Search results for "Dynamic"

1993

4-(4-Carboxyphenyl)-3,5-dioxo-1,2,4-triazolidin-1-yl moieties resulting from 4-(3,5-dioxo-1,2,4-triazolin-4-yl)benzoic acid (U4A) randomly attached to 1,4-polybutadiene form supramolecular aggregates which act as effective junction zones in new thermoplastic elastomers. Deuteron nuclear magnetic resonance (2H NMR) spectroscopy was used to investigate the molecular dynamics of the polymer backbone and the junction zones in selectively labelled samples. The spectra show motional heterogeneity along the polymer chain as well as in the supramolecular domains. Polybutadiene segments which are adjacent to these polar clusters are restricted in their mobility, even at temperatures 100 K above the …

Effects of pressure and of thermal history on the structural phase transition of KCN

1992

The cubic-noncubic structural phase transition of a KCN single crystal is studied as a function of thermal history and of hydrostatic pressure up to 2 kbar. The standard sequence of phases is cubic-monoclinic-orthorhombic on cooling and orthorhombic-cubic on heating. The monoclinic phase is also absent in first cooling runs at low pressures (p≦250 bar). The width of the monoclinic field inp, T phase diagram is increased in second cooling runs. The effects are discussed in terms of a martensitic transformation behavior and random strain fields.

Crystallization Behaviour at High Cooling Rates of Two Polypropylenes

1993

Phase distribution of quenched samples of two isotactic polypropylenes, having different molecular weight distributions, was evaluated by a deconvolution procedure of WAXD spectra. The dependence on cooling rate of the two resins shows the low molecular weights rich polymer is characterized by a faster kinetics with an α-monoclinic to mesomorphic transition taking place at higher cooling rates.

Combined main chain/side chain polymers. A new class of liquid crystalline polymers with unusual structural, thermodynamic and dynamic properties

1990

Abstract Combined main chain/side chain polymers carry rigid rod-like mesogenic units both in the side chain and along the chain backbone. The properties of such combined systems are expected to be controlled by the competition of the interactions between the mesogenic units in the side and main chains as well as the tendency of the chain backbones to maximize their entropy. The thermodynamic, structural and dynamic properties of such combined main chain/side chain liquid-crystalline polymers were investigated for various chain architectures. The combined systems were found to display properties corresponding in many cases to a favourable superposition of properties characteristic of both m…

Elastic Properties of Liquid Crystal Elastomer Balloons

2001

We introduce a method to measure elastic properties of smectic liquid crystalline elastomers. Freely suspended smectic polymer films containing photoreactive groups are inflated to spherical bubbles and crosslinked by UV light irradiation. After crosslinking, the balloon volume is varied and elastic properties of the material are determined from the relation between radius and inner excess pressure. The influence of the network topology on the elastic behaviour is discussed.

Disentangling the Role of Chain Conformation on the Mechanics of Polymer Tethered Particle Materials

2019

[Image: see text] The linear elastic properties of isotropic materials of polymer tethered nanoparticles (NPs) are evaluated using noncontact Brillouin light spectroscopy. While the mechanical properties of dense brush materials follow predicted trends with NP composition, a surprising increase in elastic moduli is observed in the case of sparsely grafted particle systems at approximately equal NP filling ratio. Complementary molecular dynamics simulations reveal that the stiffening is caused by the coil-like conformations of the grafted chains, which lead to stronger polymer–polymer interactions compared to densely grafted NPs with short chains. Our results point to novel opportunities to …

Structured Nanoparticles from the Self-Assembly of Polymer Blends through Rapid Solvent Exchange

2017

Molecular dynamics simulations were performed to study systematically the rapid mixing of a polymer blend in solution with a miscible nonsolvent. In agreement with experiments, we observe that polymers self-assemble into complex nanoparticles, such as Janus and core-shell particles, when the good solvent is displaced by the poor solvent. The emerging structures can be predicted on the basis of the surface tensions between the polymers as well as between the polymers and the surrounding liquid. Furthermore, the size of the nanoparticles can be independently tuned through the mixing rate and the polymer concentration in the feed stream; meanwhile, the composition of the nanoparticles can be c…

Interfacial Tensions from Drop Retraction versus Pendant Drop Data and Polydispersity Effects

2004

Interfacial tensions sigma were measured by means of both methods for the following polymer pair: polyisobutylene (PIB 3) plus poly(dimethylsiloxane) (PDMS 152) and poly(dimethyl-co-methylphenylsiloxane) (CoP26*) plus PDMS 48. The numbers after the abbreviation state the molar masses in kilograms; the homopolymers exhibit polydispersities on the order of 2. The reliability of the method of drop retraction is backed up by systematic measurements, which demonstrate that it is possible to study the time evolution of sigma. Because of the free choice of the phases (drop or matrix) and the possibility to vary the overall composition of the system in a wide range, drop retraction yields more info…

Pearl-necklace structures of molecular brushes with rigid backbone under poor solvent conditions: A simulation study

2010

Bottle-brush polymers, where flexible side chains containing N=20 to 50 effective monomers are grafted to a rigid backbone, are studied by molecular dynamics simulations, varying the grafting density σ and the solvent quality. Whereas for poor solvents and large enough σ the molecular brush is a cylindrical object, homogeneous in axial direction, for intermediate values of σ an axially inhomogeneous structure of "pearl-necklace" type is formed. The "pearls," however, have a strongly nonspherical ellipsoidal shape, due to the fact that several side chains cluster together in one pearl, qualitatively consistent with predictions of Sheiko et al. [Eur. Phys. J. E 13, 125 (2004)] We analyze the …

Multi-scale simulations of polymeric nanoparticle aggregation during rapid solvent exchange.

2018

Using a multi-scale approach which combines both molecular dynamics (MD) and kinetic Monte Carlo (KMC) simulations, we study a simple and scalable method for fabricating charge-stabilized nanoparticles through a rapid solvent exchange, i.e., Flash NanoPrecipitation (FNP). This multi-scale approach is based on microscopic information from MD simulations and uses a KMC algorithm to access macroscopic length- and time scales, which allows direct comparison with experiments and quantitative predictions. We find good agreement of our simulation results with the experiments. In addition, the model allows us to understand the aggregation mechanism on both microscopic and macroscopic levels and det…