Principal Investigator: Andrew Ault

Year Awarded: 2018

Institution: University of Michigan

This project aims to determine fundamental properties of water layers and their acidity or basicity across a range of model systems for indoor materials, actual indoor materials, and authentic samples from a residential environment. This will involve using recently developed methods for experimentally probing the pH values of difficult to probe systems, such as indoor surfaces. The project will determine the range pH values, which have been thought to possibly range from acidic to basic, which has important implications for reactions occur within surface layers and partitioning between the gas and surface layer. We will test these questions we will take a systematic approach of:

  • Characterizing the properties of the aqueous film on model systems of indoor materials and actual indoor materials as a function of relative humidity (RH) (fresh and aged)
  • Determining the water coverage properties and pH of model systems under controlled laboratory systems
  • Determining the water coverage and pH of actual building materials both in the laboratory and after exposure in a residential setting

Two challenging aspects of indoor surfaces we are aiming to probe are organic surface films and modification by deposition. Both have been difficult to quantify, but have potential to improve our understanding of the evolution of surfaces indoors. For organic films or pockets, these are known to form on indoor surfaces, but their properties are not well known, nor is their heterogeneity. Thus, in addition to probing water coverage it is also important to probe the interactions between organics on surfaces and water. The second aspect is the modification of surfaces by the uptake of gases or aerosols.

To probe these questions, a combination of methods that span from the macro (millimeter) scale to the micro (Raman microspectroscopy), to the nano scale (atomic force microscopy with photothermal infrared spectroscopy – AFM-IR). Overall, from this grant, an improved understanding of the acidity or basicity of surfaces indoors will be obtained. Our results will provide information on surfaces that will connect with other Sloan measurement and modeling efforts.