While the dispersion of nanomaterials is known to be effective in enhancing the thermal conductivity and specific heat capacity of fluids, the mechanisms behind this enhancement remain to be elucidated. Herein, we report on highly stable, surfactant-free graphene nanofluids, based on N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF), with enhanced thermal properties. An increase of up to 48% in thermal conductivity and 18% in specific heat capacity was measured. The blue shift of several Raman bands with increasing graphene concentration in DMF indicates that there is a modification in the vibrational energy of the bonds associated with these modes, affecting all the molecules in the liquid. This result indicates that graphene has the ability to affect solvent molecules at long-range, in terms of vibrational energy. Density functional theory and molecular dynamics simulations were used to gather data on the interaction between graphene and solvent, and to investigate a possible order induced by graphene on the solvent. The simulations showed a parallel orientation of DMF towards graphene, favoring π–π stacking. Furthermore, a local order of DMF molecules around graphene was observed suggesting that both this special kind of interaction and the induced local order may contribute to the enhancement of the fluid's thermal properties.

中文翻译：

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增强石墨烯纳米流体热性能的机制†

虽然已知纳米材料的分散体在增强流体的导热率和比热容方面是有效的，但这种增长背后的机理仍有待阐明。本文中，我们报道了基于N，N-二甲基乙酰胺（DMAc）和N，N的高度稳定，不含表面活性剂的石墨烯纳米流体-二甲基甲酰胺（DMF），具有增强的热性能。测得导热率增加了48％，比热容增加了18％。随着DMF中石墨烯浓度的增加，几个拉曼带的蓝移表明与这些模式相关的键的振动能发生了变化，从而影响了液体中的所有分子。该结果表明，就振动能量而言，石墨烯具有在远距离影响溶剂分子的能力。使用密度泛函理论和分子动力学模拟来收集有关石墨烯与溶剂之间相互作用的数据，并研究石墨烯在溶剂上引起的可能阶数。模拟显示DMF与石墨烯平行取向，有利于π-π堆积。此外，