Introduction:

Viscosity is a measure of fluid resistance to flow. It can be described as the internal friction of a moving fluid or inverse fluidity. A high-viscosity fluid resists the flowing motion and takes longer time to flow compares to a low-viscosity fluid. For example, high viscosity fluid such as honey or condensed milk takes longer time to pour out of its container than low viscosity fluid such as water does. The property of fluids viscosity has variety of applications in both science and daily life. For example, viscosity plays important role in volcanology. The geologist can predict the eruption of volcano base on the viscosity of magma fluid. The lower viscosity magma, the more likely it is to erupt. On the other hand, the viscosity of the magma also play important factor in determining whether an eruption will be explosive or non-explosive. The lower viscosity magma does not cause the explosive eruption as higher viscosity magma because most of the gas contents are easy to flow in lower viscosity magma to the surface and escape. Comment by Le, Luc: The application of viscosity http://www.geology.sdsu.edu/how_volcanoes_work/Controls.htmlhttp://www.spacegrant.hawaii.edu/class_acts/ViscosityTe.htmlAnother application of viscosity in daily life is the motor oils. If an oil is too viscous and thick, it will flow slowly and have large friction to the parts of an engine leaving them vulnerable to excess wear. However, if the oil is too thin, it could not provide the cushion to protect any part of the engine from the effects of friction.

Why are some fluids more viscous than others? Viscosity depends on many fundamental molecular properties which are particular to the fluid being studied. Such size, shape, intermolecular attractions, and phase of the fluid all have a specific role in how easily atoms and molecules flow in fluid or gas. The size and shape of the molecules directly affect viscosity. If the molecules are large and have bumpy surfaces, they will create a large deal of friction as they slide past each other. Therefore, they will have higher viscosity and flow slower than liquids made up of small molecules with a smoother surface. The stronger intermolecular attractions of molecules in the fluid, the higher fluids viscosity is. Because these molecules are strongly attached to each other; then more energy will be required for them to flow past each other resulting in a liquid with high viscosity. In other aspect, temperature acts as thermo energy and has direct effect on fluids viscosity. If fluids temperature increase, the thermo energy is added to molecules of fluid and it causes molecules to move farther apart at the increasing speed. This allows the molecules to slide past each other with greater ease so the hot temperature will cause fluid viscosity decreases. The lower temperature causes molecules in fluid to compact closer together and move sluggishly; the fluid viscosity increase. It is interesting to note that gases exhibit the opposite property of temperature effect to viscosity compare to liquids. As you raise the temperature of a gas, it becomes more resistant to flow. This is due to the fact that gas molecules are spaced far apart, so they do not have to slide over one another very often in order to flow. Increasing the temperature increases the number of collisions between the molecules. Therefore, the net effect is an increase in friction and a corresponding increase in viscosityComment by Le, Luc: Pchem lab manual citingComment by Le, Luc: Need to paraphrase and cite

As the liquid flows, its layers slides over each other. The force F required is directly proportional to the area A and velocity v of the layers, and inversely proportional to the distance d between them. The proportional number is the coefficient of viscosity.

F = *A*

If is constant the fluid is called Newtonian (water, gasoline). If is not constant and depends on the gradient then the fluid is non-Newtonian (

This characteristic of viscosity will be explored in lab when determining the viscosities of uncleaved and cleaved polyvinyl alcohol polymers (PVOH). Since viscosity is dependent on intermolecular forces the viscosity of a liquid will be different than that of a gas. Gas viscosity is around 106 times smaller. The viscosity of gases arises from molecular diffusion, which transports the momentum between layers of flow. The kinetic theory of gases gives further explanation to the behavior of gas viscosities, which states that the viscosity is independent of pressure and increases as temperature increases (dependent). The increase in temperature increases the mobility of molecules, which allows for neighboring molecules to easily overcome energy barriers and slip past one another. Size and dipole moments also affects the gas viscosity.This lab will use an Ostwald viscometer to determine the viscosity of the PVOH polymer and a gas viscometer to determine the viscosity of three gasses (CO2, N2, and He). From the Ostwald viscometer, the average molecular weight of the polymers in solution can be determined.

Figure 1: 1 chain of PVOH but they are attached like this in n number of chains.Polymers are very useful at changing the viscosity of a solution. Even in dilute concentrations a polymer can greater affect how a solution will flow. This ability is dependent on the polymers hydrodynamic relationship to the molecules in the solvent. Most PVOH chains are linked head-to-tail, meaning the COH carbon is connected to a CH2 as shown in figure 1 but they can also be linked head-to-head which implies two COH groups are adjacent to each other. These bonds can be cleaved using periodate. The degree by which periodate cleaves these head-to-head molecules is independent on periodate concentration. Flory and Leutner observed this independence in 1948 when trying to determine head-to-head arrangements in PVOH. By cleaving head-to-head polymers, the molecular weight is decreased and the polymer chain is shortened. This will affect the viscosity of the liquid by making the solution more viscous.Its easy to qualitatively observe liquids with different viscosities but its also important to determine an exact quantitative value for a liquids viscosity. This can be determined experimentally using a viscometer. The intrinsic viscosity is determined by muliplying the calibration of viscometer, (mLcP/sg), times the amount of time, s, it takes the meniscus of the liquid to flow from one mark on the viscometer to the next and the density of the liquid, (g/mL). This results in equation 1:

(1) The specific viscosity relates the intrinsic viscosity to the viscosity of the pure solvent of the liquid. This will be used later in the experiment to determine the specific viscosity of PVOH polymers in high purity water, o (pure liquid).

