Search results for "Volume fraction"

Polymer solutions: Equilibrium clusters versus shear clusters

2021

Abstract Polymer solutions are inhomogeneous on mesoscopic scales as a result of chemical bonds linking their monomeric units. This situation leads to polymer clusters within which the polymer concentration c cluster is only a small fraction of the overall concentration c. The ratio c/ c cluster (overlap parameters Ω ) quantifies the number of clusters that need to overlap to yield c. Equilibrium clusters (minimization of Gibbs energy) and shear clusters (minimization of entropy production) differ fundamentally where Ω equil ≥ Ω shear . Only in the vicinity of the glass transition temperature and at high concentration the opposite is the case. Experimental information on Ω equil as a functi…

Blends of PDMS and random copolymers of dimethylsiloxane and methylphenylsiloxane: Phase separation in the quiescent state and under shear

1999

The miscibility of random copolymers (COP), consisting of dimethylsiloxane and methylphenylsiloxane units, with poly(dimethylsiloxane)s (PDMS) was studied in the absence and in the presence of shear experimentally as well as theoretically. Blends of COP 0.86 28 with PDMS 33 (subscripts: volume fraction of DMS in the copolymer, numbers after the abbreviations: weight average molar masses in kg/mol) were investigated far from critical conditions on the PDMS side of the phase diagram. According to these experiments the two phase regime increases by shear without exception and the maximum effects grow from 3 to 12 K as the PDMS concentration increases. Theoretical calculations were performed un…

Co-Assembly of A–B Diblock Copolymers with B′-type Nanoparticles in Thin Films: Effect of Copolymer Composition and Nanoparticle Shape

2014

The coassembly of A–B diblock copolymers with B′-type nanoparticles (i.e., nanoparticles that are slightly incompatible with the B domain) leads to hierarchical structures, where the block copolymer phase separates first and the nanoparticles create close-packed arrays within the B domains due to a slower, secondary phase separation process. Here we report the results of a comprehensive study, which focused on two aspects: the influence of the nanoparticle shape (spherical vs rod-like) and the effect of the volume composition of the blocks. Three polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) copolymers featuring similar molecular weights but differing in PS volume fraction were mi…

Multiscale microstructural characterization of particulate-reinforced composite with non-destructive X-ray micro- and nanotomography

2018

Abstract Methods based on X-ray tomography are developed to study the relevant statistical quantities describing the microstructural inhomogeneity of particulate reinforced composites. The developed methods are applied in estimating microstructural inhomogeneity parameters of composites containing metallic glass particles in metal matrix, extruded in varying pressure loads. This study indicates that the critical characteristics with regard to the effect of particle clustering are cluster size and shape, local volume fraction of particles in the cluster and the distance between clusters. The results demonstrate that the spatial distribution of reinforcement is very uneven and the amount of p…

Optical experiments on a crystallizing hard-sphere–polymer mixture at coexistence

2010

We report on the crystallization kinetics in an entropically attractive colloidal system using a combination of time resolved scattering methods and microscopy. Hard sphere particles are polystyrene microgels swollen in a good solvent (radius a=380nm, starting volume fraction 0.534) with the short ranged attractions induced by the presence of short polymer chains (radius of gyration rg = 3nm, starting volume fraction 0.0224). After crystallization, stacking faulted face centred cubic crystals coexist with about 5% of melt remaining in the grain boundaries. From the Bragg scattering signal we infer the amount of crystalline material, the average crystallite size and the number density of cry…

Improved limits on the lepton-flavor violating decays tau(-) -> l(-)l(+)l(-)

2007

A search for the neutrinoless, lepton-flavor violating decay of the tau lepton into three charged leptons has been performed using 376fb-1 of data collected at an e+e- center-of-mass energy around 10.58 GeV with the BABAR detector at the SLAC PEP-II storage rings. In all six decay modes considered, the numbers of events found in data are compatible with the background expectations. Upper limits on the branching fractions are set in the range (4-8)×10-8 at 90% confidence level. © 2007 The American Physical Society.

Complex permittivity of FeCl3/AOT/CCl4 microemulsions probed by AC impedance spectroscopy

2009

Abstract The complex permittivity of FeCl 3 /AOT/CCl 4 microemulsions in the 1–10 5  Hz frequency range has been measured by the conventional AC complex impedance technique. Measurements as a function of the volume fraction of the dispersed phase (FeCl 3  + AOT) and temperature at fixed salt-to-AOT molar ratio ( R , R  = 0.5) show that the entrapment of FeCl 3 clusters significantly enhances the local permittivity of the AOT reverse micelles and the number density of charge carriers resulting from the peculiar state of the confined inorganic salt. An estimate of the apparent static permittivity of the FeCl 3 ionic clusters entrapped in the core of AOT reverse micelles gives the very high an…

Normal-state bubbles and lamellae in type-I superconductors

2005

International audience; We report an extensive study of the formation of normal-state domains in type-I superconductors. Domain patterns are first considered theoretically. The magnetic interaction between domains is described in the framework of the ``current-loop'' model: the intermediate state is modeled by a set of loops of screening current encircling the domains and interacting as in the free space. This system is shown to be formally equivalent to a set of uniformly magnetized domains. An extension of the current-loop model is proposed to take into account the constraint of the magnetic shielding by the superconducting regions. We determine the free energy of a hexagonal array of cyl…

2019

Lamella-forming ABC triblock terpolymers are convenient building blocks for the synthesis of soft Janus nanoparticles (JNPs) by crosslinking the B domain that is “sandwiched” between A and C lamellae. Despite thorough synthetic variation of the B fraction to control the geometry of the sandwiched microphase, so far only Janus spheres, cylinders, and sheets have been obtained. In this combined theoretical and experimental work, we show that the blending of polybutadiene homopolymer (hPB) into lamella morphologies of polystyrene-block-polybutadiene-block-polymethylmethacrylate (SBM) triblock terpolymers allows the continuous tuning of the polybutadiene (PB) microphase. We systematically vary …

Enthalpy and Entropy Contributions to Solvent Quality and Inversions of Heat Effects with Polymer Concentration

2006

Vapor pressures above the solutions of polystyrene in either cyclohexane (32-60 °C) or toluene (10-70 °C) have been measured by a combination of head space sampling and gas chromatography as a function of the volume fraction φ of the polymer. The thus obtained Flory-Huggins interaction parameters Χ (φ; T) were complemented by data for three other systems (tert-butyl acetate/polystyrene, cyclohexane/poly(vinyl methyl ether), 2-propanol/poly(butyl methacrylate)) reported in the literature and analyzed in terms of their enthalpy and entropy parts Χ H and Χ s . Furthermore these experimental findings were modeled by means of an approach splitting the mixing process conceptually into two parts a…