Expanding the scope of gels – combining polymers with low-molecular-weight gelators to yield modified self-assembling smart materials with high-tech applications

Abstract

Combining low molecular weight gelators (LMWGs) with polymers is a broad yet relatively recent field, in a phase of rapid expansion and with huge potential for exploitation. This review provides an overview of the state-of-the-art and reflects on new technologies that might be unlocked. We divide LMWG-polymer systems into five categories: (i) polymerisation of self-assembled LMWG fibres, (ii) capture of LMWG fibres in a polymer matrix, (iii) addition of non-gelling polymer solutions to LMWGs, (iv) systems with directed interactions between polymers and LMWGs, and (v) hybrid gels containing both LMWGs and polymer gels (PGs). Polymers can have significant impacts on the nanoscale morphology and materials performance of LMWGs, and conversely LMWGs can have a major effect on the rheological properties of polymers. By combining different types of gelation system, it is possible to harness the advantages of both LMWGs and PGs, whilst avoiding their drawbacks. Combining LMWG and polymer technologies enhances materials performance which is useful in traditional applications, but it may also yield major steps forward in high-tech areas including environmental remediation, drug delivery, microfluidics and tissue engineering.

Supramolecular materials

“…Upon evaporation of the solvent at room temperature the 15 resulting xerogel (the solid remaining after liquid removal) can be doped with iodine vapour to partially convert the neutral form into the cation radical of the tetrathiafulvalene moiety, resulting in a conducting film. Warming of this film gives rise to a structural rearrangement of the fibres, witnessed by a 20 decrease in resistance as well as a change in the electron paramagnetic resonance spectrum of the material, giving the second phase ( ). On the other hand, doping followed by immediate warming leads to a distinct structure ( ) with a smooth texture and higher electronic dimensionality (as 25 indicated by electron paramagnetic resonance spectroscopy), and further heating of this material generates a fourth polymorph with larger morphological features (observed by microscopy, see Fig.…”

“…6 Moreover, materials properties are emergent and hence can depend on their structure and morphology and hence their history and formation mechanism. Let us first, then, 20 put this in a materials context.…”

“…By labelling each peptide with a different fluorescent probe, it was possible to use confocal laser scanning microscopy with super resolution (80 nm) to visualise 20 differently coloured self-sorted fibres entangled in two and three dimensions (Fig. 4).…”

Sequence Adaptive Peptide–Polysaccharide Nanostructures by Biocatalytic Self-Assembly

“…20,21 The properties of peptide nanostructures can be altered dramatically by co-assembly 22,23 with macromolecules where specific interactions (e.g. electrostatic, aromatic stacking) and templating 24 might be utilized to direct the assembly process.…”

Metal ‘turn-off’, anion ‘turn-on’ gelation cascade in pyridinylmethyl ureas

“…[1][2][3][4][5][6] The ease with which these low molecular weight gelators (LMWG) can be synthesised and the fact the properties of their gels can be modified by light, pH, redox or chemical stimuli suggests potential applications in areas such as drug delivery, biomedicine and pharmaceutical solid form control. 3,[7][8][9][10] N-pyridyl ureas have attracted considerable attention because their competitive hydrogen bonding properties allow particularly well-controlled gelation behaviour. [11][12][13][14] Typically aryl ureas with electron withdrawing substituents such as a pyridyl moiety do not form the common urea -tape motif frequently implicated in gelation behaviour because the urea carbonyl is sterically blocked by competing intramolecular CH···O interactions and NH···N pyridyl hydrogen bonding.…”