Aqueous Colloidal Dispersions Research Articles

Volume behaviour of dipalmitoylphosphatidylcholine bilayer membrane: Pressure perturbation calorimetry and densitometry

Pressure perturbation calorimetry (PPC) is a relatively new technique based on a commercially available calorimeter which enables us to determine the isobaric coefficient of the thermal expansion of a solute for aqueous polymer solutions and colloidal dispersions. We applied the PPC to the investigation on the volume behaviour of dipalmitoylphosphatidylcholine (DPPC) bilayer membrane and compared the obtained results of the expansivity α2 and the apparent molar volume ϕ2 of DPPC in its bilayer membrane with those from a conventional densitometry. The temperature dependence of ϕ2 from the PPC was in good agreement with that from the densitometry. Both techniques revealed that the α2 value changes with the phase state of the DPPC bilayer membrane in the order of ripple gel (Pβ') phase > liquid crystalline (Lα) phase > lamellar gel (Lβ') phase. From the dependence, also the change of ϕ2 at the main transition from the Pβ' phase to the Lα phase was estimated to be 22.7 ± 2.62 cm3 mol−1 from the PPC and at 24.0 cm3 mol-1 from the densitometry, which are comparable with 25.4 cm3mol−1 previously obtained by the calculation based on the Clapeyron equation. On the other hand, the change of ϕ2 at the pretransition from the Lβ' phase to the Pβ' phase could not be determined with sufficient reliability. This may be due to the small change in ϕ2 at the pretransition (less than 0.5% of ϕ2 at the temperature).

Comparison of bioavailability of amorphous versus crystalline itraconazole nanoparticles via pulmonary administration in rats

The effect of supersaturation on bioavailability of inhaled nebulized aerosols is compared for amorphous versus crystalline nanoparticulate dispersions. The nanocrystalline formulations of itraconazole (ITZ) were made by wet milling (i.e. Wet-milled ITZ), whereas amorphous nanostructured aggregates (ITZ/mannitol/lecithin=1:0.5:0.2, weight ratio) were made by an ultra-rapid freezing process (i.e. URF-ITZ). Dissolution tests revealed the extent of supersaturation was 4.7-times higher for URF-ITZ versus Wet-milled ITZ, though their dissolution rates were similar. The aerodynamic performances of both aqueous colloidal dispersions were comparable and suitable for deep lung delivery. Single-dose 24-h pharmacokinetic studies were conducted in Sprague-Dawley rats following inhalation of the nebulized colloidal dispersions (equivalent to 20mgITZ/mL dispersion in 5mL) in a nose-only dosing apparatus. Lung depositions following inhalation were similar for both compositions. In systemic circulation, Wet-milled ITZ and URF-ITZ achieved C(max) of 50 and 180ng/mL at 2.7 and 4.0h, and AUC(0-24) of 662 and 2543ngh/mL, respectively, based on a one-compartmental analysis. Pulmonary delivery of the nanoparticulate amorphous ITZ composition resulted in significantly higher systemic bioavailability than for the nanocrystalline ITZ composition, as a result of the higher supersaturation that increased the permeation.

Silver nanoparticle polymer composite based humidity sensor

Silver nanoparticles were synthesised by a chemical reduction process in order to produce an aqueous colloidal dispersion. The resulting colloids were then characterised by a combination of UV-Vis spectroscopy, dynamic light scattering, X-ray diffraction and transmission electron microscopy and the nanoparticles were found to have an average diameter of 20-22 nm. The Ag/polymer nanocomposites were then applied to platinum interdigital electrodes as sensor coatings and the capability of the resulting sensor as a humidity detector investigated. With the application of 1 V, a current developed which was found to be directly proportional to humidity levels. The sensor gives a reversible, selective and rapid response which is proportional to levels of humidity within the range of 10% RH to 60% RH. An investigation into the mechanism of the sensor's response was conducted and the response was found to correlate well with a second order Langmuir adsorption model.

