rheology

Question 1

rheology

Answer 1

the study of the deformation and flow of matter

Question 2

stress

Answer 2

the force required (per unit area) that leads to deformation

Question 3

strain

Answer 3

the resulting deformation

Question 4

elasticity

Answer 4

if the material fully recovers when the stress is removed it is elastic

Question 5

compliance

Answer 5

the ease of deformation

Question 6

dynamic viscosity=

Answer 6

F/(dv/dr) = shearing stress/rate of shear

Question 7

viscosity

Answer 7

The viscosity of a fluid is the internal resistance
(or friction) involved in the relative motion of
one layer of molecules with respect to the next

Question 8

relationship between attractions and viscosity

Answer 8

strong attractions between liquids=high dynamic viscosity

weak attractions=low dynamic viscosity

Question 9

effect of temperature on dynamic viscosity

Answer 9

gases>^temp, ^interactions=increased contact-higher viscosity
liquids>^temp, decreased reactions=decreased contact-lower viscosity

Question 10

types of viscometers

Answer 10

Ostwald viscometer. ubbelhode viscometer

Question 11

different types of viscosity

Answer 11

specific, reduced, relative, intrinsic, apparent

Question 12

what can flow properties be characterised as

Answer 12

Newtonian or non-Newtonian

Question 13

4 different flow types

Answer 13

Newtonian, plastic, pseudo plastic, dilatant

Question 14

Newtonian

Answer 14

exhibited by many simple liquids and true solutions eg caster oil, water, chloroform

Question 15

plastic

Answer 15

will not start to floe until a stress corresponding to the lower yield value is applied, exhibited by some ointments, pastes and creams

Question 16

pseudo plastic

Answer 16

substance will start to flow immediately as a stress is applied.

Question 17

apparent viscosity effect on flow properties

Answer 17

Newtonian fluids= same apparent viscosity

non-Newtonian fluids= invariable changes in apparent viscosity

Question 18

rotational viscometers

Answer 18

concentric cylinder (‘cup and bob’)
sample is sheared in the space between the cup and the bob.
couette- cup rotates
Searle-bob rotates
the torque (stress) on the rotating bob required to maintain a constant speed (shear rate) of rotation against the viscous drag is measured

Question 19

rotational viscometers

Answer 19

geometry is of a flat circular plate with a wide-angled cone placed centrally above. the sample under test is placed in the gap between the cone and plate. continuous measurement of shear stress vs shear rate produces viscosity profile of sample/fluid/solution
continuous measurement of napp necessary to determine behaviour

Question 20

falling sphere viscometer

Answer 20

stokes law

Question 21

single point viscometer

Answer 21

only one viscosity an be measured at one point, can measure the viscosity of Newtonian fluids, usually as a quality control measure for non-Newtonian fluids

Question 22

thixotropy

Answer 22

‘to change by touch’ the presence of a hysteresis loop indicated that a breakdown in structure has occurred. the area within the loop may be used as a measure of the degree of this breakdown (usually recoverable)

Question 23

pharmaceutical areas in which rheology is significant

Answer 23

mixing, particle size, pumping, stability (fluids)
spreading and adherence to skin, removal from jars, mixing of solids and liquids, release of drug from base (semisolids)
powder flow (solids)
processing efficiency (processing)