Interface water/dodecane

Linear spectroscopy Reflection - TIR, ATR, Non-Polarizable ER Interface water/dodecane 35, 36... 

This phenomenon can be explained allowing for the usual presence of dodecanol in SDS solutions. At first the salt leads to an increase in surface activity (shift of about one order of magnitude of the adsorption isotherm to lower concentration), and secondly the potential impurity dodecanol, which strongly adsorbs at the interface water/air, will more or less transfer to the dodecane phase after it has been adsorbed at the water/dodecane interface. Thus, no different mechanism is needed to describe the relaxation behaviour, as done by Bonfillon Langevin (1993). 

Dilational elasticity modulus of Triton X-lOO solutions at the water/dodecane interface determined from longitudinal wave damping according to Bonfillon Langevin (1993)... 

Sjoblom, J., Skurtveit, R., Saeten, J.O., and Gestblom, B. 1991. Structural changes in the microemulsion system didodeeyldimethylammonium bromide/water/dodecane as investigated by means of dieleetric spectroscopy. J. Colloid Interface Sci., 141, 329-337. 

The velocity distributions determined also from the movement of tracer particles contain more information than the flow patterns alone. In addition to streamlines, the axial and radial velocity components versus distance from the meniscus and the tube axis are represented for flat air/water (fig. 5) as well as water/dodecane interfaces (fig. 6). The experimental velocity values are compared with results which had been calculated theoretically by Kafka and Dussan V. [9]. 

It is worth mentioning that the axial velocity distribution at the very vicinity of the interface shows a shape similar to the curvature of the meniscus itself independently of the fact that the interface is flat or curved. The values of the axial velocity components are var)dng almost independently of the radial position at z = 0.15 (see figs. 5 and 6) in accordance with the flat shape of the water/air and water/dodecane... 

Figure 2.7 Gibbs isotherm of water/dodecane interface, (a) The water phase contains 1% 10C12, and the Span 80 concentration in the oil phase is increased from 10" % to 10" %. (h) The oil phase contains 2% Span 80, and 10C12 in the water phase is...

The next development on water-oil isotherms was presented by Mohwald s group at the Max-Planck Institute in Berlin [21,22]. They investigated monolayers of dipalmitoyl phosphatidylethanolamine (DPPE) at interfaces of water and hydrocarbons -dodecane (C]2, -hexadecane (Cig), and bicyclohexyl (BCH). The transition pressure was increased and the molecular area at transition decreased in the order Cig—C12 BCH. Also the heat of transition was decreased in the same order, and was more strongly decreasing with... 

The decrease in interfacial tension is related to the amount of extractant adsorbed at the interface through the Gibb s adsorption equation (46). The molecular areas of the extractant at the interface can thus be directly obtained from this equation. As an example, an area of 104 8 A2 is obtained for the. V,.V -dimc(hyl dibu-tyltetradecylmalonamide (DMDBTDMA) at the dodecane/water interface (4, 34). For classical surfactants, it should be noted that a nearly constant area per molecule with the addition of salt strongly suggests that anions and cations are adsorbed and extracted as pairs (47). Thus, the variation of the area per molecule with added salt can provide information on the mechanism of extraction. 

Fuerstenau, D.W., and Wakamatsu T. (1975). Effect of pH on the adsorption of sodium dodecane sulphonate at the alumina/water interface. Faraday Discussions of the Chemical Society, 59, 157-168. 

Figure 7. The repeat distance, as a function of dodecane weight fraction, for a quaternary system SDS/pentanol/water/dode-cane curve 1, computed using eqs 17 and 18 curve 2, computed by assuming that the entire surfactant and cosurfactant are adsorbed on the interface. The circles represent the experimental result of Safinya et al.24...

A demonstration of the single molecule detection at the liquid-liquid interface was reported for the fluorescent probe of l,l/-dioctadecyl-3,3,3/,. 3 -tetramethyI i ndoearboeyan i ne (Dil), which is a monovalent cation with two Cig alkyl chains. Thus, it has high adsorptivity at the dodecane-water interface. 

Aqueous phase (2.7 mm3) was placed in the thin lower compartment of the microcell and the Dil dodecane solution (63 mm3) was added on top of the aqueous layer. Fluorescence of the interfacial Dil was observed in the range of 571-575 nm. The influence of two kinds of surfactants, sodium dodecyl sulfate (SDS) and dimyristoyl phosphatidylcholine (DMPC), on the lateral diffusion dynamics of single molecules at the interface was investigated. DMPC was dissolved in chloroform, and the solution was mixed with pure diethyl ether at a ratio of 1 19 (chloroform diethyl ether) by volume. Pure water was placed in the lower container, and the DMPC solution was subsequently (5 mm3) spread carefully on the water. After evaporation of chloroform and diethyl ether, the Dil dodecane solution was added on the DMPC layer. Since Dil has a high... 

Fig. 13. Single molecule detection of Dil at the dodecane-water interface by fluorescence microscopy (left). Short photon burst in the SDS systems and (right) long burst in the DMPC systems.

