Abstract
Pluronic amphiphilic block copolymers, well known to have a phase behavior can be controlled by external conditions, have a wide range of potential for applications such as nanotemplates or nanobuilding blocks. However, the phase behaviors of Pluronic block copolymer/additive complexes with highly ordered phases have not been fully investigated. Here, we report the unusual molecular weight-dependent self-assembly of Pluronic block copolymer/additive complexes. Depending on the temperature and additive, Pluronic P65 block copolymer with a lower molecular weight showed the closed loop-like (CLL) phase behavior with the disorder-order-disorder-order phase transition in aqueous solution, whereas Pluronic P105 and P85 block copolymers with higher molecular weights underwent highly ordered continuous phase transitions with face centered cubic (FCC), hexagonal, and lamellar phases. It is expected that the specific phase behavior of the block copolymer/additive complex can be applied in optical devices such as nanotemplates or optical sensors for a highly ordered superlattice. Furthermore, this study provides a new route to control the phase behavior of the block copolymers without a complicated process.
Highlights
The formation of highly ordered lattices within confined nanostructures is an attractive phenomenon with potential applications in nanoscale systems [1,2,3]
We expected that molecules with identical substances and mass fraction would undergo the same phase transitions, our results show that the phase behavior of P65 is an exception, as it showcased the unique closed loop-like (CLL) phase transition, where the solubility of 5-methylsalicylic acid (5mS) increased with the temperature (5mS in the P65-5mS complex dissociates into water [17,18]), the increase of the 5mS solubility contributes to the decrease of the hydrophobicity of the P65-5mS complex
We report the investigation of the phase behaviors of complexes of Pluronic P105, P85, and P65 block copolymers with 5mS additive by visual inspection, Polarized Optical Microscopy (POM) measurements, and small-angle X-ray scattering (SAXS) experiments
Summary
The formation of highly ordered lattices within confined nanostructures is an attractive phenomenon with potential applications in nanoscale systems [1,2,3]. Because the 5mS molecule has an asymmetric amphiphilicity (with a relatively large hydrophobic portion (aromatic group) and small hydrophilic portion (hydroxide group)) and temperature dependent solubility in water (the solubility of 5mS increases with temperature) as well as a strong reactivity for binding with amphiphilic molecules, the steric conformation of Pluronic block copolymer can be modified depending on temperature and the concentration of 5mS molecules, allowing the formation of various phase behaviors. The SAXS analysis and visual inspection of the Pluronic block copolymer/5mS complexes revealed that, depending on temperature, both the ordered and disordered structures were formed, corresponding to solid-like gel and fluidic phases, respectively While both Pluonic P105 and P85 formed solid-like gels continuously upon changing the temperature and concentration of additives, Pluonic P65 changed repeatedly between the fluidic and solid-like gel phases. H2O was purified by a Millipore Direct Q system (Bay city, MI, USA) immediately before use
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