Networks swelling

The solvent in which the polymer network swelled is able to change the number of intermolecular bonds, to decrease observable flexibility of chain parts between points, and to stretch the system, i.e., to perform labor over it. Its influence on the Qon parameter, according to accepted approximations, is similar to the influence on the process in which only low-molecular compounds participate. Some deviation can be observed as a consequence of suppressing the solvent molecules in the network. One can find that the change of observable local rigidity of the chain as a consequence of network swelling is similar by its first approximation to its change for... 

The networks swelled isotropically indicating the co-continuous nature of the materials. The range of swelling for the PHEMA-1-PIB networks is significantly less than that of PDMAAm-i-PIB demonstrating that amphiphilic networks exhibiting various desired swelling characteristics can be obtained by the selection of network components. 

THE BERENS-HQPFENBERG MODEL. The Berens and Hopfenberg model considers the sorption process in glassy polymers as a linear superposition of independent contributions of a rapid Fickian diffusion into pre-existing holes or vacancies (adsorption) and a slower relaxation of the polymeric network (swelling).(lS) The total amount of sorption per unit weight of polymer may be expressed as... 

Madsen, F. and Peas, N.A. (1999). Complexation graft copolymer networks swelling properties, calcium binding and proteolytic enzyme inhibition. Biomaterials, 20, 1701-1708. 

Finally, in Sect. 2.5 the conformational changes in polyelectrolyte network swelling in the solutions of oppositely charged surfactants are discussed. 

Pig. 1. Dependence of the swelling parameter, a, on the quality of solvent, x, for polyelectrolyte (/), intermediate (2) and isoelectric (3) networks swelling in a salt-free one-component solvent... 

It can be seen that the character of network swelling depends essentially on the relative values of ct and ct,. Three different regimes of network swelling were distinguished and described in Refs. [20, 27] ... 

Note that the changes of a with ns are much larger if the network swells in a good solvent. 

As a rule, in experimental investigations of network swelling mixtures of two different low-molecular-weight solvents are used, i.e. the change of solvent quality is achieved by variation of the composition of the mixture. Besides, it is... 

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). 

Now, we turn to the case when one of the components of the mixed solvent in which the polymer network swells is polymeric [34, 35],... 

Let us analyze now the results for the general case when network swells in a solution of linear polymers. Let 4>p, be, respectively, the volume fractions of... 

The kinetic theory of rubber elasticity is so well known and exhaustively discussed (17, 27, 256-257, 267) that the remarks here will be confined to questions which relate only to its application in determining the concentration of elastically effective strands. In principle, both network swelling properties and elasticity measurements can provide information on network characteristics. However, swelling measurements require the evaluation of an additional parameter, the polymer-solvent interaction coefficient. They also involve examining the network in two states, one of which differs from its as-formed state. This raises some theoretical difficulties which will be discussed later. Questions on local non-uniformity in swelling (17) also complicate the interpretation. The results described here will therefore concern elasticity measurements alone. 

The expression (IV-10) can be used to advantage in a consideration of network swelling in a diluent. The equilibrium swelling will be governed by the equality of the chemical potential of the diluent inside and outside the gel-phase for the case of swelling in pure diluent this means... 

Figure 2.26 The network swelling method for determining polymer solubility parameters. Reprinted with permission from J. E. Mark, Physical Chemistry of Polymers, ACS Audio Course C-89, American Chemical Society, Washington, DC, 1986. Copyright 1986, American Chemical Society.

There are two principal approaches to forming sequential IPNs (1) form the first network, swell it with the second monomer, crosslinker and catalyst and then form the second network (2) blend the two monomers, crosslinkers and catalysts together and then crosslink them. Two different initiation processes (e.g. different temperatures) can be used in what is called in-situ sequential synthesis. Finally, an alternative consists in blending the monomers and then adding the catalysts and/or the crosslinkers sequentially. 

To evaluate the swelling behavior and the crosslinked parameters of coal networks, swelling data were obtained for seven American coals supplied in fine particles by the Pennsylvania State University coal bank. To eliminate experimental artifacts, several separations and purifications were performed prior to swelling, according to the general experimental protocol reported in earlier communications (1,12). 

Let us analyze now the results for the general case when network swells in a solution of linear polymers. Let p, C, be, respectively, the volume fractions of linear polymer and low-molecular solvent in external solution Xps. Xn and Xnp are the Flory-Huggins interaction parameters between linear polymer (P), network polymer (N) and solvent (S). 

Imagine a network model of the diamond structure (Fig. 1.17(e)), blue lattice), constructed from rubber tubes. Now inflate the network, swelling the hollow tubes. The resulting structure is a curved continuous network, enclosing the tunnels in the diamond network. If the inflation procedure is continued, the surface closes up around a complementary diamond network. The D-surface is the "half-way point" during the procedure. 

This equation is the Flory form of the elastic part of the free energy of a network. The mean-square end-to-end distance of network strands in their preparation state is 7 q. Assuming affine deformation on the length scales of a network strand, the mean-square end-to-end distance in the final state is = XRoY- Modern treatments of network swelling and elasticity utilize a more general form of Eq. (7.69) for the elastic energy of a swollen or deformed network strand, known as the Panyukov form... 

Comparing Eqs (7.76) and (7.83) shows the expected result that any network swells much more in an athermal solvent than in a 0-solvent. 

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