Controlling Factors of the Particle Size of Spherical Silica Synthesized by Wet and Dry Processes

We clarified the controlling factors of the particle size of the amorphous silica synthesized by wet and dry processes. In the wet process using methyl-trimethoxy-silane as a starting monomer, the obtained particle size can be easily controlled by changing the reaction time appropriately. However, to obtain larger particles, a relatively long time is needed. After the condensation reaction was conducted for 50h, the silica particles (D50: 3μm) were synthesized by calcination at 550oC in air. To synthesize larger silica particles, we used silica-seed particles (8μm) to obtain very large spherical silica particles (D50: 20μm). Thus, although the wet process needs a relatively long reaction time, it is very useful for synthesizing spherical silica particles with a wide range of particle size. In the dry process, we used methyl-trimethoxy-silane (MTMS), tetra-ethoxy-silane (TEOS), and octamethyl-cyclotetrasiloxane (OMCTSO) as the starting materials. In this process, the size of the silica particles was dominated by the molecular structure of the monomer, in particular, the number of silicon atoms contained in the monomer and the bulkiness of the substituent group. The largest silica particles were synthesized from OMCTSO, which contains the largest number of silicon atoms.

COOH-Terminated Silicon Quantum Dots as a Highly Efficient Drug Nanocarrier for Targeted Tumor Cell Imaging

Fluorescent silicon quantum dots (SiQDs) characterized by exceptional photostability and colloidal robustness as well as beneficial biocompatibility are fast becoming new pharmaceutical nanocarriers. With a view to efficiently loading cisplatin (CDDP) onto SiQDs, carboxylate group (COOH) terminated SiQDs were imperative because of chelate formation with CDDP. In this work, we employed a facial microwave irradiation route for rapidly synthesizing high-quality COOH-SiQDs through the use of 3-aminopropyl trimethoxy silane (APTMS) molecules to fulfil the role of silicon precursor and maleic acid (MA) as the agent for facilitating reduction. The SiQDs showed blue fluorescence with an associated photoluminescence quantum yield (PLQY) of 40.2%, the size of which was small at 3.2 ±0.6 nm, and long-lasting stability (an extensive range in pH (4-12) and concentrations of electrolytes reaching 3 Molarity of a solution of sodium chloride). As nanocarriers, carboxylic acids chelation generated a high loading of CDDP onto SiQDs (drug loading capacity, DLC up to 32.2% at pH = 9) and a drug release of CDDP up to 57.6% at pH = 5. Furthermore, the MTT assays demonstrated the non or low cytotoxicity of SiQDs and the role of the controlled release of SiQD-CDDP Finally, the prepared SiQD-CDDP were used for cell imaging, and further targeted labeling of some tumors after folic acid (FA) conjugation. These characteristics allow for the deployment of SiQDs as a highly efficient nanocarrier that facilitate the delivery of clinical drugs for the future.

SBR Vulcanizates Filled with Modified Ground Tire Rubber

Ground tire rubber (GTR) is used to decrease the cost of vulcanizates. However, insufficient interactions between GTR particles and rubber matrices make mechanical properties of vulcanizates containing GTR deteriorate. This paper compares original methods of GTR modification. The effects of surface activation of GTR by sulfuric acid (A), its modification by (3-mercaptopropyl)trimethoxy silane (M), or the hybrid treatment—combining both approaches (H), were analyzed in terms of surface energy, specific surface area and morphology of GTR particles. Vulcanizates containing virgin GTR were compared to the rubber filled with the modified GTR particles keeping the same amount of CB in the rubber mix, according to their crosslink density, mechanical and tribological properties. Contrary to the virgin GTR, the addition of modified GTR increases the stiffness of the vulcanizates. The highest changes have been observed for the samples filled with ca. 12 phr of the GTR modified with silane and ca. 25 phr of the GTR subjected to the hybrid treatment, representing the highest crosslink density of rubber vulcanizates filled with GTR. Furthermore, the addition of modified GTR, especially in the case of the samples where 10 phr of rubber was replaced, results in the significant lowering of friction but higher abrasive wear.

