Kerr effect as a tool for the investigation of dynamic heterogeneities

Abstract

We propose a dynamic Kerr effect experiment for the distinction between dynamic heterogeneous and homogeneous relaxations in glassy systems. The possibility of this distinction is due to the inherent nonlinearity of the Kerr effect signal. We model the slow reorientational molecular motion in supercooled liquids in terms of noninertial rotational diffusion. The Kerr effect response, consisting of two terms, is calculated for heterogeneous and for homogeneous variants of the stochastic model. It turns out that the experiment is able to distinguish between the two scenarios. We furthermore show that exchange between relatively "slow" and "fast" environments does not affect the possibility of frequency-selective modifications. It is demonstrated how information about changes in the width of the relaxation-time distribution can be obtained from experimental results.

Transient birefringence of liquids induced by terahertz electric-field torque on permanent molecular dipoles

“…The total P 2 -type perturbation Δ f 2 ( u , t ) due to the two torques causes transient optical birefringence that is measured in our experiment (equation (2)). By developing a simple but relatively general model24252627 for the dynamics of f ( u , t ) (see ‘Methods' section), we derive the transient optical birefringence.…”

Nonresonant holeburning in the Terahertz range: Brownian oscillator model

“…A more general case will be treated in a separate publication. 22 Furthermore, we have restricted the calculations to a quadratic expansion of the dipole moment in the normal-mode coordinates q i and included no higher terms than the quartic anharmonicity (ϰ⌰ 4 ) in the potential. We did not allow for any coupling among the modes.…”

“…22 In the present paper we are mainly interested in oscillatory motions and use the Ohmic case as the simplest model. We mention, however, that various models with a non-Markovian damping for the high frequency dynamics in liquids and glasses have been considered.…”

“…12 for stochastic dipole reorientations apart from some minor differences, which will be discussed in detail elsewhere. 22 If we consider the Fourier transform of R i (P) (t) (OU) , R i (P) () (OU) ϭ i Ϫ2 ⑀ i () and compare it to the signal measured in the frequency domain via application of a field E M e Ϫit ,…”

Simulating asymmetric colloidal mixture with adhesive hard sphere model

“…With appropriate variations of individual interparticle stickiness 11 , 22 , and 12 , and diameter ratio ␥, qualitatively different model systems can be examined. 38, this universal theoretical way, when combined with the Lagrangian theorem density functional approximation, 43 actually leads to the most accurate DFT approach for general inhomogeneous van der Waals fluids. The two-component SHS model can be utilized to study the nucleation near the colloidal particles.…”