Temperature Responsive Complex Coacervate Core Micelles With a PEO and PNIPAAm Corona

Abstract

In aqueous solutions at room temperature, poly( N-methyl-2-vinyl pyridinium iodide)- block-poly(ethylene oxide), P2MVP 38- b-PEO 211 and poly(acrylic acid)- block-poly(isopropyl acrylamide), PAA 55- b-PNIPAAm 88 spontaneously coassemble into micelles, consisting of a mixed P2MVP/PAA polyelectrolyte core and a PEO/PNIPAAm corona. These so-called complex coacervate core micelles (C3Ms), also known as polyion complex (PIC) micelles, block ionomer complexes (BIC), and interpolyelectrolyte complexes (IPEC), respond to changes in solution pH and ionic strength as their micellization is electrostatically driven. Furthermore, the PNIPAAm segments ensure temperature responsiveness as they exhibit lower critical solution temperature (LCST) behavior. Light scattering, two-dimensional 1H NMR nuclear Overhauser effect spectrometry, and cryogenic transmission electron microscopy experiments were carried out to investigate micellar structure and solution behavior at 1 mM NaNO 3, T = 25, and 60 degrees C, that is, below and above the LCST of approximately 32 degrees C. At T = 25 degrees C, C3Ms were observed for 7 < pH < 12 and NaNO 3 concentrations below approximately 105 mM. The PEO and PNIPAAm chains appear to be (randomly) mixed within the micellar corona. At T = 60 degrees C, onion-like complexes are formed, consisting of a PNIPAAm inner core, a mixed P2MVP/PAA complex coacervate shell, and a PEO corona.

Electrostatic hierarchical co-assembly in aqueous solutions of two oppositely charged double hydrophilic diblock copolymers

“…Clearly, the force balance is delicate: strongly segregating neutral blocks cannot be employed, as they might lead to dissociation of the micelles, while on the other hand too compatible hydrophilic blocks will result in a mixed corona. This concept has been explored in a series of recent papers [11,12,[24][25][26] where we observed that a pair of relatively miscible hydrophilic blocks yielded spherical C3Ms with a mixed shell and a pair of relatively immiscible hydrophilic blocks yielded ellipsoidal micelles with a laterally segregated corona (Janus-micelles). A combination of poly(2-(N,N-dimethylamino)ethyl methacrylate)-blockpoly(glyceryl methacrylate), PDMAEMA 45 -b-PGMA 90 and poly(acrylic acid)-block-poly(acrylamide), PAA 42 -bPAAm 417 resulted in spherical micelles with a mixed corona [11], while the Janus-type segregation was achieved in aqueous mixtures of poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP 42 -b-PEO 446 and poly(acrylic acid)-block-poly(acrylamide), PAA 42 -bPAAm 417 [12,24,25].…”

Environment-sensitive stabilisation of silver nanoparticles in aqueous solutions

“…In a previous publication [24], we have shown that micelles of P2MVP 38 -b-PEO 211 and PAA 55 -b-PNIPAAm 88 are responsive to a number of experimental parameters, such as pH, ionic strength, and temperature. The C3Ms reversibly associate and dissociate upon cycling the ionic strength of the solution through the so-called ''critical ionic strength" (corresponding to the ionic strength above which micelles can no longer be detected), which is approximately 105 mM for this particular system [24].…”

“…The stock solutions were mixed in a 1:1 ratio of chargeable groups; i.e., at a mixing fraction, f + of 0.5. For pH = 7.7, this mixing fraction corresponds to the so-called preferred micellar composition (PMC) [24]. The mixing fraction, f + is defined as the ratio between the number of positively chargeable monomers and the sum of the numbers of positively and negatively chargeable monomers, i.e.,…”

“…The C3Ms reversibly associate and dissociate upon cycling the ionic strength of the solution through the so-called ''critical ionic strength" (corresponding to the ionic strength above which micelles can no longer be detected), which is approximately 105 mM for this particular system [24]. Upon raising the temperature from 25°C to 60°C, the C3Ms undergo a structural transition from core-shell C3Ms at T = 25°C with the polyelectrolyte blocks in the core to a core-shell-corona system at T = 60°C with the polyelectrolyte blocks in the shell.…”

“…) has been synthesised by RAFT (PDI $ 1.10), according to a procedure described elsewhere [24,27]. All polymers and other chemicals were used as received, without further purification.…”