Advances in the field of supramolecular chemistry have made it possible, in many situations, to reliably engineer soft materials to address a specific technological problem. Particularly exciting are “smart” gels that undergo reversible physical changes on exposure to remote, non-invasive environmental stimuli. This review explores the development of gels which are transformed by heat, light and ultrasound, as well as other mechanical inputs, applied voltages and magnetic fields. Focusing on small-molecule gelators, but with reference to organic polymers and metal–organic systems, we examine how the structures of gelator assemblies influence the physical and chemical mechanisms leading to thermo-, photo- and mechano-switchable behaviour. In addition, we evaluate how the unique and versatile properties of smart materials may be exploited in a wide range of applications, including catalysis, crystal growth, ion sensing, drug delivery, data storage and biomaterial replacement.

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Gels with sense: supramolecular materials that respond to heat, light and sound

The cellulose nanofibers of bacterial cellulose aerogel (BCA) are modified only on their surfaces using a trimethylsilylation reaction with trimethyichlorosilane in liquid phase followed by freeze-drying. The obtained hydrophobic bacterial cellulose aerogels (HBCAs) exhibit low density (≤6.77 mg/cm3), high surface area (≥169.1 m2/g), and high porosity (≈ 99.6%), which are nearly the same as those of BCA owing to the low degrees of substitution (≤0.132). Because the surface energy of cellulose nanofibers decreased and the three-dimensional web-like microstructure, which was comprised of ultrathin (20–80 nm) cellulose nanofibers, is maintained during the trimethylsilylation process, the HBCAs have hydrophobic and oleophilic properties (water/air contact angle as high as 146.5°) that endow them with excellent selectivity for oil adsorption from water. The HBCAs are able to collect a wide range of organic solvents and oils with absorption capacities up to 185 g/g, which depends on the density of the liquids. ...

Surface modification of bacterial cellulose aerogels' web-like skeleton for oil/water separation.

Supramolecular hydrogels assembled from amino acids and peptide-derived hydrogelators have shown great potential as biomimetic three-dimensional (3D) extracellular matrices because of their merits over conventional polymeric hydrogels, such as non-covalent or physical interactions, controllable self-assembly, and biocompatibility. These merits enable hydrogels to be made not only by using external stimuli, but also under physiological conditions by rationally designing gelator structures, as well as in situ encapsulation of cells into hydrogels for 3D culture. This review will assess current progress in the preparation of amino acids and peptide-based hydrogels under various kinds of external stimuli, and in situ encapsulation of cells into the hydrogels, with a focus on understanding the associations between their structures, properties, and functions during cell culture, and the remaining challenges in this field. The amino acids and peptide-based hydrogelators with rationally designed structures have promising applications in the fields of regenerative medicine, tissue engineering, and pre-clinical evaluation.

Amino Acids and Peptide-Based Supramolecular Hydrogels for Three-Dimensional Cell Culture.

Effective removal of crude oils, petroleum products, organic solvents, and dyes from water is of significance in oceanography, environmental protection, and industrial production. Various techniques including physical and chemical absorption have been developed, but they suffer from problems such as low separation selectivity, a complicated and lengthy process, as well as high costs for reagents and devices. We present here a new material, termed nitrogen-rich carbon aerogels (NRC aerogels,) with highly porous structure and nitrogen-rich surfaces, exhibiting highly efficient separation of specific substances such as oils and organic pollutants. More importantly, we demonstrate that the fabricated NRC aerogels can also collect micrometer-sized oil droplets from an oil-water mixture with high efficiency that is well beyond what can be achieved by most existing separation methods, but is extremely important in practical marine oil-spill recovery because a certain amount of oils often shears into many microme...

Nitrogen-Rich and Fire-Resistant Carbon Aerogels for the Removal of Oil Contaminants from Water

Owing to the severe environmental and ecological issues arising from oil spills and toxic chemical leakage, the separation of oil from water presents a worldwide challenge to save the endangered environment. A versatile absorbent which can deal with different types of oil contaminants is in high demanded for this issue. In this work, we obtain an ultralight, fire-resistant, and compressible foam (UFC foam) by pyrolysis and post hydrophobic-modified treatment using commercially available poly(melamine formaldehyde) foams as precursors. The present UFC foam not only effectively separates oils from water as expected, but also possesses a very high absorption capacity for the removal of oils from water up to 158 times its own weight. More importantly, due to its fire resistance and compressibility, distillation, combustion and squeezing, or a combination of these can be applied for recycling the foams depending on the type of pollutants, making them versatile and comprehensive absorbents to satisfy various practical separation requirements.

