Published: Aug. 31, 2020 By

The overall objective of this work is to develop a novel methodology of surface modification, which can be broadly applied to polymer networks such as elastomer and hydrogel. Two types of polymerization mechanisms, namely, step-growth and chain-growth polymerization, at the interface between a solid and a liquid, were served as the modification tool, which is referred to as solid-liquid interfacial polymerization (SLIP) process throughout this thesis. In this thesis, three different cases of the solid phase were investigated including, a poly (dimethyl siloxane) (PDMS) elastomer, a homogenous hydrogel, and a heterogeneous hydrogel, all of which are commonly used across different applications. The step growth polymerization systems, trimesoyl chloride (TMC) reacting with m-phenylene diamine (MPD) or piperazine (PIP), are used in polyamide (PA) layer formation in thin film composite membrane industry. The chain growth polymerization was based on free-radical polymerization of vinyl functional monomers.

Our research shows that the SLIP process using both step-growth and free radical chain polymerization can effectively modify the PDMS surface by forming a hybrid skin layer. In contrast, the SLIP process on hydrogels results in a thin film formation by creating a bilayer structure. By controlling the SLIP process parameters, such as monomer concentration, reaction time, characteristics of the solid phase, the morphology and properties of modified hybrid skin layers and thin films can be tuned systematically.

All in all, the SLIP process is unique in that it allows for modification not only on a planar surface but also on a curved, even lithographically patterned surface or the inner wall of a closed microchannel. The pretreatment-free procedure makes this modification approach convenient and reduces energy consumption. Furthermore, the substrate material can sustain mechanical loading and deformation prior, during, or after the SLIP modification, which offers additional capability of tuning the surface morphology in addition to the chemical modification. Lastly, the SLIP process can help to advance our understanding of complex interfacial polymerization mechanisms and assist the design and optimization of surfaces for improving material or device performances in many fields. In this study, applications on designing snake-skin surfaces for reducing dry friction as well as developing skin layer for reducing gas or vapor permeation are demonstrated in the thesis.

Full pdf - https://www.colorado.edu/mse/node/533/attachment