Silica Agglomerates Research Articles

Network evolutions in both pure and silica-filled natural rubbers during cyclic shear loading

During the fatigue process, the loose silica agglomerates are disrupted and then the closed ones can also be gradually broken down, and the filler particles become more and more homogeneous.

Synthesis and Characteristic of Precipitated Nano-Silica

The reaction of precipitation of amorphous silicon dioxide from aqueous solution of sodium silicate and sulfuric acid has been studied. The factors affecting the precipitation process of the sodium silicate solution such as sodium silicate concentration and addition of anionic surfactant (sodium dodecyl sulfate, SDS) on particle size, size distribution and degree of agglomeration of the precipitated silica were examined. The precipitation of silica from the produced sodium silicate solution was carried out using sulfuric acid at pH 7. Scaning electron microscope (SEM), transmission electron microscope (TEM) and Dynamic light scattering (DLS) have been used for characterization of the produced nano-silica. The surface area of silica was tested by oil absorption method according to ASTM standard. Results showed that the particle size of the precipitated silica gel was decreased with increasing Na2SiO3 and SDS concentrations and Particle size of about 44nm can be achieved at 20% Na2SiO3 and 200ppm SDS. But with decreasing particle size, degree of agglomeration also increased.

The Influence of CB, Silica and CaCO<sub>3</sub> on Tensile and Morphological Properties of vPE/rPE/EPDM Blends

The virgin polyethylene (vPE) and recycled polyethylene (rPE) was melt blended with ethylene propylene diene terpolymer (EPDM) in different ratio by using a Haake Rheomix at 180°C and 50 rpm were prepared. The characterization such as tensile properties and morphology were examined. Results indicated that, the tensile strength and youngs modulus of vPE/rPE/EPDM with CB show the highest value compared to silica and CaCO3 except for elongation at break. The scanning electron microscopy (SEM) studies proved that, better dispersion and less agglomeration of CB and silica filled particles as compared to the CaCO3.

The Influence of CB, Silica and CaCO<sub>3</sub> on Tensile and Morphological Properties of vPE/rPE/EPDM Blends

The virgin polyethylene (vPE) and recycled polyethylene (rPE) was melt blended with ethylene propylene diene terpolymer (EPDM) in different ratio by using a Haake Rheomix at 180°C and 50 rpm were prepared. The characterization such as tensile properties and morphology were examined. Results indicated that, the tensile strength and youngs modulus of vPE/rPE/EPDM with CB show the highest value compared to silica and CaCO3 except for elongation at break. The scanning electron microscopy (SEM) studies proved that, better dispersion and less agglomeration of CB and silica filled particles as compared to the CaCO3.

Nanocomposites of silica reinforced polypropylene: Correlation between morphology and properties

Polypropylene/fumed hydrophilic silica nanocomposites were prepared via melt mixing method using a single‐screw extruder. Comparative study with and without compatibilizing copolymer agent (maleic anhydride grafted polypropylene: PP‐g‐AM) was conducted. The obtained results were interpreted in terms of silica nanoparticle–silica nanoparticle and silica nanoparticle‐polymer interactions. These results have shown that the addition of nanofillers improves the properties of the nanocomposites. From transmission electron microscopy, it was found that agglomerations of silica particles into the PP matrix increased in average size with increasing silica contents, except in presence of the copolymer. Storage modulus values of the nanocomposites measured by dynamic mechanical thermal analysis were sensitive to the microstructure of the nanocomposites. Higher silica contents resulted in higher storage modulus, revealing that the material became stiffer. By adding the compatibilizer, a further increase of storage modulus was observed due to the finer dispersion of the filler in the matrix and the increased interfacial adhesion. Crystallization rates were found to increase with the increase of silica nanoparticles as well as PP‐g‐MA content. In addition, silica nanoparticles and the compatibilizing agent present centers of germination and nucleation of crystallites. Thus, the use of the coupling agent resulted in a further enhancement of mechanical properties of the nanocomposites due to the reduction of silica agglomeration. POLYM. ENG. SCI., 54:2187–2196, 2014. © 2013 Society of Plastics Engineers

Collision of a chondrule with matrix: Relation between static strength of matrix and impact pressure

