Investigations of the properties of the manganese dioxide suspensions in the presence of guar gum and carboxymethylcellulose

Properties of manganese dioxide suspensions in the presence of two polysaccharides: non-ionic guar gum (GG) and anionic carboxymethylcellulose (CMC) were investigated using NaCl as a background electrolyte. The colloidal stability of MnO₂ suspensions in the presence and absence of these two polymers was measured. It was found that both polymers improve stability of measured suspensions. This fact results from steric stabilization (low polymer concentrations) and depletion stabilization (high polymer concentrations) for MnO₂ particles covered with macromolecules. Next the kinetics of the adsorption of these two polymers on MnO₂ as well as the heats of GG and CMC adsorption processes were measured. The obtained data proved that CMC is adsorbed more effectively on the manganese dioxide surface than guar gum. To obtain more information about the changes of adsorption of these polymers on MnO₂ some factors influencing this process (pH, ionic strength of the background electrolyte) were investigated. The data obtained from the surface charge density and the zeta potential measurements allowed the analysis of the structure of the electric double layer created by polymers on the solid surface.     

Use of the Tension Cell to Monitor Particle Interactions in Suspensions

The tension cell was able to monitor the effect of adsorbing either a nonionic or ionic surface active agent on particle arrangements in kaolinite suspensions. Adsorption of polysorbate 80 affected particle interactions by steric stabilization. Adsorption of sodium dodecylbenzenosulfonate produced dispersion by a combination of electrostatic repulsion and steric stabilization. The interpretation of the effect of the adsorbed surface active agents was supported by rheological studies     

The stability of BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanoparticles in polar solvents

We have studied suspensions of hard-magnetic BaFe₁₂O₁₉ particles in water, ethanol and 1-butanol. The surfaces of these particles were previously modified with the surfactant dodecylbenzylsulphonic acid. The stabilities of the suspensions were estimated from their saturation concentrations and zeta potentials. We found that the 1-butanol suspensions were more stable than the ethanol-based suspensions and much more stable than the water-based suspensions. We analyzed the suspensions and the dispersed particles using gravimetry, conductometry and transmission electron microscopy, measured their zeta potentials, and calculated the interparticle-attraction interaction energies due to the van der Waals and magnetic dipole–dipole forces. The magnitudes of the attraction energies varied significantly with the particles’ sizes and the separation distances between the particles, and we found that the contribution of the van der Waals attraction energy can be neglected with respect to the magnetic dipole–dipole attraction. The observed differences in the stability of the suspensions were explained on the basis of the calculated electrostatic and steric repulsion energies. Electrosteric stabilization was possible in the 1-butanol and the ethanol for particles with radii and thicknesses up to 15 nm, while a too small electrostatic repulsion and the absence of steric repulsion in the water resulted in rapid agglomeration.     

纳米TiO2表面吸附聚乙二醇及其分散稳定性的研究

通过四氯化钛水解法制备纳米TiO2，讨论聚乙二醇(PEG)在其水悬浮体系中的吸附行为．IR和吸附实验结果表明：纳米TiO2通过氢键吸附PEG，其表面吸附行为与PEG浓度、PEG分子量、pH值和晶粒尺寸等因素相关．吸附PEG以后，纳米TiO2颗粒的表面电荷和(电位发生变化．悬浮体系吸光度的变化和TEM分析表明：纳米TiO2吸附PEG后，增加了颗粒间的空间位阻作用，有效地阻止了纳米TiO2的团聚；但若PEG加入量达到过饱和，反而会破坏纳米TiO2的分散稳定性．     

Simultaneous quantification of polymeric and surface active stabilizers of nanosuspensions by using near-infrared spectroscopy

