Rheology Flashcards
1
Q
What is Rheology?
A
- Science describing the deformation and flow properties of matter under stress
2
Q
What is Rheological Behaviour Influenced by?
A
- Strength of the interaction between layers (intermolecular bonding)
- Shape of the particles
- Size of the particles
- Molecular, colloidal or coarse
- Number of particles (concentration)
- When the hydrocarbon chain increases, viscosity increases
3
Q
Discuss the Relationship between viscosity and structure of Pure Liquids
A
- Small and consistent shape of molecules
- Viscosity increases as size of molecule increases
- Viscosity increases as interactions between molecules increase
4
Q
Discuss the Relationship between viscosity and structure of Solutions
A
- Solutes have a relatively compact and consistent shape
- Viscosity increases as size of solute molecule increases
5
Q
Discuss Flow Behaviour: Newtonian
A
- Nature of the interaction between layers consistent, irrespective of stress applied
- Constant relationship between shear stress and rate of shear
6
Q
Discuss Flow Behaviour: Non-Newtonian
A
- When stress is doubled, the rate of shear doesn’t double
- Viscosity changes with increased stress or rate of shear
7
Q
Discuss Flow Behaviour: Pseudoplastic
A
- Resistance of adjacent layers flowing over eachother decreases as stress is increased
- Dispersed particles align in the direction of the applied stress and slip/slide over eachother more easily
- Dispersed particles change their shape
- Reduced inter-particle bonding
- Viscosity decreases with increased stress
- ‘Shear Thinning’
8
Q
Discuss the Influence of Charge on the Shape of Polymers
A
- Low pH: little ionisation
- Polymer bunches up because of atomic attraction
- Intermediate pH: some ionisation to minus charges
- Polymer is somewhat extended
- High pH: most of the carboxyl groups are ionised to minus charges
- Polymer is fully extended and interacts with polar solvent
9
Q
Discuss Non-Newtonian Flow: Plastic (a.k.a. Bingham Bodies)
A
- At low stress, there is not gradient between layers
- Yield value apparent, being the stress required to initiate flow
- Often displayed by the same materials with pseudoplastic flow but:
- Greater interaction between layers
- More concentrated dispersons of polymers
- Folcculated systems
- Polymers with increased cross-linking
- Polymers of larger Mwts
10
Q
Discuss Non-Newtonian Flow: Dilatant
A
- As stress increases, there is a disproportionate decrease in gradient between layers
- Resistance to flow (viscosity) increases as stress increases
- ‘Shear Thickening’
11
Q
Discuss Non-Newtonian Flow: Time Dependent
A
- Original position of displaced particles not restored immediately
- Time to restore position depends on:
- Size of particle and resistance of solvent
- Complexity of original arrangement(s)
12
Q
Define Thixotropy
A
- Time it takes to get back to original system
13
Q
How is Viscosity Measured?
A
- Ostwald Viscometer
- Add liquid to A
- Draw liquid up to above B
- Record time for the level to move to C as liquid passes through capillary (D)
- Liquid of known viscosity and density used as calibration standard
- Value determined for C
14
Q
What are two Applications of Rheology to Pharmaceuticals?
A
- Mucomyst
- Opthalmic Solutions
15
Q
Discuss the Application of Rheology in Mucomyst
A
- Viscosity of pulmonary mucous depends on the level of mucoprotein and to a lesser extent DNA
- Mucoprotein is a polymer of CHO and protein
- EXtensively cross-linked by disulphife bonding
- Excessive production in patients with cystic fibrosis
- Mucolytic action related to nucleophilic attack of sulphydryl group on disulphide linkages in mucous
- Viscosity is lowered by reduced cross-linking
