RAPID REDISPERSION OF PH-SENSITIVE MICROGEL FLOCCULATION WITH POLY(LYSINE)

A concentrated aqueous flocculation of an ultrafine microgel of methyl methacrylate-acrylic acid (MMA-AA) copolymer mixed with poly(L-lysine) (PLL) exhibited rapid and reversible redispersion when the solution was shifted to pH 10-11. In lower pH where PLL was ionized, the microgel underwent bridging flocculation. A pH increase induced PLL to transform from an ionized coil to an alpha-helix conformation, which resulted in desorption of the bridging PLL to bulk solution from the microgel surfaces. The desorption was assisted by electrostatic repulsion between the microgels, whose charge was converted to be highly negative by the neutralization of the PLL. Removal of the PLL chain from microgels (spatial shift) due to its conformational change in concurrence with pH-dependent shrinkage of microgels instantaneously separated an individual microgel, which resulted in remarkably rapid and reversible redispersion. The large magnitude of the change in absorbance at the transition may be applied for electrooptical devices.