Theta conditions, definition

An interesting result of the present modeling is an uncommon option to realize theta conditions. Maintaining its definition in terms of A2 = 0, leading to Xo = 0-5 ... 

Unperturbed radii of gyration (fi-om scattering experiments) always seem to indicate theta conditions (cf. Ref 5 12) but the database is too small to allow definite proof Unperturbed dimensions from hydrodynamic measiu e-ments in single solvents sometimes do not coincide with the theta state (ef Refs. 366,466,5 12) see also Section 1.2. Hydrodynamic measurements in mixed solvents very often deliver different unpertimbed dimensions for theta conditions (cf Refs. 31,83,95,154). 

This second definition of theta point is used to describe a solvent. In a solvent where Xi < 1/2, we have a better than theta solvent conditions with a second virial coefficient B2, which is positive. In a solvent where Xi > 1/2 we have less than theta solvent conditions with a second virial coefficient B2, which is negative. 

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... 

---