FINAL 01 - Interfacial Phenomena and Coarse Dispersion Flashcards
When phases exist together, the boundary between two of them is known as __________
Interfaces
The term __________ is used when referring to either a gas-solid or a gas-liquid interface
Surface
Is the force per unit length existing at the interface between two immiscible liquid phases
Interfacial tension
2 surface and interfacial tensions unit
dynes/cm, N/m
Is the difference between the work of adhesion and the work of cohesion
Spreading coefficient
Is the energy required to break the attraction between the unlike molecules
Work of adhesion
Is the energy required to separate the molecules of spreading liquid so that it can flow over the sublayer
Work of cohesion
The ability of the micells to increase the solubility of materials that are normally insoluble, or only slightly soluble, in the dispersion medium used
Solubilization
A thermodynamically unstable system containing two immiscible liquid phases stabilized by emulsifying agent
Emulsion
Type of emulsion used mainly for internal/oral use as bitter or disagreeable taste and odor of drugs can be masked by emulsification
Oil-in-water (o/w)
Type of emulsion where the oil is the continuous phase
Water-in-oil (w/O)
Type of emulsion which involves colloidal systems consisting of vesicle forming phospholipids and water
Liposome formulations
Type of emulsion which involves colloidal systems consisting of vesicle forming phospholipids, surfactants, and lipids dispersed in water
Nanoemulsions
Type of emulsion which involves a colloidal semi-liquid o/w or w/o emulsion systems consisting of a complex mixture of lipo- and hydrophilic surfactants and water
Microemulsions
Are amphiphilic compounds; stabilizer of the droplet form of the internal phase
Emulsifier
Are adsorbed at oil-water interfaces to form mononuclear films and reduce interfacial tension
Surface-active agents
Form a multi-molecular film around the dispersed droplets of oil in an o/w emulsion
Hydrophilic colloids
Are adsorbed at the interface between two immiscible liquid phases and form what amounts to a film of particles around the dispersed globules
Finely divided solid particles
Theory of emulsification that states that surface-active agents or amphiphiles, reduce interfacial
tension because of their adsorption at the oil-water interface to
form monomolecular films
Monomolecular adsorption
Are surface active agents (oil-water interface); differ from synthetic surface active agents
Hydrated lyophilic colloids
Theory of emulsification that states that finely divided solid particles that are wetted to some degree by both oil and water can act as emulsifying agents
Solid-particle adsorption
2 types of adsorption
Physical adsorption, Chemical adsorption
Type of adsorption where a physically adsorbed gas can be desorbed from a solid by increasing the temperature and reducing the pressure
Physical adsorption
Type of adsorption where the adsorbate is attached to the adsorbent by primary chemical bonds
Chemical adsorption
The removal of the adsorbate from the adsorbent
Desorption
The relationship between the amount of gas physically adsorbed on a solid and the equilibrium pressure pressure or concentration at constant temperature yields an __________ when plotted
Adsorption isotherm
Is the angle between a liquid droplet and the surface over which it spreads
Contact angle
Is a surfactant that, when dissolved in water, lowers the advancing contact angle
Wetting agent
The adsorbed ions that give the surface its positive charge are referred to as the __________
Potential-determining ions
The ions, having a charge opposite to that of the potential-determining ions, are known as __________ or __________
Counterions, Gegenions
Is the surface of the solid
aa’
The limit of the region of tightly bound solvent molecules, together with some negative ions, also tightly bound to the surface
bb’
Is defined as the difference in potential between the actual surface and the electroneutral region of the solution
Nernst and Zeta potentials
The potential at the solid surface aa’ due to the potential-determining ion is the __________
Electrothermodynamic (Nernst) potential (E)
The potential located at the shear plane (bb’)
Electrokinetic (Zeta) potential (ζ)
Is defined as the difference in potential between the surface of the tightly bound layer and the electroneutral region of the solution
Zeta potential
A course dispersion in which insoluble solid particles are dispersed in a liquid medium
Suspension
Are particles in a suspension that are weakly bonded, settle rapidly, do not form a cake, and are easily resuspended
Flocculated particles
Are particles in a suspension that settle slowly and eventually form a sediment in which aggregation occurs
Deflocculated particles
Is the ratio of the sedimentation volume of the flocculated suspension to the sedimentation volume of the suspension when deflocculated
Degree of flocculation (β)
Acts as flocculating agents by reducing the electric barrier between the particles
Electrolytes
Added to retard sedimentation of the flocs
Suspending agents
