Abstract
Abstract: The spreading of aqueous mixtures of a number of surfactants, including "superspreading" trisiloxane surfactants, has been investigated as a function of surfactant concentration, substrate surface energy, temperature, humidity, and substrate roughness. The substrate surface energy, characterized in terms of the contact angle of water, was controlled by the deposition of mixed organosulfur monolayers with different terminal chemical functionalities. The data demonstrate a strong spreading rate dependence on both surfactant concentration and surface energy. Furthermore, they indicate that nonturbid trisiloxane surfactant solutions, which were previously believed not to promote rapid spreading, display superspreading characteristics, albeit on substrates which were less hydrophobic than those initially investigated. Moreover, both turbid dispersions and nonturbid solutions of nonionic surfactants lacking trisiloxane groups have also been found to promote greatly enhanced spreading on less hydrophobic surfaces. Cationic and anionic surfactants were not observed to exhibit enhanced spreading characteristics. These results indicate that surfactant-enhanced spreading denoted earlier as "superspreading", is not limited to turbid aqueous dispersions of trisiloxane surfactants, and this phenomenon may be more general and occur in a much more diverse class of compounds than previously thought.