Abstract
Aqueous two-phase systems (ATPSs), consisting of two immiscible water-rich phases, have received great attention. So far, all of ATPSs reported are formed by two water-soluble compounds in aqueous media. Herein, we report an ATPS formed in the single-component aqueous solution of α-ketooctanoic acid (KOCOOH), a weakly acidic surfactant, without any additives. Its formation originates from the coexistence of micelles and vesicles in the system, the former existing in the upper phase and the latter in the lower phase. The phase behavior and microstructures of KOCOOH in aqueous solution were determined. A concentration-driven stepwise aggregation was identified for the KOCOOH solution. With an increase in the KOCOOH concentration, vesicles, oil droplets, micelles, strip bilayers, and planar lamellar phase form successively; macroscopically, the system exhibits a homogeneous transparent single-phase, turbid dispersion, two phases, a bluish single-phase, and a colorless transparent single-phase in turn. The constantly changing ionization state of KOCOOH in aqueous solution plays an important role in the phase and aggregate structure transition. This work deepens the understanding of ATPSs, and the ATPS formed by KOCOOH may have potential applications such as in the separation and purification of biomolecules and the construction of hierarchical protocell models.
Highlights
IntroductionAqueous two-phase systems (ATPSs), consisting of two immiscible water-rich phases, have received great attention due to their fundamental and practical signi cance.[1,2,3,4,5,6,7] The formation of ATPSs is closely related to the aggregation states of solutes in water,[1,8,9,10,11,12,13,14] and research on their nature can deepen the understanding of aggregation phenomena in solution
This work deepens the understanding of Aqueous two-phase systems (ATPSs), and the ATPS formed by KOCOOH may have potential applications such as in the separation and purification of biomolecules and the construction of hierarchical protocell models
We accidentally found that KOCOOH in water at C > 160 mM can form a homogeneous transparent system, which made us realize that an ATPS could form in the KOCOOH solution within an appropriate C range
Summary
Aqueous two-phase systems (ATPSs), consisting of two immiscible water-rich phases, have received great attention due to their fundamental and practical signi cance.[1,2,3,4,5,6,7] The formation of ATPSs is closely related to the aggregation states of solutes in water,[1,8,9,10,11,12,13,14] and research on their nature can deepen the understanding of aggregation phenomena in solution. R. China bKey Laboratory of Colloid and Interface Chemistry (Ministry of Education), Shandong University, Jinan 250100, P. Xu et al.[11] reported ATPSs of lauric acid (a fatty acid) in the presence of inorganic or organic alkalis (NaOH, CsOH, or (C2H5)4NOH); Arnould et al.[14] involved an ATPS formed in the mixture between the FA myristic acid and choline hydroxide. They both introduced speci c cations to the FA solutions. To the best of our knowledge, this is the rst time to nd ATPSs formed in a single-component aqueous solution of surfactants without any additives
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