What characteristics are ideal for suspensions (5)?
Pleasant taste and odor
Pourable and flowing in syringe
Resist microbial growth
Remains uniform after dispersion until dosed/no fast settling
Sediment should not form a cake
What three ideal characteristics should a lotion have?
Spread over surface but doesn’t run off
Dries quickly on skin and remains as an elastic film of drug
Good odor and color
How do particles dispersed in a suspension aquire charges?
Selective absorption of ions
Ionization of functional groups
A difference in the dielectric constant between the particle and its dispersion medium
Selective absorption of ions, ionization of a functional group and a difference between the dielectric constant of a particle and its medium are all ways that what occurs?
Dispersed particles acquire a charge
What is the electric double layer?
A tightly bound layer of ions and a second more diffuse layer around a charged particle in suspension
A tightly bound layer of ions followed by a second more diffuse layer of ions around a particle in a suspension is called what?
The electric double layer
What is the zeta potential (electro-kinetic potential)?
The difference in potential between the surface of the tightly bound layer of ions and the electroneutral region of the suspension.
The difference between the surface of the tightly bound layer of ions and the electro-neutral region of the suspension is called what?
The Zeta potential
What is the Nernst potential?
The potential difference between the surface of the solid in a suspension and the electro-neutral bulk
What is the potential between the surface of the solid in a suspension and the electro-neutral bulk called?
The Nernst potential
A low Zeta potential correlates with what suspension behavior?
Poor stability
Poor stability correlates with what relative Zeta potential?
Low Zeta potential
A high Zeta potential correlates with what suspension behavior?
Excellent stability
Excellent stability correlates with what relative Zeta potential?
High Zeta potential
A Zeta potential of 0 to ±5 has what stability behavior?
Rapid coagulation or flocculation
A Zeta potential of ±10 to ±30 has what stability behavior?
Incipient instability
A Zeta potential of ±30 to ±40 has what stability behavior?
Moderate stability
A Zeta potential of ±40 to ±60 has what stability behavior?
Good stability
A Zeta potential of more than ±61has what stability behavior?
Excellent stability
What Zeta potential correlates with Excellent Stability?
more than ±61
What Zeta potential correlates with Good stability?
±40 to ±60
What Zeta potential correlates with Moderate stability?
±30 to ±40
What Zeta potential correlates with Incipient instability?
±10 to ±30
What Zeta potential correlates with Rapid coagulation or flocculation?
0 to ±5
What are the units for the Zeta Potential?
mV
The ions that give a particle its charge in a disperse system are called what?
Charge-determining particles
According to Stoke’s equation, what ways can the velocity of sedimentation be reduced?
Decreasing particle size
Minimizing the difference in densities between the internal and external phases
Increasing the viscosity of the vehicle
Higher viscosity of the vehicle imparts slower sedimentation and higher___________?
Stability
What are the disadvantages of increasing the viscosity of the vehicle?