INTRODUCTION
Room temperature ionic liquids (RTIL’s) are salts that are in liquid form at room temperature. Research involving these liquids has really only began to flourish since the
1990’s. This poses a slight problem: the scientific community has not had time to effectively analyze these new compounds or explore their practical uses in chemical processes. As more and more ionic liquids are synthesized, more opportunities arise to research their various chemical properties.
Ionic liquids have potential uses that span from environmentally friendly solvents to lubricants and electrochemical agents. As new combinations of cations and anions are being manufactured, the availability of physical and chemical data about these unusual liquids at different temperatures and under different conditions is often difficult to locate.
This data is needed before industrial applications can be developed. In most cases, feasibility studies are not possible unless property data is available for the ionic liquid being investigated.
It is proposed that the viscosity of different ionic liquids be obtained by use of a gravitati onal viscometer at 10, 20, 25, 30, 40, and 50°C in equilibrium with ambient air,
50% relative humidity, and 100% relative humidity. The effect of methanol, ethanol and propanol on the viscosity will also be considered. The ionic liquids to be used are: 1butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF
4
]), 1-octyl-3-methylimidazolium tetrafluoroborate ([omim][BF
4
]), 1-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide ([BMPIm][Tf
2
N]), 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf
2
N]), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf
2
N]). Experimental data will then be used to develop a correlation for viscosity as a function of water/alcohol content.
Previous studies have shown that the introduction of various alcohols into ionic liquids plays a role in their phase behavior (Crosthwaite, et al.
2,3 ). Therefore, it is proposed that ionic liquid/alcohol mixtures be studied to see if the introduction of an alcohol to an ionic liquid alters the observed viscosity. Since water can be characterized as a very simple alcohol (a hydroxide molecule attached to a hydrogen atom) and since it is very difficult to keep water out of many ionic liquids, it too will be studied. This will give a better

understanding of how ionic liquid characteristics change when exposed to common alcohols.
MATERIALS AND METHODS
The project consists of two different phases. In the first phase, the viscometer will be calibrated using three different concentrations of aqueous sucrose solution (30%, 40%, and 50% by weight) and the viscosities of the ionic liquids used in the study, in equilibrium with ambient air, will be obtained. Phase two is comprised of the following: analysis of the viscosity sensitivity to water/alcohol uptake, as well as measuring the viscosity of the liquids after allowing them to equilibrate in 50% and 100% relative humidity (RH) alcohol/water environments.
The kinematic viscosities will be calculated from the efflux times obtained using a
Cannon-Manning semi-micro, open capillary, gravitational viscometer. The viscometer will be calibrated by recording the efflux times of 30%, 40%, and 50% by weight solutions of sucrose at 10, 20, 25, 30, 40, and 50°C. The relationship between efflux time and viscosity is:
η = ρ x C o
(1BΔT) x t [1] where η is the viscosity in cP, ρ is the density in g/cm 3 , ΔT=T-22 where T is the temperature in °C, t is the efflux time in seconds, and C o
and B are the calibrated constants. Known viscosities and densities of the solutions at different temperatures are given in literature (1) , allowing for the calculation of the constants, C o
and B. The data can then be plotted in Excel with ΔT on the x-axis and η/(ρt) on the y-axis making the yintercept C o
and the slope equal to – C o
B.
η
ρt

C o

C o
B

T [2]
In phase 2 of the experiment, water (and different alcohols) will be introduced into the ionic liquids via a mixture of wet and dry nitrogen gas, using the apparatus shown in figure 1.

