Articles | Volume 16, issue 15
Research article
03 Aug 2016
Research article |  | 03 Aug 2016

A method for the direct measurement of surface tension of collected atmospherically relevant aerosol particles using atomic force microscopy

Andrew D. Hritz, Timothy M. Raymond, and Dabrina D. Dutcher

Abstract. Accurate estimates of particle surface tension are required for models concerning atmospheric aerosol nucleation and activation. However, it is difficult to collect the volumes of atmospheric aerosol required by typical instruments that measure surface tension, such as goniometers or Wilhelmy plates. In this work, a method that measures, ex situ, the surface tension of collected liquid nanoparticles using atomic force microscopy is presented. A film of particles is collected via impaction and is probed using nanoneedle tips with the atomic force microscope. This micro-Wilhelmy method allows for direct measurements of the surface tension of small amounts of sample.

This method was verified using liquids, whose surface tensions were known. Particles of ozone oxidized α-pinene, a well-characterized system, were then produced, collected, and analyzed using this method to demonstrate its applicability for liquid aerosol samples. It was determined that oxidized α-pinene particles formed in dry conditions have a surface tension similar to that of pure α-pinene, and oxidized α-pinene particles formed in more humid conditions have a surface tension that is significantly higher.

Short summary
In this manuscript, we present a novel, first-principles method for the determination of surface tension of collected liquid aerosol particles. The method uses an atomic force microscope with a specially designed probe to directly measure the surface tension, a physical parameter required for Kohler theory. The measurements were verified using a standard, check-standard and then applied to a dry and humidified oxidized α-pinene aerosol system.
Final-revised paper