Abstract
Membrane characterization is a critical necessity throughout the membrane's lifecycle. It mainly provides the connection between the fabrication and performance of the membrane. At the fabrication stage, membrane characterization allows us to study the membrane's characteristics in terms of its structure, morphology, chemical and physical properties, transport properties, etc. Membrane operation allows the determination of whether membrane cleaning is required or replacement is necessary. Finally, characterization at the end stage of membrane usability provides the causes of membrane failure which are significant data for future references. In that essence, this chapter discusses several methods that are used in membrane characterization processes, which are mainly categorized into the transport/flow, electron microscopy, scattering, and spectroscopy characterization methods.
TopIntroduction
Membrane characterization provides the connection between its fabrication and performance with relation to the membrane structure, morphology, chemical and physical properties, transport/flow properties etc. The membrane field is continuously developing owing to its branches of the study of membrane fabrication and characterization. As more and more researches are conducted on membrane production methods, an improvement on the membrane can be achieved when better understanding on how to create the best membrane is developed. Various membrane characterization techniques have been established and practised to obtain the parameters that make out the membrane characteristics. Membrane characterization can be carried out throughout the lifecycle of membrane particularly after fabrication, during the operation, and lastly at the end of membrane lifecycle. They are performed at these different periods for different reasons such as obtaining the membrane characteristics, determining whether cleaning or membrane replacement is needed, and gathering information on the factors causing membrane failure respectively.
The performance of a membrane is influenced by its characteristics attributed to the chosen fabrication technique. This mainly includes membrane pore structure: porosity, pore size distribution and pore tortuosity, crystallinity, and surface property: hydrophilic/hydrophobic property, surface charge and surface roughness. These membrane properties can be measured by methods of characterization that are shown in Table 1, which are categorized into transport/flow techniques, equilibrium techniques, and advanced techniques. In this section, several methods of membrane characterization are discussed which includes transport/flow, electron microscopy, scattering, and spectroscopy characterization methods. These methods can be used individually to characterize a certain membrane property, or collectively to obtain whole characteristics of the membrane in terms of its chemical, physical, and mechanical properties. Consequently, the correlation obtained between the fabrication method and the membrane characteristics would assist researchers in the further development of membrane with better properties.
Table 1. Common methods of membrane characterization
| Transport/Flow Methods | Equilibrium Methods | Advanced Methods |
• Bubble gas transport
• Gas permeability
• Solute rejection/ molecular weight cut-off (MWCO)
• Liquid-liquid displacement
• Mercury intrusion porosimetry | • Gas adsorption/desorption
• Thermometry
• Permporometry
• Bubble point | • Spectroscopy methods (e.g. RS, FTIR, PALS, RBS)
• Scattering methods (e.g. XRD, SAXS, and SANS)
• Electron microscopy methods (e.g. TEM, SEM, and ESEM) |
Source: (Bernstein et al., 2013)
Key Terms in this Chapter
Characterization: Critical process in membrane research and development to characterize the membrane characteristics/properties in terms of its structure, morphology, chemical and mechanical properties, transport/flow properties, etc.
Electron Microscopy: Technique used in membrane characterization that allows the imaging of the surface of the membrane to show its physical characteristics and morphology.
Membrane Characteristics: Properties that wholly define the membrane which is generally classified into structural, morphological, transport, flow, chemical, physical, and mechanical characteristics.
Morphology: Covers the form, shape, size, structure, and appearance of the membrane.
Scattering Methods: Techniques used in membrane characterization which typically use light, moving particles, x-ray etc. which are scattered and translated to provide information about the membrane characteristics.
Transport Property: Parameters that define the rate of transport (of mass, heat, etc.) such as the viscosity, diffusivity, and thermal conductivity.
Spectroscopy: Techniques used in membrane characterization which involves the splitting of light or electromagnetic radiation, which are then measured into the constituent wavelength or spectrum. The spectrum data obtained can be translated into information regarding the membrane characteristics.
Membrane Structure: The overall physical construction of the membrane.