![• In acidic medium, amino (-NH2) group of
amino acid will accept proton from the
medium and become positively charged.
• H2N-R-COOH [H+] +H3N-R-COOH
(α-amino acid)
• Hence during electrophoresis of amino acid
solution in acidic medium, the solution will
move towards negative electrode.](https://image.slidesharecdn.com/colloidalstate-210212112806/75/Colloidal-state-11-2048.jpg)
![• In alkaline medium, -COOH group of amino
acid will loose proton to the medium and
become negatively charged.
• H2N-R-COOH [OH-] H2N-R-COO-
(α-amino acid) -H2O
• Hence during electrophoresis of amino acid
solution in alkaline medium, the solution will
move towards positive electrode.](https://image.slidesharecdn.com/colloidalstate-210212112806/75/Colloidal-state-12-2048.jpg)
![• At intermediate pH a solution of amino acid will
contain dipole ions having +ive charge at one
end and –ive charge at other end i.e
+H3N-R-COO-
+H3N-R-COOH [H+] H2N-R-COOH [OH-] H2N-R-COO-
(+ Charged ion) (α-amino acid) (- charged ion)
Acidic medium Alkaline medium
(intermediate pH)
+H3N-R-COO-
(dipole ion)](https://image.slidesharecdn.com/colloidalstate-210212112806/75/Colloidal-state-13-2048.jpg)
![According to chemical thermodynamic at equilibrium, the chemical
potential of NaCl on both side of the membrane must be same. The
chemical potential µ is given by the equation
µ = µo + RTlna ------------(1)
here µo is the standard chemical potential and ‘a’ is the activity of the
chemical species.
Therefore µ NaCl (I) = µ NaCl (II)
µo + RTlna NaCl (I) = µo + RTlna NaCl (II)
a NaCl (I) = a NaCl (II)
a Na
+
(I) . aCl
-
(I) = a Na
+
(II) . aCl
-
(II) --------- (2)
For dilute solutions, the activities ‘a’ can be replaced by molar
concentration. Therefore eq. (2) will be
[Na+
(I)] . [Cl-
(I)] = [Na+
(II)] . [Cl-
(II)]
(C1-X) . (C1-X) = (C2+X) . (X)
C1
2-2C1X +X2 = C2X +X2
C1
2 = C2X + 2C1X
C1
2 = X(C2 + 2C1)
C1 . C1 = X(C2 + 2C1)](https://image.slidesharecdn.com/colloidalstate-210212112806/75/Colloidal-state-48-2048.jpg)
More Related Content
Colloidal state
- 1. Colloidal State Dr. PravinU. Singare Department of Chemistry, N.M. Institute of Science, Bhavan’s College, Andheri (West)
- 2. Crystalloids • size <10-7 cm in diameter. • solution of crystalloids is called True solution. • Particles can easily pass through the membrane. • Solution of crystalloids have particles having both + ive and – ive charges. • eg: NaCl salt solution in water Colloids • size between 10-5 to 10-7 cm in diameter. • solution of colloids is called colloidal solution (Sol). • particles can not pass through the membrane. • colloidal solution with particles having either + ve or – ive charge. • Eg: gum, glue The solution having particle size above 10-5 cm is called suspension
- 3. Colloidal Solution (Sol) Colloidalsystem consists of - Dispersed phase - Dispersion medium • Dispersion medium: is the medium in which the colloidal particles are dispersed. • Dispersed phase : colloidal particles which are dispersed in dispersion medium form dispersed phase.
