RESUMO
Annealing a supported polymer film in the melt state results in the growth of an irreversibly adsorbed layer, which has been shown to influence thin film properties such as diffusion and glass transition temperature. Adsorbed layer growth is attributed to many simultaneous interactions between individual monomer units and the substrate, stabilizing chains against desorption. In this study, adsorbed layers of polystyrene (PS), poly(methyl methacrylate) (PMMA), and their random copolymers are isolated by select solvents. While PS adsorbed layer thickness is largely unaffected by the choice of washing solvent, the PMMA adsorbed layer completely desorbs when washed with tetrahydrofuran and chloroform, as opposed to toluene. Scaling relationships between adsorbed layer thickness and degree of chain adsorption at the substrate enable the use of adsorbed layer thickness to probe specific polymer-substrate interactions. Composition-dependent desorption trends indicate non-preferential adsorption between styrene and methyl methacrylate repeat units at the substrate, despite differences in substrate interaction strength. This insight contributes to the developing mechanism for the adsorption of random copolymers during melt-state annealing, further extending the ability to predict processing-inducted changes to the properties of polymer thin films to heterogeneous systems.
Assuntos
Polímeros/química , Polimetil Metacrilato/química , Poliestirenos/química , Solventes/química , Adsorção , Clorofórmio/química , Furanos/química , Polímeros/síntese química , Solubilidade , Propriedades de Superfície , Temperatura , Tolueno/químicaRESUMO
Over the past several years, the term PFAS (per- and polyfluoroalkyl substances) has grown to be emblematic of environmental contamination, garnering public, scientific, and regulatory concern. PFAS are synthesized by two processes, direct fluorination (e.g., electrochemical fluorination) and oligomerization (e.g., fluorotelomerization). More than a megatonne of PFAS is produced yearly, and thousands of PFAS wind up in end-use products. Atmospheric and aqueous fugitive releases during manufacturing, use, and disposal have resulted in the global distribution of these compounds. Volatile PFAS facilitate long-range transport, commonly followed by complex transformation schemes to recalcitrant terminal PFAS, which do not degrade under environmental conditions and thus migrate through the environment and accumulate in biota through multiple pathways. Efforts to remediate PFAS-contaminated matrices still are in their infancy, with much current research targeting drinking water.