Electroacoustic Spectroscopy Research Articles

Optimization of the Technique for Obtaining Selenium Nanoparticles Stabilized with Cocamidopropyl Betaine.

With the aim of optimizing the technique for the synthesis of selenium nanoparticles stabilized with cocamidopropyl betaine, a multifactorial experiment with three input parameters and three levels of variation was carried out. The selenous acid, cocamidopropyl betaine, and ascorbic acid concentrations were considered as input parameters. The output parameters were the average hydrodynamic radius of the particles (r av) and ζ-potential. Photon correlation spectroscopy analysis revealed monomodal size distribution in all the samples. It was shown that the average hydrodynamic radius is most strongly influenced by the concentrations of selenous and ascorbic acids. The minimal size of the selenium nanoparticles (r av ≤ 20 nm) is achieved at selenous acid concentration of 0.05 to 0.15 M and at ascorbic acid concentrations of 0.0332 to 0.5 M. Acoustic and electroacoustic spectroscopy examination showed that the technique proposed allows formation of both positively (ζ-potential = +29.71 mV) and negatively (ζ-potential = -2.86 mV) charged nanoparticles. It was found that the ζ-potential of the selenium nanoparticles depends very heavily on the concentrations of the stabilizer and of selenous acid. For obtaining positively charged selenium nanoparticles the selenous acid concentration should not exceed 0.15 M and the cocamidopropyl betaine concentrations should be greater than 0.12 M. Negatively charged selenium nanoparticles are formed at selenous acid concentrations above 0.15 M and at cocamidopropyl betaine concentration under 0.12 M. The micelle structure for the positively charged and negatively charged selenium nanoparticles was proposed.

Carbon nanotubes added to Portland cement pastes containing nano-silica

This study assesses the effect of size, as well as binary and ternary mixtures of three different carbon nanotubes added to Portland cement pastes containing nano-silica. Carbon nanotubes were characterized in terms of size and morphology by transmission electron microscopy, particle size distribution by laser granulometry and electroacoustic attenuation spectroscopy and specific surface area by gas adsorption. The combination of more than one characterization technique helps to identify the finer or coarser carbon nanotube suspensions. The use of low amount of carbon nanotubes and nano-silica does not affect the rheological properties of cementitious matrices. The compressive strength decreases, but flexural strength improves for the finer carbon nanotube. The microstructural analysis showed the adherence of carbon nanotubes on the surface of matrix’s particles, and the nucleation of hydration products on the surface of carbon nanotubes.

Investigation of the influence of Zinc-containing compounds on the components of the colloidal phase of milk

Abstract To solve the problem of insufficient intake of essential macro - and micronutrients into the human body, particularly in the case of the essential trace element Zinc, the possibility of enriching a socially significant product (milk) with various forms of Zinc is considered. The influence of Zinc-containing compounds on the colloidal milk system's dispersed composition and stability, photon correlation spectroscopy methods, acoustic and electroacoustic spectroscopy was established in this research. It has been shown that Zinc lysinatoriboflavinate, is a colloidal and chelated organic form of the essential trace element Zinc, having the most negligible effects on the composition and stability of the dispersed phase particles. This increases the average hydrodynamic radius of the dispersed phase by 5% and the ζ-potential by 10%. A quantum-chemical simulation of the interaction of milk κ-casein sites with various forms of the essential trace element Zinc in the QChem program was performed using the IQmol molecular editor. The mechanism of action of various forms of Zinc on the components of the dispersed system of milk, in particular milk protein (casein), is suggested.

Powder grinding and nano-particle sizing: Sound, light and enlightenment

In this work, a sub-micron quartz powder produced by high energy grinding was used to explore the information contained in the particle size distribution (PSD) curves obtained by electro-acoustic spectroscopy (EAS) and dynamic light scattering (DLS). Results show that although the customarily volume-based PSD curve and its median value (d50 = 135 nm) are more amenable to differences in measurement phenomena and sample preparation methods, the area and number-based representations are more sensitive to the presence of finer particles (35 and 65 nm, respectively for the number and area-based curves obtained by EAS). These values were supported by the crystallite size calculated from X-ray diffraction (d = 44 nm) and the equivalent spherical diameter calculated from specific surface area measurements (d = 43 nm). Thus, a reliable description of the particle size of a powder requires the use of complementary techniques, suggested by the envisioned application or the particular stringency of a given processing step.