Photocatalytic activity of mesoporous films based on N-doped TiO2 nanoparticles

TiO2 based photocatalytic coatings are currently restricted to outdoor applications due to the requirement of UV light. Nitrogen doping of TiO2 was used here to activate them in indoor conditions for self-cleaning applications. We developed an original process, allowing nitridation of anatase nanoparticles dispersed within a porous silica matrix, at high temperatures (up to 800 °C), with neither structural change, nor aggregation and growth of the nanoparticles. After chemical dissolution of the silica, N-doped TiO2 particles were dispersed in water allowing the preparation of both concentrated colloidal aqueous dispersions and transparent sol–gel films in which N-doped particles are dispersed in a sol–gel silica binder with a controlled porosity. The N-doped TiO2 nanoparticles present visible light photocatalytic activity due to the presence of bulk nitrogen species. We showed that the photocatalytic activity of the films can be improved by an additional oxidative thermal treatment suppressing the Ti3+ ions which act as recombination centers in TiO2. We thus succeeded in preparing coatings twenty times more active than the reference under irradiation at 390 nm by monitoring the degradation of the Rhodamine 6G dye.

Spectral Tuning of Conjugated Polymer Colloid Light-Emitting Diodes

In recent years, the importance of the polymer light-emitting diode (PLED) has grown immensely, proving very desirable in numerous applications because of very high efficiencies, low power consumption, and ease of fabrication. Typically, these devices have been constructed in a layered, thin-film fashion consisting of either electron- and hole-transport materials doped with a luminescent dye (Hebner, T. R.; Sturm, J. C. Appl. Phys. Lett. 1998, 73, 1775. Jiang, X.; Register, R. A.; Killeen, K. A.; Thompson, M. E.; Pschenitzka, F.; Hebner, T. R.; Sturm, J. C. J. Appl. Phys. 2002, 91, 6717. Yeh, K. M.; Chen, Y. Org. Electron. 2008, 9, 45-50. Oh, G. C.; Yun, J. J.; Park, S. M.; Son, S. H.; Han, E. M.; Gu, H. B.; Jin, S. H.; Yoon, Y. S. Mol. Cryst. Liq. Cryst. 2003, 405, 43-51. Lee, J. I.; Chu, H. Y.; Kim, S. H.; Do, L. M.; Zyung, T.; Hwang, D. H. Opt. Mater. 2003, 21, 205-210. Hwang, D.-H.; Park, M.-J.; Lee, C. Synth. Met. 2005, 152, 205-208) or a conjugated polymer that can be engineered to tune the emission of the PLED to particular wavelengths. Stable PLED aqueous colloidal dispersions were prepared containing poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene], (MEH-PPV), poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO), and a binary poly(9,9-di-n-octylfluorenyl-2,7-diyl)/poly(2,5-dioctyl-1,4-phenylenevinylene) (PFO/POPPV) particle dispersion. Red-, green-, and blue-light-emitting colloidal dispersions could then be combined to achieve color-tailored emissions spanning the visible spectrum.

Synthesis and Characterization of Stable Aqueous Ceria Sols

Stable colloidal aqueous dispersions (sols) of cerium (IV) oxide of uniform size distribution were obtained by forced hydrolysis of cerium (IV) ions in the presence of diluted sulfuric or nitric acids. Synthesis of ceria sols was carried out using two commercially available precursors: Ce(SO4)2 · 4H2O salt and 0.25 mol/L Ce(NO3)4 aqueous solution. The precursors were dissolved in different concentrations of diluted sulfuric or nitric acid. After aging for various periods of time (2–24 h), the sols were cooled at room temperature. Sulfate and nitrate ions were removed from the sols particles by ultrafiltration. Characterization of the synthesized ceria sols has been made by X-ray diffraction, nitrogen adsorption/desorption, and DSC-TGA thermal analysis, as well as IR spectroscopy. Particle sizes, measured using a Zetasizer Nano equipped with a MPT-2 Autotitrator, range from 20 to 600 nm.

