Micellization and Clouding Behavior of EO–PO Block Copolymer in Aqueous Salt Solutions

Abstract

Aqueous solution properties of polyethylene oxide-block-polypropylene oxide-block-polyethylene oxide TBP [(PEO) 103 (PPO) 39 (PEO) 103 ] were studied in the presence of sodium salts with different anions (NaI, NaBr, NaCl, NaF, Na 2 SO 4 , Na 3 PO 4 ) to investigate unimer-tomicelle transition [critical micelle concentration (CMC), critical micellization temperature (CMT)], micelle size and the phase separation (cloud point). This TBP, due to its very hydrophilic (80% PEO) nature does not form micelles at ambient temperatures. Micellization can be induced much below its CMT in water on addition of sodium salts having different anions. Analytical methods viz. fluorescence, FTIR and dynamic light scattering (DLS) were used to monitor the salt-induced micellization. The hydration of respective anion and resultant contribution to its salting-out effect was found to be the governing factor in promoting micellization. The presence of salt decreases the CMC, CMT and phase separation temperature. The salts affect the aggregation process in agreement with an order mentioned in Hofmeister series.

Induced micellization and micellar transitions in aqueous solutions of non-linear block copolymer Tetronic® T904

“…Hence here the gradual increase in viscosity following the initial decrease is mainly attributed to two contributing factors: the change in shape of the micelles and the magnitude of the intermicellar interactions at higher temperatures/salt concentrations (where the micelles are large). These results are in line with those reported for similar systems in water [47,48] and salt solutions [33,42,43,49]. The sudden rise in relative viscosity was found approximately at 50°C, 45°C and 40°C for 0.25 M, 0.5 M and 1.0 M concentrations of NaCl, whereas this transition temperature for the 0.25 M Na 2 SO 4 / 0.125 M Na 3 PO 4 was about 42.5°C, which is in accordance with Hofmeister series (the effect is in the order of Cl À < SO 2À 4 < PO 3À 4 ) and discussed in detail in the clouding behavior Section 3.1.…”

“…S1, marked changes in the cloud points occurred following the admixture of strong kosmotropes (SO 2À 4 and PO 3À 4 ). The differences in CP were in the order Cl À < SO 2À 4 < PO 3À 4 which follows the Hofmeister series, supporting the working hypothesis that the 'salting out' effect increases with the multivalency of ions and decreases with the growth of the ionic radius [35,42,43].…”

“…The viscosities of the aqueous solutions of EO-PO based copolymeric surfactants are determined primarily by the concentration and shape of the micelles. The fact that the intermicellar interaction is repulsive or weakly attractive in nature plays an insignificant role in it, especially at ambient temperature and salt concentration for a given copolymer concentration [33,42,43,[47][48][49]. Hence here the gradual increase in viscosity following the initial decrease is mainly attributed to two contributing factors: the change in shape of the micelles and the magnitude of the intermicellar interactions at higher temperatures/salt concentrations (where the micelles are large).…”

“…6). An increase in the micelle size decreases the diffusion of micelles in solution and makes the structures less mobile; as observed by the increase in viscosity [42,43,50].…”

Synthesis and Self‐Assembly Behavior of Comb‐Like Surfactant Polymethyl Methacrylate‐g‐Methoxy Polyethylene Glycol

“…To determine the formation of the aggregates, the oil-soluble dye dimethyl yellow was chosen as the probe [24][25][26].…”