The effects of multivalent electrolytes on the gravity-induced flocculation of colloidal particles in binary suspensions

The effects of multivalent electrolytes on gravity-induced heteroflocculation behavior of binary suspensions under different gravity forces are investigated based on the turbidity measurement method. The heteroflocculation behavior of the binary suspensions described by the stability ratio is well analyzed by using the stability diagram and the DLVO theory. It is found that the stability ratios of the binary suspensions decrease with the increase of either the electrolyte concentration and valence or the gravity forces and with the decrease of the size ratio of the latexes components of the binary suspension. Because the theoretical stability ratios obtained by the trajectory analysis method are always higher than the corresponding heteroflocculation experimental values obtained by turbidity measurements, we successfully apply the “regressed” surface potentials determined from the flocculation experiments of monodispersed suspension to predict the stability ratios of the corresponded binary suspension.     

二氧化硅悬浮体的絮凝

微细颗粒的胶体二氧化硅广泛应用于橡胶工业、日用化学工业、无机材料工业等众多部门,它的专门用途不下千余种[1]．二氧化硅微细悬浮体是一种典型胶体分散体系,在其中加入大分子显的有机或无机絮凝剂,研究其絮凝规律,不但对研究絮凝现象的理论和实践有意义,而且有助于认识二氧化硅颗粒的表面性质和该分散体系的稳定性．1实验1·1材料和试剂二氧化硅（上海电化厂）：以燃烧法制得的）“品（白炭黑）,D＊T法测其比表面为7（）11。’·g‘．聚丙烯酸胺（＊＊M．广州南中塑料厂）：白色粉末状,用乙醇从水溶液中沉淀、提纯,粘度法测其…     

Phase diagram of alloy crystal in the exhaustively deionized suspensions of binary mixtures of colloidal spheres

Phase diagrams of liquidlike, alloy crystal-like and amorphous solid-like(AS) structures have been obtained for the exhaustively deionized aqueous suspensions of the binary mixtures of polystyrene or silica spheres. Diameter, polydispersity index (standard deviation of diameter divided by the mean diameter) and size ratio of the binary spheres (diameter of small sphere divided by that of large one) range from 85 to 136 nm, 0.07 to 0.26 and 0.76 to 0.93, respectively. Close-up color photographs of the alloy crystals are taken and the crystal structure has been analysed from reflection spectroscopy. Most of the alloy crystals aresubstitutional solid-solution (sss) type and body-contered cubic lattice structure. Formation of the alloy crystals is attributed to the important role of the expanded electrical double layers in the deionized condition and increase toward unity in the effective size ratio, which is the effective diameter of small sphere including double layer divided by that of large sphere AS structure is formed at the rather high concentrations of two spheres, where the thickness of the electrical double layer is thin and the effective size rado is comparatively small.     

Mucin Interactions with Functionalized Polystyrene Latexes

The interactions of pig gastric mucin and bovine submaxillary mucin with carboxylate (PCM) and amino (PAM) polystyrene latexes with 750 and 1000 nm diameters have been studied in vitro. The mucin interaction increased when the pH decreased from 7.4 to 3.0 and when the electrolyte concentration increased from 86 to 205 mM. The driving force of the interaction was very probably nonionic. Under certain conditions, electrostatic attraction also was important for PAM. Under all experimental conditions tested, the mucins interacted less with PAM than with PCM. The functional groups of the latexes directed the conformation of the adsorbed mucins at the interface. At low pH, the mucins probably were adsorbed in multilayers.     

Molecular dynamics simulation of the structural configuration of binary colloidal monolayers

Molecular dynamics simulations of binary colloidal monolayers, i.e., monolayers consisting of mixtures of two different particle sizes, are presented. In the simulations, the colloid particles are located at an oil-water interface and interact via an effective dipole-dipole potential. In particular, the influence of the particle ratio on the configurations of the binary monolayers is investigated for two different relative interaction strengths between the particles, and the pair correlation functions corresponding to the binary monolayers are calculated. The simulations show that the binary monolayers can only form two-dimensional crystals for certain particle ratios, for example, 2:1, 6:1, etc., while, for example, for a particle ratio of 7:1 the monolayers are found to be in a disordered, glassy state. The calculations also reveal that in analogy to the Wigner lattice the configurations are very sensitive to the relative interaction strength between the particles but not to the absolute magnitude of the interaction strength, even when particle size effects are taken into account. Consequently, it is argued that a comparison between the calculated configurations and actual binary particle monolayer systems could provide useful information on the relative interaction strength between large and small particles. Possible mechanisms giving rise to disparities in the interaction strength between large and small particles are described briefly.     