Environmentally Compliant Fluoro-Containing MMA/nBA Colloidal Dispersions; Synthesis, Molecular Modeling, and Coalescence

While aqueous phase colloidal synthesis of F-containing dispersions is often restricted by low solubility and surface tension of monomers, the use of bioactive dispersing agents, such as phospholipids, may alleviate these problems. Using 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), we copolymerized heptafluorobutyl methacrylate (FBMA), heptafluorobutyl acrylate (FBA), heptadecafluorodecyl methacrylate (FMA), heptadecafluorodecyl acrylate (FA) with methyl methacrylate (MMA) and n-butyl acrylate (nBA) monomers which resulted in the formation of stable nonspherical colloidal dispersions that contain up to 15% (w/w) of the fluoropolymer (FP) phase. These studies report for the first time an aqueous phase FP colloidal dispersion synthesis without the use of fluoro-dispersing agents. Experimentally determined by transmission electron microscopy (TEM) particle phase-separated morphologies consist of the FP phase that polymerize on the surface of p-MMA/nBA core particles. Thermodynamic molecular modeling sim...

Poly(styrene-co-n-butyl acrylate) Nanofibers with Excellent Stability against Water by Electrospinning from Aqueous Colloidal Dispersions

Less brittle nanofibers with excellent stability against water can be prepared via electrospinning of dispersions of styrene−acrylate copolymers from an aqueous environment. The versatility of emulsion polymerization technique allows us to tailor a wide range of properties of the dispersed polymer and the subsequent nanofibers. It was shown that the minimum film formation temperature (MFFT) and correspondingly the glass transition temperature (Tg) of the colloidal polymer, which can be varied by changing the composition of the monomers, have to be in the range of processing temperature, resulting in formation of the fibers with homogeneous morphology and good dimensional stability.

Formability and properties of self-standing clay film by montmorillonite with different interlayer cations

Influences of exchangeable interlayer cations were investigated on self-standing film formability, film morphology, and properties of the clay films such as flexibility and gas barrier property. Ion-exchanged montmorillonite samples were prepared by a cation exchange from naturally bearing cation, mostly Na +, to Li +, Mg 2+, Ca 2+, Al 3+, and Fe 2+, 3+. Self-standing films were prepared from aqueous colloidal dispersions of these montmorillonite samples with no additives. The montmorillonite samples with monovalent or divalent cation formed flat self-standing films while the Al-montmorillonite sample produced a distorted film. The Fe-montmorillonite sample formed many separated reddish-brown rod-shaped pieces. Clay film microstructures were different with interlayer cations. The films with monovalent interlayer cations were constructed by the stacking of units with delicately waved thin clay sheets in the whole film, but other films show different morphologies between the upper side and lower side; the upper side is laminated with thin sheets; the lower side is laminated with large thick sheets. The self-standing films’ flexibility and gas barrier property differed according to the interlayer cations. These properties were good in cases of samples with monovalent cations. The innumerable short wave and sheet thinness are considered to foster good flexibility and gas barrier properties. The differences in film formability and properties of the films are attributable to different swellability among samples with different interlayer cations. The montmorillonite samples with monovalent cations swell sufficiently by water, but those with polyvalent cations swell poorly. In the latter case, clay crystals aggregate in water, then the aggregate grows into large particles, creating a film with large particles.

Cracking in Drying Colloidal Films of Flocculated Dispersions

Understanding the mechanism of cracking during the drying of aqueous colloidal dispersions is important to preventing film failure. While most of the reported work has dealt with stable aqueous dispersions, a few studies have focused on flocculated systems. The latter especially assumes importance because the role of particle packing in the mechanism of cracking is not completely understood. In this work, we study the cracking of colloidal films cast from flocculated aqueous dispersions of alpha-alumina. Here, the extent of flocculation is controlled by varying the pH of the dispersion and characterized in terms of the final packing volume fraction of the dried film. The influence of varying the close-packed volume fraction on the critical cracking thickness and critical cracking stress is measured. The measurements are compared with the model predictions based on Griffith's energy balance, and good agreement is found between theory and experiments, suggesting that the model is universal and applies equally well to stable as well as flocculated systems.

