摘要:

AbstractAny interpretation of the dynamics in liquids requires understanding of fluctuating collective motions in the stationary limit. To this end, “eigen‐states” are defined, namedconformons. Conformons are to be considered as a new type of bosons. Their properties characterize the typical features of the dynamics in disordered systems. Eigen‐energy and “eigen‐entropy” are adjusted to each other to minimize the free energy of each mode (saturation). The whole conformon ensemble exhibits a photon statistics with a broad universal mode spectrum. Analogues of Stefan‐Boltzmann's law and of Wien's displacements law are formulated.A crucial point of our treatment is that conformons should, in principle, only become excited above a system‐typical temperature To(Vogel‐Fulcher temperature). Equilibrium properties of supercooled liquids are necessarily related to To. Cp/Cv, of the conformon ensemble should, for example, show a typical ΔT3‐dependence (ΔT=T‐To). Experimental data give evidence in support of this behaviour. As a consequence of the excluded volume supercooled liquids already solidify about 30 to 40 degrees above Toat least at the quasi‐static glass temperature Tg.Relaxation in the glass transition regime of glass formers can fully be described if relaxation modes are connected to each conformon. The description covers a set of experiments so different like mechanical and dielectric relaxation or quasi‐elastic

ISSN:1022-1360    

DOI:10.1002/masy.19950900104

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractEffects of an external orienting field and orientational cross‐section for molecular association on the kinetics of crystal nucleation and critical temperature of crystallization is discussed. Dipole and quadrupole effects of an electric (magnetic) field and quadrupole effects of hydrodynamic potential of uniaxial flow are considered. Critical temperature of crystallization, free energy barrier of nucleation and nucleation rates are orientation‐dependent. Smaller orientational cross‐sections result in stronger anisotropy of the nucleation

ISSN:1022-1360    

DOI:10.1002/masy.19950900105

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractElectro‐Optic relaxation of a poled, Non‐Linear Optical sidechain polymer with Tg140°C, containing 4‐dimethylamino‐4′‐nitrostilbene (“DANS”) in the sidechains, has been studied at 120°C with and without annealing at the same temperature. The time‐dependence of the decaying EO coefficients r(t) shows a strong departure from the classical single‐exponential Debye model, especially in the unannealed samples. This departure is attributed to physical ageing, slowing down the orientational relaxation of the sidechains. The Debye model with r(t)‐r(0). exp ‐t/τ] is modified semi‐empirically by introducing atime‐dependentcharacteristic Debye relaxation time τ(t). Of several trial expressions, one is selected which fits the relax

ISSN:1022-1360    

DOI:10.1002/masy.19950900106

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractMonte Carlo simulations of coarse–grained models of macromolecules offer a unique tool to study the interplay between coil conformations, thermodynamic properties, and chain configurational relaxation and diffusion.Two examples are discussed where the chain conformation strongly differs from a gaussian coil: (i) collapsed chains in a bad solvent, where anomalous diffusion occurs in the Rouse limit and the relaxation time increases at least with the third power of chain length. (ii) Expulsion of a chain from a semidilute polymer brush. The initially stretched chain contracts to a gaussian coil and the center of mass moves outward with constant velocity until it reaches the region of the “last blob” where crossover to diffusive behavior o

ISSN:1022-1360    

DOI:10.1002/masy.19950900107

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractABSTRACTThe elastic constantsCikof solids are related to the amplitude of the strain fluctuations which can be simulated atomistically, thus offering a possibility of determining theCikvalues of the solid of interest based on a proposed atomistic arrangement and a given interaction between the atoms. We show that the approach is practical by calculating the elastic constants of crystalline (orthorhombic) polyethylene, crystalline (monoclinic) isotactic polypropylene, and glassy bisphenol‐A‐polycarbon

ISSN:1022-1360    

DOI:10.1002/masy.19950900108

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe basic result of thecoupling modelconsists of a cross‐over from exp‐(t/τo) to exp‐(t/τ*)1‐nat a temperature insensitive microscopic timetc. We indicate how this basic result can be derived from chaotic, interacting Hamiltonian systems which include densely packed polymer molecules. Recent quasielastic neutron scattering experiments and molecular dynamics simulations are discussed and the results are shown to support this result as well. An application of thecoupling modelto find how the viscoelasticity of a polymer depends on the chemical structure of the monomer through the coupling parameter of the local segmental motion is given to illustrate the utility of

ISSN:1022-1360    

DOI:10.1002/masy.19950900109

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractUsing the neutron spin echo spectroscopy, the internal segmental diffusion of chain molecules in polymer melts and concentrated solutions was studied. These investigations show that beyond a characteristic length dtand after a cross over time τe(dt) the segmental diffusion of the single chains is strongly impeded and deviates from the Rouse dynamics. dtis polymer specific and depends on the temperature as well as on the polymer concentration.Within the framework of the reptation concept, where dtis identified with the mean distance between intermolecular entanglements or with the tube diameter, the microscopically determined dt‐values agree quite well with those derived from related macroscopic measurements of the plateau modulus. A similar good agreement is also found with respect to the segmental friction coefficients obtained either from the Rouse regime of the NSE spectra or from Theological data of corresponding short chain systems, where entanglements are not yet effecti

ISSN:1022-1360    

DOI:10.1002/masy.19950900110

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

ISSN:1022-1360    

DOI:10.1002/masy.19950900111

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractIntramolecular motion and mechanisms of local mobility were considered in linear polyesters, Including thermotropic systems, on the base of experimental results of dielectric absorption research. In some cases the role of molecular motion in the formation of the mesomorphic structure is established.

ISSN:1022-1360    

DOI:10.1002/masy.19950900112

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

ISSN:1022-1360    

DOI:10.1002/masy.19950900113

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY