Dynamic Light Scattering Analysis on Critical Behavior of Cluster Size Distribution of Polyacrylamide and Agarose Solutions near the Sol-Gel Transition Point.

Abstract

The dynamic light scattering (DLS) method was applied to measure the cluster radii of polyacrylamide and agal~ ose solutions near the sol-gel transition point. In the case of polyacrylamide, primary clusters were formed first and secondary clusters on a larger scale were sequentially formed in the progress of the polymerization process. The zaverage radius of the secondary cluster near the sol-gel transition point increased divergently with an increase in acrylamide concentration to the transition point. By fitting the data with the scaling law, the sol-gel transition concentration and the critical exponent were determined to be 1.53 % and 0.84, respectively; The z-average radius of the agarose cluster also showed a tendency to diverge with an increase in concentration to the sol-gel transition point. With fitting by the scaling law, the sol-gel transition concentration and the critical exponent of the agarose solution were determined to be 4.5 x 10-2% and 0.92, respectively~ at 27.0'C. Thus, the percolation theory was proved to be effective to describe the cluster size distributions near the sol-gel transition point for both polyacrylamide and agarose solutions.Keywords: agarose, percolation, dynamic light scattering, correlation length, critical exponent Gels are widely used in the food industry, the analytical field, and the medical field. Agarose is one of the typical natural gelling substances frequently used in these fields. In studies on the microstructure of agarose molecule, electron microscopy (Am- sterdam et al., 1975;Waki et al., 1982;Sugiyama et al., 1994) and x-ray diffraction (Arnott et al., 1 974;Foord & Atkins, 1989) revealed that molecules are in the form of double helices interconnected with side-by-side associations.In the gelation process, it has been proposed that the sol-gel transition is analogous to the critical phenomena (De Gennes, 1979), such as magnetization phenomena near the Curie point.The gelation point is also believed to be a critical threshold: only a sol exists below the gelation point just as no magnetization exists above the Curie point. On the contrary, a gel exists above the gelation point and the magnetization is non-zero below the Curie point. The behavior of the magnetization near the Curie point is well described by the percolation theory (Stauffer & Aharony, 1992). In this connection, the macroscopic property of viscosity or elastic modulus of the gelation system has been measured, and the percolation theory has been successfully applied to the behavior of those macroscopic properties near the sol-gel transition point (Adam et al., 1985;Tokita & Hikichi, 1987, Tokita, 1989Yano et al., 1993 Kawabata et al., 1 996; Kjoniksen & Nysttom, 1996a;Durand et al., 1997).However, not only those macroscopic approaches but also a microscopic approach involving cluster-size distribution analysis is necessary to elucidate the mechanism of sol-gel transition.The cluster size distribution has been analyzed by GPC technique. However, it is difficult to apply this technique without t...

Influence of Acidity Regulators on the Stability of a Soymilk Colloidal Dispersion System

“…The characteristics of acrylamide and agarose have been studied extensively during gelation [13][14][15], and crosslinking aggregation and coagulation are often observed [16,17].…”

Spontaneous shrinking of soft nanoparticles boosts their diffusion in confined media

“…To confirm this hypothesis, osmotic deswelling of the soft NPs, originating from the presence of free (un-crosslinked or dangling) agarose chains, was first ruled out 32–34 . The osmotic pressure, Π osm , inside C ag = 1% w/w agarose gels was estimated by the dialysis bag method 35–37 to be 89 Pa (see Supplementary Methods 2 and Supplementary Notes 3 for details), which is of the same order as Π osm ≈ 0.4 kPa reported for C ag = 1% w/w molten agarose solutions 32–34 at T = 37 °C. This value is about two orders of magnitude smaller than the osmotic pressure needed to induce a 30% change in NPs radius in presence of Ficoll TM 400 solutions ( Π osm = 9.1 kPa, see Supplementary Fig.…”