Search results for "Polystyrene"

Stimuli-Responsive Y-Shaped Polymer Brushes Based on Junction-Point-Reactive Block Copolymers

2012

Reversibly responsive, thin or ultrathin polymer fi lms, often referred to as “smart surfaces”, can alter their properties upon application of external stimuli. [ 1 , 2 ] One particular application fi eld represents the engineering of nanostructured fi lms mimicking cell membranes. [ 3 , 4 ] Such materials offer application potential for sensors, textiles, construction materials, and smart coatings due to a rapid change in surface energy and morphology. [ 5–7 ] The surface response can be triggered by various external stimuli such as light, temperature, electrical potential, mechanical force, magnetic fi eld, pH change, or selective solvent treatment. [ 1 , 8–12 ] A variety of different thi…

The morphology of block copolymer micelles in supercritical carbon dioxide by small-angle neutron and x-ray scattering

1997

Above its critical point, carbon dioxide forms a super-critical fluid, which promises to be an environmentally responsible replacement for the organic solvents traditionally used in polymerizations. Many lipophilic polymers such as polystyrene (PS) are insoluble in CO2, though polymerizations may be accomplished via the use of PS-fluoropolymer stabilizers, which act as emulsifying agents. Small-angle neutron and X-ray scattering have been used to show that these molecules form micelles with a CO2-phobic PS core and a CO2-philic fluoropolymer corona. When the PS block was fixed in length and the fluorinated corona block was varied, the number of block copolymer molecules per micelle (six to …

Competitive Adsorption of Functionalized Polymers

1996

The adsorption and desorption of functionalized polystyrene-block-polybutadiene diblock copolymers from dilute solutions in toluene onto silicon wafers are investigated by means of null ellipsometry. The short polybutadiene block is functionalized by a reaction with 4-(3,5-dioxo-1,2,4-triazolidin-4-yl)benzoic acid. On the average there are six functional groups per chain. The polystyrene block does not adsorb on the surface. The adsorption depends on the length of the polystyrene block, and chains with short polystyrene blocks yield higher surface coverage than larger ones. When short and long chains are put together, the short chains displace the long ones in equilibrium conditions nearly …

Coil-Globule Collapse of Polystyrene Chains in Tetrahydrofuran-Water Mixtures.

2018

We study the coil and globule states of a single polymer chain in solution by performing molecular dynamics simulations with a united atom model. Specifically, we characterize the structural properties of atactic polystyrene chains with N = 20–150 monomers in tetrahydrofuran–water mixtures at varying mixing ratios. We find that the hydrophobic polymers form rather open coils when the mole fraction of water, XW, is roughly below 0.25, whereas the chains collapse into globules when XW ≳ 0.75. We confirm the theoretically expected scaling laws for the radius of gyration, Rg, in these regimes, i.e., Rg ∝ N3/5 and Rg ∝ N1/3 for good and poor solvent conditions, respectively. For poor solvent con…

Deposition and production of highly reproducible hybrid Cu[(tBu)4Pc]-polystyrene thin layers via spin casting

2012

This study focuses on the determination of a protocol for the production of a hybrid material composed of a polymer and a macrocyclic complex, namely polystyrene and a tetra-tert-butyl-copper phthalocyanine (Cu[(tBu)4Pc]), in order to obtain a layer thickness of about 100 nm and a controlled porosity in a highly reproducible way. Several methods were implemented and their reproducibility was evaluated through elements of characterization such as optical microscopy, atomic force microscopy and scanning electron microscopy. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers

1988

Phase diagrams were calculated for flowing solutions of polystyrene in trans-decahydronaphthalene assuming that the energy (Es) stored in the sheared state has to be added to the Gibbs energy of mixing; Es is computed from viscometric data (flow curves). The resulting phase diagrams exhibit two maxima in most of the cases instead of only one for the stagnant solutions. A comparison with experimental data (Part 1) shows that the calculated demixing behaviour agrees well for moderate shear rates and concentrations of the polymer. Deviations in the semidilute region, particularly for higher values, are a consequence of the fact that so far no reliable theoretical relation has been given for th…

Combined Effects of Pressure and Shear on the Phase Separation of Polymer Solutions

1998

Experimental information available in the literature on the phase separation behavior of the system trans-decalin/polystyrene as a function of pressure and shear rate for different molar masses M o...

Probe diffusion in homogeneous diblock copolymers

1998

Forced Rayleigh scattering was used to investigate the diffusion of a photoreactive dye molecule in two homogeneous poly(styrene-b-isoprene) (SI) diblock copolymers with overall molecular weights of approximately 2000. Although diffusion rates were intermediate to TTI transport in homopolymer polystyrene (PS) and polyisoprene (PI), system dynamics appear to be largely dictated in each case by the PI block. The size of the polymer jumping unit, on the other hand, is evaluated from a free-volume analysis of the data, and is found to be governed predominantly by the PS component of the copolymer. The mechanism for tracer diffusion in low-molecular-weight block copolymers appears analogous to t…

Molecular dynamics of solid polymers as revealed by deuteron NMR

1983

Pulsed deuteron NMR spectroscopy is described, which has recently been developed to become a powerful tool for studying molecular dynamics in solid polymers. It is shown that by analyzing the line shapes of2H absorption spectra and spectra obtained via solid echo and spin alignment, respectively, both type and timescale of rotational motions can be determined over an extraordinary wide range of characteristic frequencies, approximately 10 MHz to 1 Hz. By applying these techniques to selectively deuterated polymers, motional mechanisms involving different segments of the monomer unit can be monitored. In addition, motional heterogeneities in glassy polymers can be detected. The information a…

Basis for the Preparative Fractionation of a Statistical Copolymer (SAN) with Respect to Either Chain Length or Chemical Composition

2003

The possibilities to fractionate copolymers with respect to their chemical composition on a preparative scale by means of the establishment of liquid/liquid phase equilibria were studied for random copolymers of styrene and acrylonitrile (SAN). Experiments with solutions of SAN in toluene have shown that fractionation does in this quasi-binary system, where demixing results from marginal solvent quality, take place with respect to the chain length of the polymer only. On the other hand, if phase separation is induced by a second, chemically different polymer, one can find conditions under which fractionation with respect to composition becomes dominant. This opportunity is documented for th…