Grafting of (3-Chloropropyl)-Trimethoxy Silane on Halloysite Nanotubes Surface

Modified halloysite nanotubes (HNTs-Cl) were synthesized by a coupling reaction with (3-chloropropyl) trimethoxysilane (CPTMS). The incorporation of chloro-silane onto HNTs surface creates HNTs-Cl, which has great chemical activity and is considered a good candidate as an active site that reacts with other active molecules in order to create new materials with great applications in chemical engineering and nanotechnology. The value of this work lies in the fact that improving the degree of grafting of chloro-silane onto the HNT’s surface has been accomplished by incorporation of HNTs with CPTMS under different experimental conditions. Many parameters, such as the dispersing media, the molar ratio of HNTs/CPTMS/H2O, refluxing time, and the type of catalyst were studied. The greatest degree of grafting was accomplished by using toluene as a medium for the grafting process, with a molar ratio of HNTs/CPTMS/H2O of 1:1:3, and a refluxing time of 4 h. The addition of 7.169 mmol of triethylamine (Et3N) and 25.97 mmol of ammonium hydroxide (NH4OH) led to an increase in the degree of grafting of CPTMS onto the HNT’s surface.

Molecular Simulation of Improved Mechanical Properties and Thermal Stability of Insulation Paper Cellulose by Modification with Silane-Coupling-Agent-Grafted Nano-SiO2

Cellulose is an important part of transformer insulation paper. Thermal aging of cellulose occurs in long-term operation of transformers, which deteriorates the mechanical properties and thermal stability of cellulose, resulting in a decrease in the transformer life. Therefore, improvement of the mechanical properties and thermal stability of cellulose has become a research hotspot. In this study, the effects of different silane coupling agents on the mechanical properties and thermal stability of modified cellulose were studied. The simulation results showed that the mechanical parameters of cellulose are only slightly improved by KH560 (γ-glycidyl ether oxypropyl trimethoxysilane) and KH570 (γ-methylacrylloxy propyl trimethoxy silane) modified nano-SiO2, while the mechanical parameters of cellulose are greatly improved by KH550 (γ-aminopropyl triethoxy silane) and KH792 (N-(2-aminoethyl)-3-amino propyl trimethoxy silane) modified nano-SiO2. The glass-transition temperature of the composite model is 24 K higher than that of the unmodified model. The mechanism of the change of the glass-transition temperature was analyzed from the point of view of free-volume theory. The main reason for the change of the glass-transition temperature is that the free volume abruptly changes, which increases the space for movement of the cellulose chain and accelerates the whole movement of the molecular chain. Therefore, modifying cellulose with KH792-modified nano-SiO2 can significantly enhance the thermal stability of cellulose.

The Effect of 3-(Glycidoloxy Propyl) Trimethoxy Silane Concentration on Surface modification of SiO2 nanoparticles

AbstractCoupling agent concentration plays a key role in functionalization of SiO2 nanoparticles as reinforcing particles.PurposeIn this study, the influence of 3-(glycidoloxy propyl) trimethoxy silane (GPTMS) concentration on functionalization of SiO2 nanoparticles, is experimentally investigated.MethodsThe functionalization of nano-silica were performed by 30, 50, 80 and 110 wt.% of GPTMS in order to find the optimal GPTMS concentration to complete the process. Fourier Transformation Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), Thermo Gravimetric Analysis (TGA) and X-Ray Diffraction (XRD) characterized the pure and modified samples; then, the results were compared to each other to achieve the aim of the research.ResultsFTIR results confirmed the silanization proceed due to the silane absorption peak disappearing and shifting of the hydroxyl group bonds in to the amide bonds. This test showed that 30 wt.% GPTMS has not been sufficient for full functionalization of the NPs. According to FESEM images, it seems that the NPs were better modified by 80 wt.% GPTMS due to the least NPs aggregation and lack of coupling agent deposition on the NPs. Also, TGA illustrates that this sample has higher thermal stability because of lower weight loss (11.2%) in coupling agent decomposition temperature range: 130-380°C. Furthermore, X-Ray Diffraction confirmed the FESEM and TGA results about the mentioned sample due to its highest crystallite size (increase 26.64% in crystallite size in comparison with the pure sample).ConclusionSo, the 80 wt.% of GPTMS introduced as the optimal concentration for surface modification of SiO2 nanoparticles.