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Phase Behavior and Aggregate Transition in Aqueous Mixtures of Negatively Charged Carbon Dots and Cationic Surfactants

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journal contribution
posted on 02.08.2021, 11:33 by Xiaofeng Sun, Xiaobin Dai, Shengju Zhou, Haiqiao Wang, Aoxue Xu, Litang Yan, Hongguang Li, Jingcheng Hao
To prepare supramolecular structures with interesting dimensions and morphologies using nanometer-sized building blocks is highly challenging. Herein, negatively charged carbon dots (n-CDs), which bear carboxy and hydroxyl groups on the surfaces, are mixed, respectively, with two cationic surfactants in water, i.e., 1-tetradecyl-3-methylimidazolium bromide (C14mimB) and tetradecyltrimethylammonium bromide (TTAB). The phase behavior and aggregate transition in n-CDs/C14mimB and n-CDs/TTAB mixtures were investigated in detail. At a fixed concentration of n-CDs (cn‑CDs, 0.1 mg·mL–1), both systems exhibit a phase sequence of an isotropic phase (I1), a turbid phase (T1), a precipitated phase (P), a second turbid phase (T2), and a second isotropic phase (I2) with increasing concentration of the surfactant (cs). While only vesicles were observed in the T1 phase, hexosomes were also detected in the T2 phase in addition to vesicles. The phase transition obtained by the experiments gains solid support from computer simulations using a dissipative particle dynamics method, which give structural details of the hexosomes and evidence of anion−π interaction in an n-CDs/C14mimB system. The results obtained in the current study reinforce the conclusion that CDs/surfactant is a good combination for facile construction of supramolecular structures. The aggregates with diverse morphologies open up the possibility of a variety of future applications.