The mechanics of adherent sheets is central to applications ranging from patching a band aid, coating technology, to the breakthrough discovery of peeling graphene flakes using sticky tape. These processes are often hindered by the formation of blisters and loops, which are notoriously difficult to remove. Here we describe and explain a remarkable phenomenon that arises when one attempts to remove a loop in a self-adherent sheet that is formed by, e.g., folding two adhesive sides of a tape together. One would expect the loop to simply unloop when pulling on its free ends. Surprisingly, however, the loop does not immediately open up but shrinks in size, held together by a tenuous contact region that propagates along the tape. This adhesive contact region only ruptures once the loop is reduced to a critical size. We experimentally show that the loop-shrinkage results from an interaction between the peeling front and the loop, across the contact zone. This new type of interaction falls outside the realm of the classical elastica theory and is responsible for a highly nonlinear increase in the peeling force. Our results reveal and quantify the increased force required to remove loops in self-adherent media, which is of importance for blister removal and exfoliation of graphene sheets.

粘合片的力学是应用的核心，从修补创可贴、涂层技术到使用胶带剥离石墨烯薄片的突破性发现。这些过程通常会因形成水泡和毛圈而受到阻碍，众所周知，水泡和毛圈很难去除。在这里，我们描述和解释产生的应显着的现象，当一个试图消除在由形成有自粘接片，环例如, 将胶带的两个粘性面折叠在一起。人们会期望在拉动其自由端时循环会简单地解开。然而，令人惊讶的是，环并没有立即打开，而是缩小了尺寸，由沿胶带传播的脆弱接触区域保持在一起。该粘合剂接触区域仅在环减小到临界尺寸时破裂。我们通过实验表明，环收缩是由剥离前沿和环之间的相互作用引起的，跨越接触区。这种新型相互作用不属于经典弹性理论的范畴，它是剥离力高度非线性增加的原因。我们的结果揭示并量化了去除自粘介质中的环所需的增加的力，这对于石墨烯片的水泡去除和剥落很重要。