Colloidal Dispersions 2 Flashcards Preview

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Flashcards in Colloidal Dispersions 2 Deck (29)
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1
Q

Kinetic properties of Colloids

A
Kinetic properties – those related to the particle motion of colloidal systems 
Kinetic properties of colloids – 
Brownian motion
Diffusion
Viscosity
Sedimentation
Osmotic pressure
2
Q

Brownian Motion

A

Brownian motion is the erratic motion of colloid particles (under microscope or ultramicroscopy)
Brownian motion is the result from the bombardment (collision) of the particles in the disperse medium
The velocity of the particles increases with decreasing particle size
Increasing the viscosity of the medium (e.g. by adding glycerin), decreases and finally stops the Brownianmovement

3
Q

Diffusion

A

Colloidal particle diffusion obey Fick’s first law: from high concentration to low concentration until the concentration of the system is uniform throughout
Colloidal particle diffusion is the direct results of Brownian movement
three main rules of diffusion:
(a) the velocity of the molecules increases with decreasing particle size;
(b) the velocity of the molecules increases with increasing temperature;
(c) the velocity of the molecules decreases with increasing viscosity of the medium.

4
Q

Osmotic Pressure

A

Use van Hoff equation

see slide 8

5
Q

Sedimentation Rate

A

Sedimentation of colloidal particles is slow
Stokes’ sedimentation equation (the same as suspension)

When d is too small ( gravity; lower size limit of particles obeying Stokes’s equation
Ultracentrifuge
useful for determining the molecular weight of polymers (proteins) and degree of homogeneity of the sample

6
Q

Viscosity

A

Viscosity is an expression of the resistance to flow of a system under an applied stress.
Viscosity is related to volume fraction

 = 0(1 + 2.5 )

 : apparent viscosity of the colloid
0: viscosity of dispersion media
 : volume fraction (V internal / V total)
0 and η can be determined using a capillary viscometer
Applicable for diluted dispersion of spherical particle

Viscosity of colloids is also affected by shape of the particles (e.g. Spherocolloids relatively low viscosity, whereas linear particles are more viscous

7
Q

Electrical properties of interfaces

A

Particles dispersed in liquid media may become charged;
Selective adsorption of a particular ionic species
Ionization of groups at the surface of the particles
Charges that arise from a difference in dielectric constants between particle and medium

8
Q

Electrokinetic phenomena

A

The movement of a charged surface with respect to an adjacent liquid phase (provide method s to obtain the zeta potential
Electrophoresis: movement of a charged particle by f an applied potential through a liquid
Electro-osmosis; opposite of electrophoresis( liquid moves relative to the charged surface
Sedimentation potential, the reverse of electrophoresis; creation of a potential when particles undergo sedimentation.
Streaming potential differs from electro-osmosisin; create the potential by forcing a liquid to flow through a bed of particles

9
Q

Stability of Colloid systems

A

Stabilization of colloids are accomplished by:
Provide the dispersed particles with an electric charge
Surrounding each particle with a protective solvent sheath that prevent mutual adhesion.
Stability of
Lyophobic colloids
Lyophilic colloids

10
Q

Stability of Lyophobic Colloid

A

Thermodynamically unstable
Stability of lyophobic colloids is mainly controlled by particle surface charge
Addition of electrolyte affects the stability of the system significantly
Lowering zeta potential below its critical value, and consequently lowering primary maximum – DLVO theory
Too much electrolytes may lead to irreversible aggregation (coagulation) of lyophobic colloids (which is very sensitive)

11
Q

DVLO theory of colloid stability

A

DLVO theory describes the stability of lyophobic colloids.
The forces on colloidal particles in dispersion are due to
Electrostatic repulsion (VR)
London-type van der Waal’s attraction (VA)
Therefore the total energy potential:

VT = VR + VA

Plot total potential (VT) vs. distance (H) –

12
Q

DVLO theory

A

Primary maximum (Potential repulsion barrier)
Lowering primary maximum may lead to irreversible aggregation of Lyophobic colloids
Primary minimum (attraction)
If primary maximum is smaller than thermo energy, particles can reach the primary minimum region, and coagulation occurs
Secondary minimum (attraction)
Secondary minimum is very important in controlled flocculation of coarse dispersions

13
Q

Stability of Lyophilic Colloid

A

Lyophilic colloids are usually thermodynamically stable
Stability of lyophilic colloids is related to particle charge, but not very sensitive to electrolyte changes
Addition of electrolyte in moderate amount– generally stable
Stability is mainly controlled by protective solvent sheath
Salt out: coagulate by high concentration of electrolytes: due to the desolvation by electrolytes ions
Organic solvents, such as alcohol and acetone, can also decrease the stability of hydrophilic colloids and cause coagulate. It destabilized the lyophilic nature of the colloidal interface.
Mixing oppositely charged hydrophilic colloids may leads to coacervation. e.g. gelatin(+) - acacia(-)

