Interpretation of particle growth and aggregation patterns obtained from the Coulter counter: a simple theoretical model.
We used a simple theoretical model to stimulate the changes in particle size distribution that occur when crystals grow, or disaggregate to a defined extent. The change in total particle volume was used as an index of growth, whereas aggregation and disaggregation were expressed as the change in total particle number. Indices of inhibition of growth and of aggregation in hypothetical test cases were calculated in relation to a control and compared with the inhibition index derived by the standard method of comparing the distribution of particle volume around a given arbitrary diameter on the particle distribution curve. We concluded that the expression of particle growth and aggregation in terms of total volume and number respectively is a preferable alternative to the standard technique.
Amorphous Calcium Phosphate Based Composites: Effect of Surfactants and Poly(ethylene oxide) on Filler and Composite Properties.
Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD, USA.
The uncontrolled aggregation of amorphous calcium phosphate (ACP) particulate fillers and their uneven distribution within polymer matrices can have adverse effects on the properties of ACP composites. In this paper we assessed the influence of non-ionic and anionic surfactants and poly(ethylene oxide)(PEO) introduced during the preparation of ACP on the particle size distribution and compositional properties of ACP. In addition, the mechanical strength of polymeric composites utilizing such fillers with a photo-activated binary methacrylate resin was evaluated. Zirconia-hybridized ACP (Zr-ACP) filler and its corresponding composite served as controls for this study. Surfactant- and PEO-ACPs had an average water content of 16.8 % by mass. Introduction of the anionic surfactant reduced the median particle diameter about 45 %(4.1 μm vs. 7.4 μm for the Zr-ACP control). In the presence of PEO, however, the d(m) increased to 14.1 μm. There was no improvement in the biaxial flexure strength (BFS) in any of the dry composite specimens prepared with the surfactant- and/or PEO-ACPs compared to those formulated with Zr-ACP. The BFS of wet composite specimens decreased by 50 % or more after a month-long exposure to saline solutions. Other types of surfactants and/or polymers as well as alternative surface modification protocols need to be explored for their potential to provide better dispersion of ACP into the matrix resin and better mechanical performance ACP composites.
Department of Urology, Kinki University School of Medicine, 377-2, Ohno-Higashi, Osaka-Sayama, Osaka, 589-8511, Japan. firstname.lastname@example.org
OBJECTIVE We evaluated whether osteopontin (OPN) and other proteins with the RGD sequence as in OPN (RGD family proteins) that are present in renal tubular cells (fibronectin [FN], Tamm-Horsfall glycoprotein [THP], vitronectin [VN], and laminin [LN]) inhibit the aggregation and growth of calcium oxalate (CaOx) crystals by a novel seed crystal method using collagen granules (CG) with and without OPN adhered on the surface. We also evaluated the effect of solid phase OPN, FN and THP in which the relationship between their proteins and CaOx crystallization was reported. Moreover, the state and time-course changes in CaOx crystals adhered to CG were observed under scanning electron microscopy (SEM). METHODS The inhibitory activity (IA) on the aggregation and growth of CaOx crystals was measured in vitro by the conventional seed crystal method using isotopes. In this study, the following nine samples were used: OPN alone; FN alone; THP alone; VN alone; LN alone; CG alone; and CG with OPN, FN, or THP adhered on the surface (OPN/FN/THP-immobilized CG). In addition, the state and time-course changes in CaOx crystals adhered to CG were evaluated by SEM. RESULTS Using the conventional seed crystal method, the following values of IA were obtained: 91.7%(37.5 micro g/ml) for OPN, 5.0%(100 micro g/ml) for FN, 2.0%(100 micro g/ml) for THP, 3.0%(100 micro g/ml) for VN, and 1.0%(100 micro g/ml) for LN. However, the value of IA obtained by our seed crystal method using CG was 92.1%(180cm(2)/5ml PBS) when CG alone was used. Although the value of IA was decreased by 33.6% when OPN-immobilized CG was used, it did not significantly change when FN/THP-immobilized CG was used. When CG alone was used, the evaluation of CaOx crystallization by SEM demonstrated mild adherence and aggregation of CaOx crystal suspension (seed crystals) on the CG surface, although newly formed crystals only slightly adhered to the CG surface. When OPN-immobilized CG was used, marked adherence and aggregation of seed crystals were observed, in addition to the relatively increased adherence of newly formed crystals. When FN/THP-immobilized CG was used, newly formed crystals only slightly adhered to the CG surface, although the degree of seed crystal adherence and aggregation did not significantly change. CONCLUSIONS These findings suggest that the immobilization of OPN to the CG surface enhances the adherence and aggregation of seed crystals, as well as enhancing the adherence of newly formed crystals, resulting in decreased IA of CG (overall promotion of crystal deposition). Therefore, the results of this study clarified that OPN enhances the formation and aggregation of CaOx crystals in this experimental system.
