Nanosecond time scale dynamics of pseudo-nematic domains in the isotropic phase of liquid crystals

Ultrafast to Slow Orientational Dynamics of a Homeotropically Aligned Nematic Liquid Crystal

“…The dynamics of nematogens in the isotropic phase of liquid crystals has been studied extensively both experimentally and theoretically for the past thirty years. [1][2][3][4][5][6][7][8][9][10][11][12][13] Above but close to the N-I phase transition temperature, T NI , orientational relaxation dynamics in the isotropic phase are strongly influenced by the local nematic structure (pseudo-nematic domains). 14 Within domains, the isotropic phase is nematically ordered over a distance scale characterized by the correlation length, , that diverges as the isotropic-to-nematic phase transition is approached from above.…”

“…14 Previous optical Kerr effect experiments, which measure the time derivative of the polarizability-polarizability correlation function (closely related to the orientational correlation function) revealed power law decays at short times and an exponential decay at long time. 7,9,11,12 The long time scale relaxation is attributed to the randomization of the pseudo-nematic domains that is well described by Landau-de Gennes (LdG) theory. 14 LdG theory predicts that the correlation length, , is highly dependent on temperature T according to where 0 has a value on the order of a molecular dimension, and T* is the mean-field second-order phase transition temperature, below which supercooling of the isotropic phase becomes impossible.…”

Short-Range Order Fluctuation in the Isotropic Phase of Solutions of 4-trans-4'-n-dodecylcyanobiphenyl in Benzene Studied by Nonlinear Dielectric Spectroscopy

“…de Gennes extended the Landau theory of the second order phase transitions to the weak first order nematic-isotropic phase transition [14,15] to analyze the slow time scale and long distance scale dynamics of pseudonematic domains. The Landau-de Gennes (LdG) theory was used for interpretation of the pretransitional phenomena observed in the isotropic mesogenic liquids in the vicinity of the nematic phase obtained with the light scattering [3,24] and the optical Kerr effect [4][5][6][7][8] methods. The LdG theory also correctly describes the temperature and concentration dependences of the NDE relaxation in the pretransitional region of pure 6CHBT [10], as well as 6CHBT and 6CB solutions [11,13].…”

“…The correlation length of the domains increases as the temperature of pure liquid [7,8,10,[25][26][27] or as the concentration of mesogenic molecules in solutions approaches the transition to the nematic phase [11][12][13], and such phenomena can be quantitatively described in terms of the LdG theory. It was shown [11] that the nonlinear relaxation time τ measured as a function of concentration of the mesogenic compound fulfills the following equation:…”

“…This fascinating behavior occurs even in the isotropic phase of liquid crystals in the vicinity of the isotropic to nematic (I-N) phase transition. The pretransitional phenomena are due to the existence of a short-range orientational order of the mesogenic molecules leading to the formation of pseudonematic domains in the isotropic phase, which can be observed by various experiments: magnetic [1] and electric [2] birefringence, light scattering [3], optical Kerr ef-(907) fect [4][5][6][7][8], and nonlinear dielectric effect [9][10][11][12][13]. As predicted by the Landau-de Gennes theory [14,15], the size of the domains increases as temperature of the liquid approaches to the transition to the nematic phase.…”