Viscosity-temperature relationships for dilute solutions of cellulose derivatives

Ethylcellulose Colloids Incubated in Dilute Solution

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_g⟩/⟨R_h⟩ = 0.67-0.83, were first shown to be described rather well by the theory on colloidal spheres (⟨R_g⟩ and ⟨R_h⟩ 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]_H = (1.7 ± 0.2) ×10^-3 ⟨R_h⟩^(2.1±0.3) ([η]_H and ⟨R_h⟩ in units of mL/g and nm, respectively), which may be contrasted with the Zimm model for isolated Gaussian coils, [η]_H ∼ ⟨R_h⟩¹, and the Einstein equation for isolated solid spheres, [η]_H ∼ ⟨R_h⟩⁰. 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.

The dielectric behaviour of solutions of some rigid polymers under shear

The variation of the relative permittivity of solutions of ethyl cellulose in benzene and poly- γ -benzyl-L-glutamate (PBLG) in dioxan have been studied in a Couette-type dielectric cell as a function of shear rates (up to 3 x 10 5 s -1 ) and for PBLG also as a function of frequency (400–10 6 Hz). Both systems exhibit a decrease in the low frequency permittivity with shear, tending at the limit of high shear rate to the solvent value for the PBLG system but to a larger value for ethyl cellulose. These observations are analysed in terms of the available theories for the phenomenon. From the analysis estimates for the rotatory diffusion coefficients are obtained which are consistent with dielectric loss measurements. It is suggested that the retention of a contribution of permittivity at high shear rates for ethyl cellulose is due to a polarization normal to the major axis of the macromolecule. The results also provide indications of the overall macromolecular shape of ethyl cellulose and PBLG. The dependence of relative permittivity and loss on frequency and shear rate for PBLG show that the position of the loss peak is shifted to higher frequency by the constraints of a shear field, and that at sufficiently large shear rates the frequency dependence of permittivity exhibits a maximum. Data are also presented on the concentration dependence of shear induced permittivity changes for ethyl cellulose in benzene and the behaviour discussed in terms of polymer–polymer interaction at finite concentrations.