Preparation, characterization and biodegradation of biopolymer nanocomposites based on fumed silica

PLA and PCL based nanocomposites prepared by adding three different types of fumed silica were obtained by melt blending. Materials were characterized by means of Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and Dynamic–Mechanical Thermal Analysis (DMTA).A good distribution of the fumed silica into both polymer matrices was observed. The highest thermo-mechanical improvements were reached by addition of the fumed silica with higher surface area. PLA and its nanocomposites were degraded in compost at 58 °C; at this temperature all samples presented a significant level of polymer degradation, but a certain protection action of silica towards PLA degradation was observed, whereas the addition of fumed silica did not show considerable influence on the degradation trend of PCL. These dissimilarities were attributed to the different degradation mechanism of the two polymers.     

INS and IR study of intermolecular interactions at the fumed silica-polydimethylsiloxane interphase, Part 2. Hydrophillic and silylated silica components

A vibration spectra study of the interphase formed by fumed silica andpolydimethylsiloxane (PDMS) particles highlights the microscopic interactionmechanisms in the system. Vibrations have been investigated involving bothexperimental and computational approaches. Experiments were performed in theframework of infrared (FTIR) and inelastic neutron scattering (INS and AWDS)techniques. Spectra interpretation was carried out on the basis of quantumchemical (QCh) semiempirical calculations using AM1 and PM3 parameterisation,with the application of original software for spectra analysis COSPECO,containing both the direct and inverse spectral problem solutions togetherwith the spectral assignments. This study in general involves an extendedexamination of both free silica and PDMS components together with theirabsorption complexes. The present paper is the second part of this study anddeals with the vibrational analysis of hydroxylated and silylated silicas, thelatter bearing different trimethylsiloxy (TMS) group graft ratios and sohaving controlled amounts of residual silica silanol groups. The observedsilylated silica vibrations and modes were attributed to six-member ring-likepacking of TMS units on the silica surface.     

Nitric oxide-releasing fumed silica particles: synthesis,characterization, and biomedical application

The preparation, characterization, and preliminary biomedical application of various nitric oxide (NO)-releasing fumed silica particles (0.2-0.3 microm) are reported. The tiny NO-releasing particles are synthesized by first tethering alkylamines onto the surface of the silica using amine-containing silylation reagents. These amine groups are then converted to corresponding N-diazeniumdiolate groups via reaction with NO(g) at high pressure in the presence of methoxide bases (e.g., NaOMe). N-Diazeniumdiolate groups were found to form more readily with secondary amino nitrogens than primary amino nitrogens tethered to the silica. Different alkali metal cations of the methoxide bases, however, have little effect on the degree of N-diazeniumdiolate formation. The N-diazeniumdiolate moieties attached on the silica surface undergo a primarily proton-driven dissociation to NO under physiological conditions, with an "apparent" reaction order somewhat greater than 1 owing to local increases in pH at the surface of the particles as free amine groups are generated. The rates of N-diazeniumdiolate dissociation are further related to the parent amine structures and the pH of the soaking buffer. The N-diazeniumdiolate groups also undergo slow thermal dissociation to NO, with zero-order dissociation observed at both -15 and 23 degrees C. It is further shown that the resulting NO-releasing fumed silica particles can be embedded into polymer films to create coatings that are thromboresistant, via the release of NO at fluxes that mimic healthy endothelial cells (EC). For example a polyurethane coating containing 20 wt % of NO-releasing particles prepared with pendant hexane diamine structure (i.e., Sil-2N[6]-N(2)O(2)Na) is shown to exhibit improved surface thromboresistivity (compared to controls) when used to coat the inner walls of extracorporeal circuits (ECC) employed in a rabbit model for extracorporeal blood circulation.     

