HAZWA

Assalamualaikum and Salam sejahtera kepada semua:

HAZWA Group Members: 1) Mohamad Iswandi Bin Ishak 2) Aishah Bt Mohd Marsin 3) Nor Hanisah Bt Ismail 4) Nur Ain Bt Ab Rahman 5) Siti Zainun Bt Nasir

SLIDE PRESENTATION:- []

Group Presentation:

DLVO Theory By Mohamad Iswandi Ishak

DLVO theory suggests that the stabilityof a particle in solution is dependent upon its total potential energy function VT. This theory recognizes that VT is the balance of several competing contributions: VT = VA + VR + VS where VS is the potential energy due to the solvent, it usually only makes a marginal contribution to the total potential energy over the last few nanometers of separation. Much more important is the balance between VA and VR, these are the attractive and repulsive contributions. They potentially are much larger and operate over a much larger distance VA = -A/(12 π D2) where A is the Hamaker constant and D is the particle separation. The repulsive potential VR is a far more complex function. VR = 2 π ε a ξ2 exp(- κD) where a is the particle radius, π is the solvent permeability, κ is a function of the ionic composition and ξ is the zeta potential. DLVO theory suggests that the stability of a colloidal system is determined by the sum of these van der Waals attractive (VA) and electrical double layer repulsive (VR) forces that exist between particles as they approach each other due to the Brownian motion they are undergoing. This theory proposes that an energy barrier resulting from the repulsive force prevents two particles approaching one another and adhering together. But if the particles collide with sufficient energy to overcome that barrier, the attractive force will pull them into contact where they adhere strongly and irreversibly together. Therefore if the particles have a sufficiently high repulsion, the dispersion will resist flocculation and the colloidal system will be stable. However if a repulsion mechanisms does not exist then flocculation or coagulation will eventually take place.

In certain situations (e.g. in high salt concentrations), there is a possibility of a “secondary minimum” where a much weaker and potentially reversible adhesion between particles exists together. These weak flocs are sufficiently stable not to be broken up by Brownian motion, but may dissociate under an externally applied force such as vigorous agitation.

To be continue with other presenter......