Tuning surface interactions to control shape and array behavior of diblock copolymer micelles on a silicon substrate (original) (raw)
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The Journal of Physical Chemistry C, 2011
Three block polymers, viz., L31, L64, and P123, were used as reducing agents for the synthesis of gold (Au) nanoparticles (NPs) to determine the effect of their micelle size, structure transitions, and environments on the mechanism of the reduction process leading to the overall morphology of Au NPs. Aqueous phase reduction was monitored with time at constant temperature and under the effect of temperature variation from 20 to 70°C by simultaneous measurement of UVÀvisible spectra. The ligand to metal charge transfer (LMCT) band around 300 nm, due to a charge transfer complex formation between the micelle surface cavities and AuCl 4 À ions, and Au NP absorbance around 550 nm, due to the surface plasmon resonance, were simultaneously measured to understand the mechanism of the reduction process and its dependence on the micelle structure transitions and environment of TBPs micelles. L64 micelles showed dramatic shift in the LMCT band from lower to higher wavelength due to an increase in the reduction potential of surface cavities induced by the structure transitions under the effect of temperature variations. This effect was not observed for micelles of either L31 or P123 and is explained on the basis of a difference in their micelle environments. The morphology of Au NPs thus evolved from the reduction process was studied with the help of TEM and SEM studies. Smaller micelle size with few surface cavities, as in L31, produced small NPs in comparison to large micelles with several surface cavities as in P123. Structure transitions of L64 demonstrated direct influence on the final morphology of NPs, and stronger transitions produced fused and deformed NPs in comparison to weaker transitions. The results showed that efficient reduction by the surface cavities and uninterrupted nucleation without structure transitions lead to well-defined morphologies in the presence of P123 micelles. B dx.
Block Copolymer Micelles as Nanoreactors for Self-Assembled Morphologies of Gold Nanoparticles
New micelle-like organic supports for single site catalysts based on the self-assembly of polystyrene-b-poly(4-vinylbenzoic acid) block copolymers have been designed. These block copolymers were synthesized by sequential atom transfer radical polymerization (ATRP) of styrene and methyl 4-vinylbenzoate, followed by hydrolysis. As evidenced by dynamic light scattering, self-assembly in toluene that is a selective solvent of polystyrene, induced the formation of micelle-like nanoparticles composed of a poly(4-vinylbenzoic acid) core and a polystyrene corona. Further addition of trimethylaluminium (TMA) afforded in situ MAO-like species by diffusion of TMA into the core of the micelles and its subsequent reaction with the benzoic acid groups. Such reactive micelles then served as nanoreactors, MAO-like species being efficient activators of 2,6-bis[1-{(2,6-diisopropylphenyl)imino}ethyl]pyridinyl iron toward ethylene polymerization. These new micelle-like organic supports enabled the production of polyethylene beads with a spherical morphology and a high bulk density through homogeneous-like catalysis.
Macromolecules, 2005
We report several strategies for varying the diameter, the center-to-center spacing, and the areal density of block copolymer micelles, or inorganic nanoclusters synthesized in the cores of the micelles, on planar substrates. The amphiphilic block copolymer, poly(styrene-b-acrylic acid) (PS/PAA), forms micelles in toluene solution that can be spin-coated onto a substrate to create quasi-hexagonal arrays of spherical PAA domains within a PS matrix. The carboxylic acid groups within the PAA domains can be utilized in a nanoreactor synthesis scheme to create inorganic nanocluster arrays, or the PAA domains can be cavitated to expose the carboxylic acid groups to the surface for possible covalent coupling reactions. The strategies we use to vary the planar arrangements include variation of the molecular weight of PS/PAA, variation of the amount of metal loaded into the micellar solution, addition of PS homopolymer into the micellar solution, and the mixing of different micellar solutions. Through these routes, we demonstrate varying the diameter of the inorganic nanoclusters from 4.7 to 16 nm and the areal density from 8 × 10 10 to 6.5 × 10 9 nanoclusters cm-2. We are also able to create arrays of nanoclusters containing more than one inorganic species, with each nanocluster containing either one or all of the inorganic species, depending on the sequence of processing conditions employed. We characterize these arrays using energy-dispersive X-ray analysis on a scanning transmission electron microscope.
Langmuir, 2007
The self-organization of diblock copolymers into micellar structures in an appropriate solvent allows the deposition of well ordered arrays of pure metal and alloy nanoparticles on flat surfaces with narrow distributions in particle size and interparticle spacing. Here we investigated the influence of the materials (substrate and polymer) and deposition parameters (temperature and emersion velocity) on the deposition of metal salt loaded micelles by dip-coating from solution and on the order and inter-particle spacing of the micellar deposits and thus of the metal nanoparticle arrays resulting after plasma removal of the polymer shell. For identical substrate and polymer, variation of the process parameters temperature and emersion velocity enables the controlled modification of the interparticle distance within a certain length regime. Moreover, also the degree of hexagonal order of the final array depends sensitively on these parameters.
Journal of Polymer Science Part A-polymer Chemistry, 2007
Stable and aggregation-free ''gold nanoparticle-polymeric micelle'' conjugates were prepared using a new and simple protocol enabled by the hydrogen bonding between surface-capping ligands and polymeric micelles. Individual gold nanoparticles were initially capped using a phosphatidylthio-ethanol lipid and further conjugated with a star poly(styrene-block-glutamic acid) copolymer micelle using a one-pot preparation method. The morphology and stability of these gold-polymer conjugates were characterized using transmission electron microscopy (TEM) and UV-vis spectroscopy. The self-assembly of this class of polymer-b-polypeptide in aqueous an medium to form spherical micelles and further their intermicelle reorganization to form necklace-like chains was also investigated. TEM and laser light scattering techniques were employed to study the morphology and size of these micelles. Polymeric micelles were formed with diameters in the range of 65-75 nm, and supermicellular patterns were observed. V V C 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: [3570][3571][3572][3573][3574][3575][3576][3577][3578][3579] 2007 spanning the fields of chemistry, materials science, biology, and electrical engineering. 2 The potential applications of gold nanoparticles in the area of optoelectronics, sensors, electronics, photonics, biolabeling, catalysis, and so forth 3,4 are the motivation to continue tuning the material properties and further advance surface chemistries for metal nanoparticles. Preventing aggregation of gold nanoparticles and controlling particle-particle interaction are the most important factors that determine the quantum confinement effects, especially in their dispersion state. There are a vast number of strategies available for stabilizing gold nanoparticles.
Block copolymer-regulated synthesis of gold nanocrystals with sharp tips and edges
Journal of Materials Chemistry, 2010
Gold decahedra and triangular plates of small size (30 and 50 nm, respectively) were grown by a green one-step synthesis process of HAuCl 4 in the presence of citric acid and amphiphilic copolymer Tetronic T904 Ò (from BASF), which both act as reducing and stabilizing agents. Tetronic T904 Ò is a star-shaped copolymer composed of polyethylene oxide and propylene oxide units. Both compounds are key in the formation of decahedral particles due to their specific adsorption on certain crystallographic planes of the nanoparticles. Withdrawal or substitution of one of them involves the formation of irregular particles. On the other hand, by changing the reactions conditions the nanoparticle size and shape could be modified. In particular, by varying the molar ratio between the block copolymer a more efficient protection provided by the block copolymer is achieved, which allows the reaction to turn into kinetic control and, thus, a change from decahedral to triangular shape is observed. Due to the presence of acute tips and sharp edges, which sustain large electromagnetic fields upon excitation with light of appropriate energy, these nanoparticles demonstrated their utility as SERS substrates. Concentrations of up to 10Aˋ11MoftheRamanprobe4−nitrobenzenethioldisplayedareadableSERSspectrum,withelectromagneticenhancementfactorsofupto10 À11 M of the Raman probe 4-nitrobenzenethiol displayed a readable SERS spectrum, with electromagnetic enhancement factors of up to 10Aˋ11MoftheRamanprobe4−nitrobenzenethioldisplayedareadableSERSspectrum,withelectromagneticenhancementfactorsofupto4.2 Â 10 7 .
Hexagonally ordered arrays of metallic nanodots from thin films of functional block copolymers
Polymer, 2010
We demonstrate a new and simple route to fabricate highly dense arrays of hexagonally close packed inorganic nanodots using functional diblock copolymer (PS-b-P4VP) thin films. The deposition of presynthesized inorganic nanoparticles selectively into the P4VP domains of PS-b-P4VP thin films, followed by removal of the polymer, led to highly ordered metallic patterns identical to the order of the starting thin film. Examples of Au, Pt and Pd nanodot arrays are presented. The affinity of the different metal nanoparticles towards P4VP chains is also understood by extending this approach to PS-b-P4VP micellar thin films. The procedure used here is simple, eco-friendly, and compatible with the existing siliconbased technology. Also the method could be applied to various other block copolymer morphologies for generating 1-dimensional (1D) and 2-dimensional (2D) structures.
Encapsulation of Single Small Gold Nanoparticles by Diblock Copolymers
Chemphyschem, 2008
There has been considerable interest in recent years in using metal, semiconductor, and magnetic nanoparticles in biological applications. A wide range of ligation and encapsulation methods have been developed to render the nanoparticles soluble in aqueous solution, to prevent aggregation, and to provide means by which functional molecules can be attached. Among these methods, encapsulation of nanoparticles by a polymer, phospholipid, or inorganic shell is of particular interest to us, since these stable shells prevent dissociation of surface ligands and provide anchor points where biomolecules are unlikely to be lost once attached. This is a significant advantage over direct conjugation through surface ligands, since even strong thiol ligands can dissociate from or undergo exchange on gold surfaces, let alone weaker ligands on the surfaces of quantum dots or magnetic nanoparticles. Stable attachment of biomolecules would be particularly important where only a few biomolecules are selectively attached to a nanoparticle, or when multiple types of singly functionalized nanoparticles are mixed.
Gold-Decorated Block Copolymer Microspheres with Controlled Surface Nanostructures
ACS nano, 2012
Gold-decorated block copolymer microspheres (BCP-microspheres) displaying various surface morphologies were prepared by the infiltration of Au precursors into polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) microspheres. The microspheres were fabricated by emulsifying the PS-b-P4VP polymers in chloroform into a surfactant solution in water, followed by the evaporation of chloroform. The selective swelling of the P4VP domains in the microspheres by the Au precursor under acidic conditions resulted in the formation of Au-decorated BCP-microspheres with various surface nanostructures. As evidenced by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) measurements, dotted surface patterns were formed when microspheres smaller than 800 nm were synthesized, whereas fingerprint-like surface patterns were observed with microspheres larger than 800 nm. Au nanoparticles (NPs) were located inside P4VP domains near the surfaces of the prepared microspheres, as confirmed by TEM. The optical properties of the BCP-microspheres were characterized using UVÀvis absorption spectroscopy and fluorescence lifetime measurements. A maximum absorption peak was observed at approximately 580 nm, indicating that Au NPs are densely packed into P4VP