**4. Properties**

#### **4.1 Surface tension**

Surface tension is the necessary exertion which is obligatory for the enhancement of the surface area of a liquid due to intermolecular force. Surfactant helps in reducing the surface tension of the liquid. An increase in the concentration of surfactants leads to a decrease in surface tension. Gemini imidazoline surfactantcontaining stearic acid solution increased in the concentration from 0.1813 to 0.3626 g/l whereas the surface tension decreased from 42.8 to 28.6 mN/m. Again, the process repeated, the concentration of surfactant increased up to 0.6250 g/l leads to a decrease in the surface tension to 27.6 mN/m and a final increase in the concentration to 1.25 g/l and 2.5 g/l but the surface tension remained unchanged [22].

In the same study, the CMC values of 1% aqueous solution of gemini surfactants were found in the range from 0.0016 to 0.0032 mol/l that depends on the alkyl chain length (**Figure 8**). Greater the chain length of hydrophobic alkyl moiety, greater the CMC values of surfactant solutions [22].

#### **Figure 8.**

*Variation in surface tension and CMC values with hydrophobic chain [20].*

#### **4.2 Dispersion**

An arrangement in which scattered particles of one substance dispersed to another substance is known as dispersion phenomena. Surfactants help in stabilizing the dispersion phenomena. Cationic gemini imidazoline surfactant showed stable and good dispersion capability. Gemini imidazoline surfactant-containing stearic acid had a cloudiness of about 4.8 ml that decreased with time. After 5 minutes, it was 3.6 ml and decreased to 3.0 ml after 10 minutes [20, 22]. The trend was found same when the gemini surfactants of different length of hydrophobic chain

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**4.5 Wettability**

**Figure 9.**

*Gemini Imidazolinium Surfactants: A Versatile Class of Molecules*

stability of dispersion was found to be decreased (**Figure 9**).

gemini imidazoline surfactants make the fabrics soft.

**4.4 Critical micelle concentration (CMC)**

*Dispersibility of gemini surfactants based on different fatty acids.*

and the breaking point revealed the mentioned value [6].

have been studied but in addition it was also revealed that decrease in the chain length of hydrophobic group increases the dispersibility of surfactants but the

Cationic surfactants are used as fabric softening agents. The most common cationic surfactants which are used for softening agents are quaternary ammonium salts, imidazolinium salts, etc. [35]. The softening of surfactants decreases with the decrease in the length of the chain of the alkyl group. When compared with surfactants, it showed that surfactant-containing oleic acid had moderate softening behavior whereas fatty and highest alkyl chain has less softening. Fabrics treated with surfactants found to be soft as compared to untreated fabrics. Therefore,

The surface-active agent present in solutions helps in the formation of micelles

The capability of a liquid to comes in contact with a surface of a solid and maintains it; this process is known as wettability. The adhesive and cohesive interaction helps in maintaining the interaction between liquid to solid and liquid to liquid. This property of gemini imidazoline surfactant increases with a decrease in the

and this phenomenon is named as Micellization. This phenomenon occurs in critical micellar concentration or slender concentration. The surfactants can lower down the surface tension of the molecule which occurs due to the free monomer concentration and starts the micelle formation. This micelle formation in the solution is termed as critical micelle concentration. CMC is determined by the surface tension of the surfactant. An increase in concentration leads to a decrease in the surface tension until it reaches the critical micelle concentration. It was determined by plotting the graph of surface tension against the algorithm concentration of the surfactant. Critical micelle concentration and surface tension decreased with an increase in the length of the alkyl chain [10]. Zhang et al. research showed the CMC value of Gemini surfactant as 3.2\_10\_4 mol/L (194.9 mg/L) as per the graph reading in which surface tension plotted against log molar concentration of the surfactant

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

**4.3 Softening**

have been studied but in addition it was also revealed that decrease in the chain length of hydrophobic group increases the dispersibility of surfactants but the stability of dispersion was found to be decreased (**Figure 9**).
