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