Yang Dian, Cohen Adam E
School of Engineering and Applied Sciences and ‡Departments of Chemistry and Chemical Biology and of Physics, Harvard University , Cambridge, Massachusetts 02138, United States.
Langmuir. 2014 Aug 26;30(33):9972-6. doi: 10.1021/la500699z. Epub 2014 Aug 14.
We show that the solid-solid friction between bulk chiral molecular solids can depend on the relative chirality of the two materials. In menthol and 1-phenyl-1-butanol, heterochiral friction is smaller than homochiral friction, while in ibuprofen, heterochiral friction is larger. Chiral asymmetries in the coefficient of sliding friction vary with temperature and can be as large as 30%. In the three compounds tested, the sign of the difference between heterochiral and homochiral friction correlated with the sign of the difference in melting point between racemate (compound or conglomerate) and pure enantiomer. Menthol and ibuprofen each form a stable racemic compound, while 1-phenyl-1-butanol forms a racemic conglomerate. Thus, a difference between heterochiral and homochiral friction does not require the formation of a stable interfacial racemic compound. Measurements of chirality-dependent friction provide a unique means to distinguish the role of short-range intermolecular forces from all other sources of dissipation in the friction of bulk molecular solids.
我们表明，块状手性分子固体之间的固-固摩擦可能取决于两种材料的相对手性。在薄荷醇和1-苯基-1-丁醇中，异手性摩擦小于同手性摩擦，而在布洛芬中，异手性摩擦更大。滑动摩擦系数中的手性不对称随温度变化，可达30%。在所测试的三种化合物中，异手性和同手性摩擦之间差异的符号与外消旋体（化合物或聚集体）和纯对映体之间熔点差异的符号相关。薄荷醇和布洛芬各自形成稳定的外消旋化合物，而1-苯基-1-丁醇形成外消旋聚集体。因此，异手性和同手性摩擦之间的差异并不需要形成稳定的界面外消旋化合物。手性相关摩擦的测量提供了一种独特的方法，以区分短程分子间力在块状分子固体摩擦中与所有其他耗散源所起的作用。
