The non‐newtonian viscosity of polymers in relation to their molecular conformation

The non‐Newtonian viscosities of polystyrene and polyisobutylene were measured in various solvents over a wide range of shearing stress, τ (up to the order of 104 dynes/cm.2). The shear dependence of the intrinsic viscosities, [η], is closely related to the molecular extension of the polymers. The non‐Newtonian behavior of a polymer is greatest in a “good” solvent and least at Flory's Θ temperature. The maximum percentagewise drop in the intrinsic viscosities at highest attainable shearing stress was found to increase with increasing root‐mean‐square end‐to‐end distance, 〈r2〉1/2, of the polymer chains in “good” solvents. By plotting [η]τ = ∞/[η] τ = 0 against 〈r2〉1/2 / 〈rof2〉1/2(where 〈rof2〉1/2 is the theoretical 〈r2〉1/2 assuming free rotation about the chemical bonds of the polymer chains), the shear dependence of the intrinsic viscosities appeared to be absent when 〈r2〉1/2 / 〈rof2〉1/2 was extrapolated to unity. Furthermore, polymer having different degrees of chain stiffness seemed to form a composite curve in the plot, where the stiffer chains exhibited the most drastic drop in the intrinsic viscosities. Additional support was given with the experimental results of polydimethylsiloxane and cellulose triacetate solutions.