Spreading drop method

For DOC, it can be seen that the results of Williams (1967), for example, show an extra 2.1 g m DOC in the microlayer. If the thickness of the water film obtained with the screen device is taken to be —200 pm, the surface excess of DOC can be calculated as 2.1 X 200 X 10 = 4.2 X 10" g m . A reasonable lower limit to take for the molecular weight of this extra organic material in the surface film is that of a relatively short-chain acid or alcohol with —14 carbon atoms, equivalent to —170 g mole carbon. Using this minimum value, the area per molecule in the ambient type of films sampled by Williams (1967) can be calculated as > — 170/4.2 X lO" X 6.02 X 10 3 = > 70 A. It can be seen from Fig. 1 that for all surface film types except gaseous films, such an area per molecule has no effect on the surface tension of seawater, as measured by the spreading drop method, or on the damping of capillary waves. Moreover, only relatively water-soluble surfactants remain in the gaseous state at film pressures of —10 N m" ... 

Pour plate Requires no pre-drying of the agar surface Will detect lower concentrations than surface spread/surface drop methods Very small colonies of strict aerobes at the base of the agar may be missed Colonies of different species within the agar appear similar —so it is difficult to detect contaminants... 

Surface spread and surface drop methods Surface spread often gives larger colonies than pour plates—thus they are easier to count Easier to identify contaminants by appearance of the colonies Agar surface requires pre- drying to absorb sample Possibility of confluent growth, particularly with moulds, masking individual colonies... 

Effect of surface finish on the biofouling rates of different materials was studied by standardized harmonic mean (SHM) of drop spread determination method. It was observed among different materials like titanium, stainless steel, admiralty brass etc., carbon steel was the most affected (highest value of SHM). Here the corrosion causing slime formers were gram-negative bacteria like Pseudomonas species. The influence of water quality parameters on... 

Hard particles, of a diameter of 1 fim or more, when spread into flat layers will form a surface that is too rough for accurate contact angle measurement by the sessile (advancing) drop method (Chaudhury, 1984). However, by using a packed column of such particles, capillary rise velocity measurements of a liquid in that column can also yield the contact angle of that liquid with respect to the particles surface. This wicking approach can also be used for contact angle measurement of porous bodies, strands of fibers, etc. In these cases one uses the Washburn equation (Ku et al., 1985 Adamson, 1990) ... 

Methods of Measurement Methods of characterizing the rate process of wetting include four approaches as illustrated in Table 20-37. The first considers the ability of a drop to spread across the powder. This approach involves the measurement of a contact angle of a drop on a powder compact. The contact angle is a measure of the affinity of the fluid for the solid as given by the Young-Dupre equation, or... 

An increasing number of membrane proteins, in a variety of different detergents, have been crystallized in microbatch under oil. Some of these had failed to crystallize by all methods other than microbatch. Dispensing is quick and simple, even when performed manually, and the drops in oil do not spread out as they do in vapour diffusion over the siliconized coverslips (Chayen, 2006). Using robots thousands of microbatch trials can be dispensed in high-throughput mode in nanolitre volumes. 

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