Effects of Cooling Rates on Self-Assembling Structures of 12-Hydroxystearic Acid in an Ionic Liquid

Hiroyuki Takeno,Mai Kozuka

doi:10.1155/2017/4762379

Hiroyuki Takeno, Mai Kozuka

Open Access

https://doi.org/10.1155/2017/4762379

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Abstract

We investigated effects of cooling rates on self-assembling structures and mechanical and electrochemical properties of 12-hydroxystearic acid (12-HSA) in an ionic liquid (IL), 1-allyl-3-butylimidazolium bis(trifluoromethanesulfonyl) imide ([ABIm][TFSI]). The mixture of 12-HSA with [ABIm][TFSI] had an upper critical solution temperature (UCST) above the sol-gel transition temperature, and the microstructure of the ionogel was significantly affected by cooling rates, where it was prepared. The twisted self-assembling structure was formed during a slow cooling process at a rate of 0.4°C/min, whereas spherical domains caused by the liquid-liquid phase separation and radiate fibrous structure were observed for the quenched gel. The real-time small-angle X-ray scattering (SAXS) measurements for the ionogel during a slow cooling process at a rate of 0.4°C/min presented three different (001) peaks arising from long spacings of 46.5, 42.4, and 39.7 Å, which were also observed for SAXS curves of a neat 12-HSA. These results suggest that three polymorphic forms of 12-HSA are formed in the IL. The polymorphic form significantly affected the mechanical properties of the ionogel, whereas it did not affect the ionic conductivity. The ionic conductivity of the ionogel was close to that of a neat [ABIm][TFSI] irrespective of the polymorphic forms of 12-HSA.

Highlights

In the past few decades, low-molecular weight organogelators (LMOGs) have attracted many researchers for potential applications in various fields such as food chemistry, electrochemistry, cosmetics, and petroleum chemistry
We reported that different polymorphs appeared at different temperatures [14], for example, three (001) peaks (q1,(001), q2,(001), and q3,(001)) corresponding to long spacings of 46.5, 42.4, and 39.7 A, respectively, were observed for 12-Hydroxystearic acid (12-HSA) gels in phenylmethyl silicone and for a neat HSA prepared by a temperaturejump into different temperatures, and each crystal form was termed form I, form II, and form III [14]
Spherical domains which were caused by the liquid-liquid phase separation and radiate fibrous structure were observed for the quenched gels, whereas fractal-like twisted structure was observed for the gels at a cooling rate of 0.4∘C/min

Summary

Introduction

In the past few decades, low-molecular weight organogelators (LMOGs) have attracted many researchers for potential applications in various fields such as food chemistry, electrochemistry, cosmetics, and petroleum chemistry. It has been reported that different polymorphs were formed for 12-HSA gels in different solvents [13]. We reported that different polymorphs appeared at different temperatures [14], for example, three (001) peaks (q1,(001), q2,(001), and q3,(001)) corresponding to long spacings of 46.5, 42.4, and 39.7 A , respectively, were observed for 12-HSA gels in phenylmethyl silicone and for a neat HSA prepared by a temperaturejump into different temperatures, and each crystal form was termed form I, form II, and form III [14]. A different behavior was observed for 12-HSA gel in a different solvent; for example, our small-angle neutron scattering (SANS) and synchrotron SAXS studies revealed that the selfassembled structure of 12-HSA in toluene was not affected by concentrations of the gelator and temperatures, [15,16,17]. In order to clarify the above point, structures and mechanical and electrochemical properties of 12-HSA gels prepared at different cooling processes in an IL will be investigated in detail

Experimental

Results and Discussion

Conclusion

Conflicts of Interest