Chondrites are one of the major groups of meteorites. They consist of spherical objects called chondrules, which are typically (sub-)millimeter-sized, and fine-grained matrix between the chondrules. There exists a variety of models on the formation of chondrules, most of which have in common that chondrules were formed at some local place in the protoplanetary disk and later incorporated into the planetesimals which then formed the chondrite parent bodies. However, it has not yet been fully investigated how and under which conditions chondrules coalesce with the matrix. In this experimental study, we assume that chondrules and matrix were formed at different places in the protoplanetary disk and subsequently collided with each other. For this, we investigated the relation between the bulk strength of agglomerates and the impact pressure, and the threshold velocity for a chondrule to be embedded into the matrix. We performed collision experiments using three different accelerators to achieve collision velocity from 0.2 to 300ms−1. We also carried out static strength measurements for silica agglomerates which were used as targets to investigate their mechanical properties, using a compressive-strength testing machine. Finally, we measured the elastic limits of the dust agglomerate from their compression (pressure–displacement) curves. We found three types of collision outcomes: bouncing, surface sticking and intrusion of the chondrule-analog projectile. Comparing the compressive strength of the target with the impact pressure, we found that intrusion occurs when the strength of the target is smaller than the impact pressure. On the other hand, bouncing occurs when the strength of the target is larger than the impact pressure. The minimum intrusion velocities of chondrules for targets with 50% and 75% porosity were determined to be 46 and 3ms−1, respectively.

Breakup of silica agglomerates in corotating twin-screw extruder

Extensive experimental studies on silica agglomerate breakup during compounding with polymer melts of various viscosities and polarities in a modular corotating twin-screw extruder were conducted. To avoid a subjectivity of the result, due to small size particles involved, silica agglomerates were characterized by measuring their mass average values. Increasing the screw speed, melt viscosity, and silica concentration were found to increase the silica agglomerate breakup. The effect of these parameters on agglomerate breakup was ranked as follows: silica concentration > polymer viscosity ≈screw revolutions per minute (rpm). A good correlation between silica agglomerate breakage and power input was also found. Based on the experimental data and dispersion process, a composite modular kinetic model for evaluating silica agglomerate breakup during compounding in a corotating twin-screw extruder was tested. The kinetic constants of breakup and reagglomeration of silica agglomerates were calculated based on the stresses applied to the agglomerates and their cohesive strength. These constants for silica agglomerates were found to be not significantly different at high concentrations. The latter was in contrast to experimental data from available literature on compounding of calcium carbonate with polypropylene where the high reagglomeration kinetic constants of calcium carbonate in comparison with those of breakup played a major role in the agglomerate breakup. Comparison of the experimental and calculated results on the silica agglomerate size evolution during compounding with polymer melts indicated a reasonable agreement between them at high rotational speeds.

Fabrication and Evaluation of Electret Condensor Microphone with Film Lamination and Silica Spacers

The electret condenser microphones (FilmECMs) with film lamination and silica agglomerates were fabricated and the influence of the silica agglomerates on the characteristic of the FilmECM was investigated. The silica agglomerates was formed on PFA (perfluoroalkoxy) films by the application of colloidal silica using inkjet printing. The silica agglomerates for spacers formed the microgaps between the insulation films in the gap. Eventually, The silica agglomerates drastically enhanced the sensitivity of FilmECM while the resonance frequency was decreased. The size and the interval of the silica agglomerates influenced on the sensitivity and the resonance frequency. Such a influence can be explained by the density of the contact points of the films and silica agglomerates in the gap of FilmECM. Thereby the FilmECM which had the comparable sensitivity with commercial ECM was obtained. The resonant frequency was much higher than audible frequency (around 50 kHz). Hence, a wideband ECM could be obtained using FilmECM if the poor sealing of the gap and the diffraction of the sound is eliminated.

Intermeshing Rotor의 구조가 SBR/BR 합성고무 복합소재의 실리카 분산에 미치는 영향의 비교

The effects of mixing geometry (intermeshing vs. tangential rotor) for the dispersion and distribution of silica agglomerates in SBR/BR compound were investigated. Silica dispersion and distribution were found to be better with the intermeshing rotor compared to the tangential rotor. It was concluded that the intermeshing rotor compared to the tangential rotor delivered a higher shear stress due to interlocked rotor geometry to silica agglomerates leading to better dispersity and distribution of silica in the agglomerates.

