Rolling resistance moment of microspheres on surfaces: contact measurements

Using contact measurements, experimental evidence was obtained for the existence of the rolling resistance moment. The critical rolling distance prior to detachment is reported. Previously it has been argued that the critical rolling distance should be related to the lattice size and/or the molecular length of the particle and surface materials. However, there has been no theoretical prediction for the critical value and, currently, the reasons for its existence are not fully understood. For polystyrene latex (PSL) particles, measurements presented in the current study on silicon suggest much higher values for the critical rolling distance than previous anticipated levels. The current approach can also be employed to measure the work of adhesion between a spherical particle and a flat surface without the prior knowledge of the particle diameter since the rolling moment stiffness is directly proportional to the work of adhesion with no dependence on the diameter of the particle. Experimental results are compared with the available data and good agreement between the theoretical predictions and the experimental values is found.