Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Colloids”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34Linked to original sources
PubMed2006

Phase behavior in thin films of confined colloid-polymer mixtures.

Using self-consistent-field and density-functional theories, we first investigate colloidal self-assembly of colloid-polymer films confined between two soft surfaces grafted by polymers. With increasing colloidal concentrations, the film undergoes a series of transitions from disordered liquid --> sparse square --> hexagonal (or mixed square-hexagonal) --> dense square --> cylindrical structures in a plane, which results from the competition between the entropic elasticity of polymer brushes and the steric packing effect of colloidal particles. A phase diagram displays the stable regions of different in-layer ordering structures as the colloidal concentration is varied and layering transitions as the polymer-grafted density is decreased. Our results show a new control mechanism to stabilize the ordering of structures within the films.

Journal Article↗
PubMed2005

Density-functional study of interfacial properties of colloid-polymer mixtures.

Interfacial properties of colloid-polymer mixtures are examined within an effective one-component representation, where the polymer degrees of freedom are traced out, leaving a fluid of colloidal particles interacting via polymer-induced depletion forces. Restriction is made to zero-, one-, and two-body effective potentials, and a free energy functional is used that treats colloid excluded volume correlations within Rosenfeld's fundamental measure theory, and depletion-induced attraction within first-order perturbation theory. This functional allows a consistent treatment of both ideal and interacting polymers. The theory is applied to surface properties near a hard wall, to the depletion interaction between two walls, and to the fluid-fluid interface of demixed colloid-polymer mixtures. The results of the present theory compare well with predictions of a fully two-component representation of mixtures of colloids and ideal polymers (the Asakura-Oosawa model) and allow a systematic investigation of the effects of polymer-polymer interactions on interfacial properties. In particular, the wall surface tension is found to be significantly larger for interacting than for ideal polymers, whereas the opposite trend is predicted for the fluid-fluid interfacial tension.

Journal Article↗
PubMed2006

Guest-host colloid crystals: experimental study and simulations.

Disorder in colloid crystals was induced by doping them with a different number of large or small guest particles, which had a different deviation in size from the host colloids. The change in optical properties of the guest-host colloid crystals was assessed by using optical transmission spectroscopy while the variation in crystal structure was examined using scanning electron microscopy (SEM). The disruption in the crystalline lattices depended on the relative deviation in sizes of the guest and host particles and the concentration of the guest colloids. In parallel with experiments, the packing of spheres in guest-host crystals was modeled with a simulated annealing algorithm. A good correlation was found between the changes in crystal structure observed by SEM imaging and the simulated sphere packing. The experimental and simulated changes in the transmission spectra of guest-host colloid crystals were in good agreement.

Journal Article↗
PubMed2006

Preparing a magnetically responsive single-wall carbon nanohorn colloid by anchoring magnetite nanoparticles.

A single-wall carbon nanohorn (SWNH) colloid was made to be magnetically responsive by anchoring magnetite nanoparticles prepared by the homogeneous mixing of FeCl(2)-FeCl(3) and NaOH solutions. Transmission electron microscopy observation showed the high dispersion of magnetite particles of 2-9 nm on the surface of the SWNH colloid, coinciding with the broad X-ray diffraction peaks of the magnetites. The magnetization measurements showed that the magnetite nanoparticles-anchored SWNH (mag-SWNH) colloid has the hybrid property of ferrimagnetism and superparamagnetism. It was demonstrated that mag-SWNH colloid dispersed in water by sonication responded to an external magnetic field, gathering toward a magnet. N(2) adsorption experiments showed the high nanoporosity of mag-SWNHs and that magnetite nanoparticles were preferably anchored at "nanowindow" sites and the entrance sites of interstitial pores. This magnetically responsive SWNH colloid should contribute to the field of drug delivery.

Journal Article↗
PubMed2006

Dispersion stability of colloids in sub- and supercritical water.

Dispersion stability of colloids has been investigated in sub- and supercritical water by measuring the hydrodynamic diffusion coefficients of the particles by means of dynamic light scattering. It is interestingly found that coagulation of the colloids in sub- and supercritical water is a universal phenomenon irrespective of the material of the colloids. Highly charged colloids were found to be more stable in water against high temperature. Numerical analysis reveals that the stability of the colloids at elevated temperature and pressure is primarily governed by the temperature dependence of the dielectric constant of the medium. The effect of the temperature dependence of the ion product of water (pKw) was found to be very little. Surface charge density and Stern potential may change with respect to temperature due to the readjustment of the ion concentration in the diffuse layer through the enhanced ion product and reduced dielectric constant of water. These are the secondary causes of the particle coagulations in sub- and supercritical water.

