Correlation Radii for Polystyrene (PS) in Poor and ϑ Solvents from Dynamic Light and Small Angle Neutron Scattering. New Data for PS/Acetone. Remarks on PS/Acetone, PS/Cyclohexane, and PS/Methylcyclohexane

Dynamic light scattering (DLS) and small-angle neutron scattering (SANS) correlation radii, ξ and ξ SANS, are reported for polystyrene (PS)/acetone- h 6 (ACh) (DLS) and PS/ACd (DLS and SANS) solutions at near-critical concentration for (7.5 × 10 3 ≤ M w /amu ≤ 25 × 10 3 ), (0 ≤ P /MPa < 120) and (12 ≤ t /°C ≤ 91), during pressure and temperature quenches ending at or near precipitation. The data are well described in the ( T, P ) ψ cr projection using the multidimensional reduced scaling formalism introduced previously. The analysis yields scaling exponents (ν ∼ ν SANS = 0.65 ± 0.06) which are in agreement with the theoretical value, ν TH = 0.63, but (ξ) o and ξ SANS are offset from each other, ((ξ) o /ξ SANS ) ∼ 3. The superscript “o” refers to correlation radii calculated from monomodal DLS correlograms using the Stokes−Einstein relation, (ξ) o = k B T /(6πη o D ). D is the DLS diffusion coefficient, and η o is the pure solvent viscosity. For PS/cyclohexane (CH) and PS/methylcyclohexane (MCH) solutions, (ξ o /ξ SANS ) ∼7 and ∼20, but for all three solvents, agreement improves when η o is replaced with η, the solution viscosity. Then, (ξ/ξ SANS ) ∼0.3, ∼0.2, and ∼3 for PS/AC, PS/CH, and PS/MCH, respectively. The results indicate the two probes are responding to the same or closely related clustering phenomena.