- 4. Classification of colloidalsolution (Sol) • Classification based on the dispersion medium Hydrosol: water is the dispersion medium Alcosol: alcohol is the dispersion medium Aerosol: air is the dispersion medium Benzosol: benzene is the dispersion medium • Classification based on affinity between dispersed phase and dispersion medium Lyophilic colloids Lyophobic colloids
- 5. Lyophilic Colloids • affinitybetween dispersed phase and dispersion medium is more. • Dispersed phase can not be easily coagulated and the coagulated dispersed phase can be easily brought back to the colloidal state. • Reversible colloids • More stable as compared to lyophobic colloids. • When water as a dispersion medium it is called hydrophilic colloids. • eg: gum, starch Lyophobic Colloids • affinity between dispersed phase and dispersion medium is less. • Dispersed phase can be easily coagulated and the coagulated dispersed phase can not be easily brought back to the colloidal state. • Irreversible colloids • Less stable as compared to lyophilic colloids. • When water as a dispersion medium it is called hydrophobic colloids. • eg: arsenic sulphide sol, antimony sulphide sol
- 6. Origin of chargeon the colloidal particles • Self dissociation • Nature of dispersion medium • Preferential adsorption
- 7. Self dissociation • Thisphenomenon can be explained by using solution of soap in water as the dispersion medium. The soap is the sodium or potassium salt of long chain fatty acid which dissociate in water to give ions R-COONa R-COO- + Na+ R-COO- ions have affinity for each other hence they will aggregate with each other to form micelles of colloidal size (colloidal micelles).
- 8. • The micellesare formed in such a way that the alkyl group having more affinity for each other will come close while the negative charge will point in outward direction. • As a result the colloidal solution of soap will develop negative charge on the surface. • Different micelles will keep away from each other due to repulsion between the like charges.
- 9. R COO - R COO - R COO- -OOC R Colloidalsoap micelles having negative charge
- 10. Nature of dispersionmedium • Depending on the dispersion medium, the colloidal particles will get acquire on the surface. • This can be explained taking example of proteins which are formed from amino acids will get acquire charge in acidic and alkaline medium.
- 11. • In acidicmedium, amino (-NH2) group of amino acid will accept proton from the medium and become positively charged. • H2N-R-COOH [H+] +H3N-R-COOH (α-amino acid) • Hence during electrophoresis of amino acid solution in acidic medium, the solution will move towards negative electrode.
- 12. • In alkalinemedium, -COOH group of amino acid will loose proton to the medium and become negatively charged. • H2N-R-COOH [OH-] H2N-R-COO- (α-amino acid) -H2O • Hence during electrophoresis of amino acid solution in alkaline medium, the solution will move towards positive electrode.
- 13. • At intermediatepH a solution of amino acid will contain dipole ions having +ive charge at one end and –ive charge at other end i.e +H3N-R-COO- +H3N-R-COOH [H+] H2N-R-COOH [OH-] H2N-R-COO- (+ Charged ion) (α-amino acid) (- charged ion) Acidic medium Alkaline medium (intermediate pH) +H3N-R-COO- (dipole ion)
- 14. • This constitutean electrical neutral system and the solution will not show any movement under the influence of electric field. • Such dipole ions having positive charge at one end and negative charge at other end are called Zwitter Ions. • The pH at which dipole ions are formed, the system of colloidal solution will become neutral and does not show electrophoresis is called isoelectric point. • For example the isoelectric point of gelatin is 4.7 while that of haemoglobin is 7.0
- 15. Preferential adsorption • Adsorptionof the common ions from the dispersion medium on the surface of colloidal particles will results in existence of charge on the surface of colloidal particles. • Depending on the way of preparation of colloidal solution, either + iv or – ive ions from the dispersion medium will get adsorbed.
- 16. • For examplesilver iodide (AgI) sol is prepared by mixing excess of KI to dilute solution of AgNO3 . AgNO3 + KI AgI + KNO3 + K+ + I- • Due to added excess of KI, the solution will contain K+ and I- ions. • The AgI sol thus formed will adsorb I- ions (common ions) on the surface. • The AgI sol will acquire – ive charge.
