Silica Volume Fraction Research Articles

Effect of Grafting on Rheology and Structure of a Simplified Industrial Nanocomposite Silica/SBR

An un-cross-linked SBR-system filled with precipitated silica nanoparticles of radius ≈10 nm by mixing is studied as a function of the fraction of graftable matrix chains (140 kg mol–1) varying from 0% to 100%, for a low (ΦSi = 8.5 vol %) and high (16.7 vol %) silica volume fraction. The linear rheology in shear shows a strong impact of the grafting on the terminal flow regime, and a shift to longer relaxation times with increasing grafting. Simultaneously, the plateau modulus stays approximately constant for the low ΦSi, suggesting a link to the silica content. The microstructure of the silica is characterized by using a combination of transmission electron microscopy and small-angle X-ray scattering data. We apply a quantitative model of interacting aggregates, and determine the average aggregation number (decreasing from 160 to 30 with grafting), aggregate size (50 to 30 nm), and compacity (55% to 35%). While the linear rheology seems to be dominated by the matrix composition, both the mixing rheology ...

Preparation and characterization of dimethyldichlorosilane modified SiO2/PSf nanocomposite membrane

Investigations on nanocomposite membranes imply that these hybrid materials recommend promising newgeneration membranes for gas separation in future. In this study, to investigate the effects of preparation parameters on the morphology and gas transport, various parameters including nanofiller content, surface modification and polymer concentration were considered. Two types of fumed silica nanoparticles (nonmodified and modified) were used to study the surface modification effect on agglomeration, void formation and gas separation properties of prepared membranes. Prepared nanocomposite membranes were characterized by scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and tensile strength techniques. The gas permeabilities of hydrogen, methane, and carbon dioxide through pure PSf and nanocomposites were measured as a function of silica volume fraction, and permeability coefficients were determined using a variable pressure/constant volume experimental setup. Results showed that gas permeabilities increase with silica content, and proper H2/CH4 and H2/CO2 selectivities can be achieved with modified type of silica nanoparticles due to inhibition of particle agglomeration and bonding with polymer network. Hydrogen selectivity was improved by using 15 wt% polymer content instead of 9 wt% in preparation of nanocomposite membrane with same silica content. Gas permeation results indicated that increasing of feed pressure from 3 bar to 6 bar has a positive effect on selectivity of H2/CH4 but negligible effect on that of H2/CO2 for modified silica/PSf membrane.

Mechanical Properties and Cross-Link Density of Styrene–Butadiene Model Composites Containing Fillers with Bimodal Particle Size Distribution

Mechanical properties and cross-link density of model composites being solution styrene–butadiene rubbers filled with different amounts of nanosized silica particles or mixtures of nanosized silica particles and micrometer-sized borosilicate glass particles are studied. The cross-link density of the rubber matrix is measured based on a double-quantum NMR spectroscopy method. Shear data show that reinforcement and dissipation G″ in the rubber plateau range depend systematically on the total surface area of the filler per unit composite. Different contributions to reinforcement due to hydrodynamic effects, “filler network”, glassy polymer layer, and “occluded rubber” are quantified based on a comparison of linear response measurements with strain sweeps performed at different temperatures. The results show a percolation threshold at silica volume fractions of about 0.15. The load-carrying capacity of the “filler network” decreases significantly with temperature. This may indicate the existence of a glassy polymer layer on the surface of the filler particles which softens several ten degrees above the bulk Tg of the rubber matrix. Two regimes are found in the dissipation above Tg which both depend systematically on the surface area of the filler system: A strongly frequency-dependent dissipation regime with power-law behavior is observed in G″(ω) at temperatures up to 70 K above the bulk Tg, and a nearly frequency-independent G″ regime dominates at higher temperatures. The molecular nature and importance of this finding for tire applications are discussed.

