Adsorption onto colloidal particles

For adsorption onto colloidal particles two approaches are possible. The first is to determine vlscometrlcally the increase in the effective particle volume fraction upon adsorption, and the second is to measure the decrease in the particle diffusion coefficient. 

Adsorption onto Colloidal Particles. In addition to our studies of complexation with polymeric carboxylic acids, we have also investigated adsorption of the same end-tagged PEG on colloidal surfaces. Just as the hydrophobic or hydrophilic character of the acid can be changed, in colloidal... 

Removal to sediments. Removal of surface-reactive trace elements from the oceans readily occurs by adsorption onto settling particles, and this process is most pronounced in the typically high-energy, particle-rich estuarine environment. Particles are supplied by rivers, augmented by additions of organic material generated within the estuary. Also, floes are created in estuaries from such components as humic acids and Fe. The interaction between dissolved and colloidal species is enhanced by the continuous resuspension of sediments in... 

There are very important phenomena originated when a polymer is on one interface or close to one interface. Such phenomena include adsorption, adhesion, monolayer formation, coating and colloidal stabilization. In the majority of circumstances a polymer adsorbed onto colloidal particles will increase the stability of a dispersion [8], The essential feature of polymer or steric stabilization is... 

The more recent neutron reflectivity studies have established that flattened surface micelle or fragmented bilayer structure in more detail and with more certainty, using contrast variation in the surfactant and the solvent [24, 31]. However, the extent of the lateral dimension (in the plane of the surface) and the detailed structure in that direction is less certain. From those neutron reflectivity measurements [24, 31] and related SANS data on the adsorption of surfactants onto colloidal particles [5], it is known that the lateral dimension is small compared with the neutron coherence length, such that averaging in the plane is adequate to describe the data. The advent of the AFM technique and its application to surfactant adsorption [15] has provided data that suggest that there is more structure and ordering in the lateral direction than implied from other measurements. This will be discussed in more detail in a later section of the chapter. At the hydrophobic interface, although the thickness of the adsorbed layer is now consistent with a monolayer, the same uncertainties about lateral structure exist. 

The adsorption and the covalent grafting of DNA, RNA, and ODN onto colloidal particles have mostly been carried out using the classical depletion method (static method) generally used in the case of proteins and polymers. The ad-... 

Determination of the adsorption isotherm is important, since it allows establishing of the basic relationship between the adsorbed amounts of ODN onto colloidal particles as a function of residual ODN concentration (equilibrium ODN concentration). Two major pieces of information can be deduced from the adsorption isotherm (i) the affinity between the ODN and the particles revealed... 

Adsorption onto colloidal polystyrene results in very different behavior because of the hydrophobic nature of that surface. The addition of even a small amount of polystyrene particles to the polymer solution results in the complete disappearance of the excimer emission (Figure 6). In this case, the hydrophobic pyrene groups are strongly attracted to the polystyrene surface thus, the formation of excimers is precluded. A similar disappearance of the excimer was observed upon complexation with PMAA, a result indicating that the hydrophobic character of that polymer may hinder the formation of excimers by adsorbing the pyrene groups into a hydrophobic pocket. This observation is further supported by the fluorescence excitation spectra, presented in the next section. 

Excitation Spectra and Fluorescence Lifetimes. In this section, we further examine adsorption onto colloidal polystyrene by investigating the excitation spectrum of the adsorbed species. In Figure 7a, we show the excitation spectra of Py-PEG-Py(4250) before and after the addition of polystyrene particles. The spectrum undergoes a substantial red shift upon adsorption the main peak moves approximately 4 nm. A similar effect is found in the complexation with PMAA, as shown in Figure 3, where the monomer spectrum is again shifted to higher wavelengths. From these spectral shifts, we infer a spectral sensitivity to the environment. This sensitivity is illus-... 

Adsorption of polymers onto colloidal particles is of great interest for the chemical industry [88] and physical chemistry of disperse systems in cormection with the fundamental problem of colloidal stability [89]. The structure of an adsorbed polymer layer can be probed by neutron [90] or X-ray [91] scattering, while the kinetics of adsorption can be followed by absorption spectroscopy [44]. 

