| Autor: |
R. Cohen, Ivanka Stoineva, Roumen Todorov, Ivan Terziyski, Nelly Christova, Lidia Alexandrova |
| Rok vydání: |
2014 |
| Předmět: |
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| Zdroj: |
Colloids and Surfaces A: Physicochemical and Engineering Aspects. 460:299-305 |
| ISSN: |
0927-7757 |
| DOI: |
10.1016/j.colsurfa.2013.12.075 |
| Popis: |
Microscopic foam films and wetting films on SiO 2 –glass surface formed from aqueous solutions of rhamnolipid with two rhamnose groups (R2) have been studied. The wetting (receding) contact angles θ r of the solution on the glass surface have been measured, using the sessile drop method. The receding contact angles θ r versus rhamnolipid concentration C S curves showed a maximum at θ r ≈ 18° at concentrations about 2 × 10 −5 mol dm −3 R2 and a decrease in θ r reaching values of 7° at 8 × 10 −5 mol dm −3 . The addition of electrolyte (NaCl) decreases the θ r -values, respectively, decreases the hydrophobicity of the SiO 2 -glass surface. Microinterferometric methods of assessment of foam and wetting films are used which allow precise determination of the film thickness at various R2 and electrolyte concentrations. The measurements of the effect of the surfactant concentration on foam film thickness ( h ) show that the increasing adsorption of rhamnolipid ions leads to increase of the surface charge and potential at the air/liquid film interfaces until they reach plateau region at 5 × 10 −6 mol dm −3 R2. At the same concentration a minimum in h ( C S ) for wetting films is obtained. The action of additional repulsive surface forces in symmetrical and asymmetrical thin liquid films is found. The obtained results show that the surface forces are determined not only by the structure and organization of the adsorbed layers but also by the molecular state of the bulk solution. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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