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PubMed2006

Dynamic light scattering in turbid colloidal dispersions: a comparison between the modified flat-cell light-scattering instrument and 3D dynamic light-scattering instrument.

It remains a challenge to measure dynamics in dense colloidal systems. Multiple scattering and low light-transmission rates often hinder measurements in such systems. One of the well-established techniques for overcoming the problem of multiple scattering is cross-correlation techniques such as 3D dynamic light scattering (3D-DLS). However, a high degree of multiple scattering, i.e., vanishing single-scattering contribution in the signal, limits the use of the 3D-DLS technique. We present another approach to measure turbid media by way of upgrading our flat-cell light-scattering instrument (FCLSI). This instrument was originally designed for static light-scattering (SLS) experiments and is similar to a Fraunhofer setup, which features a flat sample cell. The thickness of the flat sample cell can be varied from 13 mum to 5 mm. The small thickness increases the transmission, reduces multiple scattering to a negligible amount, and therefore enables the investigation of dense colloidal systems. We upgraded this instrument for DLS measurements by the installation of an optical single-mode fiber detector in the forward scattering regime. We present our instrumentation and subsequently test its limits using a concentration series of a turbid colloidal suspension. We compare the performances of our modified flat-cell light-scattering instrument with that of standard DLS and with that of 3D-DLS. We show that 3D-DLS and FCLSI only have a comparable performance if the length of the light path in the sample using the 3D-DLS is reduced to a minimum. Otherwise, the FCLSI has some advantage.

Journal Article↗
PubMed2004

Hypothesis about the physiopathology of acute deterioration and sudden death caused by colloid cysts of the third ventricle.

In this paper, the authors review the mechanisms of acute deterioration and sudden death caused by colloid cysts (CCs). These dreaded events are widely recognized complications of CC, however the mechanism(s) in cause has been subject to controversy. Increased intracranial pressure (ICP) is a common event associated with many cerebral disorders, including colloid cysts, though compensatory mechanisms may allow ICP to remain at normal levels. However, a compensated system might decompensate for many factors such as intracranial haemorrhage, acute hydrocephalus, brain oedema, or an increase in sagittal sinus pressure (SSP). The sagittal sinus in adults with brain tumours appears to respond unpredictably when ICP increases and in some patients, when ICP increased the SSP increased too due to the fact that their sinuses collapse. We therefore speculate that the mechanism of acute deterioration and sudden death is a multifactorial and dynamic process, in which the increase in sagittal sinus pressure would appear to be an important element. It seems possible that acute deterioration is initiated by an increase in sagittal sinus pressure, which provokes acute brain swelling, with a series of often-irreversible events, leading to sudden death. Since the majority of cases of acute deterioration and death are due to CCs of the third ventricle, the authors suggest that surgical resection should be carried out on diagnosed CCs measuring over 1 cm, because sudden death has not been reported as having been caused by colloid cysts measuring less than this dimension.

Acute Disease↗
PubMed2006

Hemorrhagic colloid cyst: case report and review of the literature.

Colloid cysts are benign tumors situated in and connected to the roof of the third ventricle. The clinical presentation is diverse, varying from incidentally found cysts to acute death. This presentation is explained by an acute hydrocephalus due to an obstruction of the cerebrospinal fluid (CSF) flow at the level of the foramina of Monro. Why these lesions cause a sudden obstruction is not clear in most cases. Possible explanations of a sudden deterioration are shifts of the cysts after lumbar puncture or CSF flow obstruction after shunt dysfunction. We add an explanation for the acute deterioration of patients with colloid cysts (ie, hemorrhagic changes in the cysts). This complication has been published only 4 times before, all diagnosed at postmortem examination. A young patient is presented with a recently diagnosed and symptomatic colloid cyst who deteriorated the night before surgery because of intracystic hemorrhage. Despite emergent CSF diversion, our patient remained in a poor clinical condition. We review the literature about this topic and discuss the consequences for the neurosurgical practice.

Adult↗
PubMed1987

Mechanisms for reduced colloid osmotic pressure in preeclampsia.

