Studying kinetics of a surface reaction using elastocapillary effect

When a liquid is inserted inside a microfluidic channel, embedded within a soft elastomeric layer, e.g. poly(dimethylsiloxane) (PDMS), the thin wall of the channel deforms, due to change in solid-liquid interfacial energy. This phenomenon is known as Elastocapillary effect. The evolution of a new species at this interface too alters the interfacial energy and consequently the extent of deformation. Hence, it should be possible to monitor dynamics of physical and chemical events occurring near to the solid-liquid interface by measuring this deformation by a suitable method, e.g., optical profilometer.

Aqueous solution of a metal salt inserted into these channels reacts with Silicon-hydride present in PDMS, yielding metallic nanoparticles at the channel surface. The kinetics of this reaction was captured in real time, by measuring the wall deformation. Similarly, physical adsorption of a protein: Bovine Serum Albumin, on PDMS surface too was monitored.

The rate of change in deformation can be related to rate of these processes to extract the respective reaction rate constant. These results show that Elastocapillary effect can be a viable analytical tool for in-situ monitoring of many physical and chemical processes for which, the reaction site is inaccessible to conventional analytical methods.