Monitoring swelling and deswelling of thin polymer films by microcantilever sensors

Abstract

Microcantilever based sensors are promising devices because they are fast, low cost, portable and allow measuring extremely small quantities of substances in gas or liquid phase that are not detectable by other methods. In this work we investigate the swelling and deswelling behavior of poly(hydroxyl ethyl methacrylate), PHEMA, films with three different average molecular masses deposited onto bare silicon microcantilevers, a hydrophilic substrate, and onto polystyrene (PS) coated microcantilevers, which is a hydrophobic substrate, under humidity cycles by monitoring the deflections resulting from differential surface stress. The results found in the present study demonstrate that the micromechanical response observed are related not only to the polymer molecular weight, but also to the polymer-interface phenomena and environment-polymer interface that can play a crucial role on the signal transduction. Ellipsometric measurements evidenced that the swelling of PHEMA films with intermediate molecular weight at 80% RH follows Fickian diffusion mechanism. Nevertheless, due to the weak optical contrast or film homogeneity shorter or longer chains than PHEMA-300 could not be investigated by ellipsometry. PHEMA films deposited onto PS surfaces presented dewetting, which limited the ellipsometric measurements. In comparison to ellipsometry, monitoring swelling behavior of PHEMA by nanomechanical responses is more advantageous because it is faster and less restricted.

Simplifying Molecular Transport in Polyelectrolyte Multilayer Thin Films

“…In the swelling and de‐swelling mechanisms or in water transport, the interaction between water molecules and other functional groups of PEM is detrimental. [ 117–121 ] Using a quartz crystal microbalance assisted with dissipation (QCM‐d), the water sorption and desorption activity and the mechanical behavior of (PAH/PAA) films were investigated. [ 122 ] In situ sorption and desorption analysis were performed for two cases, that is, relative humidity (RH) and water concentration in the films.…”

Thermomechanical Response of a Representative Porin for Biomimetics

“…In particular, micro- and nanosized mechanical techniques, based on the principle that variations in electrostatic, van der Waals, and steric intermolecular interactions on the surface of functionalized cantilever cause bending (deflection) of a few nanometers, are playing a fundamental role . The combination of these miniaturized mechanical systems with electrical and, especially, optical displacement sensors has been applied for, among others, chemisorption measurements in air at room temperature with up to yoctogram (10 –24 g) resolution, , drug screening, , characterization of the thermomechanical response and the glass transition temperatures of macromolecular ultrathin films, , detection of DNA strands, observation of the hydration–dehydration (swelling–deswelling) of molecular systems, − and identification of biological species through their molecular mass and stiffness, improving the capabilities of conventional mass spectrometers. , …”

Blu-Ray-based micromechanical characterization platform for biopolymer degradation assessment

“…Micromechanical resonators have already shown their potential as sensors for temperature [11], biomarker detection [12] and material characterization [13][14][15][16]. Recently, studies on the behaviour of micrometer-sized thin film biopolymers have been performed [17][18][19] through the monitoring of the resonance frequency of spray-coated micromechanical cantilevers. The studies demonstrate that micromechanical resonators can characterize polymer films with thicknesses of even several microns and with different surface morphologies.…”