The logarithmic relaxation process and the critical temperature of liquids in nano-confined states

Hair relaxation after shaping - A kinetic approach

OBJECTIVE

Hair fibres have been shaped via either a thermal route or via a chemical route. The time-relaxation transients of the shaped hairs in air, and in water, respectively, were evaluated. The collected data were kinetically modelled in order to reveal information about the rate controlling mechanism of the recovery process.

METHODS

Hair fibres were thermally shaped at different temperatures between heated plates and left to relax in an environment of controlled humidity and temperature. Different hair fibres were chemically shaped and left to relax in water of different controlled temperatures. Relaxation data were used for modelling the kinetics of the recovery processes by using exponential and logarithmic kinetic laws. The fitting of the models to the two sets of data has been checked by using the residual sum of squares for matching the proper model to each set of data.

RESULTS

The processes of shaping and recovery were assimilated with a sequence of two successive quasi-chemical reactions, occurring at the used temperatures. Based on chemical and physical assumptions, the two groups of experiments were modelled by two different laws: an exponential law, suggesting a first-order process as the rate-determining step of the relaxation of thermally shaped fibres, and a logarithmic law, suggesting a slow relaxation, based on percolation theory, for the chemically shaped fibres. This allowed use of chemical kinetics tools for calculating the values of the activation energy in each case. The evaluated values of activation energy of the relaxation processes for both thermal and chemical shaping were found to be close to each other, in spite of the different methods of shaping.

CONCLUSION

The kinetic analysis suggests that despite different reaction sequences occurring during the different shaping-relaxation processes, the rate-controlling mechanism that manages the recovery process is the same in all cases; and this process is proposed to be the thiol-disulphide reformation of intra-protein bonds inside hair.

Effect of logarithmic perturbations in ohmic like spectral densities in dynamics of electronic excitation using variational polaron transformation approach

Electronic excitation energy transfer is a ubiquitous process that has generated prime research interest since its discovery. Recently developed variational polaron transformation-based second-order master equation is capable of interpolating between Förster and Redfield limits with exceptional accuracy. Forms of spectral density functions studied so far through the variational approach provide theoretical support for various experiments. Recently introduced ohmic like spectral density function that can account for logarithmic perturbations provides generality and exposition to a unique and practical set of environments. In this paper, we exploit the energy transfer dynamics of a two-level system attached to an ohmic like spectral density function with logarithmic perturbations using a variational polaron transformed master equation. Our results demonstrate that even for a relatively large bath coupling strength, quantum coherence effects can be increased by introducing logarithmic perturbations of the order of one and two in super-ohmic environments. Moreover, for particular values of the ohmicity parameter, the effect of logarithmic perturbations is observed to be insignificant for the overall dynamics. In regard to ohmic environments, as logarithmic perturbations increase, damping characteristics of the coherent transient dynamics also increase in general. It is also shown that, having logarithmic perturbations of the order of one in an ohmic environment can result in a less efficient energy transfer for relatively larger system bath coupling strengths.

Higher-order glass-transition singularities in nano-confined states

The self-intermediate scattering functions of confined BPM at 360 K.