- 17. AgI -I I- -I -I -I -I I- -I Fig. 1. Negativelycharged AgI sol
- 18. • Alternatively ifsilver iodide (AgI) sol is prepared by mixing excess of AgNO3 to dilute solution of KI. AgNO3 + KI AgI + KNO3 + Ag+ + NO3 - • Due to added excess of AgNO3, the solution will contain Ag+ and NO3 - ions. • The AgI sol thus formed will adsorb Ag+ ions (common ions) on the surface. • The AgI sol will acquire + ive charge.
- 19. AgI Ag+ Ag+ +Ag +Ag Ag+ +Ag Ag+ +Ag Fig. 2. Positivelycharged AgI sol
- 20. • Similarly arsenicsulphide (As2S3) sol possesses – ive charge due to preferential adsorption of sulphide (S2- ) ions (common ions) arising due to passage of excess of H2S gas. 2AsCl3 + 3H2S As2S3 + 6HCl + H+ + S2- (arsenic trichloride)
- 21. Colloidal Electrolyte • Colloidalelectrolyte are long chain high molecular hydrocarbons which undergoes ionisation in polar solvent to form ions. • For example C17H35COONa (Sodium Stearate) C17H35COONa C17H35COO- + Na+ • At low concentration of sodium sterate (colloidal electrolyte), the solution contain simple long chain stearate ions (C17H35COO- Na-)
- 22. • As theconcentration is increased, the stearate ions will aggregate together to form micelle of colloidal size. • The ions will aggregate in such a way that lyophobic hydrocarbon end will attract each other and will be away from the solution while lyophilic end will be directed towards the solution. • Thus micelle is an organised aggregate of colloidal electrolyte molecules.
- 23. • The concentrationat which the micelles appear is called Critical Micellization Concentration (CMC). R COO - R COO - R COO- -OOC R Here R = C17H35
- 24. Concentration Equivalent conductance A B C’ C CMC Fig. 3. Variationof electrical conductivity with the concentration of colloidal electrolyte
- 25. •Below CMC thestearate ions exist in the solution as simple stearate ions C17H35COO- . •As a result the conductivity of solution increases linearly with square root of concentration which is represented by straight line AB in the graph (Fig. 3). •At CMC the stearate ions get associated into micelles of size sufficient to be classified as colloids. •As a result, at CMC the break appears in the curve (Fig.3). •Under high voltage current, the curve rises from B to C’ (Fig.3) indicating the rise in conductance due to formation of highly conducting stearate ion micelles.
- 26. • While underlow voltage current the fall in conductance is observed from B to C as shown in the graph (Fig.3). • The fall in conductance at low voltage current is due to the formation of ionic atmosphere surrounding the stearate ion micelles (Fig.4).
- 27. Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Cathode Anode - - - - - - - - - Stearateion micelle (C17H35COO-) Fig.4. Na+ ion atmosphere surrounding the stearate ion micelle
- 28. Helmholtz & Stern’sConcept of Electrical Double Layer • According to this concept the solid colloidal particle when brought in contact with polar dispersion medium will acquire charge on its surface. • The charge which is developed on the surface of colloidal particle will influence the distribution of ions in the near by polar dispersion medium. • Generally the oppositely charged ions (counter ions) are attracted towards the surface and co-ions of like charge are repelled away from the surface into the bulk of dispersion medium.
- 29. Cl- H+ Cl- H+ H+ H+ H+ H+ S2- S2- S2- H+ Cl- Cl- H+ Cl- H+ H+ Cl- H+ H+ Cl- Cl- Cl- As2S3 Charge oncolloidal surface Oppositely charged counter ions Electrical Double Layer Diffused mobile Layer of mixed charges Dispersion medium 2AsCl3 + 3H2S As2S3 + Cl- + H+ (arsenic trichloride) A B C Fig.5.
- 30. • This leadsto the formation of an electrical double layer which consist of rigidly fixed layer of charge on the solid surface (here S2- ions)and nearby the surface (in the dispersion medium) there may be practically immobile layer of oppositely charged counter ions (here H+ ions) (Fig.5). •Further that in the bulk of dispersion medium there exist the diffused mobile layer of charges which may have sign same or opposite that on the adsorbed layer (here H+ and Cl- ions) (Fig.5).
