Murphy Thomas, Varela Luis M, Webber Grant B, Warr Gregory G, Atkin Rob
Priority Research Centre for Advanced Particle Processing and Transport, The University of Newcastle , NSW 2308, Callaghan, Australia.
J Phys Chem B. 2014 Oct 16;118(41):12017-24. doi: 10.1021/jp507408r. Epub 2014 Oct 7.
The thermal conductivities of nine protic ionic liquids (ILs) have been investigated between 293 and 340 K. Within this range, the thermal conductivities are between 0.18 and 0.30 W · m(-1) · K(-1). These values are higher than those typically associated with oils and aprotic ILs, but lower than those of strongly hydrogen bonding solvents like water. Weak linear decreases in thermal conductivity with temperature are noted, with the exception of ethanolammonium nitrate (EtAN) where the thermal conductivity increases with temperature. The dependence of thermal conductivity on IL type is analyzed with use of the Bahe-Varela pseudolattice theory. This theory treats the bulk IL as an array of ordered domains with intervening domains of uncorrelated structure which enable and provide barriers to heat propagation (respectively) via allowed vibrational modes. For the protic ILs investigated, thermal conductivity depends strongly on the IL cation alkyl chain length. This is because the cation alkyl chain controls the dimensions of the IL bulk nanostructure, which consists of charged (ordered domains) and uncharged regions (disordered domains). As the cation alkyl chain controls the dimensions of the disordered domains, it thus limits the thermal conductivity. To test the generality of this interpretation, the thermal conductivities of propylammonium nitrate (PAN) and PAN-octanol mixtures were examined; water selectively swells the PAN charged domain, while octanol swells the uncharged regions. Up to a certain concentration, adding water increases thermal conduction and octanol decreases it, as expected. However, at high solute concentrations the IL nanostructure is broken. When additional solvent is added above this concentration the rate of change in thermal conductivity is greatly reduced. This is because, in the absence of nanostructure, the added solvent only serves to dilute the salt solution.
已对9种质子离子液体（ILs）在293至340 K之间的热导率进行了研究。在此温度范围内，热导率在0.18至0.30 W·m⁻¹·K⁻¹之间。这些值高于通常与油类和非质子离子液体相关的值，但低于像水这样具有强氢键作用的溶剂的值。热导率随温度呈微弱线性下降，硝酸乙醇铵（EtAN）除外，其热导率随温度升高。利用Bahe-Varela伪晶格理论分析了热导率对离子液体类型的依赖性。该理论将本体离子液体视为由有序域阵列组成，其间存在不相关结构的域，这些域分别通过允许的振动模式促进和阻碍热传播。对于所研究的质子离子液体，热导率强烈依赖于离子液体阳离子的烷基链长度。这是因为阳离子烷基链控制着离子液体本体纳米结构的尺寸，该结构由带电（有序域）和不带电区域（无序域）组成。由于阳离子烷基链控制着无序域的尺寸，因此它限制了热导率。为了检验这种解释的普遍性，研究了硝酸丙铵（PAN）和PAN-辛醇混合物的热导率；水选择性地使PAN带电域膨胀，而辛醇使不带电区域膨胀。正如预期的那样，在一定浓度范围内，添加水会增加热传导，而添加辛醇会降低热传导。然而，在高溶质浓度下，离子液体的纳米结构会被破坏。当在此浓度以上添加额外溶剂时，热导率的变化速率会大大降低。这是因为，在没有纳米结构的情况下，添加的溶剂仅起到稀释盐溶液的作用。
