Correlation of Mechanical and Hydration Properties of Soft Phytoglycogen Nanoparticles

Phytoglycogen nanoparticles are highly-branched polymers of glucose that are produced as soft, compact nanoparticles by sweet corn. By combining the results of dialysis, ellipsometry and gravimetric analysis experiments, we have constructed a master plot of the osmotic pressure-concentration data for phytoglycogen nanoparticles with values ranging over seven orders of magnitude. The distinctive shape of the osmotic pressure-concentration curve for phytoglycogen differs significantly from that of dextran, a lightly-branched polysaccharide that is chemically identical but does not occur in the form of particles. Specifically, there is a well-defined plateau in the logarithm of the osmotic pressure at phytoglycogen nanoparticle concentrations corresponding to contact between the particles. By recasting the dependence of the osmotic pressure on concentration in terms of its dependence on the effective separation of the particles, we identify three distinct regimes of interactions between the particles: a weak repulsion before contact; a stronger repulsion upon initial contact and compression (intermediate regime); and an even stronger repulsion for large particle compressions (concentrated regime). This analysis has allowed us to relate the mechanical stiffness to particle hydration.