Probing the molecular interactions in the diffusion of water through epoxy and epoxy–bismaleimide networks

Abstract

ABSTRACT:Fourier transform infrared spectroscopy in the near-infrared (NIR) frequency range was used to investigate the molecular interactions occurring between absorbed water molecules and networks based on a tetrafunctional epoxy resin. One of these networks was a typical formulation containing 4,4Ј-diamino diphenylsulfone as a hardener, and the other was a modified resin containing 4,4Ј-bismaleimide-diphenylmethane (BMI) as a coreactive monomer. Molecular spectroscopy analysis confirmed the existence of mobile water localized into network defects (microvoids) that did not interact with the networks and water molecules bound to the networks through hydrogen-bonding interactions. In the BMI-containing system, the fraction of bound water decreased significantly with respect to the unmodified epoxy resin. This was a relevant result because the bound water was primarily responsible for the plasticization of the network and for the consequent worsening of mechanical performance. Water diffusion was investigated with gravimetric sorption measurements and time-resolved Fourier transform NIR spectroscopy measurements. These showed that the presence of BMI decreased the water uptake at equilibrium, enhanced the diffusivity, and reduced the activation energy for diffusion. A dual-mode model for diffusion was found to be suitable for accurately describing the mass-transport process in both investigated systems. The results of the model simulations allowed us to estimate the ratio of free and bound water, which was in good agreement with that obtained from the spectroscopic analysis.

Adhesive Quality of Self-adhesive and Conventional Adhesive Resin Cement to Y-TZP Ceramic Before and After Aging Conditions

“…8,30 Considering the influence of water storage in bond strength durability of resin cements luted to zirconia, it has been demonstrated that water sorption may cause cement hydrothermal degradation after storing. 35,39 In these studies, the shear bond strengths showed a significant decrease after thermocycling. Conventional bis-GMA based resin-luting cements did not demonstrate a durable long-term bond to high-strength ceramic materials when using silica coating or sandblasting.…”

Long‐term aging in a commercial aerospace composite sample: Chemical and physical changes

“…Previous work has shown that most aerospace composites show either a drop in the tan d peak with moisture absorption or sometimes multiple peaks; this depends on the test frequency. 11,12 At all frequencies, the DMA plots showed small but significant changes in the tan d peak position at the surfaces of the composite versus that of the center. This change in tan d may be due to oxidation stiffening of the surface layers; however, the change is small because such a thin layer has been affected.…”

“…The 100-Hz plot showed a much broader and flatter peak at the surface, which may indicate a start of the double peak often shown in high-humidity-aged samples. 11,12 Another common result of accelerated aging testing of composites under high-humidity and spiking conditions that is also thought to occur in real environmental situations is surface microcracking. 10,11,13 A microscopic examination of the unpainted surface Figure 4 Differential spectrum between the surface and center of the composite plaque (see Fig.…”

Characteristics of the sorption of water and an ethanol/water solution by light‐cured copolymers of 2‐hydroxyethyl methacrylate with dental dimethacrylates

“…Because of this plasticizing effect, the water induces swelling and causes dimensional changes in the copolymer network. 4 The sorbed water may also induce chemical oxidation and hydrolysis of copolymer chains. 5 It has been found that the modulus of elasticity 6 and the mechanical strength 7 of copolymers are reduced after storage in water, and this reduction is increased with the hydrophilicity of the copolymer.…”