All Gelatin Networks:  2. The Master Curve for Elasticity

Abstract

The rheological properties of gelatin gels from various sources (fish and mammalian) were followed in the course of the sol-gel transition and during gel maturation, by performing dynamic measurements under very small deformations. Different concentrations and molecular weights were investigated. The solvent was mainly water, but mixed solvents containing water and glycerol were also considered. Blends of gelatins from fish and mammalian in aqueous solutions were prepared and rheologically characterized. A systematic comparison was established between these measurements and those presented in paper 1 of the series. The comparison between the storage modulus and the concentration of helices leads to a master curve valid for all the samples investigated. This master curve is analyzed in terms of the percolation regime, near the threshold and in terms of a homogeneous network far from the threshold. In the percolation regime, a critical exponent of 2 is found for the storage modulus versus the distance to the threshold, in agreement with previous results. The theoretical models for rigid networks are briefly presented. The fully developed network appears as an entangled assembly of rigid rods (triple helices) connected by flexible links. This study shows that gelatin networks under small deformations do not behave like rubber-like networks, where long random coils are connected by local cross-links or entanglements.

Effect of sugars on aging of gelatin gels by vacuum-ultraviolet circular dichroism and rheological measurements

“…The shear modulus G in the vicinity of the gel point at p > p c is expressed as G ~ (p − p c ) t , where the exponent t = 2 is obtained for networks of Gaussian chains without excluded volume interactions [15]. The experimental value t = 2 in the present study and 1.8 in the literature [8] are close to the theoretical value. The value of χ c for the gel without sugars estimated in the present study was 0.15, being in agreement with the value 0.17 calculated from the literature data [8].…”

“…4 and 5 indicate the correlation between G' and θ/θ 0 in the aging of the gelatin gels, which is reasonable because the elastic modulus of gelatin gels is dominated by the helix amount [8]. In contrast, Fig.…”

“…They also showed that the values of G' at any moment in the aging process depend only on the concentration of helices defined as cχ. The critical helix concentration cχ c for gelation was 0.0035 g/cm 3 [8], corresponding to χ c = 0.17 for the 2 wt% gelatin gel. Fig.…”

“…In the rheological and polarimetric studies on the aging of gelatin gels without sugars, Joly-Duhamel et al [8] showed that G' and χ near the gelation time are represented by the equation:…”

“…Joly-Duhamel et al studied the aging of gelatin by the measurements of dynamic moduli and specific rotation [α] and estimated a fraction χ of renaturated helix amount in gelatin gels defined as [1,6]. They showed the correlation between G' and χ: G' increased with χ in the aging process and G' depended only on χ irrespective of the sources of gelatin and aging temperatures [8]. Effect of sugar on the aging of gelatin has not been studied in detail [9].…”