Variable temperature NMR of organogelators: the intensities of a single sample describe the full phase diagram

Abstract

Organogelators constitute a numerous class of compounds, able to form gels in organic solvents. Their phase diagrams are useful to understand their mechanisms of formation and their stability, but their mapping is often a tedious task. We show that liquid NMR can simplify and quicken the acquisition of phase diagrams. In liquid NMR spectra of organogels, the visible signals of the gelator represent only its soluble fraction. The intensities increase with temperature, until the gel melts. Suitable normalization of these intensities yields the solubility as a function of temperature, which is sufficient to map the phase diagram. We verified it experimentally with three organogelators, chosen because independent authors have previously mapped out their phase diagram by other techniques including DSC and rheology. We show that the curves obtained by NMR superimpose with these diagrams. A variable temperature NMR experiment with a single sample can yield the phase diagram with sensitivity of the order of 0.01 wt%.

Photocontrolled Hierarchical Self‐Assembly of Anisotropic Micropatterns of Nanofibers onto Isotropic Surfaces

“…At 0.63 × 10 −3 ± 0.02 × 10 −3 m , the regime drastically changes and permanent emissive objects are detected on the surface. This means supersaturation is reached, at the critical concentration ( c crit ) of 0.63 × 10 −3 m , which is higher than the saturation concentration ( c sat ) …”

Gel-to-gel non-variant transition of an organogel caused by polymorphism from nanotubes to crystallites

“…The increase in transmitted intensity when temperature varies indicates the temperature of the gel-sol transition. This technique has been implemented by us 14,27 and Devergnes 29,30 to map phase diagrams. For sample at c = 0.5 wt.…”

Investigation of an Organogel by Micro-Differential Scanning Calorimetry: Quantitative Relationship between the Shapes of the Thermograms and the Phase Diagram

“…We have compared the values with those obtained by other techniques. The binary c - T phase diagram of HSA/nitrobenzene provides a good comparison because it has been studied by two groups, each with different techniques and five sets of data with a good agreement [ 12 , 19 ]. There a bias between the measured values temperature and the other measurements as shown in Figure 4 b.…”

“…( b ) Superimposition of the different T values with the c - T phase diagram of HSA/nitrobenzene measured by NMR, rheology, DSC, by us and others (Christ et al: Ref. [ 19 ]; Terech: Ref. [ 12 ]).…”

“…In this study, we have studied gels of 12-hydroxystearic acid (HSA) in nitrobenzene by micro-differential scanning calorimetry (microDSC). This system was chosen because its phase diagram is well known and has been mapped by two different groups with several techniques, over almost two decades of concentrations [ 12 , 19 ]. MicroDSC operates at low heating rates, and the thermogram are less impacted by heat transfer and kinetics, and we wondered if in these conditions they reflect only the equilibrium of the gels.…”