Stimuli-responsive polymer nano-science: Shape anisotropy, responsiveness, applications

Polymeric nanomaterials capable of altering volume, color, or shape have attracted significant scientific interests as these materials become increasingly critical in advancing unique technological developments. Design, synthesis, and assembly of nanomaterials with precisely controlled shapes and directional responsiveness are particularly critical in the development of new functional, near-device level materials. Spatial anisotropies are typically introduced by the placement of symmetrically or asymmetrically located responsive components enabling either interactions with the environment manifested by dimensional or color changes, energy storage and transfer, or diffusion. This review outlines recent advances in the synthesis, fabrication, and assembly of isotropic and anisotropic polymer-based nanomaterials in which dimensional, color, and morphological changes are induced by external stimuli. Specifically, core-shell, hollow, Janus, gibbous/inverse gibbous nanoparticles prepared with precisely controlled morphologies capable of spatially responding totemperature, pH, electromagnetic radiation or biological changes are discussed. Recent advances in the nanoparticle surface modifications which are introduced to guide nanomaterials to selectively interact and communicate with the environment are also highlighted. Since high aspect ratio nanomaterials, including polymeric nanowires or nanotubes containing responsive components, are particularly attractive in the development of 3D multi-functional objects, their manufacturing as well as applications are examined. Although many uses of stimuli-responsive nanomaterials in electronics, energy conversion, sensing, or biomedicine and other technologies are already in place, there are limitless opportunities for new applications as long as proper regulatory measures are exercised to elevate the impact of these materials on the environment. Polymeric stimuli-responsive nanomaterials offer a tremendous opportunity for the development of cognitive materials' systems, particularly when protein-like polymers containing amino acids joined by polypeptide bonds with enzymes or sugar-phosphate moieties as well as other sugar-containing interactions are utilized as building blocks and components of future materials.