Low friction and high load bearing capacity layers formed by cationic-block-non-ionic bottle-brush copolymers in aqueous media

• Published in: Soft matter Vol. 9; no. 22; pp. 5361 - 5371
• Main Authors: Liu, Xiaoyan, Thormann, Esben, Dedinaite, Andra, Rutland, Mark, Visnevskij, Ceslav, Makuska, Ricardas, Claesson, Per M.
• Format: Journal Article
• Language: English
• Published: 01.01.2013
• Subjects: Adsorbed layers; Anchoring; Atomic force microscope (AFM); Atomic force microscopy; Bearing capacity; Block copolymers; Bottles; Brushes; Cationic; Colloidal probe techniques; Copolymers; Double layer force; Electrostatics; Friction; Loads (forces); Low friction coefficients; Negatively charged; Plastic coatings; Silica; Substrate surface; Surface chemistry; Surface layers; Tribology
• ISSN: 1744-683X; 1744-6848; 1744-6848
• DOI: 10.1039/c3sm27862j

Efficient lubricants should be able to build surface layers that result in low friction and high load bearing capacity. In this work we show how this can be achieved in aqueous media by means of adsorption of a diblock copolymer consisting of a cationic anchor block without side chains and an uncharged and hydrophilic bottle-brush block that protrudes into solution. Surface and friction forces were measured between negatively charged silica surfaces coated with adsorbed layers of the cationic diblock copolymer, utilizing the atomic force microscope colloidal probe technique. The interactions between the surfaces coated with this copolymer in water are purely repulsive, due to a combination of steric and electrostatic double-layer forces, and no hysteresis is observed between forces measured on approach and separation. Friction forces between the diblock copolymer layers are characterized by a low friction coefficient, mu approximately 0.03-0.04. The layers remain intact under high load and shear due to the strong electrostatic anchoring, and no destruction of the layer was noted even under the highest pressure employed (about 50 MPa). Addition of NaCl to a concentration of 155 mM weakens the anchoring of the copolymer to the substrate surface, and as a result the friction force increases.