liquid to solid at room temperature during the hydration reaction that forms kanemite. The deuterium nuclei in the water experience rapid tetrahedral jumps in a hydrogenbonded lattice like those observed in 2 H2O ice.

- by Alan Benesi
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- Multidisciplinary, Room Temperature, Langmuir

This work shows that after creating certain dual scale roughness structures by femtosecond laser irradiation different metal alloys initially show superhydrophilic behavior with complete wetting of the structured surface. However, over time, these surfaces become nearly superhydrophobic with contact angles in the vicinity of 150°a nd superhydrophobic with contact angles above 150°. The contact angle hysteresis was found to lie between 2 and 6°. The change in wetting behavior correlates with the amount of carbon on the structured surface. The explanation for the time dependency of the surface wettability lies in the combined effect of surface morphology and surface chemistry.

- by Peter Englezos
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- Multidisciplinary, Langmuir

Chemotaxis is defined as the self-generated displacement of motile microbes in the direction of an increasing concentration gradient of a chemoattractant or a decreasing concentration gradient of a chemorepellent. This work presents a Monte Carlo computer simulation of the chemotactic response in porous media. The model is based on the idealized Happel cell model underlying the colloid filtration theory (CFT), which describes the physical and chemical forces acting on an inert particle in flow through porous media. The premise of the model presented here is that bacterial chemotaxis in porous media can be successfully modeled by integrating cellular dynamics simulations with CFT particle trajectory analysis. At each time step a stochastic algorithm chooses a chemotactic velocity to be superimposed onto the deterministic velocity obtained by analytical solution for Stokes flow around the Happel sphere. The model calculates a value for the collection efficiency (the fundamental CFT parameter η) with the effects of chemotaxis incorporated. The collection efficiency is defined as the fraction of particles approaching the Happel sphere, termed the collector, that actually collides with the collector. CFT has been used extensively for the modeling of particle deposition in water treatment processes and, more recently, bacterial transport in groundwater. However, there has been little rigorous examination of the theory since it was developed in the mid-1970s. Thus, in addition to the treatment of chemotaxis, this paper provides an analysis of the theoretical underpinnings of CFT. Preliminary results suggest that chemotaxis may significantly affect η under certain conditions. 10.

- by Kirk Nelson
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- Bacterial Chemotaxis, Multidisciplinary, Porous Media, Langmuir

We demonstrate that interferometric lithography provides a fast, simple approach to the production of patterns in self-assembled monolayers (SAMs) with high resolution over square centimeter areas. As a proof of principle, two-beam interference patterns, formed using light from a frequency-doubled argon ion laser (244 nm), were used to pattern methyl-terminated SAMs on gold, facilitating the introduction of hydroxyl-terminated adsorbates and yielding patterns of surface free energy with a pitch of ca. 200 nm. The photopatterning of SAMs on Pd has been demonstrated for the first time, with interferometric exposure yielding patterns of surface free energy with similar features sizes to those obtained on gold. Gold nanostructures were formed by exposing SAMs to UV interference patterns and then immersing the samples in an ethanolic solution of mercaptoethylamine, which etched the metal substrate in exposed areas while unoxidized thiols acted as a resist and protected the metal from dissolution. Macroscopically extended gold nanowires were fabricated using single exposures and arrays of 66 nm gold dots at 180 nm centers were formed using orthogonal exposures in a fast, simple process. Exposure of oligo(ethylene glycol)-terminated SAMs to UV light caused photodegradation of the protein-resistant tail groups in a substrate-independent process. In contrast to many protein patterning methods, which utilize multiple steps to control surface binding, this single step process introduced aldehyde functional groups to the SAM surface at exposures as low as 0.3 J cm -2 , significantly less than the exposure required for oxidation of the thiol headgroup. Although interferometric methods rely upon a continuous gradient of exposure, it was possible to fabricate well-defined protein nanostructures by the introduction of aldheyde groups and removal of protein resistance in nanoscopic regions. Macroscopically extended, nanostructured assemblies of streptavidin were formed. Retention of functionality in the patterned materials was demonstrated by binding of biotinylated proteins.

- by Getachew Tizazu
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- Photochemistry, Self Assembly, Multidisciplinary, Gradient