1. Chapter 17 Colloidal Dispersions

2. Contents 1. Introduction 2. Types of Colliodal System
3. Optical Properties of Colloids
4. Kinetic Properties of Colloids
5. Electric Properties of Colloids
6. Solubilization

3. Dispersed Systems Dispersed system
consists of particulate matter, known as the
dispersed phase, distributed throughout
a continuous or dispersion medium.
Molecular dispersions
Colloidal dispersions
Coarse dispersions

4. Classification of Dispersed Systems
Particle size
Examples
Molecular dispersion
Colloidal dispersion
Coarse dispersion
< 1.0 nm
1.0 nm ~0.5m
> 0.5 m
Sugar solution
Oxygen molecules
Colloidal silver sol
Natural gum
Emulsions and suspensions
Red blood cells
Sol : 분산매가 액체인 Colloids
cf) Gel : Colloids입자 사이 가교에 의하여 고형화된 것

5. Colloids Macrohomogeneous but microheterogeneous Systems
cf. Crystalloids (정질)
Macrohomogeneous but microheterogeneous Systems
Do not pass semipermeable membrane
Diffuse very slowly
Visible in electron microscope
High specific surface area
Dialysis

6. Pharmaceutical Applications of Colloids
Surface Area
Dissolution rate
Absorption
Therapeutic effects
Ex)
Colloidal silver chloride, silver iodide, silver protein
Colloidal sulfur
Colloidal copper
Active carbon

7. Types of Colloidal Systems
Lyophilic (solvent-loving) Colloids
Lyophobic (solvent-hating) Colloids
Association Colloids
On the basis of the interaction of the particles, molecules, or ions of the dispersed phase with the molecules of the dispersion medium

8. Lyophilic Colloids “Hydrophilic colloids” “Lipophilic colloids”
; obtained simply by dissolving the material in the solvent being used
“Hydrophilic colloids”
“Lipophilic colloids”
Solvation
attraction between the dispersed phase and the dispersion medium
“Hydration”

9. Lyophobic Colloids (1) Dispersion method (2) Condensation method
; prepared by special methods
(1) Dispersion method
High-intensity-ultrasonic generator
Electric arc
Colloid mill
(2) Condensation method
Initial super-saturation followed by the formation and growth of nuclei
Chemical reaction – reduction, oxidation, hydrolysis, etc.

10. Association Colloids “Surfactant” “cmc” “Micelles”
Spherical micelle in aq. Media
Reversed micelle I non-aq. Media
Laminar micelle

11. Properties of surfactant at the cmc

12. Optical Properties of Colloids
Faraday-Tyndall Effect
Electron microscope
Light scattering

13. Kinetic Properties of Colloids
Brownian motion
Diffusion
Osmotic pressure
Sedimentation
Viscosity

14. Electrical Properties of Colloids
Zeta potential
Electrokinetic phenomena
Electrophoresis
Electroosmosis
Sedimentation potential
Streaming potential

15. Zeta potential measurement
Principle of zeta potential measurement showing
the ultramicroscope and the flow cell

16. Zeta potential measurement (2)
Smoluchowski EQ
ζ= 𝜈 𝐸 × 4𝜋𝜂 𝜀 ×(9× 10 4 )
ζ≅150 𝜈 𝐸
150 ν E  
medium: water
: Zeta potential, volt
ν : velocity of migration of the sol, cm/sec
 : the viscosity of medium, poise
 : the dielectric constant of medium, no dimension
E : the potential gradient, volt/cm
: mobility, cm2/secvolt
𝝂 𝑬

17. Stability of Colloid Systems
Schulze-Hardy rule
arrange ions in the order of their capacity
to coagulate hydrophobic colloids
Hofmeister or Lyotropic series
rank cations and anions in order of coagulation
of hydrophilic sols

18. Stability of Colloid Systems (2)
When negatively and positively charged hydrophilic colloids are mixed,
the particle may separate from the dispersion to form a layer rich in the
colloidal aggregates
Coacervate
colloid-rich layer
Coacervation
the phenomenon in which macromolecular solutions
separate into two liquid layers

19. Protective Colloidal Action
The addition of large amount of hydrophile (hydrophilic colloid) stabilized
the system, the hydrophile being adsorbed on the hydrophobic particles
Protection/Protective colloid
added hydrophile sol “protective colloid”
Gold number
The minimum weight in mg of the protective colloid
(dry weight of dispersed phase) required to prevent
a color change from red to violet in 10 mL of
a gold sol on the addition of 1 mL of a 10%
solution of sodium chloride.

20. DLVO Theory ; Lyophobic colloids stability Repulsion
(Derjaguin-Landam-Verwey-Overbeek)
; Lyophobic colloids stability
Repulsion
Secondary minimum (attraction)
Primary minimum (attraction)
Potential energy versus interparticle distance in suspension

21. Solubilization “Surfactant” “cmc” “Micelles”
Spherical micelle in aq. Media
Reversed micelle I non-aq. Media
Laminar micelle

22. A spherical micelle of nonionic surfactant molecules
A nonpolar molecule solubilized in the nonpolar region of the micelle
A more polar molecule found partly embedded in the center region and
partially extending into the palisade region
C. A polar molecule found lying well out in the palisade layer attracted by
polar forces to the polyoxyethylene chains

23. Micelle of n-PEG monoether
Schematic of nonionic micelle of n-polyoxyethylene glycol monoether
showing the intrusion of polyoxyethylene chains into the micelle core.
Micelle with palisade environment intact. (b) palisade layer partially
destroyed by loss of polyoxyethylene groups into the hydrophobic core.

24. Kraft & Cloud Points Kraft point : 계면활성제의 용해도가 cmc와 같아지는 온도
혼탁되는 온도
- 온도 증가에 따라 탈수(분자)에 따라 용해도 감소

25. Pharmaceutical Applications of Colloids
Hydrogels
Microparticles
Emulsions and Microemulsions
Liposomes
Micelles
Nanoparticles
Nanocrystals