Reinforcement and Polymer Mobility in Silica–Latex Nanocomposites with Controlled Aggregation

The tunable structure of silica–latex nanocomposites made of silica nanoparticles (radius ≈ 80 A) and a copolymer of methyl methacrylate and butyl acrylate–latex beads (radius ≈ 210 A) has been studied by small-angle neutron scattering and transmission electron microscopy. An aggregation diagram as a function of the control parameters—silica volume fraction and precursor solution pH—has been established. In this aggregation diagram, isoaggregation lines have been identified. It was used to express the small-strain reinforcement factor measured with stress–strain isotherms as a function of volume fraction at fixed aggregation number in the range from 50 to 100. The large-strain properties have been rationalized using the energy needed to rupture samples, and this quantity has been found to present an optimum at intermediate volume fractions (15%). In order to understand the striking rheology of the system, a neutron contrast-matching study has been undertaken by adding deuterated polymer beads. The bead de...

Tuning the mechanical properties in model nanocomposites: Influence of the polymer‐filler interfacial interactions

AbstractThis article presents a study of the polymer‐filler interfacial effects on filler dispersion and mechanical reinforcement in Polystyrene (PS)/silica nanocomposites by direct comparison of two model systems: ungrafted and PS‐grafted silica dispersed in PS matrix. The structure of nanoparticles has been investigated by combining small angle neutron scattering measurements and transmission electronic microscopic images. The mechanical properties were studied over a wide range of deformation by plate–plate rheology and uni‐axial stretching. At low silica volume fraction, the particles arrange, for both systems, in small finite size nonconnected aggregates and the materials exhibit a solid‐like behavior independent of the local polymer‐fillers interactions suggesting that reinforcement is dominated by additional long range effects. At high silica volume fraction, a continuous connected network is created leading to a fast increase of reinforcement whose amplitude is then directly dependent on the strength of the local particle–particle interactions and lower with grafting likely due to deformation of grafted polymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Nanocomposites based on borate esters as improved lithium-ion electrolytes

Borate esters with different lengths of ethyleneoxy units were investigated as electrolyte solvents for lithium salts such as lithium triflate, perchlorate, bis(trifluoromethanesulfonyl)imide, bis(pentafluoroethanesulfonyl)imide and bis(oxalato)borate. The ionic conductivity of the salt solutions was measured to be of the order of 10−3 to 10−4 S cm−1 at room temperature. Transference number measurements for the borate ester–lithium perchlorate system indicated roughly equal contributions of cations and anions to the total conductivity, while the borate ester–lithium bis(oxalato)borate showed predominant anionic conductivity. Nanocomposite electrolytes were prepared by heterogeneous doping of the borate esters with silica. Composites with 10 nm silica particles exhibited low-viscous electrolyte behavior with a clear but modest conductivity enhancement at very low volume fractions of silica and a depression of the conductivity value at higher volume fractions. In the case of fumed silica (7 nm) the nanocomposites had at a sufficiently high volume fraction and a jelly, transparent appearance with the favorable mechanical properties of a high-viscous semi-solid without noteworthy decrease in the Li ion conductivity. In particular the last material with its combination of favourable electrical, mechanical and optical properties, promises to be a viable candidate for various applications (Li-based batteries, solar cells).

Influence of hydrophilic silica nanoparticles to the conformation of hydrophilic polymer chain in dilute solution system

We studied interaction of hydrophilic polymer chain and hydrophilic silica nanoparticles in a dilute aqueous system using an idealized model system comprised of a well characterized polyvinyl alcohol of 100 Å R(g) and hard spherical LUDOX® silica of 80 Å radii. Interaction among the polymer chains forming polymer clusters with collective polymer structure factor induced by the polymer-mediated potentials of mean force between the nanoparticles, was observed. However, Gaussian nature of individual polymer chain remains unaltered. The dilute system of polymer with low silica volume fraction has the scattering form which was appropriately modeled as the sum of the individual profiles of spherical silica particles and polymer cluster of interchain packing. With increasing silica volume fraction in the dilute solution, the spatial range parameter between the particles is reduced; hence there is a net increase in the mean potential force and consequently to stronger interaction between the silica and polymer. In the dilute systems of high silica with low polymer volume fraction, the polymer chain apparently attracted closer to the silica and concurrently absorbed to the silica hard surface and their scattering data were excellently fit with a model form factor as comprising of one unit forming the core of the spherical silica particles and the interacting polymer as the corona. This result of severe change in polymer interchain conformation in a dilute system corroborated with reduced polymer viscosity observed.

