Characteristics of spontaneously formed nanoemulsions in octane/AOT/brine systems

Nanoemulsions were formed spontaneously by diluting water-in-oil (W/O) or brine-in-oil (B/O) microemulsions of a hydrocarbon (octane), anionic surfactant (Aerosol-OT or AOT) and water or NaCl brine in varying levels of excess brine. The water-continuous nanoemulsions were characterized by interfacial tension, dynamic light scattering, electrophoresis, optical microscopy and phase-behavior studies. The mechanism of emulsification was local supersaturation and resulting nucleation of oil during inversion. For nanoemulsions formed at low salinities with Winsor I phase behavior, octane drops grew from initial diameters of 150-250nm to 480-1000nm over 24h, depending on salinity. Growth was caused by mass transfer but seemed to approach the asymptotic stage of Ostwald ripening described by the Lifshitz-Slyozov-Wagner (LSW) theory only for dilution with salt-free water. Near the higher cross-over salinity (Winsor III), the nanoemulsions showed much slower growth with droplet size consistently remaining below 200nm over 24h and reaching 250nm after 1week. Birefringence indicated the presence of liquid crystal for these conditions, which could have contributed to the slow growth rate. At even higher salinity levels in the Winsor II domain, W/O/W multiple emulsions having drops greater than 1μm in diameter were consistently recorded for the first 5-7h, after which size decreased to values below 1μm. The number and size of internal water droplets in multiple emulsion drops was found to decrease over time, suggesting coalescence of internal droplets with the continuous water phase and mass transfer of water from internal droplets to continuous phase as possible mechanisms of the observed drop shrinkage. Electrophoresis studies showed the nanoemulsions to be highly negatively charged (zeta potentials of -60mV to -120mV). The high charge on octane droplets helped assure stability to flocculation and coalescence, thereby allowing mass transfer to control growth in the Winsor I and III regions.     

Adsorption and aggregation properties of amino acid-based N-alkyl cysteine monomeric and N,N'-dialkyl cystine gemini surfactants

An amino acid-based gemini surfactant derived from cystine (2CnCys, where n represents the hydrocarbon chain lengths of 8, 10, and 12) was synthesized by reacting cystine with n-alkyl bromide, and its adsorption and aggregation properties were characterized by measurements of equilibrium and dynamic surface tension and dynamic light scattering. The properties of 2CnCys were compared with those of an amino acid-based monomeric surfactant derived from cysteine (CnCys). For n=8 and 10, when compared to CnCys, 2CnCys exhibited excellent surface activities, such as a lower critical micelle concentration (cmc), greater efficiency in lowering the surface tension of water, and smaller area occupied per molecule. Adsorption rate at air/water interface decreased with an increase in hydrocarbon chain length, chain number, and concentration of respective compounds. Further, the kinetics were discussed using the monomer diffusion coefficient obtained from short and long time scales in dynamic surface tension plots. In addition, the aggregation properties of 2CnCys for n=8 and 10 differed from those in the case of n=12. In other words, relatively larger micelles with diameters of approximately 7 nm were formed by 2CnCys for n=8 and 10 in comparison to those formed by CnCys (2-3 nm). On the other hand, for a 0.832 mmol dm-3 2C12Cys solution, the aggregation structure investigated by cryogenic transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS) revealed the coexistence of small unilamellar vesicles and small rods.     

Synthesis of pure colloidal silver nanoparticles with high electroconductivity for printed electronic circuits: the effect of amines on their formation in aqueous media

This paper describes a practical and convenient method to prepare stable colloidal silver nanoparticles for use in printed electronic circuits. The method uses a dispersant and two kinds of reducing agents including 2-(dimethylamino) ethanol (DMAE), which play important roles in the reduction of silver ions in an aqueous medium. The effect of DMAE and dispersant, as well as the factors affecting particle size and morphology are investigated. In the formation of the silver nanoparticles, reduction occurs rapidly at room temperature and the silver particles can be separated easily from the mixture in a short time. In addition, organic solvents are not used. Pure, small and relatively uniform particles with a diameter less than 10 nm can be obtained that exhibit high electroconductivity. The silver nanoparticles are stable, and can be isolated as a dried powder that can be fully redispersed in deionized water. This method of producing colloidal silver nanoparticles will find practical use in electronics applications.     

