摘要:

We model the inter-colloidal interactions in a charge-stabilized colloidal dispersion by a hard-core Yukawa potential&fgr;(r)=&sgr;0&ggr;&hthinsp;exp(−&kgr;r)/r,r>&sgr;0and apply the rescaled mean spherical approximation to calculate its static structure factor. In conjunction with the idealized mode-coupling theory, we determine the loci of the liquid-glass transition phase boundary for a salt-free suspension of charged colloids evaluated at different counter-ion environment (characterized by the &kgr;) in terms of the macro-ion parameters: volume fraction &eegr;, chargeZ0and size&sgr;0.The calculated parametric phase diagrams are quite general since the results, with slight and straightforward modification, can be utilized to study the glass transition in a more realistic colloidal solution such as an aqueous monodisperse suspension of polystyrene charged spheres with an added electrolyte. Confining our discussion, then, to the simplest salt-free colloidal liquids, we extract from our analysis of the calculated liquid-glass transition boundaries some succinct features. Specifically, we show in this work that given a range of interaction&Vkgr;=&kgr;&sgr;0≲3.8,there is a possibility of observing theliquid&lrhar2;glass&lrhar2;liquid&lrhar2;glass(LGLG)re-entrant phenomenon in restrictive regions of the phase diagram&eegr;-&sgr;0or&eegr;-Z0for a monodisperse charge-stabilized solution. However, as the&sgr;0increases above a critical size, the LGLG re-entrant behavior vanishes. To delve into this re-entrant phenomenon, we compare, for a given &Vkgr;, the glassy Debye-Waller factor, static structure factor and their spatial counterparts for two cases—nnone for lower-Z0colloids at a high &eegr; and the other for higher-Z0colloids at a low &eegr;. For the former, the glassification is basically driven by the geometric restriction while that, for the latter, it is mainly induced by the Coulomb force. We conclude from this comparison that under the same screening environment both the excluded volume and the electrostatic effects are equally effective in impelling a charge-stabilized colloidal dispersion to undergo a structural arrest configuration and hence the liquid-glass transition. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291526

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In this report we review the most important concepts in statistical physics of polymer networks. We present the field theoretical approach to the theory of phantom networks and discuss main applications of this approach to calculate the scattering spectra of weakly charged, randomly cross-linked polymer gels. We study the phenomenon of microphase separation in the model of cross-linked block copolymer. The main models of topological entanglements in polymer networks are reviewed and a new Slip-Tube Model for nonlinear elasticity of entangled polymer networks is proposed. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291527

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We present experimental investigations on the relationship between the thickness of the viscous boundary layer and the highest excitation (or cutoff) frequency of the temperature power spectrum in turbulent convection using water as working fluid. We discuss our findings with respect to those of others obtained by the same method but for fluids of different Prandtl numbers. We then propose a new technique for determining the viscous boundary layer thickness by measuring the degree of spatial correlation in temperature fluctuations at two different locations separated by a vertical distance. The preliminary data show that the proposed technique works and should work in fluids of different Prandtl numbers. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291528

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The alleged in-plane polar structure in two-dimensional (2D) smectic-C liquid crystalline phases of Langmuir monolayers was directly confirmed by the optical second harmonic generation (SHG) spectroscopy for the first time. The SH signal associated with the in-plane polar structure was found to be comparable with that coming from the out-of-plane polar distribution of molecular orientation inherent at the air-water interface. This result indicates that there exits a strong preference for the heads and tails of the molecules to spontaneously associate one another over the otherwise isotropic water surface as a result of the 2D liquid crystalline order. When the monolayer underwent a first order phase transition from SmC to a solid-like phase under compression, both of the in-plane and out-of-plane components of SH signals were considerably reduced despite an increase in density, implying the rather subtle nature of the centro-symmetry breaking in the SmC phase ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291529

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We review recent work on fluid-solid and solid-solid phase transitions in soft matter systems such as colloidal suspensions and star polymer solutions. Starting from a given interparticle pair potential we predict the corresponding phase diagrams using computer simulations, cell theory, and density functional theory. When possible, the results are compared with experimental data. In particular, we discuss the following aspects: a cascade of freezing transitions for confined colloids, stable one-component quasicrystals for charged colloids, reentrant melting and anisotropic solid phases for star polymer solutions and reentrant nematic ordering for suspensions of the tobacco-mosaic virus. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291530

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Molecular dynamics simulations are performed for a polymer melt composed of short chains in quiescent and sheared conditions in supercooled states. In quiescent states, while the self chain motions are excellently described by the Rouse model, the stress relaxation functionG(t)exhibits a stretched exponential decay in a relatively early stage and ultimately follows the Rouse function. Transient stress evolution after application of shear obeys the linear growth∫0tdt′G(t′)for strain less than 0.1 and then saturates into a non-Newtonian viscosity. A glassy component of the stress is much enhanced as compared to the entropic component. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291531

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The polymer chain dynamics during polymerization process has been investigated by means of time-resolved dynamic light scattering (TRDLS) for linear (polystyrene; St) and branched polymer chains (polydivinylbenzene; DVB). Light scattering intensity and time-intensity correlation function (ICF) were obtained every 30 sec during bulk polymerization of St and DVB homopolymers. In the case of DVB, the ICF exhibited a power law behavior exclusively at the gelation point. On the other hand, polymerization of St resulted in formation of vitrified linear polystyrene. It was found that the TRDLS was able to detect the gelation threshold of the DVB system and vitrification of St. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291532

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Bulk metallic glass formers are shown to be stronger supercooled liquids compared to non-bulk forming amorphous alloys. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291533

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291534

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We analyzed the imaginary part of frequency dependent dielectric constant&egr;″(&ohgr;)of amorphousLiNbO3at temperatures below the crystallization using the Mode coupling theory (MCT). We found that ion transportation behavior in amorphousLiNbO3can be explained well by the MCT &agr; relaxation predictions. We observed the &agr; relaxation scaling in&egr;″(&ohgr;)and as a result of which the &agr; relaxation stretched exponent&bgr;DCwas temperature independent with&bgr;DC≃0.6.©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291535

出版商:AIP    

年代:1900

数据来源: AIP