Kinetics of the Sphere-to-Rod like Micelle Transition in a Pluronic Triblock Copolymer

Abstract

The kinetics of the sphere-to-rod transition was studied in aqueous micelle solutions of triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) pluronic P103 (PEO(17)PPO(60)PEO(17)). This transition was triggered by a temperature jump from the sphere phase to the rod phase and monitored with dynamic light scattering. The combination of the scattering intensity and the hydrodynamic radius were used to show that the micelles grow steadily as rods throughout the growth process. The transition was found to exhibit a single exponential behavior even in the case of large deviations from equilibrium. The linear increase in the decay rate with increasing copolymer concentration shows that the transition is dominated by a mechanism involving fusion and fragmentation of proper micelles. The decays of the sphere-to-rod transition were simulated for two pathways: random fusion fragmentation and successive addition of spherical micelles to rods. We show that micelle growth most likely occurs via random fusion-fragmentation. The second order rate constant for fusion and the fragmentation rate are calculated for the case of random fusion-fragmentation.

ABC Triblock Copolymer Micelles: Spherical Versus Worm-Like Micelles Depending on the Preparation Method

“…We believe that this effect may be related to the higher initial local concentration of the polymer (even though the overall concentration is constant) when the fi lm rehydration method is used and/or different kinetics of formation of the two shapes of micelles. [ 36,37 ] Although we observed no changes in micelle structures over the timescales of the experiments used here (approximately 1 h or so), it currently remains an unresolved question whether or not the micelles observed here change over much longer timescales to reach a (preparation method independent) true equilibrium state. Further experiments will be performed to investigate this aspect.…”

“…However, the most interesting and novel observation of these studies is that either worm‐like or spherical micelles can be obtained by changing only the rehydration method with all other conditions kept constant. We believe that this effect may be related to the higher initial local concentration of the polymer (even though the overall concentration is constant) when the film rehydration method is used and/or different kinetics of formation of the two shapes of micelles . Although we observed no changes in micelle structures over the timescales of the experiments used here (approximately 1 h or so), it currently remains an unresolved question whether or not the micelles observed here change over much longer timescales to reach a (preparation method independent) true equilibrium state.…”

pH induced tuning of size, charge and viscoelastic behavior of aqueous micellar solution of Pluronic ® P104–anthranilic acid mixtures: A scattering, rheology and NMR study

“…Such type of behavior is related to transformation of sol solution into dominantly elastic nature within the frequency range. The viscoelasticity originates from either formation of well-defined micellar structure or micellar growth [63][64][65][66]. In this study, the increase in viscosity has been assigned to the spherical to ellipsoidal micellar transition as also evident from DLS and SANS studies.…”

Triblock copolymer P104 detailed behavior through a density, sound velocity and DLS study

“…Light Scattering Intensity correlation function g 2 (q,t) was analyzed with the cumulants method [6] using the following equation:…”

“…DLS measurements were performed in a temperature range from 10 to 64 ºC to obtain information about the shape of the micelles from the combination of the scattering intensity and the hydrodynamic diameter [6]. The structural information of P104 molecules at the transition temperatures was obtained at a constant scattering angle of 90º for P104 concentrations of 1 and 2 %wt (Figure 1a and 1b).…”