Holographic Whole-Object Photopolymerization Preserving Director Alignment in Liquid Crystalline Actuators.

Abstract

Liquid crystalline (LC) crosslinked polymeric structures are promising for soft robotic applications, as their actuation profile is intrinsically encoded and results from the structure's shape and the LC molecular orientation (director). However, it remains challenging to fabricate 3D objects and at the same time control the director orientation within the 3D structure. Liquid crystalline molecules are commonly aligned using modified surfaces or electric/magnetic fields. However, additive manufacturing methods may locally distort the director, when fabricating 3D objects. Here, holographic microlithography is employed to form entire connected 3D objects in a single exposure by cross-linking the LC, while allowing the director orientation within the object to be freely controlled. This enables us to independently choose a global director orientation and then realize complex 3D geometries in a single fabrication step. This approach avoids the director distortion present in sequential 3D printing and lithography methods, and allows for complex actuation profiles that are directly linked to the 3D director orientation. The method presented herein permits the rapid fabrication of complex 3D connected LC structures while preserving the molecular order, and thereby enables the fabrication of more complex 3D soft actuators.