8/11/2019 Disperse System
1/35
PR 1102 Physical Pharmacy
Kang [email protected]
Disperse System
8/11/2019 Disperse System
2/35
Disperse System
Dispersed phase
Continuous phase
Interface
8/11/2019 Disperse System
3/35
Disperse System
Disperse systems consist of particulate matter(dispersed phase) distributed throughout acontinuous medium
Dispersed material ranges in size, from moleculardimensions to particles of millimeters
Many biological drugs that have been discovered aremacromolecules that exist in colloidal systems (e.g.
proteins and DNA). Nanoparticulate systems are also emerging for
improved drug delivery.
8/11/2019 Disperse System
4/35
Classification by State
a Continuous phase
Gas Liquid Solid
D i s p e r s e
d p
h a s e
Gas Nil Foam Solid foam
Liquid Liquid aerosol Emulsion Gel
Solid Sold aerosol Suspension Solid sol
http://www.naturalhealthlibrarian.com/images/asprin.gifhttp://nickobeano.files.wordpress.com/2008/01/cheese_oh_cheese.jpghttp://www.universalws.com/images/topcare%20calamine%20lotion%20(Small).JPGhttp://www.medgadget.com/archives/img/Exubera.jpghttp://www.dollychar.com/blog/wp-content/uploads/2009/01/dettol-173x300.jpghttp://www.firstpr.com.au/show-and-tell/green-ants/DSC00286-beach-foam-rainbow-colours-trippier.jpg8/11/2019 Disperse System
5/35
8/11/2019 Disperse System
6/35
Dispersion Stability
8/11/2019 Disperse System
7/35
8/11/2019 Disperse System
8/35
Brownian Motion
Spontaneous, irregular zig-zag movement ofparticles because of random collisions withmolecules .
t -time D-diffusion coefficient; r-averagedisplacement
8/11/2019 Disperse System
9/35
Reynolds Number
Re vr r is the radius of a sphere v is the velocity of the sphere is the density of the liquid is the viscosity of the liquid Reynolds number measures the relative
importance of inertia and viscosity For particles on a colloidal scale, Re is small
http://en.wikipedia.org/wiki/File:Stokes_sphere.svg8/11/2019 Disperse System
10/35
Stokess Law
6d F rv r is the radius of a sphere v is the velocity of the sphere is the viscosity of the liquid F d is the drag force Stokes law is derived from the Navier Stokes
equations for small Reynolds numbers.
http://en.wikipedia.org/wiki/File:Stokes_sphere.svg8/11/2019 Disperse System
11/35
Einsteins Relation
k B is the Boltzmanns constant D is the diffusion coefficient T is the temperature k drag is the drag coefficient
B
drag
k T D k
8/11/2019 Disperse System
12/35
Stokes-Einstein Equation
If we know the diffusion coefficient D, thenthe size of the particle can be estimated bythe Stokes-Einstein equation .
B
drag
k T D
k
6d drag F rv k v
6 Bk T D
r
8/11/2019 Disperse System
13/35
Rate of Sedimentation
To calculate v when the gravitational anddrag forces are balanced
Smaller particles and higher viscosities give
smaller sedimentation rate
3 3 34 4 4
3 3 3 g solid Liquid F r g r g r g
3463
rv r g
6d F rv
22
9
r g v
http://en.wikipedia.org/wiki/File:Stokes_sphere.svg8/11/2019 Disperse System
14/35
One Example: Suppositories
Suppository bases include cocoa butter,glycerinated gelatin, hydrogenated vegetableoils, polyethylene glycols
Cocoa butter melt to incorporate fine particlesand then cool in molds. It is a colloid-coarsedisperse system and particles may sediment
Copper sulphate suppository preparationprocess: Grind coarse powders, melt base andincorporate the find powders
http://www.detronizator.org/wp-content/uploads/2007/09/buttercocoadeo.jpg8/11/2019 Disperse System
15/35
Interactions Between Particles
Inter-particle forces DLVO theory Zeta potential
Dispersed phase interactions
8/11/2019 Disperse System
16/35
DLVO Theory Deryagin-Landau and Verwey-Overbeck The stability of a particle in solution depends on
its total potential energy function
8/11/2019 Disperse System
17/35
8/11/2019 Disperse System
18/35
Van der Waals Attractive Forces
212 A A
V d A is a constant and d is the particle separation
distance. If a repulsion mechanism does not
exist then flocculation will eventually takeplace.
