Spectrometric studies on the cloud points of Triton X-405

The effect of various chemicals on the cloud point (CP) of nonionic surfactant Triton X-405 (TX-405) in aqueous solutions has been investigated. In the measurements of cloud point temperatures, UV–visible spectrophotometer was used instead of visual observation. The values of CP for Triton X-405 could not be measured directly because TX-405 had an average number of oxyethylene units per molecule, p ≈ 35 and a CP > 100 °C. To avoid additional measurements under pressure, TX-405 had their CP lowered below the normal boiling point of their solutions by adding the salting-out, CP-lowering salts at various concentrations, measuring the depressed CP values and extrapolating them to zero salt concentration. The CP values decrease linearly with increasing concentration of salts at studied concentrations. The results showed that the addition of the simple salts and nonionic surfactant Triton X-114 (TX-114) which are infinitely miscible with water decreased the cloud point of the TX-405. In this study, the real CP values of TX-405 which are merely listed as >100 °C in the literature was found as 116 ± 1 °C in various samples. In the lyotropic series, it is expected that the effect of F⁻ > Cl⁻ > Br⁻ will be on the decrease in CP, because the ionic sizes increase along the group consequently decreasing the formal charge density on anion, thus lowering the attraction on anion and thereby lowering the attraction of water. The order of CP depression for the other anions is as follows: PO₄³⁻ > SO₄²⁻ > NO₃⁻ > Br⁻. This means that electrolyte containing trivalent anions is more effective at salting-out the PEO chain than those containing divalent anions and monovalent anions. Cations effectiveness is present in the following order for change: Na⁺ > K⁺ > NH₄⁺ because of their effect on water structure and their hydrophilicity. Overall the electrolytes and nonelectrolytes have a large amount of effect on CP of nonionic surfactant, because of their effect on water structure and their hydrophilicity.