Capillary

Capillary (pronounced kap-uh-ler-ee)

(1) Pertaining to or occurring in or as if in a tube of fine bore.

(2) Resembling a strand of hair; hair-like; slender.

(3) In physics, pertaining to capillarity; of or relating to the apparent attraction or repulsion between a liquid and a solid, observed in capillarity.

(4) In anatomy, pertaining to a capillary or capillaries; one of the minute blood vessels between the terminations of the arteries and the beginnings of the veins.  Capillaries form a network throughout the body for the exchange of oxygen, metabolic waste products, and carbon dioxide between blood and tissue cells.

(5) As capillary tube, any small-bore tube.

(6) A fine hole or narrow passage in any substance (technical use only).

1570–1580: From the Middle English, from the Latin capillāris (of or pertaining to hair), the construct being capill(us) (hair) + -ary.  The suffix –ary (of or pertaining to) was a back-formation from unary and similar, from the Latin adjectival suffixes -aris and -arius; appended to many words, often nouns, to make an adjective form.   Use was not restricted to words of Latin origin.  The etymology of the Latin capillus (hair (of the head)) is contested.  Although a relationship to caput (head) seems obvious, some doubt the connection "for formal reasons”, essentially because capillus is a diminutive, and would translate as “little head”, a perhaps tenuous relationship with “hair” but certainly not impossible and the dispute continues.  The Latin word was borrowed by early fourteenth century English as capillar (hair-like) to describe veins.

In the modern science of anatomy, used to describe “tube-like structures having so small a bore that water will not run through them”, use dates from 1742, an extension of the noun use from 1606 used to describe a “minute blood vessel”.  From 1806, experientialists used the word to describe the phenomena of the rise of liquids in tubes etc by the processes of surface tension; because the observational studies were conducted in capillary vessels, this came first to be called capillary attraction (1813).  Capillary as the "state or condition of being capillary" was first documented in 1806, from the French capillarité, from Latin capillāris.  In science, the derived terms include magnetocapillary, optocapillary & polycapillary.  The noun plural is capillaries and intercapillary is the adjective

The smaller, the bore of the tube, the greater the effect of the interaction of forces.

The process behind the counter-intuitive idea of water flowing uphill, even vertically, is called capillary action (and also capillary motion, capillarity, capillary effect, wicking or capillary attraction).  It describes the process by which liquids contained in narrow spaces are able, without the assistance of, or even in opposition to external forces such as pressure or gravity are able to move upwards.  It occurs because of the reaction of intermolecular forces between the liquid and surrounding solid surfaces; if the internal diameter of the tube is sufficiently small, then a combination of surface tension (caused by cohesion within the liquid) and adhesive forces between the liquid and wall will propel the liquid.  When the intermolecular attractive forces between the liquid and the solid surrounding surfaces (adhesive forces) are stronger than the cohesive forces within the liquid, the fluid will be pulled up the liquid column up until there is a sufficient mass of liquid for gravitational forces to counteract these forces.

The circular economy of botanical water management.

Plants use capillary action to draw water from roots and stems upwards to the trunk.  The molecules of the water are attracted to the molecules already  inside of the nominally solid stem from where they are dispersed throughout the plant.  Again, it’s the product of the relationship between adhesion and cohesion, and for plants, adhesion allows for the water to stick to their organic tissues while cohesion keeps the water molecules together.  Surface tension is the effect of intermolecular attraction that causes liquids to form a top or outer layer that behaves like a thin film of sorts.  Surface tension is responsible for the shape of water drops and for holding the structures together as plants soak up the water.  This is the circular economy of plants.

Capillary attraction and the Thorny Devil (from a BBC documentary).

Dwelling uniquely in central & western Australia, the thorny devil (Moloch horridus) is a lizard which is often seen when around 50-75 mm (2-3 inches) in length but can grow as large as 200 mm (8 inches).  Long-lived (up to 20 years), although fearsome in appearance, they are placid creatures with few apparent interests other than finding the ants and so voracious is their appetite that thousands can be consumed in a single meal.  The presence of people seems little to disturb them and thorny devils will sit on someone's shoulder for some time, apparently content and without any sign of distress.  Other than ants, their main need is for fresh water which is harvested through the channels formed in its skin between the spines.  It can collect moisture either from allowing dew to settle or by finding a water source and standing still, allowing gravity and capillary action to operate to let the fluid reach the mouth.  During rainfall events (which do happen in the Australian deserts), the process is rapid but in dry periods capillary action permits water to be taken up from damp sand and this can for months at a time be the creature’s primary method of intake.