Oscillatory dynamic surface structures in patterned liquid crystal network coatings

Controlled formation of surface topographies has led to an interesting set of applications (friction control, cell adhesion and motility, self-cleaning and many more). Utilizing light-sensitive molecules in combination with liquid crystal network (LCN) coatings allows for the creation of surface structures upon irradiation. For these LCN coatings, the alignment determines the shape of the topography and thus the application of the material. An outstanding method to control the alignment of the liquid crystals locally, is utilizing a so-called photo-alignment layer. Here, we present the use of such a layer in combination with azobenzene-doped LCN coatings to create different shapes of topographies that can be used for oscillatory deformations. Azobenzene-doped LCN coatings were made with different planar alignments and defect lines. Upon UV light actuation, we obtained asymmetric or symmetric topographies defined by the symmetry of the defect. In this way we create asymptotic, hills, valleys or continuous sinusoidal topographies. In addition we show that these topographies can be addressed locally. We induced these oscillatory deformations by utilizing polarized UV light in combination with blue light to control the cis and trans formation of the azobenzene crosslinker. Since the azobenzene has dichroic properties, this illumination method induces a local actuation of the azo-LCN coating. Upon rotation of linear polarized UV light, the actuation becomes oscillatory and the surface structures dynamic.