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3.4. Results and discussion 3912108t = 0.1 ht = 0.8 ht = 5.8 h64z [mm]20-2-4-6-8-10 -8 -6 -4 -2 0 2 4 6 8 10x [mm]Fig. 3.3: Detected interface (indicated by the symbols) in the two-phase system at three differenttimes. The experiment was performed at 25 ◦ C and the initial volume fraction ofTMOS was 0.40. The solid curves represent the fitted interfaces after optimization.same resolution and MRI parameters as in the two-phase experiments the surface tension(SFT) was determined four times. The average SFT at room temperature was 74 ± 3 mNm −1 . An additional MRI image was obtained with twice the resolution, a higher numberof signal averages and a turbo factor of 1. In this case the SFT was 71 ± 1 mN m −1 , whichagrees well with literature [67]. Furthermore, the IFT of a n-hexadecane/water samplewas measured at room temperature with the same resolution and MRI parameters as theother two-phase systems. The average value derived from four images was 47 ± 7 mNm −1 .Effect of temperature and concentrationIn the left-hand graph of Figure 3.4 the IFT is shown as a function of time for theexperiments with the initial volume fraction of TMOS of 0.40. Despite the scatter, whichis especially observed for the measurement at 45 ◦ C, it is obvious that the IFT in thesystems without initial methanol starts around 10 mN m −1 and increases gradually duringthe first two hours to at least 20 mN m −1 .A clear effect of temperature on the IFT is not found in the temperature range considered.Interestingly, the IFT in the system with the initial methanol present in theaqueous phase starts at 8 mN m −1 and remains constant in the first three hours, afterwhich it increases slowly to about 15 mN m −1 . Although the experiments without theinitial methanol had similar concentration decays of TMOS in n-hexadecane as a functionof time (see Figure 3.2), the concentration profile for the experiment with methanol wasdifferent. The latter shows a lower mass transfer rate. On the whole, the presence ofadditional methanol in the aqueous phase lowers the IFT.