From Adhesion to Wetting: Contact Mechanics at the Surfaces of Super-Soft Brush-Like Elastomers

Abstract

Fundamental understanding of rigid particle indentation into soft elastic substrates has been elusive for decades. In conventional heterogeneous and multicomponent systems, the ill-defined interplay between elastic and capillary forces has confounded explanation of the crossover region between the classical wetting and adhesion regimes. Herein, we study the indentation behavior of micrometer-sized silica particles on supersoft, solvent-free PDMS elastomers with brush-like network strands. By varying the side chain grafting density and the cross-linking density of the networks, we control their elastic modulus from ∼1 to 100 kPa without adding solvent. This isostructurally regulated balance between elastic and capillary forces allows for accurate mapping of the entire range of particle–substrate interactions by measuring indentation depth as a function of substrate stiffness and particle radius. A generalized theoretical model, accounting for the collaborative contribution of both forces to the system free...