Tribological Properties of Poly(l-lysine)-graft-poly(ethylene glycol) Films: Influence of Polymer Architecture and Adsorbed Conformation

Abstract

The tribological properties of poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG)-coated oxide interfaces have been investigated with atomic force microscopy (AFM) as a function of the molecular structure. Polymer-bearing surfaces were obtained via spontaneous adsorption of the polymer onto the oxide substrate from a buffered solution of physiological pH. Interfacial friction of these PLL-g-PEG-coated surfaces was found to be highly dependent on the duration of deposition and the architecture of PLL-g-PEG. In terms of the architecture, the PEG chain length and the grafting ratio (i.e., the molar ratio of L-lysine monomer to PEG side chain) of adsorbed PLL-g-PEG significantly influence the interfacial friction; specifically, friction is reduced as the PEG chain length increases and as the molar ratio of L-lysine monomer to PEG side chain decreases. The characteristics of the polymer deposition time and the influence of the lysine/PEG grafting ratio are rationalized in terms of spatial packing density considerations.

Influence of the molecular architecture on the adsorption onto solid surfaces: comb-like polymers

“…6). 18 The results presented in Fig. 10a confirm the above assumption: the adsorption is controlled by the energetic effect independently of the molecular nature of the main chain (G2 and G3), which agrees with the fact that the water content in both cases is very similar (Fig.…”

“…8), typical for highly plasticized polymers as a consequence of the associated water. 18,41 For the systems investigated G 0 E G 00 that is typical for gel-like materials.…”

“…9 However, at the same time the lubrication properties were significantly improved 10 as a consequence of the higher capacity of binding water by the longer PEG chains. 17 More recently, Perry et al 18 have analyzed the effect of the adsorption time on the lubrication properties of PLL-g-PEG layers and showed that after 5 minutes of adsorption the lubrication properties are not modified considerably. However, publications on the adsorption kinetics and its relation to the final performance of the adsorbed films are very scarce.…”

Total internal reflection fluorescence microscopy for determination of size of individual immobilized vesicles: Theory and experiment

“…53 In brief, a 10 lg/ml solution of PLL-g-PEG/PLL-g-PEG-Biotin (PLL (20) Surface Solutions, Switzerland) in buffer was first introduced to the flow cell using a gravity driven flow, after which it was incubated for $45 min. After subsequent rinsing, a solution of NeutrAvedin (10 mg/ml; Sigma-Aldrich, Germany) was injected and incubated for 30 min.…”

Physicochemistry aspects on frictional interfaces

“…This is attributed to the exceptional resistance to mutual interpenetration displayed by the compressed, counterion-swollen brushes, together with the fluidity of the hydration layers surrounding the charged, rubbing polymer segments. Spencer et al studied the tribological properties of the positively charged lysine as main chain, hydrophilic polyethylene glycol as side chain, and "bottle brush" type polymer (PLL-g-PEG) as a waterlubricated additive [34,35]. The polypeptide backbone with a positive charge can be anchored to the negative Fig.…”