Wetting Of Powders Flashcards
What does wetting depend on?
Surface properties of powder and vehicle
What does wetting precede?
Dissolution or dispersion of a powder,granule or tablet
What is the boundary of two phases called?
Interface
What is interfaces of gas/liquids?
Water and air , bubbles
What is the interface of gas/solids?
Table top
What is the interface of liquid/liquid?
Immiscible solvents, emulsion
What is the interface of liquid/solid?
Water drop on table, suspension
What is the interface of solid/solid?
Powder particles in contact
What are gas/liquid and gas/solid interfaces also called?
Surface
By which bonds are molecules in the bulk of each phase attracted to each other by equally in all directions?
Hydrogen bonding in water, London forced in oil
What are forces like at the boundary?
Unequal
What is the spontaneous movement of liquids?
Form the interface into the bulk
What does imbalance lead to?
Tension
What is interfacial tension?
The energy per unit area (force per unit distance) at the surface between phases
What is interfacial tension commonly expressed in?
milli-Newtons/meter
What is surface tension?
Energy required to create a unit area of surface: surface free energy / unit area = surface tension
What liquids have higher surface tension?
Liquids with higher intermolecular attraction have higher surface tension: polar liquids
What are high energy solids?
Metals and salts
What is the problems with solid surfaces?
More complex:
Lack of mobility of molecules
Direct measurement of surface energy impossible
Exposure of different crystal faces
What is sprinkled on water float on solid/liquid interface?
Talcum powder
What must occur before immersion (wetting)?
Liquid must displace air and spread over the surface of the solid
What is wettability?
The tendency of one liquid to spread on or adhere to a solid surface
What does wettability refer to?
Interaction between liquid and solid phases
What is the contact angle?
Ten angle made by the liquid with a solid surface
What is the degree of the angle when wetting is complete?
0
What can the degree of the angle increase to in non-wetting situation?
189 spherical droplet
What do factors reducing slid-liquid and liquid air interfaces favour?
Wettability- non-polar liquids have better wettability
What does the greater the value of solid-air mean?
The greater the chance for wetting (high energy solids)
What is the contact angle of a nonwettable solid on a liquid surface?
> 90
How can wettability be improved?
Reducing the surface tension of liquids (surfactants)
Use low surface tension liquids (addition of co-solvents)
What can surfactants do?
Lowers the liquid-air interfaces
Absorbs to powder surface and reduce solid-liquid interfaces
