Mechanofluorochromic Difluoroboron β‐Diketonates Based Polymer Composites: Toward Multi‐Stimuli Responsive Mechanical Stress Probes

Abstract

Developing mechano‐responsive fluorescent polymers that exhibit distinct responses to distinct mechanical stresses requires a careful design of the fluorophore in order to tune its interactions with the polymer. A series of mechanofluorochromic (MFC) polymer composites are prepared by dispersing difluoroboron diketonates complexes with various alkyl side‐chain lengths (DFB‐alkyl) in linear low‐density polyethylene. Observation of the resulting polymer composites under a microscope reveals different aggregate sizes of the three DFB‐alkyls, thus confirming the functionalization by alkyl side chains as a powerful approach to control the aggregation process in a polymer. Besides, the three polymer composite samples are shown to be sensitive to both stretching and scratching, thereby consisting in the first reported example of MFC polymer responding to these two distinct mechanical stimuli. To establish a structure–property relationship, the strategy consisted in applying controlled tensile or friction forces while simultaneously monitoring fluorescence changes. Interestingly, the intensity of the MFC response to both stretching and scratching depends on the alkyl chain length and thus on the aggregation properties of the fluorophore. According to a time‐resolved fluorescence study, the emission is found to originate from different species following the type of applied stress (tensile or friction force).

Multi-stimulus Response Behavior of Biomimetic Autocrine Waxy Materials for Potential Self-Constructing Surface Microstructures

“…Mechanical action is a common form in life and industry, and the functions of many materials or devices are based on their corresponding behavior to force stimuli. − The initial waxy layer was removed with tape, and a tubular model (made of polypropylene) applied pressure to the smooth fresh AWM surface for 3–5 s. When the pressure was removed, the material elastically deformed and recovered, and then, optical microscopy images showed rapid autography of stressed regions on the AWM surface (Figure a,b). As the internal wax continued to be secreted, a complete thin wax layer began to form on its surface.…”