Organophosphonic acids as viable linkers for the covalent attachment of polyelectrolyte brushes on silica and mica surfaces

Abstract

We report the first successful preparation of polyelectrolyte brushes using an ATRP initiator that was covalently grafted to silica and mica substrates via an organophosphonic acid.

Tribological Behavior of Surface-Immobilized Novel Biomimicking Multihierarchical Polymers: The Role of Structure and Surface Attachment

“…The kinetic friction force, F S , was determined as the average value obtained at the plateau (i.e., in the steady-state regime). In all cases, the friction behavior follows Amontons’ law (i.e., F S = μ × F N , where μ is the coefficient of friction (Figure )), as also often observed with polymer-coated substrates. − Generally, this behavior is explained by the fact that the “real” contact area is linearly proportional to the normal load and is not determined by the elastic properties of the contacting surfaces or the strength of the adhesive forces . In most cases, the extrapolation of the experimental data suggests that the F N – F S curves pass through 0, indicating that the contribution of adhesion is negligible, although adhesion was observed for chemisorbed HA in PBS and HPA under all conditions upon surface separation.…”

Lubrication with Soft and Hard Two-Dimensional Colloidal Arrays

“…In most cases, the friction behavior follows Amontons' law, i.e., F S = μ × F N where μ is the friction coefficient, as also often observed with polymer-coated substrates. 28,44,57,58 However, for large Q values (>2.5), as for PAA-25% at 0.8 particle/μm 2 , F S increases asymptotically with F N with a very low effective friction coefficient in the large load regime (Figure 4a). The immobilized PAA-25% NPs exhibit a significant decrease in the friction coefficient with increasing pH or increased swelling (Figures 4c and 5b).…”

“…In an attempt to mimic the lubricating function of the natural molecules, researchers have resorted to different polymers, − ,− more particularly, synthetic polymer brushes, ,− which are generally simpler and whose behavior is somewhat better understood than that of their natural counterparts. ,, Several studies using the surface forces apparatus (SFA) and atomic force microscopy (AFM) have been carried out for different classes of solvated polymer-bearing surfaces in order to elucidate the role of different parameters, such as polymer conformation, solvent quality, and type of substrate, in reducing friction between surfaces. ,,− In particular, water-based polymer brushes have been shown to be highly lubricious in an aqueous environment under conditions ranging from 10 nN to 30 mN loads experienced in AFM and SFA. − The good performance of such systems is attributed to their ability to maintain separated the sliding countersurfaces while presenting a solvent-rich, low shear-strength interbrush layer, providing fluid–film lubrication without the need for hydrodynamic lubrication. , This differentiates brushes from other polymer coatings . With polyelectrolyte brushes, the charges appear to provide additional repulsions between the sliding surfaces upon compression, thereby enhancing the ability of the brush to separate the surface …”

Synthetic strategies to enhance the long-term stability of polymer brush coatings

“…Because the hydrolysis of siloxanes is one of the main mechanisms for degrafting, linker molecules have been designed that do not form Si-O-Si bonds. For example, Borozenko et al 132 showed that poly(acrylic acid) (PAA) brushes grafted from phosphonic acid-based initiators resist degrafting more than brushes grown from organosiloxanes. Using density functional theory (DFT), they show that the enhanced stability is a result of the surface bond strength for organophosphonic acid initiators in water being 120 kJ mol À1 higher than for organosiloxanes.…”