Theta temperature definition

Equation (3.104) provides an alternative definition of the theta temperature, as being the proportionality constant relating AiJj to ASj. According to Eq. (3.105), the theta (or Flory) temperature can be defined as the temperature at which the condition k — ijj prevails. Substituting Eqs. (3.99) and (3.100) into Eq. (3.104) gives... 

A generally valid relationship for the temperature dependence of the excluded volume has yet to be discovered. In the vicinity of the theta temperature (for definition, see Section 6.4.2), the following is a good approximation ... 

This equation suggests that the enthalpic interactions produce a proportionate change in the excess entropy, and reveals that AHf and ASf (or alternatively x and xp) must have the same sign (i.e. either both positive or both negative). Equation (3.43) also provides an alternative definition of the theta temperature, as being the proportionality constant relating AHf to A5f. On this basis the origin of the variation of 6 from one polymer-solvent system to another is clearly evident. 

The 273.15 is exact in this definition.) Thus, the freezing point of water is 0°C and its boiling point (at 1 atm) is found to be 100°C. Note that in this text Tinvariably denotes the thermodynamic (absolute) temperature and that temperatures on the Celsius scale are denoted 6 (theta). 

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