Magnesium ion-conducting gel polymer electrolytes dispersed with fumed silica for rechargeable magnesium battery application

Effect of fumed silica dispersion on poly(vinylidene fluoride-co-hexafluoropropylene)-based magnesium ion-conducting gel polymer electrolyte has been studied using various physical and electrochemical techniques. The composite gel electrolytes are free-standing and flexible films with enough mechanical strength. The optimized composition with 3 wt.% filler offers a maximum ionic conductivity of ∼1.1 × 10⁻² S cm⁻¹ at ∼25 °C with good thermal and electrochemical stabilities. The Mg²⁺ ion conduction in the gel nanocomposite film is confirmed from the cyclic voltammetry, impedance spectroscopy, and transport number measurements. The space-charge layers formed between filler particles and gel electrolyte are responsible for the enhancement in ionic conductivity. The applicability of the gel nanocomposite to a rechargeable battery is examined by fabricating a prototype cell consisting of Mg [or Mg-multiwalled carbon nanotube (MWCNT) composite] and MoO₃ as negative and positive electrodes, respectively. The discharge capacity and the rechargeability of the cell have been improved when Mg metal is substituted by Mg-MWCNT composite. The discharge capacity of the optimized cell has found to be ∼175 mAh g⁻¹ of MoO₃ for an initial ten charge–discharge cycles.     

Dispersion stabilities and rheological properties of fumed silica suspensions

Herein, we have reviewed fumed silica suspensions in dispersing fluids, polymer melts, and polymer solutions, focusing on their dispersion stability and rheological properties as a function of the surface character of fumed silica powders and the silica volume fraction, ?. Hydrophilic fumed silica powders are well dispersed at ? < 0.01 in polar dispersing fluids or polar polymer melts, and their phase states change from sol to gel with increasing ?. Such changes should also be strongly related to the rheological responses of the hydrophilic fumed silica suspensions, which change from Newtonian flow behavior to gel-like elasticity with increasing ?. On the other hand, hydrophobic fumed silica powders are stabilized in both polar and nonpolar dispersing fluids, depending on the interactions between the surface hydrophobic moieties and the dispersing fluids, in addition to those between the residual surface silanol groups and dispersing fluid, except for the particle–particle interactions. Moreover, the effects of the adsorption and desorption of polymers, as well as of non-adsorbing polymers on the dispersion stability and rheological behavior of fumed silica suspensions are discussed, by taking account of their optical microscopic observation and SANS curves.     

Rheological behavior of fumed silica filled polyethylene oxide

Influence of molecular weight of polymer matrix on nanocomposites rheology is not yet well understood. Herein dynamic rheological responses of fumed silica (FS)/polyethylene oxide (PEO) nanocomposites are investigated as a function of viscosity‐averaged molecular weight (M_η) of PEO, volume fraction (?) and surface characteristics (hydrophilic or hydrophobic) of FS. In the nanocomposites, FS does not influence the glass transition and crystallinity of PEO in the mobile PEO phase while the interfacial interactions tend to immobilize a small fraction of PEO chains that could not undergo glass transition. In spite of the common observation that the reinforcement decreases with increasing M_η of PEO and improving hydrophobicity of FS, linear rheological responses are well reproduced by the two‐phase model, revealing the crucial contribution of the non‐Newtonian matrix undergoing microscopic strain amplified by the filler. Furthermore, nonlinear rheological responses of the nanocomposites are collapsed into master curves plotted against local strain of the matrix. Analyzing the nonlinear rheology by Fourier transform and stress waveform methods reveal the dominating contribution of the matrix and the role of strain amplification played by the filler. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 397–405     

Porous properties of silylated mesoporous silica and its hydrogen adsorption

Porous properties of mesoporous silica silylated with various organic silanes were examined and their hydrogen adsorption properties were measured at 77 K. By silylation of the mesoporous silica, the specific surface area, pore radius and pore volume steeply decreased depending on both the size of the silane and the amount actually incorporated into the mesoporous framework. The pores reduced in size depending on the amount of modifying silane and vanished completely in the samples silylated with 3-aminopropyltriethoxysilane and phenyltrichlorosilane. Hydrogen adsorption isotherms of the silylated samples were measured at 77 K. With the exception of the sample with phenyltrichlorosilane, hydrogen adsorption volumes were proportional to the surface area with a slope of around 1.1 molecules/nm². On the other hand, for the sample treated with phenyltrichlorosilane, a large hydrogen adsorption volume of around 38.1 molecules/nm² was obtained. On heating the silylated compounds at 500 °C, micropores formed and the hydrogen adsorption volume increased by 1.5 times or more due to the development of micropores.     

