When cooled or pressurized, polymer melts exhibit a tremendous reduction in molecular mobility. If the process is performed at constant rate, structural relaxation time of liquid eventually exceeds allowed for equilibration. This brings system out equilibrium, and operationally defined as glass—a solid lacking long-range order.

Conditions of rapid processing often drive polymers to adopt nonequilibrium molecular conformations, which, in turn, can give rise structural, dynamical, and mechanical properties that are significantly different from those thermodynamic equilibrium. However, despite the possibility control desired polymers, a rigorous microscopic understanding processing–property relations is currently lacking. In an attempt stimulate progress along this topical direction, we focus here on three...

The flow of dense suspensions, glasses, and granular materials is heavily influenced by frictional interactions between constituent particles. However, neither hydrodynamics nor friction has successfully explained the full range phenomena in concentrated suspensions. Particles with asperities represent a case point. Lubrication fail to completely capture two key rheological properties - namely, that viscosity increases drastically first normal stress difference can switch signs as volume...

We show that thin film star-shaped macromolecules exhibit significant differences in their average vitrification behavior, both magnitude and thickness dependence, from linear analogs. This behavior is dictated by a combination of functionality arm length. Additionally, the glass transition temperature at free surface molecule may be higher than interior, contrast to analogs where opposite true. These findings have implications for other properties, due largely origins, entropic, this behavior.

Well-characterized single-chain nanoparticles (SCNPs), synthesized from a linear polystyrene precursor through an intramolecular [4 + 4] thermal cycloaddition cross-linking reaction in dilute conditions, were added to entangled melts at different concentrations. Starting the pure melt, which is much more viscous than melt of SCNPs, zero-shear viscosity increased upon addition and reached maximum before eventually dropping value SCNP melt. Molecular simulations reveal origin this unexpected...

Time-dependent changes of thermodynamic properties due to structural relaxations and physical aging occur in all glasses. We show that the thin supported films star-shaped macromolecules, with f arms length N(arm), exhibits average dynamics are sensitive N(arm). Regions proximity interfaces age at substantially different rates than interior film; this is also true linear chain systems. This behavior may be reconciled terms a universal picture accounts only for local T(g) films.

Structural and dynamical properties of star melts have been investigated with molecular dynamics simulations a bead-spring model. Star polymers are known to be heterogeneous, but systematic simulation study their in melt conditions near the glass transition temperature was lacking. To probe properties, we expanded from linear applicability Dobkowski’s chain-length dependence correlation function [Z. Dobkowski, Eur. Polym. J. 18, 563 (1982)]. The density isokinetic temperature, based on...

The primary challenge regarding solid polymer electrolytes (SPEs) is the development of materials with enhanced mechanical modulus without sacrificing ionic conductivity. Here, we demonstrate that when stiff/rigid nanoparticles are thermodynamically miscible a utilized in blend liquid electrolyte, elastic and conductivity resulting SPEs increase compared to linear analogues. In particular, poly(methyl methacrylate), PMMA, nanoparticles, composed high functionality star-shaped were added low...

Nanoindentation studies of the mechanical properties sufficiently thin polymer films, supported by stiff substrates, indicate that moduli are generally higher than those bulk. This enhancement effective modulus, in thickness range few hundred nanometers, is indicated to be associated with propagation and impingement indentation tip induced stress field rigid underlying substrate; this so-called "substrate effect". behavior has been rationalized completely terms Poisson's ratios individual...

We show that the vitrification of star-shaped polystyrene (PS), functionality f and molecular weight per arm Mwarm, thin films supported by silicon oxide, SiOx, is strongly dependent on Mwarm f. When small, behavior similar to linear-chain PS where average glass transition, Tg, decreases with decreasing film thickness (ΔTg < 0). However, for sufficiently large small Tg becomes independent ≈ In this region, ΔTg 0, macromolecules self-assemble into ordered, periodic structures, soft spheres or...

For the next generation of safe and high energy rechargeable lithium metal batteries, we introduce nanostructured polymer particles asymmetric miktoarm star copolymers as additives to liquid electrolytes for use solid (SPE). The mechanical properties resulting SPEs are dramatically improved compared pure electrolyte (the elastic modulus increased by up 8 orders magnitude), while ionic conductivity was maintained close that electrolyte. In particular, addition 44 wt % stars, composed ion...

Nanoparticles are commonly added to polymer electrolytes enhance both their mechanical and ion transport properties. Previous work reports significant increases in the ionic conductivity Li-ion transference nanocomposite with inert, ceramic fillers. The mechanistic understanding of this property enhancement, however, assumes nanoparticle dispersion states─namely, well-dispersed or percolating aggregates─that seldom quantified using small-angle scattering. In work, we carefully control...

