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

Electrorheological Fluids of GO/Graphene-Based Nanoplates

Due to their unique anisotropic morphology and properties, graphene-based materials have received extensive attention in the field of smart materials. Recent studies show that graphene-based materials have potential application as a dispersed phase to develop high-performance electrorheological (ER) fluids, a kind of smart suspension whose viscosity and viscoelastic properties can be adjusted by external electric fields. However, pure graphene is not suitable for use as the dispersed phase of ER fluids due to the electric short circuit caused by its high electrical conductivity under electric fields. However, graphene oxide (GO) and graphene-based composites are suitable for use as the dispersed phase of ER fluids and show significantly enhanced property. In this review, we look critically at the latest developments of ER fluids based on GO and graphene-based composites, including their preparation, electrically tunable ER property, and dispersed stability. The mechanism behind enhanced ER property is discussed according to dielectric spectrum analysis. Finally, we also propose the remaining challenges and possible developments for the future outlook in this field.

Synthesis and Characterization of the CaTiO3:Eu3+ Red Phosphor by an Optimized Microwave-Assisted Sintering Process

The synthesis process has a significant influence on the properties of Ca_1-xTiO₃:Eu³⁺_x phosphors; thus, an optimized process will lead to a better performance of the Ca_1-xTiO₃:Eu³⁺_x phosphors. In this work, the feasibility of synthesizing the Ca_1-xTiO₃:Eu³⁺_x phosphor with a good luminescent performance by combining the chemical co-precipitation method and microwave-assisted sintering was studied. The precursor of Ca_1-xTiO₃:Eu³⁺_x phosphors were prepared by the chemical co-precipitation method. To find an optimized process, we applied both of the traditional (furnace) sintering and the microwave-assisted sintering to synthesize the Ca_1-xTiO₃:Eu³⁺_x phosphors. We found out that a sintering power of 528 W for 50 min (temperature around 950 °C) by a microwave oven resulted in similar emission intensity results compared to traditional furnace sintering at 900 °C for 2.5 h. The synthesized Ca_1-xTiO₃:Eu³⁺_x phosphors has an emission peak at 617 nm (⁵D₀→⁷F₂), which corresponds to the red light band. This new synthesized method is an energy efficient, time saving, and environmentally friendly means for the preparation of Ca_1-xTiO₃:Eu³⁺_x red phosphor with good luminescent performance.

The preparation and electrorheological behavior of bowl-like titanium oxide nanoparticles

Bowl-like titanium oxide nanoparticles were successfully prepared by a simple solvothermal method using absolute ethanol and isopropanol as the cosolvent. Ostwald ripening coupled with the inner-stress-induce effect were assumed to play an important role in the formation of this unique bowl-like morphology. The morphological evolution from solid nanosphere to bowl-like nanoparticle was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Besides, the structural characteristics of the as-synthesized TiO₂ nanoparticles were confirmed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and thermogravimetric analysis (TGA). Moreover, a rotational rheometer was operated to examine the electrorheological (ER) effect. Excellent ER properties were achieved when the TiO₂ particles were dispersed in silicone oil under an external electric field.

Construction of pH-responsive and up-conversion luminescent NaYF₄:Yb³⁺/Er³⁺@SiO₂@PMAA nanocomposite for colon targeted drug delivery

Colon-targeted drug delivery system has attracted much interest because it can improve therapeutic efficacy and reduce the side effect in practical clinic. Herein, we constructed a multifunctional drug delivery system with colonic targeting and tracking by up-conversion (UC) luminescence based on core-shell structured NaYF4:Yb(3+)/Er(3+)@SiO2@PMAA nanocomposite. The resultant materials exhibited bright UC luminescence, pH-responsive property and excellent biocompatibility. The drug release behaviors in different pH environment were investigated using 5-aminosalicylic acid (5-ASA) as a model drug. The 5-ASA molecules release from NaYF4:Yb(3+)/Er(3+)@SiO2@PMAA nanocomposite exhibit a significant pH-responsive colon targeted property, i.e., a little amount of drug release in simulated gastric fluid (SGF, pH = 1.2) but a large amount of drug release in simulated colonic fluid (SCF, pH = 7.4) Moreover, the drug release process could be monitored by the change of UC emission intensity. These results implied that the multifunctional nanocomposite is a promising drug carrier for targeted release of 5-ASA in the colon.

The application of low frequency dielectric spectroscopy to analyze the electrorheological behavior of monodisperse yolk-shell SiO2/TiO2 nanospheres

Monodisperse SiO2/TiO2 yolk-shell nanospheres (YSNSs) with different SiO2 core sizes were fabricated and adopted as dispersing materials for electrorheological (ER) fluids to investigate the influence of the gradual structural change of disperse particles on ER properties. The results showed that the ER performance of the YSNS-based ER fluid prominently enhanced with the decrease of SiO2 core size, which was attributed to the enhancement of electric field force between YSNSs. Combined with the analysis of dielectric spectroscopy, it was found that the increase of permittivity at low frequency (10(-2)-10(0) Hz) was due to the increase of polarized charges caused by secondary polarization (Psp). Moreover, the number of Psp closely related to the distributing change of polarized particles in ER fluid was a critical factor to assess the ER performance. Additionally, a parameter K (the absolute value of the slope of permittivity curves at 0.01 Hz) could be utilized to characterize the efficiency of structural evolution of polarized particles in ER fluid. Compared with the ER performance, it could be concluded that the value of Δε(100Hz-100kHz)' just demonstrated the initial intensity of the interface polarization in the ER fluid as the electric field was applied, which ignored the distributing evolution of polarized disperse particles in ER fluid. The polarizability Δε(0.01Hz-100kHz)' obtained in the frequency range of 10(-2)-10(5) Hz should be more suitable for analyzing the system of ER fluid. The relationships between polarizability of disperse particles, parameter K and ER properties were discussed in detail.

Graphene oxide based smart fluids

Graphene oxide (GO), a graphene-related material containing oxygen-functional groups, has attracted considerable attention because of its strongly hydrophilic behavior and potential use in GO-hybrid composites. We put our focus on the fabrication and rheological characteristics of GO-based electrorheological and magnetorheological smart fluids under electric and magnetic fields, respectively in this Highlight. A brief perspective on the significant role of GO in tribology and the amphiphilic characteristics of Pickering emulsions are also included.

Electrorheology of nanofiber suspensions

Electrorheological (ER) fluid, which can be transformed rapidly from a fluid-like state to a solid-like state under an external electric field, is considered to be one of the most important smart fluids. However, conventional ER fluids based on microparticles are subjected to challenges in practical applications due to the lack of versatile performances. Recent researches of using nanoparticles as the dispersal phase have led to new interest in the development of non-conventional ER fluids with improved performances. In this review, we especially focus on the recent researches on electrorheology of various nanofiber-based suspensions, including inorganic, organic, and inorganic/organic composite nanofibers. Our goal is to highlight the advantages of using anisotropic nanostructured materials as dispersal phases to improve ER performances.

Comment on 'Fabrication of uniform core-shell structural calcium and titanium precipitation particles and enhanced electrorheological activities'

This comment is an analysis of the static yield stress of core-shell structured SiO(2)-calcium-titanium precipitation (CTP) particle-based electrorheological (ER) suspensions under various applied electric field strengths. We find that our previously published universal yield stress equation covers both polarization and conduction regions while the polar-molecule-based linearity mechanism becomes dominant for the giant ER fluid beyond the second critical electric field strength.