Nanoscopic water layers adsorbed onto mesoporous silica aggregates and their effect on the stability and the static yield stress of their dispersion in liquid paraffin

Nanoscopic liquid-like water films were deposited onto silica mesoporous aggregates from vapour phase at 30°C and at 0.9 P/P0 or from water–paraffin emulsions. The water layers, surround entirely the silica aggregates, reduced their specific surface area from 136±5m2/g to 80±4m2/g, and leaved substantially unchanged their meso-porosity. No formation of nano-pores smaller than 1nm was observed.The dispersions in liquid paraffin of these powders, without applying any shear rate, result different from the correspondent suspensions obtained with dry silica meso-pores aggregates especially when the dispersions reach the gel-like status, i.e. after the percolation threshold θ*, set at 8.2% (v/v). For θ values less the θ* the water films act as insulation to reduce the stability of the dispersions, i.e. to reduce the net attractive forces between the silica surfaces and the paraffin.In the gel-like regime, the adsorbed water molecules play a new and emerging role. As the solid volume concentration is increased the silica aggregates covered with water layers come in to contact and form a “liquid menisci” between neighbouring films that allow the formation of a “pendular state” because of capillary forces. These capillary/viscous forces cause a second generation of gel agglomerates, few millimetres in dimension, that are interconnected between them and somewhat separated by thin voids. By comparison with the gel status formed by the dry silica agglomerate dispersions, it has been derive that the paraffin molecules migrate inside the void spaces created throughout the “pendular state”. Maximum static yield stress and separation energies equal to 2500Pa and 3×10−18J, respectively, were measured and compared with values of 1190Pa and 3×10−19J for dispersions without adsorbed water layers.

Presence of Nano-Sized Silica during In Vitro Digestion of Foods Containing Silica as a Food Additive

The presence, dissolution, agglomeration state, and release of materials in the nano-size range from food containing engineered nanoparticles during human digestion is a key question for the safety assessment of these materials. We used an in vitro model to mimic the human digestion. Food products subjected to in vitro digestion included (i) hot water, (ii) coffee with powdered creamer, (iii) instant soup, and (iv) pancake which either contained silica as the food additive E551, or to which a form of synthetic amorphous silica or 32 nm SiO(2) particles were added. The results showed that, in the mouth stage of the digestion, nano-sized silica particles with a size range of 5-50 and 50-500 nm were present in food products containing E551 or added synthetic amorphous silica. However, during the successive gastric digestion stage, this nano-sized silica was no longer present for the food matrices coffee and instant soup, while low amounts were found for pancakes. Additional experiments showed that the absence of nano-sized silica in the gastric stage can be contributed to an effect of low pH combined with high electrolyte concentrations in the gastric digestion stage. Large silica agglomerates are formed under these conditions as determined by DLS and SEM experiments and explained theoretically by the extended DLVO theory. Importantly, in the subsequent intestinal digestion stage, the nano-sized silica particles reappeared again, even in amounts higher than in the saliva (mouth) digestion stage. These findings suggest that, upon consumption of foods containing E551, the gut epithelium is most likely exposed to nano-sized silica.

G030061 シリカ凝集体を用いた耐熱エレクトレットフィルムの作製と特性評価

G030061 シリカ凝集体を用いた耐熱エレクトレットフィルムの作製と特性評価

Spinning of fibers from polypropylene/silica composite resins

Isotactic polypropylene (iPP)/silica (SiO2) composites were prepared by solution (toluene) mixing followed by either sonication or autoclaving to disaggregate the silica agglomerates. The obtained composite resins were then spun into monofilament fibers using a ThermoHaake's single screw extruder. The obtained fibers were characterized by morphological analyses (scanning electron microscope, atomic force microscopy (AFM), and Raman), crystallization profile (differential scanning calorimetry), and hot-stage microscopy. AFM images and Raman analysis maps revealed that silica particles of a submicron size range were present on the surface. The inclusion of silica particles into the resins resulted in a higher crystallization temperature ( Tc) and shrinkage resistance of the composite fiber when compared to those of the neat or toluene-prepared PP fibers, which were attributed to the nucleating effect of the silica filler with an effective reinforcement. In addition, the silica loadings (0.25–1 wt%) increased the tensile strength attributable to its change in shape from round to elongated and flattened after spinning process, except that the greatest increase (1.4-fold) was seen at 0.25 wt% silica. However, the variances were large, resulting from diameter variation arising from free-fall fibers obtained by gravitational force only. Interestingly, the surface hydrophobicity of the composite fibers was found to be higher than the neat fibers due to the increase in the surface roughness arising from the presence of particles on the surface.

