3D-structured liquid crystal networks formed by dichroic photoinitiator initiated photopolymerization

Photopolymerization of liquid crystal monomers initiated by means of a dichroic photoinitiator provides an additional degree of freedom in controlling the morphology and structure of the liquid crystal networks formed. The absorption of the dichroic photoinitiator, and thereby its initiation rate, depends on its position towards the transversal light beam used for polymerization as well as its position towards the polarization of the light beam. The photoinitiator adapts the director profile of the liquid crystal monomer. As a result planar oriented areas aligned orthogonal to the propagation direction of the light beam polymerize faster than the ones parallel to it. Similarly, planar aligned areas with their orientation parallel to the electrical field vector of the light polymerize faster than the planar aligned areas oriented perpendicular to that. Based on this principle complex lithographic structures are built, not only forming structures in the plane of the polymerizing film but also in the third dimension along its cross-section. Additionally, applying the dichroic photoinitiator together with the principle of polymerization induced diffusion in monomer blends provides a wealth of new structures, especially when combined further with complicated, but well-controlled, morphologies such as those of twisted, splayed and cholesteric liquid crystal monomers.