Stearic Acid Particles Research Articles

Factors influencing the low-temperature fluidity of kerosene-based magnetic fluid: Surfactant, volume fraction

To explore the effect factors on the fluidity of magnetic fluid at low temperatures, the magnetic fluid was prepared by dispersing stearic acid and oleic acid-modified particles into kerosene, the effect of volume fraction was also considered. The microstructure and morphology of the particles were obtained by XRD and TEM, and the surfactant content on the surface of the particles was determined by TG. The hysteresis loops of magnetic particles and magnetic fluids were obtained by VSM. As the temperature decreased, it was observed that the magnetic fluid with a high volume fraction of stearic acid-modified particles would lose fluidity quickly under a non-magnetic field. But it could respond to a certain magnetic field, and the fluidity could be restored quickly by increasing the temperature. The rheometer measured the viscosity of the magnetic fluid-dependent temperature, shear rate, and magnetic field. When a high melting point of stearic acid coated particles, the stearic acid with adequate chain length could affect the fluidity of magnetic fluid with a volume fraction greater than 5% at roughly 20 °C. The free surfactant formed micelle, the base carrier was restricted in the particles adhering to the micelles, eventually causing the magnetic fluid to lose fluidity.

Photo/Thermo Dual Stimulus-Responsive Liquid Marbles Stabilized with Polypyrrole-Coated Stearic Acid Particles.

In this study, we report on the fabrication of photo/thermo dual stimulus-responsive liquid marbles (LMs) that can be disrupted by light irradiation and/or heating. To stabilize the LMs, we synthesized micrometer-sized stearic acid (SA) particles coated with overlayers of polypyrrole (PPy) by aqueous chemical oxidative seeded dispersion polymerization. The SA/PPy core-shell particles could adsorb at the air-water interface to stabilize LMs by rolling water droplets on the particle powder bed. The presence of SA, known as a phase-change material, which undergoes a transition from solid to liquid by heating, and PPy, which can transduce light to heat, gives rise to the photo and thermo dual stimulus-responsive characters of the LMs. The disruption of the LMs could be induced in a cascade manner: light irradiation on the LM induced a temperature increase, followed by melting of the SA component on the LM surface, leading to its disruption and release of the inner water. The disruption time is linked to the PPy loading and light irradiation power, and it can be tuned from quasi-instantaneous to a few tens of seconds. The melting of SA due to a light-induced phase change from the solid to liquid state is a new mechanism to trigger the disruption of LMs. We finally demonstrated two applications of the LMs as a light-responsive microreactor and a sensor.

An Investigation of the Effects of Dopamine on the Superhydrophobicity of Carbonyl Iron Particles with Stearic Acid

Many industries produce large volumes of effluent which are made of oil and its derivatives; very common pollutants in the environment. The use of hydrophobic magnetic particles due to their low cost, low toxicity, and availability is one of the preferred methods for separating oil from water in oil spillage issues. This research aims at evaluating the effects of dopamine as a link in the hydrophobicity of carbonyl iron (CI) particles with stearic acid. In this connection, CI @ stearic acid and CI @ dopamine @ stearic acid have been synthesized. The FESEM analysis was used to observe the surface modification and structure of the particles. The magnetic properties of hydrophobic particles were also measured and the magnetic saturation of CI, CI @ stearic acid, and CI @ dopamine @ stearic acid were 200, 169, 131 emu/g respectively. Finally, the contact angle and adsorption capacity of two modified particles were measured. Based on the result, the static contact angles of water drops placed on the beds of the CI, CI @ stearic acid, and CI @ dopamine @ stearic acid were found to be 0°, 162.9°, and 168.24° respectively. The adsorption capacity range for CI@ stearic acid particles was 1.5 to 2.2 and for CI@ dopamine@ stearic acid particles was 1.8 to 3.2. Therefore, the result showed that dopamine had a good effect as a link to the hydrophobicity of carbonyl iron particles.

Concept for an electrostatic focusing device for continuous ambient pressure aerosol concentration

Abstract. We present a concept for enhancing the concentration of charged submicron aerosol particles in a continuous-flow stream using in situ electrostatic focusing. It is proposed that electrostatic focusing can enable the continuous, isothermal concentration of aerosol particles at ambient pressure, without altering their chemical composition. We model this approach theoretically and demonstrate proof of concept via laboratory measurements using a prototype. The prototype design consists of a nozzle-probe flow system analogous to a virtual impactor. The device was tested in the laboratory using submicron, monodisperse stearic acid particles. Particles were charged using a unipolar charger then concentrated using a cylindrical electrostatic immersion lens to direct the charged submicron particles into the sample probe. Under applied lens voltages ranging from 0 V to 30 kV, aerosol concentration increased up to 15 %. Observed particle enrichment varied as a function of voltage and particle diameter. These results suggest that an imposed electric field can be used to increase aerosol concentration in a continuous flow. This approach shows promise in increasing the effective enriched size range of virtual impactors or other continuous-flow methods of collection.

