Abstract
This study shows that microgel particles deswell in the presence of excluded free (i.e., non-adsorbing) polymer. The microgels investigated were poly(N-isopropyl-acrylamide-co-N,N′-methylene-bis-acrylamide (PNP-BA), poly (styrene-co-divinylbenzene) (PS-DVB) and poly(methylmethacrylate-co-methacrylic acid-co-ethyleneglycol dimethacrylate) (PMA-MAA-EM). The particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photon correlation spectroscopy (PCS). The stability of the particles to flocculation in the presence of free polymer was examined using turbidity-wavelength measurements. The PMA-MAA-EM/water/PEG (PEG=poly(ethyleneglycol)) system was the most stable toward flocculation. Osmotic deswelling of the microgel particles was most pronounced for the PNP-BA/water/PEG system. The volume of the deswollen PNP-BA particles approach that measured for the collapsed state. Osmotic deswelling occurs in the PS-DVB/ethylbenzene/free polystyrene system. However, the extent of deswelling is limited due to some penetration of the microgel particle interior by free polymer. PMA-MAA-EM microgel particles also exhibit osmotic deswelling in the presence of aqueous solutions of PEG.
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