Silica Particles Of Different Sizes Research Articles

Stabilization of aerated sugar particle systems at high sugar particle concentrations

We report on the stability of aerated sugar dispersions containing a high concentration of sugar particles and low air phase volume with a composition typical of fondant confectionery. The main instability mechanisms are creaming of the air phase and sedimentation of the solid continuous phase. The influences of particle concentration, mean particle size and the type of particles (sugar/silica) on quiescent storage stability have been investigated. It has been found that finer particles give a lower particle settling rate and a greater sediment volume due to more attractive particle–particle interactions. The creaming behaviour is mainly affected by the concentration-dependent viscosity of the dispersion, the particle settling rate, and the time-dependent network formation at high solid concentrations. Stability differences between systems containing sugar particles and silica particles of different sizes can be attributed to differences in densities and shapes of the two kinds of particles. The minimum sugar particle concentration required for creaming stability has been estimated from the apparent yield stress of the system, the measured bubble sizes, and the density differences between the gaseous and continuous phases. Due to time-dependent network formation of sugar aggregates during ageing, the sugar particle concentration required for long-term stability is lower than that estimated on the basis of the initially measured apparent yield stress.

Heterodimeric particle assemblies: Preparation of anisotropically connected spherical silica particles via surface-bound gold nanoparticles

Assemblies of heterodimeric particles were prepared through selective coupling of two kinds of spherical silica particles of different sizes by connection with gold nanoparticles attached anisotropically to the particles.

Molecularly imprinted polymer films grafted from porous or nonporous silica: novel affinity stationary phases in capillary electrochromatography.

Molecularly imprinted composite materials were evaluated as chiral stationary phases in capillary electrochromatography (CEC). These consisted of spherical silica particles of different sizes and of different porosities, containing a surface-immobilized layer of molecularly imprinted polymer (MIP) targeted to bind L-phenylalanine anilide. Fused silica capillaries were packed over a length of 8.5 cm, using a pneumate amplification pump, and the stationary phase thus obtained was tested with respect to its electrochromatographic performance. The electroendosmotic flow (EOF) mobility was evaluated with respect to the content of grafted polymer, as well as the ionic strength and the acetonitrile content of the electrolyte. Moreover, the influence of the layer thickness and of the stationary phase porosity on the performance and on the sample load capacity was investigated. The packings exhibited different relative efficiencies for the two enantiomers. The results were discussed in terms of differencies in accessibility to the binding sites of the packings and of the mechanism of EOF generation. In the wide context of the different approaches so far proposed for MIP stationary phases in CEC, these materials can be a good alternative, worthy of further development and application, not restricted to chiral separations.

Formation and Structure of Polyelectrolyte and Nanoparticle Multilayers: Effect of Particle Characteristics

The formation and structure of multilayer films containing a cationic polyelectrolyte and anionic silica nanoparticles were studied by means of ellipsometry and atomic force microscopy. Three types of silica particles of different sizes were examined. The density and thickness of the films as well as the adsorption kinetics appear to be strongly dependent on the choice of particle; smaller particles favor the formation of smooth and dense films with a higher content of the inorganic component.

Thermoresponsive properties of porous poly(N‐isopropylacrylamide) hydrogels prepared in the presence of nanosized silica particles and subsequent acid treatment

AbstractPorous poly(N‐isopropylacrylamide) hydrogels were prepared by the free‐radical polymerization of its monomer and a suitable crosslinker in the presence of spherical silica particles of different sizes (74 and 1600 nm) and by the subsequent acid extraction of silica. The yields were 81–83%, and the yields were not affected by the silica content. Scanning electron microscopy observations revealed the porous structure of the hydrogels. Porous and nonporous hydrogels showed volume phase transitions from swelling states to deswelling states at approximately 30 °C, as analyzed by the ratio of the diameter of cylinder‐shaped hydrogels to that of the glass tube used for the hydrogel preparation at the corresponding temperature. Deswelling, which was analyzed by rapid changes in the temperature of the aqueous media from 20 to 40 °C, was facilitated by decreased silica particle size and increased silica content. The deswelling rate constant of the hydrogel prepared with 74‐nm silica at 10 v/v % (silica/solvent) was more than 1500 times greater than that of conventional hydrogels. Swelling was similarly analyzed through changes in the temperature from 40 to 20 °C and was independent of the pore structure. The deswelling–swelling cycle was repeatable with reasonable reproducibility. Moreover, the mechanical strength of the porous hydrogels was significantly maintained compared with that of conventional nonporous hydrogels. This method produced thermoresponsive hydrogels of suitable mechanical strength and remarkable deswelling properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4228–4235, 2002

An Analytic Expression for the Particle Size Dependence of the Surface Acidity of Colloidal Silica

The charge formation on colloidal silica particles in aqueous solutions is described as a dissociation of acid silanol groups. For the relationship between surface charge density and surface potential on spherical particles an approximate solution of the spherical Poisson-Boltzmann equation, given by Ohshima et al., is used. An analytic equation describing the dependence of the apparent acid constant, K app S, on the degree of dissociation of surface silanol groups is derived, as is an analytic expression for calculating surface charge density-pH presentation. Surface charge density measurements on spherical silica particles of different sizes in aqueous 1-1 electrolyte solutions of different ionic strength are carried out using potentiometric titration.

Effect of particle size and modulation frequency on the photoacoustic spectra of silica powders

Investigations of the infrared spectra of crystalline and amorphous silica particles of different sizes (0.05, 5, 10, 15, 30, 45, and 260 μm) in the range of 400-4000 cm -1 using Fourier transform infrared/photoacoustic spectroscopy are reported. The change in the intensity I of the signal with porosity ∈ of powders follows the ∈/(1-∈) dependence for strong bands and ∈ dependence for weaker bands are predicted by the theory of McGovern et al. For strong bands, I also follows the empirical relation I∼D -n , where D is the particle diameter in cm and n=0.34-0.42