The determinants of plasma colloid osmotic pressure were studied in 32 patients with preeclampsia and their matched control subjects. Although plasma colloid osmotic pressure was significantly related to preeclampsia, its severity, and proteinuria, it was most highly correlated with an elevated fibronectin level, suggesting that endothelial injury, rather than proteinuria, is the major mechanism of reduced colloid osmotic pressure in preeclampsia.

Adult↗
PubMed1997

Adult colloid milium of the eyelid.

PURPOSE: To report a patient with bilateral upper and lower eyelid margin nodules that proved to be adult colloid milium. METHODS: After clinical study, biopsy specimens were obtained and analyzed histologically and ultrastructurally. RESULTS: Adult colloid milium can be diagnosed by clinicopathologic correlation. CONCLUSION: Adult colloid milium should be included in the differential diagnosis of eyelid margin nodules.

Aged↗
PubMed1987

Nanovid tracking: a new automatic method for the study of mobility in living cells based on colloidal gold and video microscopy.

We describe a new automatic technique for the study of intracellular mobility. It is based on the visualization of colloidal gold particles by video-enhanced contrast light microscopy (nanometer video microscopy) combined with modern tracking algorithms and image processing hardware. The approach can be used for determining the complete statistics of saltatory motility of a large number of individual moving markers. Complete distributions of jump time, jump velocity, stop time, and orientation can be generated. We also show that this method allows one to study the characteristics of random motion in the cytoplasm of living cells or on cell membranes. The concept is illustrated by two studies. First we present the motility of colloidal gold in an in vitro system of microtubules and a protein extract containing a kinesin-like factor. The algorithm is thoroughly tested by manual tracking of the videotapes. The second study involves the motion of gold particles microinjected in the cytoplasm of PTK-2 cells. Here the results are compared to a study using the spreading of colloidal gold particles after microinjection.

Animals↗
PubMed1992

Colloid osmotic pressure of steer crystallins: implications for the origin of the refractive index gradient and transparency of the lens.

The osmotic behavior of soluble cortical and nuclear steer lens crystallins was characterized by secondary osmometry for several ionic strength and pH conditions. Osmotic pressure versus protein concentration relationships were measured for pressures up to 1.15 x 10(6) dyn cm-2. At low concentrations (< 0.2 g ml-1), the osmotic pressure increased linearly with pressure, whereas for concentrations above 0.2 g ml-1, the pressure rose more sharply, giving progressively larger changes in osmotic pressure with increasing crystallin concentration. At a given ionic strength and applied osmotic pressure, the nuclear proteins attained a higher protein concentration than did the cortical proteins. For example, at the highest osmotic pressure of 1.15 x 10(6) dyn cm-2 at pH 7.6 and 0.1 M ionic strength, the observed protein concentrations were 0.43 g ml-1 for the cortical proteins and 0.52 g ml-1 for the nuclear proteins. For both cortical and nuclear steer crystallins, the pressure rose more steeply with concentration than do pressures for calf crystallins described in the literature. The impact of these developmental differences in osmotic pressure on lens transparency is discussed. Both the nuclear and cortical crystallins exhibited ionic strength-dependent shifts in their pressure-concentration behavior. At 0.02 M ionic strength, higher pressures were observed, whereas at 0.4 M ionic strength lower pressures were observed for a given protein concentration. The crystallins were also found to equilibrate to different protein concentrations at a constant osmotic pressure and 0.1 M ionic strength over a pH range of 4-9, with a maximum concentration around pH 5 for the cortical crystallins and pH 6 for the nuclear crystallins. Thus, the adult bovine cortical and nuclear soluble lens extracts are different in their osmotic properties, reflecting underlying differences in protein composition. The results of the ionic strength and pH experiments suggest that hard-sphere, electrostatic, and Donnan forces contribute to the total colloid osmotic pressure of the lens crystallins. However, near physiologic pH and ionic strength the charges of the proteins are screened to the extent that the colloid osmotic pressure exhibits only minor changes for large changes in ionic conditions. The differences in the osmotic behavior of the cortical and nuclear proteins are consistent with a model where regional variations in the colloid osmotic properties of the proteins across the lens help support the radial refractive index gradient that is present in vertebrate lenses. The importance of a radial concentration gradient of metabolites is also discussed.

