This work reports the development of a reversibly coagulatable and redispersible polystyrene latex system that can be triggered by N(2)/CO(2). The coagulatability and redispersibility of the latexes were achieved by employing 0.9-5.6 wt % (N-amidino)dodecyl acrylamide (DAm), a reactive switchable surfactant, in an emulsion polymerization of styrene under CO(2) atmosphere. The resulted latex particles were readily coagulated by N(2) bubbling at 60 °C and redispersed by CO(2) bubbling and ultrasonication, which switched amidine moieties between neutral and ionic states. The coagulation/redispersion processes were repeatable. The prepared latexes showed good stabilities against electrolytes, especially with higher charges.

ethyl methacrylate)block-poly(methyl methacrylate) (PDMAEMA-b-PMMA) has been used as a surfactant in the preparation of PMMA latexes that can be coagulated and redispersed reversibly. In this work, we investigated in detail the effects of the block copolymer composition on the coagulation/redispersion performance of the latexes. A series of well-defined PDMAEMA-b-PMMA samples that have 10−30 DMAEMA units and 5−45 MMA units were synthesized through a two-step solution RAFT polymerization process and were used as the surfactant in the emulsion polymerization of MMA. PMMA latexes obtained with surfactants having MMA weight fraction (F MMA ) < 58.5% were stable. The particle size of the resulting PMMA latexes decreased gradually with the increase of F MMA . The latex particles initially coagulated with a small amount of caustic soda could be repeatedly redispersed into fresh water through CO 2 bubbling with ultrasonication and coagulated through N 2 bubbling with some heating. The coagulation/redispersion process was repeatable through the CO 2 /N 2 bubbling. The latexes showed excellent redispersibility with the surfactants of F MMA < 46%. With F MMA > 46%, the latex particle sizes could increase over 20% after the coagulation/redispersion process.

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Self-organization of nanoparticles into stable, molecularly thin films provides an insightful paradigm for manipulating the manner in which materials interact at nanoscale dimensions to generate unique material assemblies at macroscopic length scales. While prior studies in this vein have focused largely on examining the performance of inorganic or organic/inorganic hybrid nanoparticles (NPs), the present work examines the stabilizing attributes of fully organic core-shell microgel (CSMG) NPs composed of a cross-linked poly(ethylene glycol dimethacrylate) (PEGDMA) core and a shell of densely grafted, but relatively short-chain, polystyrene (PS) arms. Although PS homopolymer thin films measuring from a few to many nanometers in thickness, depending on the molecular weight, typically dewet rapidly from silica supports at elevated temperatures, spin-coated CSMG NP films measuring as thin as 10 nm remain stable under identical conditions for at least 72 h. Through the use of self-assembled monolayers (SAMs) to alter the surface of a flat silica-based support, we demonstrate that such stabilization is not attributable to hydrogen bonding between the acrylic core and silica. We also document that thin NP films consisting of three or less layers (10 nm) and deposited onto SAMs can be fully dissolved even after extensive thermal treatment, whereas slightly thicker films (40 nm) on Si wafer become only partially soluble during solvent rinsing with and without sonication. Taken together, these observations indicate that the present CSMG NP films are stabilized primarily by multidirectional penetration of relatively short, unentangled NP arms caused by NP layering, rather than by chain entanglement as in linear homopolymer thin films. This nanoscale "velcro"-like mechanism permits such NP films, unlike their homopolymer counterparts of comparable chain length and thickness, to remain intact as stable, free-floating sheets on water, and thus provides a viable alternative to ultrathin organic coating strategies.

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