Temperature-sensitive polymers or "smart" polymers are materials that undergo phase separation initiated by temperature change. Some of these polymers possess phase separation temperatures close to human body temperature (37 C), thus offering a wide range of potential applications in controlled drug release or gene delivery systems, bioseparations, tissue engineering, etc. Of the polymers with a phase separation temperature close to 37 C, poly(N- isopropylacrylamide) (PNIPAM) and poly(vinyl methyl ether) (PVME) are perhaps the most important and were selected as the subjects of this study. In this work, these two polymers have been examined in the presence of low molecular weight additives, and their colloidal stability evaluated using 1 H NMR (nuclear magnetic resonance) and time-resolved 1 H NMR spin-spin relaxation time T2 experiments. An improved model of the two exchangeable states was applied for a more detailed characterization of the phase separation process. The main focus of this study was to determine the influence of additives on the phase separation behavior of the polymers (phase separation temperature, width of transition, maximum number of polymer chains participating in phase separation), reversibility of the phase separation, dynamics of solvent molecules (water and additive),...

Polymer brushes, consisting of densely end-tethered polymers to a surface, can exhibit rapid and sharp conformational transitions due to specific stimuli, which offer intriguing possibilities for surface-based sensing of the stimuli. The key toward unlocking these possibilities is the development of methods to readily transduce signals from polymer conformational changes. Herein, we report on single-fluorophore integrated ultrathin (<40 nm) polymer brush surfaces that exhibit changing fluorescence properties based on polymer conformation. The basis of our methods is the change in occupied volume as the polymer brush undergoes a collapse transition, which enhances the effective concentration and aggregation of the integrated fluorophores, leading to a self-quenching of the fluorophores’ fluorescence and thereby reduced fluorescence lifetimes. By using fluorescence lifetime imaging microscopy, we reveal spatial details on polymer brush conformational transitions across complex interfaces, including at the air–water–solid interface and at the interface of immiscible liquids that solvate the surface. Furthermore, our method identifies the swelling of polymer brushes from outside of a direct droplet (i.e., the polymer phase with vapor above), which is controlled by humidity. These solvation-sensitive surfaces offer a strong potential for surface-based sensing of stimuli-induced phase transitions of polymer brushes with spatially resolved output in high resolution.