Colloidz

COLLOIDS: INTRODUCTION: IN 1861,Thomas Graham studied ability of substance to diffuse into water through semi permeable membrane. He observed that sugar,salt etc can pass through semi permeable membrane (CRYSTALLOIDS).Where as some substances like gel cannot passthroughthis seme permeable membrane.Name this kind of substances as COLLOIDS. Colloids derived from Greek word “KOLLA” Means “GLUE”; “EIDOS” Means “LIKE”.

DEFINITION OF COLLOIDS: A mixture in which one substance is divided into minute particles (called colloidal particles) and dispersed throughout a second substance. The substances are present as larger particles than those found in solution, but are too small to be seen with a microscope. There are no strict boundaries on the size of colloidal particles, but they tend to vary between 10-9 m to 10-6 m in size.

The mixture is also called a colloidal solution, colloidal system, or colloidal dispersion. The three forms in which all matter exists are solid, liquid or gas. Colloidal systems can be any combination of these states. A colloidal system is not a true solution but it is not a suspension either because it does not settle out like a suspension will over time. Colloids are larger than most inorganic molecules and remain suspended indefinitely. They are large molecules, such as proteins, or groups of molecules. They have many properties, depending on their large specific surface. Colloid formation can be classified in two systems, namely reversible and irreversible. In an irreversible system, the products are so stable or removed so well that the original reactants cannot be reproduced. A reversible system is one in which the products can be made to react to reproduce the original reactants.

INTRODUCTION TO THE COLLOIDAL SYSTEMS: Let us leave the surface phenomena to enter into the mysterious world of the colloids. A first example of a colloid is gelatin, a strange substance: neither liquid nor solid. It is very elastic and if deformed it returns to it’s previous shape. Goofy, the friend of Mickey and Donald, learned something about it when, in the Disney film: Mickey and the Beanstalk, he was "walking" on a pudding of the Giant. The emulsion of oil in water is another substance with unusual properties. Unusual are also substances such as foams, aerosols, smokes and fogs, not to mention the solid emulsions and foams. What do all these curious substances have in common? That is what we will see before long. These substances are called colloids and they are in some ways related to the solutions and to the mixtures, even if they do not belong to the former nor latter. To understand what colloids are, it is necessary to know what solutions and mixtures are.

SOLUTIONS:

A solution is a homogeneous mixture of two or more substances. When placed in water, many substances dissolve and are called soluble, others do not dissolve and are called insoluble. Salt and sugar easily dissolve in water. If instead you put sand in water, you can mix for as long as you want, but you will not succeed in dissolving the sand. In fact, sand is insoluble in water. In a solution, the material present in greater quantity is defined solvent and that in smaller quantity solute. What does it mean to say that a substance is soluble in another? It means that the molecules of the solute separate each other and they disperse among those of the solvent. Instead, the insoluble substances keep themselves compact and their molecules do not disperse into the solvent. As solvent, we have used the example of water because many solids are soluble in water, but nearly every liquid can be a solvent. And then, why we should limit ourselves to the liquids? Let us generalize the concept of solvent and concede to all substances, solid or liquid or gaseous the possibility to be a solvent. At this point, even the solutes can belong to all of these three states of matter. For example, some solid solutions are the metal alloys such as steel (Fe+C), brass (Cu+Zn), bronze (Cu+Sn). Finally, all gases are completely soluble among each other. Also common are solutions of gases in liquids. For example, carbon dioxide is added to many beverages to make them fizz. In the water of ponds, rivers and seas, gases like oxygen, carbon dioxide and others go into solution in a natural way. The presence of these gases in the water make possible the life of the aquatic organisms. The solubility of a substance is measured as the maximum amount, in grams, which can be dissolved in 100 g of solvent. When the solute does not dissolve any more, but a deposit is formed on the bottom, the solution is defined saturated.