Simultaneous Corrosion of Fe–Si Alloys by Carbon and Oxygen

Pure iron and binary alloys containing 1, 2, 3, and 5 wt % Si were reacted at with a carbon-supersaturated, flowing gas mixture of 68% CO, 26% , and 6% ( and ). Alloy reaction products consisted of a subsurface zone of internally precipitated , an external scale of , and a voluminous superficial deposit of coke containing particles of cementite and silica. Coking and metal dusting rates both increased with alloy silicon level. Internal oxidation rates also increased with silicon concentration but net scaling rates decreased. It is proposed that increasing volume fractions of silica in the scale provides more sites for graphite nucleation, which leads to accelerated disintegration of the scale surface. This accounts for the more rapid dusting, faster coking (catalyzed by more particles), and thinner scales.

Glass transition and thermal expansivity in silica-polystyrene nanocomposites

The glass transition temperature T g and the thermal expansion coefficient have been measured using the capacitive scanning dilatometry for silica-polystyrene (PS) nanocomposites with various silica volume fraction up to 50 vol.%. The glass transition temperatures for silica-PS nancomposites show a deviation from the bulk T g together with a large scatter. Thermal expansivity decreases with increasing silica fraction both below and above T g. A clear relaxation peak can be observed in the expansivity–temperature curve for silica-PS nanocomposites. The intensity of the peak decreases with increasing silica fraction. The decrement is larger than the value expected on the assumption that silica particles do not participate in the glass transition.

Simultaneous Oxidation and Metal Dusting of Fe-Si Alloys

Pure iron and binary alloys containing 1, 2, 3 and 5 wt. % Si were reacted at 680oC with a carbon-supersaturated, flowing gas mixture of 68% CO, 26% H2 and 6% H2O (aC = 2.9, pO2 = 2 × 10-23 atm). Alloy reaction products consisted of a subsurface zone of internally precipitated SiO2, an external scale of Fe3C + SiO2, and a voluminous superficial deposit of coke containing particles of cementite and silica. Coking and metal dusting rates both increased with alloy silicon level. Internal oxidation rates also increased with silicon concentration, but net scaling rates decreased. It is proposed that increasing volume fractions of silica in the scale provide more sites for graphite nucleation, which leads to accelerated disintegration of the scale surface. This accounts for the more rapid dusting, faster coking (catalysed by more Fe3C particles) and thinner scales.

Rheology and Microstructure of Entangled Polymer Nanocomposite Melts

The rheology and microstructure of 44 nm diameter silica particles suspended in entangled poly(ethylene oxide) (PEO) melts are studied through measurement of filled melt viscosity and X-ray scattering measurement of interparticle structure factors, S(q,ϕc), where q is the scattering vector and ϕc is the silica volume fraction. The particles have a similar refractive index to PEO which minimizes van der Waals attractions acting between particles. The introduction of particles causes an elevation in the viscosity of the nanocomposite melt more than would be expected of particles merely interacting with hard core repulsions. Further addition of particles causes a rise in the elastic and viscous moduli. The rheological characterization of these nanocomposite melts is discussed in terms of several critical particle volume fractions that result from confinement of polymer, adsorption of polymer segments to the particle surface, and overlap and entanglement of adsorbed polymer as the particle volume fraction is ...

Gas transport behavior of mixed-matrix membranes composed of silica nanoparticles in a polymer of intrinsic microporosity (PIM-1)

Abstract Recently, high-free volume, glassy ladder-type polymers, referred to as polymers of intrinsic microporosity (PIM), have been developed and their reported gas transport performance exceeded the Robeson upper bound trade-off for O 2 /N 2 and CO 2 /CH 4 . The present work reports the gas transport behavior of PIM-1/silica nanocomposite membranes. The changes in free volume, as well as the presence and volume of the void cavities, were investigated by analyzing the density, thermal stability, and nano-structural morphology. The enhancement in gas permeability ( e.g ., He, H 2 , O 2 , N 2 , and CO 2 ) with increasing filler content shows that the trend is related to the true silica volume and void volume fraction.

