The Experts below are selected from a list of 8610 Experts worldwide ranked by ideXlab platform
Kenji Hanabusa - One of the best experts on this subject based on the ideXlab platform.
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Physical gelation by amides derived from trans-1,2-diaminocyclohexane and their tetrasiloxane-based Gelators
Polymer Journal, 2017Co-Authors: Haruka Nakagawa, Masahiro Suzuki, Kenji HanabusaAbstract:Four compounds were prepared from trans -1,2-diaminocyclohexane and were subsequently studied as Gelators. These two compounds were chiral trans -(1 R , 2 R )-1-(2-heptylundecanoylamino)-2-(10-undecenoylamino)cyclohexane and the corresponding racemate. The other two compounds were 1,1,3,3,5,5,7,7-octamethyltetrasiloxane-containing chiral and racemic compounds prepared by a hydrosilylation reaction. Their gelation abilities were evaluated on the basis of the minimum gel concentration, using seven solvents. The thermal stability and transparency of the gels were investigated by UV–vis spectroscopy using three-component mixed solvents of hexadecyl 2-ethylhexanoate, liquid paraffin, and decamethylcyclopentasiloxane (66 combinations). The gel-to-sol phase-transition temperatures were also studied. The viscoelastic behavior of the gels was studied by rheology measurements in the strain sweep mode. Aggregates consisting of three-dimensional networks were studied by transmission electron microscopy. Circular dichroism spectroscopy was performed to verify the existence of helical aggregates in the gel. The 1,1,3,3,5,5,7,7-octamethyltetrasiloxane-containing Gelator, ( R , R )-g/Si , was synthesized by a hydrosilylation with a gelation-driving segment based on trans-(1R, 2R)- 1,2-diaminocyclohexane. Gelation abilities were investigated in the mixed solvents of HDEH, liquid paraffin, and D5. ( R , R )-g/Si could form stable and transparent gels due to the flexible octamethyltetrasiloxane segment.
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Synthesis of Fluorescent Gelators and Direct Observation of Gelation with a Fluorescence Microscope
Chemistry: A European Journal, 2016Co-Authors: Kenji Hanabusa, Takuya Ueda, Shingo Takata, Masahiro SuzukiAbstract:Fluorescein-, benzothiazole-, quinoline-, stilbene-, and carbazole-containing fluorescent Gelators have been synthesized by connecting gelation-driving segments, including l-isoleucine, l-valine, l-phenylalanine, l-leucine residue, cyclo(l-asparaginyl-l-phenylalanyl), and trans-(1R,2R)-diaminocyclohexane. The emission behaviors of the Gelators were investigated, and their gelation abilities studied against 15 solvents. The minimum gel concentration, variable-temperature spectroscopy, transmission electron microscopy, scanning electron microscopy, fluorescence microscopy (FM), and confocal laser scanning microscopy (CLSM) were used to characterize gelation. The intermolecular hydrogen bonding between the N−H and C=O of amide, van der Waals interactions and π–π stacking play important roles in gelation. The colors of emission are related to the fluorescence structures of Gelators. Fibrous aggregates characterized by the color of their emission were observed by FM. 3D images are produced by the superposition of images captured by CLSM every 0.1 μm to a settled depth. The 3D images show that the large micrometer-sized aggregates spread out three dimensionally. FM observations of mixed Gelators are studied. In the case of gelation, two structurally related Gelators with the same gelation-driving segment lead to the Gelators build up of the same aggregates through similar hydrogen-bonding patterns. When two Gelators with structurally different gelation-driving segments induce gelation, the Gelators build up each aggregate through individual hydrogen-bonding patterns. A fluorescent reagent that was incorporated into the aggregates of gels through van der Waals interactions was developed. The addition of this fluorescent reagent enables the successful observation of nonfluorescent Gelators’ aggregates by FM.