Electroacoustic characterization of trimmed hairy nanocelluloses

ObjectiveA cellulose-derived nano-toolbox has been developed via the chemical nano-trimming of electrosterically stabilized nanocrystalline celluloses (ENCCs). ENCC is a member of the class of hairy nanocellulose (HNC). The objective of this study is to determine the properties of chemically trimmed HNCs in order to establish whether or not they overcome the surface chemistry and size restrictions of conventional nanocelluloses. The newly “so-called crew-cut ENCCs” emerged by this approach address many technological and environmental challenges in colloidal systems, i.e., drug delivery, anti-scaling and self-assembly. Despite the importance of the crew-cut species, little is known about the systematic changes and the underlying mechanisms of the trimming of their hairs (the chains protruding from both ends of the cylindrical core). ExperimentsTo quantify the effect of the hair trimming on the charge density as well as the kinetics of this process, the carboxylic acid content is determined by conductometric titration as a function of time and reaction conditions. We use electro-acoustic spectroscopy to elucidate the differences in colloidal properties of various crew-cut ENCCs. We focus on the interplay between the time of the acid-catalyzed hydrolysis reaction and tunable parameters, such as size and surface electric charge of ENCC, as well as their microrheological behavior. FindingsWe show that a range of hairy ENCCs with various sizes and charge densities is easily obtained by taking advantages of the preferential hydrolysis of the amorphous chains protruding from both ends of the nanocrystals. The trimming mediated by a HCl-catalyzed hydrolysis is initially very fast, but slows down subsequently. The formation of crew-cut species with a smaller particle size and zeta potential was electro-acoustically verified by increasing the reaction time. The longitudinal viscosities of the trimmed ENCC suspensions also decreased with prolonging the reaction time. This research shows how manipulating HNCs enables both scientists and technologists to access a collection of nanocrystals with desired colloidal properties, based on the most abundant biopolymer in the world.

A zeta potential and rheology study using electroacoustic spectroscopy on aqueous boron carbide suspensions

The zeta (ζ) potential of moderately concentrated (at 15 vol%) boron carbide (B4C) suspensions were characterised using electroacoustic spectroscopy. This technique has been validated for use in this application by correlating the ζ-potential to the suspension viscosity (at 30 vol%) across a range of pH values. Zeta potential has been shown to be effective in determining differences in B4C powders, reported to be nominally of the same specification in terms of particle size distribution and X-ray diffraction data. The isoelectric (IEP) points for three different as-received B4C powders were found to be 4, 7 and less than 2.5. The study showed that differences in ζ-potential across the powders can be minimised via heat treatment, which produced suspensions all with an IEP below 2.5. The study also established the effect of an anionic and a cationic dispersant on ζ-potential and rheology, demonstrating that excess dispersant from a ζ-potential perspective was required to obtain the lowest viscosity. The study concluded that as-received B4C powders most likely contain contaminants of a cationic nature and that electroacoustic spectroscopy is a useful tool in determining their behaviour in aqueous suspensions.

Nanoparticle Coupling to Hydrogel Networks: New Insights from Electroacoustic Spectroscopy

Nanoparticle–hydrogel interactions are important in many applications. In drug delivery, for example, these control the release rate and may prevent nanoparticle (NP) migration from a targeted site. In this paper, electroacoustic spectroscopy is used to study the NP–hydrogel interaction, focusing on the influence of polymer adsorption and hydrogel composition. Electroacoustic spectroscopy is a powerful noninvasive tool to complement microrheological characterization. We study the interaction of polyacrylamide (PA) with laponite and silica NPs as model systems with strong and weak attraction, respectively. Stronger adsorption of PA on laponite compared to silica imparts distinctly different rheological properties to PA solutions and decreases the laponite mobility significantly more than silica when embedded in PA hydrogels. However, the mobilities of both NPs exhibit qualitatively similar variations with acrylamide and chemical cross-linker concentrations, as indicated by viscoelastic and electrokinetic c...

Acoustic and electroacoustic spectroscopic determination of the critical coagulation concentration for the aggregation of fumed silica

Acoustic and electroacoustic spectroscopy were use to model varying concentrations of NH4Cl in a 25 wt% fumed silica suspension for interpretation and visualization of the critical coagulation concentration (CCC) needed to induce coagulation of the suspension. The acoustic data indicates a range for the CCC that agrees with Derjaguin and Landau, Verwey and Overbeek theory and experimental results found in literature. The electroacoustic data suggest a power law relationship between NH4Cl concentration and changes in the colloidal vibrational current, and predicts that 0.4M is the CCC for NH4Cl in a fumed silica suspension.

