Search results for "Solution theory"

Compatibility of a statistical copolymer P(EMA-co-MMA) with PS and PMMA

1999

The compositions of coexisting phases and the interface widths in blends of a statistical copolymer of poly(ethylmethacrylate-co -methylmethacrylate) (P(EMA 1-x -co-MMA x )) and a deuterated polystyrene (PS(D)) as well as a deuterated poly(methylmethacrylate) (PMMA(D)) have been investigated by neutron reflectometry (NR). Interaction parameters are calculated from the compositions of coexisting phases and the interface width values. Utilizing a novel two dimensional scheme for graphical representation of the interaction parameters, the results are in very good agreement with studies on the interaction parameters for PS/PMMA, PS/PEMA and PEMA/PMMA blends. In particular, χ EMA/MMA deduced fro…

Structure and thermodynamics in polymer blends. Neutron scattering measurements on blends of poly(methyl methacrylate) and poly(styrene-co-acrylonitr…

1992

Abstract Neutron scattering on polymer blends of deutero-poly(methyl methacrylate) (D-PMMA) and poly(styrene-co-acrylonitrile) with 19 wt% acrylonitrile (PSAN-19) exhibits excess scattering for scattering vectors Q≲0.2 nm−1 if the volume fraction of D-PMMA is less than 0.5 and greater than 0.05. The range of occurrence and the amount of excess scattering depends to a certain degree on the procedure of sample preparation. If the excess scattering is eliminated by linear extrapolation from large to small Q in the Zimm representation, the residual scattering intensity in the small and intermediate Q-range can be interpreted by the mean field approach of de Gennes with a concentration-dependent…

Equilibrium phase behavior of polyethylene oxide and of its mixtures with tetrahydronaphthalene or/and poly(ethylene oxide-block-dimethylsiloxane)

2002

Liquid/solid and liquid/liquid (LL) transition temperatures were measured by means of an automated device that monitors the light passing through the systems as a function of T at different constant cooling or heating rates q. For pure polyethylene oxide (PEO) crystallization and melting temperatures depend on |q|0.3 and become identical at the equilibrium transition temperature Tm=61.0 °C in the limit of infinitely slow cooling/heating. The reduction of Tm for PEO dissolved in tetrahydronaphthalene (THN) yields information on the Flory–Huggins interaction parameter ξ between these two compounds; ξ results negative and decreases markedly with rising polymer concentration. A tentative explan…

Random Copolymers:  Their Solution Thermodynamics as Compared with That of the Corresponding Homopolymers

2008

Vapor pressure data (at 50 °C) of solutions of poly(methyl methacrylate) [PMMA], polystyrene [PS], and poly(styrene-ran-methyl methacrylate) [P(S-ran-MMA)], with different weight fractions f of styrene units, in either CHCl3, acetone [AC], methyl acetate [MeAc], or toluene [TL] were evaluated with respect to the dependence of the Flory−Huggins interaction parameter χ on polymer concentration and on f. For all solutions under investigation, χ varies considerably with the composition of the mixture, and only for four of them [CHCl3/PS, AC/PMMA, MeAc/PS, and TL/P(S-ran-MMA) f = 0.5] is this dependence linear; another four systems exhibit a minimum [CHCl3/PMMA, CHCl3/P(S-ran-MMA) f = 0.5, TL/PM…

Intrinsic Viscosity of Aqueous Solutions of Carboxymethyl Guar in the Presence and in the Absence of Salt

2008

Intrinsic viscosities were determined for solutions of CMG in pure water and 0.9 wt.-% aqueous NaCl. To avoid the 0/0-type extrapolation typical for Huggins plots, a new procedure was used. For CMG and pure water, this requires only two adjustable parameters: the specific hydrodynamic volume of the polymer in the limit of infinite dilution and a hydrodynamic interaction parameter. The intrinsic viscosity of CMG (no salt) at room temperature is 6 050 mL · g -1 ; approximately half as large as that of Na-PSS of comparable molar mass. The ratio of the intrinsic viscosities with and without salt is ≈7 for CMG, as compared to >100 for Na-PSS. The reasons for the different behaviors of the two ty…

Theory of double beta decay

2005

Basic features of the two-neutrino double beta ( 2 ν β β ) decay and neutrinoless double beta ( 0 ν β β ) decay are discussed. A short review of the most important nuclear models, used to describe the ββ decay, is given. A deeper survey of the nuclear matrix elements, related to the above-mentioned decay modes, is performed using the proton-neutron quasiparticle random-phase approximation (pnQRPA). In particular, the extraction of a proper value of the proton-neutron particle-particle interaction parameter in this theory is addressed. The relevance of different multipoles in the multipole decomposition of the 0 ν β β matrix element is also discussed in the pnQRPA framework.

2021

Comparative analyses of the nuclear matrix elements (NMEs) related to the 0νβ+β+ decay of 106Cd to the ground state of 106Pd and the ordinary muon capture (OMC) in 106Cd are performed. This is the first time the OMC NMEs are studied for a nucleus decaying via positron-emitting/electron-capture modes of double beta decay. All the present calculations are based on the proton-neutron quasiparticle random-phase approximation with large no-core single-particle bases and realistic two-nucleon interactions. The effect of the particle-particle interaction parameter gpp of pnQRPA on the NMEs is discussed. In the case of the OMC, the effect of different bound-muon wave functions is studied.

Monte Carlo Simulation of Polymeric Materials — Still a Challenge?

1992

Monte Carlo simulation of polymeric materials is difficult, since they exhibit nontrivial structure over many different length scales, from the bond length (∼1A) to the radius of the random coil (∼102A) and still larger collective length scales, and similarly, motions occur on very different time scales. Hence it is a nontrivial problem to devise suitable coarse-grained models which capture the essential physics and are accessible to simulation.

Coriolis interaction parameters of the (2100; F2) bands of SiH4 and GeH4. A test of local mode models

1995

Abstract The high-resolution spectra of the (2100; F 2 , N ), N = 1 and 2, bands of SiH 4 and GeH 4 have been recorded and preliminary analyzed. The Coriolis interaction parameter 2 Bζ 3 is obtained; it provides a test of three widely used models: the harmonically coupled anharmonic oscillators model with two different kinds of variables, and the normal mode model with Darling-Dennison resonance included.

Instabilities of infinite matter with effective Skyrme-type interactions

2002

The stability of the equation of state predicted by Skyrme-type interactions is examined. We consider simultaneously symmetric nuclear matter and pure neutron matter. The stability is defined by the inequalities that the Landau parameters must satisfy simultaneously. A systematic study is carried out to define interaction parameter domains where the inequalities are fulfilled. It is found that there is always a critical density $\rho_{cr}$ beyond which the system becomes unstable. The results indicate in which parameter regions one can find effective forces to describe correctly finite nuclei and give at the same time a stable equation of state up to densities of 3-4 times the saturation de…