The document discusses the stability of colloids, specifically focusing on lyophobic colloids and the DLVO theory, which explains the forces acting on colloidal particles in a dispersion medium due to electrostatic repulsion and van der Waals attraction. It classifies colloids based on the nature of their interaction with solvent and explains how zeta potential affects stability in suspensions, highlighting concepts like deflocculated and flocculated suspensions. Additionally, the document references applications of DLVO theory in colloidal science and nanoparticle research.

1. Smt. B.N.B. Swaminarayan pharmacy college 1
STABILITY OF COLLOIDS
(LYOPHOBIC):DLVO THEORY
Name : Pratik B. Gondaliya
Utkarsh B. Kikani
Sem : 6th sem
College : Smt. B.N.B Swaminarayan
pharmacy college , Salvav.

2. Introduction
 Dispersion System:
The dispersion system consist of particulate matter (particles) known
as dispersed phase, distributed through out a continuous or
dispersion medium .
 According to mean diameter of particles in dispersion ,
It classify as:-
1. True solution / Molecular dispersion:-
- Size <0.01 μm
-Examples: Urea, Sucrose Solution,Oxygen gas
2. Colloidal dispersion:-
- Size: 1m-1 μm
-Examples: Acacia,Albumin, Insulin, Silver sols
3. Coarse Dispersion:-
- Size: 10-100 μm
-Examples:Calamine suspension, Magnesium oxide, RBCs
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3.  Colloidal dispersion:
colloidal system is define as those polyphesic system where
dimension of dispersed phase measures between 1nm to 1 μm.
 Characteristic of Dispersed phase:-
1. Particle size:
-influences the colour of dispersion
colloidal gold : red colour
coarse dispersion of gold : blue colour
2. Particle shape:
-Examples: sphericle particle of gold: red colour
disc like particle : blue colour
3. Surface area:
Has a higher surface area
4. Surface charge:
-colloidal particle posses charge on their surface
- Example: negative : acacia, sulphur, tragacanth
positive : gelatin (pH<4.7),Bismuth, Aluminium
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4. Classification :
1. Lyophillic colloids:
- Solvent loving
2. Lyophobic colloids:
- solvent hating
3. Association colloids:
-Amphiphilic in nature
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5. Stability of Colloids
1. Lyophilic colloids: 2. Lyophobic colloids:
 Thermodynamically stable
 Stabilize by
i. Providing electric charge
ii. Providing protective
sheath of solvent to each
particle
prevent adherence of
particle
 Thermodynamically
unstable
 Stabilize by
 only by providing electric
charge
 The Stability of lyophobic
colloids is explained by
DLVOTheory .
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6. DLVO Theory
 This theory is explain by Derjaguin , Landau ,
Verway , Overbeek So it is known as DLVO
Theory.
 According to this theory ,The forces on
colloidal particles in a dispersion medium are
due to –
1. Electrostatic Repulsion
2. London typeVander Waals Attraction
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7. Zeta Potential
 The potential difference across an electric
double layer usually between solid surface
and liquid.
 It should be optimum, increase or decrease in
zeta potential leads to instability in
suspension
 Range : -30 to +30 mV.
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8.  In this theory,When two particle close
together according to following condition :
1) Same charged particles – Repulsion
2) Opposite charged particles – Attraction
3) When two same charge particles are brought together
forcefully ( explain deflocculated suspension )
4) Effect of electrolytes on particles ( explain flocculated
suspension )
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Describe
instability

9. Potential Energy Curve
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10. 1. Same charge particles:
 When two same charge particle present in
suspension, initially positive energy (zeta
potential) is low ,
As distance between particle decrease
increase repulsive force increase zeta
potential So increase +ve energy as shown in
figure (repulsive curveVR).
 This increase in energy leads to sedimentation ,
hence leads to instability in suspension.
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11. 2. Opposite charge particles:
 When two opposite charged particles present in
suspension , initially energy (zeta potential) is
low.
 As, Distance between particles decrease
increase attractive force increase zeta
potential (-ve energy) as shown in figure
(Attraction curveVA) .
 This increase in –ve zeta potential /energy leads
to coagulation followed by sedimentation
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12. 3. Two same charge particle
brought together forcefully:
As we decrease distance between particle
increase potential energy
repulsion
But as we decrease forcefully (<0.5-2 nm)
The molecular orbital of each particle are bounded
with each other
The potential energy decrease as –ve energy leads to
attraction and form hard cake
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13.  This negative potential energy and attraction due merging of
molecular orbital of particles is known as Primary Minimum.
 Example: Hard cake formation deflocculated suspension.
Deflocculated suspension
Undisturbed long time so increase force on particle due to gravity
Particle may bound with each other as describe above
Aggregates forms
Leads to formation of hard cake
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14. 4. Effect of Electrolytes on
particles:
 Electrolyte like NaCl is added into suspension
 The +ve charged (Na+) absorbed on the particles.
 The –ve charged (Cl-) helps to form a weal bond between in
salt absorbed particles and form loosely arranged flocs.
 This causes slight decrease in negative potential energy , So
weak attractive force between the particles .
 So on agitation weakly bonded flocs easily break and
redispersed.
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15.  This slight decrease in negative potential energy
due to flocs formation is known as Secondary
Minimum.
 Example: Flocs formation in Flocculated suspension
Application:
- since 1940s DLVO theory has been used to explain
phenomena found in colloidal science, adsorption
etc.
- nanoparticle research:
DLVO theory used to explain behaviour of both
material nanoparticle (like fullerene particle) and
micro organisms.
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16. References:
1. “Physical Pharmacy - Physical Chemical
Principles InThe Pharmaceutical Science “
by Alfred Martin , James Swarbrick , Arthur
Cammarata ,3rd edition ,Varghese
Publishing House , Page no. 486
2. “Leon Lachman / Liberman’s –TheTheory
And Practice of Industrial Pharmacy “ By
Roop K Khar , S.Vyas , 4th Edition – 2013 ,
CBS Publisher And Disributors , Page no.
660
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