Abstract
The optical and spectral properties of foams and emulsions provide information about their micro-/nanostructures, chemical and time stability and molecular data of their components. Foams and emulsions are collections of different kinds of bubbles or drops with particular properties. A summary of various surfactant and emulsifier types is performed here, as well as an overview of methods for producing foams and emulsions. Absorption, reflectance, and vibrational spectroscopy (Fourier Transform Infrared spectroscopy-FTIR, Raman spectroscopy) studies are detailed in connection with the spectral characterization techniques of colloidal systems. Diffusing Wave Spectroscopy (DWS) data for foams and emulsions are likewise introduced. The utility of spectroscopic approaches has grown as processing power and analysis capabilities have improved. In addition, lasers offer advantages due to the specific properties of the emitted beams which allow focusing on very small volumes and enable accurate, fast, and high spatial resolution sample characterization. Emulsions and foams provide exceptional sensitive bases for measuring low concentrations of molecules down to the level of traces using spectroscopy techniques, thus opening new horizons in microfluidics.
Highlights
National Institute for Laser, Plasma and Radiation Physics, 077125 Magurele, Ilfov, Romania; Faculty of Physics, University of Bucharest, 077125 Magurele, Ilfov, Romania
The findings suggest that various aspects, such as bubble diameters related to foam cohesiveness, must be taken into account when considering the temporal moment of exposure of the varicose vein injected with foamed medication and exposed in the tissue to laser radiation [68]
The optical properties of foams and emulsions are of interest both for basic research and for advanced applications in biomedicine, life sciences, food science, unconventional technologies in energy production and raw materials extraction, to mention a few of their applications
Summary
Part of the colloid class, have particular structures and contain fluids (either gases or liquids) or solid-state particles. The measurement of spectral properties is appealing since emulsions’ structures produce, upon interaction, longer optical paths of the light beams in emulsion samples and in many cases, more intense optical signals. The prolonging of a foam’s lifetime, may be achieved by introducing surfactants into the liquid phase, i.e., molecular components that migrate towards the gas bubble–liquid interface These surfactants have spectral properties and if optically active, they may play roles in the optical and spectral data harvested from foams. It was used to explain why an increase in the molecular weight of the linear alkyl chain of a homogeneous series of surfactants causes an increase in surface activity (foaming) until a decrease occurs at a critical chain length This fact is important, for foaming, and in processes such as detergency and emulsification [25]
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