Utilizing electron microscopy and spectroscopy methods to understand water structure and water doping

Lior Miller, Purdue University

Abstract

Water is the second most common element in the universe and the most studied material on earth. Most of the studies concerning water are from the fields of chemistry and biology. Hence, the structure of water molecules and short range order and interactions are well characterized and understood. However, the collective arrangement of water molecules and the long range order are still missing. Understanding of this long range order in water is needed, as it is the key to many water activities. To fill this gap, this study utilizes a new direct method for characterization of water in the vapor phase. Water samples from different water types were characterized using electron energy loss spectroscopy (EELS) within a transmission electron microscope (TEM). Prior to characterizing water vapor, the measurement method for in-situ gas analysis was developed using pure gases. Water samples were also characterized using more conventional techniques, including: using cryogenic scanning electron microscopy (Cryo-SEM) in the solid state, after rapid freezing; and using high resolution TEM (HRTEM) and scanning TEM (STEM) after drying. Many other characterization techniques were evaluated but most of them were found to be not suitable, mainly due to detection limits. EELS characterization showed that samples from different water types have different electronic configurations, and they all have structures that are large enough in order to scatter electrons. From cryo SEM characterization it was found that water has nanoparticles inside with a size range of 10-100 nm, and these particles are ~500 nm apart. HRTEM/STEM characterization showed that particles from different water types have different shapes. The presence of particles provide surfaces to support water structures and the difference between the particles can explain the different properties of different water types Using tools and methods that are conventional in materials science for characterization of bulk materials and long range orders, resulted in characterization of water clusters that are significantly larger than what was known until now. By this we contribute a new point of view for water structure, which together with new insights on water properties can potentially advance later use of water as an active ingredient.

Degree

Ph.D.

Advisors

Stach, Purdue University.

Subject Area

Analytical chemistry|Materials science

COinS