Poly(dimethyl siloxane) bimodal brush: Simple method of preparation and performance enhancement of omniphobic coatings
Ziruo Lai, Jian Wang, Guojun Liu
Abstract
• PDMS bimodal brushes show improved dynamic dewetting over unimodal brushes. • Bimodal brushes reduce sliding angles, enhancing repellency, wear resistance, and flexoprinting. • Bimodal brush coatings are cost-effective to produce. End-tethered chains in a polymer brush usually have a unimodal length distribution and are commonly prepared using ’graft-from’ or ’graft-to’ methods. This paper introduces a novel self-assembly technique to create an epoxy-bearing ladder-like polysilsesquioxane (L) coating with a bimodal poly(dimethyl siloxane) (PDMS) surface brush. The process begins with synthesizing L#k, which consists of L with a minor fraction of a graft ( g ) copolymer (L- g -#k), where #k represents PDMS with a number-average molecular weight of 2.0, 5.0, or 10.0 kDa. The coating is made by casting a solution of two L#k samples mixed with a photoinitiator, allowing solvent evaporation, and then photocuring the film. During solvent evaporation, PDMS chains that are grafted to L and are of two different lengths migrate to the surface, forming a bimodal PDMS brush that reduces surface energy. PDMS layer thicknesses determined from atomic force microscopy (AFM) and cross-sectional analyses confirm brush formation from different polymer mixtures. The L coating with bimodal PDMS brushes shows reduced water and organic solvent sliding angles, enhanced graffiti paint repellency, and improved wear resistance compared to coatings bearing unimodal PDMS brushes. This study highlights a facile approach to creating bimodal polymer brushes with self-cleaning properties and potential applications in fields like flexographic printing.