碘光谱法测定非离子表面活性剂的临界胶束浓度

考察了碘光谱法测定非离子表面活性剂在水溶液中的临界胶束浓度（ｃｍｃ）的影响因素。欲得正确结果，须将碘－胶束溶液（不同浓度）放置，待碘的分配达到平衡（例如２４ｈ）后再进行测定，这样测得ＴｒｉｔｏｎＸ－１００、ＴｒｉｔｏｎＸ－３０５和单分散的纯化合物Ｃ１２Ｈ２５Ｏ（Ｃ２Ｈ４Ｏ）６Ｈ的ｃｍｃ分别为２．４×１０－４、３．５×１０－４和８．４×１０－５ｍｏｌ·ｄｍ－３，与文献中用表面张力法测得的结果一致。若按Ｒｏｓｓ和Ｏｌｉｖｅｒ将预先配好的溶液稀释后１小时内测定的方法，则所得结果偏低。只要测定时碘－胶束溶液已达平衡，则碘浓度在４～１２ｍｇ／１００ｍｌ范围内对ｃｍｃ的测定结果无明显的影响。文献中提到的碘浓度对ｃｍｃ测定值的影响可能是由于碘的分配未达平衡所致。

DETERMINATION OF CRITICAL MICELLE CONCENTRATIONS OF NONIONIC SURFACTANTS BY SPECTROMETRIC IODINE METHOD

The factors affecting the determination of cmc of nonionic surfactants by spectrometric iodine method have been investigated critically. In order to obtain the raliable cmc values,the iodine-micelle complex solutions have to be stocked a period of time (generally, e. g. 24h) for iodine partition equilibrium before measurements. By using this procedure, the cmc values of Triton X-100, Triton X-305 and Hexa-ethyleneglycol mono n-dodecyl ether obtained are 2.4×10-4mol· dm-3, 3.5×10-4mol·dm-3 and 8.4×10-5mol·dm-3 respectively, in agreement with the literature data obtained by surface tension measurements. On the other hand, by using the procedure of Ross and Oliver, in which the sample was measured in an hour after dilution of the stock solution, the cmc values obtained generally were lower than that of the above metioned procedure 10 %￣20%. Experiments also show that no significant effect of iodine concentration on cmc value can be detected if the iodine concentration is in the range of 4￣12mg/100ml and the iodine-micelle complex solutions have been stocked for equilibrium before measurements.