diffusion (redirected from Diffusion in materials)

diffusion /dif·fu·sion/ (dĭ-fu´zhun)

1. the process of becoming diffused, or widely spread.

2. the spontaneous movement of molecules or other particles in solution, owing to their random thermal motion, to reach a uniform concentration throughout the solvent, a process requiring no addition of energy to the system.

3. in hemodialysis, the movement of solutes across semipermeable membranes down concentration gradients.

4. immunodiffusion.

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double diffusion  an immunodiffusion test in which both antigen and antibody diffuse into a common area so that, if the antigen and antibody are interacting, they combine to form bands of precipitate.

gel diffusion  a test in which antigen and antibody diffuse toward one another through a gel medium to form a precipitate.

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dif·fu·sion (d-fyzhn)

n.

1. The process of diffusing or the condition of being diffused.

2. The spontaneous intermingling of the particles of two or more substances as a result of random thermal motion.

3. See dialysis.

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diffusion

[difyo̅o̅′zhən]

Etymology: L, diffundere, to spread out

the process in which particles in a fluid move from an area of higher concentration to an area of lower concentration, resulting in an even distribution of the particles in the fluid. Little or no energy is required.

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diffusion (di·fyōōˑ·zhn),

n the tendency of molecules within a gas or liquid to move from an area of higher concentration to one with lower concentration. The rate of movement depends on the size and weight of the molecules involved.

Diffusion.

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diffusion (difū´zhn),

n a property of ions or molecules of a solute that permits them to pass through a membrane or to intermingle by rapid or gradual permeation with the molecules of a solvent.

diffusion barrier,

n a thin layer of material placed between two other materials to prevent one from corrupting the other.

diffusion, facilitated,

n an absorption process during which only certain recognized molecules are allowed to pass into the receiving area.

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diffusion

1. the state or process of being widely spread.

2. the spontaneous mixing of the molecules or ions of two or more substances resulting from random thermal motion; its rate is proportional to the concentrations of the substances and it increases with the temperature.

In the body fluids the molecules of water, gases, and the ions of substances in solution are in constant motion. As each molecule moves about, it bounces off other molecules and loses some of its energy to each molecule it hits, but at the same time it gains energy from the molecules that collide with it.

The rate of diffusion is influenced by the size of the molecules; larger molecules move less rapidly, because they require more energy to move about. Molecules of a solution of higher concentration move more rapidly toward those of a solution of lesser concentration; in other words, the rate of movement from higher to lower concentration is greater than the movement in the opposite direction.

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diffusion coefficient

the number of milliliters of a gas that will diffuse at a distance of 0.001 mm over a square centimeter surface per minute, at 1 atmosphere of pressure. The diffusion coefficient for any given gas is proportional to the solubility and molecular weight of the gas. The diffusion coefficient for oxygen is 1.0, for carbon dioxide it is 20.3, and for nitrogen it is 0.53. The diffusion capacity of a gas varies directly with the diffusion coefficient.

facilitated diffusion

mechanisms in intestinal absorption which assist the passage of those products of digestion, which cannot occur by simple diffusion, across the intestinal cell membranes. They include a carrier mechanism involving proteins, and active transport which provides energy from the breakdown of high-energy phosphate bonds.

Fick's first law of diffusion

see fick's first law of diffusion.

diffusion hypoxia

a transient hypoxic episode after the cessation of nitrous oxide anesthesia if air is inhaled instead of pure oxygen; caused by the rapid diffusion of nitrous oxide out into the alveoli diluting the oxygen that is there.

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diffusion

1. Scattering of light passing through a heterogeneous medium, or being reflected irregularly by a surface, such as a sandblasted opal glass surface. Diffusion by a perfectly diffusing surface occurs in accordance with Lambert's cosine law. In this case, the luminance will be the same, regardless of the viewing direction. 2. The passive movement of ions or molecules through a medium or across a semi-permeable membrane (e.g. the ciliary epithelium) in response to a concentration gradient until equilibrium is reached. It is one of the three mechanisms that create aqueous humour. See diffuse light; diffuse reflection; ultrafiltration.