Homodispersity

Penners, N.H.G. Koopal, L.K. (1986) Preparation and optical properties of homodisperse hematite hydrosols. Colloids Surfaces 19 337-349... 

Penners, N.H.G. (1985) The preparation and stability of homodisperse colloidal hematite (a-Pe203). Ph.D. Thesis Wageningen, The Netherlands, 97 p. 

Weers JG, Tarara TE, Gill H, English BS, Dellamary LA. Homodispersion technology for HFA suspensions particle engineering to reduce dosing variance. Paper presented at RDD VII, 2000. 

Effect of ion doping. Since (photo)-electronic processes are involved at the surface of titania, this oxide was modified by ion doping, both of p- and n-type, by dissolving either tri-(Ga3+, 3+) or pentavalent (Sb5+, V +) heterocations during the preparation by the flame reactor method (ref. 16), which produced homodispersed and homogeneously doped non-... 

As depicted in Fig. 5a, the diblock copolymer polystyrene-bfock-poly (2-vinylpyridine) (PS- -P2VP), consisting of a hydrophobic apolar PS block attached to a hydrophilic polar P2VP domain, is widely used to prepare ordered monolayers of inorganic nano-objects. The solubilisation of PS- -P2VP in toluene leads to the formation of homodisperse reverse micelles made of a hydrophilic P2VP core and a hydrophobic PS outer shell interacting with the solvent molecules. 

A simple example of using preadsorbed hydrogen as reductant was the preparation of a homodispersed Pt/ AI2O3 catalyst with increasing particle sizes prepared by platinum returning to the parent Pt/Al203 catalyst saturated with irreversibly chemisorbed hydrogen [20]. 

Although In the literature a large number of isotherms for non-ionics can be found, systematic data for homodisperse samples are not abundant. In particular. Isotherms over long concentration ranges (to verily the occurrence of different adsorption regimes. If any) on surfaces of different hydrophoblclty are required, preferably In conjunction with auxiliary measurements (calorlmetiy, spectroscopy, etc.). 

Figure 2.30. Adsorption of homodisperse CjjEg on silica from aqueous solution. Temperature 25 C. (Redrawn from A. Gellan and C.H. Rochester, J. Chem. Soc., Faraday Trar s. 181 (1985) 2235.)...

Surfaces are homogeneous and smooth when particles are considered, these are spherical and homodisperse. 

CVP and ESA are techniques that appear to remain essentially valid for concentrated systems, with obvious advantages for applications. However, many systems are neither homodisperse nor do they contain spherical particles. Then, the computed -potentials are rather semlquantltatlve (but useful) electrokinetic characteristics. Loewenberg and O Brien have extended the theory to non-spherlcal particles ). 

So far, only a limited number of full dielectric relaxation spectra for well defined systems are available. Apart from the technical problems involved in the measurements (sec. 4.5e) there is the colloidal problem of synthesizing sufficiently concentrated sols with homodisperse spherical particles, preferably having different radii but fixed surface properties. Latices are popular objects because the particles are easily made homodisperse and spherical. Nevertheless they are somewhat suspect because there may be hairs on the surface, drastically affecting lateral hydrodynamic motion close to the surface. Moreover, changing the radius requires new syntheses and it is difficult to guarantee exact reproducibility of the surface structure. Inorganic particles do not have these drawbacks but it is not so ea to synthesize these as perfect spheres. 

Figure 4.39 gives another example, taken from Nature. The Corynebacterium considered here has more or less spherical, homodisperse cells, with diameters of 1.1 and 0.8 pm for the longer and shorter axis. Such cells are fascinating model colloids. The relaxation frequency, Ae and AK behave as expected for colloidal particles with a finite conduction behind the shear plane, which, in this case, is caused by the ions in the cell wall. As in the previous example, the data were analyzed with (4.8.30 and 31(, using (4.6.56] for Du. The three curves, drawn through the measuring points, refer to this interpretation with the values of indicated. The conductivity of the cell wall exceeds that of the bulk... 

When all chains of a polymer or polyelectrolyte are equally long, the macromolecules are called homodisperse or monodisperse. If this condition Is not met the system is heterodisperse or polydisperse. Synthetic polymers and polyelectro-l)Ttes usually have a certain molar mass distribution and. hence, are to some extent polydisperse. This polydlsperslty has Important implications for the adsorption behaviour because fractionation will occur upon adsorption. 

The simplest example is a mixture of two homodisperse polymer samples differing only in molecular weight. The adsorption of such a mixture is conveniently discussed In terms of the total poljmer mass (free and adsorbed) per unit area in the system (T ), which is subdivided into the amount adsorbed on the surface (f) and the free molecules in the bulk solution (T ). The parameter r is either r or r in dilute solutions, to which we shall restrict ourselves, there is no difference between r, r and r , as discussed in sec. 5.3b. The quantity may be defined as c t, where Cp is the pol rmer concentration and t the thickness of the solution layer available to the adsorbent surface. The latter parameter may also be taken as the ratio between the total solution volume and the total surface area in the system. The quantities F, F and r are expressed in the same units, e.g., mg/m. ... 

Volume fraction profiles. We start with theoretical volume fraction profiles for the adsorption of long homodisperse polymer chains and the contribution of trains (tr), loops (Ip), and tails (tl) to these profiles. Figure 5.19 gives, for N 5000 and = 10. the dependence of [Pg.679]

In most situations the experimental system is more complicated than one (homodisperse) polymer adsorbing from a single solvent. In multicomponent systems preferential adsorption always plays a role. A common example is the adsorption of a polydisperse polymer, where usually long chains adsorb preferentially over short ones, even if the adsorption energy per segment is the same. 

As shown in Figure 13.31, the curves describing the variation in the viscosity of polymers filled with homodisperse noninteractive spheres are reminiscent of those of the unfilled polymers, at least up to a solid fraction close to maximum packing (56). The data fit to the Carreau equation (47)... 

A wide variety of surfactants exist. Fundamental studies can best be done with those that are well-defined and have a relatively simple structure, i.e. consisting of one unbranched aliphatic chain as the hydrophobic tail and one head group. Moreover, all molecules in the sample should be identical. This conditions Implies homodispersity (or monodispersily), meaning that all molecules have the same tall... 

From Table I, it can be seen that for a constant metal loading (5%), the sensitivity to SMSI of the present samples varies as Ni Pt>Rh, This classification is purely qualitative and not indicative of the proper influence of the nature the metal since several parameters such as texture and dispersion can influence the extent of SMSI, For Instance, nickel is under the shape of far larger particles than Pt or Rh ones with 2 to 3 times more atoms. On the contrary, in the case of Pt catalysts, the comparison between catalysts is more meaningful since the metal crystallite size is homodispersed... 

Burchard, W. Statistics of star-shaped molecules. II. Stars with homodisperse side chains. Macromolecules 1974, 7 (6), 841-846. 

Figure 3 Radiation-induced metal clusters, (a) Silver nanoclusters stabilized by PVA (10 nm). (b) STM imaging ofa single duster of the blue sol of silver oligomers Agd formed by y irradiation (n = 4). (c) Clusters ofAg, partially reduced by irradiation and then chemically developed by EDTA. (100 nm large and 15 nm thick), (d) TEM bright-held Image ofNi , PVA clusters (5 nm). (e) Two-dimensional self-assembled array of gold dusters (PVA) on mica with remarkable homodisperse size (5 nm). (f) Monocrystalline Pt nanotubes with CPCI (10 nm diameter and a few 100 nm long), (g) Pt nanorods with CTAB (3-4 nm thick and 20-40 nm long).

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