F. Rondelez - Academia.edu (original) (raw)

Papers by F. Rondelez

Physical Review A, 1992

We present a quantitative study of the two-dimensional dendritic growth of liquid-condensed domai... more We present a quantitative study of the two-dimensional dendritic growth of liquid-condensed domains observed by fluorescence microscopy in Langmuir monolayers of 0-myristoyl alanine. The geometrical analysis of the dendrite tip region shows that the predicted relationship p2V/doD const (V is the tip growth velocity, p the tip curvature radius, do the capillary length, and D the diffusion coefficient) is reasonably verified. The determination of this constant yields an estimate of the line tension anisotropy.

Physica B: Condensed Matter, 1996

Using specular neutron reflectivity, we have measured the structure of tethered polymer layers im... more Using specular neutron reflectivity, we have measured the structure of tethered polymer layers immersed in a solution of mobile chains of the same chemical composition. The tethered polymer layer is a stable Langmuir film of a diblock copolymer spread on the air-liquid interface of a selective solvent. Due to the restricted conformational freedom of the grafted chain, a depletion layer at the grafting surface is expected. In our system, this depletion zone is enhanced and thus observable experimentally due to a repulsion between the polymer and the surface. The structure of the tethered layer is adequately described by a parabolic profile followed by an exponential tail, with a depletion layer at the surface. In the presence of mobile chains in solution, the grafted polymer layer is compressed: the thickness decreases and the monomer volume fraction increases. This compression may result from a re-equilibration of the osmotic pressure of the polymer layer, or from a screening of the monomer excluded volume interaction due to penetration of the mobile chains into the grafted layer. In this paper, we present our experimental data on the effects of mobile polymer concentration and chain length on the structure of the tethered chain. From these data, we construct a phase diagram to identify the regions of interpenetration of the mobile chains into the grafted layer.

Physical Review E, 1993

We report observations of chain stretching in diblock copolymer monolayers on the surface of a se... more We report observations of chain stretching in diblock copolymer monolayers on the surface of a selective solvent. Using neutron reflectivity, we have studied the concentration profile of the submerged block over a large range of surface density 0. (chains per area) for two different molecular weights. The observed i.ncrease in the layer thickness is weaker than the o' prediction of mean-field and scaling theories for the limiting behavior, but is in agreement with recent numerical self-consistent-field calculations by Whitmore and Noolandi [Macromolecules 23, 3321 (1990)].

Physical Review Letters, 2003

We have measured the shear viscosity in the liquid phase of several Langmuir monolayers with an a... more We have measured the shear viscosity in the liquid phase of several Langmuir monolayers with an accuracy better than 30%. The method is based on the optical monitoring of the Brownian diffusion of submicron latex spheres floating at the air-water interface. The values are between 1 and 11 10 ÿ10 N s m ÿ1 , which is 10 to 100 times lower than previous data on similar systems. For N-palmitoyl-6-n-penicillanic acid and L-dipalmitoylphosphatidylcholine, the variation of the shear viscosity with surface density agrees with a classical free area model, whereas for pentadecanoic acid we observe a compensation effect.

Plasma Processes and Polymers, 2004

... 4 P. Favia, R. d'Agostino, F. Palumbo, J. Phys. IV 1997, 7, 199. ... 12 H. Schönherr, MT... more ... 4 P. Favia, R. d'Agostino, F. Palumbo, J. Phys. IV 1997, 7, 199. ... 12 H. Schönherr, MT van Os, R. Förch, RB Timmons, W. Knoll, GJ Vancso, Chem. Mater. 2000, 12, 3689. ...

Physical Review Letters, 1995

We have monitored spontaneous chiral segregation in Langmuir films of a racemic mixture of D and ... more We have monitored spontaneous chiral segregation in Langmuir films of a racemic mixture of D and I. myristoyl-alanine. Following monolayer deposition, we observe first a strong chiral discrimination, followed at longer times by a spatial segregation between D and L domains. Evidence for discrimination has been obtained by surface pressure/area per molecule measurements, whereas segregation is inferred from optical observations using epifluorescence microscopy and from an analysis of the lattice symmetry using x-ray diffraction.