Deposition of silica agglomerates in a cast of human lung airways: Enhancement relative to spheres of equal mobility and aerodynamic diameter

This paper reports on an experimental study of the deposition of well-characterized silica agglomerates in a cast of a section of a human lung. Deposition of the agglomerates is compared with the deposition of oleic acid spheres and sodium chloride particles for a range of mobility sizes, agglomerate properties (primary particle size and mass–mobility exponent) and inspiratory flow rates. In most cases, agglomerate deposition was significantly greater than that of the oleic acid and sodium chloride particles. Deposition of agglomerates with a more open structure was greater than that of relatively more compact (but still non-spherical) agglomerates. Deposition also increased with the flow rate. Because of the large physical size of the agglomerates, as well as the crenulated flow path through the model and the flow rate dependence, it is likely that interception is responsible for the enhanced deposition of the agglomerates.

Model for the hydrodynamic dispersion of agglomerates incorporating thermoresponsive additives

Abstract A phenomenological model for the hydrodynamic dispersion of silica agglomerates modified with a thermoresponsive hydrogel (poly-N-isopropylacrylamide, PNIPAM) is presented. The model well describes experimental observations of the dependence of the dispersion behavior on the presence of additives (water and PNIPAM hydrogels) and applied hydrodynamic stress. Most importantly, the thermosensitivity of the dispersion process is captured by characterizing the agglomerate structure and cohesive force at two different temperatures (above and below the hydrogel transition temperature). The transition in dispersion mechanism between rupture-like and erosion-like regimes with system temperature can also be accommodated within the model.

테트라에톡시실란 및 염산 농도에 따른 메조다공성 실리카 마이크로스피어의 모폴로지 변동에 관한 연구

에멀션 기반의 계면활성제를 이용한 주형합성법을 이용하여 산촉매로서 염산과 실리카의 전구체인 테트라에톡시실란을 사용함으로써 메조다공성 실리카 마이크로스피어를 합성하였다. 테트라에톡시실란의 농도 증가에 의해 구형의 입자 형태가 파괴되었고, 기공구조도 크게 변하였다. 산촉매 농도 증가에 의한 구형의 입자형태 파괴 현상은 적었지만 상대적으로 작은 크기의 구형의 마이크로입자가 더 많이 생성되었다. 하지만, 산성조건에서 입자들 간의 강한 응집현상이 나타남에 따라 낱개의 분리되어 있는 단일입자를 얻기 위해서는 초음파 등의 후처리 과정이 필요하였다. Tetraethoxysilane(TEOS) as a silica precursor and hydrochloric acid as an acid catalyst have been used in a surfactant-template synthesis of micrometer-sized mesoporous silica microspheres based on the macroemulsion technique. Increase in the concentration of tetraethoxysilane of the reaction mixture has a serious destructive effect on the particle shape and pore structure. As the acid concentration increases, relatively small microspheres are formed without destroying their spherical morphology of the particles as well as the pore structures. However, due to the attractive interaction between particles in an acidic condition, strong silica agglomerates are formed, and therefore are subject to a post-ultrasonic treatment to separate into an individual single particle.

J044064 凝集体スペーサーによる,広帯域エレクトレットコンデンサマイクロフォンの高感度化([J04406]知的材料・構造システム(6))

The purpose of this study was the improvement of the sensitivity in an electret condenser microphone with film lamination (FiImECM) using agglomerates spacer. The agglomerates (Silica or Boron Nitride) were inserted between films in the gap of FiImECM. The average sensitivity ,6 was enhanced by the agglomerates. The silica agglomerates were more effective to enhance ,8 than the BN agglomerates. Increasing g resulted the decrease in the resonance frequency (f.), as predicted by an analytical model. The experimental data off. was in good agreement with the estimated data from This result indicated that the intensity of electric field in the gap would not be degraded if the agglomerates were inserted in the gap of the FiImECM.

