Surface activity of metastable colloidal solutions

Colloid and Polymer Science - On grinding a high melting crystal of a water insoluble saponin molecule, such as aescin, the particle size is reduced and a state being produced which is...     

Model of bound water formation in fractal clusters resulting from reversible aggregation of colloidal particles

A model is proposed for the formation of bound water in fractal clusters that arise in the course of the reversible aggregation of colloidal particles. The dependence of the specific content of bound (nonfreezing) water on the concentration of a colloidal solution is theoretically determined. It is found that this value is related to the concentration of the colloidal solution via a power law. It is shown that the exponent is determined by the total surface area and morphology of fractal clusters, as well as by the mechanism of their aggregation and disintegration.     

Shear history independence in colloidal aggregation

Stimulated by experiments, we have carried out detailed simulations of aggregation in the presence of shear in a model colloidal system with a short-range attractive potential. For weak shear rates, we find that the shear enhanced the aggregation and that the long-time state of the system is independent of the shear history. For strong shear rates, precipitous fragmentation occurred after the shear was turned on and, after an induction period, the aggregation quickly rebounded in a stochastic manner similar to classical nucleation phenomena. However, the long-time state of the system is, once again, independent of the shear history. Thus, for both weak and strong shear cases, the shear rate acts as a state variable of the aggregating system. Shear rates employed in the simulations can be attained in laboratory experiments, as confirmed by computing the dimensionless Péclet numbers.     

Formation of long-lived clusters and silver nucleation in the γ-irradiation of aqueous silver perchlorate solutions containing polyphosphate

It was found that long-lived positively charged and neutral silver clusters were formed by the radiation-chemical reduction of Ag⁺ ions in aqueous solutions containing sodium polyphosphate. The nuclearity of the clusters increased with absorbed dose; then, quasi-metal particles were formed. The process culminated in the formation of silver nanoparticles.Translated from Khimiya Vysokikh Energii, Vol. 39, No. 2, 2005, pp. 83–87.Original Russian Text Copyright © 2005 by Ershov, Abkhalimov, Sukhov.This revised version was published online in April 2005 with a corrected cover date.     

Unusually long-lived light-induced metastable state in a thermochromic copper(II) complex

We report the first observation of a color change from red to purple for a thermochromic complex, [Cu(dieten)2](BF4)2 (dieten = N,N-diethylethylenediamine), which is induced by illuminating with UV light.     

Antibonding plasmon modes in colloidal gold nanorod clusters

The optical response of nanoplasmonic colloids in disperse phase is strictly related to their shape. However, upon self-assembly, new optical features, for example, bonding or antibonding modes, emerge as a result of the mutual orientations of nanoparticles. The geometry of the final assemblies often determines which mode is dominating in the overall optical response. These new plasmon modes, however, are mostly observed in silico, as self-assembly in the liquid phase leads to cluster formation with a broad range of particle units. Here we show that low-symmetry clustering of gold nanorods (AuNRs) in solution can also reveal antibonding modes. We found that UV-light irradiation of colloidal dispersions of AuNRs in N-methyl-2-pyrrolidone (NMP), stabilized by poly(vinylpyrrolidone) (PVP) results in the creation of AuNRs clusters with ladderlike morphology, where antibonding modes can be identified. We propose that UV irradiation induces formation of radicals in solvent molecules, which then promote cross-linking of PVP chains on the surface of adjacent particles. This picture opens up a number of relevant questions in nanoscience and is expected to find application in light induced self-assembly of particles with various compositions and morphologies.     

Bimodal colloidal mixtures: from fast to slow aggregation regions

A Brownian dynamics simulation has been used to investigate the aggregation kinetics of bimodal colloidal mixtures with similar surface chemistries but different sizes, driven by the DLVO interaction potential. The time evolution of structural formation is examined by the mean number of neighbors under fast and slow aggregation regions. It was found that the electrolyte ionic strength affects the kinetic pattern of colloidal aggregation. Under the high electrolyte ionic strength conditions (fast aggregation), the selective aggregation of the least stable single component can take place in the early stage, while the other component is enriched in this least stable component in the later stage. With the ionic strength decreasing (towards the slow aggregation), the hybrid aggregation (selective aggregation and heteroaggregation) gradually dominates the aggregation kinetics. Also in the early stage, this evolves to the heteroaggregation of different components under lower ionic strength conditions. The volume fraction has no obvious influence on this kinetic pattern in the early stage.     

