Surfactants are the amphillic molecules that have tendency to reduce the surface tension of liquids. Imidazoline is a five membered ring with two nitrogen atom within it. moreover, imidazoline surfactants are the amphillic molecules that has imidazoline ring as its polar moiety whereas a long hydrophobic tail is made up of hydrocarbon tail that may vary in size and unsaturation depends upon their fatty material source wether that is linear or branch, their size like its C12, C14, C16, ,,,, Cn etc. Due to its pendant like structure the imidazoline pendant group easily get attached to the surfaces whereas hydrophobic tail oriented towards outside.

Imidazoline surfactants have already gained enormous interest due to their broad range of applications. Due to their availability in cationic, nonionic and zwitterionic forms, they can be exploited in almost every industry. Moreover, easy conversion of onomeric to bis-gemini form increase their efficacy in many folds.

Imidazoline is a five membered ring with two nitrogen atom within it. moreover, imidazoline surfactants are the amphillic molecules that has imidazoline ring as its polar moiety whereas a long hydrophobic tail is made up of hydrocarbon tail that may vary in size and unsaturation. Due to its pendant like structure the imidazoline pendant group easily get attached to the surfaces whereas hydrophobic tail oriented towards outside.

Imidazoline surfactants can be synthesized in any form like anionic imidazoline surfactants for example (1,3-bis(tricyanoborane)imidazolate), nonionic imidazoline surfactants, zwitterionic imidazoline surfactants and cationic surfactants.

Cationic imidazolines can be hydroxyethyl, aminoethyl and amidoethyl types of imidazolines and can be used as a lubricant, paints, inks, adhesion increaser, corrosion inhibitors, dispersants, remoisturizing substances, flocculants, conditioners, etc.

Amphoteric imidazolines examples are alkylamphodiacetates, alkylaminopropionates, alkylphosphopropionates etc. and exploited as hair conditioners, fabric softeners, liquid soap, gel due to its comfortable pH.

Nonionic imidazoline surfactants can be found very useful as corrosion inhibitors and easily applicable in desalination plants whereas anionic imidazoline can be used in laundry detergents, agriculture and related industries.

Gemini imidazoline surfactants are the molecules that have two imizazoline surfactant monomers linkes via spacer. spacer can be present in between the head groups or in between the tails. Gemini imidazolines shows much lesser CMC values than their monomeric counterparts.

Synthesis:

Imidazoline surfactants can be synthesized by reacting fatty acids and fatty alcohol with polyamines. Fatty acids and alcohols may be obtained from oil and fats and their reduced products. Oil may be obtained from plant source or animal source, edible or non-edible, essential or nonpessential. Length of hydrophobic chain depends upon the source taken from fatty material. Commonly used polyamines are diethylene tri amines, Hydroxyethyl ethanol amines etc.

Advance researches shows the use of waste resources to make them more cost effective. waste edible oil obtained after frying has proven as a great source to provide fatty alkyl chain to these molecules. This also help in recyclization of harmful waste oil after use. some examples of waste oil reported to synthesize the imidazolines or their geminis are soyabean oil, rice bran oil, rapeseed oil etc.

Properties:

Physical properties

Depends upon the type of hydrophobic tail, imidazoline may be crystalline solid to waxy solid, semi solid to viscous liquid, white, yellow or brown in color with varying melting and boiling point and different solubility and thermal stability. They are generally good water propellant with good lubricating properties and have ability to form acid stable salts.

Applications:

Imidazoline surfactants can be metered into the washing machines automatically and showed good potential to remove dirt and oil from the fabrics, their property to impart softness to fabrics make them good laundry detergents.

Good fabric softening and resiliency tendency of imidazoline surfactants encorage their usage in commercial fabric softeners.

Property of imidazolines to inhibit agglomeration make them efficient dispersants and applicable in paints and varnishes.

These compounds also show antistatic-ness and found useful dewatering agents.

Good absorbency on fabrics makes them to be exploited as rewetting agents

Some research also revealed their employability as bleach activators.

These compounds show good degradability and are mild to eyes and skin so can be used in skin preparations

Water-repellent tendency aided their use as corrosion inhibitors.

Other uses involve car washing, flocculants, oil and grease thickeners, Agriculture spray, paints, pharmacology and many more

References:

1. Bajpai, D., & Tyagi, V. K. (2006). Fatty imidazolines: chemistry, synthesis, properties and their industrial applications. Journal of oleo science, 55(7), 319-329.
2. Mehedi, M. S. A., & Tepe, J. J. (2020). Recent advances in the synthesis of imidazolines (2009–2020). Advanced Synthesis & Catalysis, 362(20), 4189-4225.
3. Zhuang, W., Wang, X., Zhu, W., Zhang, Y., Sun, D., Zhang, R., & Wu, C. (2021). Imidazoline gemini surfactants as corrosion inhibitors for carbon steel X70 in NaCl solution. ACS omega, 6(8), 5653-5660.
4. Aiad, I. A., Hafiz, A. A., El‐Awady, M. Y., & Habib, A. O. (2010). Some imidazoline derivatives as corrosion inhibitors. Journal of surfactants and detergents, 13(3), 247-254.
5. Kousar, K., Ljungdahl, T., Wetzel, A., Dowhyj, M., Oskarsson, H., Walton, A. S., ... & Lindsay, R. (2020). An exemplar imidazoline surfactant for corrosion inhibitor studies: synthesis, characterization, and physicochemical properties. Journal of Surfactants and Detergents, 23(1), 225-234.
6. Tripathy, D. B., & Mishra, A. (2017). Waste Cooking Oil‐Based Novel Gemini Imidazolinium Surfactants With Carbonate Linkage: Green Synthesis, Characterization and Properties Evaluation. Journal of Surfactants and Detergents, 20(3), 553-564.
7. Gawali, I. T., & Usmani, G. A. (2020). Synthesis, surface active properties and applications of cationic gemini surfactants from triethylenetetramine. Journal of Dispersion Science and Technology, 41(3), 450-460.
8. Khusanov, A., Kaldybayeva, B., Kramarev, S., Melnik, A., & Abilmagzhanov, A. (2015). Perspectives of low-grade vegetable oils utilization in surfactants production. Industrial technology and engineering, (2), 35-41.
9. Kousar, K., Ljungdahl, T., Wetzel, A., Dowhyj, M., Oskarsson, H., Walton, A. S., ... & Lindsay, R. (2020). An exemplar imidazoline surfactant for corrosion inhibitor studies: synthesis, characterization, and physicochemical properties. Journal of Surfactants and Detergents, 23(1), 225-234.
10. Tripathy, D. B., & Mishra, A. (2017). Microwave synthesis and characterization of waste soybean oil-based gemini imidazolinium surfactants with carbonate linkage. Surface Review and Letters, 24(05), 1750062.