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Swelling of herbal particles of coptis chinensis rhizomes in imidazolium ionic liquids

Wen Liu, Shun Yao, Jie Yang, Feng Tang, Hang Song

As green solvents, a series of 1-alkyl-3-methylimidazolium ionic liquids (ILs) with different cations and anions were used in the swelling of herbal particles and their performance was evaluated and compared. The study of ILs successfully discovered some mechanisms ofmass transfer in swelling and extraction for herbs. Themicrostructure, observed by scanning electron microscope (SEM), demonstrated the change of herbal skeleton in the process of swelling. Through the study for the effect of saturated swelling ratio, [PSMIM][H2PO4] was finally founded as the optimal IL for swelling. Saturated swelling ratio increased with the increase of temperature or reduction of particles size. Besides the acidic IL, the swelling ratio of neutral ILs was increased as [BMIM][Cl] > [BMIM][Br] > [BMIM][BF4] > [BMIM][PF6] due to the increasing hydrophilicity. Because of the viscosity and the protons, the trend of the swelling ratio of [PSMIM][H2PO4] is first increased and then decreased with increasing of its concentration