ISSN:0094-243X    

DOI:10.1063/1.42459

出版商:AIP    

年代:1992

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.42460

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In the cooling process of multicomponent Coulomb liquids, the localization of constituent ions is accomplished through various processes. In the superionic system, only a part of the constituent ions freezes at Tgand residual ‘‘mobile’’ ions still remains in the liquid state. The localization of the mobile ions occurs at temperatue region far below Tg. The localization of less‐mobile ion is detectable by thermal relaxation technique such as DSC, but no dispersion is seen in dielectric response. On the other hand, the localization of mobile ions can be detected only by dielectric response as a power‐low frequency dependence of conductivity &sgr;[&ohgr;]∼(i&ohgr;&tgr;c)n(0<n<1), and increase in the relaxation time &tgr;c.Self‐consistent semi‐quantitative analysis is given, based on the excess‐free‐volume model, to calculate the temperature and frequency dependence of conductivity and permittivity, as well as specific heat change through Tg. Also, a brief discussion is given on the mode‐coupling approach by Sjo¨gren.

ISSN:0094-243X    

DOI:10.1063/1.42461

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

X‐ray, neutron, and Raman scattering experiments have been performed on highly concentrated aqueous solutions of LiCl and ZnX2(X=Br and I) in the undercooled and glassy states as well as at room temperature. TheT1relaxation time and the self‐diffusion coefficient of the water protons in the aqueous the ZnBr2solutions have been measured at various temperatures toward the glass transition. For the concentrated LiCl solution, both X‐ray and neutron data have revealed stronger hydration of chloride ions (an increase in the hydration number and a decrease in the first neighbor Cl‐D distance) in the undercooled and glassy solutions than at ambient temperature. The X‐ray data have clearly shown the enhancement of the hydrogen bonded network of water in the undercooled and the glassy states. X‐ray and Raman data of the ZnX2solutions have demonstrated the formation of both [ZnX4]2−and [Zn(OH2)6]2+species in the undercooled and glassy solutions, in contrast to the presence of [ZnX2] and [ZnX3]−as main species at room temperature. The1H‐NMR data have revealed that the motion of water molecules in the ZnBr2solusions slows down with increasing solute concentration and lowering temperature. The translational motion of the water molecules is more retarded than the rotational motion with the decrease in temperature.

ISSN:0094-243X    

DOI:10.1063/1.42462

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Dynamics of amorphous polymers near glass transition temperature Tg has ben studied by quasielastic neutron scattering in the &ohgr;‐range of 0.02 to 10 meV. It was found that two modes of motion appear near Tg in the energy range of ca. 1 meV and 10–20 &mgr;eV. The faster and slower modes arise from 30–50 K below Tg and 10–20 K above Tg, respectively.

ISSN:0094-243X    

DOI:10.1063/1.42463

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The mode coupling equations for the description of supercooled liquid dynamics exhibit cuspoid bifurcation singularities. The simplest glass transition singularity causes a liquid to glass cross over at some ideal glass transition temperature Tc. There appear &agr;‐relaxation processes whose time scale crosses over near Tcfrom power law to Arrhenius variation. For T≳Tcthere holds the time‐temperature superposition principle and scale universality. Below Tcscales decouple and the &agr;‐scaling law may be invalid. Von Schweidler fractal decay is identified as reason for the stretching phenomenon. Simple schematic models can explain &agr;‐peaks quantitatively, in particular systematic deviations from the Kohlrausch law, &agr;’‐&agr;‐double peak patterns are obtained as result of self intersections of the bifurcation hypersurfaces. First principle calculations of the &agr;‐peaks for the hard sphere systems are discussed.

ISSN:0094-243X    

DOI:10.1063/1.42464

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The relaxation properties of the &bgr;‐process as described within the mode‐coupling theory for the dynamics of supercooled liquids is reviewed. This process is completely ruled by generic properties of underlying bifurcation singularities in the nonlinear equations of motion. The singularities belong to the cuspoid familyAkwithk≥2, and lead to various scaling scenarios involving one or more parameter scaling functions depending on the orderkof the relevant singularity. The theoretical predictions are compared with dielectric measurements on several polymeric systems, and in the relevant frequency region we find a quantitative agreement between theory and experimental results.

ISSN:0094-243X    

DOI:10.1063/1.42447

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We discuss the stochastic motion of atoms in a supercooled fluid near the glass transition point on the basis of the trapping diffusion model. We obtain the dynamical singularities in the mean square displacement, diffusion constant, incoherent scattering function and non‐Gaussian parameter. It is shown that the stochastic jump motion produces &agr;‐type relaxation.

ISSN:0094-243X    

DOI:10.1063/1.42448

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

It has been possible to account for the temperature and frequency dependence of the dielectric and quadrupolar relaxations in KBr1−xKCNx, and the temperature dependence of Tl in glassy solid Hydrogen with a hierarchically constrained relaxation model. In particular, the model can account for the small change in the glass transition temperature with probe frequency.

ISSN:0094-243X    

DOI:10.1063/1.42449

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A satisfactory microscopic theory of transport coefficients in dense fluids requires the consideration both of fast collisional events and of much slower decay mechanisms. In general, such approaches are necessarily complicated; fortunately, in ordinary and moderately supercooled liquids several physical approximations can be made to yield a considerably simpler analysis. This framework has been successfully applied to evaluate the diffusion and shear viscosity coefficients in several typical simple liquids. Further simplications are possible in the case of the diffusion coefficient, which can be expressed analytically. The practical advantages of this approach are illustrated for liquid Cs, obtaining results in good agreement with the observed data.

ISSN:0094-243X    

DOI:10.1063/1.42450

出版商:AIP    

年代:1992

数据来源: AIP