Using Thiol–Gold Bond Formation To Bridge Surfaces with a Polymer Brush: SFA Experiments and MD Simulations

Abstract

Complementary interactions between functionalized surfaces are challenging to quantify, as both kinetics and thermodynamics are important. Optimal reaction parameters are key to the efficient formation of hierarchical nanostructures. Here, we report both surface forces apparatus (SFA) studies and molecular dynamics (MD) simulations of the controlled binding of thiol functionalized polymer brushes to complementary gold surfaces. Polymer brush–brush, brush–mica, and brush–gold experiments were performed in toluene. These comparative studies reveal the subtle balance of nonspecific and specific contributions to the measured interactions. Importantly, the physical phenomena responsible for the measured force profile in the selective binding system, including the formation of thiol–gold bonds, the resulting adhesion between the surfaces, the work to separate the surfaces, and the anchor strength of the polymer brush can be extracted. Corroborating MD simulations demonstrate that hysteresis in the approach and separation of these selectively bound surfaces is not the result of kinetic effects, but rather is due to the polydispersity of the brush itself and the resulting thiolated chain end distribution. We relate our findings to observations made in the formation of hierarchical particle aggregates.