Silicon-modified surfactants and wetting: V. The spreading behaviour of trimethylsilane surfactants on energetically different solid surfaces

The spreading behaviour of defined trimethylsilane-based surfactants of gen eral formula (CH3)(3)Si(CH2)(6)(OCH2CH2)(n)OCH3, n = 2-6, on five different solid surfaces at 21 degrees C has been investigated. Compounds bearing sh ort diethylene and triethylene glycol hydrophiles do not spread. For the lo nger-chained tetraethylene to hexaethylene glycol derivatives, the ability to spread depends on the surface energy. Rapid spreading is restricted to t he slightly polar surface of 40 mN m(-1) surface energy. Lower or higher su rface energies considerably reduce the spreading rates. The phase behaviour of the solutions substantially influences the spreading process. The dispe rsed systems of the tetraethylene glycol derivative spread constantly over long time intervals. The dispersions of the pentaethylene glycol analogue a re very close to the temperature for a transition into the one-phase state. A retardation of the spreading process occurs after a few seconds. Micella r solutions of the hexaethylene glycol derivative either spread very slowly or stop spreading after a few seconds. The largest spreading areas and hig hest initial spreading rates were found for the 0.1 wt% solutions. Copyrigh t (C) 1999 John Wiley & Sons, Ltd.