Self-lubricating properties of polystyrene-polydimethylsiloxane two-phase materials

Polymeric two-phase systems containing polystyrene (PS) and poly(dimethylsiloxane) (PDMS) can be prepared as block copolymers (Cop) and as binary (PS-Cop) or ternary systems (PS-Cop-PDMS); the latter contain free PDMS oil inclusions of controlled size in a continuous PS phase. The ternary systems are prepared by polymerization of styrene in the presence of silicone oil and of a PS-PDMS block copolymer acting as an emulsifier. The presence of PDMS either as silicone oil or PDMS chain from the Cop contributes self-lubricating properties to these systems, when rubbing on a selected solid substrate such as steel or polyvinyl chloride. With the ternary systems, a layer of silicone oil is then present between the two rubbing materials and a kinetic friction coefficient of around 0.1 can be observed with an oil content above 10% in weight. Such polymer materials are interesting because of their permanent lubricating properties. The PS-PDMS block copolymer by itself also has a lubricating effect.