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

Abstract

Dynamic light scattering (DLS) and small-angle neutron scattering (SANS) correlation radii, ξ and ξSANS, are reported for polystyrene (PS)/acetone-h6 (ACh) (DLS) and PS/ACd (DLS and SANS) solutions at near-critical concentration for (7.5 × 103 ≤ Mw/amu ≤ 25 × 103), (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)ψcr projection using the multidimensional reduced scaling formalism introduced previously. The analysis yields scaling exponents (ν ∼ νSANS = 0.65 ± 0.06) which are in agreement with the theoretical value, νTH = 0.63, but (ξ)o and ξSANS are offset from each other, ((ξ)o/ξSANS) ∼ 3. The superscript “o” refers to correlation radii calculated from monomodal DLS correlograms using the Stokes−Einstein relation, (ξ)o = kBT/(6πηoD). D is the DLS diffusion coefficient, and ηo is the pure solvent viscosity. For PS/cyclohexane (CH) and PS/methylcyclohexane (MCH) solutions, (ξo/ξSANS) ∼7 and ∼20, but for all three solvents, agreement improves when ηo is replaced with η, the solution viscosity. Then, (ξ/ξSANS) ∼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.