Gel

An upturned vial of hair gel
Silica gel

A gel is a semi-solid that can have properties ranging from soft and weak to hard and tough.[1][2] Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady state, although the liquid phase may still diffuse through this system.[3]

IUPAC definition for a gel

Gels are mostly liquid by mass, yet they behave like solids because of a three-dimensional cross-linked network within the liquid. It is the cross-linking within the fluid that gives a gel its structure (hardness) and contributes to the adhesive stick (tack). In this way, gels are a dispersion of molecules of a liquid within a solid medium. The word gel was coined by 19th-century Scottish chemist Thomas Graham by clipping from gelatine.[4]

The process of forming a gel is called gelation.


  1. ^ Khademhosseini A.; Demirci U. (2016). Gels Handbook: Fundamentals, Properties and Applications. World Scientific Pub Co Inc. ISBN 9789814656108.
  2. ^ Seiffert S., ed. (2015). Supramolecular Polymer Networks and Gels. Springer. ASIN B00VR5CMW6.
  3. ^ Ferry, John D. (1980). Viscoelastic Properties of Polymers. New York: Wiley. ISBN 0471048941.
  4. ^ Harper D. "Online Etymology Dictionary: gel". Online Etymology Dictionary. Retrieved 2013-12-09.