Wettability of powders

Tabb 1.10 Contact angles of some pharmaceutical powders  

Material Contact angle Material Contact angle 

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Enhances wettability of powders Overall more costly than direct... 

The N/C ratio and the wettability of powders both increase with ran duration and fluidization ratio till reaching a plateau after 3 h. Studies are now in progress to deposit continuous thin layer of Si02 on the powders surface at low temperature. 

Lithium fluoride is an essential component of the fluorine cell electrolyte 1% LiF in the KF 2HF electrolyte improves the wettability of the carbon anodes and lowers the tendency of the cells to depolarize (18). Thermoluminescent radiation dosimeters used in personnel and environmental monitoring and in radiation therapy contain lithium fluoride powder, extmded ribbons, or rods (19). 

Spray programs of 1 and 4 pounds of 25% wettable parathion powder per 100 gallons of water were applied to Delicious apples on July 2 (plots 1 and 2). Samples were taken as soon as the fruit became dry and at 10- to 13-day intervals for a period of 32 days. These plots were sprayed again on August 3 with the same mixtures and resampled over a 30-day period (plots 3 and 4). The results and the percentage of loss of parathion are shown in Table III and Figure 1. 

Pounds of 25% wettable parathion powder per 100 gallons of water. 6 Four cover sprays applied June 7 and 23, July 2, and August 3. 

Another approach to improving the wettability of poorly soluble drugs is to treat the drug with a solution of a hydrophilic polymer. Lerk et al. [137] reported that both wettability of the powder and the rate of dissolution of hexobarbital from hard gelatin capsules could be greatly enhanced if the drug were treated with methylcellulose or hydroxyethylcellulose. In this process, called hydrophilization, a solution of the... 

Gluba, T., Heim, A., and Kochanski, B., Application of the Theory of Moments in the Estimation of Powder Granulation of Different Wettabilities, ... 

In the process of plasma polymerization, a highly crosslinked polymer is deposited on the surface The deposited plasma polymer changes the surface properties of the substrate dramatically. It modifies the surface of powders in terms of surface energy, functional groups, wettability, interaction with polymers, and dispersion... 

These systems are commonly used in the agglomeration of powdered food products. Fine particles are contacted, after their surfaces are made sticky in a controlled manner, to form clusters. After drying and cooling, the clusters have a coarse, porous structure which improves the wettability, dispersibility... 

Milk powder particles <100 pm in size are often difficult to wet and tend to become lumpy when dispersed in water (Schubert, 1987). Hence, milk powder is agglomerated during manufacture to make the powder instantly wettable in warm (>45°C) water. Agglomeration is the process of forming porous clusters of powder particles to increase the volume of occluded air, thereby increasing its dispersibility and making the powder... 

Powder characteristics of a physico-chemical nature, such as solubility, wettability, dispersability, and measures of the instant properties of powders (sludge, slowly dispersible particles, hot water sediment and coffee test), are determined by a variety of empirical physical tests, some of which incorporate subjective elements. These and the other tests for whole milk powders identified above are described in detail by Westergaard (1994) and Pisecky (1997). 

The relative wettabilities of hydrophobic pharmaceutical powders have been determined using a vacuum balance technique to measure the rates of w ater vapor uptake and the equilibrium moisture levels of the powder samples (1()5. ... 

The properties of a powder can be subdivided into those related to the particle itself and those of the ensemble of particles (bulk properties). The major particle properties include particle size and size distribution, shape, density and porosity, surface properties (van der Waals attractions, electrostatic charge), moisture content and composition. Particle properties influence the bulk properties of powders/particulates. There are a vast number of bulk properties including moisture content, bulk density, bed porosity, compressibility, flowability, permeability, sinkability, wettability and dispersibility, among others. 

The shape of particles is normally that of more or less regular spheres, dense or hollow, with smooth surfaces and sometimes cracks. This is related to the composition and the rate of solvent evaporation, with possible existence of internal pressure inside the drops when a rigid surface layer is being formed (Walton and Mumford 1999). All these characteristics will have some effect on handling properties of powders such as bulk and tapped densities, particle density, (mixing with other powders, storage) wettability and solubility, porosity, specific area (rehydration, instantisation) flowability (size, surface asperities), friability and creation/existence of dust, stability in specific atmosphere and medium (oxidation, humidification, active component release) (Huntington 2004). 

One apparently beneficial interaction was described by Braithwaite and Greene . They found that the wettability of steel and cast iron surfaces to a lubricating oil was markedly increased by the presence of a burnished molybdenum disulphide film, in terms of both rate of spread of oil droplets and the area wetted. Both effects are illustrated in Figure 13.1. The improvement in wettability was influenced by the extent of oxidation of the powder used to produce the burnished film. The least oxidised powder was the most effective, but even the most highly oxidised powders had some beneficial effect. 

Malamataris, S. Kiortsis, S. Wettability parameters and deformational behaviour of powder-liquid mixes in the funicular agglomeration phase. Int. J. Pharm. 1997, 154, 9-17. 

M. Fuji, T. Takei, T. Watanabe, and M. Chikazawa, Wettability of fine sihca powder surfaces modified with several normal alcohols. Colloids Surf. A154, 13, 1999. 

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