"Nanostructured surfaces"

Latex skater at the nanoscale: QCM study of analyte induced sliding in complex loadings with polymer beads

Kruglenko I.V., Kravchenko S.O., Burlachenko J.V., Kruglenko P.M.,
Snopok B.A.

Institute of Physics of the NAS of Ukraine. Prospect Nauki, 46, Kyiv-03039, Ukraine. E-mail: email of Corresponding kruglenko@yahoo.com
The generally accepted way of describing quartz crystal microbalance (QCM) response is based on the phenomenological Sauerbrey model, where coating characteristics are expressed by some effective values reflecting the inert nature of the loaded mass. More recently, it was recognized that resonance frequency shift could assume a variety of values which appear in more complex systems. 
The analysis of the adsorption measurements specific for films of latex nanoparticles LB1 (Sigma- Aldrich) with saturated water vapor (Figure) unambiguously indicates the manifestation of new nanoscale effects in the analytical QCM methods. When the fixation of LB1 nanoparticles on the surface was carried out using Tween compounds, a classic Sauerbry-type dependence is observed. At the same time, when particles can form large aggregates on the surface, “oscillatory” behavior of QCM response has been recorded. It was demonstrated that “transformation” of Sauerbrey into anti-Sauerbrey behavior of QCM sensors can be related to the formation of a mechanical nonlinear contact accompanied by the change in friction or surface across contact area which is induced by its interaction with the analyte. So, “massive” interfacial ensembles of LB1 with weak interfacial adhesion capable of slippage on the surface under exposure in water vapor: a loosely-coupled mechanical assembly able to move its center of mass freely across the surface disturbing the conditions of the phenomenological Sauerbrey model. Finally, it becomes clear that a volatile compound is able to change not only the mass loading, but also induce the transition from static friction to sliding in the areas when the friction coefficient locally changes owing to the adsorption.