8/11/2019 Disperse System
19/35
Electrostatic Repulsive Forces V R2
2 kd
RV r e
r is the particle radius, k is a function of theionic composition and is the zeta potential
8/11/2019 Disperse System
20/35
Colloid Stability Mechanism
8/11/2019 Disperse System
21/35
To Increase Repulsive Forces V R Steric repulsion - this involves polymers added
to the system adsorbing onto the particlesurface and preventing the particle surfaces
coming into close contact and at thoseseparations the van der Waals forces are tooweak to cause the particles to adhere
Electrostatic or charge stabilization - this is theeffect on particle interaction due to thedistribution of charged species in the system
8/11/2019 Disperse System
22/35
Charged Particle and Zeta Potential
Stern layer
Negatively charged particle
8/11/2019 Disperse System
23/35
Diffuse Layer
Diffuse layer
8/11/2019 Disperse System
24/35
Slipping Plane
Hydrodynamic planeof shear (slippingplane)
8/11/2019 Disperse System
25/35
8/11/2019 Disperse System
26/35
Zeta Potential
The zeta potential is the electrical potential atthe hydrodynamic plane of shear
It depends not only on the particle surface but
also on the dispersant It can be affected by small changes in the pH
or ionic strength of the medium Particles interact according the magnitude of
the zeta potential, not their surface charge Therefore, it can be used to predict stability
8/11/2019 Disperse System
27/35
Significance of Zeta Potential
If all the particles have a large negative orpositive zeta potential they will repel eachother and there is dispersion stability
If the particles have low zeta potential valuesthen there is no force to prevent particlescoming together and there is dispersion
instability The dividing line of stable and instable zeta
potential is +30 mV or -30mV
8/11/2019 Disperse System
28/35
Factors Affecting Zeta Potential
Changes in the pH of the sample The conductivity of the medium
(concentration and type of salt)
8/11/2019 Disperse System
29/35
pH Effects on Bovine Serum Albumin(BSA) Zeta Potential
Stable
Stable
Unstable
Z e t a P o t e n t i a
l ( m
V )
pH
The rule of thumb of stability +/- 30 mV.
8/11/2019 Disperse System
30/35
Conductivity Effects on BSA Zeta Potential
Z e t a P o t e n t i a
l ( m V
)
Concentration (Log(mol/l)
8/11/2019 Disperse System
31/35
An Example of Liposome
Plasmids Cationic liposome
Plasmid - cationic liposome complex
8/11/2019 Disperse System
32/35
Liposome Complex Zeta-potential
Molar ratio of Plasmid and liposome
Z e t a P o t e n t i a
l ( m V
)
P a r t i c
l e d i a m
e t e r ( n m
)
8/11/2019 Disperse System
33/35
PEG-coated Liposome
PEG Liposome complex
Liposome Polyethylene glycol (PEG)
8/11/2019 Disperse System
34/35
Z e t a P o t e n t i a
l ( m V
)
Ratio of PEG2000
PEG-coated Liposome Zeta-potential
8/11/2019 Disperse System
35/35
If an electric field is applied across a sample,charged particles suspended in the mdeiumare attracted towards the electrode ofopposite charge
The particles move with a velocity dependson: (i)Field strength, (ii) dielectric constant ofmedium and (iii) viscosity of the medium and(iv) zeta potential.
Parameters (i)-(iii) are know, so zeta potentialcan be determined
Measure Zeta-potential
Top Related