Multifunctional foams derived from poly(melamine formaldehyde) as recyclable oil absorbents

Ionic liquids are solvents of future. One of the promising methods to boost their uses is to solidify them in a physical way but with little interruption of their properties. It is therefore of interest to create gels of ionic liquids by using low-molecular mass compounds as gelators (LMMGs). Herein, we report a number of ionic liquid gels (ionogels) of which specially designed and synthesized cholesteryl derivatives were employed as gelators. The ionogels as obtained are thermo-reversible. In particular, the one with 1-butyl-3-methylimidazolium tetrafluoroborate (IL2) as solvent and a cholesteryl derivative containing a D-phenylalanine residue (1D) as a gelator is very stable both in neutral and acidic mediums as demonstrated by a yield stress of 76 Pa for a self-standing cylinder of the ionogel. Furthermore, the ionogel can be easily converted into a hydrogel via simple replacement of the solvent with water in situ. More interestingly, the conversion is reversible, a phenomenon never reported before. At the same time, the critical gelation concentration (CGC) of 1D for IL2 is only 0.06%, w/w, which is almost the lowest value reported for ionogels till now, and falls into the category of “super-gelator”. Magnetization of the ionogel has been realized by introduction of micro-/nano-Fe3O4 particles. As expected, the magnetic gel as obtained is responding to external magnetic field. Specifically, it changes into fluid with the presence of a magnetic field exceeding certain strength, and retains to gel upon removing the magnetic field and with a treatment of sonication and heating–cooling cycle. SEM and TEM observations revealed the continuous fibrous network structures of the molecules of the gelator in the ionogels. To the best of our knowledge, this is the first report on ionogels possessing stimulus-responsive properties, good mechanical strength, and super-gelation talent.

Cholesterol-based low-molecular mass gelators towards smart ionogels

Ultra-low density porous polystyrene monoliths have been prepared via using water/styrene gel-emulsions, which were stabilized by a low-molecular mass gelator (LMMG), as templates It was demonstrated that the porous materials as prepared possess a number of superior features such as highly adjustable internal structure and density, the lowest density could be lower than 001 g cm−3 Moreover, such materials can be used as excellent absorbents for many organic liquids including viscous oils like mineral oil and high-density oils such as dichloromethane In particular, the absorption process is fast, selective and efficient when they are used in the purification of oil contaminated water Importantly, the oils absorbed in the absorbent can be easily squeezed out, and furthermore the wet absorbent as obtained can be reused by suitable washing and natural drying More importantly, the LMMG-based gel-emulsions employed as templates are simple in preparation, only mixing and agitation at ambient temperature are required Moreover, further treatment of the wet porous materials as prepared from the templates is just washing and natural drying, which is completely different from those such as freeze-drying or supercritical drying widely adopted by others in the preparation of low density materials via routine approaches It is believed that the LMMG-based gel-emulsion template method developed in the present work may have created a novel and facile way for preparing low density materials with ideal properties

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Ultra-low density porous polystyrene monolith: facile preparation and superior application

With ever-increasing need for thin, flexible, and functional materials in electrochemical systems, various techniques have been explored for creating materials used in fuel cells, batteries, electrochromic devices, solar cells, and sensors. In the present study, a novel ferrocene (Fc) and cholesterol (Chol)-containing oligomer, oligo(FcDC-co-CholDEA), was specially designed and prepared by putting Fc in the main chain and Chol as a side group. MALDI-TOF MS and freezing point depression measurements revealed that in average each oligomer contains three Fc units and three Chol units. Cyclic voltammetric measurements revealed that the oligomer displays superior electrochemical stability if compared with other Fc derivatives containing only one Fc unit and one or two Chol unit and with poly(ferrocenylsilane) with Fc in the main chain. In particular, the Fc-containing oligomer possesses an unusual oxidation center, of which the oxidation potential could be as high as 1.81 V. The oligomer is also superior in self-assembly, as demonstrated by forming an LB film of layered structures. Furthermore, supramolecular films with high mechanical strength in the wet state can be prepared by employing a simple solution casting method. This finding demonstrates that self-assembly is a simple but effective way to create films of potential uses in real-life applications provided proper building blocks are designed and employed.

Oligo(FcDC-co-CholDEA) with Ferrocene in the Main Chain and Cholesterol as a Pendant Group—Preparation and Unusual Properties

The invention discloses a method for preparing an ultra-low density porous polystyrene block. The method comprises the following steps of: preparing a water (W)/oil (O) type gel emulsion through adopting a micromolecular gelatinizing agent as a stabilizing agent, utilizing the W/O type gel emulsion as a template, and initiating polymerization so as to obtain the ultra-low density porous polystyrene block. The method is simple in preparation process; the gel emulsion can be obtained at room temperature under stirring; and a porous material which is prepared by using the gel emulsion as the template does not need proper high energy consumption measures such as supercritical drying, freeze drying and the like, and only requires simple washing and drying at room temperature. The ultra-low density porous polystyrene block prepared by the method can selectively adsorb normal hexane, petroleum ether, kerosene, benzene, dichloromethane, salad oil and gasoline in the water with the maximum adsorbing capacities of 4.45, 5.02, 6.19, 18.71, 20.21, 2.75 and 16.49g/g; the block after the adsorption can be directly taken out from the water without other separation methods; and moreover, the extruded and washed polystyrene block can be recycled.

Method for preparing ultra-low density porous polystyrene block and application

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Cholesterol-based low-molecular mass gelators towards smart ionogels

Ultra-low density porous polystyrene monolith: facile preparation and superior application

Oligo(FcDC-co-CholDEA) with Ferrocene in the Main Chain and Cholesterol as a Pendant Group—Preparation and Unusual Properties

Method for preparing ultra-low density porous polystyrene block and application