Effect of silica content on thermal stability of fumed silica/epoxy composites

Composites of a fumed silica industrial residue and an epoxy resin were prepared and their thermal stability and thermal degradation behaviour were studied by TGA in air. Classical thermal stability parameters, based on the initial decomposition temperature (IDT), temperature of maximum rate of mass loss (T_max) and integral procedure decomposition temperature (IPDT) were calculated before and after subtraction of the filler mass from the TGA curves. Without filler mass subtraction, the thermal stability of the epoxy resin seems to be improved and the mass loss rate was reduced by the addition of fumed silica. Nevertheless, after subtraction of the filler mass, the thermal degradation behaviour of the resin was only slightly affected by the silica content. A possible negative effect of the silica content on the cure was also found.     

气相白炭黑表面处理率的影响因素及判定

气相白炭黑是一种二氧化硅纳米材料，气相白炭黑的最主要应用是用于硅橡胶的补强，但气相白炭黑在硅橡胶中很难分散，影响了补强效果，本文用六甲基二硅氮烷对白炭黑进行表面处理并对白炭黑表面处理率问题做一些探讨。     

Surface hydroxylation and silane grafting on fumed and thermal silica

The optimization of the surface functionalization of flat thermal silicon oxide by silanes was investigated. The difficulties are the low density of silanols at the surface of thermal silica, the lack of precise knowledge of the actual surface chemistry of thermal silica and of its hydroxylation, and the limited number of possible chemical analyses at flat surfaces of small area. This steered our study toward a comparative investigation of the hydroxylation and silane grafting of thermal silica and the well-known fumed silica. The silane grafting density for fumed silica that had undergone thermal treatments of dehydroxylation was related to the surface density of silanols. The surface density of silane on the flat thermal silica as measured by FTIR-ATR spectroscopy was 1.4 micromol/m2, similar to that of fumed silica dehydroxylated at 1000 degrees C. This moderate value was related to the low silanol density present on such silica surfaces. Several rehydroxylation treatments that proved their efficiency on dehydroxylated fumed silica did not lead to any noticeable improvement on thermal silicon dioxide.     

Analytical characterization of a silica gel sorbent with thioetheric sites

The sorption behavior of a newly synthesized silica gel sorbent with thioetheric sites (STS) towards microgram levels of Au(III), Pt(IV) and Pd(II) was studied. Au(III) is quantitatively (>95%) sorbed in the pH region of 1–9. The sorption of Pt(IV) starts at pH 1 and does not exceed 25% in the entire pH region examined. The sorption of Pd(II) starts at pH 7 and reaches 80% at pH 9. The sorption of Au(III) on STS at pH 1 is not affected by milligram amounts of Ni(II), Zn(II), Fe(III), Cu(II), Pb(II), Cd(II) or Co(II). Au(III) is quantitatively eluted with a 5% aqueous solution of thiourea. The adsorption capacity of STS towards Au(III) is 195 mg g⁻¹. The detection limit (DL) of Au(III) (3σ, n = 9) is 25 ng mL⁻¹. The RSD at a level of 10 × DL is about 2%. Solid-phase extraction of trace amounts of Au(III) on the STS sorbent, followed by its flame AAS determination in the eluate was applied to the determination of gold in geological samples. The results obtained for the gold content in the samples were in good agreement with those of the ICP-AES analysis.     

