Friction properties of acrylic-carboxylated latex films. 2: Effect of post added surfactant

The second part of this work aiming at investigating how specificities of thin films prepared from aqueous polymer colloids (latexes) influence their friction properties is devoted to the role of surfactants. Two acrylic latexes containing either 1 wt% or 4 wt% of acrylic acid were used, to which 0 to 9 wt% of sodium dodecyl sulfate (SDS) was post added before film formation by drying. Bulk mechanical properties were also studied in order to improve interpretation of friction results. Increasing the amount of SDS in the films has the effect of increasing Youngʹs and shear storage moduli and decreasing tan δ. SDS, forming crystallized aggregates in the bulk of the films, behaves like a reinforcing filler, except at 9 wt% where the SDS phase percolates under stress and allows film deformation by shear bands at very low stress. Friction coefficients dramatically decrease with increasing SDS concentration, especially at high strain rate. Surface shear stress is strongly decreased due to lubrication by SDS having migrated to the film surface. In order to gain more insight in the lubrication mechanisms, SDS layers were deposited on glass in increasing amounts. This part of the study seemed to indicate that organization of the SDS surface layers has more impact than their amount.