Polymer nanocomposites (PNCs) are made by combining polymers with nanometer-sized particles. These hybrid materials were first explored in the 1940s for use in rubber tires. Since that time, other uses, such as in spaceflight, electronics, and separations, have been considered. Basic understanding of the physical and chemical forces involved in these composites is still lacking, however, and limits their promise. The state of the field is described in an extensive review by Sanat Kumar, Venkat Ganesan and Robert Riggleman in the Journal of Chemical Physics.

One barrier that blocks the full practical realization of these materials is an insufficient ability to control the structure and dispersion state of the mixtures. A primary challenge in using theory to guide design of these materials is that models for polymers and particles have developed along separate paths—coarse-grained models are popular for polymer systems, while understanding phase behavior has dominated particle modeling.

As Kumar explains, the interface between the nanoparticles and the polymers is of critical importance in determining properties of the composites, so much of the work reviewed in this paper focuses on the crucial interface region. Early work relied on pairwise interactions, but recent multibody approaches have appeared and are reviewed, including some hybrid methodologies. Additional issues are also considered, including the not-fully-understood role of solvent.

One popular synthetic strategy involves functionalizing the nanoparticle with small ligands or polymeric grafts. However, most of the theoretical work to date considered an idealized spherical shape for the nanoparticle, and is of limited usefulness for grafted systems. The authors also believe another area ripe for development is modeling the behavior of PNCs in the presence of external forces, such as electric or magnetic fields.

Source: “Perspective: Outstanding theoretical questions in polymer-nanoparticle hybrids,” by Sanat K. Kumar, Venkat Ganesan, and Robert A. Riggleman, The Journal of Chemical Physics (2017). The article can be accessed at https://doi.org/10.1063/1.4990501.