Wetting behavior of polyoxyethylene-type nonionic surfactant with multi-branched chains on solid surfaces

Wetting of solid surfaces by surfactants is a fundamental phenomenon exploited in various applications, including cleaning, coating, dispersion, and adhesion, and in electronics materials. In this study, the interfacial properties and wettability of a polyoxyethylene (EO)-type nonionic surfactant with multi-branched chains (bC7-bC9EO15.8) were systematically investigated and compared with those of corresponding linear double-(C8-C8EO16.2) and single-chain (C16.8EO15.5) surfactants. Although bC7-bC9EO15.8 exhibited a higher critical micelle concentration (CMC), it significantly reduced the surface tension to 26.3-27.0 mN m^-1, exhibiting excellent surface activity due to its methyl-rich branched structure. Additionally, contact angle measurements revealed that bC7-bC9EO15.8 facilitated rapid spreading on hydrophobic surfaces even at low concentrations, with significantly lower contact angles on glass surfaces than those of its linear-type counterparts. This behavior was attributed to initial EO-chain adsorption followed by hydrophobic-chain reorientation, possibly involving micelle adsorption or partial bilayer formation at the solid/liquid interface. Moreover, bC7-bC9EO15.8 consistently exhibited the highest wetting free energy across all substrates, regardless of surface polarity. These findings highlight the key role of branched hydrophobic chains in enhancing wettability.