Capillary attraction

Kapiilar-analyse, /. capillary analysis, -an-ziehung, /. capillary attraction, -chemie, /. capillary chemistry, -druck, m. capillary pressure. 

KapiUarititt, /. capillarity. Kapillaritittsanziehung./. capillary attraction. Kapillar-kraft,/, capillary force, -kreislauf, n. capillary circulation, -rohr, -rohrchen, n, -rohre, /. capillary tube, -spaonung, /. capillary tension, -stromung, /. capillary flow, -versuch, m. capillary test or experiment. -wirkung./. capillary action. 

The highest mechanical strengths are usually obtained when the fibre is used in fine fabric form but for many purposes the fibres may be used in mat form, particularly glass fibre. The chemical properties of the laminates are largely determined by the nature of the polymer but capillary attraction along the fibre-resin interface can occur when some of these interfaces are exposed at a laminate surface. In such circumstances the resistance of both reinforcement and matrix must be considered when assessing the suitability of a laminate for use in chemical plant. Glass fibres are most commonly used for chemical plant, in conjunction with phenolic resins, and the latter with furane, epoxide and, sometimes, polyester resins. 

In the lower region of the unsaturated zone, immediately above the water table, is the capillary fringe, where water is drawn upward by capillary attraction. Above the capillary fringe, moisture coats the solid surfaces of the soil or rock particles. If the liquid coating becomes too thick to be held by surface tension, a droplet will pull away and be drawn downward by gravity. The fluid can also evaporate and move through the air space in the pores as water vapor. 

Surface area and moisture uptake have been related to the disintegration properties of excipients such as crosspovidone, starch, and alginic acid [17]. The surface areas of the three materials were measured, and a linear correlation was found between the maximum moisture sorption and specific surface area for the three disintegrants. The greater the surface area of the material, the more numerous were the sites for capillary attraction of water to its surface. It was postulated that the capillary action appears to be responsible for the disintegration properties of the materials. 

Coagulation, the result of approach, contact and coalescence of the particles of the suspensoid, is evidently hindered by any factor which may retard one of these three actions. The approach of one particle to another is brought about by the thermal or Brownian movement of the particles within the medium and factors such as low temperature, high viscosity of the medium or large particle size will evidently diminish the rate of approach. When the particles are in close proximity to one another, actual contact will be prevented if the particles possess electric charges similar in sign, due to the action of electrostatic repulsion. The particles will possess no net charge, i.e. their surface will be covered with the same number of cations and anions and will not repel one another at the isoelectric point when the capillary attraction can operate effectively (Hardy, Proc. Roy. Soo. LXVI. 110,1900). 

The rate Oi diffusion.—In order to find if the components of a double salt are dissociated in soln.—say, alum K SO. A SO saq.v K SOa+A SO g+Aq.— T. Graham 3 assumed that the dissociated parts would diffuse with different velocities, and he found that potassium and aluminium sulphates diffused at different rates from an aq. soln. of potash alum into the pure solvent. Hence, he assumed that alum is partially dissociated into its constituents when in aq. soln. He likewise inferred that the components of the double sulphates of potassium and copper, and of potassium and magnesium, are not dissociated in aq. soln. since under the same conditions there is no sign of any difference in the rates of diffusion of the components. E. Fischer and E. Schmidmer 4 determined the relative quantities of the components of double salts which were drawn up by capillary attraction into rolls of filter paper. If a double salt is dissociated a larger proportion of the more diffusible component ascends the paper. Dissociation is far more pronounced in aq. than in alcoholic soln. 

Like ferric nitrate, antimony sulfate is decomposed by water, various basic salts being formed, the simplest of which has the formula (SbOLSCL. The normal salt is stable only in rather concentrated sulfuric acid. Since this latter solvent has almost no vapor pressure at ordinary temperatures, the moist salt cannot be dried by evaporation of the solvent. It cannot be dried on absorbent paper, since the oily liquid rapidly carbonizes it. In such a case, it is best to take advantage of the drying qualities of unglazed earthenware (porous plate), such as the biscuit which forms the body of dishes. Owing to the fine pores which this material contains, liquids are sucked up by it by capillary attraction, and it is not acted upon by most reagents. 

