Department of Materials Science and Engineering, University of Delaware, Newark, DE, USA.
Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, USA.
Soft Matter. 2022 May 25;18(20):3928-3940. doi: 10.1039/d2sm00264g.
The friction generated between a finger and an object forms the mechanical stimuli behind fine touch perception. To control friction, and therefore tactile perception, current haptic devices typically rely on physical features like bumps or pins, but chemical and microscale morphology of surfaces could be harnessed to recreate a wider variety of tactile sensations. Here, we sought to develop a new way to create tactile sensations by relying on differences in microstructure as quantified by the degree of crystallinity in polymer films. To isolate crystallinity, we used polystyrene films with the same chemical formula and number averaged molecular weights, but which differed in tacticity and annealing conditions. These films were also sufficiently thin as to be rigid which minimized effects from bulk stiffness and had variations in roughness lower than detectable by humans. To connect crystallinity to human perception, we performed mechanical testing with a mock finger to form predictions about the degree of crystallinity necessary to result in successful discrimination by human subjects. Psychophysical testing verified that humans could discriminate surfaces which differed only in the degree of crystallinity. Although related, human performance was not strongly correlated with a straightforward difference in the degree of crystallinity. Rather, human performance was better explained by quantifying transitions in steady to unsteady sliding and the generation of slow frictional waves ( = 79.6%). Tuning fine touch with polymer crystallinity may lead to better engineering of existing haptic interfaces or lead to new classes of actuators based on changes in microstructure.
手指与物体之间产生的摩擦形成了精细触觉感知背后的机械刺激。为了控制摩擦，从而控制触觉，当前的触觉设备通常依赖于凸块或针脚等物理特征，但表面的化学和微观形貌也可以被利用来重新创造更广泛的触觉感觉。在这里，我们试图通过依赖聚合物薄膜的结晶度来量化的微观结构差异来开发一种创造触觉感觉的新方法。为了分离结晶度，我们使用了具有相同化学式和数均分子量但在立构规整度和退火条件上有所不同的聚苯乙烯薄膜。这些薄膜足够薄，可以保持刚性，从而最大限度地减少了来自体弹性的影响，并且粗糙度变化低于人类可检测的水平。为了将结晶度与人类感知联系起来，我们使用模拟手指进行了机械测试，以便对导致人类受试者成功区分所需的结晶度程度进行预测。心理物理测试验证了人类可以区分仅在结晶度程度上有所不同的表面。尽管相关，但人类的表现与结晶度的直接差异并没有很强的相关性。相反，通过量化稳态到非稳态滑动的转变以及产生慢摩擦波（=79.6%），可以更好地解释人类的表现。通过聚合物结晶度来调整精细触觉可能会导致更好地设计现有的触觉接口，或者导致基于微观结构变化的新型致动器。