Bimodal particle distribution for emulsions: The effect of interstitial functional particles

The location of hydroxyl functionality was investigated for thermosetting acrylic latexes. Large and small latex particles with and without hydroxyl functionality were synthesized and characterized. Such large and small latex particles with and without hydroxyl functionality were blended together and a melamine-formaldehyde (M-F) resin was added to crosslink the hydroxyl groups. Mechanical and thermo-mechanical properties were evaluated as function of blend ratio and functionality location. The packing of the latexes was dependent on small to large particle ratio. It was shown that the mechanical properties were also dependent on the location of the functionality. The higher concentration of hydroxyl groups in the small latex particles contributed more to the tensile properties of the latexes than the functionality of the large particles. The location of the M-F resin in the small latex particles resulted in a lowering of the volume fraction needed for a continuous network.     

Batch and semicontinuous emulsion copolymerization of vinyl acetat–butyl acrylate. I. Bulk,surface, and colloidal properties of copolymer latexes

Vinyl acetate (VAc)–butyl acrylate (BuA) comonomer mixtures with various composition were polymerized by batch and semicontinuous emulsion polymerization processes. PVAc and PBuA homopolymer latexes as well as the (VAc-BuA) copolymer latexes were characterized with respect to particle size, molecular weight, acid end groups on particle surfaces, and colloidal stability against electrolytes. The surface and colloidal properties of these latexes were also compared before and after aging and acid hydrolysis. The average particle size of batch latexes was independent of copolymer composition, whereas for semicontinuous latexes it decreased with increasing BuA content and was always lower than that of the corresponding batch latex. The molecular weight distribution (MWD) for batch latexes was narrower and much less dependent on composition than that of the semicontinuous latexes; bimodal MWD was found in most semicontinuous latexes with a substantial amount of low MW fraction. The total weak and strong acid end groups on particle surfaces for semicontinuous latexes is higher, and more dependent on composition, than the batch latexes. Acid-induced hydrolysis results in a drastic change in the type and concentration of the surface groups of the semicontinuous latex particles. Colloidal stability against electrolytes showed that both electrostatic (due to surface acid groups) and steric [due to surface poly(vinyl alcohol)] mechanisms are contributing. However, for semicontinuous latexes, increasing PVAc content above 50 mol % resulted in a proportional increase and ultimately dominant role of steric stabilization. The results were interpreted in terms of differences in reactivity ratios and water solubilities of the two monomers and their effects on the locus of initiation and growth in the two polymerization processes, as well as the monomer sequence within the polymer chain and degree of homogeniety of the copolymer composition within the particle.     

Phase behaviour of binary mixtures of colloidal charged spheres

As a step towards the modelling of binary metal alloys we here report on the shape of the phase boundary of two deionized charged sphere colloidal suspensions as a function of mixing ratio and particle density. Their size ratios are r = 0.68 and r = 0.56. Both aqueous suspensions of polystyrene copolymer spheres crystallize in a body-centred cubic structure. Interesting differences in the shape of the phase boundary are observed. In the first case a peaked increase of crystal stability was observed for a mixing ratio of p = 0.2–0.3, which gives the fraction of small spheres. Also in the second case the stability of the crystalline phase is larger than expected for an ideal solid solution but over a more extended range of small p. In addition at p = 0.7–0.8 we find a pronounced suppression of crystallization and furthermore some indications of a precipitation of one species at p = 0.9. While the first phase diagram resembles that of a solid solution with possibly the onset of compound formation, the second more resembles a eutectic.     

