Colloid chemistry chapter 1

Colloidal state: the state which consists of particles of the size 1 nanometer to 1 micrometer.. Lyophilic Colloids solvent-loving colloid:The classical use of the term lyophilic colloid

Dr Ngo Thanh An

COLLOID CHEMISTRY

Chapter 1 - Introduction

The term colloid was developed by Graham in 1861, from the Greek meaning glue-like Graham defined a colloid in terms

of its inability to pass through a fine membrane

Traditionally, the colloidal domain is defined as extending over a range of dimensions from a few nanometers to a few tens of micrometres.

1 Concepts

Colloidal state: the state which consists of

particles of the size 1 nanometer to 1

micrometer These "colloidal particles" are

dispersed in a continuous medium

Colloidal solution: intermediate of 'true

solutions' and 'suspensions' True solutions

are homogeneous system having the size

of dispersed particles less than 1 nm

Suspensions are heterogeneous system

and have particles which are more than

Monodisperse – all particles are the same size

Polydisperse – the particles are of many different sizes

• Surface is the term used when considering the dividing phase between: gas – liquid; gas – solid

• Interface is the term used when considering the dividing phase between: solid – liquid; liquid 1 – liquid 2; solid 1 – solid 2.

1 Concepts

What is a dispersion?

A dispersion is a collection of small particles in a matrix It has at least two phases:

1 Dispersed phase

2 Continuous medium

What is a stable dispersion?

A stable dispersion is one in which the dispersed particles remain single entities and do not coagulate Coagulation leads to phase splitting and a complete change

in the properties of the system In most situations we do not want coagulation to occur but there in certain situations it might be beneficial For example, during purification of water, we want coagulation to occur so that all the impurities come together and can be disposed of easily

1 Concepts

Types of stabilities

1 Thermodynamic stability (Of Theoretical Importance)

2 Kinetic stability (Of Practical Importance)

A system is called thermodynamically unstable when there exists a state where the system will have lower energy than it currently has

A dispersion can be thermodynamically unstable, but can still be kinetically stable If in a dispersion (even if it is thermodynamically unstable) the particles do not coagulate for a very long period of time, it is, for all intents and purposes, a stable dispersion, and is called kinetically stable.

1 Concepts

2 Place of colloid science

3 Subject of colloid chemistry

1 Lyophilic Colloids (solvent-loving colloid):

The classical use of the term lyophilic colloids refers to soluble macromolecular materials in which the individual particles (macromolecules such as synthetic polymer chains

or proteins) are of colloidal dimensions

However, there are macromolecules of colloidal dimensions containing both lyophobic and lyophilic components

2 Lyophobic Colloids (solvent-fearing colloid):

Lyophobic colloids are known by a variety of terms, depending on the nature of the phases involved

4 Classification of colloids

4 Classification of colloids

5 Fundamental forces and energy

5 Applications of colloids

Colloids play a very significant role in nature and in our daily life Some of the important applications of colloids are discussed below:

3) Purification of water:

The precipitation of colloidal impurities present in water can be done by adding certain electrolytes like alum etc the negatively charged colloidal particles of impurities get neutralized by the Al3+ ions and settle down and pure water can be decanted off

5 Applications of colloids

4) Cleansing action of soap:

Soap solution is colloidal in nature It removes the dirt particles either by adsorption or by emulsifying the greasy matter sticking to the cloth.

5 Applications of colloids

6) Smoke precipitation:

Smoke particles are actually electrically charged colloidal particles of carbon in the air Precipitation of smoke particles is carried out by Cottrell precipitator which is based on the principle of electrophoresis Smoke is allowed to pass through a chamber having a number of metal plates attached to a metal wire connected to a source of high potential Charged particles of smoke get attracted by oppositely charge electrode get precipitated after losing their charge and the hot air passes out through the chimney The dust particles are also removed in this process Thus the nuisance of smoke in big industrial cities can be avoided

7) Photography:

A colloidal solution of silver bromide in gelatin is applied on glass plates

or celluloid films or paper to from sensitive plates in photography

5 Applications of colloids

8) Artificial rain:

Artificial rain can be caused by spraying

oppositely charged colloidal dust or sand

particles over a cloud The colloidal water

particles present in the cloud will be

neutralized and coagulate to from bigger water

drops causing artificial rain.

9) Rubber industry:

Latex is a colloidal solution of negatively

charged rubber particles From latex, rubber

can be obtained by coagulation.

Rubber plated articles are prepared by

depositing negatively charged rubber particles

over the article to be rubber plated by making

that article an anode in a rubber plating bath.

10) Smoke screen:

In warfare smoke screens are used which are

nothing but colloidal dispersion of certain

substances in the air.

5 Applications of colloids

11) Other applications:

a) Blue color of the sky is due to the scattering of light by colloidal

dust particles in air (Tyndall effect) Similarly, sea water looks blue due to scattering of light by the colloidal impurities present

in sea water.

b) Tail of comets is seen as a Tyndall cone due to the scattering of

light by the tiny solid particles left by the comet in its path.

c) Blood is a colloidal solution and the stoppage of bleeding on

applying ferric chloride solution is due to coagulation of blood forming a clot.

5 Applications of colloids

6 Characterization of colloids

a Sizes of colloid

Average diameter

6 Characterization of colloids

a Sizes of colloid

6 Characterization of colloids

b Morphology

7 Electrokinetic phenomena

Sedimentation

Streaming potential

7 Electrokinetic phenomena

under influence of electric field

7 Electrokinetic phenomena

electro-osmosis: motion of liquid in porous body under influence of electric field;

7 Electrokinetic phenomena