Fast picosecond reorientation in the isotropic phase of nematogens

Fast molecular reorientations in liquid crystals

“…The models also include low components generated by the rotational diff'usion of the cylinder (coupled rotations of some tens of particles), with associated times in the range of some hundred of picoseconds. These last This result is in perfect agreement with the measured intensity of the OKE signal in the picosecond range [14]; the measured linewidth of the OKE in the same range [14], and the integrated spectrum of the wings of RS [13]. It confirms the "pseudo" individual molecular origin of the effect.…”

“…As expected, in the range 28 C -34 'C we find quite linear variations of lnIBw(rz, r~";0) with~~" , leading to r "»2 close to 30 ps. These reorientational times -a few tens of picoseconds -are in very good agreement with the ones obtained by other optical techniques [8,13,14] and QNS [9 -11]. Basically, in a model of isotropic orientational diffusion, they are related to the 1=2 spherical component of the spatially averaged orientation-dependent pair-correlation function.…”

“…Since then many optical investigations in liquid crystals have been published starting with the pioneering work in Rayleigh scattering (RS) of Amer in 1975 [13], continuing with the optical Kerr effect (OKE) [14], holographic grating (HG) [15], and degenerate four-wave-mixing (DFWM) [16,17] approaches. All these techniques have been used not only to study isotropic phases but also to explore fast rotational dynamics in thin oriented liquid-crystal samples.…”

Dynamical Study of Guest-Host Orientational Interaction in LiquidCrystalline Materials

“…Beyond the mean-field approximation, or equivalently, beyond orientational relaxation through randomization of the pseudo-nematic domains with respect to each other, the interactions between the neighboring molecules result in a number of other modes of relaxation with much shorter orientational relaxation times, reflecting molecular orientational behavior from within the pseudo-nematic domains down to individual molecules. These relaxation modes exhibit no pretransitional behavior, and have been observed experimentally, both in the frequency domain [48] and time domain [49,50,54,61,56,57].…”

“…The strong host-host interaction makes the mean-field approximation inadequate for describing the rotational dynamics of liquid crystals in the isotropic phase. This topic in fact has received considerable interests, both theoretically and experimentally, over the last three decades [34,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60]. Though a complete understanding of the subject seems still missing [58,59,60], many salient features have been understood.…”