Surfactants transport

The energetics and kinetics of film formation appear to be especially important when two or more solutes are present, since now the matter of monolayer penetration or complex formation enters the picture (see Section IV-7). Schul-man and co-workers [77, 78], in particular, noted that especially stable emulsions result when the adsorbed film of surfactant material forms strong penetration complexes with a species present in the oil phase. The stabilizing effect of such mixed films may lie in their slow desorption or elevated viscosity. The dynamic effects of surfactant transport have been investigated by Shah and coworkers [22] who show the correlation between micellar lifetime and droplet size. More stable micelles are unable to rapidly transport surfactant from the bulk to the surface, and hence they support emulsions containing larger droplets. 

How are particles, counterions, polymers, and surfactants transported across an EPID cell ... 

Surfactant Transport in Porous Media Dynamic Adsorption/Desorption Equilibria... 

Surfactant Transport in an Adsorbent Porous Medium. Chromatographic Aspects A first observation was made in all the tests in Table III. The breakthrough of both surfactants from the micellar slug always occurs simultaneously without any chromatographic effect (Figures 5 and 6). This stems both from the chemical nature of the two products selected and also from the fact that the injected concentration is much greater than the CMC of their mixtures. 

Figure 5 shows the results of a typical surfactant transport study in a 2 ft long Berea sandstone core. The AEGS 25-12 surfactant, injected at 0.05 wt%, had a low loss on Berea sandstone of 0.008 meq/100 gm rock compared to -0.05 meq/100 gm for typical petroleum sulfonates used in chemical flooding. Surfactant breakthrough occurred at 0.62 PV (Sorw =0.38 PV). The surfactant concentration is consistent with about 10% transport with the brine front. Surfactant loss and transport were monitored using the hyamine titration technique. 

Figure 13.2 shows the dynamic IFT for the two systems (1) 0.2% OP (nonionic) + 0.2% PS (petroleum sulfonate) +1.1% NaCl (without polymer), and (2) the same as (1) but with 0.1% 3530S polymer. From this figure, we can see that the IFTs for the two systems were almost the same. This figure demonstrates that there was not a strong interaction between the polymer and surfactants. However, polymer increases water viscosity to affect surfactant transport, so dynamic IFT was affected within a short time. Figure 13.2 shows that the dynamically stable IFT with addition of polymer was a little bit higher than that without polymer. 

Figure 18.10 Representation of surfactant transport at the surface and in the bulk of a liquid.

In general, the surfactant is distributed along the interface by a combination of convection and diffusion, as well as transport to and from the interface from the bulk solvents. However, in many cases, the solubility of a surfactant in the two solvents is very low, and a good approximation is that the transport from the solvents is negligible. In this case, it is said that the surfactant is an insoluble surfactant, and the total quantity of surfactant on the interface is conserved. We have notpreviously derived a bulk-phase conservation equation to describe the transport of a solute in a solvent. Hence in this section we adopt the insoluble surfactant case, and follow Stone50 in deriving a surfactant transport equation that relates only to convection and diffusion processes on the interface. 

H. A. Stone, A simple derivation of the time-dependent convective-diffusion equation for surfactant transport along a deforming interface, Phys. Fluids A 2, 111-12 (1990). 

We now turn to a case in which the interface concentration is determined by the mass transfer process to and from the bulk fluids. We begin with the case in which the fastest of the surfactant transport processes is the adsorption desorption of surfactant between the exterior bulk fluid where it is assumed to be soluble and the interface, Bi 1. In particular, we assume that Bi (ca/V,Xjk)Pe, so that, according to (7-265),... 

Siuface rheology has to be taken into account when describing siuface movement and adsorption/desoiption kinetics. Some brief information on surface rheology is given in Section 3.2. The rate of normal and lateral surfactant transport and dynamic surface tension response on external disturbances depends on relaxation properties, into which Section 3.1. introduces. 

Dynamic Adsorption Layers of Surfactants at the Surface of Buoyant Bubbles. Kinetic - Controlled Surfactant Transport TO AND from Bubble Surfaces... 

Another steam-foam model was developed at the Alberta Research Council (46, 47). It considers surfactant transport and flow resistance to foam. Thermal degradation is assumed to be first-order. The rate constant is dependent on both temperature and pH. Surfactant adsorption is... 

