Pluronics or Poloxamers are triblock amphiphilic copolymers of type A-B-A having middle hydrophobic block of poly-propylene oxide (PPO) and the terminal hydrophilic blocks of poly-ethylene oxide (PEO). The amphiphilic characteristics of the pluronics can be tuned by varying the ratio of hydrophilic and hydrophobic blocks. These are thermoresponsive, cheap, biodegradable and low volatile molecules with applications such as food additives, personal care formulations, medicines, emulsifiers, solubilizers, wetting agents and so on.<br/>Pluronics self-assemble in presence of water leading to formation of spherical and cylindrical micelles and hexagonal and lamellar phases at different concentrations. The phase transition of pluronics has been extensively studied via experiments along with a few molecular simulation studies. However, capturing the entire phase diagram of pluronics using molecular simulations is still challenging.<br/>As the all-atom (AA) simulations are limited with length and time scale thus, in this work coarse-grained (CG) simulations are carried out for the L64 (13-30-13) pluronic chain. Initially AA simulations are carried out using the previously reported force-fields. Next, the CG bonded potentials are derived by the Boltzmann Inversion of respective AA distributions. The non-bonded potentials are taken from the standard MARTINI force-field. The CG bonded distributions match well with the AA distributions, validating the suitability of the derived model. This model captures the spherical and cylindrical micelles at lower concentrations. However, CG potentials are rigid and produce artificial states not observed in experiments. Hence, the MARTINI parameters are used for both bonded and non-bonded interactions at higher concentrations.<br/>The current study captures the overall phase transitions of L64. It shows that the concentration of pluronics plays an important role in obtaining different phases. Thus, a concentration dependent control on the topologies can be extended to design functionality based suprastructures with applications in medicines and industries.

Phase behavior of Pluronic L64 using multi-scale simulations

ACS Spring Meeting 2021

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