CATEGORIES OF SOLUTIONS SOLUTE SOLVENT EXAMPLE air (nitrogen, oxygen, Gas Gas etc.) moist air (water vapor Liquid Gas in air) Solid Gas atmospheric dust Gas Liquid CO2 in water (sparkling

Liquid

Liquid

Solid

Liquid

Gas

Solid

Liquid

Solid

Solid

Solid

water) wine (water + alcohol) marine water (salt in water) gas in silicates (pumice stone) dental alloys (mercury in cadmium) metal alloys (steel, bronze)

MIXTURES As we have seen, by mixing sugar with water, a solution is obtained. If instead we mix sand into water, we obtain a mixture. Also by mixing bits of coal and iron filings we obtain a mixture. With a pair of thin tweezers it is possible to take away sand grains from the water or pieces of coal from the filings, but it is not possible to take away singly molecules of sugar from the water because they are too much small. Hence, what distinguishes a mixture from a solution? In a mixture the particles are enough large to be separated by mechanical means such as tweezers or sieves, in a solution this is not possible because the particles which form it are so small that they cannot be seen even with an electron microscope. To separate the components of a solution it is necessary to use physical method like distillation. So, mixtures are formed by quite big particles, solution are formed by very small particles. . IN CoLLOIDs we said DISPERSED PHASE similarly as SOLUTE in Solution. Where as DIPERSED MEDIUM/CONTINUOUS PHASE as solvent in solution.

COLLOIDS: We have seen that in the solutions, the molecules of the solute separate each other and disperse among those of the solvent. In the mixtures instead, the

molecules do not separate and the particles remain compact. From the point of view of the sizes, solutions are formed by very small particles (single molecules) and the mixtures by quite large particles. In an intermediate position, between mixtures and solutions, there are the colloids. They are dispersions of small particles, but not molecule sized. What distinguishes mixtures from colloids and from solutions is therefore the size of the particles which form them. By convention, a colloid is a dispersion of particles which size is comprised between 0.2 and 0.002 µm (a micrometer, or micron, = 10-6 meters). If the particles are larger than 0.2 µm, we have a mixture, if they are smaller than 0.002 µm, we have a solution. In general, the components of a colloid are formed by small aggregates of molecules, while the components of a solution are single molecules. Anyway, if these molecules are large enough, as it is the case of many macromolecules, their solution will give a colloid. So, the criterion of distinction between colloids and solutions cannot be the presence of single molecules, but as we were saying, the size of the particles which form them.

MIXTURES

COLLOIDS

SOLUTIONS

large particles

mean particles

thin particles

> 0.2 µm

0.2 - 0.002 µm

< 0.002 µm

According to the dispersing phase, colloids are distingued in gaseous, liquid and solid suspensions. Gaseous suspensions, or aerosol, are smokes and fogs. Smokes are suspensions of solid particles in a gas. Fogs are suspensions of liquid particles in a gas. Sols, gels, emulsions, foams are liquid suspensions. Oily rocks, pumice stones are solid suspensions.

Types of colloids: Colloids are usually classified according to the original states of their constituent parts:

Dispersing medium Dispersed phase

• • • •

Name

Solid

Solid

Solid sol

Solid

Liquid

Gel

Solid

Gas

Solid foam

Liquid

Solid

Sol

Liquid

Liquid

Emulsion

Liquid

Gas

Foam

Gas

Solid

Solid aerosol

Gas

Liquid

Aerosol

Dispersing medium (external phase) - the constituent found in the greater extent in the colloid. Dispersed phase (internal phase) - the constituent found in the lesser extent. A further classification is as lyophilic (solvent attracting), lyophobic (solvent repelling) or association colloids (a mixture of the two). If water is the dispersing medium, it is often known as a hydrosol.

The term colloid refers to substances with a glue-like consistency, in which the dispersant phase is therefore liquid. However, do not forget that even substances such as smokes and aerosols, in which the dispersant phase is aeriform and which we can also call gaseous suspensions, are colloids. Finally, even some solid substances, in which the dispersant phase is solid and which we can also call solid suspensions, are colloids too. Colloids have unusual properties, for example gelatin. Colloidal systems have a high ratio area/volume among the surface of the particles and their volume. In other words, as in the colloids the amount of dispersed particles is very large, their overall surface is very large too and by consequence the interaction of the two phases is important. For example, a cube of 1 cm a side has a surface area of 6 cm2, the material of the same cube divided into little cubes of 0.002 µm of side, has a surface area of 3000 m2. Because of the wide surface of contact between the two phases, often the colloids are

studied with the surface phenomena and the discipline which studies them is called surface and colloid science.

LYOPHILIC AND LYOPHOBIC COLLOIDS: The dispersion phase can be divided into two types: 1. Lyophilic colloids.(solvent loving) 2.Lyophobic colloids.(solvent hating) Lyophilic sols are those in which the dispersed phase exhibits a definite affinity for the medium or the solvent. For example: dispersion of starch,gum and protein in water. Lyophobic sols are those in which the dispersion phase has no attraction for the medium or the solvent. For example: dispersion of gold,iron hydroxide and sulphue in water.

