Studies on the Lubrication between Hydrophilic-Hydrophilic/Hydrophobic-Hydrophobic Gemini Interfaces and Complex Fluids

The frictional behaviors of implant soft materials in vivo are important to medical effect. In this study, hydroxyethyl acrylate sodium/acryloyldimethyl taurate copolymer (EMT-10) aqueous dispersions are adopted, acting as lubricants in hydrophobic polydimethylsiloxane elastomer (PDMS) Gemini interfaces or hydrophilic polyamide hydrogel (PAM) Gemini interfaces, respectively. The associations exist in EMT-10 aqueous dispersions via hydrogen bonding, electrostatic and hydrophobic interactions, similar to bio-lubricants. The EMT-10 aqueous dispersions, surface characteristics of Gemini interfaces and the axial force (N-a) during frictional experiments in Stribeck curves are studied. Under low and high concentrations of EMT-10 lubricant, the PDMS Gemini interfaces exhibit opposing sensitivity to N-a, different from the PAM Gemini interfaces, which always showing lower CoF at higher N-a. This phenomenon results from the various degree of perfection for lubrication film between the Gemini interfaces. To further distinguish the lubrication film formation, and correlate frictional surface characteristic and rheological behaviors of lubricant, a new parameter, relative thickness (phi), is established. When phi<1, the lubrication film is discrete, and the boundary lubrication regime plays dominant role during the frictional test. When phi>1, the entire lubrication film forms and the whole system enters hydrodynamic lubrication regime. For PDMS Gemini interfaces, the lubrication film is composed of the confined and adsorbed EMT-10 polymer chains owing to the strong attraction between the hydrophobic surface and the C-C backbone. As a result, the lubrication film is greatly affected by the concentration of the lubricant thus phi increases. The PDMS frictional system gradually converts from the boundary into hydrodynamic lubrication regime. For PAM Gemini interfaces, the film is made of the hydrogel surface mesh and the confined EMT-10 chains, so phi is always larger than 1, exhibiting the characteristic of hydrodynamic lubrication regime. The study tends to probe the frictional behavior of the complex fluids in the soft Gemini interfaces and unveils the mechanism behind the phenomenon. [GRAPHICS] .