Surfactants in Solution

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It seems that you're in Germany.

Publication details

We have a dedicated site for Germany. Editors: Mittal , K. This series of symposia have been smoothly running since , but the appellation "Surfactants in Solution" was used for the first time in in Lund. Since then our logo "SIS" has become very familiar to everyone involved in surfactants. Earlier three events were held under different rubrics, but proceedings of all these symposia, except the 7th SIS held in Ottawa in , have been properly documented. As a matter of fact so far 10 volumes have appeared under the title "Surfactants in Solution".

It contained a total of papers by authors from practically every corner of our planet. Just the sheer number of papers is a testimonial to the high tempo of research and tremendous interest in this wonderful class of materials. As in the past, there were plenary lectures 5 , invited talks 37 , oral presentations and poster presentations The effect of surfactants, enzymes and temperature on soils investigated using electrochemical and crystallisation techniques for detergency applications Mehrin Chowdhury.

Ion specific effects in trivalent counterion induced surface and solution self-assembly of the anionic surfactant sodium polyethylene glycol monododecyl ether sulfate. Design of hard water stable emulsifier systems for petroleum- and bio-based semi-synthetic metalworking fluids.

Julie B Zimmerman , Andres F. Clarens , Kim F. Hayes , Steven J. Theoretical and experimental investigations of electrostatic effects associated with ionic surfactant micelles Nancy Zoeller Diggs. References Publications referenced by this paper. Solution chemistry of surfactants Edited by K. Rodney L Parsons. Same concerns could be valid regarding ESA mode of electroacoustics because electric field is a primary driving force. The CVI mode of electroacoustics is free of these concerns because electric effects are secondary, electric current and electric field are too weak to produce any real disturbance of the equilibrium distributions.

Surfactants absorb at interfaces

The Electroacoustic method yields information about electric surface charge. Combining this data with conductivity results allows us to estimate size of the ions, their concentration, apparent dissociation constant, diffusion constant, and the size of the protective micelle. These parameters were not available before.

We tried several different producers of kerosene and discovered practically no influence of the kerosene origin on the results of measurements. For dielectric permittivities of these liquids shown in the legend on Figure 4 we used reference [11], but for kerosene.

Concentration-model for surfactants near the cmc

We use approximately 2 for dielectric constant of kerosene because it is not clear how impurities would affect this number. We used alumina AKP by Sumitomo as the dispersed phase. The primary particle size of the alumina is 0. We measured the particle size in the kerosene dispersions using the DT by Dispersion Technology. The acoustic sensor of this instrument allows us to characterize particle size without dilution for detail description see [8]. This sample required continuous mixing of the alumina dispersion to prevent settling, which was provided by the built-in magnetic stir bar in the DT sample chamber.

For conductivity measurements we used a Model Conductivity Meter by Scientifica. It operates at 18 Hz with an applied voltage of about 5 V rms. For electroacoustic measurement we used the Zeta Potential Probe DT for detail description see [7]. This probe could be inserted directly into the sample vessel, as it is shown in Figure 1. An external magnetic mixer prevents settling of particles. Electroacoustics determines the sign of the surface charge through the phase of the measured CVI signal.

In non-aqueous systems we might expect some variation in the CVI phase compared to traditional water based dispersions. This uncertainty in the expected CVI phase suggested that we use some independent confirmation of the sign of the particles electric charge, which we accomplished by observing the direction of motion of the charged particles in a known electric field. There is clearly large difference between different surfactants.

We plotted the same data on logarithmic scale on Figure 3 to make this more visible. In order to rule out the possibility of impurities in surfactant as a factor responsible for this conductivity, we tested two different suppliers of the SPAN The conductivity curves are practically identical, which proves that the observed effect is related to the chemistry of the surfactant molecule. The differences in the conductivity curves correlate with the HLB numbers of the corresponding surfactants: the higher HLB, the larger the conductivity.

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This agrees well with the micelle model of ionic conductivity induced by the surfactants. The higher HLB number reflects more polarity of the corresponding surfactant. Consequently, the protective micelle shell around the ion must be stronger and, perhaps, even more extended. Statistically this would lead to a larger number of ions and a higher conductivity.

However, the HLB number is not the only factor. We tested a surfactant from a different family for verifying the importance of other details in the surfactant chemistry. It might perhaps happen because the molecules can split at different binding points. Measurements in different liquid reveal that this conductivity effect depends also on the properties of the liquid.

It is interesting that there is no direct correlation with dielectric perimttivity. But these conductivity measurements of homogeneous liquids provide only limited information. That is why in the next step we will add insoluble dispersed particles for creating a heterogeneous system. Figure 5 shows the conductivity for these solutions versus SPAN 80 content. It is clearly seen that the addition of the alumina particles causes a very large change in the conductivity.

This change can be explained only by adsorption. This means that alumina particles adsorb substantial amount SPAN Below this point alumina particles adsorb practically all SPAN 80 molecules.

We could also conclude that particle either adsorb both cations and anions, or dramatically change apparent dissociation constant of the SPAN molecules. Remaining ions counter-ions would maintain at least half conductivity level comparing with the pure liquid. Here we assume following Morrison that sizes and mobilities of ions are about equal.


Is it related to just one sort of the ions? Is there any difference in adsorption between cations and anions? In order to get answers to these questions we use electroacoustic technique for characterizing surface charge of the particles. Electroacoustic method works in several steps when applied to non-aqueous systems. The bottom line in Table 1 shows values of CVI for this calibration solution. We made six measurements in order to show reproducibility. The zeta potential of this dispersion is —38mV, which is basis for calibration.

The next step is measurement of the electroacoustic signal of the pure kerosene. This gives us value of the background signal. The DT software allows us to save this value and to subsequently subtract this background signal from all further measurements. It is vector subtraction because electroacoustic signal is a vector with a certain magnitude and phase. As a simple test that this subtraction works, we measured kerosene again, this time making the background subtraction. It is seen that absolute value of the signal reduced 20 times.

The noise of the measurement is a few hundreds of absolute CVI units. All further lines in Table 1 correspond to the alumina-kerosene-SPAN 80 dispersions with suitable background subtraction. It is seen that these values are much larger than values coming from kerosene only.

Their amplitude exceeds substantially the noise level. We can attribute this electroacoustic signal to the particles and calculate their surface charge s using equation 1. Figure 6 shows results of this calculation.

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This is in a good agreement with conductivity data presented on Figure 5. The sign of the surface charge turns out to be positive. We have two confirmations for this statement. The first is a simple microscopic observation with a microelectrophoretic instrument, a PenKem model The particles move in the electric field as they would if they had a positive charge.

The second is the phase of electroacoustic signal. The values of CVI phase are shown in Table 2.

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It is seen that it is between 0 and 90 degrees, which corresponds to a positive surface charge. However, one observe that phase values are unusually rather large, large. It is known that in aqueous systems phase shift due to the particle inertia can not exceed 45 0 [9].