- 31. • There exista difference of potential between fixed electrical double layer and diffused mobile layer of charges. This potential is called Zeta potential. • In the fig. 5. point A represent potential developed on the surface of solid. Point B represent potential developed in fixed part of double layer. Point C represent potential developed in the bulk of dispersion medium. • From the graph it is clear that fall of potential between A to B is always sharp, while the fall in potential from point B to C is gradual. This total fall in potential AC = AB + BC is called Zeta potential (ζ) which is the fall in potential between fixed electrical double layer and diffused mobile layer of charges (Fig.5). • If ‘d’ is the thickness of electrical double layer, ‘ϭ’ is the amount of charge /cm3, ‘D’ is the dielectric constant of the medium, the Zeta potential is given by the equation ζ = 4πϭd D
- 32. Electrokinetic Effect • Whenthe diffused mobile layer of mixed charges (formed in liquid dispersion medium) is separated from the fixed part of the double layer (formed on the solid surface) with the help of an electric field, some effects are observed at solid-liquid interface which is known as electrokinetic effect.
- 33. Electrophoresis • Due tothe presence of electrical charge on the colloidal particles, they migrate towards one of the electrode when the sol (solution of colloidal particles) is subjected to electric field. • This migration of colloidal particles (dispersed phase) under the influence of electric field towards proper electrode is called electrophoresis or cataphoresis.
- 34. + - Reservoir tube Electrode Sol Electrolyte Moving boundary •Theapparatus for electrophoresis is called Burton Tube which consist of a U- shaped tube fitted with a stopcock at the bottom (Fig.6). • A funnel shaped reservoir tube is attached to the back side of U-shaped tube. • A small quantity of suitable electrolyte having density less than that of sol is placed in the U-shaped tube. • The sol is then introduced in the U- shaped tube through the funnel shaped reservoir tube. •Since the electrolyte is lighter than sol, the added sol will displace the electrolyte upward forming the sharp boundary in the two arms of the U- shaped tube. Fig. 6. BURTON TUBE
- 35. • When theelectrodes are immersed in the electrolyte and are connected to the suitable source of potential, all colloidal particles will move towards one of the electrodes. • If the colloidal particles are negatively charged the boundary will rise towards positively charged electrode and fall on negative side of the electrode. • If colloidal particles are positively charged the reverse phenomenon is observed. • From the direction of movement of boundary it is possible to detect the rate at which the colloidal particles migrate in presence of electric field.
- 36. •This migration ofcolloidal particles in presence of electrical field is expressed in terms of electrophoretic mobility (µ) . • Electrophoretic mobility (µ) is defined as the distance travelled by the colloidal particles in one second under the potential gradient of 1 Volt/cm. • The electrophoretic mobility (µ) is related to Zeta potential (ζ) by the equation ζ = 4πµƞ D here ƞ is the viscosity of dispersion medium and D is the dielectric constant of dispersion medium
- 37. Application of Electrophoresis Sincethe different colloidal particles in a mixture migrate at different rates, the process of electrophoresis can be used for • Removal of dust and smoke particles present in the effluent gases. • Deposition of metal i.e. Electroplating. • Analysis of mixtures of proteins eg. Proteins of human blood like albumin, α- globulin, β-globulin have their characteristic electrophoretic mobilities.
- 38. Electro-osmosis • For negativelycharged colloidal particles, the dispersion medium will have positively charge, while for positive charge colloidal particles, the dispersion medium will have negative charge. • As a result if the colloidal particles are maintained stationary, the dispersion medium would move under the influence of electrical field. • This movement of dispersion medium under the influence of electrical field toward suitable electrode is called electro- osmosis.
