Colloidal Dispersion Lab Report

Module-5 Emulsions & Colloids

Objectives:

• To understand colloids & to know about colloidal dispersions.

• To understand the properties of colloidal system.

• To understand the difference between a colloidal dispersion, solution & suspension.

• To understand about the Sol- Gel transformation process.

• To know what is an Emulsion & learn the process of its formation.

• To learn about the various types of Emulsions & the factors affecting their stability.

Introduction: Food is a complex material containing a high percentage of water in which other materials are dispersed. Thomas Graham (1850) known as father of colloidal chemistry was the first to find out the existence of colloidal state. He classified the

However, when a sol assumes a rigid form, it is referred to as a gel. There is no distinct line of separation between a sol and gel. Infact some sols become gel by increasing the concentration of dispersed solids . A typical sol is a fluid, whereas, a typical gel has a certain amount of rigidity. The difference between a sol and a gel has been illustrated in Figure below:

During sol – gel transformation, a three- dimensional network is formed by the interlocking of dispersed particles. The liquid phase is entrapped in the interstitial areas of this structure. When this happens, the sol loses its fluidity and becomes a gel. The change from sol to gel may be brought about by a change in the concentration of dispersed phase or a change in temperature. Gelatin dispersed in hot water is a sol, but when cooled it becomes a rigid, transparent gel. Other example of sols that turn to gels are fruit jellies and custards.

Many gels lose liquid upon standing and the gel structure shrinks. This is called weeping of gel or syneresis. The liquid that collects around a glass of fruit jelly or a dish of custard is an example of

There are a number of factors that affect the strength, elasticity and brittleness of the gel such as concentration of the jelling agent (particulates), salt content, pH and temperature. Polysaccharides, proteins or colloidal complex particles, such as caseinate micelles form gels at levels of 10% or less. Gums, pectin and gelatin form gels at levels of 1% or less. Salt and pH influence gel formation adversely or favourably depending upon the concentration. By the reduction in the number of charged particles and adjustment of pH or addition of salt, a sol can be transformed into a gel. Addition of sugar which competes with water in the continuous phase helps gel formation when used in the proper portion. Change in temperature has an effect on gel formation – low temperatures reduce the mobility of the colloidal molecules in the sol and increase the viscosity. This condition facilitates gel formation