Control Of Particle Morphology Research Articles

Improvement of oxidative decomposition activity on hollandite type photocatalyst against pentachlorophenol

Endocrine-disrupting chemicals such as pentachlorophenol (C6Cl5OH) are hazardous for the generative function of living creatures. Photocatalysts give us an effective route for removing these pollutants. Most of the reports are related to a photocatalyst of titanium dioxide (TiO2) fine particles loaded with metal particles such as Pt or Ag. However, a diversity of photocatalysts is required to deal with the increasing number of identified harmful chemicals which occur under a range of different conditions.Hollandites have one-dimensional tunnel-like framework structure. K2Ga2Sn6O16 (KGSO) is one of hollandite type compounds. In this study, hollandite type KGSO fine powders were fabricated using sol–gel method. The hydrolysis route was carefully observed for preparation of KGSO fine powders with high photocatalytic activity. To prepare the fine powder, the influence of hydrolysis temperature on preparation of fine powder was examined. It was found that the control of aforementioned temperature was very important for preparation of nano-sized KGSO powders with high activity. In addition, the authors controlled particle morphology of KGSO using different preparation conditions. The oxidative decomposition activity against C6Cl5OH on round shape KGSO nano-particles (78%) was much higher than that on the elongated shape KGSO particles (46.2%). It is concluded that the control of morphology and size of KGSO particles maximized the photocatalytic activity on KGSO for oxidative decomposition of C6Cl5OH. In addition, KGSO did not produce organic chlorides as by-products in the photocatalysis. Accordingly, it is expected that KGSO will be one of promising photocatalysts for decomposition of harmful aromatic compound C6Cl5OH under weak UV illumination.

Dynamics of the interaction forces at the silver/solution interface during amine adsorption.

The forces of interaction between a silver-coated particle and a flat silver surface in an aqueous medium were measured in the presence of a series of organic amines of varying concentrations. Atomic force microscopy (AFM) was used to quantify the replacement rate of adsorbed citrate molecules on the silver surfaces by a variety of amines, under conditions where the time scale of the amine adsorption was significantly slower than the time scale of the AFM measurements. The decay length of the electrostatic double-layer interaction between the silver surfaces was found to be time independent; thus, the change in surface change density (determined from the interaction forces) was used to quantify the replacement rate of adsorbed citrate by amine. In the absence of amine, the interaction force between the silver surfaces exhibited evidence of a multilayer structure of adsorbed citrate molecules on each silver surface. Upon addition of the amine, a decrease in the interaction force was always observed, where the dynamics of the force were dependent on both concentration and the molecular structure of the amine. These results are discussed with respect to formation of colloidal particles in synthesis routes where particle aggregation has a significant impact on the control of particle morphology and size.

Control of particle morphology and film structures of carboxylated poly(methyl methacrylate)/poly (n‐butylacrylate) composite latex particles

AbstractParticles with a hard core of 66% poly(methyl methacrylate)/34% poly(n‐butyl acrylate) copolymer and a soft shell of pure poly(n‐butyl acrylate) were synthesized via a two‐stage emulsion polymerization process. The particle morphology and the surface structure of the dispersion films were analyzed by atomic force microscopy (AFM). The results, concerning single particle structure and the corresponding films, are correlated to macroscopic properties similar to the minimum expected from the kinetic side. The different morphologies are compared to the findings reported in a previous article, where the corresponding soft‐core/hard‐shell dispersions were analyzed (Kirsch et al. Colloid Surf A 2001, 183–185, 725). The key parameters to tailor the particle morphology are thermodynamic factors, for example: (i) the stage ratio and (ii) the phase compatibility and kinetic factors affecting the polymer chain mobility (e.g., cross‐linking and polymer glass transition temperature). In this work, we used a core material which is in the glassy state at room temperature, however, above the polymer glass temperature (Tg) at polymerization temperature. The diffusion of the second‐stage polymer chains is therefore strongly affected. From this point of view, the major influence for the current system is expected from the kinetic side. The different morphologies of the single particles are discussed qualitatively and the effects of reaction parameters and our results from previous work are compared to the results of computer simulation work and other results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2610–2623, 2004