Radiolytic hydrogen yields in aqueous suspensions of gold particles

The effect of high concentrations of large gold particles, in the hundreds of nanometer size regime, on the yields of molecular hydrogen, G(H(2)), produced in the radiolysis of several aqueous solutions was determined. In particular we look for direct effect of radiation absorbed by the solid particles on the yield of water products. These particles, however, are catalytically active in the conversion of reducing radicals to molecular hydrogen as well. A very small increase in G(H(2)) observed in bromide solutions upon addition of 50 wt % of gold particles indicates that the radiolysis of the solid particles does not affect the yields in the aqueous phase. Very little exchange of charge carriers or energy between the two phases occurs in these large particle suspensions. On the other hand, efficient catalytic conversion of (CH(3))(2)C(*)OH radicals to H(2) is shown to occur. The efficiency of the presently studied suspensions in the redox-catalytic process is similar to that of suspensions of small particles of similar total surface area. In the presence of radicals from hydrogen atom abstraction from tert-butyl alcohol the yield decreases significantly, again similar to the behavior in suspensions of small particles. We conclude that the redox catalysis does not depend on the size of the particles when their size exceeds a few nanometers.     

Influence of concentration on the particle size analysis of polymer latexes using diffusing-wave spectroscopy

The use of a diffusing-wave spectroscopy (DWS) technique for the particle size analysis of a series of suspensions of polymer latexes with diameters ranging between 90 nm and 1300 nm and volume fractions from 0.02 to 0.18 has been investigated. Particle sizes from DWS were in reasonable agreement with those from transmission electron microscopy and disc centrifuge photosedimentometry. Photon correlation spectroscopy was applicable only to the latexes with particle sizes less than 500 nm. For polymer latexes with volume fractions (V_f) up to 0.09, the decay rate of the autocorrelation function from DWS was related to the particle size over the range of particle sizes examined. At the highest volume fraction (V_f = 0.18), it was possible to distinguish between particles with diameters of 740 and 1,300 nm from their autocorrelation functions, but not between particles with diameters of 90 and 430 nm.     

Study of the colloidal stability of concentrated bimodal magnetic fluids

In this paper, we describe an investigation of the stability and sedimentation behavior of moderately concentrated suspensions of extremely bimodal magnetite particles, including micro- (diameter 1450 nm) and nano- (diameter 8 nm) units. An original method is used, based on the determination of the time dependence of the inductance of a coil surrounding the suspensions. The method proves to be very useful for the determination of the volume fraction of magnetic material in the sensed volume. The observed changes in the resonant frequency of a parallel LC circuit demonstrate that the addition of the magnetite nanoparticles improves the stability and slows down the settling rate of the mixed suspensions. It is proposed that the observed behavior is the result of competition between two processes. One is the formation of a cloud of nanoparticles around the large magnetite units, by virtue of which the latter are maintained at distances beyond the range of DLVO and magnetic attractive interactions. At long times, these composite units will eventually sediment when some critical size is reached, as the small particles are progressively associated with the large ones. The second mechanism is mainly predominant at short times and is related to the higher viscosity of the dispersion medium (the nanoparticles dispersed in the base fluid) for higher nanoparticle concentrations. The stability of the suspensions is discussed in terms of the competition between the two mechanisms.     

Crowding promotes the switch from hairpin to pseudoknot conformation in human telomerase RNA

Formation of a pseudoknot (PK) in the conserved RNA core domain in the ribonucleoprotein human telomerase is required for function. In vitro experiments show that the PK is in equilibrium with an extended hairpin (HP) structure. We use molecular simulations of a coarse-grained model, which reproduces most of the salient features of the experimental melting profiles of PK and HP, to show that crowding enhances the stability of PK relative to HP in the wild type and in a mutant associated with dyskeratosis congenita. In monodisperse suspensions, small crowding particles increase the stability of compact structures to a greater extent than larger crowders. If the sizes of crowders in a binary mixture are smaller than that of the unfolded RNA, the increase in melting temperature due to the two components is additive. In a ternary mixture of crowders that are larger than the unfolded RNA, which mimics the composition of ribosome, large enzyme complexes and proteins in Escherichia coli , the marginal increase in stability is entirely determined by the smallest component. We predict that crowding can partially restore telomerase activity in mutants with decreased PK stability.     

