Small strain mechanical properties of latex-based acrylic nanocomposite films

A waterborne latex-based technique has been used to prepare acrylic films with laponite contents up to about 25 vol%. The laponite was attached to the surfaces of the latex particles, giving a cellular arrangement of laponite-rich regions at high laponite contents. Two regimes of reinforcement were observed, depending on whether T was above or below Tg, reinforcement at T > Tg being significantly greater than predicted by micromechanical models. Modulated differential scanning calorimetry and dynamic mechanical analysis showed part of the organic content of the films not to contribute to the glass transition. This “rigid amorphous fraction” (RAF) was argued to correspond to intercalated regions of the matrix. However, the RAF alone was insufficient to account for the observed increases in stiffness at T > Tg. The mechanical response is therefore discussed in terms of a four-phase model, in which intercalated laponite stacks are embedded in a matrix with reduced mobility, forming a foam-like structure, in turn embedded in a matrix with the properties of the bulk polymer.