Interphase characterization and modeling of tensile modulus in epoxy/silica nanocomposites

Abstract

AbstractThe incorporation of second dispersed particulate phases in a polymer matrix enhances its mechanical properties. Because of the high surface to volume ratio of nanoparticles, the molecular structure of the matrix is altered at the nanoparticle/matrix interface and the volume of this perturbed region could be significant. These improved properties are produced by the interfacial interaction of the nanometric domains. In this research, epoxy matrix modified with three different sizes of nanosilica (12, 20, and 40 nm) and the effect of the interphase characteristics on the tensile properties of nanocomposites was investigated. At first, the theoretical values of the elastic modulus using a two‐phase mathematical model compared with the experimental data obtained from the nanocomposite samples and values between 8 and 10 nm were estimated for the interphase thickness. Afterward, considering the three‐phase model, it takes into account that three different regions for interphase volume fraction, including single particles, polymer trapping, and agglomerated nanoparticles, and an equation for evaluation of interphase volume fraction are defined. Also, the interphase tensile modulus was considered continuously changing from the properties of nanoparticle to the polymer matrix properties. Finally, the overall tensile modulus of nanocomposites, which considers different key parameters including nanoparticle size, values for the interphase thickness (h), and interphase tensile modulus (Ei), were calculated. The results were compared with the experimental ones of other studies and a good agreement was found. The smallest value of h as 6 nm for samples containing 12‐nm diameter nanosilica and highest value of h as 8 nm for samples containing 40‐nm diameter nanosilica is reported.