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Summary pharaceutical technology and biopharmacyPhysical Chemistry Wouter Hinrichs
- Rheology= the branch of physics that deals with the deformation and flow of matter,
especially the non-Newtonian flow of liquids and the plastic flow of solids.
- Surfaces and interfaces
- Disperse systems
Rheology
Description of the flow of matter
- Newtonian liquids
- Non-Newtonian liquids
- Visco-elasticity
Newtonian liquids
Divide cube of liquid in stacked layers like a deck of cards, which you can spread over a table by
pushing it with your hand
Shear rate (D) is the change of the flow rate (dv) with the change of the distance perpendicular to the
fixed surface (dy)→ D= dv/dy (d=small change)
Dynamic viscosity, n, is a measure of the resistance against flow
Specific for Newtonian liquids:
When t increases twice, D becomes always twice as big
Water has a low viscosity, so higher flow rate
Higher viscosity, higher resistance against flow and higher sheared stress
Q what is the unit of dynamic viscosity, n?
Q deduce the unit of dynamic viscosity, n.
, Shear rate plotted as a function of shear stress (Newtonian
liquids)
- Straight line through the origin
- At every point on the line, the viscosity is the same
-
- Viscosity is independent on
Later we will see for non-Newtonian liquids: Viscosity is
dependent on But viscosity is always
Change of axes! Watch carefully what is on the x-axis
and what is on the y-axis
SI unit viscosity
.
Solvent→ solution: viscosity increases!!
, Molecules which are
dissolved, behaves as
particles.
(Viscosity will
increase qhen
dissolved moelcules
are much bigger.)
Assumption: diameter solute >> diameter solvent molecule→ solute molecules behaves as particle
with respect to solvent molecule. But do not confuse with suspension!!
One extreme
- Particle moves uniformly forwards without
any other movement
- Liquid behind particle should then move
uniformly as well
- Arrow indicates flow rate
- Total length of all arrows is smaller
- At a given shear stress the flow rate is smaller
- Viscosity is higher
Other extreme
- Particle moves forwards but also fully rotates
- For rotation (extra mobility)
- Shear stress is required
- Shear stress is not only used for flow but also
for rotation of particle
- Viscosity is higher
It is unknown how the
particle behaves: non-
rotating, fully rotating,
or ‘something’ in
between
→Extremes results in
increased viscosity
→Everything in
between also increased
viscosity
, There are three methods to determine viscosity etc.
1. Capillary viscometer
2. Falling sphere viscometer
3. Viscometers for non-Newtonian liquids
1. Capillary viscometer
Procedure:
- Fill reservoir 1 with liquid
- Put pressure on A or vacuum on B
- Reservoir 2 will be filled
- Releave pressure on A or vacuum on B
- Measure time reservoir 2 empties (flows back in 1)
Flow rate depends on
- Radius capillary r
- Length of the capillary L (longer length, longer it takes)
- Pressure difference over the length of capillary dp
- Viscosity of the liquid
Don’t learn the equation,
understand it!
- dp depends on the geometry of a given viscometer and also proportional to the density of
the liquid (p, rho)
- r and L are constants for given viscometer
is volume (V)/ time of flow (t), V is a constant for a given viscometer
C: constant for a given viscometer
When viscosity of certain liquid is known,
the constant, C, for a given viscometer can
be determined
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