Direct Measurement of Normal and Shear Forces between Surface-Grown Polyelectrolyte Layers

Abstract

This paper presents measurements, using the surface force balance (SFB), of the normal and shear forces in aqueous solutions between polyelectrolyte layers grown directly on mica substrates (grafted-from). The grafting-from was via surface-initiated atom transfer radical polymerization (surface-initiated ATRP) using a positively-charged methacrylate monomer. Xray reflectometry measurements confim the successful formation of polyelectrolyte layers by this method. Surface-inititated ATRP has the advantages that the polymer chains can be strongly grafted to the substrate, and that high grafting densities should be achievable. Measured normal forces in water showed a long-range repulsion arising from an electrical double layer that extended beyond the polyelectrolyte layers, and a stronger, shorter-range repulsion when the polyelectrolyte brushes were in contact. Swollen layer thicknesses were in the range 15 -40 nm. Upon addition of ~10 -2 M -10 -1 M sodium nitrate, screening effects reduced the electrical double layer force to an undetectable level. Shear force measurements in pure water were performed, and the measured friction may arise from polymer chains bridging between the surfaces.2

Depletion forces between particles immersed in nanofluids

“…In the presence of the electric double layer force, Zeng et al proposed that  =  -1 (the Debye length), and we suggest that could be generalised as the range of the soft inter-nanoparticle interaction, e.g. the thickness of adsorbed or end-anchored polymer layers on the surface[54][55][56]. The amplitude A 0 in Eq.…”

A Robust Lubrication System Using an Ionic Liquid Polymer Brush

“…There are few reports of macro scopic tribological studies with low friction systems, [22][23][24] especially for brush-bare systems, while most of tribological research involves brush-brush systems studied with nanoscopic measurements such as atomic force microscope (AFM) [25][26][27] or surface force apparatus (SFA). [28][29][30] Our present study opens a pathway to the development of the robust lubrication system based on polymer brushes, which is an example of the energy saving technology known as Green-Tribology.…”

Structure and Collapse of a Surface-Grown Strong Polyelectrolyte Brush on Sapphire

“…The synthesis protocol has been published previously 16 . All steps were carried out under ambient conditions.…”