Baddi Sravan, Madugula Sita Sirisha, Sarma D Srinivasa, Soujanya Yarasi, Palanisamy Aruna
Geochemistry Division, CSIR-National Geophysical Research Institute , Hyderabad-500007, Telangana, India.
Langmuir. 2016 Jan 26;32(3):889-99. doi: 10.1021/acs.langmuir.5b03987. Epub 2016 Jan 14.
The current study reports the one-step synthesis and gelation properties of cyclohexane-based bis(acyl-semicarbazide) gelators with an additional -NH group incorporated into urea moieties and carrying hydrophobic chains of varying length (C8-C18). The gels exhibited thermoreversibility and could be tuned in the presence of anions at different concentrations in addition their the ultrasound-responsive nature, thus making them multi-stimuli-responsive. The combined experimental and computational study on these gels reveals that the balance between two noncovalent interactions, viz., hydrogen bonding between the amide groups in acyl-semicarbazide moieties and van der Waals forces between long hydrocarbon tails, is found to be the determining factor in the process of organogelation. A systematic increase in alkyl chain length leads to equilibrium between these two types of noncovalent forces that is manifested in the spectral and thermal properties of the gels. The H-bonding interactions dominated up to a certain chain length, and further increases in the alkyl chain length led to increased van der Waals interactions as observed by IR, XRD, and thermal studies. Computational calculations were carried out on dimer structures of C8-C18 to understand the variation in noncovalent forces responsible for aggregate formation in the gel state as a function of the alkyl chain length. The results indicate that both intermolecular and intramolecular hydrogen bonding stabilize the aggregate structures. Supramolecular aggregation in the gel state led to the viscoelastic nature of the gels, and the addition of anions led to the disruption of self-assembly, which was studied by rheology.
本研究报道了基于环己烷的双（酰基 - 氨基脲）凝胶剂的一步合成及其凝胶化性质，该凝胶剂在脲部分引入了额外的 -NH 基团，并带有不同长度（C8 - C18）的疏水链。这些凝胶表现出热可逆性，除了具有超声响应特性外，在不同浓度阴离子存在下其性质还可调节，因此使其具有多刺激响应性。对这些凝胶进行的实验和计算研究相结合表明，在酰基 - 氨基脲部分的酰胺基团之间的氢键和长烃链之间的范德华力这两种非共价相互作用之间的平衡，被发现是有机凝胶化过程中的决定性因素。烷基链长度的系统性增加导致这两种非共价力之间达到平衡，这在凝胶的光谱和热性质中得以体现。在一定链长之前，氢键相互作用占主导，而如红外光谱、X 射线衍射和热研究所示，随着烷基链长度的进一步增加，范德华相互作用增强。对 C8 - C18 的二聚体结构进行了计算，以了解在凝胶状态下负责聚集体形成的非共价力随烷基链长度的变化。结果表明，分子间和分子内氢键都稳定了聚集体结构。凝胶状态下的超分子聚集导致了凝胶的粘弹性，流变学研究表明，阴离子的加入导致了自组装的破坏。
