Katana Bojana, Takács Dóra, Csapó Edit, Szabó Tamás, Jamnik Andrej, Szilagyi Istvan
Faculty of Chemistry and Chemical Technology, University of Ljubljana, SI-1000 Ljubljana, Slovenia.
J Phys Chem B. 2020 Oct 29;124(43):9757-9765. doi: 10.1021/acs.jpcb.0c07885. Epub 2020 Oct 19.
Charging and aggregation processes were studied in aqueous dispersions of halloysite nanotubes (HNTs) in the presence of monovalent inorganic electrolytes and ionic liquid (IL) constituents. The same type of co-ion (same sign of charge as HNT) was used in all systems, while the type of counterions (opposite sign of charge as HNT) was systematically varied. The affinity of the inorganic cations to the HNT surface influenced their destabilizing power leading to an increase in the critical coagulation concentration (CCC) of HNT dispersions in the Cs < K < Na order. This trend agrees with the classical Hofmeister series for negatively charged hydrophobic surfaces. For the IL cations, the CCCs increased in the order BMPY < BMPIP < BMPYR < BMIM. An unexpectedly strong adsorption of BMPY cations on the HNT surface was observed giving rise to charge neutralization and reversal of the oppositely charged outer surface of HNT. The direct Hofmeister series was extended with these IL cations. The main aggregation mechanism was rationalized within the classical theory developed by Derjaguin, Landau, Verwey, and Overbeek, while ion specific effects resulted in remarkable variation in the CCC values. The results unambiguously proved that the hydration level of the surface and the counterions plays a crucial role in the formation of the ionic composition at the solid-liquid interface and consequently, in the colloidal stability of the HNT particles in both inorganic salt and IL solutions.
在一价无机电解质和离子液体（IL）成分存在的情况下，研究了埃洛石纳米管（HNTs）水分散体中的充电和聚集过程。所有体系均使用相同类型的共离子（与HNT电荷符号相同），而反离子（与HNT电荷符号相反）的类型则系统地变化。无机阳离子对HNT表面的亲和力影响其去稳定能力，导致HNT分散体的临界聚沉浓度（CCC）按Cs < K < Na的顺序增加。这一趋势与带负电疏水表面的经典霍夫迈斯特序列一致。对于IL阳离子，CCC按BMPY < BMPIP < BMPYR < BMIM的顺序增加。观察到BMPY阳离子在HNT表面有出乎意料的强吸附，导致电荷中和以及HNT带相反电荷的外表面电荷反转。这些IL阳离子扩展了直接霍夫迈斯特序列。主要聚集机制在由Derjaguin、Landau、Verwey和Overbeek发展的经典理论中得到了合理的解释，而离子特异性效应导致CCC值有显著变化。结果明确证明，表面和反离子的水化水平在固液界面离子组成的形成中起着关键作用，因此，在无机盐和IL溶液中HNT颗粒的胶体稳定性中也起着关键作用。
