SANS study on chain dimension of polystyrenes diluted with low molecular-weight homologues in semi-dilute solutions

Chain dimension of polystyrenes diluted with low molecular-weight homologues in semi-dilute solutions was investigated, referring to the results for solutions in benzene and styrene monomer, and its concentration dependence was clarified by small-angle neutron scattering (SANS) with a “contrast-matching” method. The styrene monomer was found to act as a good solvent comparable to benzene. The polystyrene was confirmed to expand in the bulk “diluent” homologues having sufficiently low molecular-weights, and its concentration dependence of expansion factor, α, became weaker with increasing the degree of polymerization, NS, of the short “diluent” polymer. The critical NS value, NS,c, which is defined as the maximum value to give excluded volume effects, was much higher than the earlier theoretical prediction by de Gennes, i.e., N S , c ∼ N L 1 / 2 , where NL is the degree of polymerization of the long “solute” polymer. The power law exponent for NS-dependence of α seems to follow −1/16, rather than −1/8 predicted by the scaling, suggesting that screening blob size, ξ, can be scaled as ξ ∼ N S 1 / 2 , which is equivalent to the radius of gyration for the “diluent” polymers.