Quantitative and anisotropic mechanochromism of polydiacetylene over nanoscale distances remains unaddressed even after 50 years of extensive research. This is because its anisotropic structure on substrates necessitates the application of both vertical and lateral forces (shear forces) to characterize it, whereas atomic force microscopy, which is the usual technique used to investigate nanoscale forces, is only capable of quantifying vertical forces. In this study, we address this lacuna by utilizing quantitative friction force microscopy that measures lateral forces. Our data confirm that polydiacetylene reacts only to lateral forces, F // , and disprove the previously claimed hypothesis that the edges of the polymer crystals exhibit higher force sensitivity than the rest of the crystal. In addition, we report a correlation between mechanochromism and thermochromism, which can be attributed to the fact that both work and heat are different means of providing the same transition energy.

Polydiacetylene (PDA) is a popular mechanochromic material often used in biosensing. The effect of its headgroup–headgroup interactions on thermochromism such as pH or salt concentration dependency has been extensively studied before; however, their effect on mechanochromism at the nanoscale is left unstudied. In this work, nanofriction force microscopy and fluorescence microscopy were combined to study the effect of pH and ionic strength on the polydiacetylene (PDA) force sensitivity at the nanoscale. We found that the increase in pH from 5.7 to 8.2 caused an 8-fold enhancement in force sensitivity. The elevation of NaCl concentration from 10 to 200 mM also made the PDA 5 times more force-sensitive. These results suggest that the PDA force sensitivity at the nanoscale can be conveniently enhanced by “pre-stimulation” with pH or ionic strength.

The nano-friction force microscopy and the fluorescence microscopy were combined to study the effect of pH and ionic strength on the polydiacetylene (PDA) force-sensitivity at the nanoscale. We found that the increase in pH from 5.7 to 8.2 caused an enhancement in the force sensitivity by 8 folds. The elevation of NaCl concentration from 10 mM to 200 mM also made the PDA 5 times more force-sensitive. These results suggest that the PDA force sensitivity at the nanoscale can be conveniently enhanced by pre-stimulation with pH or ionic strength.

Polydiacetylene (PDA) is a popular mechanochromic material often used in biosensing. The effect of its headgroup-headgroup interactions on the thermochromism such as pH or salt concentration dependency has been extensively studied before, yet, their effect on mechanochromism at nanoscale is left unstudied. In this work, the nano-friction force microscopy and the fluorescence microscopy were combined to study the effect of pH and ionic strength on the polydiacetylene (PDA) force-sensitivity at the nanoscale. We found that the increase in pH from 5.7 to 8.2 caused an enhancement in the force sensitivity by 8 folds. The elevation of NaCl concentration from 10 mM to 200 mM also made the PDA 5 times more force-sensitive. These results suggest that the PDA force sensitivity at the nanoscale can be conveniently enhanced by “pre-stimulation” with pH or ionic strength.