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Development of low-molecular-weight Gelators and polymer-based Gelators
Polymer Journal, 2014Co-Authors: Kenji Hanabusa, Masahiro SuzukiAbstract:In this review, the development of low-molecular-weight Gelators and polymer-based Gelators is described. The driving forces for physical gelation are non-covalent bonds, such as hydrogen bonds, electrostatic interactions, van der Waals interactions and π–π interactions. When gelation occurs, the Gelator molecules self-assemble into macromolecule-like aggregates through non-covalent intermolecular interactions. The close relationship between crystallization and gelation is discussed. Crystallization is a phenomenon in which crystals are separated from solution by the formation of a three-dimensional arrangement of solute through intermolecular interactions. Conversely, physical gelation is caused by the trapping of solvent in fibrous networks that are formed by Gelator molecules through intermolecular interactions. Amino acid derivatives and cyclic dipeptides are introduced as typical Gelators. To develop Gelators that form semipermanent stable gels, a new concept termed ‘gelation-driving segments’ is proposed. Polymer-based Gelators that can form semipermanent stable gels are synthesized by connecting gelation-driving segments to polymers or oligomers. Low-molecular-weight compounds, which form physical gels, are called ‘Gelators’ and have received a great amount of scientific and technological interest. The physical gelation by Gelator results from non-covalent bonds, represented by hydrogen bond. Molecules of Gelator are first self-assembled in cooling process, producing fibrous assemblies. Then, these fibrous assemblies form a three-dimensional network structure, and gelation occurs by trapping solvent in the networks. Fibrous assemblies can be observed by electron microscope. This is a transmission electron microscopy image of tetrachloromethane gel formed by N- octadecylamide of N -benzyloxycarbonyl- L -isoleucine.
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Development of low-molecular-weight Gelators and polymer-based Gelators
Polymer Journal, 2014Co-Authors: Kenji Hanabusa, Masahiro SuzukiAbstract:Low-molecular-weight compounds, which form physical gels, are called ‘Gelators’ and have received a great amount of scientific and technological interest. The physical gelation by Gelator results from non-covalent bonds, represented by hydrogen bond. Molecules of Gelator are first self-assembled in cooling process, producing fibrous assemblies. Then, these fibrous assemblies form a three-dimensional network structure, and gelation occurs by trapping solvent in the networks. Fibrous assemblies can be observed by electron microscope. This is a transmission electron microscopy image of tetrachloromethane gel formed by N-octadecylamide of N-benzyloxycarbonyl-L-isoleucine.
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liquid crystalline gels exhibiting electrooptical light scattering properties fibrous polymerized network of a lysine based Gelator having acrylate moieties
Polymer Journal, 2012Co-Authors: Hiroki Eimura, Kenji Hanabusa, Masafumi Yoshio, Yoshiko Shoji, Takashi KatoAbstract:New liquid-crystalline (LC) gels composed of a lysine-based bisurea derivative having terminal acrylate moieties and a nematic liquid crystal, 4-cyano-4′-pentylbiphenyl, have been prepared to develop light-scattering electrooptical materials. Randomly dispersed networks of the polymerizable fibers are obtained by self-assembly of the lysine derivative through the formation of hydrogen bonds in the isotropic phase of the nematic LC molecule. After the isotropic–nematic transition of the LC molecule occurs at 35 °C on cooling, light-scattering nematic LC gels are formed because of the formation of microphase-separated structures of fibrous solids and the liquid crystal. The fibrous structures are fixed by photopolymerization, leading to the enhancement of thermal stability. The polymerized LC gels exhibit electrooptical switching between light-scattering and transparent states with lower driving voltages than the non-polymerized LC gels. The threshold voltages of the LC gels based on the polymerizable lysine Gelator are also lower than those of the LC gels containing a non-polymerizable lysine Gelator. Nematic liquid-crystalline (LC) gels showing electrooptical switching have been prepared for the mixtures of a new polymerizable lysine-based Gelator and a nematic LC compound, 4-cyano-4′-pentylbiphenyl. Finely dispersed fibrous networks are formed by self-assembly of the Gelators through the formation of hydrogen bonds. In-situ photopolymerization of the Gelators in the self-assembled state leads to thermal stabilization of the fibrous network structures. The threshold voltage of electrooptical switching for the polymerized LC gel is lower than that for non-polymerized LC gels.
Di Zhang - One of the best experts on this subject based on the ideXlab platform.
