Rheology & Formulation

Question 1

What is meant by rheology?

Answer 1

– Study of the flow and deformation of matter
(fluids)
– The term rheology originates from the Greek word “rheos”
translating as “a flowing, stream, current” and “logy” meaning “the
study of”

Question 2

What is meant by viscosity?

Answer 2

– The resistance to flow, i.e. if viscosity is high
then flow is reduced

Question 3

Why is rheology studied?

Answer 3

*semi solid preparations (needed for this)
*characterising ingredients
*understanding polymer behaviour

Question 4

What is the “basics” to viscosity equation + each element?

Answer 4

σ = η x γ

o = stress applied
n = viscosity
y = rate of flow

Question 5

What is meant by sheer stress and sheer flow rate?

Answer 5

Shear rate (y) is the velocity gradient over the height in our “block” of fluid

Shear stress (o) is the force applied (in
N) over the area of the upper surface of the block

Question 6

How do you know if a fluid is non-newtonian?

Answer 6

Fluids often decrease in
viscosity with increasing
shear rate → “shear-
thinning”
Some fluids increase in
viscosity with increasing
shear rate → “shear-
thickening” or dilatant

Fluids which deviate from this
relationship are referred to as
Non-Newtonian fluids

Question 7

What does viscosity increase with?

Answer 7

polymer concentration

Question 8

Viscosity + low polymer con?

Answer 8

• Low concentration
  – Isolated polymer chains, shape & volume determined by polymer-
  solvent and intra-polymer interactions

Question 9

Viscosity + high polymer conc?

Answer 9

• High concentration (network solution)
  – Inter-penetrating chains
  – polymer movement hindered by neighboring chains
  – Inter- and intra- polymer interactions important

Question 10

What is the BP test for viscosity?

Answer 10

A capillary viscometer may be used for determining the viscosity of
Newtonian liquids and a rotating viscometer for determining the
viscosity of Newtonian and non-Newtonian liquids. Other viscometers
may be used provided that the accuracy and precision are at least as
satisfactory as those obtained with the viscometers described in the
related chapters.

Question 11

What is a capillary viscometer used for?

Answer 11

• Only used for determining the
  viscosity of Newtonian liquids
• Flow through a thin tube is
  measured under gravity
• Apparatus can be clamped in a
  water bath at desired temperature
• Recommended minimum flow time
  should be at least 200 seconds
• Repeated until 3 readings within
  0.5 seconds are achieved

Question 12

What is a rotating viscometer used for?

Answer 12

• Used for determining the
  viscosity of Newtonian and
  Non-Newtonian liquids
• Measure drag exerted on a
  body when rotated in a fluid