Low Molecular Mass Gelators of Organic Liquids and the Properties of Their Gels

Térech, Pierre; Weiss, Richard G.

doi:10.1021/cr9700282

Cited by 3,058 publications

(2,170 citation statements)

References 201 publications

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“…There are many reviews that already provide this information. [1][2][3]5,68 Rather here we mainly focus on one example where the process of gelation has been used to lead to significantly different outcomes. This example is hydrogelators; this could be one reason why sufficient data exist on the formation of gels under different conditions because, compared with organic solvents, water as a solvent opens up many additional parameters, including variations in ionic strength, pH, and the addition of background salts.…”

Section: Process Of Assemblymentioning

confidence: 99%

Low-Molecular-Weight Gels: The State of the Art

Draper

Adams

2017

Chem

538

469

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Low-molecular-weight gels are currently a hugely important class of materials that are attracting significant interest. These gels are formed when small molecules self-assemble into one-dimensional structures that entangle and cross-link to form a network that is capable of immobilizing the solvent. Here, we critically discuss the current state of the art and highlight two key areas where we believe there is significant untapped potential. The first is the observation that the properties of the gels are highly process dependent, which means that it is possible to access materials with very different properties from a single gelator. Second, using multiple gelators offers the opportunity to prepare materials with a high degree of information content and with a wider range of properties. We aim to spark thought and discussion on these aspects. INTRODUCTIONLow-molecular-weight gels (LMWGs), or supramolecular gels, are a fascinating and useful class of material. The gels arise from the self-assembly of small molecules into long, anisotropic structures, most commonly fibers. [1][2][3][4][5] At a sufficiently high concentration, these fibers entangle or otherwise form cross-links, leading to the network that is able to immobilize the solvent through surface tension and capillary forces. 1,2 These gels differ from permanently covalently cross-linked polymer gels because the cross-linking can be reversed by the input of energy, for example, by heating. 6 LMWGs have been around for many years but are receiving considerable current interest. 4 They are also used in industrial products, 7 although this seems rarely discussed in the academic literature.In addition to the industrial applications, many recent advances and uses are being described. [8][9][10][11][12] The specific self-assembly leading to gel formation can be exploited. For example, the fiber formation is a result of molecular stacking, meaning that the self-assembly leads to aggregates that can be suitable for optoelectronic applications. 13,14 The ready reversibility of gelation can be exploited, for example, to release cells from gels on demand in a manner that does not lead to cell death. 15 Ready gel formation by a simple trigger can also be used to allow easy and efficient gel loading. [16][17][18] Unsurprisingly, therefore, there is significant interest in these materials ( Figure 1). This is a fascinating area and in many ways holds attention because of the difficulties in probing and understanding the gels. The gels arise from assembly across many length scales, and understanding all of these is difficult. At the molecular level, the molecules must interact in a manner that leads to the formation of suitable aggregates that can eventually entangle. Thus, one-dimensional growth must be favored. From this perspective, it is very frustrating that it is often extremely difficult to predict whether a molecule will form a gel or not; indeed, gelation has been described as an empirical science. 4 Structurally similar small molecules can exhibitThe Bigger Pict...

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Section: Process Of Assemblymentioning

confidence: 99%

Low-Molecular-Weight Gels: The State of the Art

Draper

Adams

2017

Chem

538

469

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“…[1][2][3][4] The increasing attention paid to supramolecular gels is related to their applicability as new soft materials in areas such as molecular electronics, controlled release, tissue engineering or catalysis among others. [2][3][4][5][6][7] Several approaches have addressed the inclusion of photonic functionalities into supramolecular gels. 8 For example, gels with chromophore units have been used as photocatalysts 9,10 and excitation energy transfer has been studied in supramolecular gels formed by photoactive fibers which contained entrapped dyes.…”

Section: Introductionmentioning

confidence: 99%

Multimodal Light-Harvesting Soft Hybrid Materials: Assisted Energy Transfer upon Thermally Reversible Gelation

et al. 2017

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Multimodal light-harvesting soft systems able to absorb UV-to-NIR radiations and convert into visible emissions have drawn much attention in the last years in order to explore new areas of application in energy, photonics, photocatalysis, sensors and so forth. Here, we present a new hybrid system combining a supramolecular photonic gel of naphthalimide-derived molecules self-assembled into fibers and upconverting NaYF 4 :Yb/Tm nanoparticles (UCNPs). The hybrid system presented here manipulates light reversibly as a result of an optical communication between the UCNPs and the photoactive gel network. Upon UV irradiation, the system shows the characteristic emission at 410 nm from the photoactive organomolecule. This emission is also activated upon 980 nm excitation thanks to an efficient energy transfer from the UCNPs to the fibrillary network. Interestingly, the intensity of this emission is thermally regulated during the reversible assembly or disassembly of the organogelator molecules, in such a way that gelator emission is only observed in the aggregated state. Additionally, the adsorption of the UCNPs with the supramolecular gel fibers enhance their emissive properties, a behavior ascribed to the isolation from solvent quenchers and surface defects, as well as an increased IR light scattering promoted by the fibrillary network. The reported system constitutes a unique case of a thermally regulated, reversible, dual UV and IR light harvesting hybrid soft material.3

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“…Despite the extensive research material in the field of gels, investigation of many aspects of their chemical and physical properties is still unresolved. After two decades of research, we still do not have an answer to the fundamental question: what are the structural requirements for a molecule to have the ability of the liquid [5][6][7][8][9]. Gelating materials that form two-phase, stable in definite ranges of temperature, but thermally reversible physical gels represent a basis for manufacturing of foodstuffs, cosmetics and pharmaceutical agents.…”

Section: Introductionmentioning

confidence: 99%

The structural parameters of rigid matrix of saccharide-based gel described by short and long diffusion regime analysis

Kowalczuk

2017

J Mater Sci

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The tortuosity-porosity relation and internal structure diameters in a selected organogel are studied. The diffusion coefficient measured by pulsed field gradient NMR at short and long observation times can be used to estimate the tortuosity and the pore surface-to-volume (S/V pore ) ratio of a porous material (Latour et al. in J Magn Res A 112:83-91, 1995; Mair et al. in Magn Res Imaging 19:345-351, 2001; Mitra et al. in Phys Rev B 47(14):8565-8574, 1993; Valiullin and Skirda in J Chem Phys 114:452-458, 2001). The value of S/V pore allows to calculate the average pore and barrier diameters. In the experiment, the timedependent diffusion coefficient of toluene in a low molecular weight gelator methyl-4,6-O-(p-nitrobenzylidene)-a-D-glucopyranoside (Gluco-NO 2 ) matrix was measured. The results revealed the relation between the diffusion coefficient of toluene and the concentration of gelator Gluco-NO 2 in the system. With increasing Gluco-NO 2 compound in the sample, the diffusion coefficient of toluene decreases. On the basis of the diffusion coefficient behaviour as a function of time and gelator concentration, the fibrous structure of the gel matrix was identified and the structural parameters of the system were investigated.

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Low Molecular Mass Gelators of Organic Liquids and the Properties of Their Gels

Cited by 3,058 publications

References 201 publications

Low-Molecular-Weight Gels: The State of the Art

Low-Molecular-Weight Gels: The State of the Art

Multimodal Light-Harvesting Soft Hybrid Materials: Assisted Energy Transfer upon Thermally Reversible Gelation

The structural parameters of rigid matrix of saccharide-based gel described by short and long diffusion regime analysis

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