Controlling Particle Morphology during Growth of Bayerite in Aluminate Solutions

To study the influence of the orientations of the faces of metal oxyhydroxides on their surface reactivity, the synthesis of bayerite [β-Al(OH)3] particles with different morphologies was studied. The growth of bayerite was performed in aqueous solution at 70 °C by continuously injecting a sodium aluminate solution and stabilizing the pH at a constant value by monitoring the injection of a nitric acid solution. The effects of the following parameters were studied: pH, flow rate of aluminate solution, total duration of synthesis, and seeding. The solids were characterized by high-resolution SEM, XRD, IR spectroscopy, thermogravimetric analysis, and surface area measurements. By choosing the growth parameters, we were able to control the morphology of particles with shapes ranging from agglomerates of rods or cones to ovoid crystallites. In certain cases, traces of gibbsite, norstandite, and pseudoboehmite were obtained in addition to bayerite, but their quantity can be minimized.

Latex Particle Morphology, Fundamental Aspects: A Review

The control of particle morphology is an essential part of producing high quality latex products for applications in coatings, adhesives, impact modifiers, and medical diagnostics, among others. A great variety of formulation and process variables are available to manipulate the particle structure and many different morphologies have been created. Techniques to characterize these morphologies are varied, but electron microscopy of both whole and sectioned particles is the most common one used. Atomic force microscopy is gaining in utility and often two or more characterization methods are simultaneously used to gain clarity of interpretation. A great deal of basic understanding of the factors controlling the morphology has been achieved by applying equilibrium thermodynamics to phase separated particles in aqueous media. Interfacial tensions at the polymer‐water interface and at the polymer–polymer interface, along with crosslinking density are found to be the dominant factors controlling the equilibrium morphology. In turn there is a significant number of formulation variables which determine the interfacial tensions and the crosslinking density. Successful models have been developed and applied to a number of different polymer systems. Much less progress has been made in understanding the development of non‐equilibrium morphologies where the possible number of particle structures is essentially infinite. Here, characterization techniques become somewhat less precise in identifying exact structure and further work is needed to advance this capability. In the dynamic reaction environment of the latex process the morphology develops within very viscous phases and is a result of competitive reaction and diffusion processes. Some progress has been made to quantitatively describe these phenomena, but more work is needed. This is even more evident when extension to carboxylic and hybrid (e.g. polyurethane/acrylic) latices is desired.

Mathematical Model for the Emulsion Polymerization Reaction Kinetics of Two Phase Latex Particles

Many of today's industrial applications of emulsion polymers require the creation of polymer particles with specifically designed structures. A fair amount of work has been done on predicting and controlling particle morphology, and it is recognized that the reaction kinetics often play an important role in determining that morphology. The present work describes a procedure to calculate the reaction rate for two‐phase latex particles by extending the classic Smith–Ewart concepts to the more complicated situation. The model involves a complete account of radical events in both polymeric phases. Eight rate parameters are necessary to completely describe the system. A particle population distribution is generated to reflect the probability of specific particles to have two distinct numbers of radicals in each phase. Simple statistics on this population allow the calculation of the average number of radicals for each polymeric phase. The model collapses to the correct answers when applied to single‐phase particles and results in the prediction of the number of radicals in each of the phases when applied to structured particles. Several examples are described for core–shell (or inverted core–shell) and hemispherical particles in which the polymer Tg, monomer concentration and radical entry rates are varied. In addition, the effects of radical transfer rates between the polymer phases are highlighted. Such effects are found to be important for some polymer systems and not so important for others. The model is readily extendible to occluded structures. Since the reaction kinetics are concluded to be significantly dependent upon the particle morphology, it is clear that morphology development and reaction kinetics are coupled processes and need to be treated simultaneously in order to produce an effective overall model for two‐phase emulsion polymers.

Studies for a new generation of acrylic binders for exterior wood coatings

Modern acrylic binders for water-based exterior wood coatings should give films which are tack-free, hard and blocking resistant and at the same time very flexible to guarantee a long service life. This study shows that multiphase acrylic emulsions with controlled particle morphology give a means to overcome these contradictory requirements. Binder parameters such as polarity, particle size and surface functionality as well as the type and quantity of surfactants used in the process also have a strong influence on fundamental wood coating properties, such as water protection, blushing resistance, viscosity, wet adhesion and durability.

