Comparative DSC kinetics of the reaction of DGEBA with aromatic diamines. II. Isothermal kinetic study of the reaction of DGEBA with m -phenylene diamine

Self-healing epoxy coating synthesis by embedment of metal 2-methyl imidazole and acetylacetonate complexes with microcapsules

The restoration of mechanical properties is desired for creating the self-healing coatings with no corrosion capabilities. The encapsulation of epoxy resins is limited by various factors in urea and melamine formaldehyde microcapsules. An improved method was developed, where epoxy resin was encapsulated by individual wrapping of poly(melamine-formaldehyde) and poly(urea-formaldehyde) shell around emulsified epoxy droplets via oil-in-water emulsion polymerization method. The synthesized materials were characterized analytically. The curing of the epoxy was achieved by adding the [Ni/Co(2-MI)₆].2NO₃ as a latent hardener and iron acetylacetonate [Fe(acac)₃] as a latent accelerator. Isothermal and non-isothermal differential scanning calorimetric analysis revealed lower curing temperature (T_onset = 116 °C) and lower activation energies (Ea ≈ 69-75 kJ/mol). The addition of microcapsules and complexes did not adversely alter the flexural strength and flexural modulus of the epoxy coatings. The adhesion strength of neat coating decreased from 6310.8 ± 31 to 4720.9 ± 60 kPa and percent healing increased from 50.83 to 67.45% in the presence of acetylacetonate complex at 10 wt% of microcapsules.

On the interplay between the slowdown of dynamics and the kinetics of aggregation: The case study of a reactive binary mixture

Modeling the kinetics of aggregation requires a proper strategy to take into account not only the reactivity of reagents but also the ability they have to diffuse. The lack of direct information about diffusion represents the most serious experimental obstacle to the use of diffusion-corrected mean-field equations, which is usually overcome by using information on the structural relaxation dynamics. A very accurate description of the entire kinetics of aggregation can be made by introducing a single time scale of diffusion, set by the structural relaxation time τ of the system according to ∼τ(ξ), with ξ a fractional exponent. Here, we apply this modeling to the case of a reactive binary mixture made of diglycidyl ether of bisphenol-A and 1,3-phenylenediamine, where the reaction proceeds along an autocatalyic (hydroxyl catalyzed) and a non-catalytic (impurity catalyzed) pathway and find that a very small value of the exponent ξ = 0.27 ± 0.03 is needed to reproduce all the data. Our results help revise some preconceived ideas: contrary to widely held assumptions, we find that (i) the time scale of diffusion neither increases proportionally to the structural relaxation time nor is related to τ by a power law with the same fractional exponent as that relating τ to conductivity; (ii) no direct connection exists between the transition to diffusion-control and the development of a gel network or formation of a glassy phase; and (iii) there is no significant difference in the enthalpy barrier for bond formation in the presence of hydroxyl or other than hydroxyl catalyst groups.