Rheological responses of the gelled (G) Snowtex 20 silica suspensions in the presence of LiCl, NaCl, and KCl have been investigated as functions of concentrations of silica and salt at pH 9.8 in terms of the Hofmeister series effect. The primary silica particle is isolated, and it is coagulated to form a gel above at 0.1, 0.3, and 0.5 M concentrations of LiCl, NaCl, and KCl, respectively, when the silica volume fraction φ is beyond 1.0%. The resulting G silica suspensions are classified into a strong‐link gel and their power‐law dependences of the critical strain as well as the storage modulus on the silica volume fraction were compared with the predictions by the fractal gel model. The resulting power‐law exponents of the critical strain are negative, this is in agreement with that predicted by the fractal model, and their magnitudes decrease with an increase in salt concentration, irrespective of the salt. Moreover, the magnitude of the power‐law exponent for the critical strain is well related to the Hofmeister series effect, namely it decreases in the order Li+, Na+, and K+, and the least hydrated K+ adsorbs in great enough in amount to create a less flexible network structure in the G silica suspension due to stronger attraction between the silica particles. Moreover, the stronger attraction, on the other hand, should be responsible for both the larger storage modulus and the higher power‐law exponent of the silica volume fraction dependence on the storage modulus. Therefore, the Hofmeister series effect is useful to understand the rheological properties of the G Snowtex 20 silica suspensions. 相似文献
Feasibility studies directed at the parallel increase in the elastic modulus and impact toughness of polypropylene via introduction of ultradispersed CaCO3 particles with sizes of 100 (Socal U1S2) and 60 nm (Socal 312V) have been performed. The effects of the content and sizes of CaCO3 particles and the nature of a surfactant on the character of distribution of particles, the thermophysical characteristics of the polymer matrix, and the mechanical characteristics and heat resistance of the nanocomposites are analyzed. Microscopic studies reveal that nanoparticles show a tendency toward structuring. DSC studies have proved the nucleating action of ultrafine particles during the crystallization of PP. For the composites containing 15 vol % of Socal 312V CaCO3 nanoparticles, the increase in the tensile elastic modulus achieves its maximum; depending on the nature of the surfactant, the reinforcing effect increases by 70-40%. As compared to the initial PP, the presence of ultrafine particles in the composites prevents a decrease in the storage modulus of PP with increasing temperature from 0 to 50°C; as a result, the reinforcing effect increases from 30-40% at temperatures below the glass transition temperature to 40–75% at 50°C. For the nanocomposites with U1S2 in the presence of Triton X-100 or fluorinated alcohol telomer, the impact toughness increases over the entire filler content interval; when the filler concentration is 15 vol %, the impact toughness of nanocomposites is higher than that of the initial PP by factors of 3 and 4.5, respectively. It has been found that nanocomposites containing 5 vol % CaCO3 nanoparticles show the effect of thermal stabilization, which comes up to about 50°C. 相似文献
Fluoro-aramid-based sol/gel-derived nanocomposites were synthesized by condensing a mixture of 4,4′-(hexafluoro-isopropylidene)dianiline
and 1,3-phenylenediamine with terephthaloylchloride (TPC) in dimethylacetamide. TPC was added in slight excess to produce
amide chains with carbonyl chloride end groups and then replaced with alkoxy groups using aminophenyltrimethoxysilane to develop
bonding with the silica network. Mechanical, dynamic mechanical thermal, water absorption and morphological measurements were
carried out on the thin hybrid films. Increase in the tensile strength and modulus was observed as compared to pristine polyamide.
The thermal decomposition temperature was found in the range of 400–500 °C. The water absorption was found to be reduced with
higher silica content. The glass transition temperature and the storage moduli increased with increasing silica concentration.
