Colloidal disks

Thin colloidal disks provide another example of an anisometrie eoUoidal particle as an efficient depletion agent. This problem was first eonsidered by Pieeh and Walz [61]. At the end of this seetion, where we compare spheres, rods and disks as depletion agents, we will see that the disk is intermediate in effieieney to induce depletion attraction between spheres and rods. Here we consider disks of diameter D and thickness L, see Rg. 2.30. Notiee that for the simplest ease, i.e., infinitely thin hard disks, the exeluded volume of the disks with respect to each other is nonzero and only in limit of the concentration going to zero will the disks behave thermodynamically ideal. We restrict ourselves to this limiting case. 

Depletion Interaction Due to Thin Colloidal Disks Table 2.1 Characteristic parameters for C, i and/ in (2.120)... 

A number of refinements and applications are in the literature. Corrections may be made for discreteness of charge [36] or the excluded volume of the hydrated ions [19, 37]. The effects of surface roughness on the electrical double layer have been treated by several groups [38-41] by means of perturbative expansions and numerical analysis. Several geometries have been treated, including two eccentric spheres such as found in encapsulated proteins or drugs [42], and biconcave disks with elastic membranes to model red blood cells [43]. The double-layer repulsion between two spheres has been a topic of much attention due to its importance in colloidal stability. A new numeri-... 

Colloid mills which are employed for dispersion or for emulsification fall into four main groups the hammer or turbine, the smooth-surface disk, the rough-surface type, and valve or orifice devices. 

Lei, H. and Luo, J. B., "CMP of Hard Disk Substrate Using a Colloidal Si02 Slurry Preliminary Experimental Investiga-... 

The microheterogenous and nanoheterogenous (mesoscopic) liquid-liquid systems may be concisely called the small systems. They comprise the micro- and nanodomains, described in colloidal chemistry as a variety of structures, e.g., micelles, rods, disks, vesicles, microemulsions, monolayers, and Langmuir Blodgett layers [6,17 19,70]. 

Drums and disks are not suitable for the agglomeration of sticky and highly plastic materials, for example, clays or solids containing colloids and very fine components. 

In both experimental and theoretical investigations on particle deposition steady-state conditions were assumed. The solution of the non-stationary transport equation is of more recent vintage [102, 103], The calculations of the transient deposition of particles onto a rotating disk under the perfect sink boundary conditions revealed that the relaxation time was of the order of seconds for colloidal sized particles. However, the transition time becomes large (102 104 s) when an energy barrier is present and an external force acts towards the collector. 

Schmidt, T.J. et al., Electrocatalytic activity of PtRu alloy colloids for CO and CO/H2 electrooxidation stripping voltammetry and rotating disk measurements, Langmuir, 13, 2591, 1997. 

Lyophilized copolymer was ground down to colloidal dimensions (<1 iJim) using a laboratory planetary mill (Pulverisette, Fritsch GmbH). A 110-mg sample of copolymer powder, 20 mg of bovine insulin, and 20 mg of GOD were mixed, and the mixture was compressed into a disk-shaped matrix of 5-mm thickness and 15-mm diameter. 

The electrostatic forces also play an important role in the conformation and structure of macromolecules such as polymers, polyelectrolytes, and proteins. The self-assembly of proteins from disks to virus is triggered by electrostatic interactions between neighboring subunits. In the case of polyelectrolytes (polymer molecules with charges) and charged colloids, transport behavior such as rheology is also affected significantly by charge effects, as we have already seen in Chapter 4. 

I Suspend the pigments and talc in the well stirred water and homogenize in a disk mill or in a colloid mill. 

In industrial and laboratory settings the subdivision process more commonly involves the comminution of large particles or aggregates into smaller sizes, either dry with subsequent dispersion (size reduction to the order of a few pm) or directly in a slurry (size reduction to as small as a few tenths of pm). Examples of comminution machines include agitator ball mills, colloid mills, cutting mills, disk mills, homogenizers, jet mills, mechanical impact mills, ring-roller mills, and roll crushers. 

The high precision of the disk centrifuge allowed the comparison of sedimentation velocities of colloidal particles with and without an adsorbed polymer layer, from which the hydrodynamic thickness of the adsorbed layer could be calculated (4). Here the disk centrifuge, giving complete size distributions, made the use of monodisperse samples unnecessary. 

---