Effect of carbonate precursor synthesis conditions on the formation of monodisperse Nd:YAG nanopowders

Using electroacoustic spectroscopy and X-ray diffraction, we have studied the formation of monodisperse Y3Al5O12:Nd3+ doped garnet nanopowders (1 at % Nd) from carbonate precursors in the form of a system of two basic carbonates, Y(OH)CO3 · nH2O and NH4Al(OH)2CO3, in amorphous and crystalline states. The results demonstrate that monodisperse YAG nanopowders can be obtained from weakly agglomerated carbonate precursors with a nearly unimodal size distribution of particle conglomerates, produced by chemical precipitation from a dilute (0.15 M Al3+) aqueous chloride solution with ammonium bicarbonate and subsequent aging of the precipitate at room temperature and pH 7.86–7.89. The zeta potential of the disperse system for the carbonate precipitate suspension in its dynamic equilibrium is 4.3 ± 0.5 mV at an average nanoparticle conglomerate size of 165 ± 5 nm. After heat treatment of the carbonate precursors at temperatures from 1100 to 1200°C, we obtained single-phase Nd:YAG doped garnet nanopowders. The cubic cell parameter a of the Nd:YAG varies from 1.2022 to 1.2025 nm, depending on the synthesis temperature, and its crystallite size varies from 35 to 50 nm.

Electroacoustic Spectroscopy of Nanoparticle-Doped Hydrogels

This paper probes the nanoparticle (NP) interaction with hydrogels using electroacoustic spectroscopy at MHz frequencies. We measured dynamic electrophoretic mobility spectra of silica NPs in polyacrylamide gels for a variety of NP sizes and gel concentrations. The spectra are exquisitely sensitive to NP entrapment, size, and charge as well as to gel rheology and gelation kinetics. For NPs that are large compared to the gel mesh size, many of these influences can be quantified using electrokinetic theory, which furnishes the apparent NP ζ-potential and a complex gel shear modulus at MHz frequencies. The methodology provides new insights into the NP–hydrogel interaction, since it noninvasively probes the nanostructure and the combined influences of particle and gel properties. Electroacoustic spectroscopy may therefore be a valuable new tool for characterizing soft nanocomposites—one that complements other noninvasive methods, such as bulk rheometry and microrheology.

Measuring zeta potential of protein nano-particles using electroacoustics

Electroacoustic spectroscopy offers a simple way for measuring the zeta potential of proteins in physiological solutions with high ionic strength. Ultrasound as a driving force does not generate the heat effects which complicate traditional electrophoretic measurements at high ionic strength. In addition, measurements can be conducted with concentrated protein dispersions without dilution, as is required by electrophoretic methods. This paper presents results for electroacoustic measurements of 5wt.% bovine serum albumin suspended in aqueous solutions. In these suspensions the proteins are not completely dissolved; they form nano-particles with a median size of about 180nm. We studied the dependence of zeta potential on ionic strength within a wide range of salt molarities, up to as high as 0.5mol/L. Dialysis was used for performing measurements at lower ionic strength range. We also conducted pH titrations of this system and titrations with Ca2+ ions. Our results agree well with published data for samples where such data is available.

Investigation of surface modification of rutile TiO2 nanoparticles with SiO2/Al2O3 on the properties of polyacrylic composite coating

Surface modification and characterization of TiO2 nanoparticles as an additive in a polyacrylic clear coating were investigated. For the improvement of nanoparticles dispersion and the decreasing of photocatalytic activity, the surface of nanoparticles was modified with binary SiO2/Al2O3. The surface treatment of TiO2 nanoparticles was characterized with FTIR. Microstructural analysis was done by AFM. The size, particle size distribution and zeta potential of TiO2 nanoparticles in water dispersion was measured by DLS method. For the evaluation of particle size and the stability of nanoparticles in water dispersions with higher solid content the electroacoustic spectroscopy was made. To determine the applicability and evaluate the transmittance of the nano-TiO2 composite coatings UV–VIS spectroscopy in the wavelength range of 200–800nm was employed. The results showed that surface treatment of TiO2 nanoparticles with SiO2/Al2O3 improves nanoparticles dispersion and UV protection of the clear polyacrylic composite coating.

Investigation of colloidal properties of modified silicone polymers emulsified by non-ionic surfactants

Functionalized silicones are a unique class of hybrid materials due to their simultaneous hydrophobic–oleophobic properties, which results in applications in a variety of surface modification techniques. Prior research has shown that changes in surface charge and turbidity of modified silicone emulsions as a function of pH have a marked effect on their performance in coating applications. The emulsion droplet size is also believed to play significant role in such coating applications. In this work, modified silicone polymer emulsions stabilized by non-ionic surfactants were studied using dynamic light scattering (dilute) and electroacoustic (concentrated) spectroscopy to monitor the emulsion droplet size. The dilute and concentrated regime studies showed the emulsion droplet to be in nanometer range with no appreciable change in size as a function of pH. Electroacoustic studies showed a small fraction of droplets to be present in the micron size range. The emulsions were examined using Cryo-TEM technique, and the effect of pH and dilution on hydrophobicity of nanodomains was studied by employing fluorescence spectroscopy. It is shown from pyrene excimer behavior that both the dilution and pH have an effect on emulsion stability with a presence of critical surfactant concentration after which the emulsion was destabilized. It is proposed that the emulsion stability characteristics and the particle size distribution both play a significant role in their ability to impart desired macro and nano surface properties to treated substrates through electrostatic interactions and selective binding.

