Unraveling Chemical Transformation of Reactively-Modified Interfacial Thin Films Using Neutron Reflectometry (Invited Talk)

Creating an appropriate display of chemical functionality is useful across a wide variety of applications for polymer thin films, ranging from adhesives and barrier coatings to membranes and sensing devices. In this presentation we describe our efforts to tease apart the complex connections between structure and structural rearrangement of interfacial polymer thin films and the penetration and distribution of small-molecule functionalizing agents installed by in situ modification. Model thin films based on the reactive polymer, poly(2-vinyl-4,4-dimethylazlactone) (PVDMA) are used for this purpose, and neutron reflectometry is brought to-bear as a key tool for metrology. Highly constrained analyses of neutron reflectivity prove that reactive modification is not uniform throughout the PVDMA thin film nor complete; rather, it depends on key structural parameters of the interfacial layer and the size of the small molecule functionalizing agent. This quantitative picture diverges substantially from insights generally gleaned from ellipsometric measurements of modified thin films, highlighting both key limitations in the latter method and the richness of results that may be obtained from the former technique. Overall, the findings provide broadly support efforts to produce polymer films in which various surface properties are tailored by in situ chemical modification.