LECTURE 1. ADSORPTION ON A SURFACE OF LIQUID. SURFACE-ACTIVE COMPOUNDS. TO DETERMINE THE SURFACE TENSION BY STALAGMOMETRIC METHOD. ADSORPTION ON A SURFACE OF SOLID ADSORBENTS. SURFACE PHENOMENON. AN ION-EXCHANGE ADSORPTION.

Surface  Tension. Liquids sometimes form drops, and sometimes spread over a surface and wet it.  Why does this happen, and why are raindrops never a metre wide?  A clue to the answer to the second question may be found in pictures of astronauts playing with large blobs of water in their space-craft.

The water molecules at the surface of water are surrounded partially by air and partially by water. These surface molecules would be much more stable if they could be in the interior of the liquid where all their hydrogen bonds could be fulfilled (cohesion). Therefore, water normally tends to have the smallest surface possible, i.e. it has a high surface tension, in order to achieve the lowest possible energetic state.

If a solid material more dense than water is placed on the surface of water, what happens next depends on the nature of the material. If the material is hydrophilic (“water loving”) it has a surface to which water is attracted. The adhesion of water to the surface of this material coats the surface of the object with water, reduces the surface tension, and causes the object to sink.

If the solid object is hydrophobic (“water fearing”), the unfavorable interactions between the water surface and the object make it difficult to wet the surface. Two forces now come into play — the energy it would take to overcome this repulsion and the force of gravity. If the force of gravity is strong enough, it will prevail and the object will sink (assuming that the object has a density greater than water). If the gravitational force is less than the surface tension then the object will float on the surface of the water.

The spider Argyroneta aquatica makes a net under the water, under which it traps air to make a home in which it can live and breed.  The net needs only to be fine enough for surface tension to stop the air from getting through any holes.  The curvature of a bubble or a drop is proportional to the pressure difference between the inside or the outside.  If the hole is small enough, there won’t be enough pressure to make the small radius needed for a bubble to get through the hole.  The pressure difference across a water-air surface is proportional to the curvature, that is, inversely proportional to the radius of curvature.  So a small drop has a bigger pressure difference than a big one.  The same is true of bubbles. 

Detergents are a class of chemicals that contain hydrophobic (non-polar) hydrocarbon “tails” and a hydrophilic (polar) “head” group. This general class of molecules are called surfactants. Surfactants can interact with water in a variety of ways, each of which disrupts or modifies the hydrogen bonding network of water. Since this reduces the cohesive forces in water, this leads to reduction in the surface tension and our sulfur sinks.

A typical example of a detergent molecule is sodium lauryl sulfate (read that shampoo bottle of yours!). The structure can be represented in several different ways. Notice that in the models the Na ion has been left off because the anion and cation completely dissociate in water:

When a detergent is placed in water, the long non-polar hydrocarbon tails tend to aggregate because of favorable intermolecular interactions (“like dissolves like” in the interior and ion-dipole interactions at the exterior). The surfactant molecules thereby organize themselves into 3-dimensional spheres called micelles which have a hydrocarbon core and sulfate groups around the outer surface.

Without detergent, we caot remove a greasy oily stain from clothing because grease and oil are large, non-polar, hydrophobic molecules. However, the interior core of a micelle is quite greasy just like an oily stain. When we add detergent to our wash water, the oil or grease on our clothes can dissolve in the interior of the micelles and thereby go into solution.

Surfactants can also form other structures. Rather than form a sphere, some surfactants can coat the surface of the water to form a layer one molecule thick, a molecular monolayer. This is shown diagrammatically below:

A good example of a monolayer is oil on water. A small amount of oil can be spread over a large surface of water when the oil is only one monolayer thick! A variety of related structures are also known, particularly in cell walls (lipid bilayers etc.).

There are many, many other Real World examples and applications of surfactants! Here’s just one: your body uses surfactants to reduce surface tension in the lungs. The human body does not start to produce lung surfactants until late in fetal development. Therefore, premature babies are often unable to breathe properly, a condition called Respiratory Distress Syndrome. Untreated, this is a serious illness and is often fatal, but administration of artificial surfactants virtually eliminates this health problem.

Surface Tension of Water: The surface tension of water is 72 dynes/cm at 25°C . It would take a force of 72 dynes to break a surface film of water 1 cm long. The surface tension of water decreases significantly with temperature as shown in the graph. The surface tension arises from the polar nature of the water molecule.

Hot water is a better cleaning agent because the lower surface tension makes it a better “wetting agent” to get into pores and fissures rather than bridging them with surface tension. Soaps and detergents further lower the surface tension.

The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension. The molecules at the surface do not have other like molecules on all sides of them and consequently they cohere more strongly to those directly associated with them on the surface. This forms a surface “film” which makes it more difficult to move an object through the surface than to move it when it is completely submersed.

Surface tension is typically measured in dynes/cm, the force in dynes required to break a film of length 1 cm. Equivalently, it can be stated as surface energy in ergs per square centimeter. Water at 20°C (Decrease in water surface tension with heating) has a surface tension of 72.8 dynes/cm compared to 22.3 for ethyl alcohol and 465 for mercury.

Cohesion and Surface Tension:The cohesive forces between molecules down into a liquid are shared with all neighboring atoms. Those on the surface have no neighboring atoms above, and exhibit stronger attractive forces upon their nearest neighbors on the surface. This enhancement of the intermolecular attractive forces at the surface is called surface tension.

Cohesion and Adhesion: Molecules liquid state experience strong intermolecular attractive forces. When those forces are between like molecules, they are referred to as cohesive forces. For example, the molecules of a water droplet are held together by cohesive forces, and the especially strong cohesive forces at the surface constitute surface tension.

When the attractive forces are between unlike molecules, they are said to be adhesive forces. The adhesive forces between water molecules and the walls of a glass tube are stronger than the cohesive forces lead to an upward turning meniscus at the walls of the vessel and contribute to capillary action.

The attractive forces between molecules in a liquid can be viewed as residual electrostatic forces and are sometimes called van der Waals forces or van der Waals bonds.

Surface Tension Examples

Walking on water: Small insects such as the water strider can walk on water because their weight is not enough to penetrate the surface.

Floating a needle: If carefully placed on the surface, a small needle can be made to float on the surface of water even though it is several times as dense as water. If the surface is agitated to break up the surface tension, theeedle will quickly sink.

Common tent materials are somewhat rainproof in that the surface tension of water will bridge the pores in the finely woven material. But if you touch the tent material with your finger, you break the surface tension and the rain will drip through.

Soaps and detergents: help the cleaning of clothes by lowering the surface tension of the water so that it more readily soaks into pores and soiled areas.

Clinical test for jaundice: Normal urine has a surface tension of about 66 dynes/cm but if bile is present (a test for jaundice), it drops to about 55. In the Hay test, powdered sulfur is sprinkled on the urine surface. It will float oormal urine, but sink if the S.T. is lowered by the bile.

Washing with cold water: The major reason for using hot water for washing is that its surface tension is lower and it is a better wetting agent. But if the detergent lowers the surface tension, the heating may be unneccessary.

Surface tension disinfectants: Disinfectants are usually solutions of low surface tension. This allow them to spread out on the cell walls of bacteria and disrupt them. One such disinfectant, S.T.37, has a name which points to its low surface tension compared to the 72 dynes/cm for water.

Surface Tension and Bubbles: The surface tension of water provides the necessary wall tension for the formation of bubbles with water. The tendency to minimize that wall tension pulls the bubbles into spherical shapes (LaPlace’s law

).

The pressure difference between the inside and outside of a bubble depends upon the surface tension and the radius of the bubble. The relationship can be obtained by visualizing the bubble as two hemispheres and noting that the internal pressure which tends to push the hemispheres apart is counteracted by the surface tension acting around the cirumference of the circle.

For a bubble with two surfaces providing tension tension, the pressure relationship is:

Sessile Drop Method

Optical contact angle measurement to determine the wetting behaviour of solids

Task: Determination of the static and dynamic contact angle and of the surface free energy of solids

Test results: interface-specific parameters and measuring ranges of typical instrument systems

·       Measurement of the static contact angle of sessile drops of liquid on a surface as a function of time or temperature

·       Measurement of the dynamic contact angle as a function of the dosing rate , as advancing angle or as receding angle

·       Measurement of the difference between advancing angle and receding angle (contact angle hysteresis) by metered addition or removal of liquid

·       Measurement of the contact angle or until the rolling off of the drop on a plate inclined with the angle (Tilting Plate method)

·       Calculation of the critical surface tension and of the surface free energy : determination of the dispersion as well as the non-dispersion parts (e.g. polar parts , acid/base parts , hydrogen bonding parts ) from contact angle measurements with various test liquids

·       Typical measuring ranges : 0 … 180°/0,1 mN/m … 1000 mN/m

Pendant Drop Method

Task: Determination of the interface and surface tension of liquids

Test results: interface-specific parameters and measuring ranges of typical instrument systems

·         Measurement of the static interfacial or surface tension as a function of time or of temperature

·         Measurement of the adsorption/diffusion coefficients of surfactant molecules in vibrating/relaxing drops

·         Typical measuring range : : 0,05 … 1000 mN/m

 

Adsorption

General. The situation existing at the surface of а liquid or а solid is different from that in the interior. For example, а molecule in the interior of а liquid is completely surrounded by other molecules on all sides and hence the intermolecular forces of attraction are exerted equally in all directions. However, а molecule at the surface of а liquid is surrounded by larger number of molecules in the liquid phase and fewer molecules in the vapour phase i.е. in the space above the liquid surface. As а result, these molecules lying at the surface, experience some net inward force of attraction which causes surface tension. Similar inward forces of attraction exist at the surface of а solid. Alternatively, in case of certain solids such as transition metals (like Ni) there are unutilized free valencies at the surface.

Because of the unbalanced inward forces of attraction or free valencies at the surface, liquids and solids have the property to attract and retain the molecules of а gas or а dissolved substance onto their surfaces with which they come in contact.

The phenomenon of attracting and retaining the molecules of а substance on the surface of а liquid or а solid resulting into a higher concentration of the molecules on the surface is called adsorption. The substance thus adsorbed on the surface is called the adsorbate and the substance on which it is adsorbed is called adsorbent. The reverse process e. removal of the adsorbed substance from the surface is called desorption. The adsorption of gases on the surface of metals is called occlusion.

 Difference between adsorption and absorption. The term adsorption differs from the term absorption in the fact that whereas the former refers to the attraction and retention of the molecules of а substance on the surface only, the latter involves passing of the substance through the surface into the bulk of the liquid or the solid. Where there is а doubt whether the process is true adsorption or absorption (i.е. both adsorption and absorption take place) the term sorption is simply used.

Thus in adsorption whereas the concentration is different at the surface than in the bulk, in absorption, the concentration is same throughout. Moreover whereas adsorption is fast in the beginning and then the rate decreases till equilibrium is attained, absorption takes place at uniform speed. Thus the main points of difference between adsorption and absorption may be summed up as follows:

Adsorption:

1. It is а surface phenomenon i.е. it occurs only at the surface of the adsorbent.

2. In this phenomenon, the concentration on the surface of adsorbent is different from that in the bulk.

3. Its rate is high in the beginning and then decreases till equilibrium is attained.

Absorption:

1.     It is а bulk phenomenon i.e. occurs throughout the body of the material.

2.     In this phenomenon, the concentration is same throughout the material.

3.     Its rate remains same throughout the process.

Examples of adsorption, absorption and sorption.

(i) If silica gel is placed in а vessel containing water vapours, the latter are adsorbed on the former. On the other hand, if anhydrous CaCl₂ is kept in place of silica gel, absorption takes place as the water vapours are uniformly distributed in CaCl₂  to form hydrated calcium chloride (CaCO₃ ^. 2H₂O).

(ii) Ammonia gas placed in contact with charcoal gets adsorbed on the charcoal whereas ammonia gas placed in contact with water gets absorbed into water, giving NH₄OH solution of uniform concentration.

(iii) Dyes get adsorbed as well as absorbed in the cotton fibres i.е. sorption takes place.

Positive and Negative Adsorption. In case of adsorption by solids from the solutions, mostly the solute is adsorbed on the surface of the solid adsorbent so that the concentration of solute on the surface of the adsorbent is greater than in the bulk. This is called positive adsorption. However in some cases, the solvent from the solution may be adsorbed by the adsorbent so that the concentration of the solution increases than the initial concentration. This is called negative adsorption. For example, when а concentrated solution of KCI is shaken with blood charcoal, it shows positive adsorption but with а dilute solution of КС1, it shows negative adsorption. To sum up:

When the concentration of the adsorbate is more on the surface of the adsorbent than in the bulk. it is called positive adsorption. If the concentration of the adsorbate is less relative to its concentration in the bulk, it is called negative adsorption.

