https://www.slideshare.net/BasittiHitesh/high-entropy-alloys-86564927

1. It is the linear dimension and not the no. of atoms
or weight of the particles or the physical state or
chemical composition which defines the colloidal
state.

2. Thomas Graham was pioneer in the field of colloidal science. He first used the term colloids which is derived from the Greek
word Colla meaning glue.
• Colloids usually consist of two phases, dispersed phase (Particles of 1nm-1 mm) and dispersion medium (gas, liquid or
solid). The dispersion medium is called continuous and is usually in excess.
• Initially, it was thought that the special properties of colloids are due to chemical composition, but later on it was
revealed that the higher surface area causes such properties.

4. Size and shapes of Colloids
• Colloidal particles have size in the range of 1nm-1 mm.
• Particles are not always spherical and can have a variety of shapes.
• Many colloidal particles like Au or Ag are usually spherical, but others are not. Proteins are ellipsoids, while polymers are
mostly random coils.

5. Types of Dispersions

9. Model Particles
• Particles of well defined size, shape and surface properties are known as Model particles. People are very much
interested in studying these model particles rather than the complex formed particles.
• How do we get these model particles??

10. 1.)

11. 2.) Synthesize in Laboratory

12. 3.) Nanoprecipitation

13. Characterization of Colloidal Dispersions
Size and Shape: Electron and optical Microscopy, DLS, SLS

15. Origin of charge on the surface of colloids
There are various mechanisms by which there can be charge on the surface of colloidal particles.
1. Dissociation of surface groups:
The particles with surface functional gropus when added to water/solvent under standard
conditions, can lead to dissociation of surface groups/ protonation of the groups to yield
charged surfaces.
2.Addition of some charged species (Polymers/ surfactants, ions etc) to the colloidal dispersion.
(shown in next slide).

16. Origin of charge on the surface of colloids

17. Brownian motion
Brownian motion arises because of the collisions between the colloidal particles in the
fluids and the fluid molecules.
• Perrin (J.B.) in 1920’s studied the Brownian motion and noted the trajectories of the
particles that the particles followed upon bombardment by the solvent molecules.
• His work was instrumental in demonstrating the very existence of atoms, which he
achieved by careful selection of colloidal particles.
Perrin’s work involved nearly spherical particles having same size and shape.

18. Perrin’s Particles and experiment

19. Brownian motion

20. Because Perrin knew the position of the particles at any given instant of time, he could
calculate a quantity called as mean square displacement.
D is the diffusivity of the particles and d is the dimension (1,2,3) and t is time.
From his experiments, he could calculate mean square displacement and from this
diffusivity was calculated.
Then Stoke’s Einstein equation was used and various parameters were calculated.

21. Boltzman constant KB could be calculated and from it using KB = R/NA, Avogadro’s number
could be calculated. He could also calculate the mass of H- atom and charge on electron.

23. How to choose perfect particles

25. To choose correct particles, it is necessary to have

26. Forces acting on individual particles

27. Forces acting on individual particles

28. Forces acting on individual particles

30. Forces acting on individual particles

31. Molecular Interactions: Lennard Jones potential

34. Van der Waals Interactions

35. Three sub classes of Van der Waals Interactions

37. Permanent Dipole
• Permanent Dipole are found in molecules in which one of the atom is strongly
electronegative.
• Molecules which have similar symmetry like O2, CO2, methane etc. do not have a permanent
dipole
Induced Dipole
• Induced dipole can arise in a neutral atom or molecule, when an ion (with a charge) or a
molecule with permanent dipole approaches the neutral atom or molecule.
• This arises due to disturbance in electron clouds in the neutral atom/molecule by the
approach of the charged ion/ molecule, due to which the neutral atom/ molecule is polarized.

