The micellization process of a series of cationic gemini surfactants <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$\left[{C}_{{\rm m}}{H}_{2m+1}{\left(C{H}_{3}\right)}_{2}N{\left(C{H}_{2}\right)}_{{\rm s}}N{\left(C{H}_{3}\right)}_{2}{C}_{{\rm n}}{H}_{2{\rm n}+1}\right]B{r}_{2}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mfenced close="]" open="["> <msub> <mi>C</mi> <mi mathvariant="normal">m</mi> </msub> <msub> <mi>H</mi> <mrow> <mn>2</mn> <mi>m</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <msub> <mfenced close=")" open="("> <mi>C</mi> <msub> <mi>H</mi> <mn>3</mn> </msub> </mfenced> <mn>2</mn> </msub> <mi>N</mi> <msub> <mfenced close=")" open="("> <mi>C</mi> <msub> <mi>H</mi> <mn>2</mn> </msub> </mfenced> <mi mathvariant="normal">s</mi> </msub> <mi>N</mi> <msub> <mfenced close=")" open="("> <mi>C</mi> <msub> <mi>H</mi> <mn>3</mn> </msub> </mfenced> <mn>2</mn> </msub> <msub> <mi>C</mi> <mi mathvariant="normal">n</mi> </msub> <msub> <mi>H</mi> <mrow> <mn>2</mn> <mi mathvariant="normal">n</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> </mfenced> <mi>B</mi> <msub> <mi>r</mi> <mn>2</mn> </msub> </mrow> </math></EquationSource> </InlineEquation> (designated as m-s–n with m = 10, s = 4, 6, 8 10, and n = 6, 10, and 12, symmetric with m = n) has been investigated using conductivity and isothermal titration calorimetry (ITC) as a function of temperature. The CMC values and the degrees of counterion dissociation, determined from conductivity experiments,  represent perhaps the first complete assessment for a series of symmetric and dissymmetric amphiphiles as a function of temperature and spacer length from any technique. The thermodynamic properties of micelle formation were obtained by calculating the Gibbs energies of micelle formation (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">$\Delta_{{{\text{mic}}}} G)$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi mathvariant="normal">Δ</mi> <mtext>mic</mtext> </msub> <mrow> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> from the conductivity and the counterion dissociation data at each temperature and applying the Gibbs–Helmholtz equation and the Gibbs equation to obtain the enthalpies and entropies of micelle formation (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">$\Delta_{{{\text{mic}}}} H$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi mathvariant="normal">Δ</mi> <mtext>mic</mtext> </msub> <mi>H</mi> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq4"> <EquationSource Format="TEX">$\Delta_{{{\text{mic}}}} S$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi mathvariant="normal">Δ</mi> <mtext>mic</mtext> </msub> <mi>S</mi> </mrow> </math></EquationSource> </InlineEquation>), respectively. The <InlineEquation ID="IEq5"> <EquationSource Format="TEX">$\Delta_{{{\text{mic}}}} H$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi mathvariant="normal">Δ</mi> <mtext>mic</mtext> </msub> <mi>H</mi> </mrow> </math></EquationSource> </InlineEquation> values were also obtained directly for the same systems using isothermal titration calorimetry; from the calorimetrically determined CMC values and the degrees of counterion dissociation from conductance measurements, the calorimetric <InlineEquation ID="IEq6"> <EquationSource Format="TEX">$\Delta_{{{\text{mic}}}} G$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi mathvariant="normal">Δ</mi> <mtext>mic</mtext> </msub> <mi>G</mi> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq7"> <EquationSource Format="TEX">$\Delta_{{{\text{mic}}}} S$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi mathvariant="normal">Δ</mi> <mtext>mic</mtext> </msub> <mi>S</mi> </mrow> </math></EquationSource> </InlineEquation> values were obtained. As expected, the values of the micellar thermodynamic properties from both techniques are not comparable! However, the results from both techniques agree in that only a minor effect on the CMC (and hence, the <InlineEquation ID="IEq8"> <EquationSource Format="TEX">$\Delta_{{{\text{mic}}}} G$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi mathvariant="normal">Δ</mi> <mtext>mic</mtext> </msub> <mi>G</mi> </mrow> </math></EquationSource> </InlineEquation> values) is found with changing temperature, spacer length, and the ratio of m/n (the degree of dissymmetry). However, we see large effects on both the aggregate enthalpy and entropy as both the spacer length and the degree of dissymmetry changes. The trends in the thermodynamic properties of micelle formation can be rationalized in terms of the intermolecular and intramolecular contributions to hydrophobic interactions versus hydrophobic effects and electrostatic interactions because of packing differences in the micelles.

The thermodynamics of micelle formation of 10-series symmetric and dissymmetric cationic gemini surfactants

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发表日期：

2026年1月6日

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Ahmed A. Elgendy,
Allison M. Clark,
Hunter G. Johnson,
Pratap Bahadur,
Olivia M. Singer,
Jacob G. Hoare,
Liah D. Christie,
Robert D. Singer,
D. Gerrard Marangoni

摘要

The micellization process of a series of cationic gemini surfactants $\left[{C}_{{\rm m}}{H}_{2m+1}{\left(C{H}_{3}\right)}_{2}N{\left(C{H}_{2}\right)}_{{\rm s}}N{\left(C{H}_{3}\right)}_{2}{C}_{{\rm n}}{H}_{2{\rm n}+1}\right]B{r}_{2}$ $[C_{m}, H_{2 m + 1}, {(C, H_{3})}_{2}, N, {(C, H_{2})}_{s}, N, {(C, H_{3})}_{2}, C_{n}, H_{2 n + 1}] B r_{2}$ (designated as m-s–n with m = 10, s = 4, 6, 8 10, and n = 6, 10, and 12, symmetric with m = n) has been investigated using conductivity and isothermal titration calorimetry (ITC) as a function of temperature. The CMC values and the degrees of counterion dissociation, determined from conductivity experiments, represent perhaps the first complete assessment for a series of symmetric and dissymmetric amphiphiles as a function of temperature and spacer length from any technique. The thermodynamic properties of micelle formation were obtained by calculating the Gibbs energies of micelle formation ( $\Delta_{{{\text{mic}}}} G)$ $Δ_{mic} G)$ from the conductivity and the counterion dissociation data at each temperature and applying the Gibbs–Helmholtz equation and the Gibbs equation to obtain the enthalpies and entropies of micelle formation ( $\Delta_{{{\text{mic}}}} H$ $Δ_{mic} H$ and $\Delta_{{{\text{mic}}}} S$ $Δ_{mic} S$ ), respectively. The $\Delta_{{{\text{mic}}}} H$ $Δ_{mic} H$ values were also obtained directly for the same systems using isothermal titration calorimetry; from the calorimetrically determined CMC values and the degrees of counterion dissociation from conductance measurements, the calorimetric $\Delta_{{{\text{mic}}}} G$ $Δ_{mic} G$ and $\Delta_{{{\text{mic}}}} S$ $Δ_{mic} S$ values were obtained. As expected, the values of the micellar thermodynamic properties from both techniques are not comparable! However, the results from both techniques agree in that only a minor effect on the CMC (and hence, the $\Delta_{{{\text{mic}}}} G$ $Δ_{mic} G$ values) is found with changing temperature, spacer length, and the ratio of m/n (the degree of dissymmetry). However, we see large effects on both the aggregate enthalpy and entropy as both the spacer length and the degree of dissymmetry changes. The trends in the thermodynamic properties of micelle formation can be rationalized in terms of the intermolecular and intramolecular contributions to hydrophobic interactions versus hydrophobic effects and electrostatic interactions because of packing differences in the micelles.