The maximum increase in the Tg value (345 °C) was observed with 20 wt% silica. Scanning electron microscopy revealed the uniform distribution of silica
in the matrix with an average particle size ranging from 8 to 50 nm. 相似文献
The conservation of historic sculptures is receiving growing attention because of the increasing air pollution. A hydrophobic silica coating was synthesized to protect historic sculptures from weathering by starting from a solution of tetraethoxyorthosilicate (TEOS) precursor using hexadecyltrimethoxysilane (HDTMS) as hydrophobic modifier in the presence of ammonia as a catalyst. The molar ratio of ethanol, TEOS, H2O and NH4OH was kept constant at 8:0.045:3:2.8 and the molar ratio of HDTMS/TEOS (M) was varied from 0 to 0.458. The organic modification was confirmed by infrared spectroscopic studies, and the hydrophobicity of the coating was tested by the contact angle measurements. The stone surface morphology of sample treated with silica coating was characterized. The results showed that the nanocomposites were composed of spherical particles with grain size of about 190 nm in diameter. After the limestone's surface was modified, the contact angle of limestone increased from 20° to 100° for M0.458. The protective performance evaluated with its ability to resist acid rain reveals that the protective effects are satisfying. 相似文献
The effect of preparation pH of silica hydrogel on the effective diffusion coefficient of protons in silica hydrogel (De, m2/s), on surface area of silica gel (S, m2/s) and on particle size of silica gel (Dp, 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. 相似文献
A three‐dimensional DNA hydrogel was generated by self‐assembly of short linear double‐stranded DNA (dsDNA) building blocks equipped with sticky ends. The resulting DNA hydrogel is thermoresponsive and the length of the supramolecular dsDNA structures varies with temperature. The average diffusion coefficients of the supramolecular dsDNA structures formed by self‐assembly were determined by diffusion‐ordered NMR spectroscopy (DOSY NMR) for temperatures higher than 60 °C. Temperature‐dependent rheological measurements revealed a gel point of 42±1 °C. Below this temperature, the resulting material behaved as a true gel of high viscosity with values for the storage modulus G′ being significantly larger than that for the loss modulus G′′. Frequency‐dependent rheological measurements at 20 °C revealed a mesh size (ξ) of 15 nm. AFM analysis of the diluted hydrogel in the dry state showed densely packed structures of entangled chains, which are also expected to contain multiple interlocked rings and catenanes. 相似文献
Bacterial cellulose (BC) hydrated membranes present nanometric reticulated structure that can be used as a template in the
preparation of new organic–inorganic hybrids. BC–silica hybrids were prepared from BC membranes and tetraethoxysilane, (TEOS)
at neutral pH conditions at room temperature. Macroscopically homogeneous membranes were obtained containing up to 66 wt.%
of silica spheres, 20–30 nm diameter. Scanning electron micrographs clearly show the silica spheres attached to cellulose
microfibrils. By removing the cellulose, the silica spheres can be easily recovered. The new hybrids are stable up to 300 °C
and display a broad emission band under UV excitation assigned to oxygen-related defects at the silica particles surface.
Emission color can be tuned by changing the excitation wavelength. 相似文献
Bacterial cellulose (BC) is a new biomaterial which has wide application potential in various industries. BC industrialization
requires bacterial strains with high BC productivity. The objective of this study is to increase the BC yield of a Gluconoacetobacter xylinus strain through mutagenesis induced by high hydrostatic pressure (HHP) treatment. In this study, the parental strain in its
exponential phase was treated at 250 MPa and 25 °C for 15 min to induce mutagenesis using a HHP machine. The HHP-treated strains
were incubated in glucose agar plate at 30 °C for 4 days. After the incubation, 50 larger colonies in these plates were randomly
selected and cultivated to produce BC membrane in a tailor-made glass vessel, and wet weights of the BC membranes were tested.
Compared with the parental strain, 29 mutants showed higher BC yields, of which eight mutants with BC yield >130.00 g/L were
initially screened and were then cultivated for five generations to test their genetic stabilities for BC production. Among
the eight mutants, M438, a mutant which showed the highest average BC yield (158.56 g/L) and lowest coefficient of variation (2.4%) for five generations,
was finally screened as objective mutant. HHP treatment can serve as an effective method to cause mutagenesis in BC-producing
bacteria. The HHP-treated strains with significantly higher BC yield than parental strain can be screened from the HHP-induced
mutants. 相似文献
Summary: Epoxy nanocomposites containing rod‐like silicate (attapulgite) were prepared using a simple organic modification to the nanorods. The modification led to effective interfacial adhesion between the ceramic nanorods and the epoxy resin and hence good load transfer. Scanning electron microscopy examination revealed a uniform dispersion of nanorods in the epoxy resin. Compared to the neat resin, nanocomposites with 7.47 vol.‐% nanorods exhibited an increase in the (rubbery state) storage modulus of 122.5%. In addition, the nanocomposites exhibited improved dimensional stability both above and below the Tg.
