氧乙烯基对胶团化过程热力学函数的影响

利用表面张力法测定了各种条件下C_8H_(17)(OC_2H_4)_n-SO_4Na(C_8E_nS; n=0,1,3)的cmc, 并计算了胶团的反离子结合度、胶团化过程中的自由能(ΔG°)和熵变(ΔS°)。结果发现: C_8E_nS的cmc随n的增加而下降, 并且下降的幅度逐渐变小; 胶团的反离子结合度也随n的增加而减小; ΔS°随n的增加而增加, 但增加的幅度逐渐变小, 对于离子和非离子表面活性剂都是如此。人们认为这是由于氧乙烯基(EO)具有亲水和疏水二重性, 随着EO数的增加, EO的疏水性相对减弱而亲水能力将相对增加所致。EO的这个特点, 是它在表面活性剂分子中具有特殊表现的根本原因。

EFFECTS OF OXYETHYLENE ON THERMODYNAMIC FUNCTION OF THE MICELLIZATION

The cmc's of C_8H_(17) (OC_2H_4)_nSO_4Na (C_8E_nS; n=0, 1, 3) under varied conditions have been measured by the drop-volume method. The free energy (ΔG°) and entropy (ΔS°) of the micellization of surfactants, and the counter-ion binding constant (K) of micelle have been calculated. The results show that the cmc of C_8E_nS decreases with increasing n, but the rate of declination gradually slows down; K decreases as n increased; ΔS°increases with n, but the rate of increase slows down untill ΔS°being constant, which is the general trend (for ionic or nonionic surfactants, the conclusion is correct). This may be interpreted as that the oxyethylene group (EO) decrease with the increasing of EO number. The feature of the EO decides its special function in surfactant molecules.