Supermolecular particles in acetylcellulose solutions

Abstract

AbstractThe curves of the size distribution, average radii (r), and concentration (N number of particles in 1 cc.) of finely dispersed supermolecular particles (SMP) in solutions of several batches of acetylcellulose (AC) have been determined by the method of turbidity spectra based upon the combination of two theories of Heller and co‐workers. It was observed that for some batches of AC the SMP in acetone solutions at 2% concentration are aggregates which are destroyed, forming smaller fragments when the solution is diluted. For an AC sample with high Ca++ content a twofold increase in SMP dimensions is observed. Nevertheless, the volume fraction of the population of small SMP (θ) remains constant. Temperature dependence of the dimensions of SMP r(T) in dioxane solutions has been studied. It has a smooth character with a considerable (for certain AC batches) decrease in SMP dimensions (and a corresponding increase in N) in the temperature range from 14 to 40°C. This dependence of r(T) gave rise to a suggestion about a marked influence of hydrogen bonds upon the aggregation process of the SMP fragment at room temperature (and at lower temperatures). The SMP radius corresponding to the flat part of r(T) (high temperatures‐interfragment hydrogen bonds are broken) varies with the content of bi‐ and trivalent metal cations in the AC preparation. This provides evidence of the participation of bridge bonds in the aggregation of SMP fragments: metal ions carboxyl or sulfoester groups on the surface of the SMP fragments. Comparison of r(T) and N(T) shows that on heating (as well as on dilution of the solution) SMP are destroyed without a change in θ, and in the spherical shape of SMP, i.e., N1∼D13 = N2∼D23. If the SMP population at maximum destruction (high temperature) is defined as a system of structural elements of SMP characterized by the parameters De (diameter) and Ne (reduced to the 2% polymer concentration), the above condition is given by N.r3 = Ne.re3 or N.D3 = Ne.De3. The linear dependence of the number and dimensions of SMP in a logarithmic scale resulting from the scheme log N = (log Ne + 3.log De) ‐ 3.log D, describes well the experimental results of the determination of the SMP parameters both in the AC solutions (different samples, solvents, concentrations, and temperatures) and in the viscose solutions (published data) over a wide range of the SMP dimensions. The parameters of the smallest SMP fragments which we have determined experimentally (De ∼ 500 A., Ne ∼ 1011) closely agree with the extrapolated value B = log Ne + 3.log De.