Variable temperature NMR of organogels: how to map a phase diagram with a single sample

Significance 

Organogelators are described as small molecule compounds that are able to gel solvents at low concentrations by forming fibrillar self-assemblies. Such an attribute has intensified their research with much attention being paid to the design and synthesis of a novel breed that would have functional properties. Nonetheless, there are still no well laid down rules regulating their design. As such, it has been hypothesized that phase diagrams of existing gelators should enable quantitative comparisons among them. Even though, mapping of these comparisons is limited within a narrow range of concentration with the sensitivity of the technique in use, i.e. differential scanning calorimetry and rheology, being the limiting factor and often makes the process tedious. Nuclear magnetic resonance, a highly promising technique, has seldom been implemented to map out phase diagrams. Worse off, no published work exists that highlights the relation between the nuclear magnetic resonance intensities measured at different temperatures in an organogel and its phase diagram.

Recently, French scientists at University of Strasbourg, Dr Elliot Christ, Dr. Dominique Collin, Engineer Jean-Philippe Lamps, Engineer Bruno Vincent and Dr. Philippe Mésini demonstrated that liquid nuclear magnetic resonance can be used to simplify and hasten the acquisition of phase diagrams. Specifically, they intended to show that their novel technique would generally simplify the acquisition of phase diagrams of organogels altogether. Their work is currently published in the research journal, Physical Chemistry Chemical Physics.

In brief, the research method employed commenced with the measurement of nuclear magnetic resonance intensities of three different organogels as a function of temperature. Next, differential scanning calorimetry thermograms and rheology images were recorded and captured, respectively. Lastly, the researchers compared the intensities below the melting temperature with the phasediagrams mapped by other techniques.

The authors observed that the measured intensities increased with increase in temperature until melting. Moreover, they noted that with the correct normalization, the intensities yielded the solubility as a function of temperature, which was seen to be adequate for mapping the phase diagrams. Furthermore, they proved their technique experimentally by superimposing the resulting phase diagrams with those mapped out by other techniques.

In summary, the study by University of Strasbourg scientists proved that visible signal corresponds to the soluble fraction of the gelator. Their work made it possible to draw the gel-to-sol boundary with a single sample and avoid the measurements of Tm on many samples, as required by other techniques.Their work further showed that their technique only depended on the signal/noise ratio of the nuclear magnetic resonance peaks, which in turn depended upon the accumulation time at each temperature. Altogether, they showed that the nuclear magnetic resonance intensities of a single sample related simply to the sol-gel boundary of its phase diagrams thereby making the acquisition of phase diagram of organogels quite easy.

Variable temperature NMR of organogels: how to map a phase diagram with a single sample - Advances in Engineering

About the author

Dr Elliot Christ studied chemistry at the University of Strasbourg. He obtained a M. Sc. degree in supramolecular chemistry and a second one in computational chemistry. In 2014, he joined the group of Dr P. J. Mésini at the Institute Charles Sadron in Strasbourg as a Ph. D. student. His doctorate research focused on the physical behavior of organogelators, with two publications about their phase diagrams. He also developed new gelators and studied their mechanism of self-assembly.

He is currently studying new polymers at the university of Freiburg (Germany) as a post-doc in the BASF JONAS program.

About the author

Dominique Collin obtained his Ph.D. degree in 1987 from the University Louis Pasteur (Strasbourg, France). He had studied the hydrodynamics of smectic liquid crystals under the supervision of Dr. P. Martinoty. He spent a post-doctoral year at I.B.M. (Bordeaux, France) to analyze the failure of RAM with liquid crystals. In 1988, he was appointed CNRS researcher in the “Laboratoire de Dynamique des Fluides Complexes” of Dr. J. S. Candau (Strasbourg, France). He worked on the dynamics of liquid-crystals phase transitions with ultrasound.

In collaboration with Drs. J. L. Gallani and P. Martinoty, he developed a device of rheology working with piezoelectric elements, called piezorheometer, to study dynamics of liquid crystals, polymers and liquid crystalline systems. In 2003, he obtained his habilitation and in 2008, he joined the Institut Charles Sadron in Strasbourg. His research interests include physical properties of polymers, gels and self-assembled systems.

About the author

J.P. Lamps is an engineer at the Institut Charles Sadron in Strasbourg. He studied chemistry at the University of Strasbourg (France). He entered the Centre National de la Recherche Scientifique (CNRS) in 1982.

He is an expert in anionic polymerization. In 2004 he started research on catalytic polymerization of substituted polythiophenes and has developed devices to follow in situ the formation of metallated monomers and their polymerization. His research interests also include organogelators.

About the author

Philippe Mésini is a senior scientist, at the Institute Charles Sadron (Strasbourg, France). He graduated in Chemistry at the Ecole Normale Supérieure (Paris, France) and received his Ph. D. in 1992 from the University of Strasbourg. He spent a postdoctoral period at the Scripps Research Institute in San-Diego under the supervision of Prof D. L . Boger. In 1995 he joined the Institute Charles Sadron (Strasbourg, France) as a CNRS scientist. In 1999 he was a visiting researcher at the Max Planck Institute for Polymer Research (Mainz, Germany).

His current interests are the synthesis and structural studies of organogelators and self-assembled pi-conjugated compounds.

Reference

Elliot Christ,Dominique Collin,Jean-Philippe Lamps Philippe J. Mésini. Variable temperature NMR of organogelators the intensities of a single sample describe the full phase diagram. Physical Chemistry Chemical Physics, 2018, volume 20, page 9644.

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