How to Measure Work of Adhesion and Surface Tension of Soft Material

Knowledge of the work of adhesion and surface tension plays an important role in design of new materials for applications as coatings, adhesives and lubricants. We develop an approach for obtaining work of adhesion and substrate surface tension from analysis of the equilibrium indentation data of rigid particles in contact with elastic surfaces. By comparing predictions of different models of a rigid particle in contact with a soft elastic surface we show that a crossover expression taking into account contributions of the elastic energy of the contact and surface free energy change outside and in the contact area is the best in describing the results of the coarse-grained molecular dynamics simulations. This crossover expression is applied to obtain work of adhesion and surface tension of glass particles on PDMS substrates. In particular, we study the indentations produced by silica particles with sizes varying between 0.2 and 1.5 μm on super-soft, solvent-free PDMS elastomers with brush-like network strands. By varying the side chain grafting density and the crosslinking density of the networks, we control their elastic modulus from ~3 to 600 kPa.