Ion Exchange and DNA Molecular Dip Sticks: Studying the Nanoscale Surface Wetting of Muscovite Mica

详细信息    查看全文

• 作者：Tzu-Chieh Tang ; Carlo A. Amadei ; Neil H. Thomson ; Matteo Chiesa
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：March 6, 2014
• 年：2014
• 卷：118
• 期：9
• 页码：4695-4701
• 全文大小：470K
• 年卷期：v.118,no.9(March 6, 2014)
• ISSN：1932-7455

文摘

Mica is an abundant crystal mineral that has important and interesting bulk and surface properties for a variety of applications. These properties arise from its anisotropic structure, in which layers of aluminum silicate, 1 nm thick, are ionically bonded together, typically with K⁺ ions. The surface properties of mica can be varied through ion exchange with the exposed lattice sites. In this study, the effect of kinetics on ion exchange with nickel ions (Ni²⁺) and its influence on surface water accumulation as a function of time has been investigated. Mica was ion-exchanged for 30 s or 5 min for a range of Ni²⁺ concentrations (i.e., 1.0鈥?0.0 mM), and its surface properties were measured for up to 96 h after incubation in a controlled environment. The nanoscale physicochemical properties of nickel-functionalized muscovite mica (Ni-mica) were investigated by reconstructing the conservative force profile between an atomic force microscopy (AFM) tip and the surface. This information provides a hint of the surface water accumulation and enables details of the spatial and temporal variations in surface properties due to the ion-mediated adsorption of water to be elucidated. Variations in the water-layer accumulation were confirmed using noncontact AFM imaging under ambient conditions and DNA molecules as 鈥渕olecular dip sticks鈥? It was found that the surface properties were largely independent of the incubating concentration but did depend on the incubation time during ion exchange and the aging time. For the longer incubation time of 5 min, the water-layer accumulation remained constant at around 1.5 nm deep, whereas for the short incubation time of 30 s, the accumulation was initially subnanometer but grew with aging time and converged to a similar final value after 96 h. The extracted force of adhesion (F_AD) also showed the same trends, where reduced values of F_AD indicated increased screening of the van der Waals interaction through thicker water layers.