Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Volume transition of gels

When rubbers and gels are immersed in a good solvent, they absorb solvent molecules and swell. If the tendency for the solvent to permeate into the network (osmotic pressure [Pg.150]

The volume in the reference state of the gel when it is prepared (cross-linked) is written as [Pg.151]

The gel adsorbs solvent molecules and swells to the volume V. If the number of solvent molecules inside the gel network is Nq in the initial state, the volume is V = No+nN)a. The volume fraction of the polymer inside the gel is, (p = Vdry/V, and the degree of swelling is [Pg.151]

Let be the expansion factor of the side in each direction. The swelling ratio [Pg.151]

In particular, when the gel swells under no tension, it undergoes an isotropic free expansion, so that kx=ky = kz- Let X be the expansion ratio [Pg.152]


Rg. 4.19 Volume transition of gels, (a) Experimental data of cross-linked PNIPAM gels, (b)... [Pg.154]

T Tomari, M Doi. Hysteresis and incubation in the dynamics of volume transition of spherical gels. Macromolecules 28 8334-8343, 1995. [Pg.553]

Tanaka et al. studied the volume transition of IPAAm-(sodium acrylate) copolymers gel as a function of temperature for various copolymer compositions. Gels that had been swollen at lower temperatures underwent a sharp collapse at different transition temperatures, depending on the ionic composi-... [Pg.18]

Volume Phase Transition of Gels. The volume-phase transition was experimentally discovered for a partially ionized acrylamide gel in a mixture of acetone and water by Tanaka in 1978 [19],... [Pg.9]

Calorimetry and Universality Class of the Volume-Phase Transition of Gels... [Pg.34]

Fig. 29a-d. Volume phase transitions of gels induced by the four fundamental forces (a) van der VVaals, (b) hydrophobic, (c) hydrogen bond, and (d) electrostatic forces... [Pg.50]

Before the volume phase transition was experimentally demonstrated in synthesized gels, its existence was theoretically predicted by Dusek and Patterson [4]. They suggested that the volume phase transition of gels is similar to the coil-globule transition of polymer chains and could be regarded as a first-order phase transition. [Pg.209]

This volume contains the first part of short reviews with emphasis on the authors work to show the present activity and state of knowledge in the field of volume transitions in gels. Part II will appear in Volume 110. Unfortunately, a few of the leading groups were not able to prepare a review in time due to their overcommitments. [Pg.282]

The theoretical formulation of the collapse of a polymer chain [4,6] and the volume phase transition of gels [1-3] has been developed by utilizing an analogy between the liquefaction of a real gas and the condensation of polymer segments. In fact, this analogy is quite helpful to understand the phenomenological aspect of the collapse of a polymer chain and of a polymer network. However, we do not know to what extent this analogy is valid in reed cases. Because a gel is a solid, the elastic deformation of the network may play an important role in real phase transition processes. [Pg.3]

The present article attempts to clarify the nature of the discontinuous transition of gels. First, in Sect. 2 we give an outline of the fundamental aspect of the volume phase transition on the basis of the Flory-Rehner theory of gels, with special attention to how the discontinuous transition comes about within the phenomenological treatment Then, in Sect 3 previous experimental results... [Pg.3]

The Flory-Rehner phenomenological theory [9,10] has beei most widely used to analyze the volume phase transition of gels. This theory, extended [11] to take into account the concentration dependence of the polymer-solvent interaction parameter x, can predict basic features of the phase transition. [Pg.4]

It has been established that the volume phase transition of gels is an universal phenomenon [17]. Dynamic light scattering studies indicate that the dynamic fluctuations of the density correlation diverges in the vicinity of the volume phase transition point of the gel. It has also been shown that the time scale of the density fluctuations become slow in the vicinity of the volume phase transition... [Pg.41]

The phase transitions, such as a phase separation of polymer solutions, a sol-gel transition, or a volume phase transition of gels, are always accompanied by conformation changes of polymers. Therefore, when the phase transitions are induced isothermally by external stimulation, the transitions cause efficient conformation changes. This contribution describes how such efficient stimuli-responsive polymer systems can be constructed. [Pg.50]

Fig. 12. Volume change kinetics of PVME gel (Trial 4) between states above and below the volume transition of 37 °C. Non-Fickian behaviour is observed for both swelling and shrinking. For comparison, lines are calculated which provide the closest fit of Fickian theory to the data. O Swelling (from 50 to 24°C), D = 4.0 x 10-7cm2/s Shrinking (from 23 to 50°C), D = I x 10-5 cm2/s. Reprinted from Polymer (1991) 33 990 by permission of the publishers, Butterworth Heinemann [46]... Fig. 12. Volume change kinetics of PVME gel (Trial 4) between states above and below the volume transition of 37 °C. Non-Fickian behaviour is observed for both swelling and shrinking. For comparison, lines are calculated which provide the closest fit of Fickian theory to the data. O Swelling (from 50 to 24°C), D = 4.0 x 10-7cm2/s Shrinking (from 23 to 50°C), D = I x 10-5 cm2/s. Reprinted from Polymer (1991) 33 990 by permission of the publishers, Butterworth Heinemann [46]...

See other pages where Volume transition of gels is mentioned: [Pg.8]    [Pg.9]    [Pg.515]    [Pg.150]    [Pg.151]    [Pg.153]    [Pg.155]    [Pg.8]    [Pg.9]    [Pg.515]    [Pg.150]    [Pg.151]    [Pg.153]    [Pg.155]    [Pg.150]    [Pg.8]    [Pg.10]    [Pg.47]    [Pg.49]    [Pg.59]    [Pg.209]    [Pg.279]    [Pg.8]    [Pg.17]    [Pg.24]    [Pg.25]    [Pg.27]    [Pg.97]    [Pg.128]    [Pg.160]    [Pg.161]    [Pg.201]    [Pg.204]    [Pg.214]    [Pg.218]    [Pg.273]    [Pg.45]    [Pg.401]    [Pg.146]   


SEARCH



© 2024 chempedia.info