Proteins and gums also form lyophilic colloidal systems because of a similar affinity between the dispersed particles and the continuous phase. Many natural systems such as suspensions of microorganisms, blood and isolated cells in culture are also colloidal dispersions. The molecules in a drop of food coloring added to water will eventually disperse throughout the entire medium, where the effects of molecular diffusion are more evident.
The concentration of charged colloidal particles at one side and at the base of the membrane is termed electrodecantation. At equilibrium, the distribution of the diffusible ions is unequal, being greater on the side of the membrane containing the non-diffusible ions.
As a result of Brownian motion, colloidal particles spontaneously diffuse from a region of higher concentration to one of lower concentration.
The passage of ultrasonic waves through a dispersion medium produces alternating regions of cavitation and compression in the medium. D is the diffusion coefficient and has the dimensions of area per unit time. Purification of colloidal systems Dialysis Colloidal particles are not retained by conventional filter papers but are too large to diffuse through the pores of membranes such as those made from regenerated cellulose products, e.
Kinetic properties In this section several properties of colloidal systems, which relate to the motion of particles with respect to the dispersion medium, will be considered.
Instead, the Tyndall effect is used to distinguish solutions and colloids. The process of dialysis may be hastened by stirring so as to maintain a high concentration gradient of diffusible molecules across the membrane and by renewing the outer liquid from time to time.