**1.1 Imidazolium gemini surfactant**

*Colloids - Types, Preparation and Applications*

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,

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

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

imidazolinium, amino acid, and pyrrolidinum [6] (**Figure 1**).

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the values of ΔHo

**Figure 1.**

*Gemini surfactant [4].*

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].

#### **1.2 Imidazolinium gemini surfactants**

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

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

**Figure 2.** *Gemini imidazoline surfactant [16].*

has also been done by Jianbin Huang on gemini and Bola, and the role of cephalic groups was found to be important as they alter their properties. A. Migahed et al. studied about the ligand length and its effect on the sustained release performance. The analysis showed that the shorter the length of the ligand, the better would be the effect of the sustained release [17]. Huaivu Yang et al. studied the relationship between sustained release and temperature and concluded that sustained release is directly proportional to the temperature [23]. A study done on emulsifier properties of gemini surfactants and applied it to emulsified asphalt and concluded that the minute quantity of gemini surfactant can be used in emulsified asphalt. Zhang Guanghua's et al. confirmed the sustained release effect on tinplate by synthesizing it. Yangiiang et al. studied the anti-corrosion properties of gemini surfactants and found that the surfactant works better during slow compound release [24]. All these studies analyzed the aspects of sustained release, surface properties, and length of the interval. Few of the methods used for synthesis helped in increasing the instability [25].

The gemini surfactants were compared with other single chain molecules, in which the gemini molecule structure was ambiguous. This was further studied to check the uniqueness and sustained release performance of gemini imidazoline surfactant. The comparison has been done between single- chain molecule and gemini imidazoline surfactant to observed the variations more precisely. The outcomes showed the great inhibitve efficiency in HCl solution as compared to single chain molecule. It also showed the better inhibitive effect on copper in HCl solution. The different concentration of gemini surfactant were taken to check the effect of concentration on inhibition property and it results that the inhibitive efficiency was higher when the concentration of HCl solution was less whereas for better inhibitive effect the concentration of gemini imidazoline surfactant must be more [25].
