Micellization and Micellar Structure of a Poly(ethylene oxide)/Poly(propylene oxide)/Poly(ethylene oxide) Triblock Copolymer in Water Solution, As Studied by the Spin Probe Technique

Abstract

The micellization of the triblock copolymer Pluronic P85 (poly(oxyethylene)27/poly(oxypropylene)39/poly(oxyethylene)27) in aqueous solution was followed vs temperature and addition of aliphatic alcohols, using the spin probe technique. Different types of probes properly chosen (spin-labeled (SL) poly(oxyethylene(4))nonylphenol, SL-Pluronic L62, TEMPO-laurate, TEMPO-hexanoate, CAT 4, CAT 8, CAT 11, CAT 16, and 5-, 7-, 10-, and 12-doxylstearic acids) provided information about the micellar structure (polarity, viscosity, and order degree) at different radial locations. Micellization was found to be low at room temperature, even for 10% aqueous solutions, but strongly increasing with temperature increase to about 323 K. Hydration of the poly(oxyethylene) (PEO) chains in the shell was found to diminish toward the interior and with increasing temperature. At an intermediate region of the shell, a hydration number ([H2O]/EO unit) close to 3 was found at 293 K, which decreased to ∼1 at 323 K. No hydration was found in a region corresponding to 4−6 EO units from the core. At the PPO/PEO interface, a further decrease in polarity occurred in the 323−373 K temperature range, probably due to an extension of the hydrophobic core with increasing temperature, with prevalence of the nonpolar conformations of the PPO and PEO chains. At 323 K, the order degree of the PEO chains decreased rapidly toward the interior of the shell. Addition of medium chain aliphatic alcohols to the aqueous solution of the polymer substantially enhanced micellization at room temperature. The effect increased with the alcohol chain lenght in the C4−C6 series. The addition of alcohols (C5, C6) was found to have similar effects with temperature increase, i.e., to promote micellization and to reduce the hydration and the order degree in the shell. In both cases the effects are due to an increased hydrophobe character of the core.

Effect of surfactants on plasticizer biodegradation by Bacillus subtilis ATCC 6633

“…This would be consistent with the fact that several different surface-active compounds were able to cause the large increase in the concentrations of the alcohol and monoester. Alcohols have been shown to interact closely with surfactants in an aqueous medium (Caragheorgheopol et al 1997;Lin and Jiang 1997). In particular, they have been shown to form mixed micelles with surfactant molecules and subsequently change the surface chemistry of the mixture (Patist et al 1998;Marangoni and Kwak 1991;Bockstahl and Duplatre 2001;Akhter and Al-Alawi 2000;Trotta et al 1993;Su et al 2003).…”

Effect of phenol on the aggregation characteristics of an ethylene oxide–propylene oxide triblock copolymer P65 in aqueous solution

“…Above the CMT, the micellar size generally increases progressively with an increase in temperature before the solution phase separates at the cloud point (CP). The influence of temperature [8][9][10][11][12], various watersoluble electrolytes [13][14][15][16][17], and solvents [18][19][20] on the selfassembly behaviour of these copolymers in water has previously been reported. On approaching the cloud point many of these copolymer micellar solutions exhibit sphere to rod transitions [5][6][7][8][9][10][11].…”

“…Using NMR and fluorescence-quenching studies, Almgren et al [21] showed that the surfactant induces the micellization at low concentrations of Pluronics (below the CMC) and forms mixed micelles thereafter. A limited numbers of studies on the 0021-9797/$ -see front matter © 2007 Elsevier Inc. All effect of the addition of cosolvents such as alcohols and highly polar solvents such as glycerol, propylene glycol, and other glycols on the phase behaviour of Pluronics have been reported [18][19][20]. The different glycols locate in different microdomains of Pluronic and can change the interfacial properties; the ability of this molecule has been studied and reported [18].…”

“…Leharne and co-workers report that methanol, ethanol, and formamide prevent the onset of micellization for F87 in water, while butanol and hydrazine favour micelle formation [19]. Medium-chain aliphatic alcohols have a profound effect on the micellization of P85 in water; the effect increases with the alcohol chain length (C 4 -C 6 ) [20].…”

Dynamic Light Scattering Studies on the Effect of 1‐Alkanols, Alkanediols and Alkoxyethanols on the Micelles of a Moderately Hydrophobic/Hydrophilic PEO‐PPO‐PEO Triblock Copolymer

“…An increase in hydrodynamic size may be accounted for by increased shell thickness due to higher solvation of the PEO blocks in the [23]. Addition of higher chain alcohols, replaces the water surrounding of the PPO block, and an interaction between the alkyl chain of alcohol and PPO segments may take place [24]. The location of solubilized alcohol is in the core and/ or the palisade layer of the micelles, due to the relatively less polar nature of the higher alcohol would decrease the water content in the micellar core and increase the hydrophobicity which leads to an enhanced propensity of the sphere-to-rodlike transition particularly on approaching the cloud point.…”