Micro-heterogeneity of corn hulls cellulosic fiber biopolymer studied by multiple-particle tracking (MPT)

Authors: Xu, Jingyuan - James; TSENG, YIIDER - University Of Florida

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/20/2015
Publication Date: 6/7/2015
Citation: Xu, J., Tseng, Y. 2015. Micro-heterogeneity of corn hulls cellulosic fiber biopolymer studied by multiple-particle tracking (MPT) [abstract]. 28th Annual International Symposium on Polymer Analysis and Characterization (ISPAC 2015). p. 92.

Interpretive Summary:

Technical Abstract: A novel technique named multiple-particle tracking (MPT) was used to investigate the micro-structural heterogeneities of Z-trim, a zero calorie cellulosic fiber biopolymer produced from corn hulls. The Multiple-Particle Tracking (MPT) method was used in this study, which was originally described by Apgar et al. [1]. The principle of this technique is to monitor the thermally driven motion of inert micro-spheres, which are evenly distributed within the samples, and to statistically analyze their displacement distributions. From the data of MPT measurements, information about the extent of heterogeneity can be extracted. For each experiment, a dilute suspension of 1 micrometer diameter, fluorescent, polystyrene micro-spheres (0.1 volume percent) was gently mixed with the Z-trim biopolymer. Images of the fluorescent beads were recorded onto the random-access memory of a computer via a cascade 1 k camera mounted on an inverted epifluorescence microscope. Movies were analyzed by a custom MPT routine analysis program from Tseng’s lab. The displacements of the microspheres’ centroids were simultaneously monitored in the focal plane of the microscope for 21.5 seconds at a rate of 30 fps, and the last 20 seconds (total 600 frames) of the movie was taken for particle tracking to avoid the unstable acquisition time in initialization. For each sample of Z-trim, we tracked a total of ~200 microspheres. Individual time-averaged mean squared displacements (MSD), =<[x(t+tau)-x(t)]2 + [y(t+tau)-y(t)]2>, where tau is the time lag and t is the elapsed time, were calculated from the two-dimensional trajectories [2]. From , time-lag-dependent ensemble-averaged MSD, <>, and MSD distributions were computed. The ensemble-averaged diffusion coefficient of the microspheres can be calculated as D(tau)=<>/4 tau [3]. This work indicated a relatively rapid concentration-induced transition of the properties of the Z-trim. Pre-transitional effects were apparent at low concentrations as clearly detected by the shape of the MSD distribution of imbedded particles. At lower concentration of 0.5% of Z-trim, the overall ensemble-averaged MSDs were very similar to that of a viscous homogenous liquid glycerol with a slope of unity. The diffusion coefficient for the 0.5% Z-trim was independent of time just like glycerol. The contributions of the 10%, 25%, 50% highest MSD values to the ensemble-averaged MSD for the 0.5% Z-trim were also similar to those for homogeneous solution of glycerol. Therefore, 0.5% Z-trim mostly behaved like a homogeneous viscous fluid. However, the time-dependence and asymmetry profiles of the MSD distributions and higher standard deviation of the normalized MSD distribution implied that even at 0.5% concentration, Z-trim showed a symptom of trend of heterogeneity. For the 1% Z-trim colloidal dispersion, though it behaved like a liquid from a relatively macroscopic standpoint because of its close to unity slope of ensemble-averaged MSD trace. It exhibited more heterogeneity as evidenced by the slightly time-dependence diffusion coefficient, time-dependence and asymmetry profiles of the MSD distributions, higher standard deviation of the normalized MSD distribution, and higher contributions of the 10%, 25%, 50% highest MSD values to the ensemble-averaged MSD. At higher concentration of 2% Z-trim, the heterogeneity became more evident.