Mesoscopic structure formation in colloidal aggregation and gelation

Recent small-angle light scattering experiments have revealed that diffusively aggregating spherical particles develop structure on a mesoscopic length scale (∼ tens of particles). The mesoscopic structural length scale persists even when the aggregation proceeds to the formation of a space-spanning network (a gel). We review the technique of small-angle light scattering, survey the experimental evidence for mesoscopic structure formation, discuss attempts at understanding these experimental observations by computer simulation of irreversible and reversible diffusion-limited cluster aggregation (DLCA), and propose a coherent picture for the understanding of non-equilibrium aggregation in the context of phase transitions.     

Nanosized gismondine grown in colloidal precursor solutions

A colloidal molecular sieve with GIS-type structure was prepared from aged aluminosilicate precursor solutions containing tetramethylammonium (TMA) hydroxide under hydrothermal treatment at 100 degrees C. The nucleation and the development of the GIS zeolite structure were studied by dynamic light scattering, scanning electron microscopy, X-ray diffraction, Raman and infrared spectroscopies, and liquid-state NMR spectroscopy. It is shown that the aging at room temperature leads to the formation of subcolloidal particles that incorporate TMA cations and form larger aggregates. After an extended heating of 13 days, a complete transformation from amorphous precursor material to crystalline GIS-type colloidal particles is observed. The mean hydrodynamic radius of the crystalline GIS particles is in the range of 30-50 nm. The specific template-framework interactions influence the spectral features of the TMA cations incorporated in the zeolite structure, thus making possible the use of the corresponding Raman spectra and 13C NMR data for the examination of the crystallinity of GIS-type colloidal particles stabilized in water.     

Release and formation of surface-localized ionic clusters (SLICs) into phospholipid rafts from colloidal solutions during coalescence

Stimuli-responsive behavior of phospholipids in the presence of ionic surfactants utilized in synthesis of MMA/nBA colloidal particles was investigated. Utilizing 1-myristoyl-2-hydroxy-sn-glycero-phosphocholine (MHPC) phospholipid, and sodium dioctyl sulfosuccinate (SDOSS) surfactant as dispersing media in H(2)O, narrow unimodal particle size distributions of methyl methacrylate (MMA)/n-butyl acrylate (nBA) copolymers were synthesized. The particle diameters were 154 nm when a SDOSS/MHPC mixture was used and 161 nm using MHPC as the only surface-stabilizing species. When such colloidal dispersions are exposed to 1.7, 3.3, and 6.7 mM aqueous CaCl(2) and KCl electrolyte solutions, surface-localized ionic clusters are generated at the film-air interface that may serve as lipid rafts composed of crystalline phases of MHPC deposited on poly(MMA)/nBA films. These studies illustrate that it is possible to control release and morphology developments of surface phospholipid rafts on artificial surfaces.     

Equilibrium clusters in concentrated lysozyme protein solutions

We have studied the structure of salt-free lysozyme at 293 K and pH 7.8 using molecular simulations and experimental SAXS effective potentials between proteins at three volume fractions, ?=0.012, 0.033, and 0.12. We found that the structure of lysozyme near physiological conditions strongly depends on the volume fraction of proteins. The studied lysozyme solutions are dominated by monomers only for ?≤0.012; for the strong dilution 70% of proteins are in a form of monomers. For ?=0.033 only 20% of proteins do not belong to a cluster. The clusters are mainly elongated. For ?=0.12 almost no individual particles exits, and branched, irregular clusters of large extent appear. Our simulation study provides new insight into the formation of equilibrium clusters in charged protein solutions near physiological conditions.     

The aggregation in dodecyltrimethylammonium hydroxide aqueous solutions

The aggregation of dodecyltrimethylammonium hydroxide (DTAOH) aqueous solutions has been studied by several methods. It is stepwise and four critical points were found. AtC _T=(2.51±0.10)×10^–4 mol · dm^–3 the surface excess becomes zero, atC _T=(1.300±0.041)×10^–3 mol · dm^–3 small aggregates from, which grow with concentration. AtC _T=(1.108±0.010)×10^–2 mol · dm^–3 true micelles form (CMC) and at (3.02±0.28)×10^–2 mol · dm^–3 the structure of micelles probably changes affecting their properties. The DTAOH micelles are highly ionized (=0.8) at the CMC, and decreases to reach very small values when the total concentration increases.     

