Insights into the complex interaction between hydrophilic nanoparticles and ionic surfactants at the liquid/air interface

Abstract

Combinations of nanoparticles and surfactants have been widely employed in many industrial processes, i.e., boiling and condensation in heat transfer and hydraulic fracturing in shale oil and gas production, etc. However, the underlying mechanism for various phenomena resulting from the addition of nanoparticles into the surfactant solutions is still unclear. For instance, there are contradictory conclusions from the literature regarding the variations of surface tension upon the addition of nanoparticles into surfactant solutions. In this work, the dominating factors determining if the surface activity of the surfactant solution will increase or conversely decrease when adding certain kinds of nanoparticles have been investigated. Two typical hydrophilic nanoparticles, SiO2 and TiO2 with anionic or cationic surfactants, respectively, have been considered. The surface tension has been measured in a wide range of nanoparticle and surfactant concentrations. It was found that the surface tension of the ionic surfactant solution can be further reduced only if nanoparticles of the same charge were added. For instance, a system containing 0.25 CMC SDS and 1 wt% SiO2 behaves similar to a 0.34 CMC SDS-only solution. Interestingly, the observed synergistic effect is found to be more significant if the surfactant concentration is much lower than its CMC for a given nanoparticle content. Moreover, the effect is perfectly reversible. When the nanoparticles were separated from the system, the surface tension values recovered fully to that of the pure surfactants. If nanoparticles of opposite charge were added, however, the surface tension of the surfactant solution increased. Zeta potential measurement and centrifugal treatment have been employed to reveal the interplay between nanoparticles and surfactants and the adsorption behavior of their assemblies at the liquid/air interface. Based on the experimental outcomes, a possible physical mechanism was proposed. It was concluded that the electrostatic repulsion between surfactant molecules and nanoparticles should be the dominant factor responsible for the observed reversible synergistic effect. Our study is expected to contribute to a better understanding of the interfacial phenomenon in nanoparticle-surfactant complex systems.

Charge‐Reversible Surfactant‐Induced Transformation Between Oil‐in‐Dispersion Emulsions and Pickering Emulsions

“…The negative charges on the particles are neutralized by the adsorbed cationic surfactant which forms a monolayer at low concentration, and then particles are turned positively charged due to formation of a surfactant bilayer or hemi‐micelle formation at high surfactant concentration. Similarly, the adsorption isotherm can be obtained from surface tension measurements [32, 33] (Figure S16b), as shown in Figure 5 b which indicates that the adsorption of DMUc is higher than that of DMUz in good agreement with zeta potentials. From Figure 5 b the adsorbed amount of DMUc at an initial concentration of 0.5 mM (equilibrium concentration=0.22 mM) is calculated to be 0.28 mmol g −1 , corresponding to a molecular area of 1.19 nm 2 also suggesting monolayer adsorption.…”

Study on surface properties of sodiumdodecyl sulfate and dodecyltrimethylammonium bromide mixed surfactants and their interaction with dyes

“…9). This suggests that elevated temperature is not favorable for micellization, corresponding to the CMC trends [76]. The variation of pC20 with temperature in DTAB rich is linear whereas SDS-rich slightly convex nature of the curve (Fig.…”

Synergy between Sugar‐Based Anionic‐Nonionic Surfactants and Ag‐TiO2 Nanohybrids for Enhanced Oil Recovery

“…Figure shows the surface tension versus log concentration plots of the GDA aqueous solutions in the presence and absence of Ag‐TiO 2 . It can be seen that the surface tension decreased with the increment of surfactant concentration and then reached a balance breakpoint, indicating that the surfactant molecules were saturated at the air/water interface (Jin et al, ). The results demonstrated that the cmc of GDA was 1 × 10 −3 mol L −1 and surface tension was 30.0 mN m −1 at 25 °C.…”

“…Therefore, the synergistic effect of GDA and Ag-TiO 2 had larger electric hindrance to from agglomerate clusters. Figure 8 shows the surface tension versus log concentration plots of the GDA aqueous solutions in the presence and It can be seen that the surface tension decreased with the increment of surfactant concentration and then reached a balance breakpoint, indicating that the surfactant molecules were saturated at the air/water interface (Jin et al, 2018). The results demonstrated that the cmc of GDA was 1 × 10 −3 mol L −1 and surface tension was 30.0 mN m −1 at 25 C. Almost no difference in the degree of surface-tension reduction was observed between the GDA solution and the GDA/Ag-TiO 2 suspension at low surfactant concentrations because NP are not surface active.…”