Flexible Optics: Recent Developments in Molecular Gels

Abstract

Self-assembly is an attractive bottom-up strategy for the development of the next generation of functional soft matter.[1] Molecular gels (MGs) are one class of such soft material that has garnered much attention from scientists in diverse research areas. MGs are solid-like viscoelastic materials comprising a large pool of liquid (water or organic liquid) immobilized by very small amount of nonpolymeric lowmolecular-weight amphiphiles.[2] The solvent-immobilization properties of such amphiphiles stems from their propensity to hierarchically self-assemble at the nanoscale through weak intermolecular interactions to form a microscale threedimensional (3D) network. Within this network, the solvent molecules are entrapped, resulting in the formation of a coherent gel (Scheme 1). Such gels are of particular interest owing to their nonpolymeric nature, gel-to-sol reversibility, ability to form high-aspect-ratio assemblies, and biocompatibility.Through systematic tailoring of the amphiphile structure, the MGs can be imparted with diverse functional properties. Consequently, unlike polymeric gels, MGs have been used as smart materials in a wide spectrum of applications in, for example, drug delivery, energy, food, tribology, and electronics. [3][4][5] Despite these possibilities their practical potential beyond biomedical applications has not been realized until recently. Several factors such as the multistep schemes for gelator synthesis, energy-intensive gelation steps, and low gel strengths have been the principal constraints to the full exploitation of MGs for high-volume industrial applications. However, owing to comprehensive efforts by the gel researchers over the last decade, current research has to overcome the limitations and MGs can be designed efficiently for desired bulk-scale applications.Recently, John and co-workers have developed inexpensive, eco-friendly sugar gelators that can selectively gel the oil phase from an oil-water mixture at room temperature.[6] The use of a room-temperature phase-selective gel system can be a promising approach for the treatment of oil spills. In another interesting application in the catalysis of organic reactions, the catalytic sites are present on the self-assembled network of the MG and in the liquid pool.[7] Utilization of MGs in catalysis facilitates the fine-tuning of catalyst performance, which is otherwise difficult with conventional heterogeneous catalysts. In yet another study, Yamanaka and co-workers developed hydrogels from urea/sugar-conjugated amphiphiles, which could be efficiently employed as the base in gel electrophoresis.[8] Because of the simple extraction process and unique separation pattern possible with such MGs, this new method can replace classical agarose-based gel electrophoresis techniques. Likewise, MGs have been used for developing light-harvesting materials, electronic devices, electrolytic gels for batteries, and many other smart materials. [3][4][5] Interestingly, in more recently published work of Sureshan et al. several limitations of MGs...

Semiconductor nanoparticle-based hydrogels prepared via self-initiated polymerization under sunlight, even visible light

“…In our functional hydrogels, the photoinitiator semiconductor NPs were similar to organic initiators2021, which enable spatial/temporal control and a mild curing process relative to the traditional preparation of most hydrogels22232425262728293031323334. The important advantages of this method include the use of inexhaustible sunlight as a substitute for an ultraviolet generator.…”

Protein-based soft micro-optics fabricated by femtosecond laser direct writing

“…[9][10][11][12][13][14][15][16][17] Until now, numerous fabrication methods, for instance, transferring-andprinting processes, hot-embossing technique, nano-imprinting, and self-assembly approaches, have been developed to produce flexible and stretchable micro-optics using organic, polymer, silk or hydrogel materials. [13][14][15][16][17][18][19][20] Owing to their abundance, renewability, inexpensiveness, degradability, biocompatibility and unique functionality, protein-based soft micro-optics demonstrate superior performances that exceed many devices made from currently available organic materials. However, developing a convenient, economic and ecofriendly fabrication strategy that could readily produce high-performance protein-based soft micro-optics with high accuracy and improved quality is challenging.…”

Recent Advances in Supramolecular Gels and Catalysis

“…In light of their broad potential applications in diverse research fields, supramolecular gels, as a “smart” soft material, have attracted significant attention and extensive development in the past two decades. In general, supramolecular gels are usually prepared from various low‐molecular‐mass gelators (LMMGs).…”

“…The development of metallogels was also reviewed by some groups . A number of recent reviews focused on the functional applications of supramolecular gels have appeared . Supramolecular gels applied in organic transformations and catalysis were first reviewed by Miravet and co‐workers in 2010, and one year later Díaz et al.…”