3D numerical analysis of mass diffusion in (nano) composites: the effect of the filler-matrix interphase on barrier properties

Polymer nanocomposites based on impermeable fillers have been widely developed to improve gas barrier properties. These materials have to be viewed as three phase systems: the matrix, the fillers and an interphase layer between the filler and the matrix. In this paper, the effect of the interphase layer on the overall diffusivity of nanocomposites loaded with impermeable disk-like fillers is analyzed and quantified through 3D finite element modeling of mass diffusion. Ideal ordered filler distributions as well as random filler distributions are considered for filler content in the range 1-20 vol%. A parametric study covering interphase thickness to filler thickness ratio values between 0.125 and 0.5 and interphase diffusivity ratioD(interphase)/D(matrix)values from 10(-4)to 10(6)is presented and discussed. The results show that, depending on their quality (weakly or highly diffusive), the presence of interphases can be either beneficial or totally detrimental to the nanocomposite overall barrier properties. A specific case corresponding to the exact compensation of the tortuosity effect by the diffusion in the interphase layer is evidenced and analyzed. Moreover, the effect of continuous diffusion paths, which may occur between overlapping interphases, is investigated. This effect appears to be particularly critical for the barrier performance in the case of highly diffusive interphases. Finally, a confrontation between our simulation approach and an analytical model as well experimental data is proposed.