Applications of ATR FT-IR and wettability techniques in the study of solid/liquid interfacial phenomena.

• Main Author: Jeon, Joong Suck.
• Other Authors: Raghavan, Srini
• Language: en
• Published: The University of Arizona. 1993
• Online Access: http://hdl.handle.net/10150/186433

ATR (Attenuated Total Reflection) FT-IR (Fourier Transform-Infrared Radiation) technique was applied for the study of (1) adsorption of albumin onto a polyurethane film deposited on a bare ZnSe IR crystal (internal reflection element) and onto a ZnSe surface, (2) ionic surfactant (phosphate ester) adsorption onto alumina and (3) PEO (polyethylene oxide) based nonionic surfactant adsorption onto silicon. This technique was also applied to determine the spatial orientation of adsorbed surfactant molecules at solid/liquid interface. Dynamic contact angle and zeta potential measurements were made in these systems to elucidate adsorption phenomena. Albumin adsorption was found to be dependent on the solution pH and substrate type. The adsorption density was higher at pH = 7 than that at pH = 3 or 11, and the conformations of α-helix and β-sheet of albumin in the adsorbed layer were identified from amide III band. Adsorption density was higher on the more hydrophobic polyurethane surface than on the relatively less hydrophobic ZnSe crystal surface. The adsorption isotherm of alkyl phosphate surfactant onto alumina was characterized by three regions with a maximum adsorption density of 0.63 μg/cm² corresponding to 1.2 adsorption density. Using polarized IR beams, tilting angles of alkyl chains adsorbed onto alumina surface were calculated to be 42.5° and 40.7° for 50 and 100 ppm solutions. As the solution concentration of alkyl phosphate surfactant increased, the pH value at which zeta potential reversed decreased due to the specific adsorption of surfactant at alumina/aqueous solution interface. Adsorption of PEO based nonionic surfactants from alkaline solutions onto silicon was affected by types and lengths of hydrophobic groups and lengths of hydrophilic PEO chains. For the same alkyl chain length, increasing the length of ethylene oxide chain (higher HLB number) resulted in a decrease in adsorption density as well as residual surfactant after washing. Complete wetting of hydrophobic silicon was found in the immersing/emersing cycling in the surfactant containing solutions at concentrations in the range of 50 to 100 ppm. Ozonized DI water was very effective in removal of adsorbed surfactant on silicon, but it induced oxide layer growth.