Wall colloidal deposition

Fig. 13. The wall-jet apparatus for measuring the kinetics of colloidal deposition. The evanescent wave is scattered more strongly hy the deposited particles than those in the solution.

The foregoing results demonstrate that the thickness of the capsule wall can be controlled at the nanometer level by varying the number of deposition cycles, while the shell size and shape are predetermined by the dimensions of the templating colloid employed. This approach has recently been used to produce hollow iron oxide, magnetic, and heterocomposite capsules [108], The fabrication of these and related capsules is expected to open up new areas of applications, particularly since the technology of self-assembly and colloidal templating allows unprecedented control over the geometry, size, diameter, wall thickness, and composition of the hollow capsules. This provides a means to tailor then-properties to meet the criteria of certain applications. 

The catalyst bed was a coated wall reactor using commercial CuZnAl catalyst. An alumina sol was used to enhance the adhesion of the catalyst to the channel walls. After the shims were washed thoroughly, the alumina adhesion layer was deposited using an alumina sol (NYACOL AL20DW colloidal alumina, PQ Corporation) and then dried at 60 °C. To decrease the surface tension of the wash-coat solvent, small amounts of 2-propanol were added to a catalyst slurry of ICI Synetix 33—5 catalyst, with 20 wt % alumina sol and water. The catalyst was calcined at 350—400 °C for 2 h after air-drying. Before testing, the catalyst was reduced by flowing H2/N2 over it at 280 °C. 

FIG. 1.1 A schematic illustration of colloid-mediated transport in porous media. The sketch illustrates the transport of molecular solutes by colloidal particles. The extent of such transport and its importance are determined by a number of factors, such as the extent of adsorption of molecular solutes on the colloids and on the grains, the deposition and retention of colloids in the pores, the influence of charges on the colloids and on the pore walls, and so on. 

Colloids of semiconductors are also quite interesting for the transmembrane PET, as they possess both the properties of photosensitizers and electron conductors. Fendler and co-workers [246-250] have shown that it is possible to fix the cadmium sulfide colloid particles onto the membranes of surfactant vesicles and have investigated the photochemical and photocatalytic reactions of the fixed CdS in the presence of various electron donors and acceptors. Note, that there is no vectorial transmembrane PET in these systems. The vesicle serves only as the carrier of CdS particles which are selectively fixed either on the inner or on the outer vesicle surface and are partly embedded into the membrane. However, the size of the CdS particle is 20-50 A, i.e. this particle can perhaps span across the notable part of the membrane wall. Therefore it seems attractive to use the photoconductivity of CdS for the transmembrane PET. Recently Tricot and Manassen [86] have reported the observation of PET across CdS-containing membranes (see System 32 of Table 1), but the mechanism of this process has not been elucidated. Note, that metal sulfide semiconductor photosensitizers can be deposited also onto planar BLMs [251],... 

The solubility of a block copolymer in water decreases as the concentration of electrolyte increases. When the concentration of the polymer is larger than its solubility, the polymer molecules precipitate onto the surface or form aggregates that remain dispersed into the colloidal system or deposit on the wall of the vessel that contains the colloidal dispersion. Let us start from two parallel plates, and then calculate the stability ratio of the system for spheres using the Detjaguin approximation. 

Cellulose to form the cell-wall is probably deposited as a hydrated colloid formed indirectly from starch. At this... 

A somewhat similar theory10 postulates the formation of colloidal lead by the decomposition of lead tetraethyl, which deposits on sharp points, edges, and projections in the cylinder which would otherwise aid reaction to an extent that a detonation wave would result. The theory fails to explain the action of organic amines, of di- and tetravalent. selenium, of the colloidal metal sols, and fails to account for the immediate recurrence of knocking when the antiknock dope is discontinued in the gasoline feed. However, tubes coated with lead oxide have been found to reduce the oxidation of hexane more than lead tetraethyl vapors.1158 On the basis of this finding the hypothesis was advanced that oxidation occurs to some extent prior to compression and at the first contact of the gaseous mixture with the hot walls, aud that in the presence of the lead... 

Colloidal Alumina Alumina is available in a colloidal form which can be deposited on firebrick or glass beads, or on the wall of an open tubular column, to give a porous adsorptive layer which may be modified by addition of a liquid or other adsorbent such as colloidal silica. This way a wide variety of selective separating layers can be prepared. 

The adsorbers should be protected with dust filters to prevent them from becoming filled with particulate material which would add resistance and restrict the flow of air. It is also desirable to make provision for the continuous removal of aerosols because these are not appreciably adsorbed by carbon. Smoke (a typical aerosol) is a colloidal dispersion of tars in air and, unless it is removed as soon as formed, the colloidal tars will deposit on all surfaces—walls, floors, ceilings—from which they will slowly evaporate to cause a persistent odorous environment. A typical example is a smoke-filled room on the morning after. All such after-effects can be avoided by placing... 

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