09 June 2014 | 16:57
By Jan Gorgol

Moisture affects a huge range of diverse materials in very broad industries and research areas.

One of the many tools used in characterising the effects of moisture is Microscopy , ranging from common microscopes such as light microscopies using dark-field, light field or cross-polarisation to Raman, FTIR microscopy’s and more esoteric imaging techniques such as Atomic Force Microscopy , 3D X-Ray Tomography or even PAM (photo acoustic microscopy).

Just a few of the diverse areas and industries where different kinds of microscopy can be effectively used to study the effects of moisture and humidity on real life situations include:

Pharmaceutical

  • Studies of crystallisation of amorphous samples under humidification including hydration of stable and unstable hydrates, deliquescence and liquefaction of hygroscopic samples, co-crystallisation and solvate desorption at high humilities.
  • Polarized light microscopy and birefringence can be used effectively to study Crystal morphological growth. Polymorphism can be studied by Raman, FTIR, and light microscopy. [1]

Welling and Coalescence
Light microscopy of PVP drug carrier showing welling and Coalescence at humidity

Cosmetics

  • Hair colour, pigmentation, thickness, tensile strength, shape, decomposition and effects of hair products have been studied with Light and Raman Microscopies.

Paper and environment

  • Polarised light microscopy can be used to study Sludge and dry solids from paper mill residues for evaluation of recovery of wood fibres, pigments, and other paper additives. Polarised light microscopy is also effective in Biodegradable fibres decomposition studies.

Wood

  • Characterisation of wood and vegetable fibre pigments using FTIR and Light microscopy
  • Studies of wood swelling in 3D using X-ray tomography.
  • Studies of effects of humidity on wood adhesive coatings using AFM

Food

  • Effects of humidity on flowability of lactose due to changing amorphous and crystalline content using Raman and light microscopy.
  • Moisture Induced Phase Transitions of food flavouring studied by light microscopy. Moisture content of seeds has been studied using photo acoustic microscopy helping sustainable agriculture development.
  • Moisture induced phase transitions of food flavouring studied by light microscopy.
  • Effects of humidity on dry milk powders measured using light microscopy [2]

Blog image 4
Light microscopy of Amorphous Lactose Crystallisation with humidification

a) Surface adsorption 0% RH
b) Bulk absorption &surface adsorption 50%RH
c) Recrystallisation 60%RH
d) Crystalline Material 90%RH

Microscopy 6
Photographs of Milk powder at 64%, 81% and 85% RH.

Microscopy 7Deliquescence of KBR crystal using light microscopy and GenRH-Mcell

Optical coatings

  • Use of phase interference contrast microscopy to study Degradation of anti-reflective optical coatings due to delimitation

Fibres

  • Study of humidity related swelling of wool & cotton fibres using scanning probe microscopy

Biological

  • Effects of Humidity and CO2 in live cell imaging incubators

Bacteria

  • Effects of humidity on morphology and elastic properties of Bacteria using AFM

Minerals and Rock

  • Raman Microscopy has been used to study phase changes in Portland cement

These are just a few areas where microscopy can be valuably used to study the effects of changing humidity on real life sample. To help meet Scientists and Technician’s many needs in these areas Surface Measurement Systems have developed an environmental microscopy cell GenRH-Mcell [3] to enable precise critical humidity Microscopy studies in situ.

Please feel welcome to contact me if you have any humidity generation needs in such areas or join our free workshop at the Microscience Microscopy Congress MMC 2014 in Manchester, UK at the start of July.

References
[1] Dependence of cocrystal formation and thermodynamic stability on moisture sorption by amorphous polymer. David Good,   Crystal Miranda and   Naír Rodríguez-Hornedo
CrystEngComm, 2011,13, 1181-1189
[2] SurfaceMeasurementSystems Application Note 503 – Investigating Dried Milk Powders Using Optical Microscopy at Different Humidity Conditions.
[3] SurfaceMeasurementSystems Application Note 501 – Environmental Microscopy using the GenRH-A Humidity Generator and Mcell Accessory.

About the author:
Jan Gorgol studied Physics at Bristol University followed by a Masters at Brunel University while working with XPS & SEM at the Experimental Techniques Centre. After working extensively in Surface science instrumentation globally he now is Product Manager for the GenRH series of humidity generation products at Surface Measurement Systems Ltd.


Related Article:
1. Formulation, Microscopy and Moisture