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Rheological responses of fumed silica suspensions under steady and oscillatory shear

Science China(Technological Sciences) 2009年第4期52卷 910-915页

作者： YANG HaiLin RUAN JianMing ZOU JianPeng WU QiuMei ZHOU ZhongCheng ZHOU ZhiHua State Key Laboratory of Powder Metallurgy Central South UniversityChangsha 410083China

Rheological experiments under steady and oscillatory shear were conducted for fumed silica suspen- sions in polyethylene glycol. Under steady shear the shear-thinning and thickening response were exhibited and the flow exponent N was determined. With the increase of concentration the flow exponent N showed a rapid increase, and it increased dramatically when the discontinuous shear-thickening took place. Oscillatory shear experiments were conducted at constant frequency and constant amplitude strain, respectively. The shear-thinning and the discontinuous shear-thickening behavior were observed under different constant frequencies from 10 to 80 rad/s. The correlation between complex modulus (G*) and sweep frequency (ω) was illuminated at γ =750%. It was found that the correlation between G* and ω could be fitted by equation: G*∝ωn. The indexes in shear-thinning region and shear-thickening were determined. The indexes were similar to some extent at shear-thinning region and increased dramati- cally to a much higher value when the shear-thickening occurred,especially at higher weight fractions. The behaviors can be qualitatively explained as follows: the shear-thinning owes to decrease of viscos- ity, which results from disruption of the aggregates; the cluster theory attributes the shear-thickening to the formation of metastable, flow induced clusters, which block the system.

关键词： fumed silica suspension shear-thickening steady shear dynamic oscillatory shear rheological response

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Synthesis and Properties of fumed Silicas Modified with Mixtures of Poly(methylphenylsiloxane) and Dimethyl Carbonate

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World Journal of Nano Science and Engineering 2015年第4期5卷 152-160页

作者： Iryna S. Protsak Valentyn A. Tertykh Yulia M. Bolbukh Dariusz Sternik Anna Derylo-Marczewska Department of Chemisorption Chuiko Institute of Surface Chemistry of National Academy of Sciences of Ukraine Kiev Ukraine Faculty of Chemistry Maria Curie-Sklodowska University Lublin Poland

Effect of the concentration ratios of organosiloxane/initiator and treatment temperature on the characteristics of hydrophobic products obtained by modification of surface of fumed silica with poly(methylphenylsiloxane) (PMPS) in the presence of dimethyl carbonate has been studied. Morphology, particle size, surface area and coating microstructure of modified silicas were analyzed by methods of transmission electron and atomic force microscopies, nitrogen adsorption-desorption data. Carbon contents in the grafted modifying layer of organosilicas were determined using IR spectroscopy and elemental analysis. Hydrophilic-hydrophobic properties of surface of the obtained modified silicas were estimated by measurements of contact angles of wetting. It was shown that modification of pyrogenic silicas with mixtures of poly(methylphenylsiloxane) and dimethyl carbonate allows to obtain the homogeneous hydrophobic products and serve their nanodispersity.

关键词： fumed Silica Poly(methylphenylsiloxane) Dimethyl Carbonate Surface Modification Hydrophilic-Hydrophobic Properties

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Preparation and characterization of solidified oleanolic acid–phospholipid complex aiming to improve the dissolution of oleanolic acid

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Asian Journal of Pharmaceutical Sciences 2016年第2期11卷 241-247页

作者： Xiaoxu Yang Qikun Jiang Ping Du Juanhang Zhao Tianhong Zhang School of Pharmacy Shenyang Pharmaceutical University

The purpose of this study was to prepare the oleanolic acid–phospholipid complex (OAPC) and then solidify it employing fumed silica by simple solvent evaporation technique to improve dissolution rate of oleanolic acid and oleanolic acid–phospholipid complex. The process of OA-PC was optimized and the type and proportion of fumed silica were studied by dissolution text. The structures of the phospholipid complex and solidified powder were also characterized by differential scanning calorimetry, X-ray diffraction, and scanning electron microscope. In the dissolution tests, OA from solidified powder was further released compared with that from pure OA and OA-PC in different kinds of dissolution media. These results suggest that the method of preparing solidified powder of oleanolic acid–phospholipid complex is suitable for enhancing the dissolution rate of OA and OA-PC.

