Abstract
The core-shell structured SiO2@Ni-Al layered double hydroxide (LDH) composites were prepared via self-assembly of Ni-Al LDH on the surface of SiO2 spheres. Only coating a layer of ultrathin Ni-Al LDH sheet, the resulting SiO2@Ni-Al LDH composites exhibit significantly enhanced electrorheological (ER) characteristics compared to conventional bare SiO2 spheres. The monodispersed SiO2 spheres with average diameters of 260 nm were synthesized by the hydrolysis of tetraethyl orthosilicate (TEOS), while the shell part, Ni-Al LDH sheet was prepared by the hydrothermal procedure. The morphology of the samples was investigated via scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The structure of the samples was characterized by X-ray diffraction (XRD). The species and distribution of elements in samples were confirmed by X-ray photoelectron spectroscopy (XPS), Energy dispersive analysis of X-ray (EDX) and elemental mapping in STEM. Subsequently, the ER characteristics of the composites dispersed in insulating oil were characterized by a rotational rheometer. The electric field-stimulated rheological performances (yield stress, viscosity, modulus, etc.) were observed under an external electric field, which is different from the Newtonian state in the free electric field.
Highlights
There are many examples of biological and inorganic materials with complicated and efficient hierarchical morphologies in natural world, such as marine coccolith, radiolarian shell and clay, exhibiting superior performance[1,2,3,4,5]
It can be observed from the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images, Ni-Al layered double hydroxide (LDH) sheet is irregular and thin hexagonal platelet with a mean lateral size of 300 nm, while most of the LDH sheets stack with each other
The morphology of SiO2@Ni-Al LDH composites was analyzed through SEM (Fig. 3A,B) and TEM (Fig. 3C,D) images
Summary
There are many examples of biological and inorganic materials with complicated and efficient hierarchical morphologies in natural world, such as marine coccolith, radiolarian shell and clay, exhibiting superior performance[1,2,3,4,5]. The layered double hydroxides (LDH) are hydrotalcite-like clays with the empirical formula, [MII1-xMIIIx(OH)2]x+[An− ]x/n·mH2O, where MII and MIII are divalent and trivalent metals such as Mg, Ni, Co, Al , and Fe, An− can be almost any anion with the charge number of n9–11 Due to their special and complicated structure and anion exchange property, LDH materials have been applied to many areas including catalysts[12,13,14,15,16], anion exchangers[17,18,19,20], electrodes for alkaline secondary batteries and supercapacitor[21,22], especially for electrorheological (ER) fluids[23,24,25]. The ER characteristic of the SiO2@Ni-Al LDH composite dispersed in insulating oil was characterized by a rotational rheometer
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