Kinetics of volume phase transition in poly(N-isopropylacrylamide) gels

Abstract

Kinetics of volume phase transition in poly(N-isopropylacrylamide) (NIPA) gels jumped from a low-temperature swollen phase to a high-temperature shrunken phase was studied as functions of NIPA monomer and crosslinker concentrations. We found for the first time a clear kinematical boundary at which the shrinking relaxation time of gels changes discontinuously by 102–104 times, and that the profile of the boundary correlates with the sol-gel transition line and the contour line of turbidity of gels. A “morphological” boundary which characterizes the emergence of the bubble formation on gel surface was also determined. The theoretical calculation of the phase diagram on the basis of the mean field theory shows qualitatively that the shrinking speed of gels could be connected with the depth of the thermodynamic region of the spinodal instability (K+4μ/3=0) into which they are transferred where K and μ are the bulk and the shear moduli, respectively. A mechanism of discontinuous change of the shrinking speed is discussed in connection with the thermodynamic properties as well as the inhomogeneity of network structure.

Photolatently modulable hydrogels using unilamellar titania nanosheets as photocatalytic crosslinkers

“…2b, the hydrogel prepared with the TiNS crosslinker (IPAAm/TiNSs ¼ 10.0/0.4 wt%) remained sharply thermoresponsive even when integrated into a patterned poly(dimethylsiloxane) (PDMS) matrix. In accordance with the literature 35 , we employed an organic crosslinker ( Fig. 1a; N,N 0 -methylenebis(acrylamide) (MBAAm), 0.1 wt%), instead of TiNSs, for the preparation of a reference hydrogel film (Supplementary Methods).…”

Hydrophobic and hydrophilic polyrotaxane based movable cross-linkers for thermo-sensitive poly(<i>N</i>-isopropylacrylamide) gels

“…This contrasts to the generalized behavior that homogeneous gel shrinking kinetics is slower than that for an inhomogeneous gel. 23 Bubble formation is the indication of spatial inhomogeneities in the gel, therefore, it may be speculated that the use of movable cross-linker facilitates complete removal of spatial inhomogeneities. Figure 5b represents the deswlling rate of TN a (1), R wi N(1), and R ws N(1) gels after a temperature jump from 20 to 40 o C. The relaxation time, τ was estimated from the plots of ln[d(t)/d(0)] versus t, assuming that the deswelling rate follows first-order kinetics.…”

“…Research to-date include numerous attempts to obtain mechanically strong and fast shrinking poly(NIPA) gels. The various means used to accelerate shrinking rate of poly(NIPA) gels are the preparation of hydrogels with a bulky heterogeneous structure 7 or with a macro porous network based on the porosigen technique, 8 rendering a portion of the gel network hydrophilic 9 or introduction of freely mobile dangling chains onto the gel network. 10 Although significant improvements in terms of stimuli sensitivity could be achieved, these approaches are, in most cases, associated with loss of mechanical integrity.…”

Thermo-Responsive Poly(N-isopropylacrylamide) Gel Containing Polymeric Surfactant Poly(2-(methacryloyloxyl)decylphosphate): Correlation between Rapid Collapsing Characters and Micelles of Polymeric Surfactant

“…Poly(N-isopropylacrylamide) (NIPA) gel is a well-known thermo-responsive hydrogel and has attracted wide attention from either academic or technological aspects [1][2][3][4][5][6] , since it shows an abrupt volume change at a phase transition temperature (ca. 34 ) 1) .…”