The high surface area of single-walled carbon nanotubes (SWCNTs) dictates that the interface with their surroundings is important in determining their properties or functionality. For example, the interface of SWCNTs with their surroundings is important to their application in polymer composites, devices, drug delivery, bioimaging and biosensing. Understanding and ultimately controlling these surface layers is important because of its influence on reactivity, adsorption of pollutants, and interaction with biological materials. For example, the surfactant orientation on the SWCNT surface plays an important role in their separation by nearly any method. Our group has focused on characterizing and controlling these SWCNT interfaces. Here we present the equilibrium constants associated with surfactant exchange on the surface of different (n,m) SWCNT types using optical spectroscopy. The exchange of surfactant is found to be reversible and occurs at specific co-surfactant mixtures for each (n,m) type. Comparing the equilibrium states with the desorption characteristics during chromatographic separation enables a better understanding of the surface state that leads to desorption from the hydrogel.