Fabrication of photoprocessible azo polymer microwires through a soft lithographic approach

In this work, a soft lithographic approach has been developed to fabricate free-standing azo polymer microwires with unique photoprocessible characteristics. In the process, an epoxy-based azo polymer (BP-AZ-CA) was used to prepare both the soft lithographic masters and the microwires. The masters were prepared by photofabricating surface relief gratings on BP-AZ-CA thin films. Then the elastomeric stamps were prepared by replica molding of poly(dimethylsiloxane) prepolymer against the masters. With use of the stamps and a solution of BP-AZ-CA as "ink", the microwires were prepared by contact printing and wet etching. The microwires possessed a uniform sub-micrometer-scale transverse dimension and macroscopic longitudinal dimension. Those characteristic sizes depended on the adjustable features of the masters and stamps used in the process. The transverse dimension of the microwires could be altered after exposure to a linearly polarized Ar+ laser single beam with the polarization direction perpendicular to the longitudinal axes of the microwires. Upon irradiation of interfering p-polarized Ar+ laser beams, regular surface relief structures could be inscribed on the microwires along the longitudinal direction, which coincided with both the polarization direction of the laser beams and the grating vector direction of the interference pattern. The microwires with photoprocessible properties are potentially usable as sub-micrometer-scale materials in future miniaturized components and devices. The approach reported in this work can be further extended to the fabrication of nano-/microwires from other polymeric materials.