Study of blue phases transition kinetics by thermal lens spectroscopy in cholesteryl nonanoate

Abstract

The thermal lens signal distortion recorded on the BPI supercooled blue phase of a cholesteryl nonanoate thin sample was studied. Results showed that the distortion develops as the induced thermal gradient generated by the excitation beam incidence promotes local transitions to the BPII and BPIII blue phases and to the isotropic liquid. BPII Bragg scattering of the excitation beam wavelength along with a thermo-optic coefficient change produces a thermal lens effect decay. As this phase disappears the signal recovers strength and reaches a steady state. On lowering the sample temperature, the peak value of the distortion shifts to longer times. Considering Johnson-Mehl-Avrami-Kolmogorov-type kinetics, the effective rate constants, the preexponential factor, and the overall effective activation energy for the transformations BPI to BPII and BPII to isotropic liquid were determined. A mathematical model was developed to represent the thermal lens signal variation produced during each transformation. This article shows an interesting application of thermal lens spectroscopy to the determination of phase transition kinetic parameters of cholesteric liquid crystals.

Probing Intermolecular Interaction through Thermal-Lens Spectroscopy

“…Thus, in our case, considering that the interactions between the methanol (absorber) and the other solvent (viz. CCl 4 , DCM, DMSO, CD 3 OH) are ideal, we can use the Lorentz-Lorentz equation, Similarly, under these conditions, the density, thermal conductivity, and thermal expansion coefficient are given by the following equations (5) where n, x, ρ, κ, and β refer to the refactive index, mole fraction, density, thermal conductivity, and thermal expansion coefficient, respectively. Indices 1 and 2 refer to the components of the mixture.…”

“…[1][2][3][4][5][6] TL spectroscopy is also widely used in characterizing absorptive materials. 7 The TL effect 8 was reported as early as 1965; however, the development of an extra-cavity single-beam thermallens spectrometer 9 came as late as 1973.…”

Self-Organized 3D Photonic Superstructure: Blue Phase Liquid Crystal

“…The first investigation of nonlinear optical response in BPs was carried out by Mayén-Mondragón and Yáñez-Limón in 2006 [144]. They monitored the dynamics of photothermal lens signals to study the kinetics of phase transitions in a dye doped BPLC (Carmín de Grana, 1 wt%) [144].…”

Probing Intermolecular Interactions in Binary Liquid Mixtures Using Femtosecond Laser-Induced Self-Defocusing

“…The TL process has pronounced importance in molecular and solid-state laser engineering applications and as such there have been several reports on TL effect. [1][2][3][4][5][6][7][8][9] The thermal lens effect has also led to the development of TL spectroscopy, 10,11 which is widely used in the characterization of absorptive materials. Several improvements, such as the extra-cavity single-beam thermal-lens spectrometer and dual-beam Z-scan technique, have resulted in TL spectroscopy.…”