Simple Method for Determining the Vapor Pressure of Materials Using UV-Absorbance Spectroscopy

Abstract

Accurate thermodynamic parameters of thin films of materials are crucial in understanding their behavior in the nanometer scale. A new and simple method for determining the vapor pressure and thermodynamic properties of nanometer thick films of materials was developed based on UV-absorbance spectroscopy. Well-characterized benzoic acid was used to calibrate the spectrometer and the experimental conditions. The thermodynamic properties of pentaerythritol tetranitrate (PETN) were determined to validate the use of this new method. The estimated values of the thermodynamic parameters of PETN are in excellent agreement with the values reported using the most widely used Knudsen effusion method for determining vapor pressure lower than 1 pascal. The elegance of this method is its simplicity. The results indicate that UV-absorbance spectroscopy is a model-free and powerful technique in determining thermodynamic parameters in the nanoscale.

Rapid Estimation of Thermodynamic Parameters and Vapor Pressures of Volatile Materials at Nanoscale

“…This value is in agreement with the values of the activation energy of sublimation of benzoic acid that have been reported in the literature (84.0-95.5 kJ mol À1 ). [12] However, the frequency factor calculated here is one order of magnitude smaller than that calculated isothermally. Our value is in agreement with the activation energy values reported by Zielenkiewicz et al [20] and Ribeiro da Silva et al, [21] who used gas saturation and torsion effusion methods, respectively.…”

“…In addition, this calculated value, although slightly smaller, agrees well with our isothermally determined value of 87 AE 1 kJmol À1 . [12] However, the frequency factor calculated here is one order of magnitude smaller than that calculated isothermally. This smaller value can be explained by the approximation used in Equation (8), since the intercept is more sensitive to the degree of approximation than the activation energy.…”

“…Agreement between this value and the isothermally one determined previously [2 10 7 (Pa cm 2 s mg À1 )] was obtained. [12,13]…”

“…[11][12][13] This method was shown to be the simplest and most accurate model-free method in determining thermodynamic parameters at nanoscale to date. [11][12][13] This method was shown to be the simplest and most accurate model-free method in determining thermodynamic parameters at nanoscale to date.…”

“…We have recently reported the first use of optical absorbance spectroscopy in determining Arrhenius parameters as well as vapor pressures of nanofilms of materials isothermally. [11][12][13] This method was shown to be the simplest and most accurate model-free method in determining thermodynamic parameters at nanoscale to date. However, in spite of being much faster than other techniques (up to hours), isothermal absorbance spectroscopy is still a time-consuming method and a relatively faster procedure would be of great impact.…”