Figure 1. Apparatus used to introduce water into the ionic liquids.
The N
2
flow through each line is controlled by a mass flow meter (AALBORG, AFC2600).
The “wet” gas is bubbled through a gas dispersion tube into de-ionized water or alcohol.
The resulting gas will be mixed with the dry gas from the other line and introduced into the ionic liquid using a gas sparger. The mixing of the 2 lines in different proportions allows for different percent humidity. The ionic liquid will be allowed to equilibrate with the product gas for 72 hours before viscosity analysis is performed. Water analysis will be performed using the same procedure outlined in phase one. As for the alcohol content of the liquids, experimental data for different alcohol solubilities, reported in literature, will be used to calculate the percent by weight present in the mixture. Efflux time measurements will be taken at the same temperature intervals as used in the first phase. Before efflux times can be measured in the viscometer it will first need to be cleaned with acetone, then methanol, and finally RBS 35® (Dichromate-Sulfuric mixture alternative). The viscometer will then be placed in an evacuated oven at 60°C for 2 hours before charging. Three efflux time readings will be taken at each temperature for accuracy. Viscometer and sample will be kept in an isothermal reservoir during the entire experiment. The sample will be allowed to equilibrate with the water bath temperature until temperature variations are negligible or approximately five minutes.

To ensure that the temperature is not affecting the ionic liquid structure, viscosity measurements will be taken up to 50 °C then back down to 10 °C for comparison. Water content analysis will be performed on the liquids pre and post exposure to H
2
O using an automatic volumetric Karl Fischer Titrator (Metrohm 795 Titrino). The sample will be drawn into a syringe, massed, released into the titration vessel, and back weighing will be performed. The mass of the sample can then be entered into the instrument, allowing for the calculation of percent water by mass. Needles and syringes will be cleaned with acetonitrile, and allowed to air dry for 12 hours in the hood. Alcohol concentrations will be determined by using published solubility data.
TIMELINE
Summer 2006

Develop apparatus to introduce alcohols and water.

Measure sensitivity of water content on viscosity.
Spring 2007

Finish measurements using water.

Start viscosity measurements of ionic liquid/alcohol systems.
Fall 2007

Finish measurements of viscosities of ionic liquid/alcohol systems.

Write thesis.
RESULTS TO DATE
The constant values for equation one, listed in table one, were obtained through the experimental procedure outlined above. These values will be used in all viscosity calculations throughout the project.
Table 1. Defined constants for equation 1.
Constant Value
C o
B
.222744
413.72 x 10 -6 /°C
Figure 2 contains initial data on the effect of water concentrations on the viscosity of
BmimBF
4
. Here, viscosity is plotted on a log scale versus the inverse temperature. As the water content increases the viscosity of the ionic liquid decreases.

1000
100
10
Ambient Air (.1212% Water)
50% RH (3.3764% Water)
100% RH (9.1778% Water)
1
3.08
3.18
3.28
3.48
Figure 2. BmimBF
4
Viscosity in Equilibrium with Ambient Air and 50% and 100% RH
It can therefore be hypothesized that this same behavior will be observed when other ionic liquids are exposed to water. Since water is a simple alcohol it is expected that a decrease in viscosity of ionic liquids exposed to different alcohols will also be observed.
It has also been found that different ionic liquids are affected differently by water concentration than others. After testing multiple ionic liquids containing the tetrafluoroborate anion, it has shown a considerably higher affinity towards water than
BmimTf
2
N. This in hand led to a greater affect on viscosity.

REFERENCES
1. Barber, E.J. “Calculation of Density and Viscosity of Sucrose Solutions as a
Function of Concentration and Temperature.” Natl. Cancer Inst. Monogr. 21
(1966): 219-239.
2. Crosthwaite, et al. "Liquid Phase Behavior of Ionic Liquids with Alcohols:
Experimental Studies and Modeling." Journal of Physical Chemistry B 110
(2006): 9354-9361.
3. Crosthwaite, et al. "Liquid Phase Behavior of Imadazolium-Based Ionic Liquids with Alcohols." Journal of Physical Chemistry B 108 (2004): 5113-5119.
4. Jacquemin, J., P. Husson, A. A. H. Padua, and V. Majer. "Density and Viscosity of Several Pure and Water-Saturated Ionic Liquids." Green Chemistry 8 (2006):
172-180.
5. Harris, K.R. “Temperature and Pressure Dependence of the Viscosity of the Ionic
Liquids 1-Methyl-3-octylimidazolium Hexafluorophosphate and 1-Methyl-3octylimidazolium Tetrafluoroborate.” J. Chem. Eng. Data 51 (2006): 1161-1167.