Surface Stress, Thickness, and Mass of the First Few Layers of Polyelectrolyte

Abstract

The effects of surface stress and mass loading upon the adsorption of polyelectrolytes onto flexible silicon micromechanical cantilever sensors (MCSs) were studied in situ. A self-assembled monolayer of 2-mercaptoethylamine chloride (2-MEA) on gold was used to achieve single-side adsorption on the MCS. Such a preparation gave a positive surface potential, whereas a bare SiOx surface gave a negative surface potential. Wide scan X-ray photoelectron spectroscopy confirmed that the adsorption of polystyrenesulfonate (PSS) and polyallylamine hydrochloride (PAH) followed the general rule expected from the electrostatic interaction between the substrate and the polyelectrolyte, whereas the adsorption polyethyleneimine (PEI) did not. The adsorption of PAH on SiO(x) from a 3 mM water solution containing 1 M NaCl was associated with a deflection of the MCS toward the polyelectrolyte monolayer (tensile surface stress) owing to the hydrogen bonding between neighboring amino groups. Here, a surface stress change of 1.4 +/- 0.1 N/m was estimated. The adsorption of PSS from a 3 mM water solution containing 1 M NaCl on a 2-MEA surface induced a deflection of the MCS away from the polyelectrolyte layer (compressive stress), toward the SiO(x) side. Here, a surface stress change of 3.1 +/- 0.3 N/m was determined. The formation of a PAH layer on top of the PSS layer resulted in a deflection of the MCS toward the PAH layer. This indicated that the adjacent PSS layer was deswelling, corresponding to a surface stress change of 0.5 +/- 0.1 N/m.

Multispectral sensing of biological liquids with hollow-core microstructured optical fibres

“…However, the average thickness increase is 1.8 ± 0.3 nm and 7.0 ± 1.3 nm per bilayer for the salt-free PE solutions and in the presence of 0.15 M NaCl, respectively. These values differ from previously published data for LbL coating of planar substrates, where the average thickness per PE layer was ~1–3 nm 23 , 31 – 33 . We attribute this discrepancy to different hydrodynamic conditions for PE adsorption in our study 22 and the effect of the charged capillary surface.…”

Functional Polymer Coatings

“…In contrast the 5th and 6th line (fig. 4.46) are quite homogenous and the thickness of 70 nm and 65 nm scales with 3 nm per BL which was found in previous studies [135] for the classical LbL process by x-ray reflectivity using a salt concentration of 1 mol/L. In this case the liquid did not evaporate completely and had a contact time of 3 to 6 s. So it can be concluded that it is important to keep a minimum adsorption time which is limited by the total evaporation time of the solvent.…”

Young's modulus of plasma‐polymerized allylamine films using micromechanical cantilever sensor and laser‐based surface acoustic wave techniques

“…The change in stress within the swollen ppAA film could be calculated from the deflection magnitude of MCS using Stoney's formula . Within the entire H range from 10 to 80%, we measured a larger stress change for the ppAA film deposited at 90 W compared with that deposited at 5 W (Figure ).…”