The effects of electrolytes, alcohols, and urea on the aggregation of SDS, CTAB, and Triton X-100 at 25℃ have been investigated by fluorescence probing of pyrene. Both electrolytes and alcohols reduce the critical mi...The effects of electrolytes, alcohols, and urea on the aggregation of SDS, CTAB, and Triton X-100 at 25℃ have been investigated by fluorescence probing of pyrene. Both electrolytes and alcohols reduce the critical micelle concentration (CMC) of the ionic surfactants, while the effect of the former is more pronounced. It is shown that the effects of electrolytes mainly depend on the concentrations and especially the valence of the opposite charge ions, and only slightly depend on the same charge ions in respect of ion aggregate of micelle. The logarithm of CMC is not linearly correlated with the concentrations of the counter ion or the electrolytes. The results are rationalized in terms of Hartley's model. Propanol increases the CMC of TX-100, while electrolytes and urea do not. In all the three kinds of surfactant micelles the excitation spectrum of pyrene slightly red-shifts (ca. 4 nm) from that in water, but is not affected by the additives. The micropolarity of the environment in which pyrene molecule resides in SDS micelle decreases with the increase of the concentrations of electrolytes. This is not the case when alcohols and urea were added to SDS or to TX-100. It is suggested that the addition of electrolytes would result in more orderly orientation of SDS molecules. It is the binding strength of the counter ions that dominates the effects of additives on the aggregation of surfactants.展开更多
基金Project supported by the National Naural Science Foundation of China the State Education Commission Foundation of China.
文摘The effects of electrolytes, alcohols, and urea on the aggregation of SDS, CTAB, and Triton X-100 at 25℃ have been investigated by fluorescence probing of pyrene. Both electrolytes and alcohols reduce the critical micelle concentration (CMC) of the ionic surfactants, while the effect of the former is more pronounced. It is shown that the effects of electrolytes mainly depend on the concentrations and especially the valence of the opposite charge ions, and only slightly depend on the same charge ions in respect of ion aggregate of micelle. The logarithm of CMC is not linearly correlated with the concentrations of the counter ion or the electrolytes. The results are rationalized in terms of Hartley's model. Propanol increases the CMC of TX-100, while electrolytes and urea do not. In all the three kinds of surfactant micelles the excitation spectrum of pyrene slightly red-shifts (ca. 4 nm) from that in water, but is not affected by the additives. The micropolarity of the environment in which pyrene molecule resides in SDS micelle decreases with the increase of the concentrations of electrolytes. This is not the case when alcohols and urea were added to SDS or to TX-100. It is suggested that the addition of electrolytes would result in more orderly orientation of SDS molecules. It is the binding strength of the counter ions that dominates the effects of additives on the aggregation of surfactants.
