Search results for "dynamics."

Structure and phase transitions of a liquid crystalline polymer

1981

The structures, textures as well as thermodynamic properties of a side chain polymer exhibiting a liquid crystalline phase in addition to a partially crystalline state and the isotropic fluid state were investigated. Furthermore the kinetics of phase transitions between these states were analyzed. It was found that the properties of this polymer are intermediate between that of low molecular weight liquid crystals and common polymers. In particular it was observed that the relation between the liquid crystalline texture and the structure is different from that of low molecular weight liquid crystals and that the properties of the crystalline and liquid crystalline state depend strongly on t…

Liquid-liquid phase equilibria in polymer solutions and polymer mixtures

2002

The pressure dependence of liquid-liquid equilibria in weakly interacting binary macromolecular systems (homopolymer solutions and blends) will be discussed. The common origin of the separate high-temperature/low-temperature and high-pressure/low-pressure branches of demixing curves will be demonstrated by extending the study into the region of metastable liquid states including the undercooled, overheated and stretched states (i.e. states at negative pressures). The seemingly different response of the UCST-branch of solutions and blends when pressurized (pressure induced mixing for most polymer solutions, pressure induced demixing for most blends) will be explained in terms of the location…

1995

Surfaces have a profound effect on the structure and related properties of multiphase polymeric materials, such as polymer mixtures and block copolymer mesophases. In particular, phase transitions in the bulk (unmixing, microphase separation, etc.) may be complemented by surface-induced transitions (formation of wetting layers, surface-directed spinodal decomposition, surface-induced ordering). This review gives a brief introduction to the phenomenological theories of such phenomena, emphasizing the simplest approach based on Flory—Huggins—de Gennes free energy functionals and associated Monte Carlo simulations. More sophisticated theories and recent experiments are mentioned briefly.

One- and two-component bottle-brush polymers: simulations compared to theoretical predictions

2007

Scaling predictions and results from self-consistent field calculations for bottle-brush polymers with a rigid backbone and flexible side chains under good solvent conditions are summarized and their validity and applicability is assessed by a comparison with Monte Carlo simulations of a simple lattice model. It is shown that under typical conditions, as they are also present in experiments, only a rather weak stretching of the side chains is realized, and then the scaling predictions based on the extension of the Daoud-Cotton blob picture are not applicable. Also two-component bottle brush polymers are considered, where two types (A,B) of side chains are grafted, assuming that monomers of …

A kinetic study of the formation of smectic phases in novel liquid crystal ionogens

2013

[EN] A multi-rate non-isothermal kinetic analysis of the isotropic-melt to liquid crystalline phase transition of novel liquid crystalline ionogenic copolymers, LCIs, the 10-(4-methoxyazobenzene-4'-oxy)decyl methacrylate]-co-2-(acrylamido-2-methyl-1-propanesulfonic acid)s, 10-MeOAzB/AMPS, copolymers, has been performed by means of calorimetric experiments. An analytical methodology which includes the study of the phase transition rate parameter, the determination of the activation energies by using Kissinger and Flynn-Wall-Ozawa models, and the study of the phase transition kinetics by the use of the Avrami theory, has been applied. The formation of the mesophases from the isotropic state o…

Effects of solvent perturbation on gelation driven by spinodal demixing

1999

We study effects of solvent perturbation on kinetic competition between spinodal demixing and gelation in agarose solutions at a concentration of 5 g/l. Two different cosolutes (tert-butyl alcohol and trimethyl amine N-oxide) known for altering in opposite way solvent-mediated interactions are chosen. By rheometry, static and dynamic light scattering experiments, we show that the cosolute presence shifts the boundary of the instability region of solution leaving unaffected temperature and polymer concentration values required for percolation. Results suggest that an appropriate choice of quenching temperature and solvent allows controlling the gelation time and the gel structural properties.

Reaction kinetics in dense two-dimensional polymer solutions : an excimer probe study

1994

We report measurements of the time dependent reaction rate of excimer formation in two-dimensional solutions of a polymerized amphiphile with partially pyrene-labelled chains in monolayers at the air-water-interface. We find a time dependent reaction rate for excimer formation obeying a power law r(t) ∞ t -β . The exponent β has a value of 0.22±0.12. This value is consistent with β=1/4, as has been predicted for bimolecular diffusion-controlled reactions in two-dimensional polymer melts by de Gennes. The measurements demonstrate the usefulness of the excimer technique to explore polymer dynamics

Scaling theory of star polymers and general polymer networks in bulk and semi-infinite good solvents

1988

Theorie d'echelle utilisant l'equivalence entre la fonction generatrice du nombre total de configuration et la fonction de correlation a plusieurs spins du modele de Heisenberg classique a n composantes dans la limite n→0

Third virial coefficient for 4-arm and 6-arm star polymers

2008

We discuss the computation of the third virial coefficient in polymer systems, focusing on an additional contribution absent in the case of monoatomic fluids. We determine the interpenetration ratio and several quantities that involve the third virial coefficient for star polymers with 4 and 6 arms in the good-solvent regime, in the limit of a large degree of polymerization.

GPU Based Molecular Dynamics Simulations of Polymer Rings in Concentrated Solution: Structure and Scaling

2011

We report on equilibrium properties of a concentrated solution of non-concatenated ring polymers by Molecular dynamics simulations using HooMD-blue, a fast implementation on graphics processor units (GPUs). We are able to identify the intermediate scaling regime for the radius of gyration Rg ∝ N as well as indication for a crossover to Rg ∝ N for rings with chain length N in our fully flexible off-lattice polymer model. This crossover takes place between a ring size of 2500 and 7500 monomers for monomer density ρ = 0.5. Our results are in agreement with recent studies for lattice and stiff off-lattice models and show once again that this scaling is not model dependent at all. Furthermore th…