Compaction experiments on ice‐silica particle mixtures: Implication for residual porosity of small icy bodies

To evaluate the residual porosity of small icy bodies, we performed compaction experiments on ice‐silica mixtures and studied the effects of silica content, temperature, and compaction time scale on residual porosity. To simulate the compositions of real icy bodies, we used ice‐silica mixtures with different silica volume fractions (0–0.29). The mixtures were compacted at a constant compression speed of 0.2 or 2.0 mm/min and the temperature was set to −10°C or a lower temperature (from −55 to −67°C). For the −10°C case, the mixtures were compressed to pressures of 30 MPa, while the lower temperature measurements were compressed to 80 MPa. In both cases, the residual porosity was found to be larger for higher silica fractions. At −10°C and 30 MPa, the residual porosity varied from 0.01 to 0.14 for silica fractions of 0–0.29, whereas for the −55 to −67°C and 80 MPa case, the corresponding residual porosities were 2–10 times larger. A two‐layer model was proposed to calculate the compaction curves of ice‐silica mixtures from the curves of the corresponding pure materials. We estimated the residual porosity of small icy bodies using this two‐layer model. From our calculations, we expect that icy bodies with diameters smaller than 700 km have residual porosity larger than 0.3 when the temperature is lower than −55°C.

Effect of Nanoparticle Concentration on the Convective Deposition of Binary Suspensions

We investigate the coupling between the suspension properties and the deposition process during convective deposition of aqueous binary suspensions of 1 microm silica microspheres and 100 nm polystyrene (PS) nanoparticles. The structures formed from this rapid and scalable process have use in a variety of optical, chemical, and biochemical sensing applications. At conditions that produce a well-ordered microsphere monolayer at a silica volume fraction of 20% in the absence of nanoparticles, we examine the effect of varying the concentration of nanoparticles from 0% to 16% on the quality of the microsphere deposition and the exposure of the microspheres within the PS layer. At low concentrations of nanoparticles, the deposition results in an instability that forms stripes parallel to the receding contact line. Optimum deposition occurs between 6% and 8% PS and forms a monolayer having the same high degree of uniformity as the monodisperse suspension is fabricated. For higher concentrations, the deposition is increasingly less uniform as a result of nanoparticle depletion destabilizing the microspheres. The degree to which each microsphere is buried by the nanoparticles in the deposited thin film increases with nanoparticle concentration. This variation in coverage also suggests interplay between deposition and nanoparticle engineered properties of the suspension that influence the deposited morphology.

Viscoelastic properties of nanosilica-filled epoxy composites investigated by dynamic nanoindentation

The viscoelastic properties of the epoxy filled with silica nanoparicles have been investigated by dynamic nanoindentation and characterized by the storage modulus and loss tangent. The materials studied are neat epoxy and silica/epoxy composites with silica volume fraction of 1, 3, 6, 10, and 14 vol %, respectively. The silica nanoparticles with an average diameter of 25 nm are found to disperse homogeneously in the epoxy matrix. The effect of the particle content, force frequency, and penetration load on the viscoelastic behavior is studied and discussed. The comparison with traditional testing methods such as tension, bending, and DMTA is made. Besides, theoretical results by using micromechanics models are also obtained and compared with the experimental results. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1030–1038, 2009

Effects of Added Clay on the Properties of Freeze-Casted Composites of Silica Nanoparticles

An experimental study was performed to investigate the effects of added clay particles on the structure and properties of porous, freeze-dried composites produced from silica nanoparticles. The sol–gel transition of the silica suspension arrests the sedimentation of the dense clay platelets to produce a gel, containing large clay particles dispersed throughout. No chemical additives other than sodium chloride were needed to cause the gelation. Dry composites were obtained by subjecting the gelled suspensions to rapid freezing in one of the following ways: submersion in liquid nitrogen or liquid propane, or exposure to low-temperature refrigeration. Frozen samples were then sublimated under vacuum to remove the water. Scanning electron microscope images of the dried composites showed a porous material whose pore sizes decrease with an increasing rate of freezing. The dependence on freeze rate suggests that the porous structure is the result of ice formation. Addition of the clay particles significantly increases the rate of gel formation. Furthermore, the strength of the clay/nanoparticle composites, as measured by normal compression tests, was substantially greater than that of a similar material made with only silica nanoparticles. Finally, BET surface area analysis shows a decreasing surface area with increasing volume fraction of clay at a constant volume fraction of silica.