- 39. z x y P1 P2 T1 T2 •Theapparatus for electro-osmosis consist of a vessel having capillary tubes T1 and T2 divided into three compartments (X, Y & Z) by using a porous partition membranes P1 and P2 (Fig.7). • The colloidal solution (sol) is placed in compartment X. • The compartments Y and Z are filled with the same dispersion medium as that of sol. • The porous partition membrane prevents electrophoresis but will allow the dispersion medium to pass through it. • As a result when the potential is applied between the electrodes placed near the membranes, the level of dispersion medium will found to rise in one arm of capillary tube while in the other arm of capillary tube the level of dispersion medium will fall. + - Fig.7 Electro-osmosis
- 40. • For positivelycharged colloidal particles, the dispersion medium would be negatively charged and hence the movement of dispersion medium will be from compartment Z to compartment Y(as in the figure 7) . • While for negatively charged colloidal particles, the dispersion medium would be positively charged and hence the movement of dispersion medium will be from compartment Y to compartment Z. • In both the cases the level of dispersion medium will fall in one arm of the capillary tube and will rise in other arm of the capillary tube. • This flow of dispersion medium under the influence of electric field is called electro-osmotic flow. • The pressure required to counter balance the electro-osmotic flow is called electro-osmotic pressure (P) which is related to Zeta potential (ζ) by the equation ζ = Pπr2 2DE Here P is the electro-osmotic pressure in N/m2; r is the radius of the capillary tube in cm; D is the dielectric constant of the medium; E is the applied potential in electrostatic unit
- 41. Streaming Potential • Itis a mechanical effect in which potential is developed due to movement of dispersion medium across the stationary dispersed phase (colloidal particles). • Streaming potential is exactly reverse of electro- osmosis. • In electro-osmosis flow of liquid dispersion medium take place due to potential applied, while in streaming potential, the potential is developed due to flow of liquid dispersion medium.
- 42. • When twocompatible Calomel electrode are kept on the two side of the porous partition membrane (Fig.7), the streaming potential (S) developed due to forced movement of liquid dispersion medium across the membrane can be measured. • The streaming potential (S) and Zeta potential (ζ) are related by the equation ζ = 4πƞkS PD here k is the specific conductance of a liquid dispersion medium, ƞ is the viscosity of dispersion medium, D is the dielectric constant of the medium and P is the pressure applied to cause the flow of liquid dispersion medium.
- 43. Sedimentation potential (DornEffect) • If a colloidal solution is kept undisturbed for a long time, the colloidal particles will tend to fall down (settle down) due to gravitational force. • The gravitational force will cause heavier particles to settle at relatively lower portion of the vessel while the lighter particles will settle at the top. • Such distribution is called sedimentation and the potential developed between the upper and lower layer is called sedimentation potential or Dorn effect.
- 44. • Sedimentation potentialis a mechanical effect in which the potential is developed due to movement of colloidal particles (dispersed phase) with respect to stationary dispersion medium. • Sedimentation potential is reverse of electrophoretic effect. • In electrophoresis the colloidal particles (dispersed phase) move due to potential applied, while in sedimentation potential, due to movement of colloidal particles (dispersed phase) the potential is developed.
- 45. Electrophoresis Sedimentation potential Electro- osmosis Streaming potential Type of effect Electricaleffect Mechanical effect Electrical effect Mechanical effect What is applied? Potential is applied Mechanical force Potential is applied Mechanical force What will move? Dispersed phase (colloidal particles) Dispersed phase (colloidal particles) Dispersion medium Dispersion medium What will remain stationary ? Dispersion medium Dispersion medium Dispersed phase (colloidal particles) Dispersed phase (colloidal particles) What is the result? Migration of dispersed phase Potential is developed Migration of dispersion medium Potential is developed
- 46. Donnan Membrane Equilibrium •TheDonnan membrane equilibrium arises when a salt solution containing large non diffusible ion is separated from a salt solution like NaCl containing diffusible ions by means of porous partition membrane. • At equilibrium, it is expected that the diffusible ion should get equally distributed on both side of the membrane. •However in practice the distribution is unequal. •This was shown by Donnan and hence named as Donnan membrane equilibrium.