Chemical bath deposition of CdS thin films was first reported by Mokrushin and Tkachev [34] and later by many other authors [35-41]. The basic mechanism of film formation was supposed to be either (i) an ion-by-ion condensation of Cd and S on the substrate from an aqueous basic medium, containing thiourea and cadmium ions in the form of a complex species, as indicated in Equation 5.11, or (ii) the result of the adsorption of colloidal particles of CdS onto the substrate surface. CdS film formation may be achieved using one of the following three complexing methods [42]. 

Buijs, J., Ramstrom, M., Danfelter, M., et al. (2003) Localized changes in the structural stability of myoglobin upon adsorption onto silica particles, as studied with hydrogen/deuterium exchange mass spectrometry. J Colloid Interface Sci, 263 (2), 441-448. 

Figure 44 Repeated adsorption of anionic and cationic polyelectrolyte polymers onto colloidal particle templates followed by excavation of the core domain gives micro-Znanocapsules. Reproduced with permission from Quinn, J. F. Johnston, A. P. R. Such, G. K. etal. Chem. Soc. Rev. 2007, 36, 707-718,and Wang, Y. Angelatos, A. S. Caruso, F. Chem. Mater. 2008,20,848-858. ...

LbL capsules are spherical compartments with walls formed by adsorption of alternating layers of positively and negatively charged polyelectrolytes [83]. Assembly of LbL capsules is achieved by consecutive deposition of complementary polymers onto colloidal particles (LbL deposition technique), followed by removal of the colloidal template by addition of acids [16,84-86]. CaC03 nanoparticles are commonly used as templates because they have low toxicity and are biodegradable. LbL capsules are an interesting platform for the design of nanoreactors because their permeability can be selectively modified... 

Jada, A., Hoffstetter, J., Siffert, B. and Dumas, Ph. (1999) MiceUization in water and adsorption onto solid particles ofblock copolymers. Colloid. Surface. A Physicochem. Eng., 149,315-322. 

At the certain concentration the ( -potential levels off and the polyelectrolyte is mostly adsorbed on the particles depleting the bulk from the majority of polyelectrolyte molecules. The further increasing of bulk polyelectrolyte concentration does not influence on i -potential and amount of polyelectrolyte on the particles. Thus, the layer-by-layer assembling of the polyelectrolytes onto colloidal particles can be performed in two different ways [28-30]. Either the concentration of polyelectrolyte added at each step is just sufficient to form a saturated layer or adsorption is curried on at excess of polyelectrolyte concentration. (Fig. 2.3). 

Docoslis, A., Wu, W., Giese, R. F., and van Oss, C. J. (2000b) Measurements of the kinetic constants of protein adsorption onto silica particles Colloids Surfaces B Biointerfaces, 13, 83-104. 

In addition to the preparation of Langmuir and Langmuir-Blodgett films, the use of self-assembly techniques also plays an important role in the formation of particle films. Both physisorption, as, for example, electrostatic adsorption of charged particles from colloidal solution, and chemisorption onto a substrate have been investigated. In Section V.A, electrostatic adsorption will be reviewed chemisorption is the subject of Section V.B. 

Honeyman and Santschi 1989). Therefore, flocculation of colloids to form settling particles in estuaries is an important mechanism for trace element removal (Sholkovitz 1977). This is particularly true of Fe, which is a ubiquitous colloidal species and is removed at low salinities. Additional removal may occur by adsorption onto floes, as demonstrated by mixing of organic-rich waters with seawater in the laboratory (Sholkovitz 1977). 

The link between colloids and surfaces follows naturally from the fact that particulate matter has a high surface area to mass ratio. The surface area of a 1cm diameter sphere (4jtr ) is 3.14 cm, whereas the surface area of the same amount of material but in the form of 0.1 pm diameter spheres (i.e. the size of the particles in latex paint) is 314 000 cm. The enormous difference in surface area is one of the reasons why the properties of the surface become very important for colloidal solutions. One everyday example is that organic dye molecules or pollutants can be effectively removed from water by adsorption onto particulate activated charcoal because of its high surface area. This process is widely used for water purification and in the oral treatment of poison victims. 

---