Effect of associating polymer on the viscosity behavior of suspensions consisting of particles with different surface properties

Associating polymers which consist of water-soluble long-chain molecules containing a small fraction of hydrophobic groups (hydrophobes) behave as flocculants in aqueous suspensions. The effects of associating polymers on the rheological behavior are studied for single suspensions of particles with hydrophilic and hydrophobic surfaces, and their mixtures. For particles with hydrophilic surfaces, the suspensions are highly flocculated by a bridging mechanism, because the water-soluble chains adsorb onto hydrophilic surfaces. On the other hand, the particles with hydrophobic surfaces cannot be dispersed in water without polymer and the additions of a small amount of polymer are required for preparation of homogeneous suspensions. The associating polymer acts as a dispersant at low concentrations. However, further additions of polymer lead to a drastic increase in viscosity. Since the hydrophobes on one end of molecules adsorb onto hydrophobic surfaces and other hydrophobes tending from the particles can form micelles, the particles are connected by linkage of interchain associations. By mixing two suspensions of particles with hydrophilic and hydrophobic surfaces, the viscosity is substantially reduced and the flow becomes nearly Newtonian. The associating polymer in complex suspensions acts as a binder between the hydrophilic and hydrophobic surfaces. The hetero-flocculation which leads to the formation of composite particles may be responsible for the viscosity reduction of complex suspensions.     

Hypersonic acoustic excitations in binary colloidal crystals: big versus small hard sphere control

The phononic band structure of two binary colloidal crystals, at hypersonic frequencies, is studied by means of Brillouin light scattering and analyzed in conjunction with corresponding dispersion diagrams of the single colloidal crystals of the constituent particles. Besides the acoustic band of the average medium, the authors' results show the existence of narrow bands originating from resonant multipole modes of the individual particles as well as Bragg-type modes due to the (short-range) periodicity. Strong interaction, leading to the occurrence of hybridization gaps, is observed between the acoustic band and the band of quadrupole modes of the particles that occupy the largest fractional volume of the mixed crystal; the effective radius is either that of the large (in the symmetric NaCl-type crystalline phase) or the small (in the asymmetric NaZn(13)-type crystalline phase) particles. The possibility to reveal a universal behavior of the phononic band structure for different single and binary colloidal crystalline suspensions, by representing in the dispersion diagrams reduced quantities using an appropriate length scale, is discussed.     

交联剂含量对憎水改性缔合型增稠剂性能的影响

以甲基丙烯酸、丙烯酸乙酯和功能单体二十二烷基聚氧乙烯醚甲基丙烯酸酯为原料,过硫酸铵为引发剂,变化交联剂邻苯二甲酸二烯丙酯(DAP)的量,采用半连续乳液聚合方法合成了DAP含量不同的憎水改性缔合型增稠剂乳液.测定了乳液的黏度和乳胶粒粒径及其分布等性能.考察了乳液运动黏度和透光率随pH的变化.随着pH值的增加,乳液的透光率...     

Influence of a depletion interaction on dynamical heterogeneity in a dense quasi-two-dimensional colloid liquid

We report the results of digital video microscopy studies of the large particle displacements in a quasi-two-dimensional binary mixture of large (L) and small (S) colloid particles with diameter ratio sigma(L)/sigma(S)=4.65, as a function of the large and small colloid particle densities. As in the case of the one-component quasi-two-dimensional colloid system, the binary mixtures exhibit structural and dynamical heterogeneity. The distribution of large particle displacements over the time scale examined provides evidence for (at least) two different mechanisms of motion, one associated with particles in locally ordered regions and the other associated with particles in locally disordered regions. When rhoL*=Npisigma(L) (2)/4A< or =0.35, the addition of small colloid particles leads to a monotonic decrease in the large particle diffusion coefficient with increasing small particle volume fraction. When rhoL* > or =0.35 the addition of small colloid particles to a dense system of large colloid particles at first leads to an increase in the large particle diffusion coefficient, which is then followed by the expected decrease of the large particle diffusion coefficient with increasing small colloid particle volume fraction. The mode coupling theory of the ideal glass transition in three-dimensional systems makes a qualitative prediction that agrees with the initial increase in the large particle diffusion coefficient with increasing small particle density. Nevertheless, because the structural and dynamical heterogeneities of the quasi-two-dimensional colloid liquid occur within the field of equilibrium states, and the fluctuations generate locally ordered domains rather than just disordered regions of higher and lower density, it is suggested that mode coupling theory does not account for all classes of relevant fluctuations in a quasi-two-dimensional liquid.     