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Gelator polysaccharide hybrid hydrogel for selective and controllable dye release
Journal of Colloid and Interface Science, 2012Co-Authors: Ping Li, Yi Tian Tang, Chuan Liang Feng, Jiajun Gu, Di ZhangAbstract:In this paper, 1,4-bi(phenylalanine-diglycol)-benzene (PDB) based Low-Molecular-Weight-Gelator (LMWG) hydrogels are modified using hydrophilic polysaccharide (sodium alginate). A set of techniques including Fourier transform infrared (FT-IR) spectroscopy, 1H Nuclear Magnetic Resonance (1H NMR), X-ray powder diffraction (XRD), Ultraviolet–Visible (UV–Vis), and circular dichroism (CD) had confirmed a β-turn arrangement of PDB Gelators and a semi-interpenetrating network (semi-IPN), which was formed through hydrogen bonds between LMWG fibers and polysaccharide chains. The evaluation of physicochemical properties of hydrogels indicates that Gelator-polysaccharide hybrid hydrogels possess better mechanical and water retention properties than LMWG hydrogels. The release study of dyes (model drug) from both LMWG and hybrid hydrogels was carried out. Compared with PDB based hydrogels, hybrid hydrogels show a selective and controllable release property for certain dyes. The results suggest LMWG-polysaccharide hybrid gels may find potential applications as promising drug delivery vehicles for drug molecules.
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Gelator-polysaccharide hybrid hydrogel for selective and controllable dye release
Journal of Colloid and Interface Science, 2012Co-Authors: Ping Li, Xiao Qiu Dou, Yi Tian Tang, Chuan Liang Feng, Shenmin. Zhu, Jiajun Gu, Di ZhangAbstract:In this paper, 1,4-bi(phenylalanine-diglycol)-benzene (PDB) based Low-Molecular-Weight-Gelator (LMWG) hydrogels are modified using hydrophilic polysaccharide (sodium alginate). A set of techniques including Fourier transform infrared (FT-IR) spectroscopy, 1H Nuclear Magnetic Resonance (1H NMR), X-ray powder diffraction (XRD), Ultraviolet-Visible (UV-Vis), and circular dichroism (CD) had confirmed a β-turn arrangement of PDB Gelators and a semi-interpenetrating network (semi-IPN), which was formed through hydrogen bonds between LMWG fibers and polysaccharide chains. The evaluation of physicochemical properties of hydrogels indicates that Gelator-polysaccharide hybrid hydrogels possess better mechanical and water retention properties than LMWG hydrogels. The release study of dyes (model drug) from both LMWG and hybrid hydrogels was carried out. Compared with PDB based hydrogels, hybrid hydrogels show a selective and controllable release property for certain dyes. The results suggest LMWG-polysaccharide hybrid gels may find potential applications as promising drug delivery vehicles for drug molecules. © 2012 Elsevier Inc.
Masahiro Suzuki - One of the best experts on this subject based on the ideXlab platform.
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Physical gelation by amides derived from trans-1,2-diaminocyclohexane and their tetrasiloxane-based Gelators
Polymer Journal, 2017Co-Authors: Haruka Nakagawa, Masahiro Suzuki, Kenji HanabusaAbstract:Four compounds were prepared from trans -1,2-diaminocyclohexane and were subsequently studied as Gelators. These two compounds were chiral trans -(1 R , 2 R )-1-(2-heptylundecanoylamino)-2-(10-undecenoylamino)cyclohexane and the corresponding racemate. The other two compounds were 1,1,3,3,5,5,7,7-octamethyltetrasiloxane-containing chiral and racemic compounds prepared by a hydrosilylation reaction. Their gelation abilities were evaluated on the basis of the minimum gel concentration, using seven solvents. The thermal stability and transparency of the gels were investigated by UV–vis spectroscopy using three-component mixed solvents of hexadecyl 2-ethylhexanoate, liquid paraffin, and decamethylcyclopentasiloxane (66 combinations). The gel-to-sol phase-transition temperatures were also studied. The viscoelastic behavior of the gels was studied by rheology measurements in the strain sweep mode. Aggregates consisting of three-dimensional networks were studied by transmission electron microscopy. Circular dichroism spectroscopy was performed to verify the existence of helical aggregates in the gel. The 1,1,3,3,5,5,7,7-octamethyltetrasiloxane-containing Gelator, ( R , R )-g/Si , was synthesized by a hydrosilylation with a gelation-driving segment based on trans-(1R, 2R)- 1,2-diaminocyclohexane. Gelation abilities were investigated in the mixed solvents of HDEH, liquid paraffin, and D5. ( R , R )-g/Si could form stable and transparent gels due to the flexible octamethyltetrasiloxane segment.