Aging↗
PubMed2003

Preparation and characterization of polypyrrole-silica colloidal nanocomposites in water-methanol mixtures.

The effect of methanol cosolvent on the synthesis of polypyrrole-silica colloidal nanocomposites using ultrafine silica sols in combination with both FeCl3 and APS oxidants has been investigated. Two protocols were evaluated: the addition of methanol to an aqueous silica sol and the addition of water to a methanolic silica sol. The latter protocol proved to be more robust, since it allowed colloidally stable dispersions to be prepared at higher methanol content (up to 50 vol% using the APS oxidant). This allowed greater control over the particle size of the nanocomposite particles. In general, the spectroscopic data, the particle size range, silica contents and electrical conductivities of these nanocomposites were similar to those reported earlier for purely aqueous formulations. Polypyrrole contents ranged from 49 to 71% by mass and particle diameters varied from around 160 to 360 nm. In terms of colloid stability, the APS oxidant was preferred for nanocomposite syntheses in the presence of methanol. However, the FeCl3 oxidant generally gave higher conductivities and narrower size distributions under comparable conditions. HF etching experiments combined with transmission electron microscopy studies indicated that, to a first approximation, these nanocomposite particles had core-shell morphologies, with a hydrophobic polypyrrole core and a hydrophilic silica shell that compose approximately one monolayer of silica sol particles. Finally, aqueous electrophoresis measurements suggested that the polypyrrole-silica nanocomposites were silica-rich and that the methanolic silica sol was more hydrophobic (lower surface charge density) than the aqueous silica sol.

Journal Article↗
PubMed2003

Charge and salt-driven reentrant order-disorder and gas-solid transitions in charged colloids.

Monte Carlo simulations have been performed for aqueous charged colloidal suspensions as a function of effective charge density (sigma) on the particles and salt concentration C(s). We vary the effective charge density in our simulations over a range where a reentrant solid-liquid transition in suspensions of silica and polymer latex particles has been reported by Yamanaka et al. (Phys. Rev. Lett. 80 (1998) 5806). We show that at low ionic strengths a homogeneous liquid-like ordered suspension undergoes crystallization upon increasing sigma. Further increase in sigma resulted once again in a disordered state, which is in agreement with experimental observations. In addition to this reentrant order-disorder transition, we observe an inhomogeneous-to-homogeneous transition in our simulations when salt is added to the disordered inhomogeneous state. This inhomogeneous-to-homogeneous disordered transition is analogous to the solid-gas transition of atomic systems and has not yet been observed in charged colloids. The reported experimental observations on charged colloidal suspensions are discussed in the light of present simulation results.

Journal Article↗
PubMed2003

Synthesis of colloidal aluminosilicate for light-scattering investigations.

To develop a binary colloidal system with a slight index of refraction mismatch suitable for light scattering studies, pure silica particles synthesized by the method of Stöber were mixed with aluminosilicate colloids synthesized using a novel approach. With this, index-matching for one component allowed extraction of the spatial distribution of the other. In addition, it was observed that by varying the solvent, interactions between colloids could be tuned from purely repulsive to weakly attractive.

Journal Article↗
PubMed2003

Photoinduced interaction between fluorescein ester derivatives and CdS colloid.

The photoinduced interaction of fluorescein ester derivatives, fluorescein's butyl ester (FL4) and fluorescein's anthraquinone-methyl ester (FL-AQ), and colloidal CdS was examined by absorption, fluorescence spectroscopy, and photoinduced ESR spectroscopy. It is found that FL4 and FL-AQ molecules are adsorbed on the surfaces of CdS colloid by an electrostatic interaction forming the surface complex of the type CdS-FL4 or CdS-FL-AQ. The apparent association constant (K(app)) and the degree of association (alpha) of CdS-FL4 obtained from absorption spectra are 2.25 x 10(4) M(-1) and 0.78, respectively. The values of K(app) and alpha of CdS-FL4 as determined from fluorescence spectra are 1.54 x 10(4) M(-1) and 0.82, respectively, which matches well with that determined from the absorption spectra changes. And the values of K(app) and alpha of CdS-FL-AQ obtained from absorption spectra are 4.18 x 10(4) M(-1) and 0.83, respectively. These data indicate that there is a strong interaction between the dye and the CdS particle surface. But there was no evidence for interfacial electron transfer from FL4 or FL-AQ to colloidal CdS by photoinduced ESR experiments. The fluorescence quenching is due to the formation of a nonfluorescent complex. The related phenomena are discussed in this paper.