High-resolution electron microscopy and microanalysis of ordered arrays of size-controlled amorphous gallium nitride nanoparticles synthesizedin situin a block copolymer matrix

Abstract The objective of this work was to produce an ordered array of size-controlled gallium nitride (GaN) nanoparticles. The synthesis was performed by the in situ formulation and subsequent decomposition of cyclotrigallazane in a polystyrene (PS)-b-poly(4-vinylpyridine) (b-P4VP) block copolymer matrix. The matrix served as a templating medium to constrain the particle size and to allow the control of particle morphology, spacing and packing arrangement. The size and spacing of nanoparticles were controlled by the molecular weight of the entire polymer chain (81 000g mol−1), and the particle morphology and packing arrangement were controlled by the ratio of the sequestering block to the matrix block (21 wt% P4VP to 79 wt% PS by elemental analysis). High-resolution and analytical transmission electron microscopy revealed the amorphous nanoparticles to be composed mainly of gallium and nitrogen (with oxygen detected in some particles) about 10nm in diameter with an average interparticle distance of 60 nm and organized in a regular hexagonal packing arrangement. The impact of this synthesis technique is to afford the means to investigate systematically the effect of quantum confinement and quantum coupling on the optical properties of small GaN particles.

High-resolution electron microscopy and microanalysis of ordered arrays of size-controlled amorphous gallium nitride nanoparticles synthesized in situ in a block copolymer matrix

Abstract The objective of this work was to produce an ordered array of size-controlled gallium nitride (GaN) nanoparticles. The synthesis was performed by the in situ formulation and subsequent decomposition of cyclotrigallazane in a polystyrene (PS)-b-poly(4-vinylpyridine) (b-P4VP) block copolymer matrix. The matrix served as a templating medium to constrain the particle size and to allow the control of particle morphology, spacing and packing arrangement. The size and spacing of nanoparticles were controlled by the molecular weight of the entire polymer chain (81 000g mol−1), and the particle morphology and packing arrangement were controlled by the ratio of the sequestering block to the matrix block (21 wt% P4VP to 79 wt% PS by elemental analysis). High-resolution and analytical transmission electron microscopy revealed the amorphous nanoparticles to be composed mainly of gallium and nitrogen (with oxygen detected in some particles) about 10nm in diameter with an average interparticle distance of 60 nm and organized in a regular hexagonal packing arrangement. The impact of this synthesis technique is to afford the means to investigate systematically the effect of quantum confinement and quantum coupling on the optical properties of small GaN particles.

Polymer-Assisted Control of Particle Morphology and Particle Size of Zinc Oxide Precipitated from Aqueous Solution

Water-soluble poly(ethylene oxide-block-methacrylic acid) (P(EO-b-MAA)) and poly(ethylene oxide-block-styrene sulfonic acid) (P(EO-b-SSH)) diblock copolymers were used to control the particle morphologies, sizes and size distributions of zinc oxide precipitated from aqueous solution. With P(EO-b-MAA) copolymers, hexagonal prismatic particles form. Their sizes and size distributions depend on the degrees of polymerization of the blocks. With P(EO-b-SSH) copolymers, the particle shape reminds one of a “stack of pancakes”. These samples have narrow size distributions, regardless of the degrees of polymerization of the P(EO-b-SSH) copolymers. All crystals have a central grain boundary assigned to twinning. There is evidence for P(EO-b-MAA) copolymer adsorption onto the basal planes of the zinc oxide particles, whereas with P(EO-b-SSH) also an adsorption onto the side faces seems possible. The polymers are incorporated to some extent in the crystals and the amount of the polymer incorporated depends on the initial polymer concentration of the reaction solution.

Gold Colloids from Cationic Surfactant Solutions. 1. Mechanisms That Control Particle Morphology

The mechanism of formation of gold particles by reduction of AuIII in solutions of alcyltrimethylammonium chloride surfactants was studied in the absence and in the presence of NaCl. AuIII anions interact strongly with trimethylammonium cations forming insoluble ion pairs (Torigoe et al. Langmuir 1992, 8, 59). Above the surfactant critical micelle concentration, the ion pairs are solubilized in the micelles returning to the solution. Gold particles were produced by photochemical reduction of the clear micellar solutions. The coupling between surfactant aggregation and inorganic crystallization phenomena in these systems was investigated using transmission electron microscopy (TEM), UV−vis, and time-resolved fluorescence spectroscopy. At concentrations close to the phase boundary of the L1 phase with the lyotropic liquid crystalline phases many gold particles have a threadlike morphology, as previously noted by Esumi et al. (Langmuir 1995, 11, 3285). The presence of NaCl modifies the micellar size and affects the gold crystallization process in surprising and unexpected ways, as evidenced by intermediate structures observed by TEM. Our observations support the idea that the formation of threadlike gold particles occurs primarily through a combination of crystal aggregation and specific crystal face stabilization and not through templating mechanisms.