Department of Urology, Kinki University School of Medicine, Osaka, Japan. email@example.com
Using seed crystal method, whole-urine method, and scanning electron microscopy, the inhibitory effects of sialic acid and osteopontin (OPN) on aggregation/growth of CaOx crystals were investigated. Using the seed crystal method, sialic acid showed an inhibitory effect on CaOx crystal aggregation/growth in a concentration-dependent manner, but almost no effect was observed using the whole-urine method. OPN showed an inhibitory effect on aggregation/growth in both experimental systems. The inhibitory effect of asialo-OPN on aggregation/growth was approximately 20% lower than that of OPN in the experiment using the seed crystal method and approximately 15% lower in the experiment using the whole-urine method. Scanning electron microscopy showed that OPN and sialic acid inhibit the aggregation of CaOx crystals. The above findings show that sialic acid accounts for about 15-20% of the involvement of OPN in CaOx crystallization.
Department of Chemistry, University of the Balearic Islands, Palma de Mallorca, Spain.
The effect of natural admixtures occurring in human urine (citrate, pyrophosphate and glycosaminoglycans) on the precipitation of stone-forming compounds was studied. Experiments were carried out under conditions closely simulating the early stages of renal stone formation. Among the studied admixtures, citrate was determined as the most effective substance preventing the phosphate particle formation. Indeed, in the presence of citrate, some calcium oxalate monohydrate crystals were found. Pyrophosphate induced the formation of calcium oxalate dihydrate crystals. Phosphate crystals appeared at pH 6 and never at pH 5. The easy formation of phosphate particles supports the hypothesis that these crystals represent a very important heterogeneous nucleus-initiating oxalocalcic calculus formation in the kidney. Reported results also indicated uric acid as a significant heterogeneous nucleus of calcium oxalate monohydrate crystals at urinary pH equal or lower than 5 and the important role of bacteria in increasing the organic detritus deposited on the solid surfaces.
Department of Urology, Faculty of Health Sciences, University Hospital, Linköping, Sweden.
PURPOSE: We determine whether stone formers and normal subjects can be distinguished in terms of supersaturation with calcium oxalate, and inhibition of calcium oxalate growth and aggregation. MATERIALS AND METHODS: An estimate of the ion activity product of calcium oxalate was obtained from the analysis of calcium, oxalate, citrate and magnesium in 16-hour urine samples obtained between 6 a.m. and 10 p.m. The inhibition of calcium oxalate crystal growth and aggregation was assessed in 8-hour urine specimens obtained between 10 p.m. and 6 a.m. RESULTS: The ion activity product of calcium oxalate was higher and inhibition of crystal aggregation was lower in stone formers than in normal subjects. Inhibition of crystal growth was lower only in male stone formers. Quotient 1 (10(2) x ion activity product of calcium oxalate/inhibition of crystal growth), quotient 2 (10(2) x ion activity product of calcium oxalate/inhibition of crystal aggregation) and quotient 3 (10(4) x ion activity product of calcium oxalate/[inhibition of crystal growth x inhibition of crystal aggregation]) were significantly higher in stone formers. CONCLUSIONS: The biochemical risk situation in calcium oxalate stone formers can be summarized by quotient 2 or 3.
Effect of two new polysaccharides on growth, agglomeration and zeta potential of calcium phosphate crystals.
Department of Urology, Erasmus University, Rotterdam, The Netherlands.
PURPOSE: To study the effect of semisynthetic sulphated polysaccharides in the different calcium phosphate crystallization processes in vitro. MATERIALS AND METHODS: Crystallization of hydroxyapatite (HAP) and brushite (DCPD) in the presence and absence of 2 new semisynthetic sulphated polysaccharides (G871, G872) were defined by a constant composition technique, particle size analysis and zeta potential measurement. RESULTS: These polysaccharides demonstrated strong inhibitory effect on HAP and DCPD crystal growth and agglomeration. The increase of negative zeta potential values after addition of polysaccharides suggests the binding of these polysaccharides to HAP and DCPD crystals. CONCLUSION: We conclude that both G871 and G872 could be of potential use for calcium phosphate urolithiasis prevention in addition to their use for calcium oxalate.
Inhibition of chondroitin sulphate and heparin on the growth and agglomeration of calcium oxalate monohydrate crystals in vitro.
Seed experiments on the growth of calcium oxalate monohydrate in vitro have given the following results. Chondroitin sulphate does not influence the growth but only the agglomeration. The main influence of heparin at all concentrations is to inhibit the agglomeration, but at concentrations greater than about 10(-8) mol/l the growth is also inhibited. In the range 0.05-30 mumol/l there is a linear dependence between the percentage inhibition of the growth and the concentration of heparin.
The effect of urine, pyrophosphate, citrate, magnesium and glycosaminoglycans on the growth and aggregation of calcium oxalate crystals in vitro.
The effects of pyrophosphate, citrate, magnesium, heparin and chondroitin sulphate on the growth and aggregation of calcium oxalate crystals were measured at concentrations likely to be found in 1% urine. The degrees of inhibition of growth and of aggregation caused by these compounds were related to the effects of normal 1% urine on these processes. It was concluded that chondroitin sulphate is responsible for the major portion of the inhibitory effect of urine on crystal aggregation, but that the effect on crystal growth is probably due to the additive or synergistic effects of a number of urinary constituents.
A method has been developed for inducing and quantifying calcium oxalate crystallisation in whole human urine. The propensity of a given urine to induce crystal formation was described in two ways: its ability to resist spontaneous nucleation of calcium oxalate crystals was assessed by titrating 20 mls of the urine with increasing quantities of sodium oxalate (0-150 mumol) to determine its practical metastable limit. This limit was inversely related to the endogenous calcium concentration; its capacity to inhibit crystal growth was quantified by determining the rate of growth of calcium oxalate crystals precipitated in response to a fixed oxalate load (30 mumol) above its metastable limit. The crystals produced were predominantly calcium oxalate dihydrate and were morphologically identical to those occurring naturally in urine. Citrate had no effect on the metastable limits of 3 urines examined, but markedly inhibited crystal growth. Pyrophosphate had a similar effect on crystal growth, and in addition, raised the metastable limit of one of the urine samples.
Analysis of particle size distribution of hydroxyapatite crystallites in the presence of synthetic and natural polymers.
Department of Chemistry, State University of New York, Buffalo 14214.
The particle size distribution (PSD) of suspended hydroxyapatite crystallites both at equilibrium and during crystal growth has been measured by a laser scattering technique. Addition of high-molecular-weight polyacrylate (PAA/C) resulted in appreciable crystallite aggregation, probably by polymer bridging of particles. In contrast, a lower-molecular-weight PAA was unable to bridge the hydrodynamic gap between particles and resulted in an overall dispersion. The addition of human serum albumin also markedly influenced the PSD and, with concomitant change in zeta potential to more negative values, resulted in dispersion due to steric interaction and electrostatic repulsion between the particles. The complex behavior of human saliva is illustrated by its tendency both to aggregate and to disperse hydroxyapatite crystallites, displaying the combined effects of different adsorbing macromolecules.
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An evidence-based approach to hypercalciuria: is it really necessary for the study of the role of calcium in urolithiasis?
Department of Surgery, Flinders Medical Centre, Bedford Park, South Australia.
An abnormally raised 24-h urinary excretion of calcium has long been regarded as a common feature of calcium stone disease. However, hypercalciuria can be defined only by reference to a range of values measured in a representative population of individuals who have never suffered from stone disease. To date, there have been significant flaws in all published studies reporting normal ranges for daily urinary calcium excretion. There is no doubt that additional, carefully performed and documented investigations need to be undertaken to establish what is truly abnormal for a given population; the persistent use of arbitrarily defined limits may be hindering rather than helping to unravel the role of calcium in the pathogenesis of calcium stones.
Department of Surgery, Flinders Medical Centre, Bedford Park, South Australia.
Department of Surgery, Flinders University School of Medicine, Flinders Medical Centre, Bedford Park, South Australia, Australia. firstname.lastname@example.org
The ultimate aim of our research is to understand the role of macromolecules in the formation of human kidney stones, particularly their interactions with calcium oxalate (CaOx) crystals. The invariable association of stones with proteins raises the possibility that proteins play a role in their formation, similar to the role of proteins in healthy biomineralization. Do these proteins induce mineralization? Are they merely a response to the disease process? Or are they protective molecules that were overwhelmed by mineral supersaturation? A protein of particular interest is fragment 1 (F1) of prothrombin. We have shown that mRNA for prothrombin is present in the kidney. Because the F1 fragment of prothrombin present in urine is slightly different from that found in the blood, we refer to this protein as "urinary prothrombin fragment 1"(UPTF1). Available evidence suggests that the kidney manufactures the protein for protection against stone disease and that the protein has a directive role in stone formation. We now have evidence that proteins are interred within CaOx crystals precipitated from human urine, where it is distributed in continuous channels. These proteins could facilitate crystal deconstruction and removal after attachment to the renal epithelium and endocytosis. We suspect that the formation of CaOx crystals in the urine is a normal process designed to permit harmless disposal of an excess of calcium, oxalate, or both. The incorporation of proteins provides a second line of defense against stone formation by enabling the destruction and removal of retained crystals. Understanding the basic molecular strategies by which plants produce protein-containing CaOx crystals may provide insight into human CaOx stone formation.
Department of Surgery, Flinders Medical Centre, Bedford Park, Australia.
1. Increasing the concentration of dissolved urate promotes the crystallization of calcium oxalate from urine. The possibility was investigated that this effect may be caused by heterogeneous nucleation of calcium oxalate by particles of crystalline urate. 2. Urine samples were collected from 10 healthy men, centrifuged and filtered, and a solution of sodium urate was added to increase the medium urate concentration from 2.2 to 5.6 mmol/l. Calcium oxalate crystallization was induced by the addition of oxalate, followed by incubation for 90 min in a shaking waterbath at 37 degrees C. The crystalline material was filtered out and the urate concentration was determined in the filtrate. 3. No difference in the urate concentration before and after induction of calcium oxalate crystallization was observed. These findings were confirmed by infra-red spectroscopy, X-ray powder diffraction and ultraviolet wet chemical analysis with detection limits of 5-10, 1.0 and 0.055%, respectively; urate was not detected in the calcium oxalate crystals. 4. In addition, three urine samples were collected and passed through 10 kDa ultrafiltration membranes to remove any colloidal particles which might have been present. The urate concentration was increased and an oxalate load was added as before, prior to incubation at 37 degrees C in a shaking water bath for 5 min, followed by passage through 10 kDa ultrafiltration membranes. Scanning electron microscopy revealed no particles on the membranes thereby indicating that colloidal or crystalline urate was not formed early in the crystallization experiments.(ABSTRACT TRUNCATED AT 250 WORDS)
Tamm-Horsfall mucoprotein reduces promotion of calcium oxalate crystal aggregation induced by urate in human urine in vitro.
Department of Surgery, Flinders Medical Centre, Bedford Park, South Australia.