Synthesis, characterization, electrical transport and magnetic properties of PEDOT–DBSA–Fe 3O 4 conducting nanocomposite

Electrical transport and magnetic properties of newly synthesized conducting polymer nanocomposites involving poly(3,4-ethylenedioxythiophene) (PEDOT) and Fe 3O 4 nanoparticles are studied. Nanocomposite samples of varying proportions of inorganic to organic components were synthesized by adding EDOT monomer stabilized in miceller solution of DBSA (dodecylbenzene sulphonic acid) to aqueous colloidal dispersion of Fe 3O 4 nanoparticles, followed by oxidative polymerization using ammonium peroxodisulphate (APS). Transmission electron microscopic (TEM) photographs show presence of distinct spherical Fe 3O 4 naonparticles having diameter range of 20–40 nm and they are incorporated within the polymer chain in the nanocomposite samples. Temperature-dependent DC conductivity analysis indicates a smooth cross-over of the charge conduction from the high temperature 3D Mott's variable range hopping (VRH) mechanism to the 2D ES (Efros and Shklovoskii)-VRH behaviour at low temperature. Temperature-dependent DC magnetization studies reveal enhancement of blocking temperature ( T B ) in the nanocomposite samples compared to that of bare Fe 3O 4 nanoparticles. Core shell morphology of the nanoparticles seems to be the cause for lowering the value of saturation magnetization of the Fe 3O 4 nanoparticles. Estimated magnetic domain sizes are comparable to those of grain sizes for the nanocomposite samples having lower content of nanoparticles (P 50 and P 100). Temperature-dependent AC-susceptibility data also supports the superparamagnetic behaviour.

High Temperature Strategy for Oxide Nanoparticle Synthesis

Compared with noble metals and quantum dots, dielectric complex oxide nanoparticles are significantly less popular due to their high crystallization temperature, making difficult their synthesis in the 10-100 nm range for which surface effects are reduced. We report here an original process permitting thermal annealing of complex oxide nanoparticles at high temperature without aggregation and growth. Thus, after thermal treatment, these annealed particles can be dispersed in water, leading to concentrated aqueous colloidal dispersions containing isolated highly crystalline particles. This contrasts with usual colloidal techniques for which the production of particles in the 10-100 nm range generally leads to poorly crystallized particles, especially for multicomponent oxides. From two examples, we show some possibilities offered by this type of process. This concerns the synthesis of lanthanide-doped oxide nanoparticles exhibiting a bulk behavior for their luminescence properties and the control of the composition in nitrogen-doped titanium oxide particles without sintering and size change.

Amorphous cyclosporin nanodispersions for enhanced pulmonary deposition and dissolution

Aqueous colloidal dispersions of amorphous cyclosporin A (CsA) nanoparticles, intended for pulmonary delivery, were formed by antisolvent precipitation and stabilized with 10% polysorbate 80. Dissolution of the dispersion of CsA nanoparticles produced supersaturation values 18 times the aqueous equilibrium solubility. Nebulization of the dispersion to mice produced therapeutic lung levels and systemic concentrations below toxic limits. The sizes of the aerosolized aqueous droplets are optimal for deep lung deposition, whereas the amorphous drug nanoparticles facilitate rapid dissolution. A dissolution/permeation model was developed to characterize the effects of particle size, solubility, and drug dose on the absorption half-lives of poorly water soluble drugs in the alveolar epithelium. For crystalline 3µm particles with a solubility of 1µg/mL, the half-life for absorption was estimated to be 500 min. The half-life may be reduced to less than 1 min by increasing the solubility by a factor of 100 with an amorphous form as well as by decreasing the particle size 10-fold. The in vitro and in vivo data, as well as the dissolution/permeation model, indicate that nebulization of amorphous nanoparticle suspensions has the potential to enhance lung epithelial absorption markedly for poorly water soluble drugs, relative to respiratory delivery of crystalline, micron-sized particles.

