BINARY BRUSHES: A NOVEL APPROACH TOWARDS ENHANCED INTERFACIAL TUNABILITY IN MULTIFUNCTONAL POLYMER NANOCOMPOSITES

摘要

High surface energy nanoparticles are found to phase separate in organic polymer matrices, thereby compromising on promised property enhancements of the resulting polymer nanocomposites. One approach taken to alleviate this incompatibility is to graft polymer chains onto the particle surface. Yet, conventional homopolymer (x=0) monomodal brush grafted particles have a narrow window for achieving good dispersions due to a delicate balance between the enthalpic screening of particle cores and entropic wettability of the grafted brush. A brush with low surface coverage (σ) exposes the particle surface, leading to the self assembly of fillers into anisotropic string and sheet like morphologies [1]. On the other hand, a high graft density brush excludes matrix chains (autophobic dewetting) causing an isotropic nonzero entropic surface tension at the interface. This leads to the agglomeration of particles even in the absence of excess enthalpic interaction [2]. An approach to decouple this enthalpic and entropic balance is to use two different brush populations: a densely grafted short brush for enthalpic shielding of the core and a sparsely grafted long brush encouraging favorable brush penetration [5]. These populations could be chemically identical (bimodal) or different (mixed), in which case the short population can be independently used to introduce desired functionality. These binary brushes have been synthesized on a multitude of surfaces, but have mostly found use as environmentally responsive systems to various solvent conditions.