New insights on the solution behavior and self-assembly of polystyrene/poly(2-vinylpyridine) ‘hairy’ heteroarm star copolymers with highly asymmetric arms in polar organic and aqueous media

Supramolecular block copolymers incorporating chiral and achiral chromophores for the bottom-up assembly of nanomaterials

The coordination of the chiral metalloporphyrin ([5,10,15,20-[4-([Formula: see text]-2-[Formula: see text]-octadecylamidoethyloxiphenyl]porphyrin] zinc (II)) and an achiral homologue to an amphiphilic block copolymer of poly(styrene-[Formula: see text]-4-vinyl pyridine) (PS-[Formula: see text]-P4VP) have been studied in solution and as cast material. The resulting chiral dye-polymer hybrid material has been accomplished via axial coordination between the zinc (II) metal ion in the core of the porphyrin ring and the pyridyl units of the block-copolymer in a non-coordinative solvent. The supramolecular organization and possible chirality transfer to the hybrid material have been studied in solution by UV-visible absorption spectroscopy, fluorescence spectroscopy, Nuclear Magnetic Resonance and Circular Dichroism. The morphology of the chiral and achiral doped polymers has been studied in solid state by Transmission Electron Microscopy and Atomic Force Microscopy. We show that the nanostructures formed depend greatly upon the nature of the side-chains on the porphyrins, where a chiral group leads to a very homogeneous phase-separated material, perhaps indicating that chiral side groups are useful for the preparation of this type of supramolecular hybrid.

PNIPAM-based heteroarm star-graft quarterpolymers: synthesis, characterization and pH-dependent thermoresponsiveness in aqueous media

We report the design of PS_n(P2VP-b-PAA-g-PNIPAM)_n heteroarm star-graft quarterpolymers, the thermoresponsiveness of which is strongly dependent on pH ionic strength, and their macromolecular features, e.g. arm number and grafting density.

Star polymer unimicelles on graphene oxide flakes

We report the interfacial assembly of amphiphilic heteroarm star copolymers (PSnP2VPn and PSn(P2VP-b-PtBA)n (n = 28 arms)) on graphene oxide flakes at the air-water interface. Adsorption, spreading, and ordering of star polymer micelles on the surface of the basal plane and edge of monolayer graphene oxide sheets were investigated on a Langmuir trough. This interface-mediated assembly resulted in micelle-decorated graphene oxide sheets with uniform spacing and organized morphology. We found that the surface activity of solvated graphene oxide sheets enables star polymer surfactants to subsequently adsorb on the presuspended graphene oxide sheets, thereby producing a bilayer complex. The positively charged heterocyclic pyridine-containing star polymers exhibited strong affinity onto the basal plane and edge of graphene oxide, leading to a well-organized and long-range ordered discrete micelle assembly. The preferred binding can be related to the increased conformational entropy due to the reduction of interarm repulsion. The extent of coverage was tuned by controlling assembly parameters such as concentration and solvent polarity. The polymer micelles on the basal plane remained incompressible under lateral compression in contrast to ones on the water surface due to strongly repulsive confined arms on the polar surface of graphene oxide and a preventive barrier in the form of the sheet edges. The densely packed biphasic tile-like morphology was evident, suggesting the high interfacial stability and mechanically stiff nature of graphene oxide sheets decorated with star polymer micelles. This noncovalent assembly represents a facile route for the control and fabrication of graphene oxide-inclusive ultrathin hybrid films applicable for layered nanocomposites.

pH responsive self assemblies from an A(n)-core-(B-b-C)n heteroarm star block terpolymer bearing oppositely charged segments

We report on the association capability of a novel multisegmented, multiarm star terpolymer to form a diversity of pH-responsive amphoteric micellar nanostructured self-assemblies.

Monte Carlo simulation of fluorescence correlation spectroscopy data

We employed the Monte Carlo simulation methodology to emulate the diffusion of fluorescently labeled particles and understand the source of differences between values of diffusion coefficients (and consequently hydrodynamic radii) of fluorescently labeled nanoparticles measured by fluorescence correlation spectroscopy (FCS) and dynamic light scattering (DLS). We used the simulation program developed in our laboratory and studied the diffusion of spherical particles of different sizes, which are labeled on their surface. In this study, we focused on two complicating effects: (i) multiple labeling and (ii) rotational diffusion which affect the fluorescence signal from large particles and hinder the analysis of autocorrelation functions according to simple analytical models. We have shown that the fluorescence fluctuations can be well fitted using the analytical model for small point-like particles, but the obtained parameters deviate in some cases significantly from the real ones. It means that the current data treatment yields apparent values of diffusion coefficients and other parameters only and the interpretation of experimental results for systems of particles with sizes comparable to the size of the active illuminated volume requires great care and precaution.

Self-assembly of poly(4-methylstyrene)-g-poly(methacrylic acid) graft copolymer in selective solvents for grafts: scattering and molecular dynamics simulation study

Poly(4-methylstyrene)-g-poly(methacrylic acid) (P4MS-g-PMAA) graft copolymer was synthesized by the grafting-onto method from poly(4-methylstyrene), selectively brominated on methyl groups, and "living" poly(tert-butyl methacrylate). The average degree of polymerization of the backbone and the grafts and the average number of grafts per backbone were 251, 21, and 25, respectively. The self-assembly of P4MS-g-PMAA was studied in methanol and aqueous buffers (selective solvents for grafts). Micelles of P4MS-g-PMAA in methanol were studied by a combination of static and dynamic light scattering, TEM and SAXS. It was found that their spherical core/shell morphology resembles that of diblock copolymer micelles but they have a very low aggregation number (approximately 3) and a high cmc (approximately 0.8 mg/mL). The spherical core-shell structure revealed by SAXS was confirmed by the molecular dynamics study emulating an associate of comblike copolymers with structural parameters close to those of the experimentally studied system. Because P4MS-g-PMAA was not directly soluble in water, its aqueous solutions had to be prepared by dialysis of the methanolic solutions. In aqueous solutions, unlike in methanol, small P4MS-g-PMAA micelles (approximately 20 nm in diameter) form large secondary aggregates (approximately 100-400 nm).

Direct observation of single molecule mobility in semidilute polymer solutions

We determine the mobility of dye-labeled polystyrene molecules in solution by fluorescence correlation spectroscopy (FCS) over a wide range of concentrations and molecular weights (ranging from 3.9 x 10{3} to 1550 x 10{3} g/mol ). In order to obtain absolute values of the diffusion coefficient, which can be compared to diffusion coefficients determined by other methods, the size of the focal volume has been determined by independent experiments and theoretical calculations. All data demonstrate that FCS is uniquely suited to explore polymer dynamics in solution. The mobility of the chains as expressed through the self-diffusion coefficient is significantly slowed down above the overlap concentration c{*}. The dependence of c{*} on molecular weight is well described by the power law c{*} proportional, variant M{w};{1-3nu} ( nu: Flory exponent). A comparison with the data taken from the literature demonstrates that the overlap concentration presents a robust concept that holds for a wide range of molecular weights.

Atomic Force Microscopy and Light Scattering Study of Onion-Type Micelles Formed by Polystyrene-block-poly(2-vinylpyridine) and Poly(2-vinylpyridine)-block-poly(ethylene oxide) Copolymers in Aqueous Solutions

The three-layer onion micelles formed in aqueous solution by hierarchical self-assembly of polystyrene-block-poly(2-vinylpyridine) micelles, PS-PVP, and poly(2-vinylpyridine)-block-poly(ethylene oxide) chains, PVP-PEO, were studied by a combination of light scattering (LS) and atomic force microscopy (AFM). Section analysis of AFM images of micelles deposited on mica in combination with LS data from micellar solutions provide distribution functions of sizes from which the number and mass distributions of molar masses of micelles can be evaluated. Both light scattering and AFM data reveal that the used preparation protocol yields onion micelles accompanied by an admixture of PVP-PEO micelles. It means that only a certain amount of PVP-PEO self-assembles with PS-PVP and forms onion micelles. The remaining PVP-PEO copolymer forms either small PVP-PEO micelles or participates in formation of large aggregates at longer times. The time-dependent measurements show that both onion-type and core-shell PVP-PEO micelles are fairly stable over a long time period and only a low fraction of large aggregate forms on the timescale of weeks and at longer times, the solution does not change any more.