Fine particles of icosahedral quasicrystal formed by gas evaporation technique

Al-T (T=Mn, V, Cr) particles in the icosahedral phase have been prepared by evaporation and condensation of metals in an inactive gas. The particles were spherical in shape, with diameters ranging from 50 to 300 nm, and showed speckled contrast in bright and dark field images. Each particle consisted of fine grains of several nm with small misorientations (less than a few degrees). Patterson functions of the icosahedral Al-Mn were also calculated from electron diffraction data. Among several structure models examined in the present study, a model with an array of two-shell Mackay icosahedra gave the best fit with the Patterson functions.     

Encapsulation of Inorganic Particles by Dispersion Polymerization in Polar Media: 2. Effect of Silica Size and Concentration on the Morphology of Silica–Polystyrene Composite Particles

Following a previous work (Bourgeat-Lami, E., and Lang, J.,J. Colloid Interface Sci.197, 293 (1998)), encapsulation of silica beads has been achieved by dispersion polymerization of styrene in an aqueous ethanol medium using poly(N-vinyl pyrrolidone) as stabilizer. Silica beads, prepared according to the Stöber method, were coated prior to polymerization by grafting 3-(trimethoxysilyl)propyl methacrylate onto the surface. A great number of silica beads per composite particle were previously found using beads that had diameters between 49 and 120 nm. In the present work, larger silica beads with diameters between 191 and 629 nm are investigated. We demonstrate by transmission electron microscopy that, consequently, only a small number of silica beads are contained in the composite particles. By counting the composite particles containing precisely zero, one, two, three, four, and more than four silica beads, it clearly appears that the encapsulation of only one silica bead can be obtained simply by increasing the size of the beads. Under our experimental conditions, the optimal bead diameter for achieving composite particles containing only one silica bead turns out to be around 450 nm. We show that increasing the silica bead size above this value results in an increased number of composite particles without silica beads. In contrast, the number of composite particles with two, three, four, or more than four silica beads increases with decreasing silica bead size. In addition to the above variations in composition of the composite particles, changes in particle shapes were also observed as a function of the size of the silica beads and the styrene concentration in the polymerization medium. Hypotheses concerning these variations are presented.     

In Vitro Skin Permeation Enhancement of KIOM-MA-128 by Monoolein Cubosomes

Monoolein (MO) cubosomes were investigated in terms of in vitro skin permeation enhancer of KIOM-MA-128 (MA-128), a natural product known to be efficacious against atopic dermatitis. First, an aqueous suspension of MA-128 was prepared by homogenizing the powder in Pluronic F-127 (a dispersant) solution in water. The Pluronic F-127 concentration and the pH have no significant effect on the size and the zeta potential of MA-128 particles. The mean diameters and the zeta potentials fell within 1000–1500 nm and ?10 to ?20 mV, respectively. The sedimentation rate of the particles was lower at a higher concentration of the polymeric dispersant, possibly because the polymeric surfactant can act as a spring and push away approaching particles. The size of MO cubosomes was tens to hundreds of nanometers and exhibited black and white stripes. Cumulative amount of MA-128 permeated through hairless mouse skin was obviously higher when the cubosome was included in the MA-128 suspensions. However, the cumulative permeation amount was inversely proportional to the content of cubosomes, when the contents of cubosome in the suspension increased from 0.5% to 2.0% with MA-128 concentrations kept constant (2%).     

CeOHCO3和CeO2束状纳米结构的制备及表征

The cantaloupe-like particles of CeOHCO₃ were synthesized in aqueous solution by using cetyltrimethylammonium bromide (CTAB) as soft template. Then, the bunchiness rods of CeO₂ were obtained by calcining CeOHCO₃ at 450 ℃. The results of thermogravimetric/differential thermal analysis reveal that an endothermic reaction with decomposition is involved in the transformation process from CeOHCO₃ to CeO₂. By scanning electron microscopy and X-ray diffraction analysis, it is found that the orthorhombic phase CeOHCO₃ particles are constituted of short nanorods with diameters ranging from several tens nm to over 100 nm, and the cubic phase CeO₂ rods are composed of small particles with diameter ca. 15 nm. From the results of UV-Vis absorption and photoluminescence analysis, it is found that the CeO₂ possess abundant defects, and the band gaps of the CeO₂ and CeOHCO₃ are ca. 2.70 eV and 3.87 eV, respectively.     

