Reshapeable,rehealable and recyclable sensor fabricated by direct ink writing of conductive composites based on covalent adaptable network polymers

Covalent adaptable network(CAN)polymers doped with conductive nanoparticles are an ideal candidate to create reshapeable,rehealable,and fully recyclable electronics.On the other hand,3D printing as a deterministic manufacturing method has a significant potential to fabricate electronics with low cost and high design freedom.In this paper,we incorporate a conductive composite consisting of polyimine CAN and multi-wall carbon nanotubes into direct-ink-writing 3D printing to create polymeric sensors with outstanding reshaping,repairing,and recycling capabilities.The developed printable ink exhibits good printability,conductivity,and recyclability.The conductivity of printed polyimine composites is investigated at different temperatures and deformation strain levels.Their shape-reforming and Joule heating-induced interfacial welding effects are demonstrated and characterized.Finally,a temperature sensor is 3D printed with defined patterns of conductive pathways,which can be easily mounted onto 3D surfaces,repaired after damage,and recycled using solvents.The sensing capability of printed sensors is maintained after the repairing and recycling.Overall,the 3D printed reshapeable,rehealable,and recyclable sensors possess complex geometry and extend service life,which assist in the development of polymer-based electronics toward broad and sustainable applications.

A spatiotemporally-nonlocal continuum field theory of polymer networks

A physically-based continuum theory that captures the microstructure-dependent and temporal effects of both permanent and transient polymer networks is still lacking,despite the fact that it is greatly needed for the analysis of polymeric microstructures.To fill in this gap,this work proposes a physically-based spatiotemporally nonlocal continuum field theory.A general frame-work is established that quantitatively connects microscopic descriptions of polymer networks(chain energetics,chain-length distribution,assembly structure of the interpenetrating network,and rate of bond exchange reactions)to key components in the spatiotemporally nonlocal constitutive relations(explicit form of the nonlocal kernel function,magnitude of nonlocal characteris-tic length,two-phase weighting factors,and explicit form of the relaxation function),based on three hypotheses on the continuum viewpoint of the underlying discrete network structure:the existence of a finite bottom bound of volume to define intensive quan-tities,uniformity of energy density field inside the representative volume of a polymer network,and the condition for initiation of chain stretch.Applying the general framework to a permanent 8-chain concentric network yields a concrete two-phase nonlocal elasticity constitutive relation,where the explicit form of the kernel function can be derived by simply assuming an implicit form.Application to a transient network with bond exchange reactions yields a spatiotemporally nonlocal constitutive relation.The spatiotemporally nonlocal continuum theory can be helpful for exploring transformative and subversive high-performance materials involving the specific spatial stacking and arrangement of functional units through artificial design.

NFSI-catalyzed S–S bond exchange reaction for the synthesis of unsymmetrical disulfides

The metal-free S–S bond exchange reaction of symmetrical disulfides catalyzed by NFSI is described. This novel protocol provides a facile and efficient approach to accessing important unsymmetrical disulfides.Furthermore, this strategy could also be utilized in the late-stage functionalization of amino acids, drugs,and natural products. The broad substrate scope, good functional group tolerance and easy accessibility of catalyst indicate that this strategy affords a green and practical complementary method to various unsymmetrical disulfides.