Mamusa M, Sirieix-Plénet J, Cousin F, Perzynski R, Dubois E, Peyre V
Laboratoire PECSA, Université Pierre et Marie Curie-4 place Jussieu, 75252 Paris cedex 5, France.
J Phys Condens Matter. 2014 Jul 16;26(28):284113. doi: 10.1088/0953-8984/26/28/284113. Epub 2014 Jun 12.
In order to better identify the key parameters governing colloidal stability in ionic liquids we probe the influence of the nature of the initial counterion of citrate-coated maghemite nanoparticles (NP), with Na(+), Li(+) and ethylammonium (EA(+)) on their dispersions in ethylammonium nitrate (EAN). Chemical analysis shows that sodium and lithium counterions remain at the nanoparticle surface after their transfer from water to EAN, despite their low concentration compared with EA(+). Macroscopically, all suspensions are stable over the range of volume fractions ΦNP tested (∼ 1% to 8%). A microstructural study coupling small angle scattering and magneto-optic birefringence measurements shows that nanoparticles are perfectly dispersed with sodium counterions and interact through weak repulsions. Conversely, small clusters of a few nanoparticles are formed with lithium counterions, with the aggregation number increasing with ΦNP. However, such clusters are fragile; evidence that the attractions responsible for aggregation are of weak amplitude. Suspensions with EA(+) counterions show an intermediate behaviour. Our results demonstrate the determining role of initial counterions of the nanoparticles on the microstructure of colloidal dispersions in ionic liquids and therefore, the essential role of the interfacial zone between the solid and the liquid.
为了更好地确定控制离子液体中胶体稳定性的关键参数，我们探究了柠檬酸盐包覆的磁赤铁矿纳米颗粒（NP）的初始抗衡离子性质（分别为Na⁺、Li⁺和乙铵（EA⁺））对其在硝酸乙铵（EAN）中分散体的影响。化学分析表明，钠和锂抗衡离子从水转移到EAN后仍保留在纳米颗粒表面，尽管与EA⁺相比它们的浓度较低。从宏观上看，在所测试的体积分数ΦNP范围内（约1%至8%），所有悬浮液都是稳定的。一项结合小角散射和磁光双折射测量的微观结构研究表明，纳米颗粒与钠抗衡离子完美分散，并通过弱排斥相互作用。相反，锂抗衡离子会形成由几个纳米颗粒组成的小簇，聚集数随ΦNP增加。然而，这些簇很脆弱；这证明导致聚集的吸引力幅度较弱。含有EA⁺抗衡离子的悬浮液表现出中间行为。我们的结果证明了纳米颗粒的初始抗衡离子对离子液体中胶体分散体微观结构的决定性作用，因此也证明了固液界面区的重要作用。
