TY  - JOUR
A1  - Ilnytskyi, Jaroslav M.
A1  - Neher, Dieter
A1  - Saphiannikova, Marina
T1  - Opposite photo-induced deformations in azobenzene-containing polymers with different molecular architecture molecular dynamics study
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - Photo-induced deformations in azobenzene-containing polymers (azo-polymers) are central to a number of applications, such as optical storage and fabrication of diffractive elements. The microscopic nature of the underlying opto-mechanical coupling is yet not clear. In this study, we address the experimental finding that the scenario of the effects depends on molecular architecture of the used azo-polymer. Typically, opposite deformations in respect to the direction of light polarization are observed for liquid crystalline and amorphous azo-polymers. In this study, we undertake molecular dynamics simulations of two different models that mimic these two types of azo-polymers. We employ hybrid force field modeling and consider only trans-isomers of azobenzene, represented as Gay-Berne sites. The effect of illumination on the orientation of the chromophores is considered on the level of orientational hole burning and emphasis is given to the resulting deformation of the polymer matrix. We reproduce deformations of opposite sign for the two models being considered here and discuss the relevant microscopic mechanisms in both cases.
KW  - amorphous state
KW  - light polarisation
KW  - liquid crystal polymers
KW  - molecular dynamics method
KW  - optical hole burning
KW  - photochemistry
Y1  - 2011
U6  - https://doi.org/10.1063/1.3614499
SN  - 0021-9606
VL  - 135
IS  - 4
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Ilnytskyi, Jaroslav M.
A1  - Saphiannikova, Marina
A1  - Neher, Dieter
A1  - Allen, Michael P.
T1  - Modelling elasticity and memory effects in liquid crystalline elastomers by molecular dynamics simulations
JF  - Soft matter
N2  - We performed molecular dynamics simulations of a liquid crystal elastomer of side-chain architecture. The network is formed from a melt of 28 molecules each having a backbone of 100 hydrocarbon monomers, to which 50 side chains are attached in a syndiotactic way. Crosslinking is performed in the smectic A phase. We observe an increase of the smectic-isotropic phase transition temperature of about 5 degrees as compared to the uncrosslinked melt. Memory effects in liquid crystalline order and in sample shape are well reproduced when the elastomer is driven through the smectic-isotropic transition. Above this transition, in the isotropic phase, the polydomain smectic phase is induced by a uniaxial load. Below the transition, in a monodomain smectic A phase, both experimentally observed effects of homogeneous director reorientation and stripe formation are reproduced when the sample is stretched along the director. When the load is applied perpendicularly to the director, the sample demonstrates reversible deformation with no change of liquid crystalline order, indicating elasticity of the two-dimensional network of polymer layers.
Y1  - 2012
U6  - https://doi.org/10.1039/c2sm26499d
SN  - 1744-683X
VL  - 8
IS  - 43
SP  - 11123
EP  - 11134
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  -