(42d) Ultra-Smooth, Chemically Functional Silica Surfaces for Surface Interaction Measurements and Optical/Interferometry-Based Techniques

The ability to measure the molecular interaction forces and energies is crucial for shedding light on interfacial phenomena where van der Waals, electrostatic, adhesion, polymer, or hydration forces can all play a critical role depending on the system. Studying these physical forces is critical to developing an understanding of the fundamental and technologically relevant processes that occur at different interfaces – processes such as electrochemical reactions, catalysis, adhesion/repulsion, frictional wear, and self-assembly of mono- and multilayers.

Studying intermolecular forces and processes of interfaces at the sub-nano scale has proven difficult due to limitations in surface preparation methods. Here we present a method for fabricating reflective, deformable composite layers that expose an ultra-smooth silica (SiO₂) surface (RMS roughness <0.4 nm) for interferometric applications. The robust design allows for cleaning and reusing the same surfaces for over a week of continuous experimentation without degradation. The electric double-layer forces measured using the composite surfaces are within 10% of the theoretically predicted values. We also demonstrate that standard chemisorption and physisorption procedures on silica can be applied to chemically modify the surfaces; as an example of this, the composite surfaces were successfully modified with octadecyltrichlorosilane (OTS) to study their hydrophobic interactions in water using a Surface Force Apparatus (SFA). These composite surfaces provide a basis for the preparation of a variety of new surfaces and should be particularly beneficial for the SFA and colloidal probe methods that employ optical/interferometric and electrochemical techniques, enabling characterization of previously unattainable surface and interfacial phenomena.