Wetting Of Powders

Question 0

What does wetting depend on?

Answer 0

Surface properties of powder and vehicle

Question 1

What does wetting precede?

Answer 1

Dissolution or dispersion of a powder,granule or tablet

Question 2

What is the boundary of two phases called?

Answer 2

Interface

Question 3

What is interfaces of gas/liquids?

Answer 3

Water and air , bubbles

Question 4

What is the interface of gas/solids?

Answer 4

Table top

Question 5

What is the interface of liquid/liquid?

Answer 5

Immiscible solvents, emulsion

Question 6

What is the interface of liquid/solid?

Answer 6

Water drop on table, suspension

Question 7

What is the interface of solid/solid?

Answer 7

Powder particles in contact

Question 8

What are gas/liquid and gas/solid interfaces also called?

Answer 8

Surface

Question 9

By which bonds are molecules in the bulk of each phase attracted to each other by equally in all directions?

Answer 9

Hydrogen bonding in water, London forced in oil

Question 10

What are forces like at the boundary?

Answer 10

Unequal

Question 11

What is the spontaneous movement of liquids?

Answer 11

Form the interface into the bulk

Question 12

What does imbalance lead to?

Answer 12

Tension

Question 13

What is interfacial tension?

Answer 13

The energy per unit area (force per unit distance) at the surface between phases

Question 14

What is interfacial tension commonly expressed in?

Answer 14

milli-Newtons/meter

Question 15

What is surface tension?

Answer 15

Energy required to create a unit area of surface: surface free energy / unit area = surface tension

Question 16

What liquids have higher surface tension?

Answer 16

Liquids with higher intermolecular attraction have higher surface tension: polar liquids

Question 17

What are high energy solids?

Answer 17

Metals and salts

Question 18

What is the problems with solid surfaces?

Answer 18

More complex:
Lack of mobility of molecules
Direct measurement of surface energy impossible
Exposure of different crystal faces

Question 19

What is sprinkled on water float on solid/liquid interface?

Answer 19

Talcum powder

Question 20

What must occur before immersion (wetting)?

Answer 20

Liquid must displace air and spread over the surface of the solid

Question 21

What is wettability?

Answer 21

The tendency of one liquid to spread on or adhere to a solid surface

Question 22

What does wettability refer to?

Answer 22

Interaction between liquid and solid phases

Question 23

What is the contact angle?

Answer 23

Ten angle made by the liquid with a solid surface

Question 24

What is the degree of the angle when wetting is complete?

Answer 24

0

Question 25

What can the degree of the angle increase to in non-wetting situation?

Answer 25

189 spherical droplet

Question 26

What do factors reducing slid-liquid and liquid air interfaces favour?

Answer 26

Wettability- non-polar liquids have better wettability

Question 27

What does the greater the value of solid-air mean?

Answer 27

The greater the chance for wetting (high energy solids)

Question 28

What is the contact angle of a nonwettable solid on a liquid surface?

Answer 28

> 90

Question 29

How can wettability be improved?

Answer 29

Reducing the surface tension of liquids (surfactants)

Use low surface tension liquids (addition of co-solvents)

Question 30

What can surfactants do?

Answer 30

Lowers the liquid-air interfaces

Absorbs to powder surface and reduce solid-liquid interfaces