Unperturbed statistical coil

Unperturbed Statistical Coils, in the Kirkewood and Riseman model, the polymer is represented as a collection of beads interconnected by bonds of length L... 

Theta solvents ru Solvents for a particular polymer in dilute solution, and at a temperature called the theta temperature that slows the polymer chains to assume their unperturbed, random-coil configurations with theoretical root-mean-square distances between chain ends. Kamide K, Dobashi T (2000) Physical chemistry of polymer solutions. Elsevier, New York. Flory PJ (1969) Statistical mechanics of chain molecules. Interscience Publishers... 

The unperturbed dimension refers to the size of the molecule, exclusive of solvent effects. It arises from a combination of free rotations and intermolecular steric and polar interactions. The expansion factor arises from interactions between the polymer and the solvent. In a good solvent a will be greater than 1 and the actual (perturbed) dimensions of the polymer will exceed its unperturbed dimensions. The greater the value of a, the better the solvent. For the special case where a = 1, the polymer adopts its unperturbed dimensions and behaves as an ideal statistical coil . 

Statistical Coils in Perturbed Mode. This model is also called the Flory-Fox model. In the previous model, the effect of excluded volume was not taken into consideration. According to the Flory and Fox analysis, the latter model applies only to the case of unperturbed chains under 8 conditions the case of chains in a good solvent requires a separate freatment. The Flory-Fox model is based on the assumption that long-range interactions and the perturbations that they cause do not modify the flow of a solution ... 

In earlier chapters an unperturbed coil referred to molecular dimensions as predicted by random flight statistics. We saw in the last chapter that this thermodynamic criterion is met under 0 conditions. 

It can be proved that these unperturbed dimensions approximate to the statistically determined dimensions of the isolated chain under 0 conditions the excluded volume effect is compensated by a positive, i. e. unfavorable, polymer-solvent interaction enogy. The rmperturbed dimensions of polymer chains are, therefore, subject in general to direct experimental determination in dilute solution in appropriate solvents in which the volume exclusion effect upon coil dimensions is nullified. 

Earlier literature has suggested that polymer coils in critical regions undergo a contraction or so called collapse transition the statistical physics of which is covered in detail in a review by Lifshitz et Volkova et al. have found that poly(a-methyl styrene) coils in cyclohexane are compacted to about 2/5 of unperturbed dimensions in the critical region Tager et al. make similar observations for polystyrene in three solvents. 

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