Journal Article↗
PubMed2004

Monitoring the transformation of colloidal crystals by styrene vapor using atomic force microscopy.

The stages of transformation of a colloidal crystalline film of latex spheres to a new periodic structure were imaged by atomic force microscopy. Colloidal crystalline films were prepared with 320 nm diameter poly(styrene-co-2-hydroxyethyl methacrylate) (PSt/HEMA) spheres. The hexagonally ordered surfaces of the colloidal crystalline films were transformed with styrene vapor at room temperature to a new morphology having holes in the surface and the same periodicity as the original films. The surfaces of colloidal crystals and the transformed films have a raspberry-like texture superposed on the 320 nm hexagonal periodicity. Both height images and phase images reveal that the latex spheres shrink and the transformation proceeds by an order-disorder-order sequence. The final structure is an interconnected colloidal array with smaller polystyrene particles dispersed in a continuous PSt/HEMA matrix.

Journal Article↗
PubMed2004

Nanoparticle-mediated epitaxial assembly of colloidal crystals on patterned substrates.

We have studied the assembly of 3-D colloidal crystals from binary mixtures of colloidal microspheres and highly charged nanoparticles on flat and epitaxially patterned substrates created by focused ion beam milling. The microspheres were settled onto these substrates from dilute binary mixtures. Laser scanning confocal microscopy was used to directly observe microsphere structural evolution during sedimentation, nanoparticle gelation, and subsequent drying. After microsphere settling, the nanoparticle solution surrounding the colloidal crystal was gelled in situ by introducing ammonia vapor, which increased the pH and enabled drying with minimal microsphere rearrangement. By infilling the dried colloidal crystals with an index-matched fluorescent dye solution, we generated full 3-D reconstructions of their structure including defects as a function of initial suspension composition and pitch of the patterned features. Through proper control over these important parameters, 3-D colloidal crystals were created with low defect densities suitable for use as templates for photonic crystals and photonic band gap materials.

Journal Article↗
PubMed2005

Colloid surface engineering via deposition of multilayered thin films from polyelectrolyte blend solutions.

Multilayer thin films were constructed on polystyrene colloidal particles by depositing alternating layers of poly(allylamine hydrochloride) (PAH) at pH 7.5 and varying composition blends of poly(acrylic acid) (PAA) and poly(styrenesulfonate) (PSS) at pH 3.5. Following the deposition of each layer, microelectrophoresis experiments showed alternating zeta-potentials, suggesting the formation of multilayered films on the particles. Scanning and transmission electron microscopy were used to examine the surface morphology of the colloidal particles, with homogeneous surface coatings apparent for films deposited from PAA/PSS blend solutions containing up to 90 wt % PAA. The colloidal stability of these particles is greater than those coated with individual PAH and PAA layers. In the case of the blend PAA/PSS = 25:75 wt %, up to 20 layers were assembled without compromising the colloidal stability of the dispersion. The results demonstrate that the deposition of layers from PE blend solutions containing a strong and weak PE can be used as a facile method for controlling the surface properties and hence the colloidal stability of core-shell particles, as well as the thickness and morphology of the coatings. Control of these parameters is important for subsequent processing and application of these particles in controlled delivery, photonics, catalytic, and separation applications.

Journal Article↗
PubMed2005

Modeling of drying in films of colloidal particles.

The process of film formation on a solid substrate from polymer colloid dispersion during solvent evaporation has been investigated by means of the Monte Carlo simulation method. Colloid particles are modeled as hard spheres. Time evolution of the colloid density distribution and coverage of the solid substrate are studied. Both density and structure of colloid film is shown to depend strongly on the evaporation rate. At a low evaporation rate, the coexistence of hexagonal and tetragonal domains of dried colloid monolayer has been observed. The results of monolayer structure are in good agreement with the confocal scanning laser microscopy observations of Dullens et al. (2004).

Comment↗
PubMed2005

Close-packed colloidal crystalline arrays composed of polystyrene latex coated with titania nanosheets.

We have demonstrated that polystyrene latex coated with titania nanosheets can be fabricated into a close-packed colloidal crystalline array, and that these coated colloidal spheres can be used to control the peak position of optical stop bands through the coating. The titania-nanosheets-coated polystyrene latex was prepared by the layer-by-layer (LBL) assembly coating process, involving alternating lamination of cationic polyelectrolytes and anionic titania nanosheets on monodisperse polystyrene latex particles. The Bragg diffraction peak of the colloidal crystalline array shifted to longer wavelengths with the coating of titania nanosheets. This red shift was caused by an increase in refractive index upon coating, as revealed by angle-resolved reflection spectra measurements. The current work suggests new possibilities for the creation of advanced colloidal crystals having tunable optical properties from tailored colloidal spheres.

