Reaction pathways of biochemical processes are influenced by the dissipative electrostatic interaction of the reagents with solvent water molecules. The simulation of these interactions requires a parametrization of the permanent and induced dipole moments. However, the underlying molecular polarizability of water and its dependence on ions are partially unknown. Here, we apply intense terahertz pulses to liquid water, whose oscillations match the timescale of orientational relaxation. Using a combination of terahertz pump / optical probe experiments, molecular dynamics simulations, and a Langevin dynamics model, we demonstrate a transient orientation of their dipole moments, not possible by optical excitation. The resulting birefringence reveals that the polarizability of water is lower along its dipole moment than the average value perpendicular to it. This anisotropy, also observed in heavy water and alcohols, increases with the concentration of sodium iodide dissolved in water. Our results enable a more accurate parametrization and a benchmarking of existing and future water models.

/pdf/molecular-polarizability-anisotropy-of-liquid-water-revealed-17tgo8d8zo.pdf

Molecular polarizability anisotropy of liquid water revealed by terahertz-induced transient orientation

A review and computer simulation of the structure and dynamics of liquid chloroform

A new tolane-base liquid crystal, 4'-heptyl-3-fluoro-4-isothiocyanatotolane (7TOLF), and a biphenyl-base nematogen, 4'-heptyl-3-fluoro-4-isothiocyanatobiphenyl (7BF), have been investigated for the first time to determine their electro-optical behaviour and third order non-linearity using the static Kerr effect method. Both the nematic compounds have a fluorine atom attached to the phenyl-NCS moiety. They possess the same polar head group (-NCS) and alkyl tail (-C7H15). So the effect of the tolane group of nematogen on the electro-optical behaviour was investigated and compared. The temperature dependence of the electric Kerr constant in the isotropic phase and the pre-transitional behaviour has been investigated for these high birefringence compounds in the isotropic phase. Both the compounds have a positive and large Kerr constant which increases with decrease in temperature. The Landau–de Gennes model was obeyed for these compounds. For 7TOLF, the observed value of susceptibility, χ3 is about 228 times higher than that of CS2. The experimental Kerr effect data were also compared with those of the well-studied nematic liquid crystals.

https://iopscience.iop.org/article/10.1088/0022-3727/39/8/007/pdf

Electro-optical Kerr effect of two high birefringence nematic liquid crystals

The Electro-optical kerr effect in eutectic nematic mixtures of E7 and E8

We study a nanosecond electro-optic response of a nematic liquid crystal in a geometry where an applied electric field $\mathbf{E}$ modifies the tensor order parameter but does not change the orientation of the optic axis (director $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{N}}$). We use a nematic with negative dielectric anisotropy with the electric field applied perpendicularly to $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{N}}$. The field changes the dielectric tensor at optical frequencies (optic tensor) due to the following mechanisms: (a) nanosecond creation of the biaxial orientational order, (b) uniaxial modification of the orientational order that occurs over time scales of tens of nanoseconds, and (c) the quenching of director fluctuations with a wide range of characteristic times up to milliseconds. We develop a model to describe the dynamics of all three mechanisms. We design the experimental conditions to selectively suppress the contributions from the quenching of director fluctuations (c) and from the biaxial order effect (a) and thus, separate the contributions of the three mechanisms in the electro-optic response. As a result, the experimental data can be well fitted with the model parameters. The analysis provides a rather detailed physical picture of how the liquid crystal responds to a strong electric field on a time scale of nanoseconds. The paper provides a useful guidance in the current search for the biaxial nematic phase. Namely, the temperature dependence of the biaxial susceptibility allows one to estimate the temperature of the potential uniaxial-to-biaxial phase transition. An analysis of the quenching of director fluctuations indicates that on a time scale of nanoseconds, the classic model with constant viscoelastic material parameters might reach its limit of validity. The effect of nanosecond electric modification of the order parameter can be used in applications in which one needs to achieve ultrafast (nanosecond) changes in optical characteristics, such as birefringence.

https://link.aps.org/accepted/10.1103/PhysRevE.90.062504

Nanosecond electro-optics of a nematic liquid crystal with negative dielectric anisotropy.

An apparatus is described to measure the Kerr constant of conducting as well as non-conducting liquids and solutions. High-voltage pulses of short duration (1.5 μs) are applied across the Kerr cell and the resultant birefringence is measured by a novel signal-nulling technique. New expressions are derived for the null conditions for an optically active birefringent medium. Results are presented at 633 nm and 293 K for water, methanol, ethanol, propan-1-ol and propan-2-ol. The Kerr constant of water (3.0 × 10-14 m V-2) was in good agreement with recent determinations.

Beevers

Papers

Measurement of Kerr Constants of Conducting Liquids