Sum Frequency Generation Vibrational Spectroscopy Studies of Molecular Orientation at Interfaces
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Sum frequency generation (SFG) vibrational spectroscopy has been developed into a powerful technique to detect molecular conformation and chemical group orientation at different interfaces. This article will focus on recent SFG research of interfacial polymers and proteins. Understanding of molecular structures and conformations at interfaces involving polymer and/or protein molecules is widely desired because they determine the interfacial properties that play crucial roles in many important applications. For example, the interfaces between polymer implants and proteins determine the biocompatibility of such devices. Consequently, improved control of these interfaces can increase human life expectancy. The interfaces between antibiofouling polymer coatings and underwater glue proteins secreted by marine organisms such as mussels and barnacles dictate the performance of these coatings. Characterization of the molecular structures of such interfaces can aid in the design of environmentally benign polymer coatings with better antifouling properties, saving energy required to operate marine vessels. The use of polymer-based adhesives is of major importance in a variety of modern microelectronic and photonic applications. Understanding the molecular structures of these adhesives at interfaces is essential for the design of better adhesive materials.
The molecular-level understanding of structures of surfaces/interfaces involving polymers and/or proteins has been a challenge, as such structures are usually considered to be complicated and hard to examine in situ. Here we will present recent advances in characterizing molecular conformations and chemical group orientations of polymer surfaces and protein molecules at various interfaces using SFG. We will introduce the SFG technique, discuss SFG studies on buried polymer interfaces, and show SFG detection of interfacial protein conformations.