Viscosity of a Liquid Crystal near the Nematic–SmecticAPhase Transition

Abstract

We report the results of an x-ray scattering study where both the dynamic and the static properties of a liquid crystal (8OCB) near the nematic-smectic A phase transition were probed. The static, time-averaged data show the gradual formation of smectic layers in the nematic phase, and we find that the smectic order correlation length parallel to the molecular axis diverges with the critical exponent nu( parallel )=0.70(4) at the transition. The literature value is nu( perpendicular )=0.58 for the perpendicular direction. By x-ray photon correlation spectroscopy, we find that the viscosity coefficient eta(3) shows critical, diverging behavior at the phase transition with a critical exponent x=0.95(5). This contradicts previous light scattering work (x=0.50), but is in good agreement with the theoretical prediction x=3nu( parallel )-2nu( perpendicular ) by Hossain et al.

Effects of partial coherence on correlation functions measured by x-ray photon correlation spectroscopy

“…[1][2][3][4][5][6][7][8][9][10][11] At third-generation synchrotrons it is nowadays possible to produce intense x-ray beam with a high degree of coherence. The scattered intensity distribution of such an x-ray beam coming from a rough surface provides a speckle pattern due to destructive and constructive interference.…”

Small-Angle X-Ray Scattering of Ionic Liquids

“…Research areas that have benefitted considerably from XPCS include but are not limited to equilibrium dynamics of concentrated colloidal suspensions [90][91][92][93][94][95], glassy dynamics [96,97], atomic diffusion [98,99], dynamical heterogeneities in soft matter [100,101], critical fluctuations of liquid crystals [102,103], near-equilibrium coarsening fluctuation in alloys [104] and weakly disturbed soft condensed matter systems [96,[105][106][107], and surface dynamics of fluidic and polymeric systems [108][109][110][111][112][113][114]. Most of these systems share some common traits, namely, the dynamical fluctuations happen on a length scale between nanometers and micrometers, and the dynamic timescale is greater than a microsecond.…”

The Influence of Natural and Model Nanoinclusions on the Properties of Nematic Phase

“…The theory of the critical behavior of cybotactic nematic was given by Jähnig and Brochard [12]. Although these smectic cybotactic intrusions are not solid, but under favourable conditions could act like solid-like ones, which manifests in, e.g., twist and bend elastic constants K 22 and K 33 [13,14], rotational viscosity coefficient c 1 [13,15] and Miesowicz viscosity coefficient g 2 (directorn n is parallel to the flow viscosity v * ,n njj v * ) [13, [16][17][18][19][20][21]. This work concentrates on influence the inclusions have on the Miesowicz viscosity coefficient g 2 [16] in the liquid crystalline nematic phase.…”