Spatially Resolving Polymer Brush Conformation: Opportunities Ahead

Abstract

Surfaces that respond to local environmental stimuli offer intriguing possibilities for new surface-based sensing concepts to emerge. An attractive concept is to push beyond the milli-to micrometer lateral resolution limit in sensing, toward the ultimate surface-sensitive device; one capable of real-time sensing of the nanoscopic, or molecular "touch." This sensing needs an approach that is capable of spatially transducing information on nanotouch. Polymer brushes are a class of surface that provides dramatic changes in surface properties depending on stimuli that affect the conformation of end-tethered polymer chains. However, the brush response is typically quantified by measuring changes in polymer brush "height". That is, the ensemble average distance over which polymer density exists away from the anchoring surface (i.e., a single parameter to describe the surface). Moving beyond this conceptual paradigm of quantifying the ensemble average height in a single dimension over the entire surface under applied stimuli, developing methods for spatially resolving chain conformation has the very real potential to lead to extraordinary possibilities in the applied sciences. In this perspective, the current paradigms and methods forward for extracting rich details on polymer brush conformational dynamics that is spatially resolved, which can lead to new understandings of surface contact, are discussed and pointed out.

Fluorescence-readout as a powerful macromolecular characterisation tool

“…In addition, it is worth mentioning that the transduction from conformational changes in stimuli-responsive polymer brushes to the fluorescence signal is particularly attractive for developing surface-based sensors for sensing environmental stimuli, such as temperature, humidity and mechanical force. 374,375,377,388,389…”

“…The spatial read-out capability of uorescence microscopy further allows to spatially resolve the polymer brush conformation. [372][373][374][375][376] Polymer brush surfaces with the ability to change the conformation and structure of polymer chains in response to external stimuli hold signicant potential for applications in drug delivery, self-healing coatings, sensors and actuators. 339,364 These external stimuli include temperature, light, applied force and a variety of chemical stimuli, such as solvent type, pH and ionic strength.…”

“…In addition, it is worth mentioning that the transduction from conformational changes in stimuli-responsive polymer brushes to the uorescence signal is particularly attractive for developing surface-based sensors for sensing environmental stimuli, such as temperature, humidity and mechanical force. 374,375,377,388,389 Examples here focus on planar surfaces, yet uorescencebased methods are no less important for the characterisation of non-planar surfaces, including nanoparticles, and we refer readers to the relevant literature. [390][391][392][393] High spatiotemporal resolution and non-invasive characteristic of uorescencebased techniques allow the study of surface graing kinetics as well as polymer chain dynamics, which will lead to a better understanding of the process and mechanism of surface modication and, in turn, will facilitate the development of more complex polymer surfaces with special properties.…”

Messenger Materials Moving Forward: The Role of Functional Polymer Architectures as Enablers for Dynamic Nano‐to‐Macro Messaging

“…At this point in the polymer science community, polymers have been designed, synthesized, and reported that are capable of responding to most imaginable real‐world stimuli. [ 12 ] This includes general stimuli (temperature, pH, ionic strength, solvent, etc.) as well as extraordinarily specific stimuli (solutes, biomolecules, specific wavelengths of light, etc.…”

Swelling and Orientation Behavior of End-Grafted Polymer Chains by In Situ Attenuated Total Reflection Fourier Transform Infrared Spectroscopy Complementing In Situ Ellipsometry

“…22 Recently, new methods have been developed to spatially resolve the brush height by employing fluorophores in the polymer chains. 21,25 Nevertheless, none of these methods can directly assess the chain conformation and quantify the orientation of end-grafted polymeric chains.…”