Three-phase cyanate ester composites with fumed silica and negative-CTE reinforcements

Three-phase cyanate ester adhesives have been developed using a bisphenol E cyanate ester resin, fumed silica, and negative-CTE (coefficient of thermal expansion) reinforcements: short carbon fiber or zirconium tungstate (ZrW₂O ₈ ). Fumed silica was used to impart thixotropic behavior on the resin and decrease settling in the adhesives. The cured composites were evaluated using various thermal analysis techniques for their thermal-mechanical properties. Composites with short carbon fiber showed enhanced modulus and decreased thermal expansion (70% reduction for 20 vol%) and showed little phase separation. While settling of the dense ceramic particles could not be completely eliminated for the zirconium tungstate composites through rheological modification of the adhesive with added fumed silica, a reduction in CTE of 84% was achieved in the composite (58 vol%) compared to the neat resin. In addition, the effect of thermal history on the cure and temperature induced ZrW₂O₈ phase transitions, and their corresponding influence on thermal strains vs. temperature, are examined by thermomechanical analysis.     

Synthesis and characterization of silica gel from siliceous sands of southern Tunisia

The present work aimed to achieve valorization of Albian sands for the preparation of sodium silicates that are commonly used as a precursor to prepare silica gel. A siliceous sand sample was mixed with sodium carbonate and heated at a high temperature (1060 °C) to prepare sodium silicates. The sodium silicates were dissolved in distilled water to obtain high quality sodium silicate solution. Hydrochloric acid was then slowly added to the hydrated sodium silicates to obtain silica gel. The collected raw siliceous sands, as well as the prepared silica gels, were characterized by different techniques, such as X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis (DSC). XRF confirmed that the detrital sand deposits of southern Tunisia contain high amounts of silica, with content ranging from 88.8% to 97.5%. The internal porosity varied between 17% and 22%, and the specific surface area was less than 5 m²/g. After the treatment described above, it was observed that the porosity of the obtained silica gel reached 57% and the specific surface area exceeded 340 m²/g. Nitrogen adsorption isotherms showed that the prepared silica gels are microporous and mesoporous materials with high adsorption capacities. These results suggest that the obtained silica gels are promising materials for numerous environmental applications.     

Preparation and characterization of carbosilane dendrimer-bonded silica gel and its use in LC

Divergently synthesized carbosilane dendrimers generations 1(G1) and 2 (G2) with allyl end groups were bonded onto silica gel. Reactions between the dendrimers and acid-processed silica gel took place, with toluene reflux and organic base as catalyst. Chemically bonded silica gel was characterized by transmission electron microscopy (TEM), infrared (IR), and other methods. The chemically modified silica gels were packed into high-pressure liquid chromatography (HPLC) column and their separation characters were evaluated. G2-bonded silica gel was effective in separating homologous compounds of alcohol, alkyl-substituted benzene, N-substituted benzene, metacrylic acid ester and phthalate. __________ Translated from Journal of Shandong University, 2005, 40(6) (in Chinese)     

Interaction of poly(ethylene oxide) with fumed silica

Interaction of poly(ethylene oxide) (PEO, 600 kDa) with fumed silica A-300 (SBET = 316 m2/g) was investigated under different conditions using adsorption, infrared (IR), thermal analysis (TG-DTA), AFM, and quantum chemical methods. The studied dried silica/PEO samples were also carbonized in a flow reactor at 773 K. The structural characteristics of fumed silica, PEO/silica, and pyrocarbon/fumed silica were investigated using nitrogen adsorption-desorption at 77.4 K. PEO adsorption isotherm depicts a high affinity of PEO to the fumed silica surface in aqueous medium. PEO adsorbed in the amount of 50 mg per gram of silica (PEO monolayer corresponds to CPEO approximately 190 mg/g) can disturb approximately 70% of isolated surface silanols. However, at the monolayer coverage, only 20% of oxygen atoms of PEO molecules take part in the hydrogen bonding with the surface silanols. An increase in the PEO amount adsorbed on fumed silica leads to a diminution of the specific surface area and contributions of micro- (pore radius R < 1 nm) and mesopores (1 < R < 25 nm) to the pore volume but contribution of macropores (R > 25 nm) increases with CPEO. Quantum chemical calculations of a complex of a PEO fragment with a tripple bond SiOH group of a silica cluster in the gas phase and with consideration for the solvent (water) effect show a reduction of interaction energy in the aqueous medium. However, the complex remains strong enough to provide durability of the PEO adsorption complexes on fumed silica; i.e., PEO/fumed silica nanocomposites could be stable in both gaseous and liquid media.     