14
Q

Protection vs Sensitization

A

Protection: adding large amount of hydrophilic colloids to a hydrophobic colloids (as protective colloids) to stabilize hydrophobic colloidal system

Sensitization: adding a small amount of oppositely charged colloid to a hydrophobic colloid to sensitize or coagulate the particles.
Reduction of zeta potential
Reduction of ionic layer

15
Q

Aggregation

A

(a general term): collection of particles into groups

16
Q

Coagulation

A

closely aggregated and difficult to re-disperse

17
Q

Coacervation

A

separation of a colloid rich layer (coacervate) from a lyophilic colloid.

One application of coacervation – Microencapsulation: an application of coacervation to coating small particles by adding them in an colloid in which contains polymers that coacervate and aggregate at the interface.

18
Q

Pharmaceutical application of colloids

A

Colloids are extensively used for modifying the properties of pharmaceutical agents
Optimize solubility by solubilization
Colloidal forms of many drugs (nanopharmaceuticals) exhibits different properties when compared with traditional dosage forms
Drug delivery systems
Drug targeting by size

19
Q

Colloid based dosage forms and DDS

A
Gels (hydrogels) 
Micelles
Liposome 
Microemulsion & nanoemulsions
Microparticle
Nanoparticle 
Nanocrystals
Biopharmaceuticals (macromolecules)
20
Q

Advantages and disadvantages of microemulsions

A

Advantages and applications for drug delivery:
Solubilize drugs
Rapid and efficient oral absorption of drugs: big surface area of droplets
Enhanced transdermal drug delivery: increased drug diffusion into the skin
Drug targeting: in the targeting of cytotoxic drugs to cancer cells
Engineering of artificial red blood cells
Disadvantage:
Require suitable surfactant, need high surfactant %
Difficult to formulate a stable microemulsion

21
Q

ME on the market

A

Cyclosporin microemulsion: oral delivery
mono-di-triglycerides, polyoxyl 40 hydrogenated castor oil, propylene glycol, ethanol, DL-α- tocopherol USP

Silicone microemulsions: hair conditioner

22
Q

Liposomes

A
Vesicles formed by bilayers of phospholipids enclosing a central aqueous compartment
Unilamellar or multilamellar
Size varies from 50nm to
 few micrometers
uni or muiltilamellar
Uses: subcutaneous, 
intramuscular, topical, iv (size!)

Unilamellar liposomes: single phospholipid bilayer
Multilamellar liposomes: onion structure

23
Q

Advantages of liposomes

A

Composed of biocompatible materials

Relatively easy to prepare

24
Q

Components of Liposomes

A

Phospholipids: phosphatidylcholine (lecithin)
Cholesterol
Surfactants (such as taurodeoxycholate)

Modulation of carrier-cell/tissue interaction
charge: cationic lipids (such as phosphatidylethanolamine)
Mucoadhesive: chitosan, monoolein, carbopol

Functionalization: “decorated” liposomes
Long circulation
Active targeting: antibodies, ligands for endocytosis (folic acid)

25
Q

Limitations of Liposomes

A

Stability
Cost of phospholipids

On the market:
Liposomal Vitamin C
Liposomal amphotericin B (antifungal)
Liposomal doxorubicin

26
Q

DOXIL (Janssen)

A

Doxorubicin hydrochloride

  • Stealth liposomes
  • Red fluid administered via intravenous (IV)
27
Q

Nanoparticles

A
Polymeric nanoparticles (10-1000 nm)
Nanocapsules
Nanospheres
Composed of synthetic or semi-synthetic biodegradable, biocompatible polymers
Solid lipid nanoparticles
exchange the liquid lipid (oil) of the emulsions by a solid lipid
 Other types
Hydrogel nanoparticles
Ceramic nanoparticles
…
28
Q

Loading drug for delivery

A

The drug of interest is entrapped, dissolved, dispersed, or adsorbed or attached into the particle matrix or surface.
Control/ modify drug release
Use of biodegradable polymers for implants
Uses: intramuscular, subcutaneous, topical, oral
Functionalize: modification of surface

29
Q

From colloidal chemistry to nanotech

A
Scale of Nanotech: 1-100 nm
Advanced tools of Nanotech:
Fabrication
Detection and characterization
Diversity of Nanotech
Top-down approach 
Bottom-up approach 
E.g. 
http://pubs.rsc.org/en/content/articlelanding/2011/cp/c0cp02549f#!divAbstract
Trend of integrative engineering
Biology and Toxicology of  Nanotech
Application to Drug Development…