Self-Assembly of Hyperbranched Protic Poly(ionic liquid)s with Variable Peripheral Amphiphilicity

Abstract

We demonstrated that the aggregation behavior of hyperbranched amphiphilic protic poly(ionic liquid)s (HBP-ILs) can be controlled by varying not only the number of peripheral hydrophobic arms and nature of counterions. Additionally, increasing the hydrophobicity of the HBP-ILs led to a condensed monolayer phase at the air-water interface. The balance of intermolecular interactions mediated by the presence of the ionic liquid component in the inner shell of micelles determines the final morphology in solution and at interfaces.Poly(ionic liquid)s (PILs) are an emerging class of macromolecules capable of forming hierarchically structured building blocks for the bottom-up assembly of functional nanomaterials. 15 Owing to the chemical diversity of the polymerized IL functionalities, a variety of structure directing interactions can be exploited to tune the morphology and properties of the assemblies. 610 For example, by varying the length of the alkyl tails associated with imidazole component®and hence the PIL hydrophobicity®assemblies ranging from unilamellar vesicular to 'onion-like' mesostructures were observed. 1113 We have previously demonstrated that introducing complex molecular topologies (e.g., branching) is an additional avenue of influencing the supramolecular organization of PILs. For instance, it was shown that star PILs can form closely-packed monolayers at the air-water interface in contrast to their linear analogues, and that their incorporation into layer-by-layer structures can yield membranes whose nanoscale texture and porosity depend on the degree of polymerization and topology of the PILs.14 Furthermore, studies of IL-based hydroxylterminated aliphatic hyperbranched polyesters (HBP-ILs) revealed that the terminal ionic groups, counterions, and the degree of ionization (controlled by solution ionic strength or pH) defined the assembly behavior of micelles into nanoscale aggregates. 1518 Although it was established that the long hydrophobic tails have a significant influence on the size of the micelles, the effect of varying their relative ratio in the overall molecular architecture and the presence of different ionic liquid components was not explored to date.

Thermally Responsive Hyperbranched Poly(ionic liquid)s: Assembly and Phase Transformations

“…These weakly associated aggregates include few hundreds of individual hydrogenated molecules as can be estimated from direct comparison of molecular volumes for extreme cases of loosely (V m ) and densely (V ρ ) packed molecules with volumes of spherical domains (Tables S1−S3). 24,25 The domain morphology and effective dimensions change dramatically after grafting PNIPAM chains, as shown by the dramatic rise in scattering intensity in the intermediate range indicating the presence of the highly contrasted hydrogenated central core with large size and addition of a number of tails (Figure 5, Tables S1 and S2). For all linear and branched compounds with PNIPAM chains, the prolate ellipsoidal form factor was found to be the best fitting model (see fitting results in Figure 5 and corresponding parameters in Tables S1−S3).…”

“…The flattened shape of dried micelles and their aggregates resembles the microcapsule-like morphology with collapsed inner volume after drying. 24,25 However, AFM cannot resolve the internal morphology of these micelles in both swollen and dried conditions. Therefore, to elucidate the internal structure of these micelle aggregates under swollen conditions, SANS was measured over a Q range spanning more than 2 orders of magnitude at temperatures below and above the LCST transition (Figure 5, section SI2).…”

Self-assembly as a key player for materials nanoarchitectonics

“…Structures of unit polymers for self-assembly strategies are not limited to linear ones. Self-assembly of hyperbranched polymers is also attractive subject as seen in research work on self-assembly of hyperbranched poly(ionic liquid)s with controlled peripheral amphiphilicity reported by Tsukruk and coworkers [164]. They investigated self-assembly behaviours of amphiphilic hyperbranched poly(ionic liquid) molecules with various number ratio of peripheral hydrophobic arms to the hydrophilic ionic groups in water and at the air-water interface.…”

Topology Affecting Block Copolymer Nanoassemblies: Linear Block Copolymers versus Star Block Copolymers under PISA Conditions

“…Block copolymer (BCP) nanoassemblies dispersed in solvent have attracted great attention for their various morphologies and their potential applications in many fields. − Block copolymer morphology is correlative to several parameters including solvent character, − block copolymer concentration, − and block copolymer architecture. − Of all these parameters, polymer architecture is the most prominent. For examples, star BCPs include multiple arms of linear BCP tethered onto one central core, − and these star BCPs combine special features of both linear BCPs − and star polymers − into one entity.…”

“…Mays et al discovered that higher-order thin film morphologies were formed for Y-shaped [poly­(2-vinylpyridine)] 2 –polystyrene [(P2VP) 2 –PS] compared to the linear polystyrene- b -poly­(2-vinylpyridine) with similar molecular weight . Moreover, Tsukruk and co-workers reported highly branched polymers possess complex and unique assembly behavior in solution at surfaces and interfaces as compared to their linear counterparts. − …”