Triggering Forces at the Nanoscale: Technologies for Single‐Chain Mechanical Activation and Manipulation

Abstract

Over the past decades, polymer mechanochemistry has focused on the development and application of advanced force application methods to better understand the mechanochemical response of mechanophores. In this regard, techniques such as ultrasonication and single‐molecule force spectroscopy (SMFS) are used to activate and detect up to thousands of chemical events within a polymer single chain, allowing the researchers to probe the mechanochemical reactivity of these stress‐responsive motifs. Here, the most recent contributions of the single‐molecule force spectroscopy technique to this field are presented, putting emphasis on the fundamental parameters of the technique for triggering specific force responses and on the description of force–extension curves measured for single‐ and multi‐mechanophore polymers. Moreover, new contributions of microscopy‐based techniques in the field of polymer mechanochemistry, as well as the potential application of single‐chain nanoparticles as mechanoresponsive materials, are highlighted.

Rotaxane-Based Dual Function Mechanophores Exhibiting Reversible and Irreversible Responses

“…Mechanochromic mechanophores are molecular motifs whose optical absorption or emission characteristics change when they experience a certain mechanical force. − Polymers comprising such moieties can display force-induced optical changes, which in turn are useful to signal these mechanical events. The operating mechanism of many mechanophores involves covalent bond scission, for example in spiropyran − and naphthopyran detivatives, − 1,2-dioxetanes, , Diels–Alder adducts, , radical-generating motifs, − benzoxazoles, and others. − Breaking covalent bonds typically requires activation forces in excess of 200 pN, − and with few exceptions, the re-formation of the severed bonds is kinetically or thermodynamically stifled, limiting the reversibility of the responsive behavior. A different possibility to achieve mechanochromic effects is to mechanically alter structures formed by weak inter- or intramolecular interactions. ,− Examples of such “noncovalent” mechanophores include motifs in which mechanically induced changes of host–guest or charge-transfer interactions alter the photophysical properties.…”

Action of Mechanical Forces on Polymerization and Polymers

“…According to experts, approximately 80% of all manufactured plastics are trained in mixing equipment before processing. Mechanochemical treatment (mechanical milling and alloying) is the mechanical treatment of solid mixtures, as a result of which the plastic deformation of substances occurs, mass transfer is accelerated, the mixing of the components of the mixture at the atomic level is carried out and the chemical interaction of solid reagents is activated [ 62 ].…”

“…Ultrasonic impacts are now very widespread and a search is underway to expand their application in modern technologies. In particular, probing the mechanophore’s activity by ultrasonication and/or by nanoscale single-molecule force spectroscopy (SMFS) experiments provides a way to optimize solid-state activation methods for polymers as shown by Deneke et al [ 1 ], Radiom et al [ 60 , 61 ] and Martínez-Tong et al [ 62 ]. Mechanochemical transformations under the action of ultrasound and SMFS are clearly manifested when using multi-MP polymers, as shown by Bowser and Craig [ 63 ].…”

Terraced and 3D Pyramid‐Shaped Polymer Single Crystal via Low Temperature‐Assisted Microfluidic Technology

“…The PEO single crystals formed a smooth and graded PEO singlecrystal film (Figure 1a). Atomic force microscopy (AFM) is an effective tool for studying polymer phase separation, [25] apparent morphology, [26][27][28] nanomechanics, [12] nanomanipulation, [29,30] and even folding of various materials. [31] As shown in Figure 1b, a rectangular patterned PEO crystal morphology design strategy is illustrated.…”