Continuous production of LiCoO2 fine crystals for lithium batteries by hydrothermal synthesis under supercritical condition

Specific features of supercritical hydrothermal crystallization synthesis (SHCS) by a rapid heating flow type method are reviewed. The attractive features of the method are (i) quantitative production of ultrafine particles, and (u) control of particle morphology or crystal structure by varying the pressure, temperature or reaction atmosphere (reducing or oxidizing). In this study, we use this method to continuously produce LiCoOz fine crystals that are used as for the cathode materials of rechargeable lithium ion batteries. LiOH and Co(NO& were chosen as starting materials. For oxidizing Co(II) to Co(III), O2 was introduced into the reactor after decomposing HzOz aqueous solution in a preheating tubing. LiCoO2 particles were formed in a single phase at supercritical conditions. scanning electron micrographs showed that the particle size was in the range of 500 to 1,000 nm in diameter. Electrochemical characterization was performed by a constant current discharge and charge test. Little decrease in the discharge capacity suggests high stability of the LiCoOz crystals prepared by this method.

Control of particle morphology and film structures of carboxylated poly ( n butylacrylate)/poly (methyl methacrylate) composite latex particles

Particles with a soft (s) core of poly ( n-butyl acrylate)/poly (methyl methacrylate) (PBA/PMMA) copolymer and a hard (h) shell of PMMA were synthesized via a two-stage polymerization process. Two synthesis parameters were investigated: (i) the phase ratio of the core and the shell; and (ii) the compatibility of the two phases. The s/h phase ratio was varied from 100:0 to 0:100. The compatibility between the two phases was changed by (i) using acrylic acid (AA); (ii) by using pure PBA as core material; and (iii) by cross-linking the shell. Particle morphology was characterized by atomic force microscopy (AFM) on freeze-dried and on tempered single particles. The degree of coverage was found to depend on the shell content and the phase compatibility. The results are in good agreement with findings from transmission electron microscopy and solid state NMR given in Acta Polymerica [50 (1999) 347]. The experimental results are compared to predictions from simulation work on the particle morphology based on thermodynamic and kinetic considerations. The second part of the paper focuses on the phase distribution and the film morphology of films formed by the structured particles. Phase distribution at the surfaces, degree of film formation and the phase distribution in the bulk are characterized by AFM, cross-correlated and compared to the findings regarding particle structure in the first part of the paper. This approach is to our knowledge unique regarding its completeness and new in its methodology. The microscopic results concerning the bulk, the single particle and the surface properties are correlated to macroscopic properties like the minimum film forming temperature, pendulum hardness and gloss.

A new way to control particle morphology in heterophase polymerizations

The formation of microphase separated structures in the confined space of latex particles is reported. Three different systems are investigated: emulsion polymerizations started either with polymeric radicals or with persulfate in the presence of ionic chain transfer agents, aqueous dispersions of well defined polystyrene model oligomers with sulfonate end groups, and miniemulsion polymerization in the presence of large amounts of preformed polymer in the droplets. In any of these cases microphase separation leads to the formation of inhomogeneities in the particles. Electron microscopy, atomic force microscopy, and X-ray absorption microscopy show identical structures and hence prove that the inhomogeneities already exit in the dispersed state.

Investigation of polymer-protected noble metal nanoparticles by transmission electron microscopy: control of particle morphology and shape

Noble metal nanoparticles were prepared by the in situ reduction of the respective metal salt precursors in the presence of various protective polymers. Transmission electron microscopy (TEM) has been used to determine the particle shapes and morphologies. These are strongly influenced by the reduction methods and conditions chosen, but the choice of the protective polymer is equally important for controlling the particle morphologies and for the stabilization of the colloids. A whole spectrum of nanoparticle morphologies and shapes was obtained, ranging from nanoagglomerates which are nevertheless well-defined and well-stabilized to nanosized single crystals with triangular shape.

