285 research outputs found
Effective Soft-Core Potentials and Mesoscopic Simulations of Binary Polymer Mixtures
Mesoscopic molecular dynamics simulations are used to determine the large
scale structure of several binary polymer mixtures of various chemical
architecture, concentration, and thermodynamic conditions. By implementing an
analytical formalism, which is based on the solution to the Ornstein-Zernike
equation, each polymer chain is mapped onto the level of a single soft colloid.
From the appropriate closure relation, the effective, soft-core potential
between coarse-grained units is obtained and used as input to our mesoscale
simulations. The potential derived in this manner is analytical and explicitly
parameter dependent, making it general and transferable to numerous systems of
interest. From computer simulations performed under various thermodynamic
conditions the structure of the polymer mixture, through pair correlation
functions, is determined over the entire miscible region of the phase diagram.
In the athermal regime mesoscale simulations exhibit quantitative agreement
with united atom simulations. Furthermore, they also provide information at
larger scales than can be attained by united atom simulations and in the
thermal regime approaching the phase transition.Comment: 19 pages, 11 figures, 3 table
Sulfonated Styrene-(ethylene-co-butylene)-styrene/Montmorillonite Clay Nanocomposites: Synthesis, Morphology, and Properties
Sulfonated styrene-(ethylene-butylene)-styrene triblock copolymer (SSEBS) was synthesized by reaction of acetyl sulfate with SEBS. SSESB-clay nanocomposites were then prepared from hydrophilic Na-montmorillonite (MT) and organically (quaternary amine) modified hydrophobic nanoclay (OMT) at very low loading. SEBS did not show improvement in properties with MT-based nanocomposites. On sulfonation (3 and 6 weight%) of SEBS, hydrophilic MT clay-based nanocomposites exhibited better mechanical, dynamic mechanical, and thermal properties, and also controlled water–methanol mixture uptake and permeation and AC resistance. Microstructure determined by X-ray diffraction, atomic force microscopy, and transmission electron microscopy due to better dispersion of MT nanoclay particles and interaction of MT with SSEBS matrix was responsible for this effect. The resulting nanocomposites have potential as proton transfer membranes for Fuel Cell applications
Hexagonally Perforated Layer Morphology in PS-b-P4VP(PDP) Supramolecules
Supramolecular complexes of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymers and small molecules such as pentadecylphenol (PDP) have been studied extensively in recent years. In the present study, PS-b-P4VP(PDP) complexes with a minority P4VP(PDP) block are morphologically characterized focusing on the region between the lamellar and cylindrical phase. Dynamic mechanical measurements and small-angle X-ray scattering are used to follow the transitions between the ordered states upon heating/cooling. The self-assembled state at various temperatures is determined by small-angle X-ray scattering and transmission electron microscopy. In contrast to the opposite case of majority P4VP(PDP) blocks, where the transition from lamellar to cylindrical structures frequently occurs via the gyroid morphology, the complexes adopt the hexagonally perforated layered morphology in a broad range of compositions. Although known as a metastable phase in pure diblock copolymers, the hexagonally perforated layered phase appears as an equilibrium phase in PS-b-P4VP(PDP) complexes, being stabilized by the presence of the hydrogen-bonded PDP side chains in the minority component domains
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