Journal Article↗
PubMed2006

Close-packed colloidal crystalline arrays composed of silica spheres coated with titania.

Titania coated monodisperse silica spheres have been synthesized and fabricated as a close-packed colloidal crystalline array. We have demonstrated that the coated colloidal sphere can be used to control the peak position of the optical stop band through variation of the coating thickness. The titania coated silica spheres were prepared by the layer-by-layer assembly coating process, which reciprocally laminates the cationic polyelectrolyte and the anionic titania nanosheets on a monodisperse silica spheres, and were sintered to change the titania nanosheets to anatase. The Bragg diffraction peak of the colloidal crystalline array shifted to the long wavelength region with an increase of thickness of the titania layer. Angle-resolved reflection spectra measurements clarified that the red shift was caused by increasing of the refractive index with increase of the thickness of the layer. The current work suggests new possibilities for the creation of advanced colloidal crystalline arrays with tunable optical properties from tailored colloidal spheres.

Journal Article↗
PubMed2006

Influence of humidity on the fabrication of high-quality colloidal crystals via a capillary-enhanced process.

Three-dimensional colloidal crystals have attracted a great deal of attention because of their potential use in photonic crystal, sensors, and other applications, but the bottlenecks in fabricating colloidal crystals include longer processing time and the lack of large-area ordered samples. A proposed capillary-enhanced method, which is a novel, efficient process for fabricating high-quality colloidal crystals in 24 h, is reported. It is necessary for increasing the processing rate by elevating the evaporation temperature but commonly resulted in the deposition of less-ordered crystals. However, high-quality colloidal crystals can be obtained in a controlled high-humidity system, resulting from the existence of secondary capillary forces present in high ambient humidity. Furthermore, the effect of secondary capillary forces will be confirmed, and it will increase with increasing humidity levels according to the semiquantitative analysis view of the surface thermodynamic behavior of small particles, including the modified Kelvin and Young-Laplace equations. Therefore, it can fine tune the relative position of the neighboring particles in the microarray and efficiently decrease the number of defects, resulting in the formation of perfect colloidal crystals with the assistance of enhanced secondary capillary forces.

Journal Article↗
PubMed2006

Dynamics and collapse of two-dimensional colloidal lattices.

One interesting aspect of colloidal particles is the formation of colloidal crystals at the 2D and 3D levels. Here we report the dynamics and collapse of colloidal lattices at liquid-liquid interfaces using Pickering emulsions as an experimental template. The colloidal particles oscillate around their equilibrium positions. The short-time diffusion constant (<10 s) of single particles increases with increasing lattice spacing; the oil-phase viscosity has an effect on diffusion only at large interparticle distances. Strikingly, we observe that the equilibrium structure can be disturbed when increasing the output laser intensity in a confocal laser scanning microscope, which leads to the collapse of colloidal lattices in the presence of small laser powers.

Journal Article↗
PubMed2003

A colloidal model system with an interaction tunable from hard sphere to soft and dipolar.

Monodisperse colloidal suspensions of micrometre-sized spheres are playing an increasingly important role as model systems to study, in real space, a variety of phenomena in condensed matter physics--such as glass transitions and crystal nucleation. But to date, no quantitative real-space studies have been performed on crystal melting, or have investigated systems with long-range repulsive potentials. Here we demonstrate a charge- and sterically stabilized colloidal suspension--poly(methyl methacrylate) spheres in a mixture of cycloheptyl (or cyclohexyl) bromide and decalin--where both the repulsive range and the anisotropy of the interparticle interaction potential can be controlled. This combination of two independent tuning parameters gives rise to a rich phase behaviour, with several unusual colloidal (liquid) crystalline phases, which we explore in real space by confocal microscopy. The softness of the interaction is tuned in this colloidal suspension by varying the solvent salt concentration; the anisotropic (dipolar) contribution to the interaction potential can be independently controlled with an external electric field ranging from a small perturbation to the point where it completely determines the phase behaviour. We also demonstrate that the electric field can be used as a pseudo-thermodynamic temperature switch to enable real-space studies of melting transitions. We expect studies of this colloidal model system to contribute to our understanding of, for example, electro- and magneto-rheological fluids.

Journal Article↗
PubMed2004

In situ observation of colloidal monolayer nucleation driven by an alternating electric field.