Separation of radionuclides in colloidal form from aqueous solutions

A review is presented on the separation of colloidal radionuclides from aqueous solutions involving the sorption and flotation methods.     

Positively charged colloidal species in aqueous anionic surfactant solutions

The solution chemistry of fatty acids was reassessed. Transmittance measurements confirmed the existence of a colloidal precipitate in accordance with the constructed thermodynamic diagram. The electrokinetic potential of the precipitate and its dependence on pH was examined and an i.e.p. was found around pH 3. It results then that positively charged species exist below pH 3 in the broad range of fatty acid aqueous solution concentrations.     

Ordering of lipid A-monophosphate clusters in aqueous solutions

In this investigation, a study of the self-assembly of electrostatically stabilized aqueous dispersions of nanometric lipid A-monophosphate clusters from Escherichia coli was carried out in three different volume-fraction regimes. The experimental techniques used in the investigation were osmotic pressure, static and quasielastic light scattering, scanning electron microscopy and transmission electron microscopy, and small-angle x-ray scattering. Experiments were carried out at low ionic strength (I=0.1-5.0 mM NaCl) at 25 degrees C. At volume fractions between 1.5x10(-4)相似文献   

Transient entanglements and clusters in dilute polymer solutions

A convenient method to monitor polymer dissolution is to measure the pressure drop created by passing a polymer solution through a capillary constriction rheometer. In this work, we studied the dissolution of polyethylene oxide (PEO) and cationic starch (C‐starch). We found that for freshly dissolved and entangled PEO, the main contribution to the overall pressure drop is due to the contraction and expansion of PEO entanglements at the entrance and exit of the capillary, and that the friction in the capillary plays a minor role. On the other hand, for well‐dissolved PEO, because of the absence of PEO entanglements, the loss of pressure is mainly due to friction. At high velocities the contraction and expansion coefficient for freshly dissolved PEO was more than 20 times higher than for well‐dissolved PEO, resulting in a three times higher overall pressure drop. C‐starch consists of amylopectin (～ 85%) and amylose and is known to contain clusters when freshly dissolved, likely formed from the globular amylopectin molecules. For C‐starch, the main contribution to the overall pressure drop is due to friction. Entrance and exit effects contribute only 10% to the overall pressure drop, which might be due to the linear amylose molecules in C‐starch. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 253–262, 2008     

Evaporation and aggregation in aqueous monododecyltrimethylammonium n-dodecanephosphonate solutions

 Electrobalance evaporation rate measurements were used to measure solute weights in the aqueous catanionic system monododecyltri-methylammonium-n-dodecanephos-phonate. At very low concentration premicelles composed of ion pairs between 3.6 and 7 were found, which increased with concentration. Above the cmc the aggregates increased in size with concentration much more rapidly. Aggregates had 54 ion pairs at the higher studied concentration (6×10^-3 mol dm^-3). This value agrees with literature data of other similar systems. Since the system is probably polydisperse and the evaporation rate method gives number average weights, the true aggregation numbers are probably higher than those found. In this system the cmc did not indicate the starting point of aggregation, but a change in the aggregates structure and growing regime. Received: 23 June 1997 Accepted: 13 August 1997     

A general criterion based on the implicit function theorem to model aggregation and adsorption in colloidal dispersions

This paper, which may interest not only colloid scientists and physical chemists but also applied mathematicians, completes some previous results on aqueous silicon nitride dispersions. Experimental data on adsorption from liquid solution were first obtained by a titration method and then used to derive the number of solid particles from an equilibrium constraint. To discuss the complex mechanisms affecting simultaneous solid particle aggregation and small ion adsorption at the solid/liquid interface, the Dini implicit function theorem (DT) has been applied to the equilibrium condition for a former suspension Gibbs free energy. It was able to relate the average particle number to the ion concentration adsorbed, but not to unequivocally specify their dependence on the liquid phase pH. We attempt here to model aggregation both through bulk and interfacial quantities. The generalized DT-based criterion has first been formulated in all generality, and then adopted according to a wider investigation. The results obtained confirm the original guess, i.e., to regard solid aggregation as dominated by interfacial mechanisms.