Stimuli-Responsive Semi-Fluorinated Polymer Brushes on Porous Silica Substrates Anthony M. Granville, William J. Brittain* Department of Polymer Science, University of Akron, 170 University Ave., Akron, OH 44325, USA Fax: (þ1) 330 972-5290; E-mail: wjbritt@uakron.edu Received: May 11, 2004; Revised: May 25, 2004; Accepted: May 26, 2004; DOI: 10.1002/marc.200400193 Keywords: atom transfer radical polymerization (ATRP); polymer brushes; stimuli-sensitive polymers Introduction Chemical gating is the ability to control the permeability of a given material through the opening and closing of a barrier or gate. [1,2] The environmental trigger for this gating effect is chemical in nature and has been mostly performed using pH [1] and temperature; [2] however, solubility and ionic strength have also been investigated. Recently, studies on chemical gates have consisted of homopolymer brushes of functionalized polyacrylates, [1,2] polypyridinium salts, [1,2] or poly(N-isopropylacrylamide) (PNIPAAm). [3,4] The gat- ing of these materials relies on the extension and contrac- tion of the tethered polymer brush chains induced by an external chemical stimulus. Polymer brushes can be described as polymer chains te- thered to a surface or interface with a sufficiently high grafting density such that the chains are forced to stretch away from the tethering site. [5] The formation of these tethered chains can be achieved by two techniques, phy- sisorption [6] or chemical bonding of chains to an interface. Covalently grafting chains, by a ‘‘grafting from’’ technique, leads to the formation of high-grafting-density polymer brushes that are generated using an in situ polymerization reaction from a surface-immobilized initiator. [7] The initi- ator is immobilized by a self-assembled monolayer (SAM) technique. [8] Previous studies have shown that immiscible diblock copolymer brushes undergo surface rearrangement when exposed to various solvents. [9] Research performed in this lab has also shown that semi-fluorinated diblock copolymer brushes can undergo a similar surface rearrangement when treated with both selective solvents or thermal anneal- ing. [10,11] Utilizing this type of diblock copolymer brush surface rearrangement, we synthesized semi-fluorinated diblock brushes on porous silica substrates. The solvent- and thermal-induced surface rearrangement may control gating of the pore channels in conjunction with a surface property change from that of a hydrocarbon polymer to a fluoropolymer, depending on the external stimulus. Homo- polymer brushes consisting of a fluoropolymer material Summary: A diblock copolymer brush consisting of poly- (methyl acrylate)-block-poly(pentafluoropropyl acrylate) (Si/SiO 2 //PMA-b-PPFA) was synthesized on a porous silica substrate. The brush was exposed to selective solvents, as well as thermal treatments, to induce a surface rearrange- ment. The rearrangement resulted in the selective loss or creation of an ultrahydrophobic layer by location of the fluoropolymer segment. This work demonstrates that surface rearrangements observed on flat surfaces can be transferred to porous substrates. Image of a water droplet in contact with an Si/SiO 2 //PMA-b- PPFA ultrahydrophobic polymer brush, synthesized from a porous silica substrate. Macromol. Rapid Commun. 2004, 25, 1298–1302 DOI: 10.1002/marc.200400193 ß 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1298 Communication