Characterisation of silica nanoparticles prior to in vitro studies: from primary particles to agglomerates

The size, surface charge and agglomeration state of nanoparticles under physiological conditions are fundamental parameters to be determined prior to their application in toxicological studies. Although silica-based materials are among the most promising candidates for biomedical applications, more systematic studies concerning the characterisation before performing toxicological studies are necessary. This interest is based on the necessity to elucidate the mechanisms affecting its toxicity. We present here TEM, SAXS and SMPS as a combination of methods allowing an accurate determination of single nanoparticle sizes. For the commercial material, Ludox TM50 single particle sizes around 30 nm were found in solution. DLS measurements of single particles are rather affected by polydispersity and particles concentration but this technique is useful to monitor their agglomeration state. Here, the influence of nanoparticle concentration, ionic strength (IS), pH and bath sonication on the agglomeration behaviour of silica particles in solution has been systematically investigated. Moreover, the colloidal stability of silica particles in the presence of BSA has been investigated showing a correlation between silica and protein concentrations and the formation of agglomerates. Finally, the colloidal stability of silica particles in standard cell culture medium has been tested, concluding the necessity of surface modification in order to preserve silica as primary particles in the presence of serum. The results presented here have major implications on toxicity investigations because silica agglomeration will change the probability and uptake mechanisms and thereby may affect toxicity.

Phospholipid Langmuir Film as Template for in Situ Silica Nanoparticle Formation at the Air/Water Interface

This study describes for the first time the in situ formation of small-sized silica nanoparticles after the polycondensation of tetraethylorthosilicate (TEOS) at the air/water interface. Mixtures of TEOS and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) are prepared with different molar ratios (TEOS/DPPC 15:1, 50:1, 500:1, and 5000:1) and dissolved in chloroform. Spreading TEOS/DPPC 15:1 and 50:1 on the water surface of a Langmuir trough leads to an initial increase of the surface pressure ( approximately 26-29 mN/m) after allowing chloroform to evaporate. Within the reaction time of 21 h, only a slight decrease of the surface pressure by approximately 2 mN/m occurs. Films of silica/DPPC mixtures are transferred from the air/water interface to silicon wafers by dip-coating. The morphologies of the silica nanoparticles and agglomerates together with DPPC are observed using tapping mode atomic force microscopy (AFM). An ordered array of silica nanoparticles can be observed after 21 h reaction of the precursor solution of TEOS/DPPC 500:1 and transfer onto hydrophilic silicon substrate. A mixture with a molar ratio of TEOS/DPPC of 5000:1 is also placed onto the water surface. DPPC forms a uniform film observed by AFM after film transfer. Silica rich domains can be observed with mesoporous morphology.

Fabrication and Crystallization Temperature of Silica/Polypropylene Nanocomposites by Simple Method without any Hydrophobic Treatment of Nano-Silica Surfaces

A simple method for the fabrication of silica/polypropylene (PP) nanocomposites was investigated, whereby silica particles of 190nm in diameter without any surface modification were dispersed uniformly through mechanical breakdown of loosely packed agglomerates of silica nanoparticles with low fracture strength in a kneaded PP melt during direct melt-compounding. The method consists of two stages. The first stage involves preparation of the loosely packed silica agglomerate by destabilizing a colloidal aqueous solution of nanometer-size spherical silica via pH control and KBr addition, and the second stage involves melt-compounding of an isotactic PP with the silica agglomerates. The pore structure and strength of the silica agglomerate prepared in the first stage were found to control the dispersion state of the silica nanoparticles in the silica/PP composite, and the use of loosely packed silica agglomerates with numerous large pores was shown to be effective for achieving a uniform dispersion of isolated primary silica nanoparticles in the PP matrix. Non-isothermal differential scanning calorimetry (DSC) analyses of the fabricated composites revealed that the crystallization temperature of the PP matrix phase shifts towards higher one with decreasing dispersion size of silica and increasing content of distributed nano-silica. A DSC analysis may be a potential candidate for useful method to evaluate the dispersion characteristics of the inorganic nano-fillers in crystalline polymer-based nanocomposites.