45. Emulsions
▪ Emulsions are defined as dispersed systems for which the phases are immiscible or partially miscible liquids.
▪ The emulsions are dispersions of one liquid (oil) in another, often water (w), and are thus typically classified as oil-in-
water or water-in-oil emulsions.
▪ They are relatively static systems with rather large droplets (diameter of about 1 μm). The word emulsion comes
from Latin and means “to milk”.
▪ Emulsions are typically highly unstable liquid–liquid systems which will eventually phase separate and require
emulsifiers, most often mixed surfactants (or other substances, e.g. synthetic polymers or proteins).
In milk, the emulsifier is the protein casein
Figure 12.1 Casein is the protein that has the function of emulsifier in milk. Without the casein (milk’s “natural polymer”), the milk would be
destabilized, since the fat globules, via coagulation or coalescence, would result in destruction of the colloidal dispersion.

46. Emulsions are colloidal systems and, thus, are unstable. They require surfactants (large amounts in the case of microemulsions) to
reduce the interfacial tension and achieve stabilization. The work, W, required to make an emulsion is given by:
W = γΔA
where ΔA is the change in surface area and γ is the interfacial surface tension.
• Milk is not a homogenous white liquid, although it may look like one. However, the fact that it is not transparent
is an indication that milk is an emulsion, a “colloidal system”.
• It is actually a quite complicated mixture. If you look at milk under an electronic microscope, you will see that it contains
fat globules that are about a micrometre in diameter. Even smaller are the protein (casein) molecules between the fat
globules.
• Casein is the protein (“polymer”) of the milk.
• Finally, milk also contains a substantial amount of dissolved substances. Among these are lactose (a saccharide or sugar)
and many minerals. Milk powder consists mainly of proteins, lactose, the minerals in the milk and smaller amounts of fat:
much of the fat is largely removed by centrifugation and used for making butter.
• Many more food products are emulsions, e.g. mayonnaise.
• Without the casein (milk’s “natural polymer”), the milk would be destroyed, since the fat globules, through coagulation
or coalescence, would result in destruction of the colloidal dispersion. This does not happen (or actually it is being
delayed) since the adsorbed casein molecules provide stabilization when the fat globules collide with each other.
Milk

47. • Homogenized milk contains only about 3% fat (compared to almost 6% fat in raw milk) and offers good stability.
The droplets are much smaller (0.2–0.4 μm) than in the raw milk (4 μm) and contribute to the high stability due
simply to fewer particle encounters.
• Small droplets (about 1 μm) are also present in cream, which has about 40% fat, but the stability is relatively good.
Of course, we will observe “creaming” (phase separation) after a certain time.
• In the so-called homogenization process, milk is pushed through small, tapered tubes or pores. As the diameter
shrinks and the flow of milk remains constant, pressure builds up and fat globules break apart in the turbulence. The
higher the pressure, the smaller the particles.
• Mechanical shaking of cream makes the fat globules burst whereby the fat is released and butter can be formed. It
is the crystals in the fat globules that cut open the globules.

48. Ice cream

49. Destabilization of emulsions
• Emulsions are thermodynamically unstable. We cannot completely stop or avoid this process as the droplets collide;
▪ what is of course important is that the droplets do not adhere (stick) when they collide with each other.
▪ The emulsions can be destabilized in many different ways (Figure below): creaming, flocculation or coagulation, and
coalescence/ breaking
Creaming or sedimentation can be caused by density differences.
▪ Sometimes, many of the above phenomena are termed generally as aggregation. In the case of coalescence, the droplets
must encounter each other, they then lose their original shape; coalescence is an irreversible phenomenon that eventually
may lead to complete phase separation (breaking).
▪ On the other hand, flocculation and creaming are reversible. The number of individual droplets can actually be counted
experimentally using, for example, laser diffraction techniques and this is a way to “control” stability even if macroscopically.