SOL: A sol is a dispersion of very thin solid particles in a liquid. It has a liquid consistency and resembles a true solution. An aqueous sol appears clear, very similar to common water. Anyway, if you shine an intense beam of light across it, a part of the light will be diffused from the particles which are in suspension. These particles are very small, but they are still enough large to obstruct the light and diffuse it. This phenomenon is called Tyndall effect. You can observe it with sols, but not with true solutions. 1 - Tyndall effect. In a transparent jar, put some clayey earth 1/4 of the volume and water until attain 3/4 of the container. Close the jar with its cap and shake until all the earth is "dissolved". Leave the pot to rest for a day to allow the clay particles to settle. The liquid which is above the sediment should have become clear. Shining an intense bundle of light through the jar, you should see the Tyndall effect. Do the same thing with a glass of pure water and compare the results.

REASONS: Sun seems to be appear as blue in colour because of TYDALL EFFECT. And at sunset sky seem to be orange because of this effect.

LIGHT

TYNDALL

PAINT

GEL: A gel is a dispersion of very thin solid particles in a liquid and it has a gelatinous consistency. Increasing the concentration of the particles, a sol can pass to the state of gel. On the contrary, by diluting a gel you will obtain a sol. So, what makes a sol different from a gel is its fluid or gelatinous consistency. Also the temperature can determine the passage from sol to gel and vice versa. For example, broth gelatin is gelatinous at room temperature, but it becomes liquid when it is heated. Animal gelatin is a reversible gel because depending on the temperature it can pass from gel to sol and vice versa The albumen of eggs instead is not reversible because when heated it coagulates and it does not come back to the state of sol. Silica gel absorbs moisture and keeps its properties with broad concentrations of water. Because its affinity for water it is used as dehumidifier. When left to rest, a sol can spontaneously jell and come back to the state of sol simply by mixing it (eg: aqueous suspensions of kaolin).

JELLY

1 - Making gelatin. in warm water and, determine what is the gelatin necessary to temperature. Do not

Buy some dry gelatin. Dissolve it with subsequent dilutions, minimum concentration of dry obtain a normal gelatin at room keep gelatins a long time because

they easily become cultures of bacteria. Store them in a refrigerator and, after a day, throw them away. 2 - Reversibility of the gelatin. By means of the temperature, make some gelatin pass from the gel to sol states and vice versa.

EMULSIONS:An emulsion is a dispersion of an insoluble liquid in another liquid. For instance, the oil is not soluble in water. If you pour some oil in a container with water, it will float it and keeps separate from the water. Instead, if you vigorously shake the container, you will obtain a dispersion of small drops of oil in water, however these drops quickly join together, so that in a short time nearly all the oil will return as before. To make the emulsion more stable, before shaking the container, add some detergent. The surfactant molecules will arrange on the surface of the oil drops with the heads outward. As these heads have an electrical charge and as this charge is always the same, the oil drops will repel each other and be unable to return to the homogeneous layer as before. So, surfactants can help you to obtain more stable emulsions. There are special surfactants for emulsions, endowed of a higher capability to stabilize the oil drops than the detergents. There are also emulsifying agents for alimentary use such as lecithin and emulsifiers for industrial purposes which are not edible. Butter is formed by small water drops suspended in fat. Cheese and mayonnaise too are considered emulsions. A lot of creams used both in pharmacy and in cosmetics are emulsions. Fuels emulsified with water have been produced. Emulsified oils are used in machine working to make it easier to cut metals with machine tools. In fact, metal cutting can create an intense heat, which has to be removed if you want to avoid burning the tools. The oil and water in the cutting fluid help remove the heat and make it possible to cut metals efficiently. Milk is another emulsion made up by small greasy drops in an aqueous phase.

MILK.