Studying homogeneity and zeta potential of membranes using electroacoustics

Abstract The goal of this paper is to show that electroacoustic spectroscopy can be used as a viable means for characterizing membranes. A novel set-up was designed for performing these experiments with a standard electroacoustic zeta potential probe typically used for measuring ζ-potential in concentrated dispersions. Calculation of zeta (ζ) potential from the measured signal was performed with a newly derived electroacoustic theory that takes into account overlap of double layers in the membrane pores (nano-filtration membrane NF 270 manufactured by Dow Chemicals). Several titrations were performed: two salt titrations with potassium chloride and copper sulfate, and pH titration in several solutions of KCl. In all these experiments, changes in ionic environment caused changes in the ζ-potential within the pores of the membrane, as was measured by changes in electroacoustic current. In all cases the results were consistent with theoretical expectations based on prior research and knowledge of ion effects on ζ-potential. Lastly, differences in electroacoustic signal from one area of the membrane to the next (all of the same material) shed some light into the homogeneity of the membrane itself.

Changes in Colloidal Properties of Oil in Water Emulsions Stabilized with Sodium Caseinate Observed by Acoustic and Electroacoustic Spectroscopy

Sodium caseinate is a commonly used emulsifier in foods, as it adsorbs on the surface of oil droplets and stabilizes them via electrostatic and steric stabilization, forming a polyelectrolyte layer at the interface. Since the protein interface is affected by varying environmental conditions such as pH, ionic strength, concentration of unadsorbed polymers, these emulsions are prone to a variety of destabilization mechanisms. The objective of the present work was to observe the destabilization of sodium caseinate stabilized oil in water emulsions using electroacoustic spectroscopy. This technique can be utilized for the characterization of concentrated colloidal systems in situ, without dilution. The electroacoustic and ultrasonic properties of soy oil in water emulsions were determined for sodium caseinate stabilized emulsions under conditions known to cause destabilization. Ultrasonic attenuation and electrophoretic mobility (ζ-potential) could clearly follow the changes occurring in the emulsion droplets, under minimal sample disruption. This is critical for these systems in a very fragile, metastable state. The emulsions were stable to the addition of high methoxyl pectin (HMP) up to 0.1% HMP. Addition of free sodium caseinate induced depletion flocculation, causing a decrease in the attenuation and electrophoretic mobility measured. The presence of HMP limited depletion interactions. Acidification of the emulsion droplets resulted in a clear sol–gel transition, as shown by a steep increase in the particle size and a decrease in attenuation. Again, destabilization was limited by HMP addition. It was concluded that ultrasonics and electroacoustics are suitable techniques to understand the details of the destabilization processes occurring to food emulsions, measured in situ.

Effect of the molecular weight on the physicochemical properties of poly(lactic acid) nanoparticles and on the amount of ovalbumin adsorption

Poly(lactic acid) (PLA) nanoparticles were prepared to be used as potential platform for vaccine systems. Commercial high molecular weight PLA (PLAHMW) with Mw 1.5 × 105 and low molecular weight poly(lactic acid) (PLALMW) with Mw 9.3 × 103 were obtained by direct polycondensation from D,L lactic acid and used to prepare nanoparticles by solvent displacement method. The effect of the molecular weight on the physicochemical properties of the polymers, on the nanoparticles dispersions and the amount of ovalbumin (OVA) adsorption was studied. The PLAHMW and PLALMW were characterized by Fourier transformed infrared spectroscopy (FTIR), thermogravimetrical analysis (TGA), modulated temperature differential scanning calorimetry (MTDSC) and gel permeation chromatography (GPC). The particle size distribution and ζ-potential of the obtained dispersions were measured by dynamic light scattering (DLS) and electroacoustic spectroscopy, respectively. The ovalbumin adsorption on nanoparticles was evaluated by the Bradford method. PLALMW dispersion showed lower ζ-potential values and larger sizes compared to PLAHMW dispersion. A minor OVA adsorption was achieved for PLALMW.

