An infrared spectroscopy study of the hydrogen bonding and water restructuring as a trisiloxane superspreading surfactant adsorbs onto an aqueous-hydrophobic surface

摘要

Trisiloxanes are surfactants with a compact trisiloxane group ((CH3)(3)Si-O-Si(CH3)(C3H6-E-j)-O-Si(CH3)(3)) as the nonpolar moiety and an oligomeric polyethylene oxide chain, E-j ((OCH2CH2)(j)-R) as the polar group. ("R" is the cap of the polar group.) Trisiloxane surfactants with four to eight ethoxylates facilitate the rapid and complete spreading of drops of their aqueous solutions on very hydrophobic surfaces not otherwise wet by water. This superspreading ability, which is not completely understood, is unique to these amphiphiles in that solutions of conventional alkyl chain surfactants do not wet out on very hydrophobic surfaces. In this study, in an effort to understand the origin of superspreading, we use Fourier transform infrared spectroscopy in total attenuated internal reflection mode (FTIR-ATR) to gain a molecular picture of the adsorption of a trisiloxane surfactant onto an aqueous/hydrophobic-solid interface, and for comparison a nonsuperspreading allcyl chain surfactant. We focus on the OH stretch of water molecules to detail the changes in the hydrogen bonding structure of water at the interface, and methyl and methylene stretches to measure the adsorption densities.