Cyclohexane solvation thermodynamics

Table 3 Comparison Between TCP Calculated with SPT and the Isothermal Compressibility Method (ITC), and Between Experimental (E) and Calculated Solvation Thermodynamics Water (hrst row), Benzene (second row), Carbon Tetrachloride (third row), and Cyclohexane (fourth row)... 

In a mixture of solvents, the solvation thermodynamics become functions of mixture composition. In these systems it is interesting to determine the optimal mixture composition for dissolving a certain solute. Figure 10 shows solvation thermodynamics for cyclohexane, in the same water and benzene mixture, as a function of solvent mole fraction. It is interesting to remark that cyclohexane starts to dissolve in this mixture when the benzene concentration is about 25%. 

The intrinsic viscosity [r ] of a polymer increases with rising solvent quality (see Solvent in Chap. 5) due to the increased solvating envelope of the polymer chain. An increased effective volume of the chain leads to an expansion of the polymer coil and therefore to an increased intrinsic viscosity (see Fig. 5.2). The solvent quality can also be seen in the exponent a of the [q]-M-relationship. In the case that the interactions of the solvent molecules with the chain are so small that the coil is not contracted or expanded, theta-conditions are reached and the coil has its unperturbed dimensions in solution. A theta solvent is referred to as a thermodynamically poor solvent. In this solution state a theoretical value for the exponent a=0.5 can be derived (the required Eqs. 8.22 and 8.33 are discussed in detail in A deeper insight into in Chap. 8). This value of a=0.5 is also experimentally observed as shown in Fig. 6.7 for the theta system poIy(styrene) in cyclohexane (T=34.5 C). 

---