Polymer Nanocomposites

AbstractThere has been significant interest in polymer nanocomposites (PNCs) because of their promising property enhancements – however, achieving these improvements are contingent on controlling the nanoparticle (NP) dispersion state in the polymer matrix. The inherent incompatibility between a hydrophilic filler and a hydrophobic polymer is the ultimate barrier for obtaining controlled NP spatial dispersion. We can mediate this unfavorable interaction by incorporating moieties on the chains that interact favorably with the NP surface, but preparation strategies typically used to prepare nanocomposites, e.g., casting from a common solvent or melt blending, frequently result in (far) out‐of‐equilibrium NP dispersion states with the degree of non‐equilibrium character sensitively dependent on the particular preparation technique employed. This is due to the energy landscape of even a simple PNC material being very highly complex with many local equilibria and large barriers. Most theoretical studies and our current understanding are based on the assumption that an equilibrium description of the nanocomposite applies, i.e., the system attains its global minimum state. However, different preparation conditions can place the system in different local basinsandthe extremely slow relaxation times of these systems to go from the “as cast” state to the equilibrium state imply that nanocomposites can end up in out‐of‐equilibrium conditions,including stateswhere properties might be favorable. These points, which are elaborated in this review, speak to the importance of preparation and annealing conditions in the NP dispersion state and hence the properties of this novel class of materials. This topic is the focus of this chapter.