Isotope Effect in the Interaction between Gas-Phase Isotopologues and Polymer-Coated Porous Silicon Over Silicon Microcantilevers

Abstract

A kinetic isotope effect is observed in the guest-induced bending curves of poly-4-vinylpyridine-coated microcantilevers. Protiated (nondeuterated) and deuterated isotopologues of ethanol, water, and acetone exhibit a clear difference in their time dependent bending response patterns. While most protiated species exhibit Langmuir-type absorption bending curves, the bending curves of deuterated species are characterized by a clear overshoot. Time-dependent Fourier-transform infrared measurements provide further insight into the interrelation between molecular level interactions and macroscopic mechanical bending. A model is suggested to interpret these observations.

Simple physical model for chemomechanics

“…The asymmetrization process included deposition of a 50 nm gold protective mask atop one of the microcantilever faces followed by fabrication of a porous silicon layer on the opposite face using reaction induced vapor phase stain etching, 21,22 Figure 1. The microcantilever arrays were mounted on a holder above a vessel containing 40 mL of HNO 3 (65%) and 10 mL of HF (49%).…”

“…22 In this system, the guest molecules have a characteristic time-constant for reaching steady-state concentration in the gas phase above the microcantilever system [G] interface (t). This can be approximated by a first-order process, eq 9.…”

“…22 For example, the bonding of D 2 O molecules progressed from loose binding at the early stages of the absorption of water into the polymer to strong binding at steady state. 22 The D 2 O was also characterized by a slight lag in its bonding onset when compared with H 2 O.…”

“…21,22 We proposed a four-state phenomenological model to account for the observations. Different models attempts to link the chemical process taking place between guest molecules and organic layers harnessed to microcantilevers with the resulting macroscopic mechanical microcantilever deformation.…”

Detection of Alkylating Agents Using Optical, Electrical and Mechanical Means

“…To monitor the effect of different analytes on the bending pattern, nitrogen served as an inert carrier gas and a special evaporation chamber allowed mixing the analytes with nitrogen. During baseline and desorption stages the polymer microcantilever chip was exposed to pure nitrogen, while during absorption to a mixture of nitrogen and one of the analytes (Shemesh et al, 2011). Fig.…”