关键词： Oleanolic acid Phospholipid complex fumed silica Dissolution

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Effect of Electric Field Strength and Water Content on the Electrorheology of Silica Dispersions

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Materials Sciences and Applications 2017年第4期8卷 281-290页

作者： Habauka M. Kwaambwa Faculty of Health and Applied Sciences Namibia University of Science and Technology Windhoek Namibia

The effect of water content on the electrorheological effect (ERE) behaviour of silica dispersions has been investigated. The types of silica powders were fumed silica, precipitated and acid washed silica and colloidal silica. Silica dispersions with a water content varying in the range 10% - 30%, and with conducting ions deliberately added, were redispersed in chlorinated hydrocarbon oil and then the ER behaviour studied. Samples were tested on a static yield rig (SYR), an instrument which can measure both the yield stress and the conductivity. The effects of electric field strength and water content on the ERE were studied. The yield stress initially increased with increase in electric field strength and then decreased at high electric fields suggesting a breakdown in structure of the electrorheological fluid samples tested. It was also found that the ERE increased and electric saturation or electric breakdown shifted to lower electric fields as the water content increased. Higher electric fields caused a drop in the ERE.

关键词： Colloidal Silica Electrorheological Effect Electrorheological Fluid fumed Silica Precipitated and Acid Washed Silica Static Yield Rig Yield Stress

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Improvement of Dissolution Rate of Gliclazide Using Solid Dispersions with Aerosil 380 and Its Effect on Alloxan Induced Diabetic Rats

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Pharmacology & Pharmacy 2019年第8期10卷 365-385页

作者： Subrata Paul Md. Nur Islam Md. Ashraf Ali Ranjan Kumar Barman Mir Imam Ibne Wahed Bytul M. Rahman Department of Pharmacy Faculty of Science Rajshahi University Rajshahi Bangladesh Department of Pharmacy Faculty of Life Science Mawlana Bhashani Science and Technology University Tangail Bangladesh

The main objective of this research is to conduct a comprehensive study for enhancing the aqueous solubility of poorly water soluble gliclazide using hydrophilic fumed silica particles (Aerosil®380) and evaluating the influence of silica on drug release profile and pharmacological activity on alloxan induced diabetic rats. Solid dispersions (SD’s) of gliclazide were prepared using solvent evaporation method. The dissolution profiles and solid state characterization of the SD’s prepared were all evaluated. The dissolution rate of gliclazide in the SD’s with fumed silica (weight ratio, 1:1) was approximately 38%, which is about 10 fold higher than that of the pure drug after 30 min. After forming the SD’s, gliclazide changed into an amorphous state, which can infer from differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD). Fourier transform infrared spectroscopy (FTIR) also revealed the formation of weak hydrogen bonding through the interactions between the secondary amine groups of gliclazide and silanol groups of silica particles in the SD’s. The rapid dissolution rate from the SD’s might be attributed to the amorphization of drug, improved specific surface area and wettability than the original drug crystals. Further, we investigated the antidiabetic effects of SD’s of gliclazide in alloxan induced diabetic rats. The SD’s of gliclazide decrease the blood glucose level 64% whereas the conventional gliclazide decreases only 37% in diabetic rats. Lipid profiles, kidney and liver functions are remarkably improved in diabetic rat treated with SD’s of gliclazide than that of conventional gliclazide. These results suggest that SD’s of gliclazide have much more bioavailability and hence are more pharmacologically active than that of conventional gliclazide form.

关键词： In-Vitro Dissolution fumed Silica Solid Dispersions Gliclazide Alloxan Diabetes

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