Search results for "Fluid Dynamic"
showing 10 items of 1034 documents
Phase Behaviour of Dye-Containing Liquid Crystalline Copolymers and their Mixtures with Low Molecular Weight Liquid Crystals
1985
Liquid crystalline side-chain polymers can be obtained by connecting the mesogenic groups and the polymer chain via a flexible spacer. The liquid crystalline polymers combine the well-known properties of low molecular weight liquid crystals with those of polymers.1
Frictional drag between polymer bearing surfaces
2002
Some fundamental features of friction between two polymer bearing surfaces in relative sliding motion are investigated by molecular dynamics simulations. End-tethered and adsorbed polymers are considered under good and poor solvent conditions. The shear stress is measured while varying the solvent's viscosity, surface separation, degree of polymerization and grafting density. For all systems we observe shear thinning that is attributed to the orientation of the chains along the shear direction. This effect is particularly strong for brushes, for which the shear stress during the steady sliding state is mainly determined by the degree of overlap between the brushes.
Phase Behavior of the System Linear Polyglycerol + Methanol + Carbon Dioxide
2011
To compare the phase behavior of linear and hyperbranched polymers, the phase envelopes of the ternary system linear polyglycerol + methanol + carbon dioxide were determined for polymers of varying molar mass. Phase changes were detected by a static synthetic method using the Cailletet setup for temperatures between 331 K and 421 K and pressures up to 13.1 MPa. Besides the vapor–liquid and liquid–liquid equilibria, also the vapor–liquid to vapor–liquid–liquid and vapor–liquid–liquid to liquid–liquid phase boundaries are reported. The experimental results are similar to systems with hyperbranched polymers (rather than linear polymers). For the systems with linear polymers, however, the bubbl…
Scattering function and the dynamics of phase separation in polymer mixtures under shear flow
1988
The phenomenological mean-field theory describing concentration fluctuations and spinodal decomposition of binary mixtures of long flexible macromolecules is generalized to mixtures under steady shear flow. This shear flow leads to a partial orientation and stretching of the coils, as well as to an anisotropic deformation of concentration fluctuations. Generalizing the approach of Onuki and Kawasaki, we obtain the collective scattering function describing these concentration fluctuations in the mixture under shear flow. Both the steady-state situation in the one-phase region and the initial stages of spinodal decomposition for concentrations inside of the spinodal curve are considered.
Transient birefringence of polymer melts in intermittent shear flow: Model analysis of the non-linear viscoelastic behaviour
1977
A non-linear viscoelastic model has been used to interpret transient flow birefringence in changing shear flow for a polymer melt. It is shown how the new model is consistent with the basic hypothesis of the linear stress-optical law. Stress growth in shear flow and relaxation after different amounts of shearing are compared with the predictions of the non-linear model. A good agreement between experimental data and theoretical predictions is found.
Viscometric behaviour of polymer blends based on poly (vinylidene fluoride)
1994
The viscosity behaviour of dilute dimethylformamide solutions of poly(vinylidene fluoride)-poly (methyl methacrylate) and poly(vinylidene fluoride)-polystyrene has been studied at 25°C. The polymer concentration ranges are such that neither phase separation nor microgel formation occurs, although we are very close to theta conditions. The intrinsic viscosity and viscosity interaction parameter of the ternary mixtures have been calculated. The estimation of the compatibility of the above polymer pairs has been studied based on: a) specific viscosities; b) viscosity interaction parameters, according to Krigbaum and Wall formalism, and c) viscosity interaction parameters of a system formed by …
Nonisothermal elongational behavior of blends with liquid crystalline polymers
1994
Measurements of melt strength and breaking stretching ratio of several blends of thermoplastic polymers with liquid crystalline polymers are presented. The melt strength behavior depends not only on the viscosity of the blends but also on the temperature dependence of the viscosity. In particular, even if the viscosities of the blends are, at the extrusion temperature, lower than that of the thermoplastic matrices, the melt strength can be larger than that of the pure thermoplastics if its viscosity-temperature curve exceeds that of the matrices far from the solidification temperature. This behavior allows one to spin or film blow these blends despite the low viscosity.
Shear flow characterization of blends containing liquid crystal polymers
1992
A simple phenomenological approach is proposed in order to predict the presence of minima in the viscosity-composition curves of blends of thermoplastic with liquid crystal polymer (LCP). When the viscosity of the liquid crystal polymer is larger than that of the thermoplastic matrix, a minimum is observed. A possible explanation of the presence of yield stress in the flow curves of these blends is also given.
Optimized Continuous Application of Hyperpolarized Xenon to Liquids
2018
International audience; In recent years, NMR with hyperpolarized (HP) xenon inside functionalized host structures (e.g. cryptophanes) have become a potential candidate for the direct observation of metabolic processes (i.e. molecular imaging). A critical issue for real applications is the dissolution of the HP-gas in the liquid which contains the host. In this work, we present recent developments for an improved and controlled dissolution of HP-Xe in liquids using hollow fiber membranes and different compressor systems. The designed apparatus consists of a compressor and a membrane unit. The compressor provides HP-129 Xe continuously at small adjustable pressures and in a polarization-prese…
Conduit dynamics and post explosion degassing on Stromboli: A combined UV camera and numerical modeling treatment
2016
Recent gas flux measurements have shown that Strombolian explosions are often followed by periods of elevated flux, or “gas codas,” with durations of order a minute. Here we present UV camera data from 200 events recorded at Stromboli volcano to constrain the nature of these codas for the first time, providing estimates for combined explosion plus coda SO2 masses of ≈18–225 kg. Numerical simulations of gas slug ascent show that substantial proportions of the initial gas mass can be distributed into a train of “daughter bubbles” released from the base of the slug, which we suggest, generate the codas, on bursting at the surface. This process could also cause transitioning of slugs into cap b…