Functional and responsive surfaces via initiated chemical vapor deposition (iCVD)

Abstract

Stimuli-responsive polymers provide a method to control system behavior through the use of an external stimulus, such as temperature, pH, or electric fields among others. Temperature-responsive polymers, especially those based on N-isopropylacryalmide (NIPAAm), are of particular research interest due the ease of implementation of temperature changes to systems as well as the large accessible range of hydrophilic / hydrophobic switching. Initiated chemical vapor deposition (iCVD) is shown to be a useful technique for surface modification with NIPAAm-based polymers due to its ability to provide complete functional retention and applicability to "real world" substrates, which many times have varying compositions and / or micro- or nano-structured surfaces. The novel copolymer thin film of iCVD poly(NIPAAm-co-di(ethylene glycol) divinyl ether) (p(NIPAAm-co-DEGDVE)) is shown to exhibit a sharp lower critical solution temperature (LCST) transition, better-than or equivalent to other surface modification techniques, while also being able to achieve a wider range of thicknesses from the nano- to micro-scale, which is especially useful for flow control, actuator or sensor applications. The bottom-up film growth of iCVD allows for compositional gradients throughout the thickness of a polymer film. A novel NIPAAm-based copolymer with a NIPAAm-rich surface layer is developed which exhibits both fast swelling and deswelling kinetics. Quartz crystal microbalance with dissipation monitoring (QCM-D) is used to study the transition behavior of these films. These data provide valuable information relating to the polymer conformational changes throughout the transition region and help elucidate thermodynamic and mesh characteristics of the films. Finally, an application is developed which utilizes both iCVD and a complementary technique, oxidative CVD (oCVD), to create self-heating membranes with responsive permeability characteristics.