arXiv subjects

Prasanth P. Jose

Publications and source records attributed to Prasanth P. Jose.

6 recordsLinked to original sources

arXiv2023

Relation between local density and density relaxation near glass transition in a glass forming binary mixture

Many investigations shed light on various correlations between structure and dynamics in supercooled liquids; however, a general relation between structure and dynamics remains elusive. This molecular dynamics simulation study identifies the interrelationship between the growth of the highest peak of the radial distribution function, variation in the radial force from this peak, and the slowdown of the density relaxation in the supercooled states of a model binary glass former. From the microscopic string-like motion in supercooled liquids, we argue that the surface density on a spherical shell around a reference particle at the highest peak of the radial distribution function can represent the free volume available for motion. We further show from these arguments and simulations that density relaxtion time and local density are connected; in this expression, the dynamics diverge at a higher critical value of local density. This relation is similar to the Vogel Fulcher Tammann relation in supercooled liquids, thus giving insight into the structural origin of the VFT as the jamming of particles in a channel of density relaxation.

cond-mat.soft↗

arXiv2020

Violation of Stokes-Einstein and Stokes-Einstein-Debye relations in polymers at the gas-supercooled liquid coexistence

Molecular dynamics simulations are performed on a system of model linear polymers to look at the violations of Stokes-Einstein (SE) and Stokes-Einstein-Debye (SED) relations near the mode coupling theory transition temperature $T_c$ at three (one higher and two lower) densities. At low temperatures, both lower density systems show stable gas-supercooled-liquid coexistence whereas the higher density system is homogeneous. We show that monomer density relaxation exhibits SE violation for all three densities, whereas molecular density relaxation shows a weak violation of the SE relation near $T_c$ in both lower density systems. This study identifies disparity in monomer mobility and observation of jumplike motion in the typical monomer trajectories resulting in the SE violations. In addition to the SE violation, a weak SED violation is observed in the gas-supercooled-liquid coexisting domains of the lower densities. Both lower density systems also show a decoupling of translational and rotational dynamics in this polymer system.

cond-mat.soft↗

arXiv2008

Thermodynamic and transport anomalies near isotropic-nematic phase transition

A theoretical study of the variation of thermodynamic and transport properties of calamitic liquid crystals across the isotropic-nematic phase transition is carried out by calculating the {\it wavenumber (k) and time (t)} dependent intermediate scattering function of the liquid, via computer simulations of model nematogens. The objective is to understand the experimentally observed anomalies and sharp variation in many thermodynamic and transport properties, namely specific heat $C$, sound attenuation coefficient $Γ$, thermal diffusivity $D_T$ and sound velocity $c_s$ are as the I-N transition is approached from the isotropic side. The small wavelength limit of the calculated intermediate scattering function $F(k,t)$ is used to obtain the ratio of specific heats $γ$ and other properties mentioned above. We find that all of them show non-monotonic variations near the I-N transition, with $Γ$ showing a cusp-like behavior. We suggest that the observed anomalous features are a direct consequence of the existence of pseudo-nematic domains in the system near the phase boundary and the melting and formation of such domains give rise to sound attenuation and also to the observed specific heat anomaly. A theoretical description of these anomalies should invoke translation-rotation coupling at molecular level. While the heterogeneous dynamics observed here bear resemblance to that in deeply supercooled liquids near glass transition, the thermodynamic anomalies articulated here are largely absent in supercooled liquids.

cond-mat.soft↗

arXiv2005

Complete breakdown of the Debye model of rotational relaxation near the isotropic-nematic phase boundary: Effects of intermolecular correlations in orientational dynamics

The Debye-Stokes-Einstein (DSE) model of rotational diffusion predicts that the rotational correlation times $τ_{l}$ vary as $[l(l+1)]^{-1}$, where $l$ is the rank of the orientational correlation function (given in terms of the Legendre polynomial of rank $l$). One often finds significant deviation from this prediction, in either direction. In supercooled molecular liquids where the ratio $τ_{1}/τ_{2}$ falls considerably below three (the Debye limit), one usually invokes a jump diffusion model to explain the approach of the ratio $τ_{1}/τ_{2}$ to unity. Here we show in a computer simulation study of a standard model system for thermotropic liquid crystals that this ratio becomes much less than unity as the isotropic-nematic phase boundary is approached from the isotropic side. Simultaneously, the ratio $τ_2/η$ (where $η$ is the shear viscosity of the liquid) becomes {\it much larger} than hydrodynamic value near the I-N transition. We have also analyzed the break down of the Debye model of rotational diffusion in ratios of higher order rotational correlation times. We show that the break down of the DSE model is due to the growth of orientational pair correlation and provide a mode coupling theory analysis to explain the results.

cond-mat.soft↗

arXiv2005

Universal power law in the orientational relaxation in thermotropic liquid crystals

We observe a surprisingly general power law decay at short to intermediate times in orientational relaxation in a variety of model systems (both calamitic and discotic, and also discrete) for thermotropic liquid crystals. As all these systems transit across the isotropic-nematic phase boundary, two power law relaxation regimes, separated by a plateau, emerge giving rise to a step-like feature (well-known in glassy liquids) in the single-particle second-rank orientational time correlation function. In contrast to its probable dynamical origin in supercooled liquids, we show that the power law here can originate from the thermodynamic fluctuations of the orientational order parameter, driven by the rapid growth in the second-rank orientational correlation length.

cond-mat.soft↗

arXiv2005

Anomalous glassy relaxation near the isotropic-nematic phase transition

Dynamical heterogeneity in a system of Gay-Berne ellipsoids near its isotropic-nematic (I-N) transition and also in an equimolar mixture of Lennard-Jones spheres and Gay-Berne ellipsoids in deeply supercooled regime is probed by the time evolution of non-Gaussian parameter (NGP). The appearance of a dominant second peak in the rotational NGP near the I-N transition signals the growth of pseudonematic domains. Surprisingly such a second peak is instead observed in the translational NGP for glassy binary mixture. Localization of orientational motion near the I-N transition is found to be responsible for the observed anomalous orientational relaxation.

cond-mat.soft↗