Multiple modulations for supramolecular hydrogels of bola-form surfactants bearing rigid and flexible groups

Co-Assembled Supramolecular Organohydrogels of Amphiphilic Zwitterion and Polyoxometalate with Controlled Microstructures

The organization of modifiable and functional building components into various superstructures is of great interest due to their broad applications. Supramolecular self-assembly, based on rationally designed building blocks and appropriately utilized driving forces, is a promising and widely used strategy for constructing superstructures with well-defined nanostructures and diverse morphologies across multiple length scales. In this study, two homogeneous organohydrogels with distinct appearances were constructed by simply mixing polyoxometalate (phosphomolybdic acid, HPMo) and a double-tailed zwitterionic quaternary ammonium amphiphile in a binary solvent of water and dimethyl sulfoxide (DMSO). The delicate balance between electrostatic attraction and repulsion of anionic HPMo clusters and zwitterionic structures drove them to co-assemble into homogeneous organohydrogels with diverse microstructures. Notably, the morphologies of the organohydrogels, including unilamellar vesicles, onion-like vesicles, and spherical aggregates, can be controlled by adjusting the ionic interactions between the zwitterionic amphiphiles and phosphomolybdic acid clusters. Furthermore, we observed an organohydrogel fabricated with densely stacked onion-like structures (multilamellar vesicles) consisting of more than a dozen layers at certain proportions. Additionally, the relationships between the self-assembled architectures and the intermolecular interactions among the polyoxometalate, zwitterionic amphiphile, and solvent molecules were elucidated. This study offers valuable insights into the mechanisms of polyoxometalate-zwitterionic amphiphile co-assembly, which are essential for the development of materials with specific structures and emerging functionalities.

Cationic Azobenzenes as Light-Responsive Crosslinkers for Alginate-Based Supramolecular Hydrogels

Azobenzene photoswitches are fundamental components in contemporary approaches aimed at light-driven control of intelligent materials. Significant endeavors are directed towards enhancing the light-triggered reactivity of azobenzenes for such applications and obtaining water-soluble molecules able to act as crosslinkers in a hydrogel. Here, we report the rational design and the synthesis of azobenzene/alginate photoresponsive hydrogels endowed with fast reversible sol-gel transition. We started with the synthesis of three cationic azobenzenes (AZOs A, B, and C) and then incorporated them in sodium alginate (SA) to obtain photoresponsive supramolecular hydrogels (SMHGs). The photoresponsive properties of the azobenzenes were investigated by UV-Vis and 1H NMR spectroscopy. Upon irradiation with 365 nm UV light, the azobenzenes demonstrated efficient trans-to-cis isomerization, with complete isomerization occurring within seconds. The return to the trans form took several hours, with AZO C exhibiting the fastest return, possibly due to higher trans isomer stability. In the photoresponsive SMHGs, the minimum gelation concentration (MGC) of azobenzenes was determined for different compositions, indicating that small amounts of azobenzenes could induce gel formation, particularly in 5 wt% SA. Upon exposure to 365 nm UV light, the SMHGs exhibited reversible gel-sol transitions, underscoring their photoresponsive nature. This research offers valuable insights into the synthesis and photoresponsive properties of cationic, water-soluble azobenzenes, as well as their potential application in the development of photoresponsive hydrogels.

Supramolecular topological hydrogels: from material design to applications

Supramolecular topological hydrogels are constructed by introducing different dynamic topological structures into polymeric networks and thus exhibit a wide variety of stimuli-responsive properties and versatile applications.

Nicotinamide-based supergelator self-assembling via asymmetric hydrogen bonding NH⋯OC and H⋯Br- pattern for reusable, moldable and self-healable nontoxic fuel gels

HYPOTHESIS

Development of highly efficient low-molecular weight gelators (LMWGs) for safe energy storage materials is of great demand. Energy storage materials as fuel gels are often achieved by construction of hybrid organic frameworks capable of multiple noncovalent interactions in self-assembly, which allow tuning required properties at the molecular level by altering individual building blocks of the LMWG. However, LMWGs have limited rechargeable capability due to their chemical instability.

EXPERIMENTS

We designed, synthesized and characterized a novel, bio-inspired chiral gemini amphiphile derivative 1 containing N-hexadecyl aliphatic tails from quaternized nicotinamide-based segment and bromide anion showing supergelation ability in water, alcohols, aprotic polar and aromatic solvents, with critical gel concentrations as low as 0.1 and 0.035 wt% in isopropanol and water, respectively.

FINDINGS

Nanostructural architecture of the network depended on the solvent used and showed variations in size and shape of 1D nanofibers. Supergelation is attributed to a unique asymmetric NH⋯OC, H⋯Br^- hydrogen bonding pattern between H-2 hydrogens from nicotinamide-based segment, amide functional groups from chiral trans-cyclohexane-1,2-diamide-based segment and bromide ions, supporting the intermolecular amide-amide interactions appearing across one strand of the self-assembly. Gels formed from 1 exhibit high stiffness, self-healing, moldable and colorable properties. In addition, isopropanol gels of 1 are attractive as reusable, shape-persistent non-toxic fuels maintaining the chemical structure with gelation efficiency for at least five consecutive burning cycles.