Phase diagram of the Pluronic L64-H2O micellar system from mechanical spectroscopy

Molecular Insights on Morphology, Composition, and Stability of Mixed Micelles Formed by Ionic Surfactant and Nonionic Block Copolymer in Water Using Coarse-Grained Molecular Dynamics Simulations

The nanoscale association domains are the ultimate determinants of the macroscopic properties of complex fluids involving amphiphilic polymers and surfactants, and hence, it is foremost important to understand the role of polymer/surfactant concentration on these domains. We have used coarse-grained molecular dynamics simulations to investigate the effect of polymer/surfactant concentration on the morphology of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO, i.e., pluronics or poloxamers) block copolymer, and ionic surfactants sodium dodecyl sulfate (SDS), mixed micelles in aqueous solution. The proclivity of the surfactant to form the mixed micelles is also probed using umbrella sampling simulations. In this study, we observed that the core of the pluronic + SDS formed mixed micelles consists of PPO, the alkyl tail of SDS, and some water molecules, whereas the PEO, water, and sulfate headgroups of SDS form a shell, consistent with experimental observations. The micelles are spherical at high-pluronic/low-SDS compositions, ellipsoidal at high-SDS/low-pluronic compositions, and wormlike-cylindrical at high-pluronic/high-SDS compositions. The transitions in micelle morphology are governed by the solvent accessible surface area of mixed aggregates, electrostatic repulsion between SDS-headgroups, and dehydration of PEO and PPO segments. The free energy barrier for SDS escape is much higher in mixed micelles than in pure SDS micelles, indicating a stronger tendency for SDS to form pluronic-SDS mixed micelles.

Unusual Self-Assembly of Amphiphilic Block Copolymer Blends Induced by Control of Hydrophobic Interaction

Block copolymer blend systems have been of great interest for a wide range of potential applications, such as nanobuilding blocks or guidance materials, because they can provide a rich phase behavior according to external conditions. However, a new and unique phase behavior of block copolymers, which can give us their more extended potential applications, has not yet been reported. Herein, we report the unusual self-assembly of two different types of Pluronic P65 and PE6200 triblock copolymer blends dependent on temperature and PE6200 concentration, which is unique for the block copolymer blends in aqueous solution. As the temperature and concentration of PE6200 (as an additive) increased, the Pluronic P65/PE6200 copolymer blends sequentially self-assembled into an isotropic micellar-hexagonal-isotropic micellar or isotropic micellar-hexagonal-isotropic micellar-lamellar phase, which is a discontinuous ordered phase (called a closed looplike phase transition), and their phase transition temperature could be controlled. To the best of our knowledge, this is the first report of a closed looplike phase transition of Pluronic block copolymer blends in aqueous solution, which can be easily applied to nanosized templates for temperature-selective highly ordered structures and optical devices such as optoelectronics or optical sensors.

Insights into the Phase Diagram of Pluronic L64 Using Coarse-Grained Molecular Dynamics Simulations

We investigate the concentration-dependent phase diagram of pluronic L64 in aqueous media at 300 and 320 K using coarse-grained (CG) molecular dynamics (MD) simulations. The CG model is derived by adapting the Martini model for nonbonded interactions along with the Boltzmann inversion (BI) of bonded interactions from all-atom (AA) simulations. Our derived CG model successfully captures the experimentally observed micellar-, hexagonal-, lamellar-, and polymer-rich solution phase. The end-to-end distance reveals the conformational change from an open-chain structure in the micellar phase to a folded-chain structure in the lamellar phase, increasing the orientational order. An increase in temperature leads to expulsion of water molecules from the L64 moiety, suggesting an increase in L64 hydrophobicity. Thermodynamic analysis using the two-phase thermodynamics (2PT) method suggests the entropy of the system decreases with increasing L64 concentration and the decrease in free energy (F) with temperature is mainly driven by the entropic factor (-TS). Further, the increase in aggregation number at lower concentrations and self-assembly at very high concentrations is energetically driven, whereas the change from the micellar phase to the lamellar phase with increasing L64 concentration is entropically driven. Our model provides molecular insights into L64 phases which can be further explored to design functionality-based suprastructures for drug delivery and tissue engineering applications.

The treatment of paediatric burns with concentrated surfactant gel technology: a case series

Objective:

To assess the safety and efficacy of a surfactant-based technology for the management of burns.

