arXiv subjects

Madhusudan Tyagi

Publications and source records attributed to Madhusudan Tyagi.

3 recordsLinked to original sources

arXiv2021

Dynamics of water and ethanol in graphene oxide

We utilized the momentum transfer(Q)-dependence of Quasi-Elastic Neutron Scattering (QENS) to reveal the dynamics of water and ethanol confined in Graphene Oxide (GO) powder or membranes at different temperatures and in different orientations. The dynamics was measured across different length and time scales using several spectrometers. We found reduced diffusivities (up to 30\% in the case of water) and a depression of the transition temperatures. While water showed near Arrhenius behavior with an almost bulk-like activation barrier in a temperature range of 280-310 K, the diffusivity of ethanol showed little temperature dependence. For both water and ethanol, we found evidence for immobile and mobile fractions of the confined liquid. The mobile fraction exhibited jump diffusion, with a jump length consistent with the expected average spacing of hydroxide groups in the GO surfaces. From anisotropy measurements, we found weak anisotropy in diffusion, with the surprising result that diffusion was faster perpendicular to membrane than parallel to it.

cond-mat.soft↗

arXiv2016

Johari-Goldstein Relaxation Events Are Metabasin Transitions

We show that by representing quasi-elastic and inelastic neutron scattering from propylene carbonate (PC) with an explicitly heterogeneous model, we recover two distinct dynamic signatures in addition to diffusive motion. The intermediate scattering function provides access to the time-dependence of these two dynamic processes, and they appear to correspond to transitions between inherent states and between metabasins on a potential energy landscape. By fitting the full q-dependence of inelastic scattering, we confirm that that the Johari-Goldstein ($β_{JG}$) relaxation in PC is indistinguishable from metabasin transitions.

cond-mat.soft↗

arXiv2014

Picosecond Dynamic Heterogeneity, Hopping and Johari-Goldstein Relaxation in Glassforming Liquids

We show that incoherent quasi-elastic neutron scattering (QENS) from molecular liquids reveals a two-state dynamic heterogeneity on a 1 ps timescale, where molecules are either highly confined or are free to undergo relatively large excursions. Data ranging from deep in the glassy state to well above the melting point allows us to observe temperature-dependent population levels and exchange between these two states. A simple physical picture emerges from this data, combined with published work, that provides a mechanism for "hopping" and for the Johari-Goldstein ($β_{JG}$) relaxation, and allows us to accurately calculate the diffusion coefficient, $D_T$, and characteristic times for $α$, and $β_{JG}$ relaxations from ps timescale neutron data.

cond-mat.soft↗