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Synthesis of Fluorescent Gelators and Direct Observation of Gelation with a Fluorescence Microscope
Chemistry: A European Journal, 2016Co-Authors: Kenji Hanabusa, Takuya Ueda, Shingo Takata, Masahiro SuzukiAbstract:Fluorescein-, benzothiazole-, quinoline-, stilbene-, and carbazole-containing fluorescent Gelators have been synthesized by connecting gelation-driving segments, including l-isoleucine, l-valine, l-phenylalanine, l-leucine residue, cyclo(l-asparaginyl-l-phenylalanyl), and trans-(1R,2R)-diaminocyclohexane. The emission behaviors of the Gelators were investigated, and their gelation abilities studied against 15 solvents. The minimum gel concentration, variable-temperature spectroscopy, transmission electron microscopy, scanning electron microscopy, fluorescence microscopy (FM), and confocal laser scanning microscopy (CLSM) were used to characterize gelation. The intermolecular hydrogen bonding between the N−H and C=O of amide, van der Waals interactions and π–π stacking play important roles in gelation. The colors of emission are related to the fluorescence structures of Gelators. Fibrous aggregates characterized by the color of their emission were observed by FM. 3D images are produced by the superposition of images captured by CLSM every 0.1 μm to a settled depth. The 3D images show that the large micrometer-sized aggregates spread out three dimensionally. FM observations of mixed Gelators are studied. In the case of gelation, two structurally related Gelators with the same gelation-driving segment lead to the Gelators build up of the same aggregates through similar hydrogen-bonding patterns. When two Gelators with structurally different gelation-driving segments induce gelation, the Gelators build up each aggregate through individual hydrogen-bonding patterns. A fluorescent reagent that was incorporated into the aggregates of gels through van der Waals interactions was developed. The addition of this fluorescent reagent enables the successful observation of nonfluorescent Gelators’ aggregates by FM.
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Development of low-molecular-weight Gelators and polymer-based Gelators
Polymer Journal, 2014Co-Authors: Kenji Hanabusa, Masahiro SuzukiAbstract:In this review, the development of low-molecular-weight Gelators and polymer-based Gelators is described. The driving forces for physical gelation are non-covalent bonds, such as hydrogen bonds, electrostatic interactions, van der Waals interactions and π–π interactions. When gelation occurs, the Gelator molecules self-assemble into macromolecule-like aggregates through non-covalent intermolecular interactions. The close relationship between crystallization and gelation is discussed. Crystallization is a phenomenon in which crystals are separated from solution by the formation of a three-dimensional arrangement of solute through intermolecular interactions. Conversely, physical gelation is caused by the trapping of solvent in fibrous networks that are formed by Gelator molecules through intermolecular interactions. Amino acid derivatives and cyclic dipeptides are introduced as typical Gelators. To develop Gelators that form semipermanent stable gels, a new concept termed ‘gelation-driving segments’ is proposed. Polymer-based Gelators that can form semipermanent stable gels are synthesized by connecting gelation-driving segments to polymers or oligomers. Low-molecular-weight compounds, which form physical gels, are called ‘Gelators’ and have received a great amount of scientific and technological interest. The physical gelation by Gelator results from non-covalent bonds, represented by hydrogen bond. Molecules of Gelator are first self-assembled in cooling process, producing fibrous assemblies. Then, these fibrous assemblies form a three-dimensional network structure, and gelation occurs by trapping solvent in the networks. Fibrous assemblies can be observed by electron microscope. This is a transmission electron microscopy image of tetrachloromethane gel formed by N- octadecylamide of N -benzyloxycarbonyl- L -isoleucine.
