Researchers looking for sustainable materials with optimal mechanical properties may draw inspiration from a baseball tradition. For nearly 100 y, a mysterious mud harvested from an undisclosed river site in New Jersey (USA) has been the agent of choice in the USA’s Major League Baseball for “de-glossing” new baseballs. It is unclear, however, what makes this “Rubbing Mud” work. Here, we perform a multiscale investigation of the rheology and tribology of this mud material under baseball-relevant conditions and identify three mechanisms by which the mud alters the surface properties of the baseball. First, the mud creates a more uniform baseball surface by filling in pores in the leather; this is possible because of its relatively high cohesion (clays and organics) making the material remarkably shear thinning. Second, the residue of cohesive particles coating the baseball effectively doubles contact adhesion. Third, a sparse population of angular sand grains are bonded to the baseball by clay-sized particles, leaving a studded surface that enhances friction. The proportions of cohesive, frictional, and viscous elements in Rubbing Mud conspire to create a soft material with an unusual mix of properties, that could find other applications in the development of sustainable geomaterials. Our improved understanding of the flow and friction of natural muds may also find use in modeling natural hazards such as mudslides and for locomotion in muddy environments.

中文翻译：

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棒球摩擦泥的软物质力学


寻找具有最佳机械性能的可持续材料的研究人员可能会从棒球传统中汲取灵感。近 100 年来，从新泽西州（美国）一个未公开的河流地点收集的神秘泥浆一直是美国职业棒球大联盟“去光泽”新棒球的首选代理。然而，目前尚不清楚是什么让这个 “Rubbing Mud” 发挥作用。在这里，我们对这种泥浆材料在棒球相关条件下的流变学和摩擦学进行了多尺度研究，并确定了泥浆改变棒球表面特性的三种机制。首先，泥浆通过填充皮革中的孔隙来创造更均匀的棒球表面;这是可能的，因为它相对较高的内聚力（粘土和有机物）使材料显著的剪切稀化。其次，覆盖棒球的粘性颗粒残留物有效地使接触附着力加倍。第三，稀疏的棱角分明的沙粒通过粘土大小的颗粒粘合到棒球上，留下一个增强摩擦力的镶嵌表面。Rubbing Mud 中粘性、摩擦和粘性元素的比例共同创造了一种具有不寻常特性组合的柔软材料，可以在可持续土工材料的开发中找到其他应用。我们对天然泥浆流动和摩擦的加深理解也可能用于模拟泥石流等自然灾害和在泥泞环境中的运动。