The Interaction of Nonionic Surfactants with Iodine. II.

Abstract

Authors reported in the previous paper that aqueous solution of nonionic surfactant of polyethenoxy ether becomes reddish and turdid when aqueous iodine-potassium iodide solution is added dropwise and that the quantity of iodine solution required to produce the turbidity is related with the number of moles of ethylene oxide added in the surfactant.In this report, it was found that the maximum wavelength in the absorption spectrum of aqueous iodine-potassium iodide solution, when a nonionic surfactant is added into this solution, remained at constant of 350mμ in the lower concentration, but bigan to shift towards the longer wavelength at a definite concentration, and above this concentration it reached at 363374mμ and became constant (Fig. 1). The relation between the concentration of the surfactant and the wavelength of absorption maximum is shown in Fig. 3 and the concentration at which the shift of wavelength will begin can be obtained from this graph.It is believed that this dues to the molecular dispersion at low concentration of surfactant and micelle begins to form when it reaches to a certain concentration and that this micelle forms complex with iodine and begins to discolor (Fig. 4). It is assummed that the concentration at which this discoloration, or the shift of wavelength begins, is the CMC of this surfactant.Hence, a series of solutions which contain various quantities of nonionic surfactant in a definite quantiy of iodine-potassium iodide were prepared, then their spectra were measured and the concentration “Cm” at which the shift of absorption maximum wavelength began was determined (Fig. 57).From these results, it was found that Cm is correlated with n, the number of moles of ethylene oxide added (Table 1), and that the shift begins at higher concentration with the increase in number of moles aded (Fig. 8). Further, between “n” and “Cm” in the unit of 10-4mole/liter, there are linear relations as below.OP-series logCm=0.012n+0.31NP-series logCm=0.0125n-0.18C-series logCm=0.010n-0.65In connection with this study, Ross et al. and Becker reported recently, independently from the authors' research, that CMC has been obtained from the change in extinction at 360mμ of the colored complex of iodine and surfactant micelle. However, the color of the complex has a tendency to fade (cf. Fig. 1 and 2) and its use in determination of CMC will introduce uncertainty. On the contrary, as the maximum wavelength used in this report does no change with time, its use for determination of CMC is considered to be quite reasonable.On the other hand, in case of polyethylene glycol solution the concentration at which the maximumm wavelength begins to shift is considerably high (10 g/100 ml, for carbowax 400), and in the case of carbowax 4, 000 the absorption disappears occassionally (Fig. 9). It is considered that in the case of polyethylene glycol micelle is not formed, but the shift of absorption maximum dues, rather, to the solvent effect (Fig. 10).