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Development of low-molecular-weight Gelators and polymer-based Gelators
Polymer Journal, 2014Co-Authors: Kenji Hanabusa, Masahiro SuzukiAbstract:Low-molecular-weight compounds, which form physical gels, are called ‘Gelators’ and have received a great amount of scientific and technological interest. The physical gelation by Gelator results from non-covalent bonds, represented by hydrogen bond. Molecules of Gelator are first self-assembled in cooling process, producing fibrous assemblies. Then, these fibrous assemblies form a three-dimensional network structure, and gelation occurs by trapping solvent in the networks. Fibrous assemblies can be observed by electron microscope. This is a transmission electron microscopy image of tetrachloromethane gel formed by N-octadecylamide of N-benzyloxycarbonyl-L-isoleucine.
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polymer organoGelators that make supramolecular organogels through physical cross linking and self assembly
Chemical Society Reviews, 2010Co-Authors: Masahiro Suzuki, Kenji HanabusaAbstract:This tutorial review highlights recent and current advances in polymer organoGelators, which are rare compared with low molecular weight Gelators. In this review, we classify polymer organoGelators in three categories: the formation of supramolecular crosslinking points by conformational changes, the addition of crosslinking agents and the self-assembly of gelation-causing segments. Highly stereoregular polymers form a physical gel in organic solvents, involving conformational changes such as helix formation. The addition of cross-linking agents into polymer solutions provides stimuli-sensitive organogels. Furthermore, polymer organoGelators, which consist of versatile polymers, such as poly(ethylene glycol)s, polycarbonates, polyesters, polycaprolactones, polyolefins and low molecular weight Gelators, function as good organoGelators that can form organogels in many organic solvents at low concentration. The organogelation properties of polymer organoGelators are significantly affected by the chemical structures of the introduced low molecular weight Gelators and polymer backbones, the molecular weight of the polymer backbones and the linking mode between the low molecular weight Gelator segment and the polymer.
David K Smith - One of the best experts on this subject based on the ideXlab platform.
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Shaping and structuring supramolecular gels
Nature Reviews Materials, 2019Co-Authors: Phillip R. A. Chivers, David K SmithAbstract:Supramolecular gels assemble via non-covalent interactions between low-molecular-weight Gelators (LMWGs). The gels form a solid-like nanoscale network spanning a liquid-like continuous phase, translating molecular-scale information into materials performance. However, gels based on LMWGs are often difficult to manipulate, easily destroyed and have poor rheological performance. The recurring image of newly discovered supramolecular gels is that of an inverted vial showing that the gel can support its own weight against gravity. Such images reflect the limitation that these gels simply fill the vessel in which they are made, with limited ability to be shaped. This property prevents supramolecular gels from having the same impact as polymer gels, despite greater synthetic tunability, reversibility and bio/environmental compatibility. In this Review, we evaluate strategies for imposing different shapes onto supramolecular gels and for patterning structures within them. We review fabrication methods including moulding, self-healing, 3D printing, photopatterning, diffusion and surface-mediated patterning. We discuss Gelator chemistries amenable to each method, highlighting how a multicomponent approach can aid shaping and structuring. Supramolecular gels with defined shapes, or patterned structures with precisely controlled compositions, have the potential to intervene in applications, such as tissue engineering and nanoscale electronics, as well as opening up new technologies. Supramolecular gels comprise low-molecular weight Gelators that assemble by non-covalent interactions. In this Review, a range of fabrication methods, as well as strategies for shaping, structuring and patterning supramolecular gels are discussed.
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self sorting multi Gelator gels mixing and ageing effects in thermally addressable supramolecular soft nanomaterials
Soft Matter, 2011Co-Authors: Michelle M Smith, David K SmithAbstract:The self-sorting of a multi-Gelator gel containing a protected sorbitol derivative and a cholesterol-based Gelator is described. Using differential scanning calorimetry (DSC), NMR spectroscopy, and scanning electron microscopy (SEM), we have shown how the self-sorting of two independent nanoscale networks within the gel can be detected at molecular, nano/meso and macro length-scales. DSC allows us to observe the thermal characteristics associated with each individual Gelator network within the self-sorted gel. We also report that one component within the gel exhibits significant and unusual ageing effects, with the morphology of the gel nanostructure evolving over time, and leading to materials with enhanced thermal stabilities. These properties are transferred into the multi-Gelator gel, which also exhibits enhanced gel properties on ageing. In combination, the results in this paper demonstrate how individual Gelators can act independently within multi-Gelator gel soft materials.
