Ethylcellulose Colloids Incubated in Dilute Solution

Abstract

This study revealed, for the first time, that dilute solutions made of a representative series of commercial ethylcellulose (EC; molecular weights 77-305 kDa, provided by the manufacturer) and four distinct organic solvents (α-terpineol, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (TPIB), tetrahydrofuran (THF), and benzene) can be used to foster stabilized, nearly monodisperse, nanoscale (pure) polymer colloid, with no isolated chains present. Using combined light-scattering (dynamic light scattering, static form factor, and Zimm/Berry plots) and intrinsic viscosity (Tanglertpaibul-Rao, Huggins, and Kraemer plots) analyses, the structural features of colloidal EC aggregates, ρ = ⟨R⟩/⟨R⟩ = 0.67-0.83, were first shown to be described rather well by the theory on colloidal spheres (⟨R⟩ and ⟨R⟩ being the mean radius of gyration and the hydrodynamic radius, respectively). An empirical scaling law relating the intrinsic viscosity to the mean colloid size can thus be established: [η] = (1.7 ± 0.2) ×10 ⟨R⟩ ([η] and ⟨R⟩ in units of mL/g and nm, respectively), which may be contrasted with the Zimm model for isolated Gaussian coils, [η] ∼ ⟨R⟩, and the Einstein equation for isolated solid spheres, [η] ∼ ⟨R⟩. Optical microscopy images of thin films cast from different EC solutions clearly revealed the abundance of micron EC agglomerates, contrary to the uniform thin-film morphology produced from a dilute polystyrene solution, which serves as a reference solution composed of isolated chains. These observations point to new features and applications of EC dispersions.