Synthesis of cyclo‐olefin copolymer latexes and their carbon nanotube composite nanoparticles

An efficient and environmentally benign synthetic method for the production of the stabilized cyclo‐olefin copolymer latexes and their carbon nanotube composite nanoparticles has been developed using an emulsion ring opening metathesis copolymerization catalyzed by the 2nd generation Grubbs catalyst in aqueous solution. Homopolymerizations of norbornene (NB) and dicyclopentadiene (DCPD) in aqueous solution yield unstable polymer latexes in combination with a large amount of their flocculation fractions. Copolymerizations of NB or DCPD with a selected liquid cyclo‐olefin comonomer dramatically improve not only the colloidal stability of the copolymer latexes but also the thermal stability of the copolymer nanoparticles. The liquid cyclo‐olefin comonomer plays a double role as a liquefied agent for the solid NB and DCPD monomers before the emulsification treatment, and a reactive comonomer itself to control entirely the copolymerization system. The as‐prepared cyclo‐olefin copolymer latexes exhibit an exceptionally high compatibility with a well‐dispersed carbon nanotube (CNT) in aqueous solution due to strong π–π interactions between the graphitic surfaces of the CNT with the C‐C double bonds located on the cyclo‐olefin copolymer main chains. Accordingly, a binary blending of these two well‐dispersed colloidal systems in aqueous solution led to the fabrication, for the first time, of the highly electrical conductive cyclo‐olefin copolymer/CNT composite nanoparticles. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4584–4591     

A Surfactant Bridge Model for the Nonlinear Electrorheological Effects of Surfactant-Activated ER Suspensions

In surfactant-activated electrorheological (ER) suspensions it is observed that the ER response shows linear ER behavior (F~E(2)) at small surfactant concentrations and nonlinear ER behavior (F~E(n), n approximately 1) at large surfactant concentrations. Here, a surfactant bridge model is developed to explain the nonlinear ER behavior of surfactant-activated ER suspensions. The model shows that the formation and size of a surfactant bridge depend on various variables, especially the electric field strength, the surfactant surface tension, and the initially adsorbed amount of surfactants on particles. The predicted dependence of the formation and size of a surfactant bridge on the electric field strength and the initially adsorbed amount of surfactants is consistent with the observations. Also, the model indicates that there is a critical minimum electric field E(crit) for the formation of a surfactant bridge, and the estimated E(crit) shows good agreement with the observations. The force acting between particles is composed of the electrostatic force and force associated with surface tension. However, it is found that the contribution of the force associated with surface tension can be ignored and the electrostatic force is dominant regardless of the formation of surfactant bridges between particles. When surfactant bridges are formed between particles, the predicted force shows nonlinear ER behavior (F~E(n), n approximately 1), consistent with the observed nonlinear ER behavior at large surfactant concentrations. When no surfactant bridge is formed, the predicted force is proportional to the electric field squared (F~E(2)), consistent with the interfacial polarization. The model can successfully predict the nonlinear ER behavior at large surfactant concentrations, confirming that the nonlinear ER behavior of surfactant-activated ER suspensions arises from the observed formation of surfactant bridges between particles. Copyright 2001 Academic Press.     

Regularities of latex filtration through microfiltration membranes

Filtration of suspensions of emulsifier-free monodisperse polystyrene latexes with particle sizes of 0.25, 0.3, and 0.4 μm through acetylcellulose microfilters is studied as depending on the composition of liquid phases, the rate and time of filtration, and the particle-to-pore size ratios. The effect of particle-membrane interactions, which are governed by the electrostatic repulsion and molecular attraction forces, on particle rejection by membranes is considered. It is shown that, when analyzing the mechanism for the rejection, it is necessary to take into account the electrophoretic motion of particles in the field of the streaming potential arising in the course of suspension filtration.     

Stability of Dispersions of Fluorine-Containing Latexes and Its Effect on the Properties of Forming Films

The stability of latexes of poly(1,1-dihydroperfluoroheptyl acrylate) (LFM-3), poly(vinyl chloride-co-vinylidene chloride) (SVKh), poly(butadiene-co-methacrylic acid) (SKD-1), and their mixtures, as well as the wettability of the films produced on their basis are studied. It is revealed that, in some cases, the stability of binary systems exceeds that of individual dispersions. A correlation is established between the stability of latexes (varying in the film-formation process) and the critical concentration of their coagulation, on the one hand, and the water contact angles, on the other hand. It is shown that the aggregation of latex particles considerably affects the texture of hydrophobic films.