Factors affecting adsorption of gases by solids. Almost all solids adsorb gases to some extent. However, the exact amount of а gas adsorbed depends upon а number of factors, as briefly explained below:

(i) Nature and Surface area of the adsorbent. If is observed that the same gas is adsorbed to different extents by different solids at the same temperature. Further, as may be expected, the greater the surface area of the adsorbent, greater is the volume of the gas adsorbed. It is for this reason that substances like charcoal and silica gel are excellent adsorbents because they have highly porous structures and hence large surface areas.

For the same reason, finely divided substances have larger adsorption power than when they are present in the compact form.

Since the surface area of adsorbents cannot always be determined readily, the common practice is to express the gas adsorbed per gram of the adsorbent (The surface area per gram of the adsorbent is called specific area).

(ii) Nature of the gas being adsorbed. Different gases are adsorbed to different extents by the same adsorbent at the same temperature.

(iii) Temperature. Studying the adsorption of any particular gas by some particular adsorbent. It is observed that the adsorption decreases with increase of temperature and vice versa. For example, one gram of charcoal adsorbs about 10 cm³ of N₂ at 273 K, 20 cm³ at 244 K and 45 cm³ at 195 K. The decrease of adsorption with increase of temperature may be explained as follows:

Like any other equilibrium, adsorption is а process involving а true equilibrium. The two opposing processes involved are condensation (i.е. adsorption) of the gas molecules on the surface of the solid and evaporation (i.е. desorption) of the gas molecules from the surface of the solid into the gaseous phase. Moreover, the process of condensation (or adsorption) is exothermic so that the equilibrium may be represented as:

Applying be Chatelier’s principle, it can be seen that increase of temperature decreases the adsorption and vice versa.

The amount of heat evolved when one mole of the gas is adsorbed on the adsorbent is called the heat of adsorption.

(iv) Pressure. At constant temperature, the adsorption of а gas increases with increase of pressure. It is observed that at low temperature, the adsorption of а gas increases very rapidly as the pressure is increased from small values.

(v) Activation of the solid Adsorbent. It constant temperature, the adsorbing power of an adsorbent. This is usually done by increasing the surface area (or the specific area) of the adsorbent which can be achieved in any of the following ways:

(а) By making the surface of the adsorbent rough e.g. by mechanical rubbing or by chemical action or by depositing finely dispersed metals on the surface of the adsorbent by electroplating.

(b) By subdividing the adsorbent into smaller pieces or drains. No doubt this method increases the surface area but it has а practical limitation, that is, if the adsorbent is broken into too fine particles that it becomes almost powder, then the penetration of the gas becomes difficult and this will obstruct adsorption.

(с) By removing the gases already adsorbed e.g. charcoal is activated by heating in superheated steam or in vacuum at а temperature between 623 to 1273 К.

Types of adsorption. An experimental study of the adsorption of various types on solids shows that there are two main types of adsorption. These are briefly explained below:

(i) Physical adsorption or van der Waal’s adsorption or physicosorption. When а gas is held (adsorbed) on the surface of а solid by van-der-Waal’s forces (which are weak intermolecular forces of attraction) without resulting into the formation of any chemical bond between the adsorbate and the adsorbent, it is called “physical adsorption” or “van-der-Waal’s adsorption” or “physicosorption”. This type of adsorption is characterized by low heats of adsorption i.e. about 40 kJ per mole. Further, physical adsorption of а gas by а solid is generally reversible. Increase of pressure causes more gas to be adsorbed and the release of pressure frees the adsorbed gas. Similarly, decrease of temperature increases adsorption but the gas adsorbed at low temperature can be freed again by heating.

(ii) Chemical adsorption or Chemisorption or Langmuir adsorption. When а gas is held on to the surface of а solid by forces similar to those of а chemical bond, the type of adsorption is called chemical adsorption or chemisorption. This type of adsorption results into the formation of what is called а “surface compound”. That the forces involved are similar to those of chemical bond is confirmed by the fact that the heats evolved during chemisorption are high (i.е. about 400 kJ/mole) which are of the same magnitude as those involved in chemical reactions. Further, as chemisorption is something similar to а chemical change, it is usually irreversible. The efforts to free the adsorbed gas often gives some definite compound instead of the free gas. For example, oxygen adsorbed on tungsten or carbon is liberated as tungsten oxide or as carbon monoxide and carbon dioxide.