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solvent Gelator interactions using empirical solvent parameters to better understand the self assembly of gel phase materials
Soft Matter, 2011Co-Authors: William Edwards, Cecile A Lagadec, David K SmithAbstract:By studying a family of L-lysine bis-urea Gelators with variable peripheral groups in different solvents, a more detailed understanding of the way in which Gelator fibres interact with the surrounding solvent environment is obtained. In all cases, these Gelators establish the same hydrogen bonding molecular recognition pathways—however, this process is mediated by the nature of the solvent. In terms of Kamlet–Taft parameters, the α parameter of the solvent (hydrogen bond donor ability) has primary importance in controlling whether the Gelator can establish a hydrogen bond network; the β parameter (hydrogen bond acceptor ability) plays a secondary role in tuning the thermal stability of the gel, and the π* parameter (polarisability) controls the solvation of the peripheral groups on the Gelator by the solvent, and hence tunes the gel stability and the ability of the Gelator to establish fibre–fibre interactions, as evidenced by scanning electron microscopy imaging. Considering solvent parameters allows us to gain a unique insight into hierarchical assembly processes at different length scales, i.e., molecular scale Gelator–Gelator interactions, and nanoscale fibre–fibre and fibre–solvent interactions. These processes are at the heart of developing effective models for the dynamic assembly of gel-phase soft materials.
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low molecular weight Gelators elucidating the principles of gelation based on Gelator solubility and a cooperative self assembly model
Journal of the American Chemical Society, 2008Co-Authors: Andrew R Hirst, Valeria Castelletto, Ian W. Hamley, Ian A Coates, Thomas R Boucheteau, Juan F Miravet, Beatriu Escuder, David K SmithAbstract:This paper highlights the key role played by solubility in influencing gelation and demonstrates that many facets of the gelation process depend on this vital parameter. In particular, we relate thermal stability (Tgel) and minimum gelation concentration (MGC) values of small-molecule gelation in terms of the solubility and cooperative self-assembly of Gelator building blocks. By employing a van’t Hoff analysis of solubility data, determined from simple NMR measurements, we are able to generate Tcalc values that reflect the calculated temperature for complete solubilization of the networked Gelator. The concentration dependence of Tcalc allows the previously difficult to rationalize “plateau-region” thermal stability values to be elucidated in terms of Gelator molecular design. This is demonstrated for a family of four Gelators with lysine units attached to each end of an aliphatic diamine, with different peripheral groups (Z or Boc) in different locations on the periphery of the molecule. By tuning the p...
Richard G Weiss - One of the best experts on this subject based on the ideXlab platform.
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Systematic modifications of alkane-based molecular Gelators and the consequences to the structures and properties of their gels
New Journal of Chemistry, 2020Co-Authors: Michael A. Rogers, Richard G WeissAbstract:A systematic structural development of molecular Gelators based on n-alkanes is presented. The properties of the resultant molecular gels with a wide range of liquids can, in some cases, be correlated with the structural modifications to the Gelators and the natures of their self-assembled fibrillar networks as analyzed at different distance scales. A special emphasis is placed on 12-hydroxystearic acid and its derivatives in which the chirality, placement, and functionality of the hydroxyl group center have been varied and the carboxylic head group has been modified systematically. The resulting correlations between molecular Gelator structure and the various properties of their gels provide a basis for the design of structurally more complex Gelators. However, the nuances of the systems explored demonstrate that additional factors, some of which are currently not well understood, must be considered before a priori design of molecular Gelators with specific gelating abilities will be possible.
