Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 11/5/2010
Publication Date: 5/26/2011
Citation: Xu, J., Cheng, W., Inglett, G.E., Wu, P., Kim, S., Liu, S.X., Tseng, Y. 2011. Micro-heterogeneity of corn hulls cellulosic fiber biopolymer studied by multiple-particle tracking (MPT). Meeting Abstract. 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 principle of MPT 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 µm 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 fluorescence microscope. Individual time-averaged mean squared displacements (MSD) were calculated from the two-dimensional trajectories. From the individual time-averaged MSD, time-lag-dependent ensemble-averaged MSD, and MSD distributions were computed. 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.