| Thousand of years ago, the Eqyptions and Chinese used naturally occurring polymers to stabilize colloidal dispersions. They mixed carbon black and a polymeric stabilizer (e.g. gum arabic or egg albumin) and then dried the mixture into a pen-like shape. When they needed ink, they dipped the "pen" into water. The carbon black was redispersed immediately to form the ink. In fact, the polymer formed a protective sheath around the colloidal particles to prevent their aggregation. Today, stabilization of colloidal dispersions is widely applied in the paint, electronics, ceramics, oil recovery, food, waste treatment and pharmaceutical science. In pharmaceutical industry, aqueous colloidal dispersions are used as drug carriers and film-coating materials. In the film coating, the water-insoluble polymer is dispersed in an aqueous medium and sprayed onto tablets or beads. For a uniform film coat, the colloidal dispersion must be stable. In addition, aggregated particles may clot the spray nozzles causing trouble to the coating process or even interrupt the film formation process. |
| Stabilization of Aqueous Colloidal Dispersions-Basic Concept Zhion, Spring 2006 |
DISPERSION
When a solid is dispersed into colloidal-sized particles in a
continuous medium, the total interfacial area as well as the
"interfacial free energy" are increased. This system is very
thermodynamically unstable. Consequently, the colloidal particles
aggregate rapidly.
ELECTROSTATIC STABILIZATION
To stablize the system, a repulsive interaction among the colloidal
particles must be overcome the attractive force. The simpliest way to
obtain this repulsive interaction is through "charge repulsion" or
electrostatic stablization among the particles
STERIC STABILIZATION
Steric stabilization involves the adsorption of polymers onto the
particle surface to prevent particle aggregation.
Steric stabilization has several advantages over electrostatic
stabilization: (1) It is less sensative to the ionic strength of the
medium; (2) It alows a high solid content dispersion with low
viscosity; (3) It is equally effective in aqueous and nonaqueous
dispersion media. Consequently, steric stablization is widely used in
various industrial products such as paints, inks, pharmaceutical and
food dispersions.
CATASTROPHIC FLOCCULATION
A minimum thickness of the adsorbed layer is needed for steric
stabilization. Its thickness is strongly affected by the medium
solvency. A decrease in solvency for the stabilizing moieties will
cause a "catastrophic flocculation".
BRIDGING FLOCCULATION
Bridging flocculation is related to the adsorption of polymers to
particle surface, as what happens in steric stabilization. However,
the polymer here is so "big" that the polymer attaches to a few
particles simultaneously. In this situation, the polymer is a flocculant
instead of a stabilizer.
DEPLETION FLOCCULATION
When free, non-adsorbed polymer concentration increases and
reaches the critical flocculation concentration, a sudden change
such as an increase in viscosity in dispersion behavior occurs.
DEPLETION STABILIZATION
When the free, non-adsorbed polymer concentration continues to
increase to a concentration that the colloids redisperse or restabilize
again.
When a solid is dispersed into colloidal-sized particles in a
continuous medium, the total interfacial area as well as the
"interfacial free energy" are increased. This system is very
thermodynamically unstable. Consequently, the colloidal particles
aggregate rapidly.
ELECTROSTATIC STABILIZATION
To stablize the system, a repulsive interaction among the colloidal
particles must be overcome the attractive force. The simpliest way to
obtain this repulsive interaction is through "charge repulsion" or
electrostatic stablization among the particles
STERIC STABILIZATION
Steric stabilization involves the adsorption of polymers onto the
particle surface to prevent particle aggregation.
Steric stabilization has several advantages over electrostatic
stabilization: (1) It is less sensative to the ionic strength of the
medium; (2) It alows a high solid content dispersion with low
viscosity; (3) It is equally effective in aqueous and nonaqueous
dispersion media. Consequently, steric stablization is widely used in
various industrial products such as paints, inks, pharmaceutical and
food dispersions.
CATASTROPHIC FLOCCULATION
A minimum thickness of the adsorbed layer is needed for steric
stabilization. Its thickness is strongly affected by the medium
solvency. A decrease in solvency for the stabilizing moieties will
cause a "catastrophic flocculation".
