Glossary - C

capillary action

Assuming the radius of a capillary is small and the fluid inside forms a hemispherical meniscus at the surface - further motion through the capillary is resisted because of a pressure gradient across the interface. Difference in P is ~ Y/R :(Laplace's Formula)- smaller the radius of the pore (capillary) greater the resisting pressure .

Thus the force (= pressure gradient) preventing further motion of the drop can be decreased by

• decreasing the interfacial tension ( Y )
• increasing the radius of the capillary pore (R).

carbohydrates

A group of compounds that includes simple sugars and all larger molecules constucted of sugar molecules. One of the six classes of nutrients. One gram of carbohydrate provides 4 calories of energy on oxidation.

cell membrane

A term often used to refer to the outer, plasma membrane, of a cell. However, most cells contain a great many membranes in addition to the plasma membrane.

colloidal suspension

A system consisting of small particles kept dispersed (i.e. prevented from clustering together) by molecular motion in the surrounding medium, the solvent.

concave

Curving inwards: like the inside of a small cup.

contact angle

• contact angle = zero for full wetting
• contact angle = 180 degrees for immiscible liquids
• contact angle = 90 degrees for meniscus maintaining fluids.

On adding surfactant to the oil-water interface the contact angle decreases.
This can be understood as: surfactants reduce (interfacial tension): Cosine(contact angle) ~1/(interfacial tension), therefore as Cosine(contact angle) increases the contact angle decreases.

convex

Curving outwards: like the exterior surface of a baseball.

covalent

covalent bonding

The principal method of bonding between atoms in molecules which involves `sharing' electrons from each atom.

crinkled

In normal English crinkled simply means something that is twisted or crumpled. However, physicists who study the properties of membranes sometimes use crinkled to refer to a particular phase that is not flat yet not crumpled (this use is rather technical).

critical micelle concentration

Depending upon the relative strengths of the hydrophilic repulsion and the hydrophobic attraction and the temperature ,this is the minimum concentration(number of molecules per unit volume) needed for the resultant micelle to be stable.

crumple

crumpled

Just as in plain English, physicists use crumpled to mean something that has irregular wrinkles, is collapsed or crushed. A simple example would be to crumple a piece of paper by crushing it in your hands. See also crumpling transition.

crumpled phase

crumpling transition

Some physical systems such as membranes will be crumpled under certain conditions and are said to exhibit a crumpled phase . The conditions that make the system become crumpled are said to cause the crumpling transition. The crumpling transition is just the transition from one phase, a flat phase for example, to a crumpled phase.

cytoskeleton

(cyto = cell)

The cytoskeleton is a network of protein filaments and microtubules in the cytoplasm, just inside the cell membrane. It provides the internal framework that supports the shape of the cell, helps organize the contents and provides the machinery required to move the cell and its constitiuents.