Fakultät Physik, Technische Universität Dortmund, D-44221 Dortmund, Germany.
J Chem Phys. 2019 Mar 14;150(10):104501. doi: 10.1063/1.5086529.
Monohydroxy alcohols (MAs) with methyl and hydroxyl side groups attached to the same carbon atom in the alkyl backbone can display very weak structural and supramolecular dielectric relaxation processes when probed in the regime of small electrical fields. This can render their separation and assignment difficult in the pure liquids. When mixing with bromoalkanes, a faint Debye-like process can be resolved dielectrically for 4-methyl-4-heptanol. To achieve a separation of structural and supramolecular processes in pure 4-methyl-4-heptanol and 3-methyl-3-heptanol, mechanical experiments are carried out in the linear-response regime as well as using medium-angle oscillatory shear amplitudes. It is demonstrated that first-order and third-order nonlinear mechanical effects allow for a clear identification of supramolecular viscoelastic modes even for alcohols in which they leave only a weak signature in the linear-response shear modulus. Additionally, the nonlinear rheological behavior of 2-ethyl-1-hexanol is studied, revealing that its linearly detected terminal mode does not coincide with that revealed beyond the linear-response regime. This finding contrasts with those for the other MAs studied in this work.
单羟基醇（MAs）的甲基和羟基侧基连接在烷基主链的同一个碳原子上，当在小电场范围内探测时，它们的结构和超分子介电弛豫过程非常微弱。这使得它们在纯液体中的分离和分配变得困难。当与溴代烷烃混合时，可以在介电方面分辨出微弱的类德拜过程，用于 4-甲基-4-庚醇。为了在纯 4-甲基-4-庚醇和 3-甲基-3-庚醇中分离结构和超分子过程，在线性响应区以及使用中角振荡剪切幅度进行了机械实验。结果表明，即使对于在线性响应剪切模量中仅留下微弱特征的醇，一阶和三阶非线性机械效应也允许对超分子粘弹性模式进行清晰识别。此外，还研究了 2-乙基-1-己醇的非线性流变行为，表明其在线性检测的末端模式与超出线性响应区揭示的模式不一致。这一发现与这项工作中研究的其他 MAs 的发现形成对比。
