Under spreading (engl. Spreading ) is the propagation and surface distribution of insoluble substances on surfaces.
It is a phenomenon that is observed and researched in the field of surface physics .
If a liquid is dripped onto a surface , a hemispherical structure is initially formed. This structure becomes flatter over time (the contact angle becomes smaller), the liquid covers an increasingly larger area.
The spreading can proceed so far that the liquid only exists as a layer in molecular expansion.
The spreading depends on
- the liquid or substance used
- the nature and material of the surface to which it is applied
- Temperature and time
Wherever statements about spreading are to be made, standard liquids of a defined amount are used on certain surfaces ( steel , glass , brass ) with a defined surface quality and the time is measured in which a certain surface is covered at a certain temperature. The data obtained are used as comparisons.
The spreading is of particular importance in the case of lubricating oils , as here it is often desired that the oil should remain at the lubrication point as far as possible and not be distributed over the entire device.
- G. Adam, P. Läuger, G. Stark: Physical chemistry and biophysics . 2nd edition, Springer, Berlin 1988.