Journal Article↗
PubMed2003

Interpretation of colloidal dyeing of polyester fabrics pretreated with ethyl xanthogenate in terms of zeta potential and surface free energy balance.

Data are presented on the adsorption of the colloidal dye Disperse Blue 3 onto polyester fabric (Dacron 54, Stile 777), the fabric being pretreated with different amounts of the surfactant potassium ethyl xanthogenate (PEX). This study has been made by means of both the evolution of the zeta potential of the fiber/dye interface and the behaviour of the surface free energy components of the above systems. The kinetics of adsorption of the process of dyeing, using 10(-4) M of PEX in the pretreatment of the fabric, shows that increasing temperature of adsorption decrease the amount of colloidal dye adsorbed onto the fabric. This fact shows that the principal mechanism involved in this adsorption process is physical in nature. The adsorption isotherms of the colloidal dye onto polyester pretreated with different amounts of PEX, shows that the adsorption of the dye is favored with the increase in the concentration of the surfactant used in the pretreatment. This fact shows that the pretreatment with PEX is a very interesting aspect of interest in textile industry. The zeta potential of the system fabric/surfactant shows that this parameter is negative (about -25 mV) for the untreated fiber and decreases in absolute value for increasing concentration of the surfactant on the fiber, the value of the zeta potential of the system being -5 mV for 10(-2) M of PEX. This behavior can be explained for the chemical reaction nucleophilic attack between the carboxyl groups of polyester, ionized at pH 8, and the thiocarbonyl group of the xanthogenate ion. On the other hand, the zeta potential of the system polyester pretreated with PEX/Disperse Blue 3 at increasing concentrations of the surfactant and the dye shows that this parameter increases its negative value strongly with increasing concentration of the surfactant used in the treatment. This can be explained for the hydrogen bonds between the hydroxy groups of the dye and the S- ions of the thiocarbonyl group of the surfactant preadsorbed onto the fiber.

Journal Article↗
PubMed2003

Viscosity of concentrated colloidal suspensions: comparison of bidisperse models.

In this paper, recent advances in the study of rheological behavior of concentrated bimodal suspensions are briefly reviewed. The predictive models are divided into two categories, namely, the effective volume fraction (or hard sphere scaling) approach and the separation of contributions approach. Predictions of both approaches are compared with experimental data of electrostatically and sterically stabilized suspensions. It is shown that the predictions of both hard sphere scaling and the scaling method of Zaman and Moudgil (J. Colloid Interface Sci. 212 (1999) 167) to separate the contributions of fine and coarse particles are in good agreement with the experimentally observed results. The approach by Dames, Morrison, Wilenbacher (Rheol. Acta 40 (2001) 434) to separate the hard-sphere and non-hard-sphere contributions is investigated using the aqueous silica and polystyrene suspensions respectively. A good agreement is shown for aqueous silica suspensions. However, significant differences between the predictions and experimental data are found for the sterically stabilized polystyrene suspensions, suggesting a more generalized expression is needed. As an attempt to classify the models on the viscosity of colloidal suspensions, the present study will provide guidelines for interpretation of experimental results and for the development of more comprehensive predictive methodologies for polydispersed colloidal dispersions.

Journal Article↗
PubMed2003

Juvenile colloid milium associated with conjunctival and gingival involvement.

Juvenile colloid milium is an uncommon cutaneous disease characterized by translucent papules distributed on sun-exposed areas with early onset. Association of juvenile colloid milium with conjunctival and gingival deposits is uncommon and interesting. We report a case of juvenile colloid milium associated with conjunctival and gingivai deposits of an amyloid-like homogeneous eosinophilic material. It seems that all 3 of these in our patient may be different expressions of the same pathologic disease.

Adult↗
PubMed1983

Colloid cyst of the third ventricle--a neurological emergency.