Method:

In a retrospective review, paediatric patients with different types of burns were treated with the gel technology. In some patients, the treatment was combined with a topical antimicrobial agent. Primary objectives of the review were the assessment of healing, healing times and ease of use of the material.

Results:

The wounds of 15 paediatric patients with different types of burns, particularly with regard to depth and anatomical location, were evaluated using a retrospective chart review. It was found that the surfactant gel technology, with or without the topical antimicrobial agent, assisted in autolytic debridement, and that time to re-epithelialisation was short and within the range of those obtained with other established treatments.

Conclusion:

The number of patients and wounds in this evaluation is small but the study indicates that the gel technology provides a safe and effective way to treat smaller burns in paediatric patients.

An experimental rheological phase diagram of a tri-block co-polymer in water validated against dissipative particle dynamics simulations

Aqueous solutions of tri-block co-polymer surfactants are able to aggregate into a rich variety of microstructures, which can exhibit different rheological behaviors. In this work, we study the diversity of structures detected in aqueous solutions of Pluronic L64 at various concentrations and temperatures by experimental rheometry and dissipative particle dynamics (DPD) simulations. Mixtures of Pluronic L64 in water (ranging from 0 to 90 wt% Pluronic L64) have been studied in both linear and non-linear regimes by oscillatory and steady shear flow. The measurements allowed for the determination of a complete rheological phase diagram of the Pluronic L64-water system. The linear and non-linear regimes have been compared to equilibrium and non-equilibrium DPD bulk simulations of similar systems obtained by using the software LAMMPS. The molecular results are capable of reproducing the equilibrium structures, which are in complete agreement with the ones predicted through experimental linear rheology. The simulations also depict micellar microstructures after long time periods when a strong flow is applied. These structures are directly compared, from a qualitative point of view, with the corresponding experimental results and differences between the equilibrium and non-equilibrium phase diagrams are highlighted, proving the capability of detecting morphological changes caused by deformation in both experiments and DPD simulations. The effect of temperature on the rheology of the systems has been eventually investigated and compared with the already existing non-rheological phase diagram.

Unexpected Phase Behavior of Pluronic Polymer-Organic Derivative Mixtures Depending on Temperature in Aqueous Solution

The phase behavior of amphiphilic Pluronic block copolymers in aqueous solution is of importance for a broad spectrum of practical applications but has not been fully exploited yet. Here, the phase behavior of the mixture of the Pluronic P65 and P105 triblock copolymer, (which have the same composition of PEO and PPO but the different molecular weight) and organic derivative, 5-methyl salicylic acid (5mS), in aqueous solution has been investigated by using small angle neutron scattering (SANS). According to the temperature and the 5mS concentration, SANS measurements showed that the P65-5mS mixtures sequentially transform into a random coil, sphere, vesicle, cylinder, and vesicle again, while the P105-5mS mixtures form spherical particles with two different sizes without any topological phase transition. Upon heating, the formation of two different kinds of the vesicle structure of amphiphilic block copolymer in aqueous solution is very unusual. This phase behavior was explained as the coupled effect of the simultaneous increase of the hydrophobicity of the polymer and the solubility of 5mS molecules upon heating. This result gives fundamental information for the practical use of Pluronic polymers in nano- and bio-science and it provides a simple route for the fabrication of the nanostructure without a complicated procedure.

Dielectric Behavior and Phase Behavior of Block Copolymer PEO13-PPO30-PEO13 Aqueous Solution

Dielectric spectroscopy can be applied to study the structure and dynamics of block polymer. In this work, dielectric measurements of block copolymer Pluronic L64 solution are carried out in the frequency range between 40 Hz and 110 MHz with variable temperatures and concentrations. We analyze the phase behavior of the PEO₁₃-PPO₃₀-PEO₁₃ (Pluronic L64) aqueous system according to the concentration/temperature-dependence of direct current conductivity. The result indicates the sensitivity of the phase behavior and conductivity of the Pluronic L64 solution to temperature. Besides, two relaxations were observed: relaxation 1 (0.5 MHz) is related to the gelation process, while relaxation 2 (5 MHz) is caused by the interface polarization. On the basis of relaxation 2, the volume fraction and permittivity of the particle were calculated. The formations of the block copolymer micelle and gel are monitored successfully by the temperature/concentration-dependence of the dielectric parameters and the volume fraction.

Passive optical mapping of structural evolution in complex fluids

Low-coherence optical scattering allows probing the complex structure of self-assembling systems over extended ranges of the temperature and concentrations.