Effect of Cross-Linking Density on Swelling Behavior of NIPA Gel Particles

Abstract

Submicrometer-sized N-isopropylacrylamide(NIPA) gel particles with various composition of cross-linker are prepared by precipitation polymerization and their swelling behaviors are examined by using photon correlation spectroscopy(PCS) technique. Theoretically, Hu et al.'s double-lattice model has been modified by introducing a new universal constant and simplifying the expression of the Helmholtz energy of mixing. The modified double-lattice model(MDL) describes very well the lower critical solution temperature (LCST) behavior of linear PNIPA/water system. For cross-linked NIPA gel particles in water, we have combined MDL theory with Flory and Erman's theory of elasticity, which takes into account the nonaffine displacements of network junctions under high degree of swelling. Energy parameters obtained from the linear PNIPA/water system were directly used to predict swelling equilibria for the NIPA gel/ water system. Our results represented that an affine network model explained the swelling behavior at high swelling ratio more accurately than that of the phantom network model. To correct the deviation of the continuous volume transition temperature, we have considered the interaction energy parameter between cross-linker segment and solvent molecule. The corrected model was applied to the swelling equilibria of gel particles with various cross-linking density and agreed well with their experimental data with no adjustable model parameters.

Poly(N-isopropylacrylamide) with hydrolyzable lactic acid ester side groups: a new type of thermosensitive polymer

“…The LCST of poly-NIPAAm reported in literature is 30 -34 8C [4][5][6][7][8][9][10] . Apart from the homopolymer of NIPAAm, also block copolymers with e. g. poly(ethylene glycol) 11) or poly(lactic acid) 12) , NIPAAm containing hydrogels 13) and random copolymers of NIPAAm with acrylamide/(methyl)acrylate derivatives [14][15][16][17] are under investigation at present. Recently, an interesting poly-NIPAAm-based gel with a degradable crosslinker based on a phosphazene trimer was described by Oh et al 18) The LCST of NIPAAm containing block copolymers is essentially the same as for poly-NIPAAm.…”

Volume phase transition in thermo-responsive hydrogels: constitutive modeling and structure–property relations

“…To compare observations on macro-and microgels, swelling diagrams [43] are fitted on PNIPA submicrometer spheres prepared by precipitation polymerization of NIPA monomers with MBAA as a cross-linker, APS as an initiator, and polysorbate surfactant Tween-20 as an emulsifier. Gel particles were manufactured at T prep = 70 • C under nitrogen blowing.…”

“…8 with those reported in Figs. 7 and 8 of [43], where the free energy of mixing was calculated with reference to the classical Flory-Huggins concept and to the multi-component lattice model. Comparison of swelling diagrams on hydrogels with various compositions reveals that the steepness of these curves in the vicinity of the critical temperature T * decreases when the concentrations of monomers and cross-linker grow.…”

Synthesis and Characterization of Porous Crosslinked Copolymers for Oil Spill Sorption

“…Submicrometer-sized gel particles respond to external stimuli more quickly than bulk gels [27]. Networks with dangling chains can easily expand or collapse upon an external stimulus because one side of the dangling chain is free [28].…”