**Abstract**

Gemini imidazolinium surfactants fascinated the researchers and many industries towards it due to their distinct molecular structure. It belongs to the cationic surfactant group. The variation in the physicochemical properties of the gemini surfactant can be achieved by changing the characteristics in the structure. There are several applications of imidazolinium such as antistatic agents, fabric softener that makes it a demanding surfactant in detergent industries as well as in the laundry industries due to the immense number of properties like dispersibility, viscosity, desirable storage stability, emulsification, critical micelle concentration and fabric conditioning etc. This book chapter discussed about the Gemini imidazolinium surfactants and its various properties, synthesis methods and applications in various fields.

**Keywords:** gemini, surfactants, imidazoline, imidazolinium, emulsification

## **1. Introduction**

The use of surfactants has been increasing due to their enormous applications in the field of chemistry. They belong to the organic compound group used in oil recovery, pharmaceuticals, nanoscience, biological activity, fabric softener, antibacterial and anti-foaming agents, and other technologies [1, 2]. Gemini is categorized as a surfactant and was first used by Menger in 1990 [3]. The word gemini means dimeric, an amphiphilic molecule, earlier it used to be synthesized by joining the two discrete surfactant molecules by a rigid spacer. It contains two terminal hydrocarbon tails (short or long); two polar head groups (cationic, anionic, or nonionic); and a spacer (short or long, flexible or rigid) [4]. The gemini surfactant has an efficiency of self- assembling at low concentration. In assessment with other surfactants, the gemini surfactant shows better surface activity. The presence of two polar groups and two terminal tails also made it more hydrophobic and hydrophilic as compared to monomeric surfactant systems. The substantial qualities of gemini viz., economic efficiency, flexibility, and functionality lead to its speedy demand in the field of research as well as in industry for examination and the use of it in various products. They also have other enhanced properties like low critical micelle concentration, wetting properties, efficient for high adsorption process, low surface tension, vesicle formation, helps in reduction of interfacial tension, and have the quality for aggregation [5]. The variation in the physicochemical properties of the gemini surfactant can be achieved by changing the characteristics in the structure. The cationic gemini surfactant has a wide range of purposes in the synthesis of

nanorods, nanoparticles, construction of porous material, the formation of skincare products, drug development, gene therapy, and in antimicrobial process. Some examples of cationic gemini surfactants are piperidinum, pyridinium, imidazolium, imidazolinium, amino acid, and pyrrolidinum [6] (**Figure 1**).

**Figure 1.** *Gemini surfactant [4].*

As per the conducted studies, the spacer in the gemini surfactant has played a significant role in aggregation property. Examination conducted by Wanger et al. on cationic Gemini surfactants showed that spacer group has effect on the aggregation properties in aqueous solution. The use of hydrophilic compound and flexible spacer group helped in the formation of closely packed micelle structure as compared to the surfactant with rigid spacer group and hydrophobic compound. The micelle formation leads to decrease in surface tension of gemini surfactant which helps in increasing the surface area of surfactant. Therefore, use of hydrophilic compound and flexible spacer is in favorable condition for a better version of gemini surfactants. On gemini quaternary ammonium surfactants Zana et al. observed the behavior of association due to the spacer group in aqueous solution. Studies were conducted by Grosmaire et al. [7] on gemini surfactant spacer group to check the importance of carbon number on the micellization enthalpy for alkanediyl-α, ω-bis (dimethyl alkyl ammonium bromide) surfactants showed that the values of ΔHo m were strongly dependent on the spacer carbon number. In the transmission electron microscopy, the carbon position of C12-C-C12 reflected the thread-like formation of micelle when concentration was less than 2% wt. and when the solution contained C12-3-C12 with 7% wt.; the micelles shape was elongated. To cover better surface area, the formation of micelle concentration is crucial in

**65**

*Gemini Imidazolinium Surfactants: A Versatile Class of Molecules*

surfactant as it lowers the surface tensions and hence, the minimum amount of gemini surfactant can be used in formulation process and for the applications.

The imidazolium is one of the varieties of cationic gemini Surfactant hence named gemini Imidazolium Surfactants. The nature of imidazolium is inherent and has greater potential than any other conventional surfactant. It has a self-aggregation tendency because of the high polarization nature of its head group. Researchers are focusing on imidazolium for advanced applications and for generating an enhanced variety [8]. Studies were conducted by Bhadani et al. for the synthesis of gemini surfactants taken from cardanol oil. They synthesized two sequences of imidazolium and pyridinium based upon phenoxy ring. The hydroxyl substituted pyridinium gemini surfactants with inconstant tail length and the other sequence with a variable length of the spacer group containing hydroxyl groups in their hydrophobic carbon chains for synthesis process [9, 10]. The synthesis of the gemini surfactant with variable length of the spacer comprising hydroxyl groups in their hydrophobic carbon chains Gemini surfactant has reported by P. Patial et al. [11]. They further assessed the surface properties of the synthesized surfactants [7, 12]. This carbon chain length is useful factor in the efficiency of surfactant, shorter the length of carbon chain, higher the suppressive efficiency of gemini surfactant [13].

Gemini imidazoline surfactant fascinated the researchers and many industries towards it due to their distinct molecular structure. The bonding groups involvement is the crucial aspect in gemini surfactant for the modification of structure which affects the interface and solution properties [13, 14]. Conventional imidazolinium surfactant used to form with a polar imidazolinium head group and a long hydrocarbon tails, it used to be single chain structures whereas the Gemini imidazolinium surfactants are made up of two polar imidazolinium head group and two tails of hydrocarbon in which head groups are linked by a spacer [15]. It has enhanced surface-active properties than the conventional surfactants like corrosion inhibition, dispersibility, low critical micelle concentration, and hold better qualities as a softening agent [13, 16–18]. The Gemini surfactants are formed by adding two monomer surfactants with a binding group where the length of the monomer end chain can vary in length. It can be anionic, non-anionic, or cationic whereas the binding group varies in length and can be inflexible, soft, aromatic, or aliphatic. Other distinct chemicals and physical properties of gemini imidazoline surfactants are lower kraft point, the ability of self-assembling, high density, compatibility, inimitable rheological properties, etc. It has some other applications in drug delivery, nanoscience, and nanotechnology, molecular biology, in porous constituents, biological activity, etc. The applications of imidazolinium such as antistatic agents, fabric softener make it a demanding surfactant in detergent industries as well as the laundry industries due to the immense number of properties like dispersibility, viscosity, desirable

As per the researches, the adaptation of various methods for synthesis and designing has been adopted which leads to the variation and enhancement in the synthesis methods and a better product. Some of the researchers prepared the gemini imidazolinium surfactant by microwave synthesis process that enhanced synthesis efficiency and also studied their surface properties. The microwave synthesized the surfactant in 5–10 minutes with a better yield of 80–91% as compared to conventional method i.e. thermal condensation which produced 75–80% [19–22]. The comparative study

*DOI: http://dx.doi.org/10.5772/intechopen.94209*

**1.1 Imidazolium gemini surfactant**

**1.2 Imidazolinium gemini surfactants**

storage stability and fabric conditioning [16] (**Figure 2**).

surfactant as it lowers the surface tensions and hence, the minimum amount of gemini surfactant can be used in formulation process and for the applications.
