Hairy particles are composed of a core and a layer of polymer chains that are densely tethered by one end via a covalent bond (i.e., polymer brushes) on the surface of the core. These hybrid particles can be designed to respond to environmental changes, exhibiting different structures and properties under different conditions; examples include various stimuli (e.g., temperature, pH, and light)-responsive hairy particles and multicomponent polymer brush-grafted particles. In this talk, I will present several types of environmentally responsive hairy particles, particularly binary mixed homopolymer brush-grafted silica particles. Mixed brushes are composed of two chemically distinct homopolymers randomly or alternately immobilized by one end on a solid surface with sufficient grafting densities for both polymers. The fascinating responsive properties and the rich phase behavior of binary mixed brushes have attracted tremendous interest in the past two decades. We have developed a unique strategy to grow well-defined mixed brushes with controlled molecular weights and narrow polydispersities from asymmetric difunctional initiator-functionalized silica surfaces by using two different 'living'/controlled radical polymerization techniques, atom transfer radical polymerization and nitroxide-mediated radical polymerization. The use of silica particles as substrates allows for direct visualization by transmission electron microscopy of the nanostructures formed by self-assembly of mixed brushes. These hairy particles exhibit distinct morphologies under different environmental conditions. The effects of chain length disparity, overall grafting density, and substrate curvature on phase morphology of mixed brushes will be discussed. ***Coffee and cookies will be served. ****http://nanohour.beckman.illinois.edu