KEYTERMS CHAP 1&2

Adherend

A material substrate that is bonded to another material by means of an adhesive.

Adhesion

—A molecular or atomic attraction between two contacting surfaces promoted by the interfacial force of attraction between the molecules or atoms of two different species; adhesion may occur as chemical adhesion, mechanical adhesion (structural interlocking), or a combination of both.

Adhesive

Substance that promotes adhesion of one substance or material to another.

Adhesive bonding

Process of joining two materials by means of an adhesive agent that solidifies.

Cohesion

Force of molecular attraction between molecules or atoms of the same species

Contact angle

Angle of intersection between a liquid and a surface of a solid that is measured from the solid surface through the liquid to the liquid/vapor tangent line originating at the terminus of the liquid/solid interface; used as a measure of wettability, whereby no wetting occurs at a contact angle of 180° and complete wetting occurs at an angle of 0°

Diffusion coefficient

—Proportionality constant representing the rate at which a substance is transported through a unit area and a unit thickness under the influence of a unit concentration gradient at a given temperature.

Glass transition temperature (Tg)

—Temperature above which a sharp increase in the thermal expansion coefficient occurs, indicating increased molecular mobility

Heat of vaporization

Thermal energy required to convert a solid to a vapor

Latent heat of fusion

—Thermal energy required to convert a solid to a liquid.

Melting temperature (melting point)

—Equilibrium temperature at which heating of a pure metal, compound, or eutectic alloy produces a change from a solid to a liquid.

Metallic bond

Primary bond between metal atoms.

Micromechanical bonding

Mechanical adhesion associated with bonding of an adhesive to a roughened adherend surface.

Self-diffusion

Thermally driven transfer of an atom to an adjacent lattice site in a crystal composed of the same atomic species.

Stress concentration

—State of elevated stress in a solid caused by surface or internal defects or by marked changes in contour.

Supercooled liquid

A liquid that has been cooled at a sufficiently rapid rate to a point below the temperature at which an equilibrium phase change can occur.

Surface energy

Same as surface tension but expressed in mJ/m2 .

Surface tension

A measurement of the cohesive energy present at an interface; in the case of a liquid, it is the liquid/air interface. This energy is the result of molecules on the surface of a liquid experiencing an imbalance of attraction between molecules. It has units of mN/m.

Thermal expansion coefficient

—Relative linear change in length per unit of initial length during heating of a solid per K within a specified temperature range.

Wetting

The ability of a liquid to maintain contact with a solid surface; it reflects the intermolecular interactions when the two are brought in intimate contact.

Wetting agent

A surface-active substance that can be applied to a solid substrate to reduce the surface tension of the liquid to be placed on the solid; the purpose is to promote wetting or adhesion.

Vacancy

Unoccupied atom lattice site in a crystalline solid.

van der Waals forces

Short-range force of physical attraction that promotes adhesion between molecules of liquids or molecular crystals.