The cure reaction, rheology, volume shrinkage, and thermomechanical behavior of epoxy-TiO2 nanocomposites based on diglycidyl ether of bisphenol A cured with 4,4′-diaminodiphenylsulfone have been investigated. The FTIR results show that, at the initial curing stage, TiO2 acts as a catalyst and facilitates the curing. The catalytic effect of TiO2 was further confirmed by the decrease in maximum exothermal peak temperature (DSC results); however, it was also found that the addition of TiO2 decreases the overall degree of cure, as evidenced by lower total heat of reaction of the cured composites compared to neat epoxy. The importance of cure rheology in the microstructure formation during curing was explored by using rheometry. From the PVT studies, it was found that TiO2 decreases the volume shrinkage behavior of the epoxy matrix. The mechanical properties of the cured epoxy composites, such as tensile strength, tensile modulus, flexural strength, flexural modulus, impact strength, and fracture toughness of the polymer composites, were examined. The nanocomposites exhibited good improvement in dimensional, thermal, and mechanical properties with respect to neat cross-linked epoxy system. FESEM micrographs of fractured surfaces were examined to understand the toughening mechanism. 1. Introduction Epoxy resins are widely used in industrial applications, such as matrices in composite materials, and for aerospace applications, adhesives, coating, electronic circuit board-laminates, and so forth due to their excellent mechanical and thermal properties, low cost, ease of processing, fine adhesion to many substrates, good chemical resistance, good weathering resistance, low specific weight, and long pot life period [1]. The major problems with epoxy are low stiffness and low strength compared to metals and also cured epoxy resins are highly brittle, which greatly limits their application in some areas [2]. Toughness reinforcement of epoxy resins has attracted considerable attention for over the last 30 years. A new approach aiming to overcome this basic problem is related to nanotechnology and uses fillers in the nanometer scale. Nanoparticles embedded in polymer matrix have attracted increasing interest because of the unique mechanical, optical, electrical, and magnetic properties displayed by the nanocomposites [3]. Nanoparticles can significantly alter the mechanical properties of the polymer close to a particle surface due to the changes in polymer chain mobility. The enhancement in toughness is attributed to the size of the nanoparticles, since they can
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