Study Set Content:
“resistance” of a fluid which is being deformed by either shear stress or tensile stress.
Viscosity
Viscosity other word
- "thickness" or "internal friction“
The study of flowing matter is known which includes viscosity and related concepts.
Rheology
used to measure viscosity
Ostwald viscometer
is the ratio of the absolute viscosity of the fluid on the viscosity of water at a certain temperature
Relative Viscosity
is force (dyne) necessary to move the layer of liquid 1 cm2 in speed 1 cm/sec on another layer of liquid and the distance between them is 1cm.
Viscosity coefficient
Viscosity coefficients cam be defined in two way
Dynamic viscosity
Kinematic viscosity
(absolute viscosity)
Dynamic viscosity
the more usual one (typical units Pa•s, Poise, P);
Dynamic viscosity
is the dynamic viscosity divided by the density (typical units m2/s, Stokes, St).
Kinematic viscosity
Factors effect on the viscosity:
Temperature Molecular weights Pressure
used for those fluids which cannot be defined by a single value of viscosity.
Rheometer
a device used to measure the viscosity of the liquid with a known density.
Ostwald viscometer
Ostwald viscometer other names
r (Wilhelm Ostwald) (Utube Viscometer, Capillary Viscometer)
Measuring the time for a known volume of the liquid (the volume contained between the marks A and B) to flow through the capillary under the influence of gravity.
Ostwald viscometer
- close temperature control of the fluid
Rheometer -used for those
The instrument must first be calibrated with materials of known viscosity such as
pure (deionized) water.
Knowing the value of viscosity of one liquid, one can calculate the viscosity of
other liquid.
Where η1 and η2 are viscosity coefficients of the liquid and water, and ρ1 and ρ2 are the densities of liquid and water, respectively
you can calculate the viscosity of the other liquid
Enumerate the different pharmaceutical dosage forms which viscosity is part of the minimum test requirement.
Suspensions
Emulsions
Creams
Ointments (External Lotion)
