Micropillar adhesives have gained increasing attention because they generate high pull-off forces. The generation of high friction, however, has been proven difficult with such geometries, because micropillars tend to buckle under shear loading. Here, we fabricated orthogonal arrays of composite poly-dimethoxysiloxane (PDMS) micropillars with a stiff core and spin-coated them with PDMS solutions to form a soft coating, as well as bridges between neighboring micropillars. We used 10 wt% and 5 wt% PDMS solution to obtain thick or thin bridges, respectively. The micropillars had an average height of about 60 µm and a diameter of 40 µm. Adhesion and friction measurements were performed with three types of adhesives (i.e., without bridges and with either thin or thick bridges) as well as unpatterned samples as reference, on stiff glass substrates and on deformable PDMS substrates. We found that, on PDMS substrates, bridging resulted in increased friction, compared to non-bridged micropillars. Friction increased with increasing bridge thickness, presumably due to buckling prevention. The adhesives were also subjected to 99 repeating friction cycles to test the effect of micropillar bridging on the durability of the adhesives. The results showed that adhesives with thick micropillar bridges preserved their friction performance over the cycles, whereas adhesives with no bridges or thin bridges exhibited a gradual decay of friction.

中文翻译：

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横向加固件对微柱胶粘着力和摩擦力的影响

微柱粘合剂因其产生高拉脱力而受到越来越多的关注。然而，已经证明这种几何形状很难产生高摩擦，因为微柱在剪切载荷下往往会弯曲。在这里，我们制造了具有刚性核心的复合聚二甲氧基硅氧烷 (PDMS) 微柱的正交阵列，并用 PDMS 溶液旋涂它们以形成软涂层，以及相邻微柱之间的桥梁。我们分别使用 10 wt% 和 5 wt% PDMS 溶液来获得厚桥或薄桥。微柱的平均高度约为 60 µm，直径为 40 µm。使用三种类型的粘合剂（即，无桥接和薄桥接或厚桥接）以及未图案化样品作为参考进行粘附力和摩擦测量，在坚硬的玻璃基板和可变形的 PDMS 基板上。我们发现，在 PDMS 基材上，与非桥接微柱相比，桥接导致摩擦增加。摩擦力随着桥梁厚度的增加而增加，大概是由于防止屈曲。粘合剂还经受了 99 次重复摩擦循环，以测试微柱桥接对粘合剂耐久性的影响。结果表明，具有厚微柱桥的粘合剂在循环过程中保持了它们的摩擦性能，而没有桥或细桥的粘合剂则表现出摩擦力的逐渐衰减。粘合剂还经受了 99 次重复摩擦循环，以测试微柱桥接对粘合剂耐久性的影响。结果表明，具有厚微柱桥的粘合剂在循环过程中保持了它们的摩擦性能，而没有桥或细桥的粘合剂则表现出摩擦力的逐渐衰减。粘合剂还经受了 99 次重复摩擦循环，以测试微柱桥接对粘合剂耐久性的影响。结果表明，具有厚微柱桥的粘合剂在循环过程中保持了它们的摩擦性能，而没有桥或细桥的粘合剂则表现出摩擦力的逐渐衰减。