3.2. Critical micelle concentration of CTAB and TX-100 mixture
The values of the CMC of TX-100 as well as the TX-100 and CTABmixture in the water + ethanol solution were determined from theisotherms of the surface tension (Figs. 3, S6–S8 and Tables S9–S12),density (Fig. S9), dynamic viscosity (Fig. S10) and for the TX-100and CTAB mixture also from the specific conductivity (Fig. 4). Thevalues of the CTAB CMC were taken from our previous paper [31].Independently of the method used for the CMC determination, itsvalues decrease slightly to the minimum (Figs. 5 and 6), accordingto the suggestions of some investigators dealing with the aque-ous solutions of single surfactants at low ethanol concentration[32–35]. This minimum appears at different ethanol concentrationsdepending on the composition of the TX-100 and CTAB mixture.It is known that there are two decisive effects in the process ofsurfactant micellization, and these are enthalpy and entropy. Thedecrease of enthalpy and the increase of entropy cause the CMCdecrease. We have shown earlier that the surfactant mixture prac-tically does not affect the apparent and partial volume of ethanoland water. It means that the interactions between the ethanolmolecules and those of water are stronger than between surfactantsand water or surfactants and ethanol. However, it is possible thatwater molecules bonded to the oxyethylene groups of TX-100 andthe hydrophilic group of CTAB can be removed by ethanol ones and then the decrease of the repulsive forces between the hydrophilicgroups of surfactants occurs and the tendency of the surfactantsto form micelles increases. This process can be connected with thedecrease of the enthalpy in the micellization process and the smallchanges of the entropy effect. However, at the higher ethanol con-centration, the decrease of the entropy effect on the micellization ofsurfactants takes place and therefore the CMC increase is observed.At the ethanol concentration close to its CAC, the micelle formationwas not detected by any method used for the CMC determination.Of course, it is in accordance with the suggestions of Zana [36] butcontrary to the conclusions drawn by Nazir et al. [35] from theirstudies dealing with single surfactants.
3.2. Critical micelle concentration of CTAB and TX-100 mixture
The values of the CMC of TX-100 as well as the TX-100 and CTABmixture in the water + ethanol solution were determined from theisotherms of the surface tension (Figs. 3, S6–S8 and Tables S9–S12),density (Fig. S9), dynamic viscosity (Fig. S10) and for the TX-100and CTAB mixture also from the specific conductivity (Fig. 4). Thevalues of the CTAB CMC were taken from our previous paper [31].Independently of the method used for the CMC determination, itsvalues decrease slightly to the minimum (Figs. 5 and 6), accordingto the suggestions of some investigators dealing with the aque-ous solutions of single surfactants at low ethanol concentration[32–35]. This minimum appears at different ethanol concentrationsdepending on the composition of the TX-100 and CTAB mixture.It is known that there are two decisive effects in the process ofsurfactant micellization, and these are enthalpy and entropy. Thedecrease of enthalpy and the increase of entropy cause the CMCdecrease. We have shown earlier that the surfactant mixture prac-tically does not affect the apparent and partial volume of ethanoland water. It means that the interactions between the ethanolmolecules and those of water are stronger than between surfactantsand water or surfactants and ethanol. However, it is possible thatwater molecules bonded to the oxyethylene groups of TX-100 andthe hydrophilic group of CTAB can be removed by ethanol ones and then the decrease of the repulsive forces between the hydrophilicgroups of surfactants occurs and the tendency of the surfactantsto form micelles increases. This process can be connected with thedecrease of the enthalpy in the micellization process and the smallchanges of the entropy effect. However, at the higher ethanol con-centration, the decrease of the entropy effect on the micellization ofsurfactants takes place and therefore the CMC increase is observed.At the ethanol concentration close to its CAC, the micelle formationwas not detected by any method used for the CMC determination.Of course, it is in accordance with the suggestions of Zana [36] butcontrary to the conclusions drawn by Nazir et al. [35] from theirstudies dealing with single surfactants.
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