Surface and interfacial phenomena

Question 1

What do surfaces and interfaces affect?

Answer 1

• 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)

Question 2

What is interface?

Answer 2

It is the boundary between two phases e.g oil and water

Question 3

What is meant by a surface?

Answer 3

when one of the phases is gas/vapour eg surface of a cup of water. A surface is a special type of interface

Question 4

The downward force is the origin of surface tension. TRUE OR FALSE/

Answer 4

TRUE

Question 5

What is surface tension?

Answer 5

It is a horizontal force acting along the surface

Question 6

After work is done to a system, the energy level of the system is lower. TRUE OR FALSE?

Answer 6

FALSE

Question 7

When is a system more stable?

Answer 7

When its energy level is lower

Question 8

Work can be converted into energy and vice versa. TRUE OR FALSE?

Answer 8

TRUE

Question 9

Surface tension can be expressed as force per unit length of film. TRUE OR FALSE?

Answer 9

TRUE

Question 10

Surface tension can be expressed as surface energy per unit area of film. TRUE OR FALSE?

Answer 10

TRUE

Question 11

What is the equation for surface energy?

Answer 11

Surface tension * surface area

Question 12

What is the equation for force?

Answer 12

Surface tension * Length

Question 13

The larger the surface area, the higher the surface energy. TRUE OR FALSE?

Answer 13

TRUE

Question 14

The higher the surface tension, the lower the surface energy. TRUE OR FALSE?

Answer 14

FALSE

Question 15

What is the equation for surface tension?

Answer 15

ST = energy/Unit area

Question 16

Surface tension is the free energy per unit area of the surface. TRUE OR FALSE?

Answer 16

TRUE

Question 17

Do solids have surface tension/interfecial tensions? Give example

Answer 17

YES e.g solid/air, solid/liquid

Question 18

The pressure inside a bubble is higher than atmospheric pressure outside. TRUE OR FALSE?

Answer 18

TRUE

Question 19

What is work adhesion?

Answer 19

Is the work required to separate the two phases at their interface

Question 20

What is work of cohesion?

Answer 20

Is work required to produce two new surfaces between the like molecules

Question 21

The larger the work of adhesion the stronger the attraction between the unlike surfaces. TRUE OR FALSE?

Answer 21

TRUE

Question 22

The larger the work of cohesion, the weaker the attraction between the like molecules. TRUE OR FALSE?

Answer 22

FALSE

Question 23

Work of adhesion is an indication of the attractive strength between unlike surfaces. TRUE OR FALSE?

Answer 23

TRUE

Question 24

Work of cohesion is an indication of the attractive strength between like surfaces. TRUE OR FALSE?

Answer 24

TRUE

Question 25

When does spreading occur?

Answer 25

It occurs if Spreading coefficient is greater than equals to 0 or when work of adhesion is greater than equal to work of cohesion.

Question 26

what is spreading coefficient calculated from?

Answer 26

Work of adhesion and cohesion

Question 27

With small contact angle, liquid/solid will spread. TRUE OR FALSE?

Answer 27

TRUE

Question 28

Contact angle is not affected by pressure. TRUE OR FALSE?

Answer 28

FALSE

Question 29

What are amphiphiles?

Answer 29

Both lipophilic and hydrophobic

Question 30

What are micelles?

Answer 30

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).

Question 31

What are the factors that affect adsorption?

Answer 31

- 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