Solid Lipid Nanoparticles and Nanostructured Lipid Carriers – Innovative Generations of Solid Lipid Carriers

The first generation of solid lipid carrier systems in nanometer range, Solid Lipid Nanoparticles (SLN), was introduced as an alternative to liposomes. SLN are aqueous colloidal dispersions, the matrix of which comprises of solid biodegradable lipids. SLN are manufactured by techniques like high pressure homogenization, solvent diffusion method etc. They exhibit major advantages such as modulated release, improved bioavailability, protection of chemically labile molecules like retinol, peptides from degradation, cost effective excipients, improved drug incorporation and wide application spectrum. However there are certain limitations associated with SLN, like limited drug loading capacity and drug expulsion during storage, which can be minimized by the next generation of solid lipids, Nanostructured lipid carriers (NLC). NLC are lipid particles with a controlled nanostructure that improves drug loading and firmly incorporates the drug during storage. Owing to their properties and advantages, SLN and NLC may find extensive application in topical drug delivery, oral and parenteral administration of cosmetic and pharmaceutical actives. Cosmeceuticals is emerging as the biggest application target of these carriers. Carrier systems like SLN and NLC were developed with a perspective to meet industrial needs like scale up, qualification and validation, simple technology, low cost etc. This paper reviews present status of SLN and NLC as carrier systems with special emphasis on their application in Cosmeceuticals; it also gives an overview about various manufacturing techniques of SLN and NLC.

Structure−Property Relations for the Rheology of Dispersions of Charged Colloids

The effect of electrostatic interactions on the rheology of aqueous colloidal dispersions is a topic of longstanding interest. Electroviscous were first quantified experimentally in the semidilute regime by Stone-Masui and Watillon in 1968, substantiating an earlier dilute theory and subsequent predictions for pair interactions. Experiments demonstrating the development of yield stresses at higher concentrations, stimulating exploration of the fluid-to-solid transition and later characterization of plastic flow and melting transitions in the solid phase. More recently, an extensive parametric study of rheology in the fluid phase, demonstrating the effects of particle size, ionic strength, and volume fraction. This paper reports a correlation for the low shear viscosity of the fluid phase suggested by the semidilute theories, an effort that is complicated by incomplete knowledge of the surface charge and ionic strength at finite volume fractions.

Graphite Oxide-Intercalated Anionic Clay and Its Decomposition to Graphene−Inorganic Material Nanocomposites

A graphite oxide-intercalated anionic clay (nickel zinc hydroxysalt) has been prepared using the aqueous colloidal dispersions of negatively charged graphite oxide sheets and aminobenzoate-intercalated anionic clay layers as precursors. When the two colloidal dispersions are reacted, the interlayer aminobenzoate ions are displaced from the anionic clay and the negatively charged graphite oxide sheets are intercalated between the positively charged layers of the anionic clay. The thermal decomposition of the intercalated solid at different temperatures yields graphene-metal oxide/metal nanocomposites. Electron microscopic analysis of the composites indicates that the nanoparticles are intercalated between the layers of graphite in many regions of these solids although the graphite layers are largely exfoliated and not stacked well together.

Fabrication and Modulation of Magnetically Supramolecular Hydrogels

For the fabrication of magnetically supramolecular hydrogels, the aqueous colloidal dispersion of magnetic iron oxide nanoparticles was first stabilized by an amphiphilic poly(epsilon-caprolactone)-poly(ethylene glycol) (PEG-PCL) block copolymer and then mixed with an aqueous solution of a cyclic oligosaccharide. Due to the host-guest interaction between the used block copolymer and the cyclic oligosaccharide in the aqueous mixed system, such a fabrication process could result in the formation of a novel hydrogel nanocomposite with superparamagnetic property, as confirmed by the analyses from rheology and X-ray diffraction as well as magnetization curve measurements. For the resultant magnetically supramolecular hydrogel, its formation kinetics and mechanical strength could be modulated by the amount of the used PEG-PCL block copolymer, the cyclic oligosaccharide, or the incorporated iron oxide nanoparticles.

