SURFACTANT-ENHANCED SPREADING

The spreading of aqueous mixtures of a number of surfactants, includin g ''superspreading'' trisiloxane surfactants, has been investigated as a function of surfactant concentration, substrate surface energy, tem perature, humidity, and substrate roughness. The substrate surface ene rgy, characterized in terms of the contact angle of water, was control led by the deposition of mixed organosulfur monolayers with different terminal chemical functionalities. The data demonstrate a strong sprea ding rate dependence on both surfactant concentration and surface ener gy. Furthermore, they indicate that nonturbid trisiloxane surfactant s olutions, which were previously believed not to promote rapid spreadin g, display superspreading characteristics, albeit on substrates which were less hydrophobic than those initially investigated. Moreover, bot h turbid dispersions and nonturbid solutions of nonionic surfactants l acking trisiloxane groups have also been found to promote greatly enha nced spreading on less hydrophobic surfaces. Cationic and anionic surf actants were not observed to exhibit enhanced spreading characteristic s. These results indicate that surfactant-enhanced spreading denoted e arlier as ''superspreading'', is not limited to turbid aqueous dispers ions of trisiloxane surfactants, and this phenomenon may be more gener al. and occur in a much more diverse class of compounds than previousl y thought.