Multi-dimensional visualization for the morphology of lubricant stearic acid particles and their distribution in tablets

The shapes of particles and their distribution in tablets, controlled by pretreatment and tableting process, determine the pharmaceutical performance of excipient like lubricant. This study aims to provide deeper insights to the relationship of the morphology and spatial distribution of stearic acid (SA) with the lubrication efficiency, as well as the resulting tablet property. Unmodified SA particles as flat sheet-like particles were firstly reprocessed by emulsification in hot water to obtain the reprocessed SA particles with spherical morphology. The three-dimensional (3D) information of SA particles in tablets was detected by a quantitative and non-invasive 3D structure elucidation technique, namely, synchrotron radiation X-ray micro-computed tomography (SR-µCT). SA particles in glipizide tablets prepared by using unmodified SA (GUT), reprocessed SA (GRT), as well as reference listed drug (RLD) of glipizide tablets were analyzed by SR-µCT. The results showed that the reprocessed SA with better flowability contributed to similarity of breaking forces between that of GRT and RLD. SA particles in GRT were very similar to those in RLD with uniform morphology and particle size, while SA particles in GUT were not evenly distributed. These findings not only demonstrated the feasibility of SR-µCT as a new method in revealing the morphology and spatial distribution of excipient in drug delivery system, but also deepened insights of solid dosage form design into a new scale by powder engineering.

Production of solid lipid nanoparticles with a supercritical fluid assisted process

In this work, a supercritical fluid continuous process, the Supercritical Assisted Injection in a Liquid Antisolvent (SAILA), was proposed for the production of solid lipid nanoparticles (SLNs).SLNs of soy lecithin, cholesterol and stearic acid were produced in this work. Acetone and ethanol were used as solvents. The effect of lipid concentration on particles size distribution and morphology was studied. SLNs with mean dimensions included between 158 ± 53 nm and 326 ± 169 nm were obtained for soy lecithin particles, between 151 ± 74 nm and 207 ± 57 nm for cholesterol and from 364 ± 77 nm to 462 ± 88 nm for stearic acid particles. All the suspensions were stable over 30 days of observation.

Novel fabrication of a robust superhydrophobic PU@ZnO@Fe3O4@SA sponge and its application in oil-water separations

We report a novel superhydrophobic material based on commercially available polyurethane (PU) sponge with high porosity, low density and good elasticity. The fabrication of a superhydrophobic sponge capable of efficiently separating oil from water was achieved by imitating or mimicking nature’s designs. The original PU sponge was coated with zinc oxide (ZnO), stearic acid (SA) and iron oxide particles (Fe3O4) via a facile and environmentally friendly method. After each treatment, the properties of the modified sponge were characterized, and the changes in wettability were examined. Water contact angle (WCA) measurements confirmed the excellent superhydrophobicity of the material withhigh static WCA of 161° andlow dynamic WCA (sliding WCA of 7° and shedding WCA of 8°). The fabricated sponge showed high efficiency in separation (over 99%) of different oils from water. Additionally, the fabricated PU@ZnO@Fe3O4@SA sponge could be magnetically guided to quickly absorb oil floating on the water surface. Moreover, the fabricated sponge showed excellent stability and reusability in terms of superhydrophobicity and oil absorption capacity. The durable, magnetic and superhydrophobic properties of the fabricated sponge render it applicable to the cleanup of marine oil spills and other oil-water separation issues, with eco-friendly recovery of the oil by simple squeezing process.

Effect of stearic acid modified HAp nanoparticles in different solvents on the properties of Pickering emulsions and HAp/PLLA composites