The adsorption of PNP to a wide variety of interfaces has been studied by SHG. The adsorption isotherm at the dodecane/water interface is shown in Figure 1.4. The adsorption isotherms typically used to fit the surface tension and SHG data at the fiquid/liquid interfaces are in terms of the interfacial coverage 0 and the bulk phase concentration c, the Langmuir (13) and the Frumkin isotherms (14)... 

FIGURE 1.4. SHG signal from PNP at the dodecane/water interface. The fit to a Frumkin isotherm is shown as the dotted line. Adapted from ref. [48] reproduced by permission of the PCCP Owner Societies. 

Considerable care needs to be taken in extracting the interfacial concentration from the SHG intensities because of the interaction between surface density and surface order on the SHG process [49]. Table 1 shows a comparison of the values of Aahydrocarbon/water interfaces determined by SHG methods. The different results obtained at the dodecane/water interface where different isotherms were used to fit the SHG data suggest that the determination of—AadsG° at the heptane/water interface using only a Langmuir isotherm gives a value that is too high and thus this value should be re-examined. 

The addition of tributyl phosphate (TBP) to the dodecane acts to reduce the SHG signal from an initial (partial) monolayer of PNP at the dodecane/water interface the dependence shown in Figure 1.5 can be fitted to a Langmuir-like equation (15) from which an effective free energy of adsorption for TBP, AadsG Bp. can be extracted [48]. 

The possibility of absorption of the SHG signal by the upper medium complicates the interpretation of SHG from liquid/liquid studies compared to similar studies of the air/liquid interface. The same problem is of course faced by studies of the liquid/solid interface or total internal reflection studies at the air/liquid interface. In the case of the experiments on the dodecane/water interface, the possibility existed that the absorption... 

The static experiments show that there is a complex between TBP and PNP at the dodecane/water interface. Even by simply mixing the two solutions it was clear that this interaction was time-dependent. However, the decay rate was sufficiently fast so that given the need to ensure uniform mixing in the bulk phases and the time required to accumulate a reasonable S/N, only the long time tail of the decay curve could be measured. No accurate estimate of the decay rate could be made in the Petri-dish. The solution was to construct a flow cell to measure the kinetics of the TBP and PNP interaction at the dodecane/water interface [48]. 

The design of the flow cell (Figure 1.6) ensured that a stable dodecane/water interface would form and then allow the two liquids to be separated. The flow rate was variable and the interface could be probed at various distances along the flow. The cell contained two horizontal flat glass plates located on the central plane of the cell that... 

The flow cell translates time into distance and the combination of the three and varying the flow rates gave a range of observations from 0 to 30 s. SHG measurements of the static aqueous/dodecane interface were made at each port before and after the flow experiment to calibrate the observations from each port For a laminar (non-turbulent) flow, the two flow rates should be in the inverse ratio of the fluid viscosities this ratio for dodecane on water is 0.65 at 25°C, very close to the observed flow rate ratio of 0.67. The bulk flow rates for each liquid were measured by collecting the volume of liquid flowing in a known time. Since the cell operates under non-turbulent conditions, the velocity of each layer at the interface must be the same, but the average velocities of the two layers are different. Ideally a model of the flow conditions inside the cell would be used to accurately determine the velocity of the interface. Since this was not... 

For comparison, the measured adsorption rate for PNP to the air/water interface gave a rate constant of it = 4.4 0.2 x 10 s but a desorption rate of 6 2 s [52]. The rapid adsorption to the air/water interface is quite consistent with the very rapid establishment of the SHG signal from PNP at the dodecane/water interface observed in these flow cell experiments. However, the observed decay rate constant in the presence of TBP of ca. 0.5 s is much faster than the desorption rate constant that would be implied from the air/water experiments. This further implicates a reorganization process involving bonding between TBP and PNP as the cause of the loss of SHG intensity, which results in an overall loss of orientational order. 

In the example of the adsorption of TBP from the dodecane phase (density p = 766 kg m and molar mass of 0.17 kg mol" ) to die dodecane/water interface, the conversion to the mole fraction scale gives... 

FIGURE 10.5. The left figure shows the schematic illustration of laser-induced fluorescence microscopy under the total internal reflection for the detection of single Dil molecules at the dodecane-water interface. Abbreviations ND, ND filter XJ2, kl2 plate M, mirror L, lens C, microcell containing dodecane and aqueous phases O, objective (60 x ) F, bandpath filter P, pinhole APD, avalanche photodiode detector. The right portion of the figure shows the composition of the tnicrocell. 

FIGURE 10.6. Molecular structure of Dtl (left) and a snapshot of the MD simulation of Dil adsorbed at the dodecane/water interface (right). 

TABLE 10.1. Effects of surfactants on the lateral diffusion coefficient (Di) of single Dil molecules, apparent viscosity (rji) and intrinsic viscosity (jji) at the dodecane/water interface. 

---