Quest for Thermoresponsive Block Copolymer Nanoparticles with Liquid–Crystalline Surfactant Cores

Abstract

This work reports on the preparation and characterization of anisotropic composition nanoparticles based on the electrostatic binding of dodecyltrimethylammonium surfactant to poly(acrylic acid) blocks of diblock copolymers with poly(ethylene oxide) (PEO) and poly( N -isopropyl acrylamide) (PNIPAm). These nanoparticles form kinetically stable dispersions and display liquid–crystalline cores with a micellar cubic structure, as determined by small-angle X-ray scattering. Mixtures with different proportions of the two block copolymers and stoichiometric amounts of C 12 TA + were prepared and their behavior was compared with that of the parent nanoparticles. Upon heating, dilute dispersions (0.01 and 0.1 wt %) analyzed by dynamic light scattering display a slight decrease in the hydrodynamic radius, consistent with the dehydration of PNIPAm and mixed PNIPAm–PEO blocks at the shell. At higher concentrations, 2 wt %, the nanoparticles with pure PNIPAm shell undergo macroscopic phase separation above 32 °C. Nanoparticles with a pure PEO shell do not display temperature sensitivity. For the mixtures, no visual change is observed, but the dynamic light scattering results evidence the formation of clusters, whose size and reversibility depend on the PEO/PNIPAm proportion. This indicates the formation of mixed nanoparticles containing both PEO and PNIPAm blocks. Nuclear Overhauser enhancement spectroscopy NMR analyses of the mixtures do not show the correlation peak expected for PEO and PNIPAm blocks in close proximity, suggesting their segregation at the nanoparticle shell. On the basis of these results, we discuss the possibilities of the neutral blocks distribution on the shell of mixed nanoparticles. Overall, we have confirmed that these nanoparticles may display a temperature-controlled reversible aggregation while preserving their internal liquid–crystalline structures.

Planet–Satellite Nanostructures Based on Block Copolymer‐Surfactant Nanoparticles Surface‐Decorated with Gold and Silver: A New Strategy for Interfacial Catalysis

“…The peaks with a spacing ratio of 4 1/2 :5 1/2 :6 1/2 indicated a Pm 3̅ n micellar cubic liquid crystalline structure, with a lattice parameter of 8.4 nm. Interestingly, it shows that the dispersion of stoichiometric CS containing water‐soluble neutral blocks produced particles with core structures that agree with the phases previously observed for maximally water‐swollen corresponding homopolymer CS …”

“…Core–shell particles, collectively known as complex coacervate core micelles (C3Ms), made from charged−neutral block copolymers and oppositely charged surfactant ions have been widely reported in the last years and the most studied systems are comprised of alkyltrimethylammonium cationic surfactants and the block copolymer poly(acrylamide)‐ block ‐poly(acrylic acid) (PAAm‐ b ‐PAA) . The particles core contains several densely packed‐surfactant micelles surrounded by the anionic block of the copolymer and the outer part consists in a corona composed by the neutral PAAm chains.…”

“…The particles core contains several densely packed‐surfactant micelles surrounded by the anionic block of the copolymer and the outer part consists in a corona composed by the neutral PAAm chains. By using the “complex salt” (CS) approach, the production of dispersed particles with a variety of surfactant‐rich liquid crystalline cores were shown to be achieved. In addition, these particles, refereed here as CS, were shown to display enhanced colloidal stability .…”

“…By using the “complex salt” (CS) approach, the production of dispersed particles with a variety of surfactant‐rich liquid crystalline cores were shown to be achieved. In addition, these particles, refereed here as CS, were shown to display enhanced colloidal stability . It was noted that the CS particles display different properties, such as size, surface charge, and core structure, if compared with those typically found for particles, referred here as CP, prepared by the conventional procedure of mixing polyelectrolyte and surfactant in water, with their respective simple counterions ( Scheme ) …”

“…Because liquid crystalline particles have been widely studied for a variety of applications, specially the loading and release of substances, and have been reported to display long‐term colloidal stability, the selective attachment of Au and Ag NPs to the surface of CS particles was investigated in the present work aiming at the fabrication of functional nanoconjugates owing to the combination of the properties of both nanomaterials ( Scheme ). As a control experiment, CP particles were also conjugated with metal NPs (Scheme ).…”