Nanosuspension technology is an attractive approach for the formulation and solubility enhancement of poorly water-soluble drug compounds. The technology requires adequate excipients for stabilizing the suspensions during nanogrinding and storage. This study aimed at establishing a near-infrared (NIR) method for assaying simultaneously the two nanoparticle stabilizers, sodium dodecyl sulphate (SDS) and hydroxypropylcellulose (HPC), in miconazole nanosuspensions. Second derivative of NIR signals was used to establish calibration curves in concentration ranges of interest of SDS (0.03-0.3%) and HPC (0.75-7.5%). The suitability and applicability of the NIR method was verified by evaluating the linearity, accuracy, precision, and specificity of the obtained data. The method was then used to quantify indirectly the amount of SDS and HPC adsorbed onto miconazole nanoparticles. Within the concentration range of interest, SDS adsorption increased up to 122 μg/m(2) (4.2?×?10(-7) mol/m(2)) with increasing SDS concentration, and HPC adsorption was in the range of 800-1000 μg/m(2) (21-27?×?10(-7) mol/m(2)) for nanosuspensions containing nominally 5% HPC and 12.5% or 20% miconazole. Interestingly, some of the adsorbed HPC was displaced upon increase of SDS concentration and adsorption. The data were also confirmed by surface tension measurements of aqueous solutions of SDS and HPC and nanosuspension supernatants. The availability of a fast and nondestructive method for quantifying simultaneously the adsorption of two stabilizers onto nanoground particles may not only speed up nanosuspension development, but also provide insight into the mechanisms of nanoparticle stabilization regarding competitive adsorption and electrostatic versus steric stabilization.     

Effect of aminosilane adsorption on rheology of silica powders in nonaqueous media

An aminosilane,N-(3-acryloxy-2-hydroxyl propyl)-3-amino-propyltriethoxysilane (AHAS), was used to disperse and stabilize Stober silica suspensions via steric stabilization in nonaqueous media. The effect of variables, such as the calcination temperature of the silica, the water content of the solvents, the physicochemical properties of solvent media, the particle size distributions of the silica, and the proportions of mixed solvent were studied. Viscosity measurements were conducted to assess the dispersion behaviour of the silica suspensions. Fourier transform-infrared analysis was used to deduce the mechanism of AHAS adsorption on the silica surface. The effect of the water content in the silica suspension was found to be highly dependent upon the degree of silica surface hydration before AHAS addition and also upon the kind of solvent medium used. It was observed that electrostatic contribution to the silica stabilization was appreciably greater than anticipated and was found to be a function of the relative acid-base nature of the organic solvent. Analyses of rheological data and infrared spectra were used to explain the behaviour of the silica suspensions.     

Adsorption of polyvinylpyrrolidone (PVP) and its effect on the consolidation of suspensions of nanocrystalline CeO2 particles

CeO₂ particles with an average size of 9 nm were synthesized under hydrothermal conditions. The adsorption of polyvinylpyrrolidone (PVP) on to the particle surfaces was measured in aqueous suspensions in the pH range of 3.7 to 11.5. The amount of adsorbed PVP decreased significantly with increasing pH value. For suspensions prepared at a pH value of 3.7, complete adsorption occurred for 2.5 wt% of PVP added to the suspension. Further additions of PVP produced a gradual increase in the adsorption until a limiting value was reached when the total amount of PVP added to the suspension was 10 wt%. At this PVP concentration, 6 wt% of the PVP was adsorbed and 4 wt% remained free in solution. The effect of the adsorbed PVP on the microstructural homogeneity of films deposited by spin coating of suspensions was investigated. With no addition of PVP, crack-like voids were prevalent in the dried and sintered films. Crack-free films were obtained from suspensions containing 10 wt% of PVP. Higher PVP additions (25 wt%) produced an increase in the viscosity of the suspension but no observable change in the microstructural homogeneity of the films. The use of adsorbed polymers for steric stabilization coupled with data from the adsorption isotherms is shown to provide a rational approach to the deposition of homogeneous films from suspensions of nanocrystalline particles.     

The modification of rheologic properties of clays with PVA effect

The rheological parameters of clay suspensions can be used to examine particle–particle interactions. The polymers that have been added to the clay suspensions interact with clay particles, according to their ionic or non-ionic character. In this study, the changes in the rheologic properties of three different samples, which are two different bentonitic clays and hectorite, have been studied with various concentrations of polyvinyl alcohol (PVA). It has been determined that the flow properties, such as apparent and plastic viscosity, shear stress and yield value point, change with the clay type, chemical properties of the additive material and their concentration. All the results have been commented by taking the interaction between the clay and the polymer molecules into consideration. XRD studied showed that natural bentonite samples have more expandable, up to 24 Å, than other samples, which their expandibilities are relatively constant at about 15 Å.     

Effect of superplasticizers on the rheological properties of cements

In this paper, the rheological properties of cement pastes made with different types of cement and superplasticizers are discussed. As a tool for the discussion, experiments involving dispersion of cement particles, fluidity, viscosity, yield stress and zeta potential have been conducted. The results obtained show that the chemical compositions of the cements such as C₃A and sulfate content, alkali and ground lime content are important features controlling the rheology of cement pastes. Three types of sulfonated superplasticizers (lignosulonate-based, melamine formaldehyde sulfonic acid, naphthalene formaldehyde sulfonic acid) and one type of polycarboxylic acid polymer were used. The results revealed that the mechanism by which these polymers disperse cement particles differs fundamentally. Sulfonated superplasticizers induced a negative charge on cement particles dispersing them by electrostatic repulsion, whereas with the polycarboxylate-based polymer the dispersion mechanism is mainly controlled by steric hindrance. A model for the adsorption of superplasticizer on a cement particle is proposed.     

Stability of poly(ethylene glycol)-graft-polyethylenimine copolymer/DNA complexes: influences of PEG molecular weight and PEGylation degree

Polyethylenimine (PEI) is one of the most widely investigated cationic polymers for gene delivery. However, PEI/DNA complexes are unstable and tend to aggregate. PEGylation was used to improve the stability. The stability of polymer/DNA complexes was investigated including complexation stability, aggregation stability, sedimentation stability, and nuclease stability. PEI25K/DNA complexes were liable to aggregate to large particles (500–700 nm). The aggregation was proved to be induced by phosphate anion. In the medium without phosphate anion, aggregation was prevented by electrostatic repulsion. Owing to more efficient steric repulsion, PEG2 and PEG5K excelled PEG750 in facilitating copolymers to form stable small polyplexes (below 100 nm) without aggregation regardless of phosphate anion. The steric repulsion predominated over electrostatic repulsion in stabilization.     

Simultaneous quantification of polymeric and surface active stabilizers of nanosuspensions by using near-infrared spectroscopy

Nanosuspension technology is an attractive approach for the formulation and solubility enhancement of poorly water-soluble drug compounds. The technology requires adequate excipients for stabilizing the suspensions during nanogrinding and storage. This study aimed at establishing a near-infrared (NIR) method for assaying simultaneously the two nanoparticle stabilizers, sodium dodecyl sulphate (SDS) and hydroxypropylcellulose (HPC), in miconazole nanosuspensions. Second derivative of NIR signals was used to establish calibration curves in concentration ranges of interest of SDS (0.03–0.3%) and HPC (0.75–7.5%). The suitability and applicability of the NIR method was verified by evaluating the linearity, accuracy, precision, and specificity of the obtained data. The method was then used to quantify indirectly the amount of SDS and HPC adsorbed onto miconazole nanoparticles. Within the concentration range of interest, SDS adsorption increased up to 122 µg/m² (4.2?×?10^?7 mol/m²) with increasing SDS concentration, and HPC adsorption was in the range of 800–1000 µg/m² (21–27?×?10^?7 mol/m²) for nanosuspensions containing nominally 5% HPC and 12.5% or 20% miconazole. Interestingly, some of the adsorbed HPC was displaced upon increase of SDS concentration and adsorption. The data were also confirmed by surface tension measurements of aqueous solutions of SDS and HPC and nanosuspension supernatants. The availability of a fast and nondestructive method for quantifying simultaneously the adsorption of two stabilizers onto nanoground particles may not only speed up nanosuspension development, but also provide insight into the mechanisms of nanoparticle stabilization regarding competitive adsorption and electrostatic versus steric stabilization.     

丙烯酸-丙烯酸酯共聚物对钛酸铋水悬浮液性质的影响

研究了丙烯酸－丙烯酸酯共聚物对钛酸铋（Bi4Ti3O12)悬浮液表面化学性质及流变性的影响。结果表明，共聚物的加入使Bi4Ti3O12的等电点向低pH值方向偏移。共聚物在粉体表面的吸附属于物理吸附，其含量的变化可以引起共聚物在粉体表面吸附构型的变化，当共聚物含量＞1．5wt%时，部分高分子脱附。共聚物的加入可以显著改善悬浮液的稳定性，在低共聚物含量和高共聚物含量均可制备稳定的悬浮液，共聚物含量≤1．5wt%时，浆料的稳定通过静电位阻稳定机理来实现，共聚物含量≥2.0wt%时，可能通过空位稳定机理来实现。     

磺化木质素蜜胺甲醛超塑化剂对水泥颗粒的分散稳定机理

系统研究了磺化木质素蜜胺甲醛超塑化剂(SLMF)的引气性能、在水泥颗粒表面的吸附性能、对水泥颗粒表面Zeta电位的影响.结果表明,SLMF0对水泥-水体系的分散机理是其含有的-SO-3和-COO-带电产生的静电斥力、在水泥颗粒表面吸附层产生的空间位阻力以及引气产生"滚珠"效应的共同作用;SLMF对水泥-水分散体系的稳定...     

Y-TZP悬浮液的界面吸附特性

本文利用聚电解质分散剂聚丙烯酸铵（ＮＨ_４ＰＡＡ）制备了稳定的Ｙ－ＴＺＰ悬浮液．通过等温吸附实验和电动特性测定发现,分散剂浓度为２ｗｔ％时,在粉体颗粒表面的吸附达饱和,悬浮液的等电点（ＩＥＰ）向酸性区移动．扫描俄歇能谱（ＳＡＭ）分析和原子力显微镜（ＡＦＭ）研究表明,粉体的表面化学键结构因分散剂的吸附而改变,悬浮颗粒之间的相互排斥能增大．悬浮液的粘度在分散剂饱和吸附时达到最小值,浆料的悬浮稳定性得到了提高.     

Interfacial Adsorption of Polymers and Surfactants: Implications for the Properties of Disperse Systems of Pharmaceutical Interest

This review considers basic aspects of the interfacial adsorption of polymers and surfactants, with particular reference to the relevance of these processes for the formulation of pharmaceutical disperse systems. First, we discuss different approaches to the interpretation of adsorption isotherms, paying particular attention to systems containing more than one adsorbate. Second, we consider the implications of adsorption for the properties of suspensions, emulsions, and colloidal systems, particularly as regards the use of polymers and surfactants for stabilizing disperse systems, for controlling flocculation, and for modifying the biopharmaceutical behavior of colloidal drug carriers. Finally, we present a number of representative examples of the importance of adsorption of macromolecules in pharmaceutical systems.     

Interfacial Adsorption of Polymers and Surfactants: Implications for the Properties of Disperse Systems of Pharmaceutical Interest

This review considers basic aspects of the interfacial adsorption of polymers and surfactants, with particular reference to the relevance of these processes for the formulation of pharmaceutical disperse systems. First, we discuss different approaches to the interpretation of adsorption isotherms, paying particular attention to systems containing more than one adsorbate. Second, we consider the implications of adsorption for the properties of suspensions, emulsions, and colloidal systems, particularly as regards the use of polymers and surfactants for stabilizing disperse systems, for controlling flocculation, and for modifying the biopharmaceutical behavior of colloidal drug carriers. Finally, we present a number of representative examples of the importance of adsorption of macromolecules in pharmaceutical systems.     

INTERACTION OF GRAVITY AND ELECTROSTATIC EFFECTS IN PIPE FLOW OF A GAS-PARTICLE SUSPENSION

The interaction of gravity and electrostatic effects in isothermal, fully developed, horizontal turbulent pipe flow of dilute suspensions has been examined. Experimental study has validated the fact that, in the presence of gravity, increased space charge associated with increased local concentration due to gravity accentuates the asymmetry in mass flux and particles density distributions in the vertical plane passing through the pipe centerline. The space charge effect on the particle mass flux distribution near the pipe bottom is enhanced by increased particle density. Measurements were made with air suspensions of monodispensed particles of alumina and latex with non-uniform particle charge in pipes of 51 mm and 127 mm diameters.     

Simulation of the packing of granular mixtures of non-convex particles and voids characterization

The simulation of granular materials has considerably developed in the last decades essentially with simple geometry particles. The purpose of this paper is to study granular systems of non-convex particles which are present in many industrial processes. Two shapes of large and two shapes of small non-convex particles resulting from the cutting of a hollow cylinder are modelled, and binary mixtures containing varying proportions of small and large particles are generated with a Monte Carlo simulation. Two different states of the granular systems are studied: suspensions and packings obtained after sedimentation. No contact force model is used and only steric repulsion is taken into account. The density, the pore size distribution and the tortuosity of the granular systems are studied. The results are compared to those obtained with granular systems of convex particles.     

Novel aspects of wet milling for the production of microsuspensions and nanosuspensions of poorly water-soluble drugs

Micronization and nanoparticle production of poorly water-soluble drugs was investigated using single wet milling equipment operating in the attritor and stirred media modes. The drug particles in the median size range of 0.2?2??m were prepared by changing the milling mode and operating conditions of a Micros mill with a purpose of elucidating the dynamics of the wet milling process. It was determined that particle breakage due to mechanical stresses and aggregation due to insufficient stabilization are two competing mechanisms which together control the wet milling dynamics of the poorly water-soluble drugs. The study in the attritor mode using four different classes of stabilizers with six drugs indicated that steric stabilization worked better than electrostatic stabilization for the drugs studied. In addition, the existence of different minimum polymer concentrations for the stabilization of microsuspensions and nanosuspensions was indicated. The major role of a non-ionic polymer during the production of fine particles is its stabilization action through steric effects, and no experimental evidence was found to support the so-called Rehbinder effect. Periodic addition of the polymer as opposed to the addition of the polymer at the start of milling process was introduced as a novel processing method. This novel method of polymer addition provided effective stabilization and breakage of drug particles leading to a narrower and finer particle size distribution. Alternatively, it may allow shorter processing time and lower overall power consumption of the milling process for a desired particle size.     

A STUDY OF MULTI-FUNCTIONAL ELECTROLYTIC OLIGOMERS AS DISPERSANTS FOR CONCENTRATED AQUEOUS ALUMINA SUSPENSIONS

ABSTRACT

The effects of dispersant charge density, active binding site density, and hydrophilic/hydrophobic balance on the rheology of concentrated aqueous alumina suspensions have been studied. Twenty-one three- and four-component oligomeric dispersants with varying monomer composition were synthesized by free-radical telomerization of acrylic acid (AA), acrylamide (AAm), methyl acrylate (MA), and sodium acrylamido-2-methyl-propanesulfonate (NaAMPS). The monomer compositions for the dispersants were varied between 40 and 75%, 3 and 50%, 3 and 30%, and 0 and 15% for AA, AAm, MA, and NaAMPS, respectively. Aqueous alumina suspensions of volume fraction 0.50 at pH 9.5 were obtainable with all the dispersants. Rheological measurements of these suspensions revealed that most of these dispersants produced suspensions with similar viscosity with only a few exceptions. Rheological comparison of these suspensions with suspensions produced with poly(acrylic acid) of molecular weight 1800 (PAA-1800) showed that a good number of the multi-component were more effective than the PAA-1800, This material is recognized as being one of the most effective dispersants for alumina suspensions under conditions used in this study, according to the unpublished ERC results. Zeta-potential measurements and adsorption studies gave a good indication that differences between PAA-1800 and the multi-component dispersants may be due to steric forces brought about by differences in dispersant conformation and adsorption behavior.