Microspectroscopic analysis of green fluorescent proteins infiltrated into mesoporous silica nanochannels

The infiltration of enhanced green fluorescent protein (EGFP) into nanochannels of different diameters in mesoporous silica particles was studied in detail by fluorescence microspectroscopy at room temperature. Silica particles from the MCM-41, ASNCs and SBA-15 families possessing nanometer-sized (3-8 nm in diameter) channels, comparable to the dimensions of the infiltrated guest protein EGFP (barrel structure with dimensions of 2.4 nm × 4.2 nm), were used as hosts. We found that it is necessary to first functionalize the surfaces of the silica particles with an amino-silane for effective encapsulation of EGFP. We demonstrated successful infiltration of the protein into the nanochannels based on fluorescence microspectroscopy and loading capacity calculations, even for nanochannel diameters approaching the protein dimensions. We studied the spatial distributions of the EGFPs within the silica particles by confocal laser scanning microscopy (CLSM) and multimode microscopy. Upon infiltration, the fluorescence lifetime drops as expected for an emitter embedded in a high refractive index medium. Further, the spectral properties of EGFP are preserved, confirming the structural integrity of the infiltrated protein. This inorganic-protein host-guest system is an example of a nanobiophotonic hybrid system that may lead to composite materials with novel optical properties.     

Versatile phase transfer of gold nanoparticles from aqueous media to different organic media

A novel, simple, and very efficient method to prepare hydrophobically modified gold particles is presented. Gold nanoparticles of different sizes and polydispersities were prepared. The diameter of the gold particles ranges from 5 to 37 nm. All systems were prepared in aqueous solution stabilized by citrate and afterwards transferred into an organic phase by using amphiphilic alkylamine ligands with different alkyl chain lengths. The chain length was varied between 8 and 18 alkyl groups. Depending on the particle size and the alkylamine, different transfer efficiencies were obtained. In some cases, the phase transfer has a yield of about 100%. After drying, the particles can be redispersed in different organic solvents. Characterization of the particles before and after transfer was performed by using UV/Vis spectroscopy, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS) techniques. The effect of organic solvents with various refractive indices on the plasmon band position was investigated.     

V（acac）3—AI（i—BU）2CI催化体系相态的研究

研究了V(acac)3-AI(i-BU)2CI催化体系的相态。通过Tyndall效应、电镜观察和超过渡实验,证明了在溶有丁二烯的甲苯溶剂中V(acac)3-AI(i-BU)2CI催化体系以小颗粒分散,粒径在1－100nm之间,为胶体催化剂,属于高度分散的多相催化体系。催化剂颗粒是无定形的,其活性中心位于胶粒表面,以较佳配比所得到的催化剂颗粒较小、分布均匀,对丁二烯聚合反应具有较高的催化活性。     

Study of Recrystallization Kinetics of AgBr Microcrystals in Water–Gelatin Gel

Recrystallization kinetics (Ostwald ripening) of silver bromide microcrystals in gelatin gel was studied. The study was made on model mixtures containing small silver bromide particles (about 60 nm) and larger microcrystals of different sizes (100–400 nm) and habits (cubic and octahedral). Variations in the average size of large crystals in the system were controlled by spectral turbidimetry. The growth rate of the large crystals was found to be directly proportional to the total solubility of a substance constituting the dispersed phase, as well as to difference in sizes of large and small particles. The kinetics of large crystal growth was also shown significantly to depend on the average distance between particles of the system. The theoretical model describing mass transfer during the Ostwald ripening in the closed disperse system was proposed, providing that interacting particles are immovable.     