Another aspect in which chemisorption differs from physical adsorption is the fact that whereas physical adsorption takes place between every gas and а solid i.е. is not specific iature (because it involves van der Waal’s forces which exist among the molecules of every two substances), the chemisorption is specific iature and occurs only where there is а tendency towards compound formation between the gas and the adsorbent. Further unlike physical adsorption, the chemisorption like the most of chemical changes, increases with increase of temperature. For this reason, а gas may be physically adsorbed at low temperature but chemisorbed at higher temperature. For example, it happens in case of adsorption of hydrogen on nickel. When chemisorption takes place by raising the temperature i.е. by supplying activation energy, the process is called “activated adsorption”.

Physical adsorption:

1. The forces operating in these cases are weak van-der-Waal’s forces.

2. The heats of adsorption are low viz. about 20 – 40 kJ/mol

3. No compound formation takes place in these cases.

4. The process is reversible i.е. desorption of the gas occurs by increasing the temperature or decreasing the pressure.

5. It does not require any а activation energy.

б. This type of adsorption decreases with increase of temperature.

7. It is not specific iature i.е. all gases are adsorbed on all solids to some extent.

8. The amount of the gas adsorbed is related to the ease of liquefaction of the gas.

9. It forms multimolecular layer.

Chemisorption:

1. The forces operating in these cases are similar to those of а chemical bond.

2. The heats of adsorption are high viz. about 400-400 kJ/mol

3. Surface compounds are formed.

4. The process is irreversible. Efforts to free the adsorbed gas give some definite compound.

5. It requires activation energy.

6. This type of adsorption first increases with increase of temperature. The effect is called activated adsorption.

7. It is specific iature and occurs only when there is some possibility of compound formation between the gas being adsorbed and the solid adsorbent.

8. There is no such correlation.

9. It forms unimolecular layer.

Adsorption from solutions. Solid surfaces can also adsorb solutes from the solutions. An application of adsorption from solution is the use of activated charcoal for decolorising sugar solutions. Activated charcoal can adsorb colouring impurities from the solutions of organic compounds. Adsorption from solution can also involve colourless solutions. Adsorption of ammonia from ammonium hydroxide solution and acetic acid from its solution in water by activated charcoal are such examples.

This type of adsorption is also affected by temperature and concentration. The extent of adsorption decreases with increase in temperature and increases with increase in concentration. The isotherm for the adsorption of solutes from solutions (by the solid adsorbents) is found to be similar to that shown in Fig. 2. Hence the relationship between  x/m (mass of the solute adsorbed per gram of the adsorbent) and the equilibrium concentration, С of the solute in the solution is also similar i.e:

X/m =KC^1/n

Taking logarithms of both sides of the equation, we get:

log x/m = log К  + 1/n log C

This equation implies that а plot of log x/m against log С should be а straight line with slope1/n and intercept log Х. This is found to be so over small ranges of concentration.

The equation for adsorption from solutions is found to give better results than for adsorption of gases by solids.

Adsorption isobars. As already discussed, adsorption is а case of dynamic equilibrium in which forward process (adsorption) is exothermic while backward process (desorption) is endothermic. Thus applying be Chatelier’s principle, increase of temperature will favour the backward process i.е., adsorption decreases.

 А graph drawn between the amount adsorbed (x/m) and temperature ‘t’ at а constant equilibrium pressure of adsorbate gas is known as adsorption isobar.

Adsorption isobars of physical adsorption and chemical adsorption show important difference [Fig.3 (а) and (b)] and this difference is helpful in distinguishing these two types of adsorption. The physical adsorption isobar shows а с1есгеаье in х/m throughout with rise in temperature, the chemisorption isobar shows an initial increase with temperature and then the expected decrease. The initial increase is because of the fact that the heat supplied acts as activation energy required in chemisorption (like chemical reactions).

b

Fig.3. (а) Physical adsorption isobar. (b) Chemisorption isobar.

Application of adsorption.  Adsorption finds extensive applications both in research laboratory and in industry. А few applications are briefly described below:

In preserving vacuum. In Dewar flasks activated charcoal is placed between the walls of the flask so that any gas which enters into the annular space either due to glass imperfection or diffusion through glass is adsorbed.

In gas masks. All gas masks are devices containing suitable adsorbent so that the poisonous gases present in the atmosphere are preferentially adsorbed and the air for breathing is purified.