The nucleation of crystalline materials is a hotly debated subject in the physical sciences. Despite the emergence of several theories in recent decades, much confusion still surrounds the dynamic processes of nucleation. This has been due in part to the limitations of existing experimental evidence. Charged colloidal suspensions have been used as experimental model systems for the study of crystal nucleation and structural phase transitions, as their crystallization phase diagram is analogous to that of atomic and molecular systems, but they can be visualized using microscopy. Previously, three-dimensional imaging of colloidal nucleation dynamics was achieved using confocal microscopy. However, the limited temporal resolution of the confocal microscope is of concern when trying to capture real-time colloidal crystal nucleation events. Moreover, as the thermodynamic driving force has remained undefined, data on key factors such as the critical nuclei size are at best semiquantitative. Here we present real-time direct imaging and quantitative measurements of the pre- and post-nucleation processes of colloidal spheres, and the kinetics of nucleation driven by an alternating electric field, under well-defined thermodynamic driving forces. Our imaging approach could facilitate the observation of other rarely observed phenomena, such as defect and grain-boundary formation and the effects of foreign particles during crystallization. Furthermore, it may prove useful in identifying optical and biological technologies based on colloids.

Journal Article↗
PubMed1999

Treatment of malignant pericardial effusion with 32P-colloid.

Malignant pericardial effusion is usually treated only when signs of cardiac tamponade develop. Several methods of treatment have been reported with an overall response rate of approximately 75%. Since our initial study using intrapericardial 32P-colloid instillation as a treatment modality for pericardial effusion demonstrated a significant higher response rate, this study was conducted to further evaluate the efficacy of intrapericardial 32P-colloid in terms of response rates and duration of remissions. Intrapericardial instillation of 185-370 MBq (5-10 mCi) 32P-colloid in 36 patients with malignant pericardial effusion resulted in a complete remission rate of 94.5% (34 patients) whereas two patients did not respond to treatment due to a foudroyant formation of pericardial fluid. The median duration time was 8 months. No side-effects were observed. These results suggest that intrapericardial instillation of 32P-colloid is a simple, reliable and safe treatment strategy for patients with malignant pericardial effusions. Therefore, since further evidence is provided that 32P-colloid is significantly more effective than external radiation or non-radioactive sclerosing agents, this treatment modality should be considered for the management of malignant pericardial effusion.

Breast Neoplasms↗
PubMed1999

Familial fatal and near-fatal third ventricle colloid cysts.

BACKGROUND: Despite having a presumed congenital origin, familial cases of colloid cysts have been reported only rarely. The first case of a brother and sister with colloid cysts is reported here, and the relevant literature is reviewed. METHODS: A 25-year-old man presented with a 24-h history of headache and vomiting. He rapidly became unconscious and fulfilled the criteria for brain death on arrival at hospital. No surgical intervention was performed. RESULTS: The patient's sister presented at the age of 41 with headaches and rapidly became unconscious. The sister had urgent bilateral ventriculostomies. followed by transcallosal removal of a colloid cyst. CONCLUSIONS: These cases support the hypothesis that colloid cysts are congenital lesions and provide some evidence of a possible genetic predisposition to their formation. Sudden death remains a real risk for patients harbouring a colloid cyst.

Adult↗
PubMed2000

Solubility, absorption, and anti-Helicobacter pylori activity of bismuth subnitrate and colloidal bismuth subcitrate: In vitro data Do not predict In vivo efficacy.

OBJECTIVES: The aim of this study was to compare the dissolution, bioavailability, and anti-Helicobacter pylori activity of bismuth subnitrate and colloidal bismuth subcitrate. This could, first, provide insights into the mechanism of action of bismuth and, second, help to develop optimal therapeutic strategies. METHODS: Solubility and aquated size of bismuth species were determined in human gastric juice, while absorption into blood and urinary excretion of bismuth was determined in volunteers. Activity against H. pylori was determined in vitro in the presence and absence of antibiotics, while H. pylori eradication was compared in vivo. RESULTS: Bismuth from colloidal bismuth subcitrate was at least 10% soluble and ultrafilterable and was absorbed in volunteers (>0.5%), whereas that from bismuth subnitrate was insoluble and not absorbed (<0.01%). Colloidal bismuth subcitrate was active against H. pylori (mean inhibitory concentration, </=12.5 microg/ml), while bismuth subnitrate was inactive (>400 microg/ml); neither was synergistic with antibiotics. With in vivo triple therapy, bismuth subnitrate was as effective as colloidal bismuth subcitrate in eradicating H. pylori (74% and 70% eradicated, respectively). CONCLUSIONS: Colloidal bismuth subcitrate, unlike bismuth subnitrate, is partially soluble, absorbed in humans, and directly toxic to H. pylori in vitro. Surprisingly, however, these preparations had similar efficacy in vivo against H. pylori within triple therapy, suggesting that bismuth compounds may also exhibit indirect antimicrobial effects. We propose that this is an effect on the gastric mucus layer. Nonabsorbable bismuth compounds should be preferentially considered in bismuth-based therapies against H. pylori, as they would minimize toxicity while maintaining efficacy.

Anti-Bacterial Agents↗