Polyelectrolyte complexes of poly(methacryloxyethyl trimethylammonium chloride) and poly(ethylene oxide)-block-poly(sodium methacrylate) studied by asymmetrical flow field-flow fractionation and dynamic light scattering

Polyelectrolyte complex (PEC) formation between cationic poly(methacryloxyethyl trimethylammonium chloride) (PMOTAC) and anionic poly(ethylene oxide)-block-poly(sodium methacrylate) (PEO-b-PMANa) was studied by asymmetrical flow field-flow fractionation and dynamic light scattering. The influence of ionic strength and mixing ratios of the charged units of the polyelectrolytes on the complex formation was evaluated. The diffusion coefficients and the hydrodynamic diameter distributions of the free and complexed polyelectrolytes were measured. In the absence of salt, the weight averaged hydrodynamic diameters were 48 and 28 nm for PMOTAC and PEO-b-PMANa, respectively. In the presence of salt, the particles were smaller, with weight averaged hydrodynamic diameters of 44-45 and 8-10 nm, respectively. In salt-free solution, at 1:1 mixing ratio of the charged monomer units of PMOTAC and PEO-b-PMANa, polydisperse particles with diameters of 2000-4000 nm were formed. In the presence of 20, 80, and 160 mM of sodium chloride, the 1:1 complexes were relatively monodisperse particles with weight averaged hydrodynamic diameters of 93, 124, and 120 nm, respectively.     

Preparation and flow cytometry of uniform silica-fluorescent dye microspheres

Uniform fluorescent silica-dye microspheres have been prepared by coating preformed monodispersed silica particles with silica layers containing rhodamine 6G or acridine orange. The resulting dispersions exhibit intense fluorescent emission between 500 and 600 nm, over a broad excitation wavelength range of 460 to 550 nm, even with exceedingly small amounts of dyes incorporated into the silica particles (10-30 ppm, expressed as weight of dye relative to weight of dry particles). The fluorescent particles can be prepared in micrometer diameters suitable for analyses using flow cytometry with 488-nm laser excitation.     

细乳液聚合法制备磁性复合微球及其表征

在制备超细Fe3O4 磁性粒子的基础上 ,以 3种低分子量聚合物Disperbyk 1 0 6、Disperbyk 1 0 8和Disperbyk 1 1 1为Fe3O4 微粒在单体相中的分散稳定剂 ,采用细乳液聚合法制备了平均粒径为 3 40nm的PS Fe3O4 磁性复合微球 .详细研究了分散剂种类对细乳液聚合制备磁性复合微球的影响 ,并采用XRD、TGA和TEM等手段对磁性复合微球的形态、结构及磁响应性等进行了表征 .实验结果证明分散剂的选择对磁性复合微球的成功制备起着至关重要的作用 ,兼具酸性和碱性功能基的分散剂Disperbyk 1 0 6具有更好的分散和稳定效果 .TEM结果表明 ,所制备的复合微球具有一些缺陷 ,而缺陷处往往是Fe3O4 磁性粒子聚集的地方     

Poly(ethylene imine)-controlled calcium phosphate mineralization

The current paper shows that poly(ethylene imine) (PEI) is an efficient template for the fabrication of spherical calcium phosphate (CaP)/polymer hybrid particles at pH values above 8. The polymer forms spherical entities, which contain one or a few CaP particles with diameters of ca. 6 nm. The samples contain up to 20 wt % polymer, which appears to be wrapped around the small CaP particles. The particles form via a mineralization-trapping pathway, where at the beginning of the precipitation small CaP particles form. Further particle growth is then prevented by precipitation of the PEI onto these particles at pH values of ca. 8. Stabilization of the particles is provided by the re-protonation of the PEI, which is adsorbed on the CaP particles, during the remainder of the mineralization process. At low pH, much larger particles form. They most likely grow via heterogeneous nucleation and growth on existing, polymer-modified CaP surfaces.     

Phase transfer of large gold nanoparticles to organic solvents with increased stability

In this paper, we describe a new procedure to phase transfer large gold nanoparticles (diameters > 45 nm) from aqueous solution to organic solvents. This is accomplished using a covalent amide coupling reaction that incorporates dicyclohexylamine (DCHA) headgroups on the surface of mercaptoacetic acid (MAA) functionalized gold nanoparticles. Gold nanoparticles are first synthesized in aqueous solution by the citrate-reduction method, and nanoparticle size is controlled by the molar ratio of the reducing agent (sodium citrate) and the gold precursor (KAuCl4). MAA is then adsorbed to the surface of the gold nanoparticles followed by an amide-coupling reaction to covalently attach DCHA to the surface-immobilized MAA. The bulky dicyclohexyl groups entropically stabilize gold nanoparticles in organic solvents. This procedure was used to reliably transfer gold nanoparticles with diameters between 45 and 100 nm from aqueous solution to organic solvents such as dimethyl sulfoxide and chloroform.     

