Yuchuan Cheng

Facile Approach to Large-Scale Synthesis of 1D Calcium and Titanium Precipitate (CTP) with High Electrorheological Activity

Nanorods of calcium and titanium precipitate (CTP) were prepared via a simple precipitation route in an ethanol/water mixed solution system under mild conditions. The obtained rodlike particles were highly uniform in width (23 ± 3 nm), and its length could be tuned by adjusting the concentration of oxalic acid reactant. The nanorods materials show a promising electrorheological activity, of which ER efficiency was about 4 times higher that of granular CTP suspensions. The facile synthesis route may be regarded as a green chemistry method, and its novelty relies on the large-scale production of 1D CTP giant ER materials.

Preparation of uniform titania microspheres with good electrorheological performance and their size effect

Titania is a potential high-performance electrorheological (ER) material due to its relatively high dielectric constant and polarization ability. The size and shape of titania particles are critical factors influencing ER activity. In this paper, we have developed an acetic acid (AA) assisted sol–gel strategy for the synthesis of uniform titania microspheres with good ER effect. The diameter of the titania microspheres (from 420 to 240 nm) can be tuned by changing the amount of AA added. The facile route has the great potential in bulk synthesis of the titania based ER materials. Results from surface area, rheological, conductivity and dielectric properties measurements indicate that the enhanced ER performance is due to the combined effect of the increased polar molecules content and reduced particle size.

Fabrication of uniform core–shell structural calcium and titanium precipitation particles and enhanced electrorheological activities

A simple co-precipitation route was developed to synthesize uniform core-shell structured calcium and titanium precipitation (CTP) particles with ideal morphology and no aggregation. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), and interface tension/contact angle (CA) measurement were utilized to characterize the components, structure, morphology, and wettability of the SiO(2)-CTP materials. The obtained core-shell structural SiO(2)-CTP particles were well dispersed spherical nanoparticles with a narrow size distribution. The electrorheological (ER) properties were studied by the shear stress under various electric fields. The SiO(2) (2.3 wt%)-CTP ER fluid showed notable ER activity with a shear stress of about 109 kPa (at 5 kV mm(-1)), which outclassed the shear stress (65 kPa) of the CTP ER fluid. The ER properties of samples can be tuned by a few factors in the experimental process, such as the concentration of SiO(2) particles and citric acid, pointing out the great potential for application of this route in bulk synthesis of many other types of ER materials.

Size-controllable synthesis of monodispersed colloidal silica nanoparticles via hydrolysis of elemental silicon

A new method is presented for preparing monodisperse and uniform-size silica nanoparticles using a two-stage hydrolysis of silicon powder in aqueous medium. The influence of synthesis conditions including solution composition and temperature on the formation of silica nanoparticles were systematically investigated. The structure and morphology of the silica particles were characterized via transmission electron microscopy (TEM) and dynamic light scattering (DLS). Various-sized particles in the range 10-100 nm were synthesized. The size of the nanoparticles can be precisely controlled by using a facile regrowth procedure in the same reaction media.

The influence of high dielectric constant core on the activity of core–shell structure electrorheological fluid

The core-shell structural dielectric particles are applied widely in the electrorheological (ER) fluids. The properties of the dielectric core are critical factors influencing their ER activity. In this paper, we successfully synthesized two kinds of core-shell hydroxyl titanium oxalate (TOC) particles with SiO(2) and TiO(2) as core, respectively. The obtained core-shell structural SiO(2)-TOC and TiO(2)-TOC particles were well-dispersed spherical nanoparticles with ideal morphology and a narrow size distribution. Under DC electric fields, the TiO(2)-TOC ER fluid showed notable ER activity with a yield stress of about 96 kPa (at 4 kV/mm), which is 3 times of that SiO(2)-TOC ER fluid and outclassed the yield stress of the TOC ER fluid. The dielectric spectra indicated that the higher dielectric constant of TiO(2) core induces the stronger interaction between the neighboring particles, which contribute to the enhancement of ER activity.

Preparation of rod-like calcium titanyl oxalate with enhanced electrorheological activity and their morphological effect

Insufficient yield stress and electrorheological (ER) efficiency have already become the limitations for the practical application of ER fluids. Herein, we report a simple and scalable co-precipitation method for synthesizing surfactant-modified calcium titanyl oxalate (SCTO) particles with a rod-like structure. The obtained SCTO materials not only present a yield stress twice as that of granular CTO ER fluids but also demonstrate low zero-field viscosity, which results in a high ER efficiency. In terms of microstructure and dielectric analysis, we infer that the exceptional ER activity is in large part due the anisotropic morphology and improved wettability of the rod-like SCTO. This work provides the basis for the future development of ER fluids and the promotion of their practical application.

Fabrication of graphene oxide/Ag hybrids and their surface-enhanced Raman scattering characteristics

A kind of surface-enhanced Raman scattering (SERS) substrate with high sensitivity was prepared via covalent assembly between silver nanoparticles (AgNPs) and graphene oxide (GO) sheets. With the high specific surface area, GO sheets can adsorb plenty of AgNPs; moreover, these adsorbed AgNPs formed some gathered state which can generate more hot spots of SERS. 4-Mercaptopyridine (4-MPY) was used to evaluate the SERS performance of the as-prepared substrate. The Raman enhancement factor (EF) of 4-MPY on the GO/AgNPs hybrids was up to 5.04×10(7), and the detection limit was estimated to be as low as 1 nM. The result showed that GO/AgNPs hybrids can produce stronger signals compared to silver colloids.

Formamide-modified titanium oxide nanoparticles with high electrorheological activity

TiOx-based nanospheres modified by formamide (FA) as dielectric particles for electrorheological (ER) fluids were successfully synthesized through simple sol–gel hydrolysis and self-assembly. The suspension containing TiOx–FA displays superior ER activity, with a yield stress of 148 kPa (at 5 kV mm−1) under a DC electric field, which is 10 times that of ER fluids containing pure TiOx nanoparticles. More importantly, comparison between the FA and N,N-dimethylformamide (DMF) as the shell structure indicated that the ER performance was positively correlated with the dielectric constant of the polar molecule shell. The result represents a critical step towards an in depth understanding the enhancement effect of polar molecules. This study can afford a new strategy to achieve optimal performance in ER fluids.

Electric-field-induced structure and optical properties of electrorheological fluids with attapulgite nanorods

Attapulgite (ATP) is a type of crystalloid hydrous magnesium-aluminum silicate mineral with natural one-dimensional (1D) fibrous morphology. In this study, the authors investigated the optical and mechanical performances of ATP nanorods in silicone oil under an electric field. It was observed that the optical transmittance of ATP suspensions decreased rapidly under the low electric field, using ultraviolet-visible (UV-Vis) spectroscopy. The results of optical microscopy and scanning electron microscopy (SEM) indicated that the electromigration of ATP nanorods was the major cause of such an aberrant optical phenomenon. Further, the electrorheological (ER) response of the samples was measured by the height-controlled method. The change trend of the normal force was illustrated by the dynamic assembly behavior of ATP in the applied electric field. This work provided intuitive evidence for an in-depth understanding of the mechanism of ER fluids containing 1D dielectric materials.

Yield stress analysis of 1D calcium and titanium precipitate-based giant electrorheological fluids

Abstract1D calcium and titanium composite nanorods synthesized were applied as electrorheological (ER) active materials with extremely high static yield stresses, i.e., giant ER effect. The yield stress of this giant ER fluid was analyzed using a new universal yield stress scaling equation in the form of the modified Bessel functions with two different limiting behaviors in a low and high electric field region. The universal yield stress equation collapsed the yield stress data onto a single curve.