A Semimicro Diffusion Method for the Characterization of High-Polymer Fractions

Abstract

The studies here described were carried out in connection with a program which required the characterization with respect to molecular weight of nitrocellulose fractions available only in small quantities. A diffusion method has been developed which offers the advantages of simplicity of construction and operation of the apparatus and interpretation of results. Although diffusion is less sensitive to molecular weight than viscosity, the method submitted appears to be simpler for use on a milligram scale and to afford sufficient precision for many requirements.The diffusion method reported herein differs from other diffusion methods in that the liquid medium is held fixed in position by a matrix of fine-grained filamentous material; more specifically, in these experiments the matrix was composed of a pad of filter papers. This feature effectively dampens out convection currents in the liquid medium; yet the matris is not sufficiently dense t o interfere appreciably with the diffusion process.Experimental and theoretical diffusion studies have been extensively reviewed by Longsn-orth (6) and by Killiams and Cady (8). The latter authors have given solutions of the diffusion equation for several sets of initial and/or boundary values. In principle, the diffusion constant can he calculated from an accurate knowledge of these initial and boundary values and one set of concentration, position, and time measurrmentq at some time after diffusion has been allowed to commence. In pr:icticr, : I numher of sets of measurements are made and the diffusion constant iz wported aftcr home ar-?raging process has been

The Investigation of the Properties of Nitrocellulose Molecules in Solution by Light-Scattering Methods. II. Experimental Results and Intepretations.

“…If these conclusions are valid we should expect that R, the root-mean-square distance between ends of the molecule, would increase with the square root of z, the degree of polymerization, provided that z is not too small. Actually the calculated R: z1 is found to decrease slightly with z, as may be seen in table 4 and figure 5. An even stronger trend was observed for cellulose acetate by Stein and Doty (17).…”