ИСТИНА

Various phenomena happened at interfaces of two immiscible liquids usually lead to changes in electrocapillary (interfacial tension) and differential capacitance curves. For example, adsorption of nanoparticles or molecular aggregates influences both of these curves.[1] On the other hand, chaotropes such as urea can break the structure of the water, weakening the hydrophobic effect and leading to changes of properties of liquid-liquid interfaces (LLIs). Here, we proposed a robust, cheap and very accessible method to study changes in both electrocapillary (interfacial tension) and differential capacitance curves from a single pendant drop. Despite a range of proposed designs of electrochemical cells,[2,3,4] we used a simpler setup that can be assemble without introducing complex glassware, where the organic phase was place in a syringe positioned in the volume of the aqueous phase. The effect of urea concentration on properties of water-trifluorotoluene (TFT) interface is present in Fig.1A and B. The position of the maximum for both curves remained within 40 mV window around zero Galvani potential difference. In general, those values were significantly lower than 90 mV difference between capacitance and electrocapillary curves determined by Samec et al.[5] The gradual decrease of surface tension and increase of differential capacitance with increasing of urea concentration were observed reflecting the nature of chaotropic agent such as urea. Fig. 1. Effect of urea on electrocapillary (A) and differential capacitance curves (B). The Galvani potential difference is given in TEA+-scale. References: [1] B. Su, J.-P. Abid, D.J. Fermin, H.H. Girault, H. Hoffmannová, P. Krtil, Z. Samec, Reversible voltage-induced assembly of au nanoparticles at liquid/liquid interfaces, JACS, 126 (2004) 915-919, DOI: 10.1021/ja0386187. [2] A. Trojánek, V. Mareček, Z. Samec, Visualization of the interfacial turbulence associated with remarkable faradaic current amplification at a polarized water/1,2-dichloroethane interface, Electrochem. Commun. 80 (2017) 1–4. DOI:10.1016/J.ELECOM.2017.04.019. [3] B.R. Silver, V. Fülöp, P.R. Unwin, Protein crystallization at oil/water interfaces, New J. Chem. 35 (2011) 602. DOI:10.1039/c0nj00822b. [4] M.C. Martins, C.M. Pereira, H.H. Girault, F. Silva, Specific adsorption of tetraalkylammonium cations on the 1,2-dicloroethane/water interface, Electrochim. Acta. 50 (2004) 135–139. DOI:10.1016/J.ELECTACTA.2004.07.023. [5] A. Lhotský, V. Mareček, S. Záliš, Z. Samec, Specific adsorption of tetraalkylammonium cations at the water|1,2-dichloroethane interface revisited, J. Electroanal. Chem. 585 (2005) 269–274. doi:10.1016/j.jelechem.2005.07.026.