1. Increasing the concentration of dissolved urate promotes calcium oxalate crystallization in urine from which Tamm-Horsfall mucoprotein, an inhibitor of calcium oxalate crystal aggregation, has almost completely been removed. This study aimed to determine whether the effect of urate could be reduced or abolished by a physiological concentration of Tamm-Horsfall mucoprotein. This was approached in two ways. 2. The effect of Tamm-Horsfall mucoprotein on calcium oxalate crystallization induced by urate was tested in ultrafiltered (10 kDa) urine samples from 10 healthy men. Tamm-Horsfall mucoprotein (35 mg/l) was added to half of each specimen, the urate concentration was increased by the addition of sodium urate solution and crystallization was induced by a standard load of oxalate. The remainder of each urine specimen was used as a control; these specimens were treated with an identical amount of urate solution, but contained no Tamm-Horsfall mucoprotein. Tamm-Horsfall mucoprotein had no effect on the urinary metastable limit or on the deposition of calcium oxalate, but significantly reduced the size of the particles precipitated. 3. The effect of increasing the urate concentration in the presence of Tamm-Horsfall mucoprotein was tested. Tamm-Horsfall mucoprotein (35 mg/l) was added to 10 ultrafiltered urine samples as before, the samples were divided, and the concentration of urate was increased in half of each specimen. Compared with the control to which no urate was added, urate significantly reduced the amount of oxalate required to induce spontaneous calcium oxalate nucleation and increased the median volume and the particle size of the material deposited.(ABSTRACT TRUNCATED AT 250 WORDS)
Calcium oxalate crystal matrix extract: the most potent macromolecular inhibitor of crystal growth and aggregation yet tested in undiluted human urine in vitro.
Department of Surgery, Flinders Medical Centre, Bedford Park, South Australia.
Demineralization of calcium oxalate (CaOx) crystals precipitated from human urine in vitro yields an organic crystal matrix extract (CME) consisting predominantly of a single protein which we originally named crystal matrix protein but have subsequently shown to be a urinary form of prothrombin activation peptide fragment 1 (F1). The aim of this study was to determine whether CME is a promoter or inhibitor of CaOx crystallization. The effect of CME on CaOx crystal growth and aggregation was tested using a standard seeded crystallization system, and its effect quantified by use of particle size analysis and a computer model. In addition, the effect of CME on the crystallization of CaOx was tested in undiluted, ultrafiltered human urine using Coulter Counter analysis and scanning electron microscopy. It was shown that CME is a potent inhibitor of CaOx crystal growth and aggregation in a seeded metastable solution. However, of greater significance is that at a concentration of 10 mg/l it completely reversed the formation of large crystalline aggregates that form upon the removal of urinary macromolecules from undiluted urine. It was concluded that CME is the most potent macromolecular urinary inhibitor yet to be tested in urine in vitro. By preventing the aggregation of newly formed crystals, the components of CME may significantly reduce the probability of particle retention in vivo and therefore the occurrence of urolithiasis.
Department of Surgery, Flinders Medical Centre, Australia.
The aim of this study was to determine the immunohistochemical distribution and quantification of crystal matrix protein (CMP). CMP, a 31 kDa glycoprotein, is the principal macromolecule found in calcium oxalate crystals generated in human urine, and is a potent inhibitor of crystal aggregation. A polyclonal rabbit anti-human CMP antibody was used to examine renal tissue by immunohistochemical techniques and light microscopy (N = 45). Twenty-five other human organs were similarly assessed. Quantification was performed using a visual analogue scale. CMP was visible as cytoplasmic staining in the epithelial cells of the TALH and the distal convoluted tubule including the macula densa in a subgroup of nephrons. CMP was not identified elsewhere in the urinary tract or in the extrarenal organs examined. Despite a trend indicating that the kidneys of normal men had more CMP than those of normal women, the difference failed to reach significance (P = 0.11). There was, however, more CMP in the stone formers group compared with either normal men (P < 0.01) or normal women (P < 0.01). This protein may be an important determinant of calcium oxalate kidney stone disease.
Independent assessment of the growth and aggregation of calcium oxalate crystals using the Coulter counter.
The growth and aggregation of calcium oxalate seed crystals in a metastable solution of this salt were assessed separately by using the Coulter counter to measure the net increase in total crystal volume and the percentage change in total crystal number respectively. The value of assessing crystal growth and aggregation in these terms was shown by using these parameters to measure the inhibitory effect of a normal human urine. Independent assessment of growth and aggregation enabled a more accurate interpretation of experimental events than was possible by considering the two processes in combination. The method therefore has the potential of improving the discrimination between the inhibitory activities of different urines.
