Viscosity is the resistance for a fluid to flow. Shear stress and shear rate are defined as the force and speed of moving a fluid respectively. Rheology is the study of these viscous fluids and their movement and deformation properties.
Part 1
In the part 1 of the experiment, the viscosity of 3 different concentrations of methylcellulose is measured using a Brookfield viscometer (50 r.m.p). As shown on the graph, the viscosity has a direct relationship with the concentration. As shown below, the structure of methylcellulose encompasses a hydrophilic structure which forms hydrogen bond when mixed with water. As the concentration of methyl cellulose increases so does the number of hydrogen bonds hence the solution becomes more viscous. Graph 1 below confirms the theory explained.
Part 2
1% PVP solution is passed through the Ostwald viscometer’s capillary in 2 different temperature (24°C and 40°C). Time taken for PVP to flow under gravity was 191.5 seconds in 24°C and 279.5 seconds in 40°C. The results illustrate a decrease in viscosity when the temperature is increased. There is about 90 seconds difference between them.
As temperature rises, high energy in surroundings causes the bonds to break more easily. The breakage of these polymers into shorter forms causes the solution to be less viscous.
Part 3
Tragacanth (0.8%) is a psudoplastic fluid as a decrease in viscosity causes an increase in shear rate. It is also thixotropic as the viscosity depends on time when the shear rate is invariable. It is a non Newtonian fluid as there is a non-linear relationship between shear rate and viscosity.
The resulting hysteresis loop from graph 2, illustrates a breakdown in the structure. If otherwise, both lines should have collapsed on each other. However the area between the two lines is very small showing an insignificant error. The extent intermolecular breakdown causing an increase in viscosity as hydrogen bonds are formed. Therefore the solution is a non Newtonian pseudoplastic thixotropic. (Aulton, 2007)
In conclusion the viscosity has a positive relationship with concentration and temperature. These properties relate to the intermolecular forces of the solution. If hydrophilic, they tend to attract each other and form a more viscous solution.
Table 1
Table 2
Series 1: up ramp, Series 2: dawn ramp
Bibliography
Aulton, M. E. (2007). The Design And Manufacture Of Medicine. Edinburgh: churchill livingstone.