Polydisperse colloid

The polyelectrolyte microgels have been established as model soft spheres as, in addition to the above features, their softness and properties can be tuned by altering the physico-chemical environment (pH, ionic strength, degree of ionization) [152-160], The response varies from that of colloidal (polydisperse hard-sphere) suspensions and that of polymer gels and in this respect such microgels fit within the theme of Fig. 1 [157-160],... 

Protein solutions are monodisperse solutions whose particles, namely the protein molecules, are of the same size as the composite particles of colloidal solutions. It is to be expected, therefore, that protein solutions will manifest certain properties in common with colloidal polydisperse solutions of organic or inorganic materials, as well as certain different properties. 

Abstract This article reviews the recent progress that has been made in the application of computer simulations to study crystal nucleation in colloidal systems. We discuss the concept and the numerical methods that allow for a quantitative prediction of crystal nucleation rates. The computed nucleation rates are predicted from first principles and can be directly compared to experiments. These techniques have been applied to study crystal nucleation in hard-sphere colloids, polydisperse hard-sphere colloids, weakly charged or slightly soft colloids and hard-sphere colloids that are confined between two plane hard walls. 

Rowell and co-workers [62-64] have developed an electrophoretic fingerprint to uniquely characterize the properties of charged colloidal particles. They present contour diagrams of the electrophoretic mobility as a function of the suspension pH and specific conductance, pX. These fingerprints illustrate anomalies and specific characteristics of the charged colloidal surface. A more sophisticated electroacoustic measurement provides the particle size distribution and potential in a polydisperse suspension. Not limited to dilute suspensions, in this experiment, one characterizes the sonic waves generated by the motion of particles in an alternating electric field. O Brien and co-workers have an excellent review of this technique [65]. 

Even when carefully prepared, model colloids are almost never perfectly monodisperse. The spread in particle sizes, or polydispersity, is usually expressed as the relative widtli of tire size distribution,... 

The major class of plate-like colloids is tliat of clay suspensions [21]. Many of tliese swell in water to give a stack of parallel, tliin sheets, stabilized by electrical charges. Natural clays tend to be quite polydisperse. The syntlietic clay laponite is comparatively well defined, consisting of discs of about 1 nm in tliickness and 25 nm in diameter. It has been used in a number of studies (e.g. [22]). 

The fonnation of colloidal crystals requires particles tliat are fairly monodisperse—experimentally, hard sphere crystals are only observed to fonn in samples witli a polydispersity below about 0.08 [69]. Using computer... 

Salgi P and Rajagopalan R 1993 Polydispersity in colloids—implications to static structure and scattering Adv. Colloid Interface Sc/. 43 169-288... 

FIG. 22-44 E mpirical relationship between 2), the volumetric fraction of hq-iiid in common polydisperse foam, and K, the electrical conductivity of the foam divided hy the electrical conductivity of the liquid. [Chang and Lemhch, J. Colloid Interface Sci., 73, 224 (1980).]... 

Several colloidal systems, that are of practical importance, contain spherically symmetric particles the size of which changes continuously. Polydisperse fluid mixtures can be described by a continuous probability density of one or more particle attributes, such as particle size. Thus, they may be viewed as containing an infinite number of components. It has been several decades since the introduction of polydispersity as a model for molecular mixtures [73], but only recently has it received widespread attention [74-82]. Initially, work was concentrated on nearly monodisperse mixtures and the polydispersity was accounted for by the construction of perturbation expansions with a pure, monodispersive, component as the reference fluid [77,80]. Subsequently, Kofke and Glandt [79] have obtained the equation of state using a theory based on the distinction of particular species in a polydispersive mixture, not by their intermolecular potentials but by a specific form of the distribution of their chemical potentials. Quite recently, Lado [81,82] has generalized the usual OZ equation to the case of a polydispersive mixture. Recently, the latter theory has been also extended to the case of polydisperse quenched-annealed mixtures [83,84]. As this approach has not been reviewed previously, we shall consider it in some detail. 

However, in subsequent studies [23-25,88-90] it was demonstrated that in reality the particle deposition is not a purely geometric effect, and the maximum surface coverage depends on several parameters, such as transport of particles to the surface, external forces, particle-surface and particle-particle interactions such as repulsive electrostatic forces [25], polydispersity of the particles [89], and ionic strength of the colloidal solution [23,88,90]. Using different kinds of particles and substrates, values of the maximum surface coverage varied by as much as a factor of 10 between the different studies. 

In an attempt to create particles with different sizes and properties, ligands other than dodecanethiol were used to create polydispersed colloids from the SMAD method. Thus, dodecylamine, trioctyl phosphine, and dodecyl alcohol were used in addition to dodecanethiol. The results of these studies led to nearly monodispersed stable colloids for the phosphine protected particles at 6.3 nm in diameter (Figure 13). 

V. Mishra, S. M. Kresta, J. H. Masliyah 1998, (Self-preservation of the drop size distribution function and variation in the stability ratio for rapid coalescence of a polydisperse emulsion in a simple shear field), J. Colloid Interface Sci. 197, 57. 

Concentration effects for Ag-acetone were also studied in our laboratory. These colloidal solutions were black as compared with purple for Au-acetone. They were also sensitive to light (see later). According to TEM the Ag particles from acetone were much larger ( 30 nm) compared with Au (2-9 nm). The Ag particles appeared to be denser and perhaps more crystalline. They contained much less organic residue than the Au particles. Particle size for Ag was also dependent on Ag-acetone concentration in the same way as for Au, and the Ag particles were more polydisperse ranging from 20-40 nm. 

Colloids are larger molecular weight solutions (more than 30,000 daltons) that have been recommended for use in conjunction with or as replacements for crystalloid solutions. Albumin is a monodisperse colloid because all of its molecules are of the same molecular weight, whereas hetastarch and dextran solutions are polydisperse compounds with molecules of varying molecular weights. 

Heterodisperse Suspensions. The rate laws given above apply to monodisperse colloids. In polydisperse systems the particle size and the distribution of particle sizes have pronounced effects on the kinetics of agglomeration (O Melia, 1978). For the various transport mechanisms (Brownian diffusion, fluid shear, and differential settling), the rates at which particles come into contact are given in Table 7.2. 

Tomaic, J., and V. Zuti6 (1988), "Humic Material Polydispersity in Adsorption at Hydrous Alumina Seawater Interface", J. Colloid and Interface Sci. 126, 482-492. 

Considerable research effort was focused on systems of colloidal gold of which a broad variety of synthetic procedures were reported [140 b, fj. While native colloidal gold solutions are only stable for a restricted time, Brust et al. [141] were able to overcome this problem by developing a simple method for the in situ preparation of alkyl thiol-stabihzed gold nanoparticles. This synthetic route yields air-stable and easy to handle passivated nanoparticles of moderate polydispersity, and is now commonly employed for the preparation of inorganic-organic core-shell composites. Such composites are used as catalytic systems with principally two different functions of the protective 3D-SAM layer. Either the metal nanoparticle core can be used as the catalytically active center and the thiol layer is only used to stabihze the system [142], or the 3D-SAM is used as a Hnker system to chemically attach further catalytic functions [143]. 

Advincula et al. used the same initiator type (DPE activated with u-BuIi) to perform LASIP from colloidal sihca [265] or clay [266, 267]. The spacer between the DPE unit and the surface active group (quatemized amine for clay and chlorodi-methylsilane for silica) was a long n-alkyl chain. In all cases, a relatively broad polydispersity for the prepared polystyrene bmsh (PDI = 1.2-2) was observed. 

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