Rationalizing the Design of Pluronics−Surfactant Mixed Micelles through Molecular Simulations and Experiments

resumo

Aqueous systems comprising polymers and surfactants are technologically important complex fluids with tunable features dependent on the chemical nature of each constituent, overall composition in mixed systems, and solution conditions. The phase behavior and self-assembly of amphiphilic polymers can be changed drastically in the presence of conventional ionic surfactants and need to be clearly understood. Here, the self-aggregation dynamics of a triblock copolymer (Pluronics L81, EO3PO43EO3) in the presence of three cationic surfactants (with a 12C long alkyl chain but with different structural features), viz., dodecyltrimethylammonium bromide (DTAB), didodecyldimethylammonium bromide (DDAB), and ethanediyl-1,2-bis- (dimethyldodecylammonium bromide) (12-2-12), were investigated in an aqueous solution environment. The nanoscale micellar size expressed as hydrodynamic diameter (Dh) of copolymer−surfactant mixed aggregates was evaluated using dynamic light scattering, while the presence of a varied micellar geometry of L81−cationic surfactant mixed micelles were probed using small-angle neutron scattering. The obtained findings were further validated from molecular dynamics (MD) simulations, employing a simple and transferable coarse-grained molecular model based on the MARTINI force field. L81 remained molecularly dissolved up to ∼20 °C but phase separated, forming turbid/translucent dispersion, close to its cloud point (CP) and existed as unstable vesicles. However, it exhibited interesting solution behavior expressed in terms of the blue point (BP) and the double CP in the presence of different surfactants, leading to mixed micellar systems with a triggered morphology transition from unstable vesicles to polymer-rich micelles and cationic surfactant-rich micelles. Such an amendment in the morphology of copolymer nanoaggregates in the presence of cationic surfactants has been well observed from scattering data. This is further rationalized employing the MD approach, which validated the effective interactions between Pluronics−cationic surfactant mixed micelles. Thus, our experimental results integrated with MD yield a deep insight into the nanoscale interactions controlling the micellar aggregation (Pluronics-rich micelles and surfactant-rich micelles) in the investigated mixed system.

autores

Divya Patel, Germán Pérez-Sánchez, Miguel Jorge, Debes Ray, Vinod K. Aswal, Ketan Kuperkar, João A. P. Coutinho, and Pratap Bahadur

nossos autores

agradecimentos

The authors acknowledge the Sardar Vallabhbhai National Institute of Technology (SVNIT), Gujarat, India, for providing the instrumentation facilities. The computational part of this work was funded by CICECO-Aveiro Institute of Materials under the projects UIDB/50011/2020, UIDP/50011/2020, and LA/P/0006/2020 and financed by national funds through the FCT/MEC (PIDDAC). G.P.-S. acknowledges national funds (OE), through FCT−Fundação para a Ciência e a Tecnologia, I.P., in the scope of the framework contract foreseen in the numbers 4, 5, and 6 of the articles 23, of the Decree-Law 57/2016, of August 29th, changed by Law 57/ 2017, of July 19th.

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