Differential scanning calorimetry of epoxy cure: isothermal cure kinetics☆

The isoconversional kinetic analysis has been applied to nonisothermal DSC data on the cure of an epoxynovolac resin. The process reveals a dependence of the activation energy (Eα) on conversion (α). The shape of the dependence has been interpreted in the terms of the reaction mechanisms. It has been found that the model dα/dt = (k1 + αmk2)(1 − α)n used for the kinetically controlled cure gives rise to the dependence of Eα on α similar to the experimentally found one. To completely describe the diffusion-controlled cure, the effect of both T and α on the change in diffusivity has been taken into account. The equation for the specific rate constant of diffusion, kD(T,α) = Do exp(−ED/RT + Kα), has been induced. Its use allows us to obtain a model dependence of Eα on α closely matching the experimental one. A technique of predicting isothermal cure from the sole dependence of Eα on α has been considered.

Mechanism and Kinetics of Epoxy-Amine Cure Studied by Differential Scanning Calorimetry

ICTAC Kinetics Committee recommendations for analysis of multi-step kinetics

This review focuses on our studies over the past ten years which reveal that the mitochondrial inner membrane is a fluid-state rather than a solid-state membrane and that all membrane proteins and redox components which catalyze electron transport and ATP synthesis are in constant and independent diffusional motion. The studies reviewed represent the experimental basis for the random collision model of electron transport. We present five fundamental postulates upon which the random collision model of mitochondrial electron transport is founded: All redox components are independent lateral diffusants; Cytochrome c diffuses primarily in three dimensions; Electron transport is a diffusion-coupled kinetic process; Electron transport is a multicollisional, obstructed, long-range diffusional process; The rates of diffusion of the redox components have a direct influence on the overall kinetic process of electron transport and can be rate limiting, as in diffusion control. The experimental rationales and the results obtained in testing each of the five postulates of the random collision model are presented. In addition, we offer the basic concepts, criteria and experimental strategies that we believe are essential in considering the significance of the relationship between diffusion and electron transport. Finally, we critically explore and assess other contemporary studies on the diffusion of inner membrane components related to electron transport including studies on: rotational diffusion, immobile fractions, complex formation, dynamic aggregates, and rates of diffusion. Review of all available data confirms the random collision model and no data appear to exist that contravene it. It is concluded that mitochondrial electron transport is a diffusion-based random collision process and that diffusion has an integral and controlling affect on electron transport.

E. Rabinowitch

Papers

Collision, co-ordination, diffusion and reaction velocity in condensed systems