Aggregates of chemically conjugated microgels regarded as a model of gels

Abstract

In the crosslinking reaction of primary polymers, the rate constant R ( i , j ) can be described by R ( i , j ) = i α j α (α ≤ 1). If α ≤ 1 2 or 1 2 < α ≤ 1 , products are microgels or macrogels, respectively. Clusters of μm-order sizes were prepared by the crosslinking of St(styrene)-HEMA (hydroxyethylmethacrylate) microgels ( d = 260 nm) with glutaraldehyde (crosslinking agent) and HCl (catalyst), as a model of gels. These clusters were observed under the microscope. The microscopic negatives of the clusters were illuminated with light and the fractal dimension D of the clusters was determined by the transmittance of the light. The cluster size ( 0.9 3.0 μm ) did not affect the value of D (2.65–2.82). The concentration (0.4–2.0 wt%) of HCl also did not affect D of the clusters. When the microgels were crosslinked in the medium containing NaCl (2 wt%), D decreased (2.11–2.67). The ‘rapid aggregation’ of the gels occurred because of large ionic strength.