Colloidal aqueous dispersion of polyaniline nanotubes grafted non-covalently with poly(ethylene oxide)-block-poly(acrylic acid) copolymer

Polyaniline (PANI) nanotubes were prepared by oxidative polymerization of aniline in the presence of two structure-directing agents—salicylic acid (SA) and sodium dodecyl sulfate (SDS). When using only SA, mainly aggregated nanotube dendrites or coral-like structures have been obtained. Addition of a very small amount of the surfactant SDS, much less than the critical micelle concentration, results in substantial reduction of the aggregated nanotube morphology on the account of isolated PANI nanotubes, which is the favorable structure from the point of view of further modification. In order to make the isolated nanotubes water dispersible, their surface was modified by complex formation (non-covalent grafting) with hydrophilic poly(ethylene oxide)-block-poly(acrylic acid) copolymer. These water-dispersible PANI nanotubes might be good candidates for some biochemical and biomedical applications.

A comparative study of porous limestones treated with silicon-based strengthening agents

Porous bioclastic limestones of small pore radii and sandy limestones of large pore radii were treated with silicon-based strengthening products, such as tetraethoxysilane, elastified silicic acid ethyl ester (PP), an aqueous colloidal dispersion of silica particles (LD), as well as an oligomeric siloxane water repellent (HP). Changes in color, water vapor permeability, porosity, pore size distribution and tensile strength were evaluated after treatment. Energy Dispersive X-ray Fluorescence (EDXRF) indicated that the products reached a depth from the surface of 30 mm and were evenly distributed inside the stone, except for LD, which accumulated up to the first 10 mm from the surface. Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) showed that linkages created between limestone and gels, due to the hydroxyl groups of the quartz and aluminosilicate minerals included in the limestones. PP and LD reduced the water vapor permeability coefficient to acceptable limits and induced the least chromatic variation. Mercury intrusion porosimetry (MIP) results indicated that the precipitation of the formed gel increased the specific surface area. The porosity and pore size decreased in the treated bioclastic limestones and in the KS and LD treated sandy limestones. In contrast, the PP and PP + HP treated sandy limestones showed an increase in porosity and average pore radius, as a result of the polymer cracking. When polymers were applied to the sandy limestones of large pore radii, the formed gels underwent cracking from drying shrinkage and the mechanical resistance of the stone was reduced. The gels when deposited in the small pore radii of bioclastic limestones behaved as thin films, thereby no cracking was induced by the consolidant from drying shrinkage. This study demonstrated that the performance of a consolidant is greatly dependent on the pore size of the stone. None of the above studied products can be recommended for consolidation of the sandy limestones, while the elastified silicic acid ethyl ester (PP) is only recommended for consolidating the bioclastic limestones.

Development of sustained release fast-disintegrating tablets using various polymer-coated ion-exchange resin complexes

Complex formation between drugs and ion-exchange resins was investigated and the effects of coating by various aqueous polymeric dispersions on the complexes were evaluated for developing new sustained-release fast-disintegrating tablets (FDTs). Complexes of ion-exchange resin and dextromethorphan, a model drug, were prepared using different particle sizes of the resins. Aqueous colloidal dispersions of ethylcellulose (EC) and poly(vinyl acetate) (Kollicoat ® SR30D) were used for fluid-bed coating. Based on drug loading, release profiles, and scanning electron microscopy (SEM) images, the coated particles were granulated with suitable tablet excipients and then compressed into the tablets. Drug release profiles and SEM pictures were compared before and after the manufacturing processes. As the particle size of resins increased, the drug loading and release rate decreased due to the reduced effective diffusion coefficient and surface area. Higher coating level decreased the release rate further. In contrast to EC, Kollicoat ® SR30D coated particles could be compressed into tablets without any rupture or cracks on the coating since the mechanical properties of the polymer was more resistant to the manufacturing processes. This resulted in no significant changes in release rates. SEM showed the mechanical strength of the polymers affected the morphological change after compression. When the drug release profiles were applied into Boyd model and Higuchi equation, the linear relationship was observed, indicating that the diffusion within the resin matrix is the rate-controlling step.