Surface and interfacial phenomena Flashcards
What do surfaces and interfaces affect?
- It affects the dissolution of drugs (i,e total surface area and wetting and spreading)
- It affects the absorption of many drugs (i.e dissolution and property biomembrane)
What is interface?
It is the boundary between two phases e.g oil and water
What is meant by a surface?
when one of the phases is gas/vapour eg surface of a cup of water. A surface is a special type of interface
The downward force is the origin of surface tension. TRUE OR FALSE/
TRUE
What is surface tension?
It is a horizontal force acting along the surface
After work is done to a system, the energy level of the system is lower. TRUE OR FALSE?
FALSE
When is a system more stable?
When its energy level is lower
Work can be converted into energy and vice versa. TRUE OR FALSE?
TRUE
Surface tension can be expressed as force per unit length of film. TRUE OR FALSE?
TRUE
Surface tension can be expressed as surface energy per unit area of film. TRUE OR FALSE?
TRUE
What is the equation for surface energy?
Surface tension * surface area
What is the equation for force?
Surface tension * Length
The larger the surface area, the higher the surface energy. TRUE OR FALSE?
TRUE
The higher the surface tension, the lower the surface energy. TRUE OR FALSE?
FALSE
What is the equation for surface tension?
ST = energy/Unit area
Surface tension is the free energy per unit area of the surface. TRUE OR FALSE?
TRUE
Do solids have surface tension/interfecial tensions? Give example
YES e.g solid/air, solid/liquid
The pressure inside a bubble is higher than atmospheric pressure outside. TRUE OR FALSE?
TRUE
What is work adhesion?
Is the work required to separate the two phases at their interface
What is work of cohesion?
Is work required to produce two new surfaces between the like molecules
The larger the work of adhesion the stronger the attraction between the unlike surfaces. TRUE OR FALSE?
TRUE
The larger the work of cohesion, the weaker the attraction between the like molecules. TRUE OR FALSE?
FALSE
Work of adhesion is an indication of the attractive strength between unlike surfaces. TRUE OR FALSE?
TRUE
Work of cohesion is an indication of the attractive strength between like surfaces. TRUE OR FALSE?
TRUE
When does spreading occur?
It occurs if Spreading coefficient is greater than equals to 0 or when work of adhesion is greater than equal to work of cohesion.
what is spreading coefficient calculated from?
Work of adhesion and cohesion
With small contact angle, liquid/solid will spread. TRUE OR FALSE?
TRUE
Contact angle is not affected by pressure. TRUE OR FALSE?
FALSE
What are amphiphiles?
Both lipophilic and hydrophobic
What are micelles?
Micelles are lipid molecules that arrange themselves in a spherical form in aqueous solutions. The formation of a micelle is a response to the amphipathic nature of fatty acids, meaning that they contain both hydrophilic regions (polar head groups) as well as hydrophobic regions (the long hydrophobic chain).
What are the factors that affect adsorption?
- Concentration of solute
- Temperature - increased temp will increase adsorption
- Surface area / increase in porosity will increases surface area
- pH depending on species whether ionised or unionised