聚N-异丙基丙烯酰胺硅胶键合固定相的制备与评价

以3-巯丙基三甲氧基硅烷为偶联剂,将聚N-异丙基丙烯酰胺(PNIPAM)键合到硅胶上,制得了键合固定相（SI-PNIPAM）填料,并用元素分析、红外光谱等对其进行了表征。以甲醇-水为二元流动相,用多环芳烃、碱性物质对该固定相进行了色谱评价,并考察了该固定相的适用pH范围及水解稳定性。结果表明:该固定相具有较好的色谱性能与温敏特性,并且在pH 2.5～7.5时稳定性良好。     

Modification of silica gel with diethylamino group by novel reaction and its characterization

1,3,5,7-Tetramethylcyclotetrasiloxane (H₄) was deposited on silica gel at 80°C by utilizing a chemical vapor deposition (CVD) method, where it was catalytically polymerized to form a surface coating of polymethylsiloxane (PMS). Treated silica gel (PMS-Si) increased in weight up to a plateau level, and there was no further increase with increasing reaction time. The film of PMS was partially cross linked; typical values of crosslinking ratio and film thickness were 2% and 0.6 nm, respectively. An anionic ion exchanger containing diethylamino groups was synthesized from PMS-Si by hydrosilylation of allyl glycidyl ether followed by treatment with diethylamine. Its structure was confirmed by¹³C and²⁹Si CP/MAS NMR spectroscopy and FT-IR spectrophotometry. Characterization of silica gel (DEA-Si) modified with diethylamino group was evaluated by a packing of the column for liquid chromatography. As a mixture of five nucleotides was completely separated, it was recognized that DEA-Si was operated by ion exchange action. Because the surface of the silica gel was covered with hydrophobic PMS, the peak heights and retention times did not change after washing of the column with alkaline solution.     

Fumed silica synthesis. Influence of hydrogen chloride on the fumed silica particle formation process

Interaction of silicon dioxide molecule up to the small silica protoparticle and primary particle formation, and influence of hydrogen chloride (HCl), water (H₂O) and inert molecules (nitrogen N₂) “under flame condition” and “after cooling” on structure and properties of fumed silica were investigated by quantum-chemical simulations. An attempt to give definition of surface concept on atomic level was made.     

Diffusion of protons in silica hydrogel

The effect of preparation pH of silica hydrogel on the effective diffusion coefficient of protons in silica hydrogel (D _e , m²/s), on surface area of silica gel (S, m²/s) and on particle size of silica gel (D _p , mm) was studied. Silica hydrosols were obtained by adding water glass to sulfuric acid. The effective diffusion coefficient of proton in silica hydrogel was determined by the method of diffusion from silica hydrogel plane sheet to a stirred solution of a limited volume. A numerical solution was obtained for the diffusion equation using the Regula Falsi method. Regression analyses of experimental data were conducted.Diffusion of protons in silica hydrogel is a complicated process due to a decelerating effect of the porous structure of silica hydrogel and to the accelerating effects of slow ions such as Na⁺ and surface diffusion. The effective diffusion coefficient increased with surface area of silica gel, indicating the diffusion of protons on the surface of the silica particles.