Photo-induced deformations in azobenzene-containing side-chain polymers: molecular dynamics study

摘要

We perform molecular dynamics simulations of azobenzene containing side-chain liquid crystalline polymerudsubject to an external model field that mimicks the reorientations of the azobenzenes upon irradiation with polarizedudlight. The smectic phase of the polymer is studied with the field applied parallel to the nematic director,udforcing the trans isomers to reorient perpendicularly to the field (the direction of which can be assosiated withudthe light polarization). The coupling between the reorientation of azobenzenes and mechanical deformationudof the sample is found to depend on the field strength. In a weak field the original smectic order is meltedudgradually with no apparent change in the simulation box shape, whereas in a strong field two regimes areudobserved. During the first one a rapid melting of the liquid crystalline order is accompanied by the contractionudof the polymer along the field direction (the effect similar to the one observed experimentally in azobenzeneudcontaining elastomers). During the slower second regime, the smectic layers are rebuilt to accomodate theudpreferential direction of chromophores perperdicular to the field.