The fabrication of a supra-amphiphile for dissipative self-assembly

Formulating Polyethylene Glycol as Supramolecular Emulsifiers for One-Step Double Emulsions

One-step double emulsions via only one-step emulsification are leading to an attractive branch of emulsion research studies owing to the ease of preparation and reduced surfactant numbers. In addition to controlling the oil/water ratio, exploiting emulsifiers with desirable amphiphilicity that can stabilize both the inner and outer water/oil interfaces is crucial to the formation of one-step double emulsions. In particular, new emulsifiers with saving laborious efforts are highly preferred in consideration of low cost and practical applications. In this work, a commonly used homopolymer, polyethylene glycol (PEG), was attempted as emulsifiers to prepare emulsions via one-step emulsification. PEG is generally considered as a hydrophilic polymer and always anchored with a hydrophobic polymer to make the copolymer amphiphilic. In the water-chloroform binary system, PEG itself exhibits amphiphilic performance and tailors the formation of single emulsions or double W/O/W emulsions on the dependence of the oil/water ratio and the PEG concentration. A possible mechanism as explained by dissipative particle dynamics simulation was proposed to demonstrate the amphiphilic feature and emulsification capability of PEG. The amphiphilicity of PEG was further tuned by interacting with iodine as a result of the formation of a supramolecular complex, which, in turn, led to the conversion from single emulsions to O/W/O double emulsions. It is believed that this line of research provides inspiration for the preparation of controllable emulsions through supramolecular routes.

Temporal switching of an amphiphilic self-assembly by a chemical fuel-driven conformational response

The spatial and temporal control of self-assemblies is the latest scientific hurdle in supramolecular chemistry which is inspired by the functioning of biological systems fueled by chemical signals. In this study, we work towards alleviating this scenario by employing a unique amphiphilic foldamer that operates under the effect of a chemical fuel. The conformational changes in the foldamer amplify into observable morphological changes in its amphiphilic assembly that are controlled by external molecular cues (fuel). We take advantage of this redox responsive foldamer to affect its conformation in a temporal manner by an enzymatic pathway. The temporal characteristics of the transient conformation/assembly can be modulated by varying the concentrations of the fuel and enzyme. We believe that such a design strategy can have positive consequences in designing molecular and supramolecular systems for future active, adaptive and autonomous materials.

Autonomous unimer-vesicle oscillation by totally synthetic diblock copolymers: effect of block length and polymer concentration on spatio-temporal structures

In this study, factors controlling autonomous vesicle oscillations exhibited by self-oscillating diblock copolymers were investigated. The self-oscillating diblock copolymer contains poly(ethylene oxide) (PEO) as the hydrophilic block and a random copolymer composed of N-isopropylacrylamide (NIPAAm) with side chains of ruthenium tris(2,2'-bipyridine) (Ru(bpy)₃), which catalyzes the Belousov-Zhabotinsky (BZ) reaction, as the self-oscillating block. Recently, our group has reported that a diblock copolymer exhibits a unique autonomous disintegration and reconstruction of the vesicles driven by the periodic redox changes of Ru(bpy)₃ in a catalyst-free BZ reaction solution. Nevertheless, the effect of the diblock copolymer architecture on the structure of the vesicles under equilibrium conditions, as well as their oscillation properties under non-equilibrium conditions, has not been clarified thus far. Hence, self-oscillating diblock copolymers with different block lengths were systematically synthesized, and the effects of the block length and polymer concentration on the spatio-temporal vesicle structures were comprehensively discussed.

Transient self-assembly of molecular nanostructures driven by chemical fuels

Over the past decades, chemists have mastered the art of assembling small molecules into complex nanostructures using non-covalent interactions. The driving force for self-assembly is thermodynamics: the self-assembled structure is more stable than the separate components. However, biological self-assembly processes are often energetically uphill and require the consumption of chemical energy. This allows nature to control the activation and duration of chemical functions associated with the assembled state. Synthetic chemical systems that operate in the same way are essential for creating the next generation of intelligent, adaptive materials, nanomachines and delivery systems. This review focuses on synthetic molecular nanostructures which self-assemble under dissipative conditions. The chemical function associated with the transient assemblies is operational as long as chemical fuel is present.

Tunable assembly and disassembly of responsive supramolecular polymer brushes

Tunable assembly and disassembly of stimuli-responsive supramolecular polymer brushes are induced by using host–guest interactions between β-cyclodextrin and azobenzene groups.

Effect of substrate concentrations on the aggregation behavior and dynamic oscillatory properties of self-oscillating block copolymers

The effect of substrate concentrations of the BZ reaction as well as specific salts on the dynamic properties of self-oscillating block copolymers was studied in detail.

Kinetic trapping - a strategy for directing the self-assembly of unique functional nanostructures

Supramolecular self-assembly into various nano- or microscopic structures based on non-covalent interactions between molecules has been recognized as a very efficient approach that leads to functional materials. Since most non-covalent interactions are relatively weak and form and break without significant activation barriers, the thermodynamic equilibrium of many supramolecular systems can be easily influenced by processing pathways that allow the system to stay in a kinetically trapped state. Thus far, kinetic traps have been found to be very important in producing more elaborate structural and functional diversity of self-assembled systems. In this review, we try to summarize the approaches that can produce kinetically trapped self-assemblies based on examples made by us. We focus on the following subjects: (1) supramolecular pathway dependent self-assembly, including kinetically trapped self-assemblies facilitated by host-guest chemistry, coordination chemistry, and electrostatic interactions; (2) physical processing pathway dependent self-assembly, including solvent quality controlled self-assembly, evaporation induced self-assembly and crystallization induced self-assembly.

Pillar[7]arene-based host–guest complex in water: dual-responsiveness and application in controllable self-assembly

A dual-responsive supra-amphiphile was constructed based on a water-soluble pillar[7]arene and a pyrene-containing guest. The self-assembly morphology of this supra-amphiphile could be adjusted by changing pH or irradiation by UV light.