The effect of moisture is evident in a variety of materials used in research areas and industries. Microscopy is one of the common tools used in the characterization of moisture effects.
Different kinds of microscopic techniques are used for this purpose, starting from common techniques, such as light microscopes, that use cross-polarization, light field, or dark-field, to FTIR and Raman microscopic techniques and more esoteric imaging methods such as photo acoustic microscopy, 3D X-Ray tomography, and atomic force microscopy (AFM).
These microscopic techniques are being used in a number of industries for the characterization of the effects of moisture and humidity.
In the pharmaceutical industry, the effects of humidity on the crystallization of amorphous samples are analyzed. These analyses include solvate desorption and co-crystallization at high humidity, liquefaction and deliquescence of hygroscopic samples (Figure 1), and hydration of stable and unstable hydrates.
Crystal morphological growth can be effectively studied using polarized light microscopy and birefringence (Figure 2). Light, FTIR, and Raman microscopic techniques are used to study polymorphism.
Figure 1. Deliquescence of KBR crystal using light microscopy and GenRH-Mcell
Figure 2. Light microscopy of PVP drug carrier showing welling and Coalescence at humidity
Paper and Environment
Paper mill residues such as sludge and dry solids have been studied using polarized light microscopy to evaluate the recovery of wood fibers and paper additives such as pigments. The decomposition of biodegradable fibers can be effectively characterized using polarized light microscopy.
In the cosmetics industry, light and Raman microscopies are used to study the effects of moisture and humidity on hair color, shape, thickness, tensile strength, and decomposition. Furthermore, the effects of hair products have also be explored.
Wood and vegetable fiber pigments can be effectively characterized using light and FTIR microscopy. X-ray tomography can perform 3D analyses of wood swelling. AFM can be used to study the effects of humidity on wood adhesive coatings.
Fibers and Minerals and Rock
Scanning probe microscopy can be used to study swelling of wool and cotton fibers caused by humidification. Phase changes in Portland cement can be studied using Raman microscopy.
Degradation of anti-reflective optical coatings caused by delimitation can be effectively studied using phase interference contrast microscopy.
Raman and light microscopy can be used to study the humidity effect on material flow (lactose) owing to varying amorphous and crystalline content (Figure 3). Light microscopy is used to explore moisture-induced phase transitions of food flavoring.
Photo acoustic microscopy is used to study moisture content of seeds to support sustainable agriculture development. Light microscopy is also used to study the impact of humidity on dry milk powders.
Figure 3. Light microscopy of amorphous lactose crystallization under humidification. a) Surface adsorption 0% RH. b) Bulk absorption & surface adsorption 50%RH. c) Recrystallization 60%RH. d) Crystalline material 90%RH
Figure 4. Photographs of milk powder at 64%, 81% and 85% RH
Bacteria and Biological
AFM is used to study the effects of humidity on elastic and morphological characteristics of bacteria. The impact of carbon dioxide and humidity in live cell imaging incubators can be studied.
This article covered some of the applications of microscopy to explore the impact of varying humidity on real life samples. GenRH-Mcell, an environmental microscopy cell from Surface Measurement Systems Ltd, helps to meet the requirements of technicians and researchers in these applications by enabling accurate in-situ microscopic studies of humidity effects.
This information has been sourced, reviewed and adapted from materials provided by Surface Measurement Systems Ltd.
For more information on this source, please visit Surface Measurement Systems Ltd.