Tailored syntheses of nanostructured silicas: Control of particle morphology, particle size and pore size

Ordered mesoporous silicas with spherical morphology and average particle size in the range between 100 nm and 2 μm were synthesised according to two novel routes. Both synthesis routes used tetraethoxysilane, water, alcohol and aqueous ammonia for producing spherical silica beads. The porosity was created by adding two different kinds of pore structure directing agents to the starting solution: one was an n-alkyltrialkoxysilane which was covalently bonded to the silica framework, the other was an n-alkylamine which acted as a nonionic template. After calcination and post treatment the resulting particles showed a specific surface area up to 1000 m 2 g -1, a specific pore volume of up to 0.8 cm 3g -1 and an average pore diameter between 2 and 6 nm.

Coaxial nozzle for control of particle morphology in precipitation with a compressed fluid antisolvent

A coaxial nozzle was developed to achieve further control over the morphology of microparticles precipitated from solution by carbon dioxide as a compressed fluid antisolvent. The polymer solution was sprayed through the core of the nozzle and CO2 through the annulus. For the coaxial nozzle versus a standard nozzle, polystyrene and poly(L-lactic acid) particles can be larger by a factor of 3–8 with less flocculation. A reduction in the Weber number reduces atomization and larger droplets are formed in the jet, delaying precipitation. However, because of the much higher Reynolds number for the high velocity CO2, the mass transfer in the suspension outside of the jet is faster leading to less flocculation and agglomeration. For polyacrylonitrile, the delayed precipitation produces a transition from highly oriented microfibrils to microparticles. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2105–2118, 1997

Coaxial nozzle for control of particle morphology in precipitation with a compressed fluid antisolvent

A coaxial nozzle was developed to achieve further control over the morphology of microparticles precipitated from solution by carbon dioxide as a compressed fluid antisolvent. The polymer solution was sprayed through the core of the nozzle and CO2 through the annulus. For the coaxial nozzle versus a standard nozzle, polystyrene and poly(L-lactic acid) particles can be larger by a factor of 3–8 with less flocculation. A reduction in the Weber number reduces atomization and larger droplets are formed in the jet, delaying precipitation. However, because of the much higher Reynolds number for the high velocity CO2, the mass transfer in the suspension outside of the jet is faster leading to less flocculation and agglomeration. For polyacrylonitrile, the delayed precipitation produces a transition from highly oriented microfibrils to microparticles. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2105–2118, 1997

Effect of Particle Morphology on Emitted Dose of Fatty Acid-Treated Disodium Cromoglycate Powder Aerosols

ABSTRACTThese studies assess the quantity and morphology of the emitted aerosolized dose of irregularly shaped disodium cromoglycate particles in the fine particle fraction using in vitro methods. Disodium cromoglycate was treated with a homologous series of saturated fatty acids, between Cs and C18, in a range of concentrations. The products of these treatments were powders with a variety of particle size, shape, and aggregation characteristics. Samples of these powders were loaded in gelatin capsules, generated as aerosols from a Rotahaler® and collected in a two-stage liquid impinger or eight-stage inertial impactor. Particles were examined directly by scanning electron microscopy and subsequently the images were analyzed to define morphology. The aerodynamic fine-particle fraction determined by the two-stage impinger increased approximately twofold with lauric acid treatment (0.0317 g/g, 6.7%) and threefold with stearic acid treatment (0.58 gig; 9.7%) compared with disodium cromoglycate alone (0 g/g, 3.56%). The lauric acid formulation appeared to alter deposition primarily by changing particle morphology. Stearic acid altered particle shape to some extent and the increase in the fine-particle fraction appeared to be attributable to improved particle dispersion properties. The uncontrolled presence of irregular-shaped particles can introduce dosing errors due to effects on dispersion and aerodynamic behavior. Conversely, controlled particle morphology and size may be employed to optimize the dose delivered to the lungs particularly if particle-particle and particle-surface interactions can be minimized.

Control of particle morphology and homogeneity during spray pyrolysis

Control of particle morphology and homogeneity during spray pyrolysis