BRIDGING FLOCCULATION
Bridging flocculation is related to the adsorption of polymers to
particle surface, as what happens in steric stabilization. However,
the polymer here is so "big" that the polymer attaches to a few
particles simultaneously. In this situation, the polymer is a flocculant
instead of a stabilizer.
DEPLETION FLOCCULATION
When free, non-adsorbed polymer concentration increases and
reaches the critical flocculation concentration, a sudden change
such as an increase in viscosity in dispersion behavior occurs.
DEPLETION STABILIZATION
When the free, non-adsorbed polymer concentration continues to
increase to a concentration that the colloids redisperse or restabilize
again.
PHARMCEUTICAL
INDUSTRY
Foundamental
Science
Colloidal
Stabilization
Drug Product
Development
Patent Application
Product
Development
Product
Ingredients
Colorant
Scale up a batch 1
Drug Delivery
Industry
Drug Delivery -
Smart Bomb
Lotion, Cream,
Preps
Enteric
Coating-Eudragit
Enteric
Coating-Nutrateric
SR
Coating-Aquacoat
Drug Industry
Drug
Competitions
Drug in
Development
Cholesterol-lowering
Drug-Terminologies
Packaging
Materials
Market
Drug Dev- 2004
Drug Dev -
2005Q1
Drug Dev- 2005Q2
Drug
Dev-2005Summer
Drug Dev-2005Q3
Orphan Drug
Protein Drug
Niche Market
Novo Norkdisk
R&D
Equipment
Blenders
CONTRACT
MANUFACT.
Nutrition
Supplements
NEW DRUGS
Arranon
Actoplus Met
Alfuzosin
Ambien CR
Avastin
Asmanex(R)
Erbitux
(cetuximab)
Gardasil
GRN163
Herceptin
Increlex (rhIGF-1)
Lidoerm
(Lidocaine)
Liraglutide
Lyrica (pregabalin)
Rozerem
Sorafenib
Sutent
Tamsulosin
Torcetrapib
Zometa
OLD DRUGS
Lithium Carbonate
DRUG NOTES
[CONSTRUCT]
Clinical Research
Terminologies
FDA ALERTS
Protein Drug
Market
Niche Market
Orphan Drug
levothyroxine
Protein Drug 1
Protein Drug2
Double-blind
Study
INDUSTRY
Foundamental
Science
Colloidal
Stabilization
Drug Product
Development
Patent Application
Product
Development
Product
Ingredients
Colorant
Scale up a batch 1
Drug Delivery
Industry
Drug Delivery -
Smart Bomb
Lotion, Cream,
Preps
Enteric
Coating-Eudragit
Enteric
Coating-Nutrateric
SR
Coating-Aquacoat
Drug Industry
Drug
Competitions
Drug in
Development
Cholesterol-lowering
Drug-Terminologies
Packaging
Materials
Market
Drug Dev- 2004
Drug Dev -
2005Q1
Drug Dev- 2005Q2
Drug
Dev-2005Summer
Drug Dev-2005Q3
Orphan Drug
Protein Drug
Niche Market
Novo Norkdisk
R&D
Equipment
Blenders
CONTRACT
MANUFACT.
Nutrition
Supplements
NEW DRUGS
Arranon
Actoplus Met
Alfuzosin
Ambien CR
Avastin
Asmanex(R)
Erbitux
(cetuximab)
Gardasil
GRN163
Herceptin
Increlex (rhIGF-1)
Lidoerm
(Lidocaine)
Liraglutide
Lyrica (pregabalin)
Rozerem
Sorafenib
Sutent
Tamsulosin
Torcetrapib
Zometa
OLD DRUGS
Lithium Carbonate
DRUG NOTES
[CONSTRUCT]
Clinical Research
Terminologies
FDA ALERTS
Protein Drug
Market
Niche Market
Orphan Drug
levothyroxine
Protein Drug 1
Protein Drug2
Double-blind
Study