Dendron-like growth of silver nanoparticles using a water-soluble oligopeptide

A dendron-like nanostructure of silver was grown in solution using a water-soluble tetrapeptide Tyr-Aib-Tyr-Val (Aib, alpha-amino isobutyric acid), silver nitrate, and methanol. These structures are composed of silver nanoparticles having a bimodal size distribution with the median diameters around 2.0 and 19.5 nm, respectively. The dendron-like growth is ascribed to the effect of the local electric field generated by the dipoles associated with the peptide molecules. The optical absorption spectra have been analyzed by Mie scattering theory, which shows that there is a metal-nonmetal transition in silver particles having diameters less than approximately 2.0 nm.     

A straightforward way to form close-packed TiO2 particle monolayers at an air/water interface

The aim of this study was to analyze if and how monolayers of TiO(2) particles could be directly formed at the air/water interface and if these monolayers could be transferred to a solid surface. TiO(2) particles with diameters of 300 nm, 500 nm, 1 μm, 5 μm, 10 μm, and 20 μm formed stable monolayers at pH 2. At low surface pressures, the particles formed small two-dimensional aggregates. Particles up to a radius of 5 μm displayed close packing at increased surface pressures. Particles of 10 μm radius formed a loose network, which is attributed to the strong adhesion caused by the weight-induced lateral capillary attraction. Every monolayer of particles could be transformed to a solid surface by the Langmuir-Blodgett deposition. At pH 6 or 11, the particles did not form stable monolayers at the air/water interface. They were instead dispersed in the aqueous phase and eventually sank to the bottom of the trough. At pH 11 the monolayer could, however, be stabilized by the addition of salt (0.5 M NaCl). The results are interpreted based on a changed wettability of the particles depending on pH and salt concentration.     

Inverse Suspension Polymerization of Partially Neutralized and Lightly Cross-Linked Acrylic Acid: Effect of Reaction Parameters

An inverse suspension polymerization was carried out in laboratory in one Liter Buchi glass reactor to produce superabsorbent polymers (SAPs) based on acrylic monomers for hygiene applications. Strongly water absorbing polymers, based on acrylic acid, sodium acrylate were prepared by copolymerization using potassium per sulfate as initiator and N-N′ methylene-bisacrylamide (MBA) as crosslinking agent. The effect of varying monomer, crosslinker, initiator, dispersant concentration, time of reaction and degree of neutralization, on absorption capacities was investigated. In the present studies, the continuous hydrocarbon phase was taken as 50:50 mixture of n-heptane and cyclohexane (aliphatic-alicyclic) because the availability of crosslinker in the aqueous phase is controlled by the partition coefficient of the crosslinker between the aqueous phase and the continuous hydrocarbon phase. The SAPs were evaluated for their free absorption capacities in distilled water, saline (0.9% NaCl), and also absorption under load (AUL). The experimental results show that these SAPs have good absorbency both in water and NaCl solutions. It was observed that SAP synthesized from acrylic acid with about 70% degree of neutralization, containing 1% cross-linker, and 0.5–1.0% initiator concentration with 10% dispersant exhibited absorption capacities in water, saline and AUL as 220 g/g, 70 g/g and 27 g/g respectively.     

Study on the preparation and the self‐assembly of poly(propyleneimine)–poly(styrene) nanoparticles

Using 2‐chloropropionamide derivative of poly(propyleneimine) dendrimer DAB‐dendr‐(NH₂)₃₂ (DAB‐32‐Cl) as the macroinitiator, atom transfer radical polymerization of styrene was successfully carried out in DMF medium. The monodisperse poly(propyleneimine)–polystyrene (dendrimer–PSt) particles with diameters smaller than 100 nm could be prepared. The morphology, size, and size distribution of the dendrimer–PSt particles were characterized by transmission electron microscopy (TEM) and photon correlation spectroscopy (PCS). The effects of reaction temperature, the ratio of St/macroinitiator, and reaction time on the size, and size distribution of the dendrimer–PSt nanoparticles were investigated. In a selective solvent (DMF/H₂O), polymers can self‐assemble into different aggregate configurations such as regular microsphere and wire‐like thread. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2658–2666, 2008