Yongjun Men

Thermoresponsive polyelectrolytes derived from ionic liquids

Ionic liquid (IL)-based polyelectrolytes (PILs), referred to as polymeric ILs, polymerised ILs, or poly(IL)s are a new subclass of polymer materials. They are distinct from conventional polyelectrolytes due to their unique physico-chemical properties originated from a dense packing of ILs in the macromolecular architecture. Mixtures of PILs and solvents, in particular, water have attracted a great deal of interest especially in terms of their compatibilities depending on temperature, namely, thermoresponsiveness of PIL/solvent mixtures. Apart from static compatibility, such as the compatibility of PILs with solvents, which do not change largely by a temperature change, there are mainly two types of dynamic phase changes, an upper critical solution temperature (UCST)- and a lower critical solution temperature (LCST)-type phase behaviour. Some PILs dissolved in solvents homogenise upon heating; this behaviour is classified as UCST behaviour. On the other hand, only in the last two years have PIL/water mixtures with LCST been discovered. This article summarises rapidly growing studies on the design of thermoresponsive PIL systems with water or organic solvents. The hydrophobicity/hydrophilicity balance of the starting IL monomers features the phase behaviour of the resulting polyelectrolytes, and some IL monomers that show thermoresponsive phase behaviour in solvents were found to maintain their thermoresponsiveness even after the polymerisation. Based on their unique combination of properties derived from an ionic and thermoresponsive nature, these thermoresponsive PILs will attract considerable interest, and their wide applications are expected in the fields of separation, sensing and desalination.

Supramolecular Adaptive Nanomotors with Magnetotaxis Behavior

With a convenient bottom-up approach, magnetic metallic nickel is grown in situ of a supramolecular nanomotor using the catalytic activities of preloaded platinum nanoparticles. After introducing magnetic segments, simultaneous guidance and steering of catalytically powered motors with additional magnetic fields are achieved. Guided motion in a tissue model is demonstrated.

Self-propelled supramolecular nanomotors with temperature-responsive speed regulation

Self-propelled catalytic micro- and nanomotors have been the subject of intense study over the past few years, but it remains a continuing challenge to build in an effective speed-regulation mechanism. Movement of these motors is generally fully dependent on the concentration of accessible fuel, with propulsive movement only ceasing when the fuel consumption is complete. Here we report a demonstration of control over the movement of self-assembled stomatocyte nanomotors via a molecularly built, stimulus-responsive regulatory mechanism. A temperature-sensitive polymer brush is chemically grown onto the nanomotor, whereby the opening of the stomatocytes is enlarged or narrowed on temperature change, which thus controls the access of hydrogen peroxide fuel and, in turn, regulates movement. To the best of our knowledge, this represents the first nanosized chemically driven motor for which motion can be reversibly controlled by a thermally responsive valve/brake. We envision that such artificial responsive nanosystems could have potential applications in controllable cargo transportation.

Biodegradable Hybrid Stomatocyte Nanomotors for Drug Delivery

We report the self-assembly of a biodegradable platinum nanoparticle-loaded stomatocyte nanomotor containing both PEG-b-PCL and PEG-b-PS as a potential candidate for anticancer drug delivery. Well-defined stomatocyte structures could be formed even after incorporation of 50% PEG-b-PCL polymer. Demixing of the two polymers was expected at high percentage of semicrystalline poly(ε-caprolactone) (PCL), resulting in PCL domain formation onto the membrane due to different properties of two polymers. The biodegradable motor system was further shown to move directionally with speeds up to 39 μm/s by converting chemical fuel, hydrogen peroxide, into mechanical motion as well as rapidly delivering the drug to the targeted cancer cell. Uptake by cancer cells and fast doxorubicin drug release was demonstrated during the degradation of the motor system. Such biodegradable nanomotors provide a convenient and efficient platform for the delivery and controlled release of therapeutic drugs.

