The Liquid–Liquid Interface as a Medium To Generate Nanocrystalline Films of Inorganic Materials

Abstract

Unlike the air-water interface, the organic-aqueous (liquid-liquid) interface has not been exploited sufficiently for materials synthesis. In this Account, we demonstrate how ultrathin nanocrystalline films of metals such as gold and silver as well as of inorganic materials such as semiconducting metal chalcogenides (e.g., CdS, CuS, CdSe) and oxides are readily generated at the liquid-liquid interface. What is particularly noteworthy is that single-crystalline films of certain metal chalcogenides are also obtained by this method. The as-prepared gold films at the toluene-water interface comprise fairly monodisperse nanocrystals that are closely packed, the nature and properties of the films being influenced by various reaction parameters such as reaction temperature, time, reactant concentrations, mechanical vibrations, and the viscosity of the medium. The surface plasmon band of gold is markedly red-shifted in the films due to electronic coupling between the particles. The shift of the surface plasmon band of the Au film toward higher wavelengths with an accompanying increase in intensity as a function of reaction time marks the growth of the film. Depending on the reaction temperature, the Au films show interesting electrical transport properties. Films of metals such as gold are disintegrated by the addition of alkanethiols, the effectiveness depending on the alkane chain length, clearly evidenced by shifts of the surface plasmon bands. A time evolution study of the polycrystalline Au and CdS films as well as the single-crystalline CuS films is carried out by employing atomic force microscopy. X-ray reflectivity studies reveal the formation of a monolayer of capped clusters having 13 gold atoms each, arranged in a hexagonal manner at the toluene-water interface. The measurements also reveal an extremely small value of the interfacial tension. Besides describing features of such nanocrystalline films and their mode of formation, their rheological properties have been examined. Interfacial rheological studies show that the nanocrystalline film of Ag nanoparticles, the single-crystalline CuS film, and the multilayered CdS film exhibit a viscoelastic behavior strongly reminiscent of soft-glassy systems. Though both CuS and CdS films exhibit a finite yield stress under steady shear, the CdS films are found to rupture at high shear rates. An important advantage of the study of materials formed at the liquid-liquid interface is that it provides a means to investigate the interface itself. In addition, it enables one to obtain substrate-free single-crystalline films of materials.

Growth of nanocrystals and thin films at the water–oil interface

“…In contrast, synthetic chemists generally regard such an interface as an intractable barrier to be circumvented by the use of phase transfer reagents. A small number of studies have explored the use of the water-oil interface to synthesize inorganic nanostructures, materials that have assumed great significance in recent times (Faraday 1857;Brust et al 1994;Rao et al 2005;Fan et al 2007a,b;Rao & Kalyanikutty 2008). In these studies, the use of the interface leads to remarkably simple and straightforward routes to complex solids.…”

Thiol anchoring and catalysis of gold nanoparticles at the liquid interface of thin-organic film-modified electrodes

“…1A), as a consequence of the blocking of the L/L interface and hindering the ion transfer. The role of the standard potential difference between the two redox reactants, as a main driving force of the reaction (1) [12][13][14], the rate of the metal deposition and the morphology of the deposit depend on various factors, the most important being the reactant concentration ratio and the potential difference at the NB/W interface controlled by the partition of common ClO 4 − ions. For gold deposition, the morphology and ordering of the particles can be controlled by a thiol anchoring from both sides of the L/L interface.…”

“…Their application ranges from determination of thermodynamic [2,3] and kinetic parameters of ion [4,5] and/or electron transfers [1,6], mechanistic [7] and biomimetic studies of membrane processes [8], to bioelectroanalysis [9,10]. Besides, it has been demonstrated that TFE are an excellent scaffold for studying metal nanoparticle deposition at the L/L interfaces [11], which is a unique environment due to its molecular smoothness [12]. Owing to the pronounced sensitivity of the voltammetric response of TFE to the properties of the liquid interfacial region, the aggregation of nanoparticles can be effectively examined by means of voltammetric techniques [11].…”

Growth of nanocrystalline thin films of metal sulfides [CdS, ZnS, CuS and PbS] at the water–oil interface

“…The region in the vicinity of the interface is host to a ra of singular process that govern the transport of ions and direct the structure of the emergent mesostructure. [5][6][7] Advantages of this method include simplicity, low-costs and convenience in that crystalline deposits can be obtained at low temperatures and transferred to a variety of substrates. However, our understanding of the underlying mechanisms are poor.…”

“…Molecular precursor mediated interfacial deposition of nanostructures is one such scheme. A recent revival of interest in this area [5][6][7] has led to materials of topical interest such as thin lms made of pyramidal PbS nanocrystals bound by high energy {331} surfaces, 8 nanorod structures of CdS 9 and Bi 2 S 3 .…”