Stearic acid (Sa) was used to modify the surface properties of hydroxyapatite (HAp) in different solvents (water, ethanol or dichloromethane(CH2Cl2)). Effect of different solvents on the properties of HAp particles (activation ratio, grafting ratio, chemical properties), emulsion properties (emulsion stability, emulsion type, droplet morphology) as well as the cured materials (morphology, average pore size) were studied. FT-IR and XPS results confirmed the interaction occurred between stearic acid and HAp particles. Stable O/W and W/O type Pickering emulsions were prepared using unmodified and Sa modified HAp nanoparticles respectively, which indicated a catastrophic inversion of the Pickering emulsion happened possibly because of the enhanced hydrophobicity of HAp particles after surface modification. Porous materials with different structures and pore sizes were obtained using Pickering emulsion as the template via in situ evaporation solvent method. The results indicated the microstructures of cured samples are different form each other when HAp was surface modified in different solvents. HAp particles fabricated using ethanol as solvent has higher activation ratio and grafting ratio. Pickering emulsion with higher stability and cured porous materials with uniform morphology were obtained compared with samples prepared using water and CH2Cl2 as solvents. In conclusion, surface modification of HAp in different solvents played a very important role for its stabilized Pickering emulsion as well as the microstructure of cured samples. It is better to use ethanol as the solvent for Sa modified HAp particles, which could increase the stability of Pickering emulsion and obtain cured samples with uniform pore size.

The effect of calcium on the foam behaviour of aqueous sodium alkyl benzene sulphonate solutions. 4. The role of particles in triglyceride-based antifoam mixtures

Mixtures of triolein with stearic acid were significantly less effective as antifoams than mixtures with tristearin. Measurements of contact angles at oil-water and air-water surfaces combined with consideration of crystal morphology have permitted exploration of the possibility that these differences concern the relative effectiveness of particles in rupturing triolein-water-air pseudoemulsion films. No significant difference in the theoretical effectiveness of tristearin and stearic acid in their potential to rupture pseudoemulsion films is however apparent. This suggests that the earlier finding that relative antifoam effectiveness rather concerned particle size and aggregation where stearic acid particles were, for example, more than an order of magnitude larger than the tristearin particles, implying lower probabilities of presence in drops and films.

The effect of calcium on the foam behaviour of aqueous sodium alkyl benzene sulphonate solutions. 3. The role of the oil in triglyceride-based antifoams

A feature of mixtures of triolein with either stearic acid or tristearin particles as antifoams for certain micellar solutions of sodium dodecyl benzene sulphonate is that they are effective only during foam generation but no longer function after foam generation has ceased. Antifoam action by the antifoam oil is determined by positive values of the bridging coefficient. Bridging coefficients were found to be negative under the near equilibrium conditions prevailing after foam generation ceased. However measurements of dynamic surface tensions indicated that if surface ages >0.1s prevailed under the dynamic conditions of foam generation then that would alter the sign of the bridging coefficients. Such dynamic conditions were replicated by drawing single foam films at different rates from solutions containing triolein-based antifoam. Antifoam effectiveness was significantly reduced in the case of foam films drawn at extremely slow rates so that near equilibrium conditions prevailed.

The effect of calcium on the foam behaviour of aqueous sodium alkyl benzene sulphonate solutions. 2. In the Presence of triglyceride-based antifoam mixtures

Here we have sought to establish the likely key ingredients which determine the antifoam behaviour of model sebum together with key specific aspects of their mode of action. Since the overall composition of sebum is dominated by unsaturated triglycerides we selected triolein as the oil. Tristearin and stearic acid were selected as particulate components since both are only sparingly soluble in triolein and are likely to replicate the absence of strong dependence upon changes in pH or [Ca2+] found with sebum. Triolein/tristearin mixtures were, under most circumstances, at least as effective as the model sebum but totally unaffected by changes in [Ca2+] and pH. However triolein/stearic acid mixtuures replicated the weak dependence upon [Ca2+] of model sebum and pH but were less effective. The ineffectiveness of the former appeared to concern the relatively large size of stearic acid particles crystalizing from a melt in triolein – at least an order of magnitude larger than the particle sizes of tristearin prepared in a similar manner, showing a tendency to aggregate and form large, ineffective, triolein/stearic acid agglomerates. The large particle size of stearic acid particles also leads to a high probability of formation of ineffective particle-free drops upon dispersal in solution.

Novel stearic acid/graphene core–shell composite microcapsule as a phase change material exhibiting high shape stability and performance

A stearic acid (SA)/graphene composite microcapsule, having a core–shell structure, is prepared for the first time using a latex technology for use as a novel composite phase change material (PCM) for thermal energy management. Melted SA is dispersed in water using an anionic surfactant as a stabilizer and cooled to prepare a water-based latex containing negatively charged SA particles. A simple mixing of this latex with an aqueous dispersion of graphene, prepared with aid of a cationic surfactant, results in the self-assembly of graphene on a SA particle surface by an electrostatic interaction, allowing for the encapsulation of SA with graphene to form a core–shell composite microcapsule. The protective graphene shell gives an excellent shape stability to the composite during phase change and a substantial improvement in thermal stability of the active SA core. In addition, the core–shell structure contains a high weight fraction of the active core material due to the ultra-thin graphene shell having high thermal conductivity. This results in a high performance PCM with a large latent heat and an improved thermal conductivity.

