Azobenzene-containing smart materials are able to transform the energy of light into directional mechanical stress. We develop a theory of time-dependent light-induced ordering and deformation in azobenzene materials starting from the kinetic equations of photoisomerization. The liquid crystalline (LC) interactions between rod-like trans-isomers are taken into account. Angular selectivity of the photoisomerization known as an "angular hole burning" or the Weigert effect leads to the light-induced ordering and deformation of the azobenzene materials. The time evolution of ordering and deformation is found as a function of intensity of light depending on the opto-mechanical characteristics of the materials, such as probabilities of the optical excitation of trans- and cis-isomers, angular jump during the single isomerization event, viscosity of the materials, strength of the LC interactions in both the isotropic and LC materials, and the angular distribution of chromophores in polymer chains. Established structural-property relationships are in agreement with a number of experiments and can be used for the construction of light-controllable smart materials for practical applications.

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Two-component polymer networks containing liquid crystalline (LC) mesogens and azobenzene chromophores belong to a class of smart materials which combine uniquely the orientation order of liquid crystals and light-induced deformation of photosensitive polymers. In the present study we develop a theory of light-induced deformation of azobenzene-containing LC networks. It is shown that preferential reorientation of chromophores perpendicular to the polarization direction of the light E leads to the reorientation of the mesogens due to LC interactions between the components. Reorientation of the chromophores and mesogens results in the light-induced deformation of the polymer network. The sign of deformation (expansion/contraction with respect to the vector E) depends on the orientation distribution of the mesogens and chromophores inside the network strands. The magnitude of deformation increases with increase of the volume fraction of chromophores and the strength of LC interactions between the components. The influence of the dilution of azobenzene-containing networks by the bent cis-isomers of the chromophores on the light-induced deformation is discussed.