Kinetics of sol–gel transition in thermoreversible gelation of gelatin

Abstract

The sol–gel transition in dilute gels of gelatin are studied by differential scanning calorimetry (DSC) and static light scattering techniques. The sol–gel phase diagram clearly shows the existence of an upper critical solution temperature in this system. In addition, the DSC data conclusively exhibits two more phase curves in the sol state—one pertaining to the coexistence of monomers and aggregates and the second one separating the random coil and helix domains in the solution phase. The Ferry–Eldridge equation has been used to determine the enthalpy of the melting of the gel structure (ΔHg) which is equal to (30±2.0) kcal mol−1. The gelation temperature Tg is correlated to Flory’s statistical model of gelation, which gives the enthalpy of melting of pure gelatin crystallites (ΔHv) as ΔHv=(35±2.0) kcal cm−3 and crystallite melting temperature (Tm) as Tm=(588±20.0) K. The Flory–Huggins interaction parameter (χ) has been determined as χ=0.49±0.05. Interesting scaling behavior has been observed through light scattering measurements. The intensity of scattered light, Is∼ε−γ and Is∼ε0−β; ε=(T/Tg−1); T≥Tg and ε0=(t/tg−1); t≥tg, where t is the time and tg is the gelation time for ε and ε0≤0.5 with γ≂β≂0.02±0.005. The initial phase of cooling of the sol has been analyzed within the framework of Smoluchowski aggregation kinetics. On the basis of the above results it is being proposed that the sol–gel transition path in this polymer has three distinct steps—monomer aggregation, coil–single-helix transition, and single-helix–triple-helix transition followed by gelation.

Urea and Thiourea Derivatives as Low Molecular‐Mass Organogelators

“…The nature of the changes in Figure 1 are commonly observed for organogels. [16] Plots of these data for 1 c and 2 c according to the Ferry-Eldridge equation (i.e., log[LMOG] versus 1/T) [56,80] gave nearly straight lines, whereas 1 a exhibited an upward concavity in the < 2 wt % concentration region ( Figure S1 in the Supporting Information). This nonlinearity may be attributed to the formation of junction zones having low heats of interaction between the gelator molecules, [80] to some of the gelator molecules remaining outside the solid network, or to the non-ideality of the sol phase obtained at T > T g .…”

Brillouin light scattering from a biopolymer gel: hypersonic sound waves in gelatin

“…Static light scattering experiments have revealed the phase diagram and the kinetics of gelation [1,2]. From small-angle neutron scattering experiments and static light scattering experiments the dynamic mesh size of the network has been found to be typical of the order of several nanometers [3,4].…”

Nucleation and growth of thermoreversible polymer gels

“…• [14], the gelatin chains have a random single-stranded coil conformation that results in a homogeneous sol phase. Below T gel , the gel phase is induced by the formation of triple helices stabilized by hydrogen bonds.…”