3 - Mayonnaise. To the ingredients of the test 2, add an egg yolk and emulsify again. The emulsion will be much more stable. Add some salt and if you want some pepper and you will have obtained a good mayonnaise. If you prefer, you can replace the vinegar with lemon juice. Why is the emulsion stable with the egg yolk? This is due to the presence of lecithin in the egg yolk. Lecithin is a surfactant and the molecules spread on the surface of the oil drops with the hydrophilic head outward. As these heads are electrically charged, the oil drops will repel and their merging is prevented. Lecithin is a phospholipid and it has a structure like that of the phospholipids which form the membranes of cells. Another well known lecithin and which you can find on the market is soy lecithin. What is lecithin? Internet keywords: emulsions, mayonnaise recipe, lecithin, soy lecithin, homemade butter, handmade butter, creams

FOAMS: Foam is a dispersion of a gas in a liquid (liquid foams) or in a solid (solid foams). Among the liquid foams, we have the ones produced by soaps and detergents, and various foods such as wine, beer and many others. Among the solid foams we have Pumice stone, earthenware, sponges, expanded plastics like expanded polystyrene and expanded polyurethane. By dispersing helium in a liquid which produced bubbles with very thin walls and which then solidified, some researchers succeeded in fabricating a solid foam lighter than air.

1 - Foam and shape of the bubbles in contact. With a drop of liquid detergent in a small basin of water, make a foam. Observe the shape of the bubbles which are in contact each other. With a microscope, observe a thin section of elder pith and compare it with the foam. 2 - Make a solid foam. Beat egg whites and some sugar, then cook it so to obtain its solidification: you will have obtained a meringue, just an edible solid foam. OTHER EXPERIMENTS WITH SURFACTANTS AND COLLOIDS

1 - Who can guess more colloids? List the colloids you have in your home or which you know by experience: (milk, mayonnaise, resin, paint, ink, expanded polystyrene, cell cytoplasm, blood serum, etc.). 2 - A half-solid fluid. Put in a cup four spoons of corn starch. Add some water until you have obtained a creamy substance. While mixing, you will notice that this substance has an odd property: if you slowly mix it, it behaves like a liquid, but if you try to mix it fast, it seems solid. By quickly lifting it on a side, you will be also able to remove this cream from the cup, but you will have some difficulties in keeping it in your hands because, even if it moves slowly, it will escape from all sides like a liquid. Liquids which change viscosity with the mixing speed are called dilatant fluids. Also wet sand behaves as dilatant fluid. Sold in the US as a child’s toy under the name of Gak or Goo, you can make your own by dissolving 1/2 cup of white glue with 1/2 cup of water, then adding 3 tablespoons of Borax, while stirring well. You will obtain a substance which is apparently solid, but which loses its shape within some minutes, becoming like a liquid puddle... which however you will able to lift it as if it was a carpet.

ATOMIZER FOR AEROSOL:How do atomizers work? There are many models of atomizers or of sprayers like those of pressurized spray paint cans, or those provided with a small pump that you press with a finger, those that work by mean of a rubber syringe or, for industrial uses, by a compressor.

1 - Anatomy of an atomizer. Disassemble a trigger spray bottle. Often, these d does not work any more and try to repair it. Trigger spray bottle. AERO.

2 - Build an atomizer. To build a small atomizer, take two thin straws and fix t mm of diameter. Under the vertical straw, mount a small bottle with water. Now an area of low pressure above the vertical can which will draw some water up t syringe. Usually, this type of atomizers is used for perfumes, but you can use it

Properties : 1.Colloidal particles are generally aggregates of numerous atoms or molecules. 2.Main property of colloids is it scattered the light.Such a property is known as “TYNDALL EFFECT’ after the British scientist John Tyndal. 3.They pass through most filter papers, but can be detected by lightscattering, sedimentation and osmosis. 4.A characteristic of colloids is absorption, as the finely divided colloidal particles have a large exposed surface area. 5. The chemical and physical properties of inorganic colloids can be changed dramaticaly when their size is reduced to a number of nanometers. This effect is due to the increasing importance of the colloid surface. 6.The presence of colloidal particles in a solution has only minor effects on its colligative properties (boiling, freezing point, etc.)

Tooth

Paste

7.Thixotropy is a property exhibited by certain gels. This is where a gel appears solid and maintains its own shape until it is subjected to some force or disturbance, such as shaking. It then tends to act as a sol, flowing freely. This behavior is reversible, and the sol will return to a gel if left undisturbed. Examples of thixotropic gels include certain paints, printing inks and clays. 8.The particles of a colloid selectively absorb ions and acquire an electric charge. The existence of an electric charge on the surfaces of the colloidal particles is a source of kinetic stability for colloids. All of the particles of a given colloid are repelled by one another as they all take on the same charge. The movement of colloidal particles through a fluid under the influence of an electric field is known as ELECTROPHORESIS. 9.When we see the colloidal particles under the ultra microscope these appeared as continuous moving tiny points in Zigzag motion. This mothion is known as “BROWNIAN MOTION”. 10.Neutralize particles have a high surface free energy.They thus come closer to each other.