(2)

Polymer viscosities are also used to study polymer synthesis. A characteristic of polyvinyl alcohol is the consistency of orientation of monomer units in the polymer chain. Polyvinyl alcohol is linear and is assumed that it forms head-to-tail links during synthesis, but head-to-head linkage may be present. The formation of a head-to-head-linkage is less common than a head-to-tail linkage due to steric hindrance during synthesis. These formations are used to determine the steric factor, S, and the activation energies for each. Head-to-head linkage formation depends on the relative rates of normal growth-step reaction and abnormal step-growth reaction. These rates depend on the activation energies given by:

(3)

(4)

where kN is the normal rate and and KAb is the abnormal rate, S is the steric factor which measures the ratio of the probability that the normal and abnormal monomer will not be hindered by sterics, and Ea is defined as the additional thermal activation energy that is needed to produce abnormal additions. In an experiment, S and Ea can be obtained by measuring two or more polymerization temperatures. The samples of head-to-head polymers can be prepared using methods, such as hydrogenation and esterification. To minimize the number of head-to-head linkages in polyvinyl alcohol, the reaction should be done at very low temperature and to maximize the number of head-to-head linkages, the reaction should be done at higher temperatures, because at higher temperatures, the additional thermal energy, Ea, makes this state more accessible.The principle of the Ostwald viscometer is also the method that is used to measure the viscosity of the gases. Like liquids and solutions, the viscosity is measured by the time it takes for the fluid to flow through the capillary, only this time, the oil displacement is taken into account. Since gas flow behaves differently than the liquids, the calculation for viscosity has been found to be complex, because one function cant apply to all gases. However, the dependence of viscosity on temperature can be calculated by using Sutherlands theory of viscosity for air. The empirical expression is

(5)

where dry air is the viscosity of air, in poise, and T is absolute temperature, K. The reason that viscosity is a function of temperature is that air behaves as an ideal gas, because the molecules are constantly moving and intermolecular forces are negligible. The viscosity of air is needed to find the apparatus constant, K, which is determined by the equation

(6)

where t is the average flow time, s, of the gas and is the gas viscosity, poise. After finding the apparatus constant with the average flow time of air and dry air, the viscosity of each gas can be found. A hypothesis that can be made for the gas viscosities is that the viscosity of nitrogen may be almost as close to the viscosity of air, because after all, air is composed of 79.1% nitrogen.

II Method experimental:

The experiment comprises of two part: measurement the viscosity of cleaved and uncleaved polymer solutions and measurement of the viscosity of three gases, CO2, He, and N2. The safety chemicals information about the substances that were used in each part of the experiment is presented in Appendix D.

The first part of the experiment, we set up two viscometer and oil bath at 30 oC as shown in figure below:

BA

One of the viscometers (ASTM rating of 50 and serial #Z 722) was used to measure the viscosity of the uncleaved polymer solutions. The second viscometer (ASTM rating of 50 and serial #Z 71) was used to measure the viscosity of the cleaved polymer solutions. These viscometers must be clean and dry before putting in the oil bath. In order to measure the viscosity of polymer solution, we first calibrated two viscometers. We pipetted 10 mL of room temperature high purity water to each viscometer. Next, we place two viscometers into the oil bath and waited for 5 mintues to alow the solution in viscometers equilibrate at 30 oC of oil bath. In order to measure the viscosity of solution, we used the rubber bulb to suck the soltuion up to mark A on the viscometer and measured the time the solution flows back to mark B. The calibration measurement was determined by three time readings. In the time waiting for calibration, we prepared the polymer solution. The 3 samples with 10 ml each of the uncleave polymer solution (8g/ml, 4g/ml, and 2g/ml) were prepared from series dilution of stock solution (16 g/ml). The cleaved solution was prepared from uncleaved solution with first adding 0.1 g of KIO4 . We heat the solution up to 70 oC so the solid disssolved and polymer cleaved. The cleaved solution was cooled to room temperature and we performed serial dilutue to get 3 samples with 10 ml each of the cleave polymer (8g/ml, 4g/ml, and 2g/ml ). Once the bath temperature was stable, the viscosity of cleaved and uncleaved polymer solutions was measured using the same method for calibration. We used #Z 722viscometer for all cleave polymer solution and #Z 71 viscometer for all uncleave polymer solution.

The second part of the experiment, we measureed the gas viscosities. The appartus of gas vicosity measurement was set up as figrued shown below.

The gas viscosity apparatus was calibrated with air. When air was introduced into the column, the oil was displaced by a couple of centimeters. The three-way stopcock in the apparatus was used to let the air out of the column through the capillary. The viscosity was measured by the time it took the air to flow through the displacement, or once the oil was equal in both arms of the apparatus. After calibrating the equipment, the viscosities of CO2, He, and N2, were measured, making sure that the column was flushed between the gases with the next gas to get good measurements of that gas. It was important to set the gas regulator diaphragm to a minimal pressure, otherwise the gas would be let out too strongly, causing the oil to pass the splash bulb and create a hazard. These measurements were taken at room temperature and pressure.2