We present an exploratory study of the tribological properties and mechanisms of porous polymer surfaces under applied loads in aqueous media. We demonstrate that it is possible to change the lubrication regime from boundary lubrication to hydrodynamic lubrication even at relatively low shearing velocities by the addition of vertical pores to a compliant polymer. It is hypothesized that the compressed, pressurized liquid in the pores produces a repulsive hydrodynamic force as it extrudes from the pores. The presence of the ï¬?uid between two shearing surfaces results in low coeï¬?cients of friction (Î¼ â?? 0.31). The coeï¬?cient of friction is reduced further by using a boundary lubricant. Probe material was varied to show that the effect is independent of the shearing surface. The curvature of the probe, the compliance of the polymer and the depth of the pores, were changed to enhance the understanding of underlying mechanisms of the proposed lubrication mechanism. Finally a surface with non- uniform distribution of pores was tested to show that the effect can be observed over a range of surface designs and patterns. By using simulations to optimize the design, these surfaces can be used as a coating for total joint replacement implants and other application where ultra-low and tunable friction is desired.
We will also be studying the effect of surface patterning on the effective modulus of PDMS. We can modify the effective modulus of polymer (PDMS) sample by varying the degree of porosity. By increasing the degree of porosity for a hard polymer and by reducing the degree of porosity for soft polymer, we can reach the same value of effective modulus for both the samples. We aim to establish a relation between the effective modulus of PDMS and the Coefficient of Friction values for different samples.