Chain-solvent interactions

At the opposite influence on the change of local rigidity and chain-solvent interaction change on R- there may exist two probable places of the reaction, symmetric relative to the chain middle (Figs. 12-14). 

According to Eq. (23), the equilibrium number of chains in conformation c depends on the number gc of arrangements of a chain in that conformation, the conformational energy Ec, the surface parameter rjs, as well as the weight factors due to the chain-solvent interactions (/>,) and to the nearest-neighbor bond correlations In the above for-... 

The aim of this lecture is to impart some insight into the mechanisms involved in gel formation. These mechanisms are determined by the balance between forces underlying chain-chain and chain--solvent interactions. Mechanisms and conformations favored by either of these interactions are listed in Table I. 

The denaturation process starts at the point where the curves begin to deviate from the baseline. This temperature is, however, difficult to identify in a reproducable way especially for the second peak, since it is not clear whether the peaks overlap or not. Instead the intercept of the extrapolated slope of the peak and the baseline, was taken as a measure of the denaturation temperature (T ). The temperature at the peak maximum (T ) was also used for relative comparisons. From Figure 3 it can Be seen that the highest denaturation temperature was obtained at pH 5 close to the isoelectric point. Only one peak was observed at low (2-3) and high (10) pH. It is obvious that the protein system is partially denatured at these pH s due to the high net charge favoring chain-solvent interactions. 

Apart from denaturation where chain-solvent interactions are favored, heating may cause aggregation due to protein-protein interactions. Turbidity measurements may be used to follow aggregation reactions. They are easy to perform but it is not possible to say whether an increase in turbidity is due to changes in the number, the size or the optical properties of the particles. 

We now consider a set of chains A (degree of polymerizationiV a) in a solvent of small molecules B Nb = 1). The chain-solvent interactions are always characterized by a Flory parameter x eq. (IV.6)] which depends on temperature T. In most (but not all) systems x(7) is a decreasing function of temperature. Experimental phase diagrams are always given in terms of a concentration c and a temperature T. For our general discussion it is more convenient to use more the fundamental quantities = ctP (volume fraction) and x(7)- The phase diagram then has an universal structure, shown in Fig. IV,8,... 

Adachi and Kotaka report Ae and relaxation times for 8.6 and 164 kDa cis-polyisoprene in the good solvent benzene and in the Theta solvent dioxane(6). Figure 7.2a shows (r ) inferred from Ae. In the good solvent, the 164 kDa polymer contracts markedly over the full range of solution concentrations in the Theta solvent, the 164 kDa polymer apparently does not contract a great deal with increasing c. From the limited number of points, in either solvent (r ) of the 8.6 kDa polymer does not appear to depend strongly on c. These results are consistent with fundamental expectations that chain-chain and chain-solvent interactions in Theta solvents substantially eliminate excluded-volume-driven chain expansion, and that excluded-volume-driven expansion is not substantial for small chains. 

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