Probing the colloidal properties of skim milk using acoustic and electroacoustic spectroscopy. Effect of concentration, heating and acidification

In colloidal systems physical-chemical changes are often a function of volume fraction and sample dilutions are critical. While most methods to characterize colloidal particles either require dilution or some disruption, acoustic spectroscopy can be performed in situ, without dilution. Objective of this work was to determine the effects of concentration, heating and acidification on the acoustic and electroacoustic properties of casein micelles in skim milk. The ultrasonic attenuation of skim milk increased with concentration of milk and frequency, and the average size of the colloidal particles calculated from the frequency dependence of attenuation was about 0.15 μm for both unheated and heated milk. When milk was concentrated by ultrafiltration, at 3× and 4× concentration (based on volume reduction), the calculated size deviated from that derived in undiluted or mildly concentrated milk, most likely because of increased particle-particle interactions. Electroacoustic measurements revealed a constant dynamic mobility of the particles in undiluted and concentrated milk, while lower mobilities were observed for milk diluted in permeate. The ζ-potential measured was significantly higher than the values measured using dynamic light scattering, with a value of -45.8 mV for casein micelles in unheated milk. With acidification, the ζ-potential decreased monotonically. Heating profoundly affected the change in charge with pH of the micelles, and it was concluded that the interaction of casein micelles with the whey proteins increased the surface charge of the casein micelles.

Electroacoustic and Acoustic Attenuation Spectroscopy as New Tools for In Situ-Monitoring of Metal Oxide Precursor Preparation in Liquid Phase

The in situ-monitoring of a solid synthesis was realised by electroacoustic and acoustic attenuation spectroscopy. These techniques were applied to track the crystal growth of alumina precursor nanoparticles used as model compound. A commercially available set-up with a circular flow detector cell for joint electroacoustic and attenuation measurements was used. Course of zeta potential as well as particle growth was measured during continuous hydrolysis of dry Al-sec-butoxide in isopropanol. Zeta potential shows minima and maxima with increasing water amount, whereas particles start to grow significantly after a defined time of operation. In some experiments the synthesis was stopped ahead of time and the formed solids were additionally studied ex situ by characterisation methods such as solid-state NMR or transmission electron microscopy. Measured ultrasound data can be correlated to elemental processes during particle formation. First experiments on monitoring of synthesis scale-up show potential for future application of this technique.

Acoustic and Electroacoustic Spectroscopy of Water-in-Diluted-Bitumen Emulsions

Water-in-oil emulsions of Athabasca bitumen diluted with toluene have been studied using the latest advances in acoustic and electroacoustic spectroscopy. From the sound attenuation spectra of emulsions, the water droplet size distribution is measured. The electrical surface charge density of the water droplets is obtained from the colloid vibration current. In the case of freshly prepared water-in-oil emulsions, the droplet size increased while the surface charge density decreased with time. The time-dependent relaxation of the surface charge ranges from several hours to 3 days, and it is probably due to the slow adsorption/desorption kinetics of bituminous components at the water-oil interface. This study illuminates the contribution of the electrostatic interactions to the stability of water-in-oil emulsions.

Characterizing Clay Mineral Suspensions using Acoustic and Electroacoustic Spectroscopy — A Review

AbstractRecently, significant advances have been made in the theory and application of acoustic and electroacoustic spectroscopies for measuring the particle-size distribution (PSD) and zeta potential (ζ potential) of colloidal suspensions, respectively. These techniques extend or replace other techniques, such as light-scattering methods, particularly in concentrated suspensions. In this review, we summarize acoustic and electroacoustic theory and published results on clay mineral suspensions, detail theoretical constraints, and indicate potential applications for the study of environmentally significant clay mineral suspensions. Using commercially available instrumentation and suspension concentrations up to 45 vol.%, acoustic spectroscopy can characterize particle sizes from 10 nm to 10 µm, or greater. Electroacoustic spectroscopy can determine the ζ potential of a suspension with a precision and accuracy in the mV range. Despite the clear potential for their use in environmental settings, to date, acoustic methods have been used mainly on clay mineral colloids with industrial application, typically combined with similar measurements such as isoelectric point (IEP) determined from shear yield stress or ζ potential from electrophoretic mobility measurements. Potential applications in environmentally relevant suspension concentrations are significant, as PSD and ζ potential are important factors influencing the transport of mineral colloids and associated contaminants through porous media. Applications include determining the effects of suspension concentration, surfactants, electrolyte strength, pH and solution composition on soil clay properties and colloidal interactions, and determining changes in PSD, aggregation and ζ potential due to adsorption or variations in the clay mineralogy.