Preparation OF COLLOIDS: There are two main ways of forming a colloid; reduction of larger particles to colloidal size or condensation of smaller particles, e.g. molecules, into colloidal particles.

1.DISPERSION METHOD. Colloidal sols can be formed by dispersion methods (e.g. by mechanical subdivision of larger particles or by dissolution in the case of lyophilic sols) or by condensation methods (from supersaturated solutions or supercooled vapours, or as the product of chemical reactions) or by a combination of these two (e.g. in an electrical discharge).

2.CONDENSATION METHOD. When a condensation method is applied, molecules (or ions) are deposited on nuclei, which may be of the same chemical species as the colloid (homogeneous nucleation) or different (heterogeneous nucleation). An aggregate of a small number of atoms, molecules or ions is called an embryo. A critical embryo has that size at which the Gibbs energy at constant pressure and temperature is a maximum. A larger embryo is called a homogeneous nucleus. A nucleating agent is a material either added to or present in the system, which induces either homogeneous or heterogeneous nucleation.The rate of nucleation is the number of nuclei formed in unit time per unit volume.

1.DISPERSION METHOD: • • • •

MECHANICAL METHOD. ELECTRICAL METHOD. ULTRA SONIC METHOD. PEPTIZATION METHOD.

2.CONDENSATION METHOD:

1.DISPERSION METHOD:

• MECHANICAL METHOD: (colloid mill) By the use of Colloidal milk.Colloidal milk consists of 2 steel plates which are near to each other and they are rotating at opposite direction. Through hopper solid and liquid is introduce into it that will breakdown them into fine particles.Now dispersing into dispersed medium we will get a colloidal sol.

•

ELECTRICAL METHOD:

There are certain metals which are dispersed by the passage of electrical arc between the 2 electrodesmade up of metals ehich is immersed in dispersion medium.Here the dispersion medium is water.

•

ULTRA SONIC METHOD:

As ultra sonic waves have high frequency. Oscillation of particles will breakdown into smaller particles. In this manners colloids are formed.

• PEPTIZATION METHOD: It is a process of breakdown of large particles into colloidal particles by addition of an electrolytes Particularly those containing the common

ion.Which is known as peptizing agent. Used in the stability of hydrophobic colloids. Some freshly precipitated ionic solids are dispersed into colloidal solution in water bt the addition of small quantities of electrolytes.

2.CONDENSATION METHODS: This is also known as AGGREGATION METHODs. These methods consist of chemical reactions or change of solvents whereby the atoms or molecules of the dispersed phase appearing first, coalesce or aggregate to form colloidal particles. The condition (temperature, concentration etc) used are such as permit the formation of sol particles but prevent the particles becoming too large and forming precipitate. The unwanted ions (spectators ions) present in sol are removed by dialysis as these ions may eventually coagulate the sol. The more important methods for preparing hydrophobic sols are listed below:

1. DOUBLE DECOMPOSITION: An arsenic sulphide (As2S3) sol is prepared by passing a slow stream of hydrogen sulphide gas through a cold solution of arsenious oxide (As2O3).This is continued till the yellow colour of the sol. Attains maximum intensity.

Excess hydrogen sulphide (electrolyte) is removed by passing in a stream of hydrogen.

2. REDUCTION: Silver sol and gold sols can be obtained by treating dilute solution of silver nitrate or gold chloride with organic reducing agents like tannic acid or ethanol (HCHO). AgNO3 +

tannic acid Ag sol

3. OXIDATION: A sol of sulphur is produced by passing hydrogen sulphide into a solution of suldioxidation. 2H2S +

SO22H2O + S

In qualitative analysis, sulphur sol is frequently encountered when H2S is passed through the solution to precipitate group 2 metals if an oxidizing agent (chromate or ferric ions) happen to be present. It can be removed by boiling (to coagulate the sulphure) and filtering through two filter papers folded together.

