Colloids surface charge

We developed a synthesis of monodisperse, highly charged colloidal particles of PNIPAM whose diameter depends on temperature (76). NIPAM was polymerized with the ionic comonomer 2-acrylamido-2-methyl-l-propane sulfonic acid to increase the colloid surface charge which facilitates CCA self-assembly. Figure 4 shows the temperature dependence of the colloidal sphere diameter, which increases from -100 nm at 40°C to -300 nm at 10 C. 

Fig. 1 Adsorption of a polyelectrolyte chain onto spherical colloidal particles for various salt concentrations C (from [35]). The ratio ajb between the colloid radius a and monomer bond length b increases from top to bottom. The colloid surface charge density is constant, hence, the colloidal charge increases with a. The adsorption threshold depends on the salt concentration and the size ratio. More details of the underlying Monte Carlo simulations are provided in Ref. [35]...

The critical value p allows us to calculate other critical quantities for polyelectrolyte adsorption, such as the critical temperature [41, 59], the critical colloid surface charge density critical temperature and the critical surface charge density have been presented and discussed [58, 59]. Thus, we summarize here our findings for only. Using the above limiting values for p, we obtain the following approximations ... 

Figures 7 and 8 provide examples of such distributions for various effective charge densities and Debye screening lengths, respectively. The a values in Figs. 7 and 8 cover the experimental range of colloid and polyelectrolyte parameters (see Fig. 11 in [59]). For the critical parameters, the density distribution P is very broad and reaches a finite value for r oo. This corresponds to a uniform polyelectrolyte monomer density and refiects the thermodynamic equilibrium between the bound and free states of the polymer. With increasing colloid surface charge density or decreasing k [65,66], the distribution becomes more confined and...

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]. 

In particular, in polar solvents, the surface of a colloidal particle tends to be charged. As will be discussed in section C2.6.4.2, this has a large influence on particle interactions. A few key concepts are introduced here. For more details, see [32] (eh 13), [33] (eh 7), [36] (eh 4) and [34] (eh 12). The presence of these surface charges gives rise to a number of electrokinetic phenomena, in particular electrophoresis. 

Figure 18-82 illustrates the relationship between solids concentration, iuterparticle cohesiveuess, and the type of sedimentation that may exist. Totally discrete particles include many mineral particles (usually greater in diameter than 20 Im), salt crystals, and similar substances that have httle tendency to cohere. Floccnleut particles generally will include those smaller than 20 [Lm (unless present in a dispersed state owing to surface charges), metal hydroxides, many chemical precipitates, and most organic substances other than true colloids. 

To avoid surface charges, all surfaces have been coated with colloidal graphite in alcohol (7). Radii of mass spectrometer 18 and 25 cm., respectively... 

Garda-Salinas M. J., Romero-Cano M. S., de las Nieves F. J.. Zeta potential study of a polystyrene latex with variable surface charge influence on the electroviscous coefficient. Progr Colloid Polym Sci (2000) 115 112-116. 

Ohshima, H Kondo, T, Electrophoretic Mobility and Donnan Potential of a Large Colloidal Particle with a Surface Charge Layer, Journal of Colloid and Interface Science 116, 305, 1987. O Neil, GA Torkelson, JM, Modeling Insight into the Diffusion-Limited Cause of the Gel Effect in Free Radical Polymerization, Macromolecules 32,411, 1999. 

Tari, G., Bobos, I., Gomes, C. and Ferreira, J. (1999) Modification of surface charge properties during kaolinate to halloysite-7A transformation. Journal of Colloid and Interface Science, 210, 360. 

The sorbent materials are supplied as finely dispersed colloidal particles, whose surfaces are smooth. Some of their properties are presented in Table 3. The sorbents cover different combinations of hydrophobicity and sign of the surface charge. Thus, the model systems presented allow systematic investigation of the influences of hydrophobicity, electric charge, and protein structural stability on protein adsorption. 

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