50. ▪ Ostwald ripening is an observed phenomenon in suspensions or emulsions that describes the change of an inhomogeneous
structure over time. In other words, over time, small crystals or dispersed particles dissolve, and redeposit onto larger
crystals or dispersed particles.
▪ Ostwald ripening is generally found in water-in-oil emulsions, while flocculation is found in oil-in-water emulsions.
▪ This thermodynamically-driven spontaneous process occurs because larger particles are more energetically favoured than
smaller particles. This originates from the fact that molecules on the surface of a particle are energetically less stable than
those in the interior.
▪ Consider, for example, a crystal of atoms where each atom has six neighbours. The atoms will all be quite stable. Atoms on
the surface, however, are only bonded to five neighbours or fewer, which makes these surface atoms less stable. Large
particles are more energetically favourable because more atoms are bonded to six neighbours and fewer atoms are at the
unfavourable surface.
▪ According to the Kelvin equation, molecules on the surface of a small particle (energetically unfavourable) will tend to detach
from the particle and diffuse into the solution. When all small particles do this, the concentration of free atoms in solution is
increased. When the free atoms in solution are supersaturated, the free atoms have a tendency to condense on the surface
of larger particles. Therefore, all smaller particles shrink, while larger particles grow, and overall the average size will increase.
After an infinite amount of time, the entire population of particles will have become one, huge, spherical particle to minimize
the total surface area.
Ostwald ripening

51. Foams
• In short, a foam is a dispersion of a gas in a liquid prepared using a foaming agent, which in most cases consists of one or
more surfactants.
• The dimension (thickness) of the thin liquid films (so-called lamellae) present in foams fall, at least in the later part of the
foam lifetime, within the colloid regime, from approximately 1 nm to 1 μm. Therefore, a foam is a system with two
dimensions in the macroscopic size range and one dimension potentially in the colloidal range.
• Foams are industrially important in many end-use products and also quite often as an undesired side effect in various
processes. Dead plant material in seawater can also lead to excessive foaming.

52. • In Foams, gas is the dispersed phase and liquid is the continuous phase.

53. ▪ Foams (or foam solutions) can be prepared from two overall processes termed condensation and dispersion.
▪ In condensation (of a gas), foam is generated from a liquid supersaturated with a gas. A beer in a can is a typical example of
this. When the can is opened, the pressure is reduced and less gas (carbon dioxide) can be contained in the liquid and
therefore comes out as bubbles and produces foam. Heating can also be used as a method of gas release.
▪ When using the dispersion method, the gas is injected into the liquid in various ways (e.g. stirring of whipped cream) or
bubbling through a porous plug. Conventional stirring or mixing of a foaming liquid is another way of ensuring gas
entrainment and thereby foaming
Preparation of Foams

54. • If we start with the food industry, foams play an important part for both appearance and taste. Ordinary bread, as an example,
is a solid foam structure, whereas whipped cream is a foam according to the traditional understanding
• Froth flotation is a process for separating minerals from nonvaluable rock and dirt by taking advantage of differences in the
particle hydrophobicities and requires extensive use of surface active agents. Froth flotation involves the capture of
hydrophobic particles by air bubbles and transport of the bubble– particle aggregates to the liquid surface (the air–water
interface is considered to be one of the most hydrophobic surfaces known). The non-valuable materials sediment.
• Foams are typically very lightweight materials. The gas is often generated upon application and therefore a large volume of
foam can be formed from a small volume of liquid. This is useful for transportation of, for example, fire-fighting foams, where
a foam concentrate, consisting of surfactants and various additives, is used.
• A “foam blanket” for firefighting is used to cool the fire and prevent contact with oxygen and flammable or toxic vapours.
Many different types of foam blankets are available for different types of fires. To form a foam blanket, a foam concentrate
and water, in combination with conventional air-aspirating or non-aspirating fire-fighting equipment, are needed. Foams with
a high water content work best because the water helps in removing heat from the system.
• Foams are also used in cosmetic, detergent and personal care products such as shaving cream, shampoo and bubble bath.
Foams are convenient to use for quick application of a lotion to the skin and are very useful for delivering pharmaceuticals to
sensitive parts of the human body.
• Powder puffs, used by girls to apply powders to the face, can also be foams. Foam structures are also present in construction
materials such as polymeric or mineral wool insulation materials and concrete.
Application of Foams

58. Anionic (~ 60% of industrial surfactants)
• Carboxylic acids and their salts including various fatty
acids tall oil acids, and hydrolyzed proteins:
• Sulfonic acids and their salts, including hydrocarbon
backbones of alkylbenzene, benzene, naphthalene, toluene,
phenolm lingin, olefins, diphenyloxide, petroleum cuts,
succinate esters etc.
• Sulfuric acid or salts including sulfated primary alcohols,
sulfated polyxyalkylenated alcohols etc.
• Alkyl xanthic acids:
• Alkyl or aryl dithiophosporic acids:
R C O- M+
O
R S O- M+
O
O
R O C
O
S- M+
• Polymeric anionics involving repeated groups containing
carboxyl acid functionality:
R S O- M+
O
O
P
S
S- M+
O
O
R
R
C
O
O- M+
R
n
Anionic surfactants