How Do Colloidal Aggregates Yield to Compressive Stress?

Aqueous dispersions of silica nanoparticles have been aggregated through the addition of Al13 polycations and then submitted to osmotic compression. The structures of these dispersions have been determined through small-angle neutron scattering, before and after compression. Some dispersions consisted of mixtures of aggregated and nonaggregated particles--actually a few aggregates dispersed in a "sea" of nonaggregated particles. In these dispersions, it was found that the resistance to osmotic compression originated from the ionic repulsions of the nonaggregated particles; the compression law that related the applied osmotic pressure Pi to the silica volume fraction Phi was Pi approximately [Phi/(1-Phi)]2. Other dispersions were fully aggregated, with all particles forming a fractal network that extended throughout the available volume. In these dispersions, it was found that the resistance to compression originated from surface-surface interparticle bonds. The application of low osmotic pressures (<50 kPa) resulted in compression at macroscopic scales only (>300 nm), while the structure of the network at local and mesoscopic scales was unchanged. Accordingly, few interparticle bonds were broken, and the deformation was primarily elastic. The compression law for this elastic deformation was in agreement with the predicted scaling law Pi approximately Phi4. The application of higher osmotic pressures (>50 kPa) resulted in compression at macroscopic and mesoscopic scales (30-300 nm), while the local structure was still retained. Accordingly, many more interparticle bonds were broken. The compression law for this plastic deformation was in agreement with a scaling prediction of Pi approximately Phi1.7. The location of the elastic-plastic transition indicated that the strength of the interparticle bonds was on the order of 5 times the thermal energies at ambient temperature.

Correlation Between Microstructure and Flow Behavior in Porous Sandstones

The correlation between permeability and petrographical parameters in cored samples can be used by extrapolations to predict permeability in uncored intervals. The core analysis described here is concerned with the study of fluid-rock interactions in rock samples from three sandstone reservoirs, in particular the effect of petrographical parameters on flow behavior. A positive correlation between liquid permeability and the volume fraction of silica is clearly demonstrated. Liquid permeability was correlated using multivariate regressions to one to five petrographical parameters, the results of which have useful application in the estimation of reservoir permeability where samples are not available for experimental testing.

Rheology and Microstructure of an Unentangled Polymer Nanocomposite Melt

The rheology and microstructure of 44 nm diameter silica particles suspended in unentangled polyethylene oxide (PEO) melts are studied through measurement of filled melt viscosity and X-ray scattering measurement of interparticle structure factors, S(q,ϕc), where q is the scattering vector and ϕc is the silica volume fraction. The neat polymer melts are Newtonian over the probed shear range. Filled melts have a constant viscosity at low particle concentrations and shear thin at high concentrations. At the same particle volume fraction, filled melt viscosities increase with polymer molecular weight. By defining an effective particle volume, assuming polymer adsorption adds 2.9Rg to the particle diameter, suspension viscosities of both molecular weights at all volume fractions resemble that of hard sphere suspensions. The particle osmotic compressibility and position and coherence of the first nearest neighbor shell suggest that the particles have radii larger than the core size due to polymer structuring n...

EFFECT OF STEEL FIBER ON THE MECHANICAL PROPERTIES OF CEMENT-BASED COMPOSITES CONTAINING SILICA FUME

An experimental program was carried out to evaluate the mechanical properties of cement-based composites. Test variables included water to cementitious ratio, dosage of silica fume and volume fraction of steel fiber. Compressive strength test, direct tensile strength test, splitting tensile strength test, abrasion resistance test and drop weight test were performed and the results were analyzed statistically. According to the results of this study, the designed direct tensile testing method was a suitable method to estimate the tensile strength of fiber cement-based composites. Addition of fibers provided better performance for the cement-based composites, while silica fume in the composites would help obtaining uniform fiber dispersion in the matrix and improve strength and the bonding between fiber and matrix resulting from extra dense calciumsilicate-hydrate gel. The combination of steel fibers and silica fume can greatly increase the mechanical properties of cement-based composites. Besides, a multiple regression analysis was conducted to correlate compressive strength, direct tensile strength, abrasion coefficient and impact number with w/cm ratio, silica fume content and steel fiber content and a fairly agreement between test data and estimated values was found.