Freundlich a German chemist is known for his work in colloids, particularly sols and gels. He introduced the term thixotropy that describes a specific behaviour of gels. He proposed an equation regarding quantity of gas adsorbed by fixed weight of adsorbent, which was later recognised as Freundlich adsorption isotherm. Freundlich's research was mainly devoted to all aspects of colloid science. He investigated colloid optics, the scattering of light by dispersed particles of various shapes. He studied the electrical properties of colloids since electrostatic charges are largely responsible for holding colloidal dispersions in place. He investigated mechanical properties in place. He investigated mechanical properties such as viscosity and elasticity, and studied the behaviour of certain systems under types of mechanical force. One application of this work has been the development of nondrip paints