Although it might seem straightforward to create stretchable conductors by mixing conductive nanomaterials with elastic polymers, the process is complicated due to the viscous nature of the prepolymers (intermediate polymers with functional groups that facilitate further polymerization), often resulting in clumping. For effective conductivity, these materials need to be evenly distributed and interconnected within a 3D network. Now, writing in Nature Communications, Won Jin Choi, Jin Young Oh, Tae Il Lee and colleagues propose an approach to integrate metal atoms with elastomers through thermal evaporation, which offers a finer scale of material mixing.

This project is the result of a long-standing collaboration dating back to 2012. “At this time, all four main authors (the first author and three corresponding authors) were working together in the same lab, as graduate students and research scientists,” comments Choi. The initial project consisted of obtaining wrinkled Au structures on different substrates, using PDMS as a transfer layer. Once, however, the Au layer was left on PDMS for several days, which initiated an unexpected transformation; the Au became intricately embedded within the PDMS matrix. “This incident marked the beginning of our realization that what we had previously thought of as a solid rubber slab was actually dynamically changing at the molecular level,” adds Lee. “Right after this discovery, we conjectured the hypothesis of a kinetics battle between the rate of evaporated metal atoms and the flux of migration of PDMS chains and found that Au atoms can actually be blended with PDMS elastomers on a sub- to nanoscale level.” In this case, the resulting structure exhibits inherent stress due to the difference in stiffness between the two materials and continues to change structurally over a few hours, resulting in a structure akin to folds in the brain.