Proceedings of SerbiaTrib '13

performed from the surfactant solution in a volumeof 20ml.In our first adsorption series withouttemperature control, a 1000ml stock solution of10 -2 M (~10cmc) CTAB was prepared at roomtemperature. Since the solubility of CTAB in waterwas low at room temperature, the solution washeated to 30-35°C. By dilution of this solution,prepared by adding the appropriate volume of ultrapure water, surfactant solution concentrationsranging from 10 -3 M (~cmc) to 10 -6 M (~cmc/1000)have been prepared. One option, called “CTABin/CTAB out“(figure 4), involves immersion andextraction from the surfactant solution at thenominal concentration. In the water dipping step,the mica samples were dipped for 30sec into 20mlof ultra pure water to remove the excess solutionand excess surfactant molecules.After the post-rinsing step, the modified micasurface was gently blown dry with nitrogen, beforethe AFM imaging or contact angle measurements.This type of protocol (at different concentrations)was repeated several times to also assess thereproducibility.During the first experiments in March, the roomtemperature was in the range 21±2°C, and a fewmonths later, in June, the conditions in thelaboratory were clearly different, 32±2°C. Asdocumented by the air temperature measuredoutside of our building, shown in figure 5, thetemperature during the summer 2003 has beenmuch higher than in spring. In several experimentsthe temperature was more than 30°C.Using the above described preparation protocolsa significant number of samples have beenprepared. The AFM images of two representativesamples obtained by the ″CTAB in/CTAB out″protocol at a concentration below the cmc areshown in figure 6. The AFM results observed at allsolution concentrations below the cmc (from 10 -4 Mto 10 -6 M), are very similar with the resultspresented in figure 6.a) 85°/30°Figure 4. ″CTAB in CTAB out″ experimentb) 82°/22°6. RESULTS OBTAINED WITHOUTTEMPERATURE CONTROLThe first two sets of experiments were realizedwithout temperature control, in March and June2003.Figure 5. Local temperature recorded in June 2003(measured at 12:40 PM in Zürich-SwissMeteo data)Figure 6. AFM images of CTAB on mica obtained withthe “CTAB in/CTAB out” protocol at a concentration of10 -4 M. Advancing and receding water contact angles arealso shown:a) in March 2003 and b) in June 2003A clear seasonal influence on SAMs adsorptionhas been observed in all experiments realizedwithout temperature control, regardless of theexperimental protocols. On the sample prepared inJune, where the air temperature outside of thelaboratory building was higher than in March(figure 5), a significant number of clusters of heightbetween 0.5nm to 3.8nm and the size around156 13 th International Conference on Tribology – Serbiatrib’13