Fabrication and self-assembly of colloidal crystals of core-shell hybrid particles

Monodisperse silica nanoparticles (SiNP) with different diameters ranging from 40-390 nm were prepared by the hydrolysis of tetraethyl orthosilicate (TEOS) in an alcoholic solution. Incorporation of diethoxydimethyl silane into the condensation of TEOS yielded smaller particles of size ~20 nm. The effect of the reagent concentration, reagent addition sequence and method of mixing on the size and morphology of silica nanoparticles were investigated. The surface functionalization of SiNP was successfully achieved by covalently binding the trimethoxy groups of a chain transfer agent (EHT) onto the SiNP. The surface-modified SiNP were used to mediate reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene (S), methyl methacrylate (MMA) and methacrylate (MA) by the “grafting from” approach to form core-shell hybrid particles with high polymer grafting density. A facile and straightforward approach was used to self-assemble two-dimensional (2D) arrays of colloidal crystal film of SiNP-PMMA hybrid particles. Additionally, the precise control obtained over particle size allowed the self-assembly of 3D colloidal crystals of core-shell SiNP-PS following fast and facile processes, based on the use of centrifugational forces and dispersion forces

Silica core-polystyrene shell nanoparticle synthesis and assembly in three dimensions

Monodisperse silica nanoparticles (SiNPs) grafted with well-defined and highly dense polystyrene brushes are used as building blocks for the formation of three-dimensional (3D) colloidal crystals. By adjusting the refractive indices and the density of the hybrid particles with those of mixed solvents, iridescent microcrystals were formed throughout the entire suspension which were characterised by confocal laser microscopy. These core-shell hybrid particles are not charged and the driving force of the crystallization relies on repulsive forces between the polymer brushes with high grafting density. The interparticle distance is correlated to Bragg's Law and can be controlled by manipulating the grafting density and the length of the polymer brushes. Finally, the uniformity of these unique core-shell particles was exploited to generate 3D assemblies by a rapid and simple process based on centrifugation

Neuronal toxicity of biopolymer-template synthesized ZnO nanoparticles

Objective(s): A simple and "green " method was developed for preparing zinc oxide nanoparticles (ZnO-NPs) in aqueous starch solutions. Starch was used as a stabilizer to control of the mobility of zinc cations and then control growth of ZnO-NPs prepared via a sol-gel method. Because of the special structure of the starch, it permits termination of the particle growth.   Materials and Methods: The dried gel was calcined at different temperatures of 400, 500, 600, and 700 °C. The prepared ZnO-NPs were characterized by different techniques such as X-ray diffraction analysis (XRD), transmittance electron microscopy (TEM), and UV-Vis absorption. Results: The XRD results displayed hexagonal (wurtzite) crystalline structure for prepared ZnO nanoparticles with mean sizes below than 50 nm. In vitro cytotoxicity studies on neuro2A cells showed a dose dependent toxicity with non-toxic effect of concentration below 6 μg/mL. Discussion: The results showed that starch is an eco-friendly material that can be used as a stabilizing agent in the sol-gel technique for preparing of ZnO-NPs in a large scale

Experimental investigation of quasi-static behavior of composite and fiber metal laminate panels modified by graphene nanoplatelets

The current study investigated the influence of incorporation of graphene nanoplatelets (GNPs) on quasi-static behavior of composite and fiber metal laminate (FML) panels. The unmodified and modified composite specimens and FML panels with 2/1 configuration were fabricated using a hand lay-up method and investigated through a quasi-static punch and indentation testing. The two sets of tests were conducted with a flat-ended indenter and the loading conditions were the same for all samples, except support spans which were varied. Following experimental testing, possible damages at the punch region were closely investigated and localized and global damages were observed. The results revealed that adding 0.2 wt% GNPs improved the strength and fracture toughness of specimens by delaying the failure modes. On the contrary, GNPs made the bonding between the aluminum and composite interface to weaken

Comparative analysis of the cytotoxic effect of 7-prenyloxycoumarin compounds and herniarin on MCF-7 cell line

Objectives: 7-prenyloxycoumarins are a group of secondary metabolites that are found mainly in plants belonging to the Rutaceae and Umbelliferae families. This study was designed to evaluate and compare the cytotoxic and apoptotic activity of 7-prenyloxycoumarin compounds and herniarin on MCF-7, a breast carcinoma cell line. Materials and Methods: Cells were cultured in RPMI medium and incubated with different concentrations of auraptene, herniarin, umbelliferone, and umbelliprenin. Cell viability was quantified by MTT assay. Apoptotic cells were determined using propidium iodide staining of DNA fragmentation by flow cytometry (sub-G1peak). Bax protein expression was detected by western blot to investigate the underlying mechanism. Results: Doses which induced 50% cell growth inhibition (IC50) against MCF-7 cells with auraptene, herniarin, umbelliferone, and umbelliprenin were calculated (59.7, 207.6, 476.3, and 73.4 µM), respectively. Auraptene induced a sub-G1 peak in the flow cytometry histogram of treated cells compared to control cells, and DNA fragmentation suggested the induction of apoptosis. Western blot analysis showed that auraptene significantly up-regulated Bax expression in MCF-7 cells compared to untreated controls. Conclusion: Auraptene exerts cytotoxic and apoptotic effects in breast carcinoma cell line and can be considered for further mechanistic evaluations in human cancer cells. These results candidate auraptene for further studies to evaluate its biosafety and anti-cancer effects

Steric Stabilization of γ‑Fe₂O₃ Superparamagnetic Nanoparticles in a Hydrophobic Ionic Liquid and the Magnetorheological Behavior of the Ferrofluid

Hydrophobic ionic liquid ferrofluids (ILFFs) are studied for use in electrospray thrusters for microsatellite propulsion under nonatmospheric and in high-temperature environments. We synthesized a hydrophobic ILFF by dispersing sterically stabilized γ-Fe₂O₃ nanoparticles (NPs) in the ionic liquid 1-ethyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide. A diblock copolymer, C4-RAFT-AA₁₀-DEAm₆₀, was synthesized to facilitate multipoint bidentate anchoring to the NP through the acrylic acid block. The DEAm₆₀ layer was incorporated to generate steric repulsion between particles to protect against the aggregation of magnetized particles arising from dipole–dipole attraction. The effect of shearing and variation in the magnetic field strength on the steric repulsion was examined using the DLVO theory. The effect of varying the magnetic field strength and particle concentration on the viscoelastic properties of the ferrofluid was evaluated using rheometry. The viscosity of the ferrofluid increased with the magnetic field strength, indicating that the magnetized particles assembled into a structure. The level of straining required to break down the structure formed by the magnetized particles increased with the magnetic field strength and particle concentration. The absence of particle interlocking during shearing was indicated by the smooth viscosity versus shear rate traces. The DLVO analysis showed that increasing the magnetic attraction between the particles causes the DEAm₆₀ brush layers on the particles to overlap more, resulting in an increase in the steric repulsion. As overlapping increases, osmotic repulsion is caused before progressing to a strong elastic repulsion. The effect of the polymer solubility and particle interaction due to hydrodynamic forces on the steric repulsion was also analyzed