Vapor-assisted room temperature nanoimprinting-induced molecular alignment in patterned poly(3-hexylthiophene) nanogratings and its stability during thermal annealing

Abstract

Vapor-assisted imprinting technology has been well explored to have good potential for practical application to fabricate topographical nanostructures of polymer film. Herein, we demonstrated that the poly(3-hexylthiophene) (P3HT) nanograting topography can be excellently fabricated via the vapor-assisted room-temperature nanoimprinting lithography (VART-NIL) technique based on a poly(dimethylsiloxane) (PDMS) template and carbon disulfide (CS₂) vapor atmosphere. Grazing incidence wide angle X-ray diffraction (GIWAXD) was employed to illustrate that the VART-NIL procedure could not only be used to fabricate the topographical pattern, but also to induce the molecular alignment transition from an edge-on to a face-on alignment, including both form II and form I crystals. Furthermore, according to GIWAXD and atomic force microscopy (AFM) investigations in situ, the stability of the nanopattern surface morphology and molecular alignment of P3HT nanograting film are dependent on the thermal annealing treatment differently. The patterned P3HT nanograting morphology largely disappears into a planar surface at elevated temperatures and the crystallographic structure of the P3HT crystal transfers from form II to form I during the elevated temperature process; however, the nanoimprint-induced face-on molecule alignment of form I conformation surprisingly remains eternal within the distorted nanograting film after the cooling step. Furthermore, the face-on molecular alignment of the form I conformation remained developed and steadily and successively enhanced during the cooling step.