Nonergodic Dynamics of a Novel Thermally Sensitive Hybrid Gel

Abstract

As the temperature decreases, the swelling of individual thermally sensitive spherical poly-(N-isopropylacrylamide) microgels in a concentrated dispersion can lead to a sol-gel transition, resulting in a hybrid bulk gel in which individual microgels were physically jam-packed into a three-dimensional network without involving electrostatic interaction, resembling the glass transition of small molecules. The dynamics of such a formed hybrid gel were studied by static and dynamic laser light scattering. Our results showed that the inhomogeneity should be characterized by the difference between the ensemble average scattering intensity and the dynamic component of the time average scattering intensity. The inhomogeneity was strongly dependent on the sol-gel transition rate and the gelling temperature. Our results have also revealed that the inhomogeneity can be completely suppressed if individual swollen microgels are closely packed together, indicating that the static nonergodic behavior originates from large voids formed during the sol-gel transition.

The slow relaxation mode: from solutions to gel networks

“…The details of the data analysis could be referred to the articles. [97][98][99][100][101][102][103][104][105][106][107]110,111 The slow mode in semidilute neutral polymer solutions When the concentration of polymer is higher than the overlap concentration (C*), polymer chains start to 'touch' each other and the solution enters the semidilute regime. C* has been differently defined as 3M/(4pN A R g 3 ), or M/(2 3/2 N A R g 3 ), and [Z] À1 , where M, R g , N A and [Z] are the molar mass, the radius of gyration of polymer chains, the Avogadro constant and the intrinsic viscosity, respectively.…”

“…75,[96][97][98][99][100][101][102][103][104][105][106][107] In this article, we mainly review what has been carried out in our laboratory during the past 10 years. We will outline the details of each system in the following sections by starting with a brief introduction of LLS.…”

Fluctuations in chemical gelation

“…This inhomogeneous structure is important to figure out properties of the cross-linked gels. Experimentally, the inhomogeneous structure can be detected as a speckle pattern in the light scattering experiment [14,15,16] and a cooperative diffusion of the hierarchical structure can be observed as the so-called gel mode [17]. As is suggested by recent experiments [16], if the speckle pattern is caused by large voids in gel networks, the scale of speckle inhomogeneity is given by ξ * p .…”

“…Experimentally, the inhomogeneous structure can be detected as a speckle pattern in the light scattering experiment [14,15,16] and a cooperative diffusion of the hierarchical structure can be observed as the so-called gel mode [17]. As is suggested by recent experiments [16], if the speckle pattern is caused by large voids in gel networks, the scale of speckle inhomogeneity is given by ξ * p . At the same time, to observe the speckle pattern in the light scattering experiment, the speckle inhomogeneity should be larger than the laser wavelength λ [18], so ξ * p should be larger than a typical laser wavelength 630 nm.…”

Toughening of Hydrogels with Double Network Structure

“…As studied by many gel scientists [10][11][12][13][14][15][16][17][18][19][20], the inhomogeneity is an intrinsic property of polymer gel obtained from radical polymerization. Wu et al pointed out that large 'voids' are formed if the growing rate of polymer 'clusters' is much higher than their relaxation rates (diffusion), and the voids between polymer 'clusters' (microgels) are much lager than the mesh size between crosslinked chains inside the microgels [16][17][18]. Consequently, the dynamics of slow mode in DN gels might result from a free motion of PAAm clusters in 'voids' of PAMPS networks.…”