Influencing factors of viscosity measurement by rotational viscometer

Influencing factors of viscosity measurement by rotational viscometer

1. Rotational Viscometer - Temperature Influence

The effect of temperature change on the viscosity of the polymer solution is significant. The viscosity of the polymer solution decreases with the increase of temperature. The reason is that the dispersed phase particles of the polymer solution are entangled with each other to form aggregates with a network structure. When the temperature is higher, the network structure is more easily destroyed, so the viscosity decreases. . In order to get good results, it is necessary to operate at a constant temperature, and strictly control the temperature change not to exceed ±0.05 °C. If the temperature exceeds this range or has a large change, the accuracy of the measurement will be affected, resulting in a lack of linearity in the drawing. relation. Generally speaking, the accuracy of the determination of the molecular weight of polymers at 25°C is higher. To avoid possible continuous changes in temperature, all solutions and solvents must be thermostatted to the same temperature prior to addition.

2. Rotational Viscometer - Effect of Concentration

The relationship between the viscosity and the concentration of the polymer solution is in line with the linear relationship of Huggins, Fouss formula. That is , theoretically, the thinner the solution, the more suitable for infinite dilution. However, if the solution is too thin, the difference between the outflow time of the solvent and the solution will be small, which will lead to a large number of experimental errors, and the adsorption of the polymer solution on the viscometer wall should be considered. The resulting change in concentration. Therefore, the initial concentration of the solution is too dilute. If the initial concentration is too large, the lateral straight line will bend upward at the large concentration, which will affect the extrapolation of the linearity, thereby affecting the viscosity value. We did a series of experiments on the effect of concentration, and obtained the corresponding intrinsic viscosity.

3. Rotational Viscometer - Effect of Aging Time

Even if the polymer solution is not affected by external factors, its viscosity also changes with time. From the experimental results, it is known that the aging time is short, the viscosity is small, and the error is large. This may be due to the fact that the polymer do not have enough time to form a network structure. The aging time is long, the viscosity is small, and the error is large. The reason for the decrease in viscosity is that the structure of polyethylene is dissolved in the solution. The experiment also shows that although the viscosity of the solution changes, the viscosity and concentration The linear relationship is still ideal. Experiments show that the aging time is about 3-4 days, and the results are satisfactory. Considering the slow dissolution rate of the polymer and the effect of aging, the solution should be prepared before the experiment.

4. Rotational Viscometer - Effect of Antifoam Amount

The polyvinyl alcohol aqueous solution is easy to foam, which brings difficulties to the experimental operation. Adding n-butanol to the solution as a defoaming agent can play a better defoaming effect, but the amount of the defoaming agent should be strictly controlled, because the n-butanol is used as a defoaming agent. The viscosity of alcohol is more than three times larger than that of water. If too much n-butanol is added, the measurement result will inevitably bring about a large error.

Digital Rotational viscometer without heater:

Brookfield with Heater: