Theta Condition Concentration Regimes

The term excluded - volume effect is used or described any effect arising from intrachain or interchain segment - segment interactions. This interaction, which Flory referred to as a long - range interference of monomer units, decidedly affects the number of conformations that the chain can take up for example, those in which two monomers occupy the same point in space are not realizable. Flory s recognition of this effect triggered the development of polymer solution studies for the last four or five decades. 

The osmotic pressure it of a dilute solution of a monodisperse polymer with molecular weight M is expressed as a power series of polymer mass concentration c (weight of polymer per unit volume of solution) as 

Where R is the gas constant, T the absolute temperature, and M the molecular weight of the polymer. This series is usually called the osmotic virial expansion, with A (i = 2, 3.) being referred to as the i-th virial coefficient of the 

Experimentally, A2 can be evaluated by determining the initial slope of n/(RTc) plotted against c. However, the estimation of A3 and the higher virial coefficients is not a simple matter for experimentalists. Available experimental information about the virial coefficients is largely limited to A2. 

For a series of homologous polymers A2 depends on M as well as T and the nature of the solvent. Experimental studies have repeatedly shown that for a given polymer there is a combination of poor solvent and temperature 0 for which A2 vanishes regardless of M. This spetial poor solvent at is called the theta solvent, and 0, the theta temperature. 

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Summary The classical treatment of the physicochemical behavior of polymers is presented in such a way that the chapter will meet the requirements of a beginner in the study of polymeric systems in solution. This chapter is an introduction to the classical conformational and thermodynamic analysis of polymeric solutions where the different theories that describe these behaviors of polymers are analyzed. Owing to the importance of the basic knowledge of the solution properties of polymers, the description of the conformational and thermodynamic behavior of polymers is presented in a classical way. The basic concepts like theta condition, excluded volume, good and poor solvents, critical phenomena, concentration regime, cosolvent effect of polymers in binary solvents, preferential adsorption are analyzed in an intelligible way. The thermodynamic theory of association equilibria which is capable to describe quantitatively the preferential adsorption of polymers by polar binary solvents is also analyzed. 

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