Fractal Dimensions of Soy Protein Nanoparticle Aggregates determined by Dynamic Mechanical Method

Abstract

AbstractThe fractal dimension of soy protein aggregates can be estimated by dynamic mechanical methods when the particle aggregates are imbedded in a polymer matrix. Composites were formed by mixing hydrolyzed soy protein isolate (HSPI) nanoparticle aggregates with styrene-butadiene (SB) latex, followed by freeze-drying and compression molding methods. The dynamic shear moduli of the elastomeric composites containing different particle fractions were measured. A logarithmic plot of shear modulus vs. particle fraction in rubber plateau region at 140 oC can be fitted with a linear line. From the slope of the fitted line, the fractal dimension of the particle aggregates was estimated using the Cluster-Cluster Aggregation (CCA) model developed by Kluppel and Heinrich. The CCA model can also be used to extract fractal dimension from dynamic strain sweep experiments. The reversible strain sweep data was then fitted with a CCA model expression developed by Huber and Vilgis to yield the fractal dimension of the particle aggregates. The results show that the fractal dimensions extracted from both linear and non-linear viscoelastic data have a good agreement with each other. The model fitting indicates HSPI has a greater fractal dimension and therefore a more compact structure than the un-hydrolyzed soy protein aggregates.