Swollen networks

Although this model has been successful for interpretation of results in a variety of systems, recent studies indicate that it represents an oversimplification" For instance dilatometry, specific conductivity and differential scanning calorimetry results obtained on networks swollen by water can be better descrobed if s of water are assumed bound, interfacial and bulk... 

Equilibrium phenomenon, operative in polymer solutions, in multicomponent solvents, and in polymer networks swollen by multicomponent solvents, that produces differences in solvent composition in the polymer-containing region and in the pure solvent which is in thermodynamic equilibrium with that region. 

Furthermore, it has been found that the so-called reentrant jumpwise collapse can be realized when a charged network swells in a mixed solvent [31]. In this case, the network having a globular structure both in A or B one-component solvents decollapses sharply in some intermediate composition range or the network swollen in pure solvent shrinks abruptly in mixed solvent (Fig. 7). 

Figure 11 shows the dependences of o on for polyelectrolyte networks swollen in the solution of incompatible polymer (yNp > 0). In this case, the network always deswells linear polymers do not penetrate inside the network... 

Fig. 12. A model of a charged polymer network swollen in a solution of oppositely charged surfactants...

The collapse of the networks was studied experimentally mainly for the case of mixed solvents. From the practical point of view, it would be interesting to generate the collapse in a purely aqueous medium. In this case, by changing the interactions between subchains of the network in aqueous solution it is possible, for example, to influence effectively diffusion in gels that are used as carriers of enzymes or pharmacologically active substances. One of the new directions in the research of network polymers is the study of their interaction with linear macromolecules. The results of the theoretical analysis of the behavior of polymer networks swollen in polymer solutions have been discussed in Ref. [34,35] (see Sect. 2.4.2). 

The empirical correction factors 4> (calculated on assumption that for all networks swollen in pure water % from Eq. (6) should be 0.48) change between 0.05 and 0.3 (see Ref. [48] for salt I the data are in Fig. 8). Generally, we can say that the effect of the positive charge on the formation and extent of transition is 5 to 10 times smaller than the effect of MNa. There are probably several reasons for the low value of (a) positive charges are localized at a larger distance from the main chain (smaller influence on the chain conformation) (b) due to the... 

Fig. 2. Average correlation distances d between deuterated crosslinks of PS/DVB networks swollen to equilibrium vs gi/3...

Fig. 4. Average correlation distancesd between crosslinks vsM1/2 in PS/DVB networks swollen to equilibrium.

It should be emphasized also that the viscosity relation applies to infinitely dilute solution. In a network swollen to equilibrium the segment concentration is far from being infinitely small. 

The relaxation behavior of the trapped chains Iras been studied by means of stress strain measurements on dry networks and on networks swollen in bad solvents63. ... 

Many studies of vulcanized elastomer blends have revealed discontinuities in physical property trends attributable to poor interfacial bonding. Recently Rehner and Wei (5) have observed discontinuities in the swelling of blended crosslinked networks swollen in a common solvent. This departure from an averaged swelling behavior, based upon compositional ratios and the swelling behavior of the two homophases, re-... 

Figure 8. Changing conditions at the interface as cure time increases. Blended networks swollen in differential solvents at —25°C.

To emphasise the role of orientational interactions in the appearance of the doublet in 2H NMR spectra, model PDMS networks have been swollen to various extents with a good solvent of PDMS [53]. Figure 15.10 shows the slopes P=A/(X2-X 1) obtained in a PDMS network swollen with chloroform. The swelling process results in stretching... 

The empirical correction factors pure water x from Eq. (6) should be 0.48) change between... 

Figure 3.18 shows an example of the variation with temperature of V2 for a network of poly(methyl trifluoropropylsiloxane) (PMTFPS) in different solvents (20). Some aspects merit additional comments. The low values of V2, around 15%, suggest a good polymer-solvent interaction (low values of X12) therefore, acetates and tetrahydrofuran can be considered good solvents for PMTFPS. The opposite behavior (high values of V2) is shown for PJvITFPS networks swollen in n-chlorobutane. 

Fully swollen modulus of end-linked PDMS networks swollen to equilibrium in toluene at 25 °C. The starting telechelic chains had = 4400 gmol and they were crosslinked at various preparation concentrations in the range 0.3 < < 1. The line is the... 

In order to construct artificial organs with an excellent function similar to the real biological organ, material innovation is urgently required, i.e., one should find a man-made soft and wet material as substitute for biotissue. Synthetic hydrogels, which consist of polymer networks swollen with large amounts of water (the same as biotissue), are the only candidates [5]. Different from biotissue, tlie water content... 

There are three combinations of the two components of nematic network gels (1) an isotropic network swollen by a nematic solvent, reminiscent of the polymer dispersed liquid crystal systems (PDLC). This case (1) was discussed by Brochard (1979) and Ballauff (1991) (2) a nematic network swollen by an isotropic solvent was actually studied experimentally by Carudo et al. (1992) and theoretically by Warner and Wang (1992a) (3) both components can order at a temperature above the glass transition. Actually the first two systems are special cases of the last one which has been experimentally investigated (Zentel, 1986 Barnes et al., 1989 Kishi et al., 1994) and theoretically studied (Wang Warner, 1997). 

Figure 5. Mooney-Rivlin plots of stress-strain data(lO) for two tetrol-based polyurethane networks from system 5 of Figures 2 and 4, prepared at various dilutions in nitrobenzene as solvent. Networks swollen in nitrobenzene at 4QOC...

Hydrogels are physically or chemically cross-linked polymer networks swollen with large amounts of water. Due to their crosslinked nature, these gels do not dissolve in aqueous media but contain an enormous amount of solvated water molecules within the entangled polymer chain matrix. Hydrogel properties are reviewed elsewhere in this book. This chapter is dedicated to a unique hydrogel family that responds to... 

Figure 1.9 Plot of concentration of polystyrene chains, Q, vs fraction p of monofunctional chains in networks swollen with benzene p = r mf...

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