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National Centre for Atmospheric Science, Division of Environmental Health & Risk Management, School of Geography, Earth & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
Particle number concentration data have been collected on a very busy road in central London (Marylebone Road). Continuous size distributions from 15 nm to 10 μm diameter, collected over 21 days, were analyzed using positive matrix factorization which identified 10 factors, five of which were observed to make major contributions (greater than 8%) to either the total number or volume of particulate matter. The sources associated with each factor were identified from the size distribution, directional association, diurnal variation and their relationship to meteorological pollution and traffic volume variables. The factors related to the emissions on Marylebone Road accounted for 40.5% of particle volume and 71.9% of particle number. These comprised nucleation mode exhaust particles (3.6% of total volume and 27.4% of total number), solid mode exhaust particles (18.8% of total volume and 38.0% of total number), brake dust (13.7% of total volume and 1.7% of total number and resuspension (4.4% of total volume and 4.8% of total number). Another six factors were associated with the urban background accounting for 59.5% of total volume and 28.2% of total particle number count. The method is extremely successful at separating the components of on-road emissions including brake wear and resuspension.
Effect of nanoparticle clustering on the effective thermal conductivity of concentrated silica colloids.
Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, USA.
Recent research on nanofluids has offered particle clustering as a possible mechanism for the abnormal enhancement of the effective thermal conductivity (k) when nanoparticles are dispersed in liquids. This paper was devoted to verify experimentally and theoretically the significance of the effect by altering the cluster structure, size distribution, and thermal conductivity of solid particles in water. Starting with well dispersed SiO2 sols in water as a reference system, we control the aggregation kinetics by adjusting pH. Contrary to previous model predictions, the present experiment showed that clustering did not show any discernable enhancement in the thermal conductivity even at high volume loading. A series of fractal model calculations not only suggested that the conductive benefit due to clustering might be completely compensated by the reduced convective contribution due to particle growth, but also recommended the need for higher thermal conductivity and optimized fractal dimension of particles for maximizing the clustering effect.
Evolution of size distribution in pressure drop induced decomposition synthesis of cobalt nanoparticles.
Department of Chemistry, Helsinki University of Technology, P.O. Box 6100, FI-02015 TKK, Finland.
Cobalt nanoparticles with average diameters of 8.8nm and a standard deviation of 8% were obtained in a pressure drop induced decomposition synthesis in an autoclave. Samples were taken during the experiment and characterized with TEM. A significant narrowing of the size distribution coincident with particle growth was observed. The standard deviation decreased from 31% to 8% while the average size increased from 5.5nm to 8.8nm. In order to explain the experimentally observed narrowing of the size distribution, a model that accounts for the influence of the capping layer on the growth rate was developed. The transfer of the reacting monomer into the capping layer was considered to be similar to an adsorption process. A rate constant of 4x10(-5)cm(4)mol(-1)s(-1) was obtained for the growth reaction, and it was thus concluded that the growth reaction proceeds under kinetic control rather than under diffusion control.
Separation of coherent and incoherent scattering contributions in ellipsometric light scattering experiments on latex mixtures.
Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
Mixtures of poly(styrene) latices were used to vary the sample polydispersity for an investigation of polydispersity effects on ellipsometric light scattering (ELS) data. A procedure for high-accuracy ELS measurements is presented and the experimental distinction of coherent and incoherent scattering contributions is demonstrated. The ellipsometric parameters tan (phiQ) and delta are solely determined from coherent scattering and represent averaged ensemble properties, independent of the width of the size distribution. The change in polydispersity shows up in the parameter tan(phiI), which is affected by incoherent contributions. The average particle size detected by ELS can be estimated from the intensity-weighted size distribution. A radial local birefringence in the particles has been detected and attributed to stress birefringence due to the action of the interface tension on the particles during their growth.
Separation of Coherent and Incoherent Scattering Contributions in Ellipsometric Light Scattering Experiments on Latex Mixtures.
Max Planck Institute of Colloids and Interfaces, Am Muhlenberg 1, 14476 Potsdam-Golm, Germany.
