Adsorption and Association of a Symmetric PEO-PPO-PEO Triblock Copolymer on Polypropylene, Polyethylene, and Cellulose Surfaces

Abstract

The association of a symmetric polyoxyethylene-polyoxypropylene-polyoxyethylene (PEO(19)-PPO(29)-PEO(19)) triblock copolymer adsorbed from aqueous solutions onto polypropylene (PP), polyethylene (PE), and cellulose surfaces was probed using Atomic Force Microscopy (AFM). Significant morphological differences between the polyolefin substrates (PP and PE) and the cellulose surfaces were observed after immersion of the films in the PEO(19)-PPO(29)-PEO(19) solutions. When the samples were scanned, while immersed in solutions of the triblock copolymer, it was revealed that the structures adsorbed on the polyolefin surfaces were smoothed by the adsorbed PEO(19)-PPO(29)-PEO(19). In contrast, those structures on the hydrophilic cellulose surfaces were sharpened. These observations were related to the roughness of the substrate and the energy of interaction between the surfaces and the PEO and PPO polymer segments. The interaction energy between each of the blocks and the surface was calculated using molecular dynamics simulations. It is speculated that the associative structures amply reported in aqueous solution at concentrations above the critical micelle concentration, CMC, are not necessarily preserved upon adsorption; instead, it appears that molecular arrangements of the anchor-buoy type and hemimicelles prevail. The reported data suggests that the roughness of the surface, as well as its degree of hydrophobicity, have a large influence on the nature of the resulting adsorbed layer. The reported observations are valuable in explaining the behavior of finishing additives and lubricants commonly used in textile and fiber processing, as well as the effect of the morphology of the boundary layers on friction and wear, especially in the case of symmetric triblock copolymers, which are commonly used as antifriction, antiwear additives.

Friction and anti-wear property of aqueous tri-block copolymer solutions in metal forming

“…It must be noted that the level of hydrophobicity of the surface also plays important role in the adsorption of the copolymers. As copolymer is known to adsorb well on hydrophobic surface [4,[14][15][16][17][18][19]25], the film formation capability of the aqueous copolymers reported here may be different on other metallic surfaces with different level of hydrophobicity.…”

“…In aqueous room temperature environment, PEO m -PPO n -PEO m copolymers adsorb via PPO middle block anchored to the surface and the two PEO end blocks extend out into bulk solution [4,[15][16][17][18]25]. This may explain the poor adsorption of the normal copolymer at above cloud point.…”

“…However the structural difference of the copolymers types is expected to influence their tribological performance, even though both have the same molecular weight and composition [6]. PEO n PPO m PEO n have been reported to adsorb well on hydrophobic surfaces such as polystyrene latex [14], polypropylene and polyethylene [15,16], poly(ethylene terephthalate), nylon, graphite [17], self-assembled hydrophobic surface [18], and hydrophobic elastomer [19] but the adsorption on metallic surfaces have not been studied.…”

Direct Measurement of Interaction Forces between Surfaces in Liquids Using Atomic Force Microscopy

“…Vakarelski et al (2004) reported that the friction between silica surfaces in a cationic surfactant solution reduced with increasing concentration and became constant at concentrations higher than the CMC. An adsorbed layer of the weak polyelectrolyte (Notley et al, 2003) and hydrophilic polymer (Li et al, 2011) also reduced the friction between surfaces, implying that any form of hydrated layer will play an important role in friction reduction.…”

Surface Film Adsorption and Lubricity of Soybean Oil In-Water Emulsion and Triblock Copolymer Aqueous Solution: A Comparative Study

“…At the high concentration (18%, above CMC), adsorption of the copolymer occurs predominantly through the micelles [34,58]. L64 micelles have core-fringe structure [59] and 17R4 micelles have core-shell structure [60]. Core-fringe structure of L64 micelles allows PPO blocks to adsorb on the surface with low PEO blocks interference.…”