- 47. • Consider NaClsolution of initial concentration C1 separated from the salt solution of NaR having initial concentration C2 by means of semipermeable membrane. • In NaR salt solution, R- is the large non diffusible ion. • When diffusion take place, consider X gm of Na+ and X gm of Cl- ions are diffused from LHS (compartment I) to RHS (compartment II). • As a result, at equilibrium conc. of Na+ and Cl- ions in LHS is decreased by X. Hence conc. of Na+ and Cl- ions in LHS will be (C1- X). • While at equilibrium, the conc. of Na+ and Cl- ions in RHS will increase by X. Hence conc. of Na+ ions in RHS which was C2 initially will now be (C2+X) and conc. of Cl- which was 0 initially will now be X. • Conc. of R- at equilibrium will be C2 which will remain same as that of initial concentration (remain unchanged). LHS (I) RHS (II) Initial Conc. Equilbrium Conc. Na+ Cl- Na+ Cl- R - C1 C1 C2 C2 0 (C1 - X)(C1 – X) (C2 + X) C2 X Semipermiable membrane
- 48. According to chemicalthermodynamic at equilibrium, the chemical potential of NaCl on both side of the membrane must be same. The chemical potential µ is given by the equation µ = µo + RTlna ------------(1) here µo is the standard chemical potential and ‘a’ is the activity of the chemical species. Therefore µ NaCl (I) = µ NaCl (II) µo + RTlna NaCl (I) = µo + RTlna NaCl (II) a NaCl (I) = a NaCl (II) a Na + (I) . aCl - (I) = a Na + (II) . aCl - (II) --------- (2) For dilute solutions, the activities ‘a’ can be replaced by molar concentration. Therefore eq. (2) will be [Na+ (I)] . [Cl- (I)] = [Na+ (II)] . [Cl- (II)] (C1-X) . (C1-X) = (C2+X) . (X) C1 2-2C1X +X2 = C2X +X2 C1 2 = C2X + 2C1X C1 2 = X(C2 + 2C1) C1 . C1 = X(C2 + 2C1)
- 49. C1 = X--------------(3) (C2 + 2C1) C1 The term X/C1 in eq.(3) indicates the fraction of NaCl that diffuses across the membrane from LHS to RHS. If the concentration of NaCl to be equal on both side of the membrane, it is necessary that X/C1 should be 1/2. From eq. (3) X/C1 will be 1/2 only if concentration C2 of non- diffusible (R-) ion = 0. But the concentration C2 of non-diffusible (R-) ion = 0 is not possible. Hence equal concentration (i.e. equal distribution) of diffusible salt on both side of the membrane is also not possible. This is due to the presence of non-diffusible (R-) ion on other side of the membrane. Thus it can be said that in presence of non-diffusible (R-) ion on other side of the membrane, the distribution of diffusible ions across the membrane is also affected.
- 50. • This effectof non-diffusible ions can be minimised when C1 >>>> C2 i.e. by taking the concentration of diffusible ions (C1) much greater than the C2 which is the concentration of non-diffusible (R-) ion. Under such conditions when C1 >>>> C2, the concentration of C2 will be negligible small in comparison to C1 and hence eq.(3) will be reduced to C1 = X (2C1) C1 1 = X 2 C1
- 51. Emulsions • The colloidalsolutions in which both the dispersed phase and dispersion medium are immiscible liquids are called emulsions. • Emulsions are classified in to two types Oil in Water (O/W) type emulsions Water in Oil (W/O) type of emulsions
- 52. • Oil inWater (O/W) type of emulsions means the dispersed phase is oil while dispersion medium is water. • Water is the continuous phase while oil is the discontinuous phase. • Eg. Milk
- 53. • Water inOil (W/O) type of emulsions means the dispersed phase is water while dispersion medium is oil. • Oil is the continuous phase while Water is the discontinuous phase. • Eg. Cold creams
- 54. water Oil W/O Type (Stable emulsion) O/WType (Stable emulsion) (Unstable emulsion) • The emulsion which consist of Oil dispersed in Water or Water dispersed in Oil are unstable because both the emulsions will soon separate in two layers (Upper Oil layer and lower water layer). • Therefore a third substance called emulsifier or emulsifying agent is added to stabilise an emulsion.