Mixtures of poly(styrene) latices were used to vary the sample polydispersity for an investigation of polydispersity effects on ellipsometric light scattering (ELS) data. A procedure for high-accuracy ELS measurements is presented and the experimental distinction of coherent and incoherent scattering contributions is demonstrated. The ellipsometric parameters tan(Psi(Q)) and Delta are solely determined from coherent scattering and represent averaged ensemble properties, independent of the width of the size distribution. The change in polydispersity shows up in the parameter tan(Psi(I)), which is affected by incoherent contributions. The average particle size detected by ELS can be estimated from the intensity-weighted size distribution. A radial local birefringence in the particles has been detected and attributed to stress birefringence due to the action of the interface tension on the particles during their growth.
Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology, Mumbai 400076, India.
Controlling the shape and size of the layered inorganic-organic hybrid particles is a challenge with conventional methods of synthesis. The co-precipitation method has been modified to synthesize Mg/Al Layered double hydroxide by controlling the particle growth using ultrasonic wave at the time of nucleation. In this project, magnesium and aluminum ions were considered as model systems with carbonate anion as intercalating agent. The resulting particles are compared with those of LDHs produced by conventional co-precipitation method at constant pH. Powder X-ray diffraction confirmed formation of the layered double hydroxide phases having crystallite size 19-20 nm in both 'a' and 'c' crystallographic directions. Transmission electron microscope and dynamic light scattering revealed nano disperse hexagonal platelets with narrow size distribution and average size was around 48 nm. The modified method reduces the particle size, increases the surface charge, narrows down the size distribution and also reduces the aspect ratio of the particles. Therefore, it is suggested that low amplitude ultrasonic wave prevents the aggregation of the nuclei, thus restricting the particle growth and results in uniform size particles.
Department of Chemical Engineering, Iowa State University, Ames, Iowa 50011.
The particle size distribution (PSD) of soyabean protein aggregates obtained by acid precipitation in a continuous stirred reactor was measured with a Coulter Counter model TA II. Effects of changes in the operating variables pH, concentration, mean residence time, power input, and ionic strength were investigated. Power input affects both growth and breakup while pH and ionic strength seem to exert their influence through solubility and aggregate strength. Changes in zeta-potential can explain most of these observations.
Department of Chemical and Biochemical Engineering, University College London, Torrington Place, London, WC1E 7JE, England.
The acid precipitation of soya protein was studied in a continuous-flow tubular reactor under conditions of turbulent flow. Preliminary batchwise experiments of a semiquantitative nature were also carried out on a bench-scale reactor to better define the parameters affecting precipitate growth. The experiments indicated the dominant growth mechanism to be the aggregation of primary precipitate particles produced by the contacting of the protein and acid streams. The rate of particle growth was observed to rise with an increase in the protein concentration as well as with greater intensity of turbulence. The final mean particle size decreased with increased intensity of turbulence. A theoretical model was set up to simulate the growth of the precipitate particles.
Scanning. ;30 (2):78-86 18241039
Emerson Process Management, Rosemont Analytical Inc., Irvine, California 92406, USA. email@example.com
Latex films have a tendency to "blush" when exposed to water. The swelling of trapped hydrophilic material, which results in pockets with different refractive indices, is proposed as a possible model for blushing. A pressure-sensitive latex was developed on the basis of this model. The blush was improved by the choice of the surfactant and control of the particle diameter. The resulting latex has an unusual particle growth behavior during polymerization. The particle size distribution (PSD) was characterized by dynamic light scattering (DLS), electron microscopy (SEM/TEM) and atomic force microscopy (AFM). The data are in a good agreement with our proposed growth model.
Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544, USA.
Ostwald ripening, the interfacial-energy-driven dissolution and reprecipitation of solutes, becomes an increasingly significant problem for nanoparticle formulations. We present the first quantitative study of Ostwald ripening for nanoparticle dispersions. The Lifshitz-Slyozov-Wagner (LSW) theory of particle growth driven by diffusion is applied to study beta-carotene nanoparticles with sizes of O(100 nm) formed by our block-copolymer protected Flash Nanoprecipitation process. A numerical implementation of the LSW theory that accounts for the original particle size distribution is presented. The predicted particle sizes from the numerical simulation are compared with the experimental results measured by dynamical light scattering. The results show quantitative agreement with no adjustable parameters. The addition of antisolvent results in the reduction of the ripening rate by dramatically decreasing bulk solubility.