59. Cationic (~ 10% of industrial surfactants)
• Long chain amines derived from animal and
vegetable acids, tall oil and synthetic amines:
R NH2
• Diamines and polyamines including ether amines
and imidazolines:
R' NH2
HN
R
• Quaternary ammonium salts including tertiary mines and
imidazolines: N+ R' M-
H
R
R"
• Quaternized and unquartenized polyoxyalkylenated
long chain amines:
N+ R' M-
H
R'''
R"
R
O
R''''
n
N O
R'
R
R"
• Amine oxides derived from tertiary amines oxidized with
hydrogen peroxide:
Cationic Surfactants

60. Non-ionic (~ 25% of industrial surfactants)
• Polyoxyethylenated alcohols, alkyl phenols, alcohol
ethoxylates including derivatives from nonyl phenol,
coconut oil, tallow, and synthetic alcohols:
OH
R
O
R''''
n
• Polyoxyethylenated glycols: CH2
O
R'''' CH2 OH
n
• Polyoxypropylenated glycols:
CH2
O
R'''' CH OH
n
CH3
• Esters of carboxylic acids and alkyene oxides:
R C O R"
O
• Alkanolamine condensates with carboxylic acids:
R C NH R"
O
OH
• Polyoxyalkylenated mercaptans: O R
S
R' OH
n
Non-ionic surfactants

61. Amphoteric or zwitterionic:
(~ 10% of industrial surfactants). Generally expensive “specialty chemicals”.
R C O- M+
O
NH
R'
R C
O
H
N R'
R"
R" C
C O- M+
O- M+
O
O
R N+
R'
R'
R" C
O
O-M+
X-
R N+
R'
R'
R" S
O
O-M+
X-
O
R S R' NH2
• Acrylic acid derivatives with amine functionality:
• Subsituted alkylamides:
• n-Alkyl betaines:
• n-Alkyl suffobetaine:
• Thio alkyl amines and amides:
Zwitterionic Surfactants

64. Micelles (“Aggregation colloids”)
lyophilic and lyophobic parts combined in one molecule
reference state water: e.g. paraffin chain ions
water: high cohesive forces (hydrogen bonding) & high dielectric constant

65. • If concentration is sufficiently high, surfactants can form aggregates in aqueous
solution  micelles.
• Typically spheroidal particles of 2.5-6 nm diameter.
Micelles

73. Physical Property Change at CMC

75. This is because an increase in hydrophobicity reduces aqueous solubility of the surfactant and increases its partitioning into the
micelles. Micellar size increases with an increase in the hydrocarbon chain length, owing to an increase in the volume
occupied per surfactant in the micelle.

77. Stability of Micelles
• The thermodynamics of micelle formation shows that the enthalpy of
formation in aqueous systems is probably positive (that is they are
endothermic) with ∆H = 1 ~ 2 kJ per mole of surfactant. The micelles
do form above cmc indicates that the entropy change accompanying
their formation then must be positive and measurements suggest a
value of +140 JK-1mol-1 at room temperature.

78. The fact that the entropy is positive even though the molecules are
clustering together shows that there must be a contribution to the entropy
from the solvent and the solvent molecules must be more free to move once
the solute molecules are herded into small clusters. This interpretation is
plausible, because each individual solute molecules is held in an organized
solvent cage, but once the micelle is formed the solvent molecules need
form only a single (admittedly larger) cage. The increase in energy when
hydrophobic groups cluster together and reduce their structural demands on
the solvent is the origin of hydrophobic interactions that tends to stabilize
groupings of hydrophobic groups in biological macromolecules. The
hydrophobic interaction is an example of an ordering process that is
stabilized by a tendency toward greater disorder of the solvent.

79. Surfactant Phases