- 55. • A longchain organic compounds with polar functional groups for eg. Soap will work as a good emulsifying agent. •Such emulsifier get adsorbed at the interface between the dispersed droplets and dispersion medium in the form of mono-molecular layer in such a way that polar end (hydrophilic end) of emulsifier will dip in Water while the hydrocarbon chain being hydrophobic will dip in Oil. •It results in bringing of two liquids (Oil & Water) in intimate contact with each other, thereby reducing the surface tension and stable emulsion is obtained.
- 56. Surfactants • Surfactants arethe substance which when added to the solvent reduces the surface tension at the solution interface. • The surface tension decreases because the concentration of the solute at the surface of a liquid is more than in the bulk of the solution. • So surfactants are also called surface active agents.
- 57. • According toGibb’s adsorption equation = - C . dγ RT dC Here S is the excess of concentration of solute/cm2 of the surface as compared to that in the bulk of solution. C is the equilibrium concentration of solute = rate of change of surface tension with concentration R is the molar gas constant T is the temperature in kelvin. dγ dC S
- 58. Case l • Ifby addition of solute to a solvent, the surface tension of the solution decreases i.e. dγ/dC in the above equation becomes – ive, then in such case, S becomes + ive indicating higher concentration of solute at the surface than that in the bulk of solution. Such solutes are called surface active agents or surfactants. Case ll • If by addition of solute to a solvent, the surface tension of the solution increases i.e. dγ/dC in the above equation becomes + ive, then in such case, S becomes - ive indicating decrease in concentration of solute at the surface than that in the bulk of solution. Such solutes are called surface inactive agents. S = - C . dγ RT dC
- 59. • Surfactants aredivided in to three classes 1. Anionic surfactants: eg. Sodium cetyl sulphate C16H33SO4 -Na+ in which the surface activity is due to the anions. 2. Cationic surfactants: eg. Cetyl trimethyl ammonium bromide C16H33N(CH3)3 +Br- in which the surface activity is due to the cations. 3. Non-ionogenic surfactants: eg. Cetyl polyglycol ether C16H33(OCH2-CH2)n-OH whose molecules can not undergo dissociation.
- 60. Surfactants used indetergents, pesticides and food industries (Industrial application of surfactants) For industries manufacturing food products, detergents and pesticides formulations, the products manufactured are generally a mixture of water and water insoluble compounds like fats, proteins, grease and toxic chemicals. To such product mixture, low concentration of added surfactants will change the surface properties of the liquid. Hence the surfactants find a wide range of applications in such industries.
- 61. • Surfactants whenused in detergents will help to improve wetting of cloth fibres and spreading of detergents. • It will also help to produce and control foam formation and modify the viscosity. • Many manufactured food are in the state of emulsion or have been in emulsified state during manufacturing. Eg.: butter and butter cream (W/O type of emulsion), ice cream, milk (O/W type of emulsion). • For such food emulsions, small quantity of surfactants are used as a emulsifying agent where they help to improve the shelf storage of food products by promoting the air retention properties of food mixture.
- 62. • For anoil soluble pesticides, oil in water emulsions are widely used which helps in getting oil soluble pesticides in a water mixture. • This helps in the active pesticide ingredients being applied as a water spray. • Surfactants when added to such oil in water pesticide emulsions will improve the emulsifying, spreading and wetting properties of pesticides. • Thus small amount of pesticides can be applied on the larger surface with almost the same effect as that of applying larger amount of pesticides.