Surface forces measured in sugar surfactant solutions between two hydrophobic thiolated silica spheres
2004 (English)In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, Vol. 233, no 1-3, 43-49 p.Article in journal (Refereed) Published
The force acting between two hydrophobic surfaces (hexadecyl-thiolated gold surfaces) across two different non-ionic sugar surfactant solutions above cmc was investigated. The two surfactants studied were n-decyl-beta-D-glucopyranoside (Glu) and n-decyl-beta-D-maltopyranoside (Mal). No long-range double-layer force was detected between the surfactant covered surfaces showing that they are non-ionic as expected. At distances from 20 nm down to a separation of 3 nm the ever-present van der Waals force creates a net attraction between the surfaces. At 3 nm the surfaces are in monolayer-monolayer contact and the system has a secondary force minimum. At shorter separations the surfactant monolayer starts to interact and a steric force develops counteracting the depletion of surfactants from the gap. As the compressive load reaches FIR approximate to 1.5 mN/m the surfaces are in hydrophobic-hydrophobic contact, where the system has its primary energy minimum. The nature of the pressure-induced depletion of surfactants from the contact zone showed a strong dependence on the approach velocity. This reveals that the time scale of the surfactants to reach their equilibrium situation under external compression is of several seconds. The surfactant with the glucoside head group offered a greater resistance against being forced out (15% higher). This was attributed to the larger adsorbed amount of Gin at the hydrophobic solid-liquid interface. It was further concluded that the forces generated from the surfactants were enough to prevent the system from coagulating but that flocculation will occur in the secondary force minimum (primary energy minimum). The hydrodynamic force was studied by changing the approach velocity of the surfaces. The position of the slipping plane coincided with the layer thickness of the adsorbed monolayer of surfactant at moderate approach velocities. The adhesion force increased with the time the surfaces were in contact and no limiting value was reached. This was attributed to surfactants remaining in the gap slowly being removed from the contact zone, thereby, increasing its hydrophobic character.
Place, publisher, year, edition, pages
2004. Vol. 233, no 1-3, 43-49 p.
n-decyl-beta-D-glucopyranoside, n-decyl-beta-D-maltopyranoside, surface forces, adhesion, wetting
IdentifiersURN: urn:nbn:se:kth:diva-45402DOI: 10.1016/j.colsurfa.2003.11.008ISI: 000220091500005ScopusID: 2-s2.0-0742321986OAI: oai:DiVA.org:kth-45402DiVA: diva2:452598
QC 201110312011-10-312011-10-282011-10-31Bibliographically approved