The saltpetre of commerce is derived principally from the East Indies, where, as also in Persia, Egypt, and Spain, it appears as an efflorescence on the surface of the soil. In some other countries, as the coast of the Adriatic, in Ceylon, North America, Africa, and Tene-riffe, it is found on the walls of natural caverns formed in limestone rocks, and which contain also felspar and magnesia. It is also found widely distributed in some parts of Hungary, but in no case extending to any great depth below the surface of the ground, nor even to such a depth as the air cannot penetrate. Its appearance on the surface of the ground is explained by its ready solubility in water, as when ite solution, in obedience to the law of capillary attraction, rises to the surface, the liquid is vaporized by the action of sun and air, and its place is immediately occupied by a fresh portion from below, which disappears in the same manner, until at last an incrustation of the salt is formed of considerable thickness, either in solid crystals, or as an effloresced mass. 

Newton adduces many different chemical reactions to illustrate his point of view and mentions other attractions, such as cohesion and capillary attraction, advancing numerous hypotheses, not all of which are at present justified. With respect to chemical attraction, however, he recognizes the varying degrees of attraction among similar actions, as when—... 

The thermometer is first dipped in the sulphuric acid, and then the drop of acid which clings to the bulb is smeared on the side of the capillary tube containing the substance. The capillary tube is then made to adhere to the thermometer (Fig. 6) by capillary attraction, so that the substance in the tube is just opposite the bulb of the thermometer. This method is much better than using a rubber band, which is apt to perish in the sulphuric acid fumes, and gives rise generally to a speedy discoloration of the acid. 

Page 27. Capillary attraction or repulsion is the cause which determines the ascent or descent of a fluid in a capillary tube. If a piece of thermometer tubing, open at each end, be plunged into water, the latter will instantly rise in the tube considerably above its external level. If, on the other hand, the tube be plunged into mercury, a repulsion instead of attraction will be exhibited, and the level of the mercury will be lower in the tube than it is outside. 

Page 29. The late Duke of Sussex was, we believe, the first to shew that a prawn might be washed upon this principle. If the tail, after pulling off the fan part, be placed in a tumbler of water, and the head be allowed to hang over the outside, the water will be sucked up the tail by capillary attraction, and will continue to run out through the head until the water in the glass has sunk so low that the tail ceases to dip into it... 

Note, that the surface and deformation forces are of the same order of magnitude. Therefore, surface forces should be as small as possible to minimise damaging and indentation of soft polymer samples. For example, sharp probes have a lower capillary attraction and adhesion forces, and therefore enable more gentle probing of a soft polymer than a blunt tip. A sharp tip can also be moved in and out of the contamination layer more readily than a blunt tip. This is particularly important for non-contact intermittent contact imaging described in Sect. 2.2.1. 

Take up some trypan blue cell suspension in a Pasteur pipette and fill a haemocytometer counting chamber by capillary attraction ( 7.2.1). Take care not to flood the channels of the chamber. Count the cells under X10 objective. 

Workers concerned with liquid/solid systems with exceptionally good wettability, such as some braze/metal workpiece systems, find that the drops do not preserve a perfectly circular area of contact because of the sensitivity of the liquid to changes in capillary attraction caused by minor variations in the surface texture of the workpiece. Because of such irregularity, some workers have used the contact area of a small volume of braze as a measure of wettability. Thus Feduska used area measurements to differentiate between the wetting of different stainless steels by a wide range of metals and alloys (Feduska 1959). 

The process depends on a liquid metal flowing over surfaces to form a fillet between components and into the gap between the components, and then solidifying to form a permanent bond. Thus it is essential that the braze experiences high temperature capillary attraction. Without such attraction, solid braze material placed between components will flow out of the gap, sweat , when it melts. Any residue of non-wetting liquid that remains within the gap will not conform to the microscopic features of the component surfaces but form an array of voids, as illustrated schematically in Figure 10.1, that is mechanically deleterious and should be avoided if at all possible. The size of such voids can be decreased if an external pressure is used to confine a non-wetting liquid braze into a gap but cannot eliminate them because the pressure needed to shrink voids increases as they become smaller. 

---