## 3 Results and Discussion
### Surface Properties of Gemini Surfactants  
The basic ability of surface active agents is their tendency to be adsorbed at interfaces. Mechanism of surface action of dimeric surfactants based on the adsorption of ammonium cations into a polar phase, and hydrocarbon chains in a nonpolar phase [48]. The keystone of all surfactants research is determination of their critical micelle concentration [49], the lowest concentration at which particles rapidly aggregate into micelles. The fact that dimeric alkylammonium salts have much lower CMC values than monomeric ones, creates great application possibilities for them [52; 63; 76; 77; 78; 79]. The determination of CMC is also important, because toxicity of gemini rises when their concentration surpasses CMC [80].  
The CMC was determined using a conductometric titration, creating dependency graphs of the characteristic conductivity in water of the obtained compounds as a function of the concentration. This relationship generates two lines with different slopes. The straight line with higher inclination illustrates behavior before micellization, whereas the line with a smaller slope indicates the process of micellization (Figure 3). The intersection of lines formed as a result of linear regression defines CMC [50; 59].  
The values for the slope ratios of linear regression in pre- and post-micellization regions allow estimating the degree of ionization (\(\alpha\)) and the degree of counterion binding parameter (\(\beta\)). These parameters demonstrate the capability of the counterion binding on  
Figure 3: Specific conductivity versus surfactant concentration in water for 16-O-16.  
Figure 2: FTIR spectra for 16-6-16 and 16-O-16.  
the micelles [50; 59]. Knowing the values of CMC and \(\beta\) allow for calculation of Gibbs free energy of micellization (\(\Delta\text{G}^{\text{o}}_{\text{mic}}\)) [81]. The experimental values of CMC, \(\alpha\), \(\beta\) and \(\Delta\text{G}^{\text{o}}_{\text{mic}}\) for the investigated gemini surfactants are given in Table 1.  
Critical micelle concentration of dimeric surfactants depends on many structural elements: length and structure of spacer and substituents and type of anion. It is well known that gemini surfactants with long (hexadecyl, octadecyl) substituents possess lower CMC values than analogues with shorter hydrocarbon chain [48; 49; 50; 57; 82; 83; 84; 85; 86]. CMCs of dimeric alkylammonium salts tested in this work are over thirty times lower, than CMC of 12-6-12 (1,6-hexamethylene-bis(\(N\)-hexadecyl-\(N\),\(N\)-dimethylammonium bromide)) which is 0.98 (mM) [57]. Surface activity of our gemini surfactants, although they have different spacer structure, is comparable. This result arein good correlation to our previous result--that an element of the structure, which essentially affects the surface activity, is the length of the substituent, not the structure of the linker [50].  
The 16-O-16 possesses a lower degree of ionization value than 16-6-16. The small \(\alpha\) is caused by the stronger binding of the counterion to the aggregates, suggesting better packing of the head groups and higher surface charge density at the interface [50; 51]. Both obtained gemini surfactants have negative \(\Delta\text{G}^{\text{o}}_{\text{mic}}\), indicating that the micellization process is spontaneous [50; 55]. Surfactant with oxygen-functionalized spacer (16-O-16) shows greater tendency to form micelles, because in this case \(\Delta\text{G}^{\text{o}}_{\text{mic}}\) is lower.