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The structural design of self-healing materials determines the ultimate performance of the product that can be used in a wide range of applications. Incorporating intrinsic self-healing moieties into puncture-resistant materials could significantly improve the failure resistance and product longevity, since their rapidly rebuilt bonds will provide additional recovery force to resist the external force. Herein, we present a series of tailored urea-modified poly(dimethylsiloxane)-based self-healing polymers (U-PDMS-SPs) that exhibit excellent puncture-resistant properties, fast autonomous self-healing, multi-cycle adhesion capabilities, and well-tunable mechanical properties. Controlling the composition of chemical and physical cross-links enables the U-PDMS-SPs to have an extensibility of 528% and a toughness of 0.6 MJ m −3 . U-PDMS-SPs exhibit fast autonomous self-healability with 25% strain recovery within 2 minutes of healing, and over 90% toughness recovery after 16 hours. We further demonstrate its puncture-resistant properties under the ASTM D5748 standard with an unbreakable feature. Furthermore, the multi-cycle adhesive properties of U-PDMS-SPs are also revealed. High puncture resistance (>327 mJ) and facile adhesion with rapid autonomous self-healability will have a broad impact on the design of adhesives, roofing materials, and many other functional materials with enhanced longevity. 

Both the dispersion state of nanoparticles (NPs) within polymer nanocomposites (PNCs) and the dynamical state of the polymer altered by the presence of the NP/polymer interfaces have a strong impact on the macroscopic properties of PNCs. In particular, mechanical properties are strongly affected by percolation of hard phases, which may be NP networks, dynamically modified polymer regions, or combinations of both. In this article, the impact on dispersion and dynamics of surface modification of the NPs by short monomethoxysilanes with eight carbons in the alkyl part (C8) is studied. As a function of grafting density and particle content, polymer dynamics is followed by broadband dielectric spectroscopy and analyzed by an interfacial layer model, whereas the particle dispersion is investigated by small-angle X-ray scattering and analyzed by reverse Monte Carlo simulations. NP dispersions are found to be destabilized only at the highest grafting. The interfacial layer formalism allows the clear identification of the volume fraction of interfacial polymer, with its characteristic time. The strongest dynamical slow-down in the polymer is found for unmodified NPs, while grafting weakens this effect progressively. The combination of all three techniques enables a unique measurement of the true thickness of the interfacial layer, which is ca. 5 nm. Finally, the comparison between longer (C18) and shorter (C8) grafts provides unprecedented insight into the efficacy and tunability of surface modification. It is shown that C8-grafting allows for a more progressive tuning, which goes beyond a pure mass effect. 

Understanding the microscopic mechanism of the transition of glass remains one of the most challenging topics in Condensed Matter Physics. What controls the sharp slowing down of molecular motion upon approaching the glass transition temperature Tg, whether there is an underlying thermodynamic transition at some finite temperature below Tg, what the role of cooperativity and heterogeneity are, and many other questions continue to be topics of active discussions. This review focuses on the mechanisms that control the steepness of the temperature dependence of structural relaxation (fragility) in glass-forming liquids. We present a brief overview of the basic theoretical models and their experimental tests, analyzing their predictions for fragility and emphasizing the successes and failures of the models. Special attention is focused on the connection of fast dynamics on picosecond time scales to the behavior of structural relaxation on much longer time scales. A separate section discusses the specific case of polymeric glass-forming liquids, which usually have extremely high fragility. We emphasize the apparent difference between the glass transitions in polymers and small molecules. We also discuss the possible role of quantum effects in the glass transition of light molecules and highlight the recent discovery of the unusually low fragility of water. At the end, we formulate the major challenges and questions remaining in this field.