Relaxation Dynamics In Liquids Research Articles

Measurements of growing surface tension of amorphous\u2013amorphous interfaces on approaching the colloidal glass transition

There is mounting evidence indicating that relaxation dynamics in liquids approaching their glass transition not only become increasingly cooperative, but the relaxing regions also become more compact in shape. Of the many theories of the glass transition, only the random first-order theory—a thermodynamic framework—anticipates the surface tension of relaxing regions to play a role in deciding both their size and morphology. However, owing to the amorphous nature of the relaxing regions, even the identification of their interfaces has not been possible in experiments hitherto. Here, we devise a method to directly quantify the dynamics of amorphous–amorphous interfaces in bulk supercooled colloidal liquids. Our procedure also helped unveil a non-monotonic evolution in dynamical correlations with supercooling in bulk liquids. We measure the surface tension of the interfaces and show that it increases rapidly across the mode-coupling area fraction. Our experiments support a thermodynamic origin of the glass transition.

Simulations of the flipping images and microparameters of molecular orientations in liquids according to the molecule string model

The relaxation dynamics of liquids is one of the fundamental problems in liquid physics, and it is also one of the key issues to understand the glass transition mechanism. It will undoubtedly provide enlightenment on understanding and calculating the relaxation dynamics if the molecular orientation flipping images and relevant microparameters of liquids are studied. In this paper, we first give five microparameters to describe the individual molecular string (MS) relaxation based on the dynamical Hamiltonian of the MS model, and then simulate the images of individual MS ensemble, and at the same time calculate the parameters of the equilibrium state. The results show that the main molecular orientation flipping image in liquids (including supercooled liquid) is similar to the random walk. In addition, two pairs of the parameters are equal, and one can be ignored compared with the other. This conclusion will effectively reduce the difficulties in calculating the individual MS relaxation based on the single-molecule orientation flipping rate of the general Glauber type, and the computer simulation time of interaction MS relaxation. Moreover, the conclusion is of reference significance for solving and simulating the multi-state MS model.

Scaling laws and memory effects in the dynamics of liquids and proteins

Recent progress in the numerical calculation of memory functions from molecular dynamics simulations allowed the gaining of deeper insight into the relaxation dynamics of liquids and proteins. The concept of memory functions goes back to the work of R. Zwanzig on the generalized Langevin equation, and it was the basis for the development of various dynamical models for liquids. In this article we present briefly a method for the numerical calculation of memory functions, which is then applied to study their scaling behavior in normal and fractional Brownian dynamics. It has been shown recently that the model of fractional Brownian dynamics constitutes effectively a link between protein dynamics on the nanosecond time scale, which is accessible to molecular dynamics simulations and thermal neutron scattering, and the much longer time scale of functional protein dynamics, which can be studied by fluorescence correlation spectroscopy.

Cluster relaxation dynamics in liquids and solids near the glass-transformation temperature

The structural relaxation in glass-forming materials is studied near the glass transformation temperature Tg indicated by the heat capacity maximum. The late-time asymptote of the Kohlrausch–Williams–Watts form of the relaxation function is rationalized via the mesoscopic-scale correlated regions in terms of the Debye-type clusters following the dynamic scaling law. It is repeatedly shown that regardless of underlying microscopic realizations in glass formers with site disorder the structural relaxation is driven by local random fields, described via the directed random walks model. The relaxation space dimension ds=3 at Tg is suggested for relaxing units of fractal dimension df=5∕2 for quadrupolar-glass clusters in ortho–parahydrogen mixtures, that is compared with entangled-chain clusters in polymers (df=1) and solid-like clusters relaxing in supercooled molecular liquids (with ds=6 and df=3). The relaxation dynamics of orientational-glass clusters in plastic crystals is attributed to the model of continuous-time random walks in space ds=6. As a by-product, the expansivity in polymers, molecular liquids, and networks is predicted.

Pressure dependence of the glass temperature in supercooled liquids

The description of the pressure evolution of the glass temperature Tg(p) based on experimental data for diethyl phtalate is discussed. First, parameterizations of Tg(P) experimental data applied are briefly given. Then a novel relation based on the modified Simon-Glatzel equation is proposed. Its applications may result in the appearance of the asymptotic temperature (theta) and the asymptotic pressure (pi) previously postulated [E. Donth,, Springer Series in Material Sci. II (Springer, Berlin, 1998), Vol. 48, pp. 6, 375]. The asymptotic pressure is hidden in the negative pressure domain. Such asymptotic behavior was absent for parameterizations of Tg(p) data in glassy liquids applied up to now.

Vibrational Relaxation Dynamics in Liquids

Vibrational Relaxation Dynamics in Liquids