Faraday Discussions, 1994

Neutron reflectivity has been used to characterize the structure of a tethered polymer layer in c... more Neutron reflectivity has been used to characterize the structure of a tethered polymer layer in contact with a solution of mobile polymer chains. The tethered polymer layer is a stable Langmuir film of block copolymer spread on the surface of a selective solvent. The ...

Journal of Colloid and Interface Science, 1991

We discuss the properties of two-dimensional (2-D) foams formed in the gas-liquid coexistence reg... more We discuss the properties of two-dimensional (2-D) foams formed in the gas-liquid coexistence region of spread monolayers on the basis of observations on a surface-active fluorescent dye. Their appearance and general behavior are analogous to those of three-dimensional (3-D) foams. The line tension between the gas and liquid 2-D phase regions plays a role similar to that of the surface tension in conventional foams. It determines the thinning of the strips of liquid monolayer phase which separate the gas cells in the 2-D polygonal surface structure: a lower surface pressure in the corner regions causes the equivalent of the Plateau-border suction. The rate of strip thinning can be slowed down by several orders ifa gradient in line tension opposes monolayer flow. Such a gradient presupposes the existence of the unidimensional equivalent of surface activity, for which there is so far only circumstantial evidence. The line tension also controls cell disproportionation, i,e., the growth of large cells at the expense of smaller ones, and "line activity" can also reduce the rate of this process. Finally, the rearrangement process, in which contact between four strips changes into two three-strip contacts, is based on the minimization of the total line energy. It was observed that this rearrangement actually occurs before a small central cell has disappeared to cause the four-strip contact. This phenomenon was shown to be theoretically expected.

Macromolecules, 1985

The temperature and molecular weight dependence of the hydrodynamic radius RH of flexible chains ... more The temperature and molecular weight dependence of the hydrodynamic radius RH of flexible chains below the 0 temperature have been investigated by analytical ultracentrifugation. The measurements have been performed on high molecular weight polystyrenes (M, = 3.8 X lo6, 4.48 X lo6, 6.77 X lo6, 8.42 X lo6, and 20.6 X lo6) of narrow polydispersity dissolved in two different solvents, cyclopentane and cyclohexane. All data can be represented on a sipgle master curve if the expansion factor aH = R H (T) / R H (~) is plotted vs. the reduced variable NIN, = (M,IT12)/(naMo). T is the reduced temperature (71 = 11-0/TI and naM, is an adjustable parameter 150 f 30 g mol-'. The small N I N , values (<3) correspond to the so-called 8 domain in which the chain is essentially Gaussian and CYH is a-constant close to unity. For large NIN, values (>20) the collapse domain is observed in which aH varies as Mw-''61~l-'~3. The molecular weight dependence of ~Y H demonstrates directly for the first time that the collapse domain is characterized by RH-The crossover between these two regimes is smooth and continuous. Our results are in agreement with the theoretical predictions advocating a continuous contraction for flexible chains in the temperature range between the 8 point and the coexistence curve. We have also observed a small residual molecular weight dependence in our scaled representation of aH. This, the slight apparent dependence of naM, with the nature of the solvent and the difference between the naM, values above and below the 8 temperature, respectively, is yet to be explained.

Colloids and Surfaces B: Biointerfaces, 2013

Competitive adsorption is a general problem both in polymer and in biological systems. The equili... more Competitive adsorption is a general problem both in polymer and in biological systems. The equilibrium composition at a surface in contact either with polymer solutions or biological fluids depends on the competition between all the surface active material present in the medium. Such competition is particularly important in cell membranes where membrane proteins generated on ribosomes have to incorporate in the cell. Here we use fluovideo microscopy to study the competition for adsorption at the air/water interface between the enzyme glucose oxidase (GOx) and fluid monolayers of pentadecanoic acid (PDA). Although water soluble, GOx has a strong affinity for the air/water interface. We show that under certain conditions it inserts in the monolayer and causes a contraction of the Langmuir film and the formation of condensed domains. When exposed to a heterogeneous surface it is inserted in the less dense regions. Its crystallization leads to the deformation of the condensed domains followed by the destruction of their initial shape. By compressing the layer the protein is not removed from the interface where it eventually forms three-dimensional structures.

The Journal of Chemical Physics, 1993

We report the results of a grazing incidence x-ray diffraction study of monolayers of F(CF2)11COO... more We report the results of a grazing incidence x-ray diffraction study of monolayers of F(CF2)11COOH and F(CF2)10CH2COOH on water at several temperatures. It is found that in both monolayers the amphiphile molecules have a very small collective tilt angle (relative to the normal to the surface). For the temperature range studied (∼4–30 °C) the data for both monolayers indicate the existence of only a first-order transition between an ordered condensed phase and a disordered dilute phase; there is no evidence, in this temperature range, for the existence of a continuous tilt transition such as has been observed in monolayers of arachidic acid. The experimental data suggest that the critical point for the transition observed is at a lower temperature for a monolayer of F(CF2)11COOH than for a monolayer of F(CF2)10CH2COOH.

Energy & Fuels, 2008

ABSTRACT We have studied the time dependence of the interfacial tension between acidic aqueous so... more ABSTRACT We have studied the time dependence of the interfacial tension between acidic aqueous solutions (pH 2) and commercial straight-run bitumen droplets of different origins by the pendent drop method. Because of the existence in bitumen of naturally occurring surface-active species, significant changes of the interfacial tension are observed over timescales of several thousands of seconds. The kinetics of the decrease is consistent with the exodiffusion of endogenous surfactants toward the bitumen−water interface and throughout the bitumen matrix. At T = 90 °C, one observes that the interfacial tension decreases as t1/2 at short times and as t−1/2 at long times when the interface becomes nearly saturated. Combining these two kinetic data allows for a direct estimate of the surface concentration of these endogenous surfactants. If one makes the assumption that they organize in a dense, close-packed monolayer, their size and concentration in bulk bitumen can also be readily derived. At T = 140 °C, the viscosity of bitumen is 20 times lower than at 90 °C and the short time kinetics can no longer be resolved with our experimental apparatus. This restricts the data analysis, but we can nevertheless obtain an estimate of the size of the surfactant molecules if one makes the reasonable hypothesis that the bulk concentration of surfactants remains unchanged between 90 and 140 °C. Our results suggest that the surface-active species at pH 2 are asphaltene moieties of basic character. They are probably in an aggregated form because the measured, nanometric size decreases at elevated temperatures. Quite remarkably, they correspond to a very small fraction of the total asphaltenes contained in bitumen, which explains why they are extremely difficult to detect analytically. To the best of our knowledge, this is the first time that quantitative data on the endogenous surfactants are obtained in industrial bitumen. The present results thus complete the numerous existing observations on model oil–water systems.

Langmuir, 1995

We address the longstanding issue of substrate effects in alkylsiloxane monolayer self-assembly. ... more We address the longstanding issue of substrate effects in alkylsiloxane monolayer self-assembly. With proper substrate prehydration, we observe formation of identical quality, compact, quasi-crystalline monolayers on oxidized silicon and gold substrates with widely different chemical character, the former capable of covalent bonding to the adsorbed molecules via silanol groups and the latter devoid of reactive surface sites. Infrared spectroscopy, ellipsometry, and wetting measurements show identical average film structures consisting of highly extended chains tilted at 10 (f2)" with significant end-gauche defect content. This obsewed substrate independence is consistent with our previous hypothesis that substrate-bound water promotes the decoupling of the organic film from the underlying solid surface. Deposition of stable, low defect, hydrophobic monolayers,lY2 on solid substrates is of significant interest in a wide variety of applications ranging from electronics3 to biological interface^.^ One of the most popular methods involves the use of solution self-assembly of long-chain alkyltrichlorosilanes (silanization) to form densely packed, highly organized, monolayer films. This simple technique was proposed almost 50 years ago by Zisman5 and advocated subsequently by Sagiv.6 The fact that many different preparation protocols have been reported in the literature suggests, however, a lack of general understanding of the precise mechanism controlling the deposition process. Recently, a unifying mechanism has been proposed78 which explains why the presence of a substratebound water film9-11 and the control of the deposition temperature below a threshold value12 are necessary in order to obtain high-density, Langmuir-like film structures. The crux of the argument is that one should decouple the monolayer film from the substrate structure as much as possible in order to allow for the in-plane lateral reorganization of the physisorbed molecules. This mech