Double‐Stimuli‐Responsive Spherical Polymer Brushes with a Poly(ionic liquid) Core and a Thermoresponsive Shell

The synthesis of poly(ionic liquid) (PIL) nanoparticles grafted with a poly(N-isopropyl acrylamide) (PNIPAM) brush shell is reported, which shows responsiveness to temperature and ionic strength in an aqueous solution. The PIL nanoparticles are first prepared via aqueous dispersion polymerization of a vinyl imidazolium-based ionic liquid monomer, which is purposely designed to bear a distal atom transfer radical polymerization (ATRP) initiating group attached to the long alkyl chain via esterification reaction. The size of the PIL nanoparticles can be readily tuned from 25 to 120 nm by polymerization at different monomer concentrations. PNIPAM brushes are successfully grafted from the surface of the poly(ionic liquid) nanoparticles via ATRP. The stimuli-responsive behavior of the poly(ionic liquid) nanoparticles grafted with PNIPAM brushes (NP-g-PNIPAM) in aqueous phase is studied in detail. Enhanced colloidal stability of the NP-g-PNIPAM brush particles at high ionic strength compared to pure PIL nanoparticles at room temperature is achieved. Above the lower critical solution temperature (LCST) of PNIPAM, the brush particles remain stable, but a decrease in hydrodynamic radius due to the collapse of the PNIPAM brush onto the PIL nanoparticle surface is observed.

Low fractions of ionic liquid or poly(ionic liquid) can activate polysaccharide biomass into shaped, flexible and fire-retardant porous carbons

Sugar-based molecules and polysaccharide biomass can be turned into porous functional carbonaceous products at comparably low temperatures of 400 °C under a nitrogen atmosphere in the presence of an ionic liquid (IL) or a poly(ionic liquid) (PIL). The IL and PIL act as “activation agents” with own structural contribution, and effectively promote the conversion and pore generation in the biomaterials even at a rather low doping ratio (7 wt%). In addition, this “induced carbonization” and pore forming phenomenon enables the preservation of the biotemplate shape to the highest extent and was employed to fabricate shaped porous carbonaceous materials from carbohydrate-based biotemplates, exemplified here with cellulose filter membranes, coffee filter paper and natural cotton. These carbonized hybrids exhibit comparably good mechanical properties, such as bendability of membranes or shape recovery of foams. Moreover, the nitrogen atoms incorporated in the final products from the IL/PIL precursors further improve the oxidation stability in the fire-retardant tests.

Methods for production of uniform small-sized polymersome with rigid membrane

We report a facile methodology for the formation of uniform small-sized poly(ethylene glycol)-block-polystyrene (PEG-b-PS) polymersomes, via extrusion and sonication methods by using organic solvent as plasticizing agent. The obtained polymersomes have diameters less than 100 nm. The size and size distribution depend on the organic solvent content and sonication time. The small-sized polymersomes are able to carry both hydrophobic and hydrophilic dyes.

Salt-confinement enables production of nitrogen-doped porous carbons in an air oven

The production of nitrogen-doped porous carbons in an air oven at 750 °C with high surface area (≥500 m2 g−1), carbonization yield up to 35 wt% and tuneable nitrogen content from ionic liquids was reported. It utilized inorganic halide salts as the reaction medium, the activation agents, and the physical barrier. This method was successfully expanded to recyclable sea salt and natural sources, such as nucleobase (adenine) and biomass (oak leaves).

Stomatocyte in Stomatocyte: A New Shape of Polymersome Induced via Chemical-Addition Methodology

Accurate control of the shape transformation of polymersome is an important and interesting challenge that spans across disciplines such as nanomedicine and nanomachine. Here, we report a fast and facile methodology of shape manipulation of polymersome via out-of-equilibrium polymer self-assembly and shape change by chemical addition of additives. Due to its increased permeability, hydrophilicity, and fusogenic properties, poly(ethylene oxide) was selected as the additive for bringing the system out of equilibrium via fast addition into the polymersome organic solution. A new shape, stomatocyte-in-stomatocyte (sto-in-sto), is obtained for the first time. Moreover, fast shape transformation within less than 1 min to other relevant shapes such as stomatocyte and large compound vesicles was also obtained and accurately controlled in a uniform dispersion. This methodology is demonstrated as a general strategy with which to push the assembly further out of equilibrium to generate unusual nanostructures in a controllable and fast manner.

Fast Conversion of Ionic Liquids and Poly(Ionic Liquid)s into Porous Nitrogen-Doped Carbons in Air

Ionic liquids and poly(ionic liquid)s have been successfully converted into nitrogen-doped porous carbons with tunable surface area up to 1200 m2/g at high temperatures in air. Compared to conventional carbonization process conducted under inert gas to produce nitrogen-doped carbons, the new production method was completed in a rather shorter time without noble gas protection.