In clarification of sugar. Sugar is decolorised by treating sugar solution with charcoal powder. The latter adsorbs the undesirable colours present.

In chromatographic analysis. The selective adsorption of certain substances from а solution by а particular solid adsorbent has helped to develop technique for the separation of the components of the mixture. This technique is called chromatographic analysis. For example, in column chromatography, а long and wide vertical tube is filled with а suitable adsorbent and the solution of the mixture poured from the top and then collected one by one from the bottom.

In catalysis. The action of certain solids as catalysts is best explained in terms of adsorption. The theory is called adsorption theory. According to this theory, the gaseous reactants are adsorbed on the surface of the solid catalyst. As а result, the concentration of the reactants increases on the surface and hence the rate of reaction increases. The theory is also able to explain the greater efficiency of а catalyst in the finely divided state, the action of catalytic promoters and poisons.

In adsorption indicators. Various dyes, which owe their use to adsorption, have been introduced as indicators particularly in precipitation titrations. For example, KBr is easily titrated with AgNO₃ using eosin as an indicator.

In softening of hard water. The use of ion exchangers for softening of hard water is based upon the principle of competing adsorption just as in chromatography.

In removing moisture from air in the storage of delicate instruments. Such instruments, which may be harmed by contact with the moist air, are kept out of contact with moisture using silica gel.

References:

Maine:

1.  Lawrence D. Didona. Analytical chemistry. – 1992: New York. – P. 700.

2.  Atkins P.W. Physical chemistry. – New York. – 1994. – P.1006.

3.  John B.Russell. General chemistry.New York.1992. – P. 615.

 

Different:

·       D.M. Ruthven Principles of Adsorption & Adsorption Processes John Wiley & Sons, New York, 1984.

·       Yiacoumi, S. and Tien, C. Kinetics of Metal Ion Adsorption from Aqueous Solutions: Models, Algorithms, and Applications.  Kluwer Academic Publishers, Norwell, 1995.

·       Cohen, Y. and Peters, R.W. Novel Adsorbents and Their Environmental Applications
AIChE, New York, 1995. 

·       Adsorption and its applications in industry and environmental protection”, Vol. I-Applications in Industry,1061 pages.

·       Adsorption by powders and porous solids F. Rouquerol, J. Rouquerol and K Sing Academic Press, 1999.

·       D.J. Shaw: Introduction to Colloid and Surface Chemistry, 3^rd Ed., Butterworths, London 1980, ISBN 0-408-71049-7

·       F. MacRitchie: Chemistry at Interfaces, Academic Press, San Diego, 1990, ISBN 0-12-464785-5

·       J.N. Israelachvili: Intermolecular and Surface Forces, 2^nd Ed., Academic Press, New York, 1991, ISBN 0-1237-5181-0

·       C.J. van Oss: Interfacial Forces in Aqueous Media, Marcel Dekker, New York, 1994, ISBN 0-8274-9168-1

·       S. Hartland, R.W. Hartley: Axissymmetric Fluid-Liquid Interfaces, Elsevier, Amsterdam, 1976, ISBN 0-4444-1396-0

·       K.L. Mittal (Ed): Adsorption at Interfaces, 5^th Ed., Wiley Interscience, New York, 1990, ISBN 0-8412-0249-4

·       D.K. Chattoraj, K.S. Birdi: Adsorption and the Gibbs Surface Excess, Plenum Press, New York, 1984, ISBN 0-306-41334-5

·       M.J. Rosen: Surfactants and Interfacial Phenomena, 2^nd Ed., John Wiley, New York, 1989, ISBN 0-471-83651-6

·       M.J. Rosen (Ed.): Structure performance relationships in surfactants, ACS, Washington, DC, 1984, ISBN 0-8412-0839-5

·       S.A. Safran: Statistical Thermodynamics of Surfaces, Interfaces, and Membranes, Addison-Wesley, Reading MA, 1994, ISBN 0-201-62633-0

·       L.E. Schramm: Dictionary of Colloid and Interface Science, 2^nd Ed., Wiley-Interscience, New York, 2001, ISBN 0-471-39406-8

·       Journal of Colloid and Interface Science, Academic Press, New York, ISSN 0021-9797

·       Colloids and Surfaces A – Physicochemical and engineering aspects, Elsevier, Amsterdam, ISSN 0927-7757

 

Prepared by PhD Halina Falfushynska