Nwoye Emmanuel, Raghuraman Shivaranjan, Costales Maya, Batteas James, Felts Jonathan R
Advanced Nanomanufacturing Laboratory, Department of Mechanical Engineering, Texas A&M University, College Station, Texas-77843-3123, USA.
Functional Atomic Force Group, Oak Ridge National Laboratory, USA.
Phys Chem Chem Phys. 2023 Nov 1;25(42):29088-29097. doi: 10.1039/d3cp02549g.
Conventional mechanochemical synthetic tools, such as ball mills, offer no methodology to quantitatively link macroscale reaction parameters, such as shaking frequency or milling ball radius, to fundamental drivers of reactivity, namely the force vectors applied to the reactive molecules. As a result, although mechanochemistry has proven to be a valuable method to make a wide variety of products, the results are seldom reproduceable between reactors, difficult to rationally optimize, and hard to ascribe to a specific reaction pathway. Here we have developed a controlled force reactor, which is a mechanochemical ball mill reactor with integrated force measurement and control during each impact. We relate two macroscale reactor parameters-impact force and impact time-to thermodynamic and kinetic transition state theories of mechanochemistry utilizing continuum contact mechanics principles. We demonstrate force controlled particle fracture of NaCl to characterize particle size evolution during reactions, and force controlled reaction between anhydrous copper(II) chloride and (1, 10) phenanthroline. During the fracture of NaCl, we monitor the evolution of particle size as a function of impact force and find that particles quickly reach a particle size of ∼100 μm largely independent of impact force, and reach steady state 10-100× faster than reaction kinetics of typical mechanochemical reactions. We monitor the copper(II) chloride reactivity by measuring color change during reaction. Applying our transition state theory developed here to the reaction curves of copper(II) chloride and (1, 10) phenanthroline at multiple impact forces results in an activation energy barrier of 0.61 ± 0.07 eV, distinctly higher than barriers for hydrated metal salts and organic ligands and distinctly lower than the direct cleavage of the CuCl bond, indicating that the reaction may be mediated by the higher affinity of Fe in the stainless steel vessel to Cl. We further show that the results in the controlled force reactor match rudimentary estimations of impact force within a commercial ball mill reactor Retsch MM400. These results demonstrate the ability to quantitatively link macroscale reactor parameters to reaction properties, motivating further work to make mechanochemical synthesis quantitative, predictable, and fundamentally insightful.
传统的机械化学合成工具，如球磨机，无法提供将宏观反应参数（如振荡频率或研磨球半径）与反应活性的基本驱动因素（即施加于反应分子的力矢量）进行定量关联的方法。因此，尽管机械化学已被证明是制备多种产品的一种有价值的方法，但结果在不同反应器之间很少具有可重复性，难以合理优化，并且难以归因于特定的反应途径。在此，我们开发了一种可控力反应器，它是一种在每次撞击过程中集成了力测量和控制功能的机械化学球磨机反应器。我们利用连续接触力学原理，将两个宏观反应器参数——撞击力和撞击时间——与机械化学的热力学和动力学过渡态理论联系起来。我们展示了通过力控制使氯化钠颗粒破碎，以表征反应过程中颗粒尺寸的演变，以及无水氯化铜(II)与（1,10）菲咯啉之间的力控制反应。在氯化钠破碎过程中，我们监测颗粒尺寸随撞击力的变化，发现颗粒迅速达到约100μm的尺寸，这在很大程度上与撞击力无关，并且达到稳态的速度比典型机械化学反应的动力学快10 - 100倍。我们通过测量反应过程中的颜色变化来监测氯化铜(II)的反应活性。将我们在此开发的过渡态理论应用于氯化铜(II)与（1,10）菲咯啉在多个撞击力下的反应曲线，得到的活化能垒为0.61±0.07eV，明显高于水合金属盐和有机配体的能垒，且明显低于氯化铜键的直接断裂能垒，这表明该反应可能是由不锈钢容器中的铁对氯的更高亲和力介导的。我们进一步表明，可控力反应器中的结果与商业球磨机反应器Retsch MM400内的撞击力初步估计值相符。这些结果证明了将宏观反应器参数与反应性质进行定量关联的能力，推动了进一步的工作，以使机械化学合成具有定量性、可预测性，并具有深刻的理论见解。
