Highly Sensitive Wearable Chromic Force Sensor Utilizing In-Plane Anisotropy in Polydiacetylene Mechanochromism

Force sensitivity is a crucial parameter in mechanochromic materials, determining their application range and practical success. In this study, we reveal an unexplored degree of freedom─in-plane anisotropy─for significantly enhancing the force sensitivity of polydiacetylene. Utilizing our newly developed dual nanofriction force/fluorescence microscopy setup, we discovered that force sensitivity reaches its peak when external forces are applied perpendicular to the polymer backbones in-plane. This phenomenon is explained by a "domino effect", where point loads propagate along the backbones and affect the polymer structure even hundreds of nanometers from the contact point. Leveraging this finding, we developed a highly sensitive, stretchable force sensor and demonstrated that aligning polydiacetylene crystals perpendicular to the force direction increased the sensor's sensitivity by up to 14-fold.