Regio‐Selective Mechanical Enhancement of Polymer‐Grafted Nanoparticle Composites via Light‐Mediated Crosslinking

Abstract

Polymer-brush-grafted nanoparticles (PGNPs) that can be covalentlycrosslinked post-processing enable the fabrication of mechanically robust andchemically stable polymer nanocomposites with high inorganic filler content.Modifying PGNP brushes to append UV-activated crosslinkers along the poly-mer chains would permit a modular crosslinking strategy applicable to a diverserange of nanocomposite compositions. Further, light-activated crosslinkingreactions enable spatial control of crosslink density to program intentionallyinhomogeneous mechanical responses. Here, a method of synthesizingcomposites using UV-crosslinkable brush-coated nanoparticles (referred to asUV-XNPs) is introduced that can be applied to various monomer compositionsby incorporating photoinitiators into the polymer brushes. UV crosslinking ofprocessed UV-XNP structures can increase their tensile modulus up to 15-foldwithout any noticeable alteration to their appearance or shape. By usingphotomasks to alter UV intensity across a sample, intentionally designedinhomogeneities in crosslink density result in predetermined anisotropic shapechanges under strain. This unique capability of UV-XNP materials is applied tostiffness-patterned flexible electronic substrates that prevent the delaminationof rigid components under deformation. The potential of UV-XNPsas functional, soft device components is further demonstrated by wearabledevices that can be modified post-fabrication to customize their performance,permitting the ability to add functionality to existing device architectures.