N-Alkyl Pyridinium Bromide류의 계면활성에 대한 열역학적 특성

Thermodynamic Characteris tics of Surface Activities of N-Alkyl Pyridinium Bromide

In relation to the preparation of Langmuir-Blodgett thin film, four kinds of N-alkylpyridinium bromide were synthesized. The values of surface tensions of these materials, measured with a Traube stalag mometer. gave the relationship between the critical micells hydrophobic radical and between CMC and temperature. Values of thermodynamic properties (ΔH⁰m, ΔS⁰m, ΔG⁰m,) for the formatoin of micelle were also obtained. Experiments gave the following results; at the temperature range between 40 and 60℃, CMC of Hexadecyl-, Octadecyl-, Eicosyl-, and Docosyl-Pyridinium Bromide were 7.64×10⁻⁴~9.13×l0⁻⁴, 3.85×l0⁻⁴~4.60×l0⁻⁴, 2.00×10⁻⁴~2.39×10⁻⁴, and 1.07×10⁻⁴~1.28×10⁻⁴ mol/l, respectively. Surface tension, γCMC, of those were 33.49~36.00, 34.78~37.61, 35.49~37.61 and 38.76~55.80 dyne/cm, respectively. The relationship between CMC and the mumber of carbon atoms in the hydrophobic radical, N was expressed as follows : Log(CMC)=A-BN where A and B are constants. At the temperature range between 40 and 60℃, the change of Gibbs energy(ΔGm) for one methylene group (-CH₂-) were -0.65RT, respectively. The minus values of enthalpy change (ΔHm) suggest that the formation of micelle is exothermic. Additionally, the overall increase in the entropy change (ΔSm) with respect to the temperature increase suggests that the formation of micelle is attained by a exothermic enthalpy directed process.