Search results for "Thermodynamics"

Thermodynamically induced shear degradation

1988

The shear degradation of polymers in semiconcentrated solutions is viewed as a function of solvent quality. It is shown that the deterioration of the thermodynamic quality of the solvent leads to a marked flow resistance due to an increasing number of contacts between the chains. This may be probed by viscosimetric measurements as well as by degradation experiments (“thermodynamically induced shear degradation”). For a detailed discussion of this phenomenon the experimental setup for the mechanochemical experiment is outlined first, followed by a survey of the kinetics of chain scission. Finally, experiments mostly obtained on polystyrene in the theta-solvent trans-decalin are discussed. Th…

Temperature and pressure dependence of phase separation of trans-decahydronaphthalene/polystyrene solution

2004

Abstract The cloud-point temperatures (Tcl’s) of trans-decahydronaphthalene (TD)/polystyrene (PS, Mw=270 kg/mol) solutions were determined by light scattering measurements over a range of temperatures (1–16 °C), pressures (100–900 bar), and compositions (4.2–21.6 vol% polymer). The system phase separates upon cooling and the Tcl was found to increase with the rising pressure for the constant composition. In the absence of special effects this finding indicates positive excess volumes. The special attention was paid to the demixing temperatures as a function of the pressure for the different polymer solutions and the plots in the T-volume fraction plane and P-volume fraction plane. The cloud…

1979

The kinetics of the anionic polymerization of styrene were investigated under pressure (1≤p/bar < 1800) with Na+ as counter ion in tetrahydropyran (THP) as solvent and with Cs+ as counter ion in 1,2-dimethoxyethane (DME) as solvent. The results yielded the activation volume of the contact ion pair ΔV and the sum (ΔV + ΔVcs) of the activation volume of the solvent separated ion pair ΔV and the volume change upon formation of solvent separated ion pairs from contact ion pairs ΔVcs. The numerical values are negative. The activation volume of the solvent separated ion pairs could be estimated.

Polymeric alloys: Model materials for the understanding of the statistical thermodynamics of mixtures

1997

Polymeric materials find industrial applications that are comparable to those of metals and ceramics.1 In addition to the great variability via the synthesis of various monomers and the choice of the degree of polymerization (N), alloying of polymers finds increasing attention for combining favorable materials properties.1,2 But polymeric (binary) alloys (A,B) of flexible polymers with chain lengths NA, NB are also most interesting for testing theoretical concepts: changing NA, NB one controls the entropy of mixing, keeping intermolecular forces invariant. Variation of these control parameters thus allows stringent tests of the theories on miscibility, unmixing etc. Furthermore, the large s…

Dynamics of Glassy Polymer Melts in Confined Geometry: A Monte Carlo Simulation

1996

Dynamic properties of a dense polymer melt confined between two hard walls are investigated over a wide range of temperatures by dynamic Monte Carlo simulation. The temperature interval ranges from the ordinary liquid to the strongly supercooled melt. The influence of temperature, density and confinement on the polymer dynamics is studied by various mean-square displacements, structural relaxation functions and quantities derived from them (relaxation times, apparent diffusion coefficients, monomer relaxation rates), yielding the following results: The motion of the monomers and polymers close to the walls is enhanced in parallel, but reduced in perpendicular direction. This dynamic anisotr…

Growing range of correlated motion in a polymer melt on cooling towards the glass transition

1999

Many liquids cooled to low temperatures form glasses (amorphous solids) instead of crystals. As the glass transition is approached, molecules become localized and relaxation times increase by many orders of magnitude1. Many features of this ‘slowing down’ are reasonably well described2 by the mode-coupling theory of supercooled liquids3. The ideal form of this theory predicts a dynamical critical temperature T c at which the molecules become permanently trapped in the ‘cage’ formed by their neighbours, and vitrification occurs. Although there is no sharp transition, because molecules do eventually escape their cage, its signature can still be observed in real and simulated liquids. Unlike c…

Stratification of polymer mixtures in drying droplets: Hydrodynamics and diffusion

2020

We study the evaporation-induced stratification of a mixture of short and long polymer chains in a drying droplet using molecular simulations. We systematically investigate the effects of hydrodynamic interactions (HI) on this process by comparing hybrid simulations accounting for HI between polymers through the multiparticle collision dynamics technique with free-draining Langevin dynamics simulations neglecting the same. We find that the dried supraparticle morphologies are homogeneous when HI are included but are stratified in core--shell structures (with the short polymers forming the shell) when HI are neglected. The simulation methodology unambiguously attributes this difference to th…

A novel approach to polymer-template mesoporous molecular sieves

2000

A novel synthesis route was developed to produce spherical silica particles. The synthesis is based on a modified Stoeber method and the room-temperature synthesis of MCM 41S-materials applying tetraethoxysilane, alcohol, water, ammonia and homopolymers as template. The specific surface area, the specific pore volume and the average pore diameter were varied in the following ranges: 5 – 1,000 m2/g; 0.1 – 1.0 cm3/g and 2-50 nm. With respect to catalytic applications hetero-atoms e.g. Al were incorporated into the silica framework.

Magnetic Soret effect in a hydrocarbon based colloid containing surfacted Mn–Zn ferrite particles

1999

Abstract The Soret effect has been investigated in a hydrocarbon based magnetic fluid containing surfacted Mn 0.5 Zn 0.5 Fe 2 O 4 nanoparticles with a magnetic volume concentration of 2.3%. The magnetic fluid fills up a vertical diffusion column which consists of a flat vertical channel between two walls and two reservoirs at the ends of the channel. One wall of the channel is being heated while the another one is cooled, maintaining a temperature gradient over the channel's width that leads to separation of particles due to the Soret effect as well as the convective flow in the channel. The combination of the two mentioned effects brings up a measurable change of the concentration of magne…

Correction: Polymer-enforced crystallization of a eutectic binary hard sphere mixture

2017

Correction for 'Polymer-enforced crystallization of a eutectic binary hard sphere mixture' by Anna Kozina et al., Soft Matter, 2012, 8, 627-630.