Modeling of Nonlinear Optical Phenomena in Host-Guest Systems Using Bond Fluctuation Monte Carlo Model: A Review.

Antoni C Mitus,Vladimir Toshchevikov,Wojciech Radosz,Marina Saphiannikova,Grzegorz Pawlik

doi:10.3390/ma14061454

Abstract

We review the results of Monte Carlo studies of chosen nonlinear optical effects in host-guest systems, using methods based on the bond-fluctuation model (BFM) for a polymer matrix. In particular, we simulate the inscription of various types of diffraction gratings in degenerate two wave mixing (DTWM) experiments (surface relief gratings (SRG), gratings in polymers doped with azo-dye molecules and gratings in biopolymers), poling effects (electric field poling of dipolar molecules and all-optical poling) and photomechanical effect. All these processes are characterized in terms of parameters measured in experiments, such as diffraction efficiency, nonlinear susceptibilities, density profiles or loading parameters. Local free volume in the BFM matrix, characterized by probabilistic distributions and correlation functions, displays a complex mosaic-like structure of scale-free clusters, which are thought to be responsible for heterogeneous dynamics of nonlinear optical processes. The photoinduced dynamics of single azopolymer chains, studied in two and three dimensions, displays complex sub-diffusive, diffusive and super-diffusive dynamical regimes. A directly related mathematical model of SRG inscription, based on the continuous time random walk (CTRW) formalism, is formulated and studied. Theoretical part of the review is devoted to the justification of the a priori assumptions made in the BFM modeling of photoinduced motion of the azo-polymer chains.

Highlights

We review the results of Monte Carlo studies of chosen nonlinear optical effects in hostguest systems, using methods based on the bond-fluctuation model (BFM) for a polymer matrix
The proposed theories can explain various experimental results for broad classes of azobenzene-containing polymers, as summarized briefly below. As it was discussed in Section 2.1.3, the orientation potential provides the mechanical stress of the magnitude 100 MPa—4 GPa at conventional light intensity I ∼ 100 mW/cm2, the stress being enough to deform irreversibly azobenzene polymers, which are deep in a glassy state [111,112,113,114,117,130,131]
Orientation interactions between the rod-like chromophores in trans-state and included liquid crystalline (LC) mesogenic fragments result in additional orientation ordering in the plane perpendicular to the polarization vector of the light leading to the biaxial ordering and deformation of azobenzene containing LC polymers [134,135,169,170,171]

Summary

Introduction

Host-guest systems play an important role in studies and applications of nonlinear optical effects [1]. Those systems consist of various types of guest molecules and particles, such as the dipolar and octupolar molecules, coated spheres, photo-isomerizable molecules, etc. The latter can be a liquid crystal, polymer, biopolymer or other material. In nonlinear optical applications the host-guest systems interact with the electromagnetic field via various types of light-matter interactions, resulting in a multitude of physical effects [1]

Methods

Results

Conclusion