Storage modulus of the neat resin and nanocomposites. 相似文献
Effects of pH on mechanical properties as well as morphological studies of sol–gel derived in situ silica in polyvinyl chloride-50%
epoxidized natural rubber (PVC-ENR50) nanocomposites are reported. In particular, a range of acid concentrations was investigated.
These nanocomposites were prepared by solution casting technique and tetraethoxysilane (TEOS) was used as the silica precursor.
The prepared nanocomposites were characterized using tensile test, scanning electron microscopy (SEM) and transmission electron
microscopy (TEM). The tensile test indicated that the highest mechanical strength was at 30% TEOS added for the nanocomposite
prepared at pH 2.0. At pH 1.0 and 1.5 the maximum tensile strength reading was at 20% TEOS added with value of 24.3 and 24.5 MPa,
respectively. SEM and TEM revealed the dispersion of silica particles in the polymer matrix. For nanocomposites prepared at
pH 1.0 and 1.5, the silica particles were finely dispersed with the average size of 60 nm until 20% TEOS added. Meanwhile
for nanocomposite prepared at pH 2.0, silica particles were homogenously distributed in the polymer matrix with average diameter
of 30 nm until 30% TEOS and agglomerated after 30% TEOS loading. 相似文献
A hydrogel nanocomposite was designed, synthesized, and evaluated for use as an auto-focusing intra-ocular lens. The hydrogel scaffold was composed of a monomer-free, thiol that contained polyacrylamide (5%), which was allowed to gel in the presence of nanoparticles at pH 7.4, 25°C. The nanoparticles consisted of a proteo-mimetic polyacrylamide nanogel (∼42 nm), bovine serum albumin (BSA) (∼6 nm), and hydrophilized silica (∼3 nm). The extent of nanoparticle loading increased with decreasing particle size. The elastic modulus increased with increasing loading of the proteo-mimetic nanogels and BSA, and it decreased with hydrophilized silica. In this investigation, the hydrogel that contained silica was the most promising class of nanocomposite hydrogels with properties comparable to that of a young porcine lens. A nanocomposite that consisted of 10% hydrogel scaffold and 24% hydrophilized silica (elastic [E] modulus of ∼1.0 kPa and refractive index [RI] of 1.42) was injected into a pre-evacuated porcine lens capsular bag. The composite lens was evaluated in a custom-designed four-arm radial stretcher, and its force-time spectrum was characterized by time constants of 60 ± 8.9 and 800 ± 32 ms. These results were comparable to a young porcine lens (E Modulus of 1.2 kPa; RI of 1.4105; time constants of 48.3 ± 0.58 and 668 ± 24.6 ms, respectively) 相似文献
Bacterial cellulose (BC) is a biocompatible biopolymer synthesized by Gluconacetobacter xylinus. In this study, BC was oxidized and aminated to produce hydrogels for biomedical applications, and the products were characterized. A carboxyl (pKa of 3.9 ± 0.1) content of 1.13 ± 0.02 mmol/g was obtained with the TEMPO-catalyzed oxidation. Epichlorohydrin-mediated amination introduced amine groups (pKa of 11.0 ± 0.1) up to 1.74 ± 0.06 mmol/g. The oxidation of BC caused a decrease in its ζ-potential to ?103 ± 6 mV, and amination increased the ζ-potential to ?4 ± 6 mV. The fibre diameter decreased after both reactions. The high absolute value of the ζ-potential for oxidized BC led to superior colloidal stability in water, and a 390 % increase in water retention. The oxidized BC hydrogel was also found to increase in water retention fivefold from pH 1 to 7, making it a smart hydrogel. The cationic and anionic BC hydrogels described here could be used for several biomedical applications, including self-assembling drug delivery devices. 相似文献