Enabling Tunable Water-Responsive Surface Adaptation of PDMS via Metal-Ligand Coordinated Dynamic Networks

Polymers are at the core of emerging flexible sensor and soft actuator technology. Ideal candidates not only respond to external stimuli but also have programmable response intensity and speed. Incorporating dynamic interactions into polymers has been widely studied. However, most research has focused on synthesis methods and on optical and mechanical effects of these interactions. Here, a new and tunable method of enabling environmentally adaptive polymers are introduced. Specifically, polar functionalities are "hidden" within polydimethylsiloxane (PDMS). When unveiled, these polar functionalities change the hydrophilicity of the polymer. Water is the stimulus that triggers the exposure of polar functionalities by disrupting interfacial equilibrium and driving surface reconstruction. This reversible adaptation is governed by the dynamics of a metal-ligand coordinated polymer, and therefore can be easily tailored by the choice of network structure, metal cations, and counter anions. PDMS is a particularly exciting polymer for this functionality because of the negative consequences of its intrinsically high hydrophobicity in many applications. However, this design concept is applicable to a wide range of polymers and can be expanded to other dynamic interactions such as reversible covalent bonding, hydrogen bonding, and ionic bonding, to empower programmable responsive functionality and therefore enhance material performance.