Journal of the Chemical Society, Faraday Transactions 2, 1986

Applied Optics, 1989

The fluorescence of uniformly distributed chromophores in an organic solution has been used to pr... more The fluorescence of uniformly distributed chromophores in an organic solution has been used to probe the energy density profile of an optical evanescent wave, generated by total internal reflection at the solidsolution interface. The results obtained in the case of an aqueous fluorescein solution in contact with a highly polished silica surface are in good quantitative agreement with the expected exponential decay of the optical energy at the interface. It also justifies the use of the newly developed evanescent wave-induced fluorescence technique to study adsorption and depletion layers of polymer in solution close to solids walls. In such experiments the fluorescence intensity is assumed to be the Laplace transform of the concentration profile of the fluorescently labeled polymer chains. The present data validate the above assumption. by the classical electromagnetic theory using Maxwell

Chemical Communications, 2008

General Methods. All chemicals were purchased from Sigma-Aldrich. NMR experiments were carried ou... more General Methods. All chemicals were purchased from Sigma-Aldrich. NMR experiments were carried out on a Bruker Avance 300 MHz. UV Analysis were performed using Perkin-Elmer, Lambda 800. FT-IR spectra were obtained using a Nicolet, Magna IR-550. The UV quartz plates (45 × 12.5 × 1.25 mm) were purchased from Hellma. Contact angles were measured with a digidrop from GBX (Romans sur Isère, France). An ellipsometer (Sentech SE 500) operating at a 70° incidence angle was used to measure the polycationic polymer layer thickness on the silicon wafer substrates. XPS measurements were performed with a Surface Science Instruments (SSI) M-Probe Spectrometer. The samples were irradiated with monochromatic Al K α X-rays (1486.6 eV) using a spot size of 150 μm and 40 W power. For each sample, two survey spectra were recorded with pass energy of 150 eV, from which the surface chemical compositions were determined. In addition, one set of high-resolution spectra (C 1s , O 1s , N 1s) was recorded with pass energy of 25 eV, from which the chemical states were determined. Charge compensation for these electrically-insulating specimens was achieved using a beam of ca. 4 to 9 eV electrons at a flood gun current of ca. 0.1 mA with an electrically grounded 90% transmission nickel mesh screen positioned ca. 1 mm above the sample surface. Atomic Force Microscopy (AFM) studies were carried out with a Nanoscope III from Digital Instruments. The images were acquired in tapping mode under ambient conditions with standard silicon cantilevers and a resonance frequency around. I. Synthesis and characterization of copolymer 2 Polymer synthesis. The starting material, poly-(vinylbenzylchloride) 1 (1g, Mn = 55000, Ip = 1.82), was dissolved dry tetrahydrofuran (30 mL). Then N,N'dimethylaminopropyltrimethoxysilane (287 µL, 1.31 mmoles) was added in a 1% stoichiometric ratio and the mixture was stirred under reflux during 6 hours at 50°C. N,N

Macromolecules, 1992

ABSTRACT We report simultaneous measurements of the concentration profile and the free energy of ... more ABSTRACT We report simultaneous measurements of the concentration profile and the free energy of the submerged PS blocks of PDMS-PS diblock copolymers spread as monolayers at the air surface of ethyl benzoate as a function of surface concentration. A parabolic ...

Langmuir, 2003

Here, we develop a system where long double-stranded DNAs (ds-DNAs) are immobilized on the surfac... more Here, we develop a system where long double-stranded DNAs (ds-DNAs) are immobilized on the surface of a polystyrene (PS) microsphere. A simple synthetic strategy is adopted in order to achieve this goal in which a single DNA chain is anchored by one of its extremities to a latex (PS) microsphere. We chose hybridization as a unique method to attach long ds-DNA chains in solution with oligonucleotides grafted on modified aminated polystyrene microspheres. The DNAs chosen were of various sizes and sources: T7A1 DNA (4.48 kilobase pair (kbp)), a plasmid DNA; and ∆DIIIT7 DNA (39.34 kbp), a mutant of bacteriophage T7 DNA. The temperature dependence of the kinetics of hybridization of T7A1 DNA (4.48 kbp) in solution with an appropriate oligonucleotide (20-mer sequence) grafted on modified aminated polystyrene microspheres yielded a value of activation energy of ∼5.3 kcal/mol, consistent with a nondiffusion-controlled mechanism.