M. Hernández

Characterization of self-healing polymers : From macroscopic healing tests to the molecular mechanism

Over the last few years, several testing methods have been introduced for the detection and quantification of autonomous and thermally stimulated healing in polymers. This review summarizes some of the most prominent state-of-the-art techniques for the characterization of polymer healing occurring at the microscopic and macroscopic levels during the repair of damage such as scratches, cracks, or ballistic perforations. In addition to phenomenological investigation of the self-healing process, a range of physical characterization techniques have been explored for elucidation of the underlying healing mechanism at the molecular or polymer network level. The present state of visual methods, spectroscopic techniques, scattering techniques, and dynamic methods is described. A short outlook is provided, discussing the future challenges and expected new trends in the characterization of self-healing polymers.

Monitoring Network and Interfacial Healing Processes by Broadband Dielectric Spectroscopy: A Case Study on Natural Rubber

Broadband dielectric spectroscopy (BDS) is introduced as a new and powerful technique to monitor network and macroscale damage healing in an elastomer. For the proof of concept, a partially cured sulfur-cured natural rubber (NR) containing reversible disulfides as the healing moiety was employed. The forms of damage healed and monitored were an invisible damage in the rubber network due to multiple straining and an imposed macroscopic crack. The relaxation times of pristine, damaged, and healed samples were determined and fitted to the Havriliak-Negami equation to obtain the characteristic polymer parameters. It is shown that seemingly full mechanical healing occurred regardless the type of damage, while BDS demonstrates that the polymer architecture in the healed material differs from that in the original one. These results represent a step forward in the understanding of damage and healing processes in intrinsic self-healing polymer systems with prospective applications such as coatings, tires, seals, and gaskets.

Reply to Comment on “Monitoring Network and Interfacial Healing Processes by Broadband Dielectric Spectroscopy: A Case Study on Natural Rubber”

Das et al. comment our publication on the use of broadband dielectric spectroscopy as a potential tool for monitoring healing processes in natural rubber. They argue that our interpretation of self-healing processes should be handled with care and that critical issues like rubber tackiness and sample fabrication for dielectric experiments were not properly addressed. We agree that tackiness in partially cured rubber does exist and that interpretation of dielectric experiments requires detailed insight into both the processes and the method, but we will try and re-argue below the correctness of our approach as reported in our publication.