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comparing and correlating solubility parameters governing the self assembly of molecular gels using 1 3 2 4 dibenzylidene sorbitol as the Gelator
Langmuir, 2014Co-Authors: Maria G. Corradini, Richard G Weiss, Ferenc Borondics, Michael A. RogersAbstract:Solvent properties play a central role in mediating the aggregation and self-assembly of molecular Gelators and their growth into fibers. Numerous attempts have been made to correlate the solubility parameters of solvents and gelation abilities of molecular Gelators, but a comprehensive comparison of the most important parameters has yet to appear. Here, the degree to which partition coefficients (log P), Henry’s law constants (HLC), dipole moments, static relative permittivities (er), solvatochromic ET(30) parameters, Kamlet–Taft parameters (β, α, and π), Catalan’s solvatochromic parameters (SPP, SB, and SA), Hildebrand solubility parameters (δi), and Hansen solubility parameters (δp, δd, δh) and the associated Hansen distance (Rij) of 62 solvents (covering a wide range of properties) can be correlated with the self-assembly and gelation of 1,3:2,4-dibenzylidene sorbitol (DBS) gelation, a classic molecular Gelator, is assessed systematically. The approach presented describes the basis for each of the par...
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pyrenyl linker glucono Gelators correlations of gel properties with Gelator structures and characterization of solvent effects
Langmuir, 2013Co-Authors: Zhiyan Xu, Yu Fang, Kevin K Diehn, Srinivasa R Raghavan, Richard G WeissAbstract:A series of glucono-appended 1-pyrenesulfonyl derivatives containing α,ω-diaminoalkane spacers (Pn, where n, the number of methylene units separating the amino groups, is 2, 3, 4, 6, 7, and 8) have been prepared. Careful analyses of correlations between the structures of these molecules and their gels have provided important insights into the factors responsible for one-dimensional aggregation of small molecules containing both lipophilic and hydrophilic parts. The gelation behavior has been examined in 30 liquids of diverse structure and polarity, and the properties of their gels and the gelation mechanisms have been investigated using a variety of techniques. Possible reasons are discussed regarding why the Pn are better Gelators than the corresponding naphthyl analogues (Nn) which had been investigated previously. P2 and P3 are ambidextrous Gelators (i.e., they gelate both water and some organic liquids), and P4–P8 gelate some organic liquids which are protic and aprotic, but not water. In at least one...
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Primary alkyl amines as latent Gelators and their organogel adducts with neutral triatomic molecules
Langmuir, 2003Co-Authors: Mathew George And, Richard G WeissAbstract:A series of organoGelator salts has been prepared from n-alkylamines by the rapid in situ and isothermal (at room temperature) uptake of a neutral triatomic molecule, CO2, NO2, SO2, or CS2. The organogels have been examined by differential scanning calorimetry, optical microscopy, and X-ray diffraction methods. The efficiency of each Gelator has been assessed on the bases of the diversity of liquids it gelled, the minimum amount of it required for gelation, and the temporal and thermal stabilities of its gels. Thus, alkylammonium alkylcarbamates, amine−CO2 adducts, are the most effective Gelators and the amine−NO2 adducts are the least efficient. Salts from longer n-alkylamines are better Gelators than those from shorter homologues. Some of the salts are reconverted to their amine and triatomic constituents by heating, while others are transformed into new compounds. In the case of the CS2 adducts, H2S is expelled and the new species formed, N,N‘-dialkylthioureas, are also Gelators.
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The influence of the cationic center, anion, and chain length of tetra-n-alkylammonium and -phosphonium salt Gelators on the properties of their thermally reversible organogels
Chemistry of Materials, 2000Co-Authors: David J. Abdallah, Richard G WeissAbstract:The phase properties of 14 tetra-n-alkylammonium and -phosphonium salts with chloride, bromide, iodide, and perchlorate as anions and alkyl chain lengths from heptyl to octadecyl have been examined as neat solids and as Gelators in thermally reversible organogels. These Gelator structures are among the simplest investigated to date. The salts with the longest alkyl chains and a nitrogen cationic center produce the most stable gels based upon temperatures at which gels form on cooling from sols, periods of stability at room temperature, and minimum concentrations of Gelator necessary to effect gelation of a liquid at room temperature. Specific gel properties are dependent upon the rate at which their (precursor) sol phases are cooled. Generally, gels with ammonium salts persist for longer periods, require less Gelator, and exhibit higher gelation temperatures than those with the corresponding phosphonium salts. Typically,