Volume 129, Issue 21, 07 December 2008
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129(2008); http://dx.doi.org/10.1063/1.3033366View Description Hide Description
The solute—solute interaction in terms of enthalpy,, the third derivative of , was experimentally determined using a Thermal Activity Monitor isothermal titration calorimeter for aqueous solutions of 2-butoxyethanol (BE) and 1-propanol (1P). This was done using both calorimetric reference and sample vessels actively. We simultaneously titrate small and exactly equal amounts of solute ( or 1P) into both cells which contain the binary mixtures at an average mole fraction, , which differs by a small amount . The appropriate amount of titrant was chosen so that the quotient can be approximated as , and so that the scatter of the results is reasonable. is the thermal response from an individual cell on titration, and we measure directly the difference in the thermal response between the two cells, . The resulting quotient, , can be approximated as and hence provides a direct experimental avenue for the enthalpy interaction function. We varied the value of to seek its appropriate size. Since contains the first derivative of with respect to , the result is the third derivative quantity. Thus we present here a third derivative quantity directly determined experimentally for the first time.