Published: November 23, 2011 r2011 American Chemical Society 872 dx.doi.org/10.1021/la203697a | Langmuir 2012, 28, 872–882 ARTICLE pubs.acs.org/Langmuir Formation of Polyampholyte Brushes via Controlled Radical Polymerization and Their Assembly in Solution Young K. Jhon, †,‡ Shafi Arifuzzaman, †,§ Ali E. € Ozc -am, †,|| Douglas J. Kiserow, †,‡ and Jan Genzer* ,† † Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905, United States ‡ Army Research Office, Research Triangle Park, North Carolina 27709-2211, United States 1. INTRODUCTION Due to their unprecedented ability to functionalize sur- faces with chemical tailoring and responsive properties, surface- anchored brushes have been employed in generating ‘smart’ responsive materials. 16 While most of the initial work involved preparation of homopolymer brushes, recent efforts have turned toward application of polymeric grafts bearing multiple chemical moieties. 7,8 To that end, the behavior of grafted macromolecular assemblies involving various chemical functionalities has been explored that involve both neutral as well as chargeable groups. 9 Initial efforts have revealed that polyampholyte brushes may re- present a convenient platform and a burgeoning area of research because of their unprecedented tailorability resulting in unique behavior on surfaces. 1015 Polyampholytes are macromolecules that bear both positive and negative charges along their backbone; these charges are either permanent (strong or quenched polyelectrolytes) or can be induced by varying the pH of the solution (weak or annealed polyelectrolytes). The conformation of polyampholytes in solu- tion thus depends on the relative amounts of the two charges and their distribution along the backbone. As in any polyelectrolyte system, the behavior of polyampholytes in solution is governed by a broad set of parameters, including the degree of polymer- ization of both blocks, the degree of dissociation (i.e., the number of charges) along each block, the concentration of external salt (i.e., the solution ionic strength), the interaction parameters between the polymer segments and solvent molecules, and the sequence distribution of the charged moieties along the macro- molecule. 16 The behavior of polyampholytes with either net positive or net negative charges is governed by strong repulsion between like charged monomers, which tends to extend the chain and help to dissolve the chains even in relatively poor solvents for the backbone (i.e., the polyelectrolyte effect). The charge sequence in neutral polyampholytes is important. For example, polyampholytes with an alternating sequence of opposite charges are typically swollen, whereas polyampholytes consisting of block (or blocky) sequences may collapse and precipitate from solution. 1719 While the bulk behavior of polyampholytes has been investigated for some time, studies of the interfacial be- havior of polyampholytes are still in their infancy. This is pri- marily due to the difficulties associated with preparing such systems and also the large set of parameters to be explored. Nearly all interfacial studies on polyampholytes reported to date involve their adsorption on solid interfaces, while only a few studies have reported preparing polyampholyte brushes on surfaces and characterizing their properties. 12,2025 Figure 1 depicts a schematic representation of conformational changes of a polycationic homopolymer brush, a polyanionic homopolymer brush, and a polyampholytic brush comprising both polycationic and polyanionic blocks as a function of the Received: September 21, 2011 Revised: November 22, 2011 ABSTRACT: We describe the formation of polyampholytic block copolymer brushes and their assembly in solution. Speci- fically, we employ “surface-initiated” activators regenerated by electron transfer atom transfer radical polymerization (ARGET- ATRP) sequentially to form diblock copolymer grafts comprising blocks of poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) and poly(sodium methacrylate) (PNaMA) on flat impenetrable silica surfaces, i.e., SiO x /PNaMA- b-PDMAEMA and SiO x /PDMAEMA- b-PNaMA. Protonation of the PNaMA block results in formation of poly(methacrylic acid) (PMAA). We demonstrate that ARGET- ATRP of NaMA provides a convenient route to preparation of PMAA, which is an alternative method to the more traditional approach based on preparing PMAA by polymerizing tert-butyl methacrylate (tBMA) followed by cleavage of the tert-butyl group. We also discuss conformational changes of the individual polyelectrolyte blocks in solution as a function of solution pH by monitoring adsorption behavior of functionalized polystyrene spheres.