The nanomechanical properties of biocompatible thin-shell hollow polymer microspheres with approximately constant ratio shell thickness to microsphere diameter were measured by nanocompression tests in aqueous conditions. These encapsulate an inert gas and are used as ultrasound contrast agents releasing free microbubbles the presence field a result leakage from shell. performed using atomic force microscope (AFM) employing force−distance curve technique. An optical microscope, on which AFM...

The equilibrium contact angles and line tensions of macroscopic droplets, composed star-shaped polystyrene (PS) macromolecules, on silicon oxide substrates, are shown to be smaller than their linear analogs, by up approximately 1 2 orders magnitude, respectively, depending the size functionality molecule. A precursor layer, lateral dimensions thicknesses order nanometers, surrounds each droplet low molecular weight PS chains. Droplets molecules possessing a sufficient number arms, reside...

This study investigates the fundamental influence of cation chemistry on ionic conductivity PEO-based electrolytes, with implications for advancing polymer electrolyte design. Two PEO systems─high molecular weight (Mw = 100 kg/mol) and low 0.35 kg/mol)─were blended LiTFSI NaTFSI salts to explore ion transport mechanisms. In high-Mw PEO, where hopping dominates, smaller Li+ ions exhibit higher (σLiTFSI > σNaTFSI). contrast, low-Mw diffusion is primary mechanism, shows larger Na+ (σNaTFSI...

This study uses atomic force microscopy (AFM) force–deformation (F–Δ) curves to investigate for the first time Young's modulus of a phospholipid microbubble (MB) ultrasound contrast agent. The stiffness MBs was calculated from gradient F–Δ curves, and MB shell by employing two different mechanical models based on Reissner elastic membrane theories. We found that relatively soft phospholipid-based behave inherently differently stiffer, polymer-based [Glynos, E.; Koutsos, V.; McDicken, W. N.;...

Time-dependent structural relaxations, physical aging, of films with thicknesses in the range 0.4 μm < H 2 star-shaped polystyrene (SPS) macromolecules were investigated. Our studies reveal that aging rates PS are appreciably slower than their linear chain analogs. The magnitude difference between and increases increasing functionality, f, decreasing molecular weight per arm, Mnarm, stars. results consistent notion constraints imposed due to architecture macromolecule suppress relaxations...

Regioregular poly(3-hexylthiophene) (RR-P3HT) is a widely used donor material for bulk heterojunction polymer solar cells. While much known about the structure and properties of RR-P3HT films, important questions regarding hole mobilities in this remain unresolved. Measurements out-of-plane mobilities, μ, films have been restricted to thickness regime on order micrometers, beyond that generally cells, where film thicknesses are typically 100 200 nm. Studies in-plane carrier conducted thinner...

The frequency ω dependent storage G′(ω) and loss G″(ω) moduli of star-shaped polystyrene (SPS) molecules a range functionalities f molecular weights per arm Ma were measured under small amplitude oscillatory shear conditions. Star-shaped macromolecules are composed an inner region, core, where the chain segments stretched "packing" density is higher than that outer corona. dependencies for low functionality (f < 8) with long arms well described by model Milner McLeish, indicating...

The adsorption and self-assembly of linear polymers on smooth surfaces are studied using coarse-grained, bead-spring molecular models Langevin dynamics computer simulations. aim is to gain insight atomic-force microscopy images polymer films mica surfaces, adsorbed from dilute solution following a good-solvent bad-solvent quenching procedure. Under certain experimental conditions, bimodal cluster distribution observed. It demonstrated that this type can be reproduced in the simulations,...

The behaviour of star polymers adsorbed on smooth surfaces is studied using coarse-grained bead-spring models and Langevin dynamics simulations. conformational properties a single polymer in good-solvent conditions are considered as functions the functionality (number arms) f, number monomers per arm N, monomer-surface interaction energy εs. Four regimes identified: linear-polymer regime; two-dimensional sombrero colloidal regime. latter three correspond to predicted theoretically by...

The ability to control the wetting properties of a polymeric liquid on given surface is important for several emerging technological applications including protective coatings, lubricants and sensors. Here we show that star-shaped polystyrene (PS) molecules exhibit notably different than their linear analogues same chemical structure can be controlled through changes functionality f (number arms per molecule). Unlike chains, macromolecules determined by competition between entropic forces....

The surface relaxation dynamics of supported star-shaped polymer thin films are shown to be slower than the bulk, persisting up temperatures at least 50 K above bulk glass transition temperature T_{g}^{bulk}. This behavior, exhibited by polystyrenes with functionality f=8 arms and molecular weights per arm M_{arm}<M_{e} (M_{e} is entanglement weight), simulations associated a preferential localization these macromolecules free surface. new phenomenon in notable contrast that linear-chain...