The present state of resecirch allows to describe the adsorption kinetics of surfactants at liquid interfaces in most cases quantitatively. The first model for interfaces with constant area was derived by Wend Tordai [3]. It is based on the assumption that the time dependence of interfacial tension, which is directly related to the interfacial concentration T of adsorbed molecules via an equation of state, is mainly caused by the surfactant transport to the interface. In the absence of any external influences this transport is controlled by diffusion and the result, the so-called diffusion controlled adsorption kinetics model, has the following form... 

The results of the preceding section allow us now to move on to describe the surfactant transport from the depth of the bulk phase to the interface or in the opposite direction. If any adsorption barriers are absent, this process determines the adsorption and desorption rates. The main step in the solution of this problem consists in the formulation of the surfactant diffusion equations for micellar solutions. The problem of surfactant diffusion to the interface was considered and solved for the first time by Lucassen for small perturbations [94]. He used the simplified model (5.146) where micelles were assumed to be monodisperse and the micellisation process was regarded as consisting of one step. Later Miller solved numerically the problem of adsorption on a fresh liquid surface using the same assumptions [146], Joos and van Hunsel applied also the same model to the interpretation of dynamic surface tension of... 

Danzer, J. (1999) Surfactant Transport and Coupled Transport of Polycyclic Aromatic Hydrocarbons (PAHs) and Surfactants in Natural Aquifer Material - Laboratory Experiments. Ttibinger Geowissenschaftliche Arbeiten (TGA), Reihe C, Nr. 49, p. 75, PhD thesis. 

Surfactant transport plays another important role, as these molecules can be transported either by advection of the main flow or through molecular diffusion either in the bulk or along the... 

Kapoor, Y Chauhan, A. Drug and surfactant transport in Cyclosporine A and Brij 98 laden p-HEMA hydrogels. J. Colloid Interface Sci. 2008,322 (2), 624-633. 

Buzza et al. (105) have presented a qualitative discussion of the various dissipative mechanisms that may be involved in the small-strain linear response to oscillatory shear. These include viscous flow in the films. Plateau borders, and dispersed-phase droplets (in the case of emulsions) the intrinsic viscosity of the surfactant monolayers, and diffusion resistance. Marangoni-type and marginal regeneration mechanisms were considered for surfactant transport. They predict that the zero-shear viscosity is usually dominated by the intrinsic dilatational viscosity of the surfactant mono-layers. As in most other studies, the discussion is limited to small-strain oscillations, and the rapid events associated with T1 processes in steady shear are not considered, even though these may be extremely important. 

The physical importance of these results is related to the fact that the coalescence of drops at the early highly dynamic stages of emulsion production is expected to be sensitive to the degree of saturation of the newly created interfaces with surfactant, and correspondingly, to the relaxation time of surfactant adsorption. The surfactant transport is especially important when the emulsion is prepared from nonpre-equilibrated liquid phases. In such cases one can observe dynamic phenomena like the cyclic dimpling (59, 60) and osmotic swelling (61), which bring about additional stabilization of the emulsions (see also Refs 1 and 62). 

Surfactant transport will now be included in the model, in an effort to obtain intermediate thinning rates as observed experimentally. 

Surfactant transport is also important in the vertical draining film surfactant concentration gradients may develop, which may in turn strongly affect the fluid flow via the Marangoni effect. When surfactant transport is considered, lubrication theory then gives three nonlinear partial differential equations for the free surface shape k(z,t), the surface velocity w z,t) and the surface concentration of surfactant (, ). The mathematical problem to be solved for these dependent variables is ... 

A classic situation of surfactant transport is the situation of a stationary drop in a moving fluid [3]. Indeed, this situation can be simply related to the situation of a moving drop by a transformation of the reference frame. Let us consider the flow in the reference frame of the drop, as shown in Fig. 2. In this frame, the drop sees a surfactant-rich flow arriving from the right and this surfactant is adsorbed on the interface between the drop and the outer fluid. However, the outer flow also creates recirculation zones inside the drop which redistribute the surfactant molecules on the rear (left) end of the drop. This situation creates an imbalance in the surfactant concentration along the drop surface, which translates into a surface stress. This surface stress in turn creates a net force on the drop from the left side to the right side, which slows down the external flow. 

The emulsification process is so dynamic and complex that an accurate model and theoretical treatment is almost impossible. With certain limitations its is possible to obtain order-of-magnitude estimates of such steps as droplet formation rate and surfactant transport and adsorption rates. However, the work involved is seldom worth the trouble in practice. Flocculation and coagulation rates during preparation are difficult to analyze because of the dynamics of the process and the turbidity of the flow involved. Collision rate theory... 

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