[[Polymer Solutions]] #### Solubility parameters: Cohesive Energy Density: amount of energy needed to move a volume of molecules from their nearest neighbors to an infinite distance - $CED = δ^2 \qquad δ = (\frac{ΔH_v - RT}{V})^2$ ΔH_v = molar enthalpy of vaporization, V = molar vol - **Strong** interactions → **high** CED, Weak interactions → low CED Enthalpy of mixing: $ΔH_m^{contact} = V_m Φ_1 Φ_2 (δ_1 - δ_2)^2$ - ΔH_m becomes less positive (more favorable) as difference between δ decreases - Cannot get negative ΔH_m - doesn’t account for **new** intermolecular interactions Estimation: $δ = \frac{ρ_p Σf_i F_i}{M_0}$ - ρ_p = density, f_i = # of i groups, F_i \= molar attraction constant Flory parameter: $X_H = \frac{V_1 (δ_1 - δ_2)^2}{RT}$ - V₁= molar vol of solvent - Accounts for **enthalpic contributions only** If difference in δ **increases**, ΔG_m **increases** (**less** favorable) Unfavorable mixing: Polymer becomes more **coiled**, favors **polymer-polymer** interactions Model is good for “like with like”, doesn’t predict new favorable interactions