A Wet Electrostatic Precipitator (WESP) for Soft Nanoparticle Collection

Many nanoparticle collection devices have limitations related to retention of particle integrity from bounce, shattering, or aggregation. Suspensions of soft nanoparticles (e.g., proteins, lipids) are required for drug delivery and therapy. To enable direct collection of soft nanoparticles into liquid media, a wet electrostatic precipitator (WESP) was designed and evaluated in this work. Different sections were used for ion generation and particle charging, for minimal contact between the corona wire and particles, which were charged using positive nitrogen ions. WESP dimensions and operating parameters were optimized using charge distribution modeling. The prototype WESP was designed for operation with a continuous flow of liquid over the collection plate, to allow continuous particle collection from the exit stream of an aerosol reactor. The collection efficiency of the WESP, in dry and wet modes, was measured using aerosols of monodisperse polystyrene latex (PSL), polydisperse sucrose, and stearic acid (soft lipid) particles, through SMPS measurements, corrected for diffusional losses, at the entry and exit of the device. Measured collection efficiency was 70%–90% for particles of sizes 80–600 nm diameter in reasonable agreement with theoretical estimates. However, for small particles (20–80 nm diameter) measured collection efficiency ranged 40%–70%, significantly lower than theoretical estimates, possibly from incomplete neutralization of negative charges attained during air-jet atomization. Transmission electron microscopy (TEM) images and dynamic light scattering (DLS) measurements confirm that wet collection produces a suspension of free, unaggregated nanoparticles with sizes similar to their measured mean mobility diameter. Copyright 2012 American Association for Aerosol Research

The release of macromolecules from fatty acid matrices: complete factorial study of factors affecting release.

A replicated complete factorial design to study the main effects and interactions of four factors: bovine serum albumin (BSA) particle size (Factor A); stearic acid particle size (Factor B); BSA loading (Factor C); and compression force (Factor D), on the release of BSA from compressed stearic acid pellets was performed in isotonic phosphate buffer pH 7.4 at 37 degrees C. Samples were withdrawn over 64 h. Analysis of variance of the percentage released at 64 h showed that A, B, and C, but not D, affected the release and the interactions AB, BC, ABC were highly significant. At low loading (5%), the surface release depended on BSA particle size. The release increased when BSA particle size was large. At high loading (20%), more release was shown when stearic acid particle size was large. More release with increasing BSA particle size occurred only when stearic acid particle size was small. It is proposed that release is due to the interconnected pore networks created, not only by BSA particles, but also by the void space between stearic acid particles. These void spaces vary according to particle size-dependent arrangements of stearic acid and BSA particles. An increase in the pellet thickness was observed probably due to the relaxation of compacted stearic acid particles.

Comparative study of the stability of venlafaxine hydrochloride sustained-release pellets prepared by double-polymer coatings and hot-melt subcoating combined with Eudragit® NE30D outercoating

The aim of this paper was to study the comparative stability of venlafaxine hydrochloride (VEN) sustained-release pellets prepared by double-polymer coatings and hot-melt subcoating combined Eudragit® NE30D outercoating. The uncoated VEN pellets, containing 45% (w/w) VEN, 45% (w/w) MCC (PH101), 10% (w/w) stearic acid and 0.5% (w/w) Carbopol974, were prepared by extrusion-spheronization. Satisfactory release profiles were obtained when VEN pellets were prepared by 4% EC subcoating combined with 4% Eudragit® NE30D outercoating and 8% hot-melt subcoating combined with 6% Eudragit® NE30D outercoating, respectively. The storage stability was monitored by measuring the drug release over six months storage at 40°C/75% RH and at room temperature (25 ± 2°C/60% RH). The release of pellets with double-polymer coatings increased markedly, while drug release of pellets prepared by hot-melt subcoating combined with polymer coating gradually decreased. Basically, the former may be attributed to the main role of drug migration into the EC subcoating, and the latter may be caused by the fusion and resolidification of stearic acid particles and the further aging of the Eudragit® NE30D outercoating. In summary, regardless of the change in release, drug dissolution met the standard requirement and the stability was acceptable during the storage period.

