When 10:30 AM - 1:00 PM Jan 11, 2023
Where NCRC B300, Room 376
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PhD Defense: Mechanistic Studies into Interfacial Interactions via Chemical Vapor Deposition Polymerization


Xiaoyang Zhong
Lahann Group

Chemical vapor deposition (CVD) polymerization is a widely used fabrication method for preparing substrate-independent thin film polymer coatings for a broad range of applications. Functional poly(p-xylylene) (PPX) coatings are specific examples of CVD polymer coatings, and they can be applied for surface functionalization and bio-conjugation. The first portion of this dissertation serves to explore the fundamental mechanism of area-selective CVD polymerization, which has a high potential to be utilized as one of the bottom-up processes. In this dissertation, we report a systematic study into the role of thermodynamically controlled processes on the area-selectivity of chemical vapor deposition (CVD) polymerization of 4-chloro-[2.2]paracyclophane (PCP-Cl). Adhesion mapping of pre-closure CVD films by atomic force microscopy (AFM) identified the exact transition between pre-closure and continuous film regimens and provided a detailed understanding of the geometric features of the polymer islands. Our results suggest a correlation between deposition conditions and deposition rate, which can switch the area-selectivity to non-area selective. These findings are further corroborated by scanning transmission electron microscopy (STEM) results indicating conformal/un-conformal CVD films on patterned Ruthenium/Silicon substrates to mimic the real industrial fabrication process. Using this approach, we garnered insights into the effect of key thermodynamic parameters, such as substrate temperature, working pressure, and feeding amount of precursors, on area-selectivity. This work culminated in a kinetic model that predicted both area-selective and non-selective CVD parameters for the same polymer/substrate. While limited to a small subset of CVD polymers and substrates, this work provides an improved mechanistic understanding of area-selective CVD polymerization and highlights the often-underappreciated role of thermodynamic control in these systems. The second portion of this dissertation serves to extend the use of CVD-based reactive PPX coatings as a surface modification strategy for either precious cell adhesion or the conjugation of multiple biomolecules. PPX coatings were engineered from different surface chemistries to meet specific requirements. In this dissertation, we address a simple, reproducible surface modification process that promotes a high yield of cell attachment to the targeted sites, utilizing two organic electronic materials as adhesion points on a biocompatible functional poly(p-xylylene) surface. Moreover, this dissertation also demonstrates the use of CVD-based co-polymer coatings as intermediate layers to immobilize both lentiviral vectors and peptides on substrates. The ability to tether lentiviral vectors together with a mesenchymal stem cell (MSC)-binding peptide enhances cell communication among MSCs and increases cell binding and differentiation, providing a safe and efficient gene therapy delivery strategy.