Effect of Pressure on Spontaneous Polarization and Tilt Angle in Ferroelectric Liquid Crystal Dobambc

Abstract

Using a thermodynamic model based on the generalized Landau free-energy density expansion, we investigate the influence of hydrostatic pressure on the spontaneous polarization and tilt angle of ferroelectric chiral smectic C (Sm C * ) phase near the Sm A-Sm C * transition in a ferroelectric mesogen DOBAMBC. It is shown that the pressure dependence of the tilt angle, spontaneous polarization and Sm A-Sm C * transition temperature (Tc) can be described in terms of four pressure-dependent Landau coefficients: two achiral coefficients a and b and two chiral coefficients Λ and d. The pressure dependence of the parameter a is due to the pressure-dependent Tc. With the increasing pressure, the stability of the Sm C * phase decreases. A close agreement between theory and experiment is found.

Thermodynamic model for the investigation of phase transition properties of homologous series ofnALandnHLferroic mesogens

“…As usual the values of P 0 , u 0 , p and S can be obtained at a given temperature as the simultaneous solutions of Equations (14)- (17). For these solutions, we require the values of Landau coupling coefficients appearing in the equations.…”

“…However, the values of S as a function of temperature are known only for one mesogen DOBAMBC. [24] Therefore, instead of using Equation (17) in the calculation, we use an empirical relation proposed by us, [20] …”

“…However, the theoretical understanding is still poor, whereas a wealth of experimental information is available. Most of the theoretical efforts [10][11][12][13][14][15][16][17][18][19][20][21] are based on the thermodynamical (phenomenological) model in which the free energy density is written as an expansion in powers of the order parameters and their coupling terms.…”

“…In Zeks' thermodynamic model, [10][11][12][13][14][15][16][17] the ferroelectric ordering of the SmC* phase is described by two order parameters: tilt vector j and polarization vector P. In none of the works based on Zeks' model the tensor orientational order parameter Q ij and the scalar smectic order parameter c are included. Mukherjee et al [18] constructed a free energy density expansion in terms of the modulus of orientational order S, the smectic order parameter c, the tilt angle u, the polarization P and the wave vector q, and the couplings between them to describe the features of direct I-SmC* transition.…”

Pressure and temperature dependences of ferroelectricity in liquid crystals

“…Using a generalised free-energy density expansion as developed by Zeks and coworkers [14,15], Singh and Singh analysed [16] the role of pressure on the ferroelectric properties of ferroic mesogens and compared the results with the available experimental data of p-( n -decyloxybenzilidene ) -p -amino-(2-methylbutyl) *Corresponding author. Email: srisingh23@gmail.com cinnamate (DOBAMBC).…”