Water resistance improvement of paper by superhydrophobic modification with microsized CaCO 3 and fatty acid coating

Nanoscaled surface roughness with a hydrophobically modified surface has been widely used for preparation of superhydrophobic materials. However, the complicated procedure, high cost and harmful compounds used in most superhydrophobic surface modifications limited their applications. This research aims at fabricating superhydrophobic cellulosic or semi-superhydrophobic papers with low cost and nontoxic materials. Commercial PCC (precipitated calcium carbonate) particles, hydrophobic stearic acid and polymer latex particles were used for surface roughness control, surface hydrophobic modification agent, and polymer binder, respectively. A simple coating or dipping method was used to produce high contact angle and high water resistance papers. It was found that the surface pretreatment of PCC with fatty acid salt prior mixing with polymer binder plays important role for improving the water contact angle (WCA). The combination of surface coating with dipping treatment will further increase the water contact angle and water resistance of the paper. A WCA near 150° over modified paper surface has been achieved. At the same degree of water resistance, the total cost of the paper can be significantly reduced by our method.

Modification of cloud condensation nucleus activity of organic aerosols by hydroxyl radical heterogeneous oxidation

The modification of cloud condensation nucleus (CCN) activity of saturated organic particles resulting from heterogeneous oxidation by OH radicals was studied. Submicron Bis-2-ethylhexyl sebacate (BES) and stearic acid particles were exposed to OH radicals in a reactor flow tube and CCN activity was monitored. The hygroscopicity parameter, κ, for monodisperse stearic acid and BES particles of 145–150 nm in size increased from <0.008 up to 0.08 as a result of OH exposures equivalent to atmospheric exposure timescales of several days to a week. The oxidation of stearic acid particles led to a 50% reduction in particle volume at high OH exposures, indicating an enhanced degree of volatilization of oxidation products compared to oxidized BES particles, along with possible shape/phase change. Surface tension measurements of water extracts of oxidized BES films showed a significant reduction in surface tension due to oxidation. Köhler calculations modeling the CCN measurements suggest that the surface active oxidation products play an important role.

Clogging of an electrically active fibrous filter material: experimental results and two-dimensional simulations

An experimental study has been undertaken in which the loading behaviour of an electrically active fibrous filter material has been investigated. In these experiments both filter pressure drop and penetration have been monitored continuously while samples of filter material have been loaded with monodisperse stearic acid particles. This paper concerns itself only with the pressure drop data. The experimental findings suggest that electrically active materials should have greater dust holding capacities than conventional materials, and a mechanistic explanation as to why this should be is presented. This mechanistic explanation is supported by two-dimensional simulations of dendrite formation.

Sampling Submicrometer Particles Suspended in Near Sonic and Supersonic Free Jets

This paper is concerned with sampling submicrometer particles in perisonic flows. The study employed a high volume (30-45 L/min) condensation aerosol generator to produce stearic acid particles having a mean diameter of 0.8μm and a geometric standard deviation of 1.28. The aerosol was diluted with dry air and accelerated to Mach 0.6, 0.8, 1.26, or 1.47 through a flow nozzle. Aerosol mass concentrations were determined using a small bore probe in the jet and by a large bore probe sampling isokinetically upstream of the jet nozzle. The results of both samples were compared to compute the sampling error associated with I ho high spood jot sample. The mass of stearic acid colloctod on polycarbonate mombrono flltors was determined by gravimoirlc and chromalogrophlc mothods. Studies at Mach 0.8 with four sampling probes having Inlet wall to bore area ratios ranging from 3.8 to 0.28 (a knife edge) demonstrated that probe wall thickness effects are not significant when the sample is extracted isokinetically. Subisokinetic experiments using the knife edged probe showed relative errors of 124 ± 12% when sampling at 2 0% of the isokinetic condition. The subisokinetic results are compared favorably with the extended empirical results of other authors. For the supersonic cases it is shown that the subsonic velocity downstream of the sampling probe bow shock can be used in estimating the sampling error.

Thermal forces on aerosol particles in a thermal precipitator

The generally accepted theory of thermal precipitation predicts that aerosol particles having high thermal conductivity would be very difficult to collect. However, no such difficulties have been reported in the literature. Accordingly, a study has been undertaken of the thermal forces on aerosol particles under greatly differing conditions of particle size, thermal conductivity of the particles, and temperature gradient. Thermal gradients were produced with a commercially available (Casella) thermal precipitator, using a ribbon filament. Thermal forces were calculated from the width of deposit, using the Stokes-Cunningham equation. The thermal forces on stearic acid particles were almost precisely those predicted by radiometer theory (Epstein's equation). The effect of particle size and of magnitude of thermal gradient were essentially those expected. However, the thermal forces on sodium chloride and iron particles were 20 to 40 times the values predicted by theory, although there was a decrease in thermal force with increasing thermal conductivity. Possible reasons for these results are discussed.