4. HYDROLYSIS: Sols of the hydroxide of iron, chrominium are readily prepared by the hydrolysis of salts of the respective metals. In order to obtain a red sol of ferric hydroxide, a few mls of 30% ferric chloride solution is added to a large volume of almost boiling water and stirred with a glass rod. FeCl3 + 3H2OFe(OH)3 + 3HCL

5. HYDROLYSIS: When a solution of sulphur or resins in ethanol is added to an excess of water,the sulphur or resin sol is formed owing to decreased in solubility.

The substance is present in molecular state in ethanol but on transference to water, the molecules precipitate out to form colloidal particles.

MILL

STABILITY of COLLOIDS: A true colloid solution is stable. Its particles do not ever coalesce and separates out. The stability is due to two factors: 1) Presence of like particles on colloidal particles. 2) Presence of solvent layer around sol particles. To maintain the stability of hydrophilic colloids we will add hydrophilic colloids. The hydrophilic colloids surrounds the hydrophobic colloids to produce a shielding effect. Therefore hydrophobic colloids is called “PROTECTIVE COLLOIDS” The stability of colloids is also maintained by addition of buffer.

COLLOIDS AS DIAGNOSTIC TOOLS: Gold(199) and technetium(98) are the radioactive substances used in CTS scanning to diagnose tumor. There are other radioactive substance also.which are helpful in diagnosing various diseases.

PROCESSING OF COLLOIDAL SYSTEM: 1. Dialysis 2. Electrodialysis 3. Ultra filtration This latter generally makes use of chemical reactions such as hydrolysis or displacement. Laboratory and industrial methods make use of several techniques.This page gives a brief overview of some of these techniques, but it should be noted that there are a broad range used in practice. A method of forming an aerosol is to tear away a liquid spray with a gas jet. The process can be helped by separating the liquid into droplets with electrostatic repulsions, done by applying a charge to the liquid. Emulsions are usually prepared by vigorously shaking the two constituents together, often with the addition of an emulsifying agent, e.g. a surfactant such as soap, in order to stabilise the product formed.

Semi-solid colloids, known as gels, may be formed from the cooling of lyophilic sols that contain large linear molecules and have a much greater viscosity than the solvent.

Colloids are often purified by dialysis, a very slow process, where the aim is to remove a large part ot any ionic material that may have accompanied their formation. A membrane is selected that will not allow colloid particles through but will let the solvent and ions permeate through. The method relies on diffusion, osmosis and ultrafiltration. Dialysis is the process of separating a colloidal sol from a colloid-free solution by a membrane permeable to all components of the system except the colloidal ones, and allowing the exchange of the components of small molar mass to proceed for a certain time.

The colloid-free solution obtained at equilibrium in dialysis is called equilibrium dialysate. Its composition approaches that of the dispersion medium (more precisely, the limit to which the composition of the dispersion medium tends at large distances from the particles). In the dialysis equilibrium an osmotic pressure difference exists between sol and equilibrium dialysate.

After (complete or incomplete) dialysis two solutions are obtained. The one free from colloidal material is called dialysate; the other one, containing the colloidal particles may be called retentate, dialysis residue, or simply residue, but should not be called dialysate.

The ultrafiltrate, prepared by ultrafiltration (filtration through a dialysis membrane), is in general not of the same composition as the equilibrium solution.

If dialysis is conducted in the presence of an electric field across the membrane(s) it is called electrodialysis. Electrodialysis may lead to local differences in concentration and density. Under the influence of gravity these density differences lead to large scale separation of sols of high and of low (often vanishingly low) concentrations. This process is called electrodecantation (electrophoresis convection).

Flotation is the removal of matter by entrainment at an interface. In particular, froth flotation is the removal of particulate matter by foaming (frothing). Foam fractionation is a method of separation in which a component of the bulk liquid is preferentially adsorbed at the L/V interface and is removed by foaming.

CONCLUSION Surface phenomena and colloids concern many objects, products and events of our everyday life, which are not immediately explainable with the physics we usually study at school. Having introduced some principles, and suggested some experiments in this field which until now may have been quite mysterious seemed to us useful and important. Not only, but you have also noticed how fascinating these topics are and how amusing is to do laboratory activities with them.

BIBLIOGRAPHY B.S.bhall. http://surfactants.net/bookstore/ Books on surfactants and colloids. R. Aveyard, D. A. Haidon: "An Introduction to the Principles of Surface Chemistry", Cambridge Chemistry Texts C. C. Miller, P. Neogi: "Interfacial Phenomena", Marcel Dekker inc., N.Y. (1985).