Colloid cyst of the third ventricle, although a benign lesion, carries with it high mortality and morbidity if not diagnosed in time. The most common presenting symptom is headache. A 31-year-old man with a history of intermittent, throbbing, unilateral headache and nausea was admitted because of exacerbation of his headache, which responded poorly to medication. A few hours after admission he became comatose. A colloid cyst of the third ventricle causing acute hydrocephaly was diagnosed by computed tomographic scan and removed in toto. Despite an uneventful postoperative course the patient was left with permanent bilateral cerebral damage. In patients with headache not responding to conventional medication, colloid cyst of the third ventricle perhaps should be ruled out, even if the symptoms are suggestive of vascular headache, such as migraine headache.

Adult↗
PubMed1989

Accessibility of colloidal gold and horseradish peroxidase to cytosolic spaces in Limulus ventral photoreceptors.

Physiological studies of intracellular messengers frequently employ intracellular injections of large molecules that either monitor or modulate the metabolism of the messenger cascade. Injected molecules have unknown mobility in the cytosol and unknown accessibility to various cytosolic compartments, including those postuiated to be traversed by intracellular messenger molecules. In order to determine whether injected molecules have access to the confined spaces through which messenger molecules must diffuse, we injected 5-nm colloidal gold or horseradish peroxidase, or both, into Limulus ventral photoreceptors. Injections were made by applying pressure pulses to the back of an intracellular micropipette that also monitored membrane voltage. The tissue was fixed at varying times after injection and processed for electron microscopy by conventional techniques. Cells fixed 1-3 min after injection contained HRP reaction product only in the cell body. HRP reaction product was found at varying distances down axons in direct relation to the interval between injection and fixation. Colloidal gold particles were found throughout the cell body but not in axons of tissue fixed 1-3 min after injection. Both HRP reaction product and 5-nm colloidal gold particles were observed within the microvillar projections of internal and external rhabdomere, as well as within the extracisternal spaces of endoplasmic reticulum. We conclude that large molecules injected from an intracellular micropipette into an arbitary locus of ventral photoreceptor cells have access to all of the presumed sites of the phototranduction cascade.

Animals↗
PubMed2001

Development of an intelligent polymerized crystalline colloidal array colorimetric reagent.

We have developed a novel colorimetric reagent for the determination of Pb2+, pH, and temperature. This colorimetric reagent consists of a dispersion of approximately 100-microm particles composed of an intelligent polymerized crystalline colloidal array (IPCCA). The IPCCA particles are composed of a hydrogel polymerized around a face-centered cubic (fcc) array of monodisperse, highly charged polystyrene colloidal particles. These IPCCA particles diffract visible light because the (111) planes of the fcc polystyrene colloidal particle array have an approximately 200-nm lattice constant. The IPCCA particles also contain a molecular recognition agent that actuates array volume changes as a result of changes in analyte concentration or temperature. This results in changes in the IPCCA lattice constants, which shifts the wavelength of light diffracted. We report here the use of these sensing materials in a liquid dispersion that can be poured into a sample solution. This diffraction measurement method is analogous to X-ray powder diffraction measurements. The diffraction wavelength is monitored at a defined angle relative to the incident light.

Journal Article↗
PubMed2001

Stable colloidal dispersions of fullerenes in polar organic solvents.

Colloidal dispersions of C60 and C70 were prepared by simply mixing a fullerene solution in a good solvent with a poor polar organic solvent for fullerenes. The process was very easy and fast and the formation of particles with average diameter in the colloidal range was detected immediately after the components were mixed. The formation and the properties of the fullerene particles were studied mainly with dynamic light scattering and high-resolution transmission electron microscopy. The most interesting findings are the long-term colloid stability of the samples in the absence of any stabilizers, the relatively narrow size distribution, and the different average sizes of the particles formed by C60, C70, and their mixtures. The influence of various factors such as fullerene concentration, mixing procedure, solvent properties, and C60/C70 ratio was investigated. It is shown that the smaller particles are formed when the total fullerene concentration in the good solvent is decreased and that the fullerene particles have crystalline structure. The measured negative values for the electrophoretic mobility of the particles suggest that fullerene dispersions in polar organic solvents are stabilized by repulsive electrostatic interactions.

Journal Article↗