Frontal
ring-opening metathesis polymerization (FROMP) catalyzed
by Grubbs-type Ru complexes enables new, rapid, and energy-efficient
syntheses of high-performance, structural plastics. Ideal catalysts
survive the extended time periods associated with resin preparation,
storage, and transportation. Current catalysts, however, induce premature
polymerization within hours to days under ambient conditions. In this
work, a thermally latent bis-N-heterocyclic carbene
complex provides exceedingly robust resins, which are viable for 8
weeks. When mixed with CuI coreagents, precatalyst activation
primes the system for rapid reactivity after thermal initiation. In
this study, more than 40 dual-component formulations successfully
catalyzed FROMP of dicyclopentadiene. The polymerization process parameters
(front temperatures and velocities), resin storability, and resultant
polymer properties (e.g., T
g) were determined for each composition. Intriguingly,
the Cu to Ru ratio dramatically impacts the observed frontal velocity
and temperature, as well as the polymer glass-transition temperature;
slower, colder reaction fronts result from formulations with large
Cu to Ru ratios. The resultant polymers display lower T
g values. Mechanistic analysis of a related model system
demonstrated that an excess Cu reagent decreases the activation and
polymerization rates.
In this paper, we present a method to create re-programmable multi-color textures that are made from a single material only. The key idea builds on the use of photochromic inks that can switch their appearance from transparent to colored when exposed to light of a certain wavelength. By mixing cyan, magenta, and yellow (CMY) photochromic dyes into a single solution and leveraging the different absorption spectra of each dye, we can control each color channel in the solution separately. Our approach can transform single-material fabrication techniques, such as coating, into high-resolution multi-color processes.We discuss the material mixing procedure, modifications to the light source, and the algorithm to control each color channel. We then show the results from an experiment in which we evaluated the available color space and the resolution of our textures. Finally, we demonstrate our user interface that allows users to transfer virtual textures onto physical objects and show a range of application examples.
This perspective details the grand challenges of designing and manufacturing multifunctional materials to impart autonomous property recovery. The susceptibility of advanced engineering composites to brittle fracture has led to the emergence of self-healing materials. This functionality has been demonstrated in bulk polymers and fibre-reinforced composites; most recently through the addition of vascular networks into the host material. These network systems enable the healing agents to be transported over long distances and provide a means by which both the resin and hardener can be replenished, thus overcoming the inherent limitations of capsule-based systems. To date, vascule fabrication methods include machining, fugitive scaffold processes, a lost-wax process and the vaporisation of sacrificial components, but recent developments in additive manufacturing (AM) technologies have paved the way for more efficient, bio-inspired vascular designs (VDs) to be realised. This perspective reviews the current progress in vascular self-healing and discusses how AM technologies and new design methods can be exploited in order to fabricate networks that are optimised for fluid transport and structural efficiency. The perspective culminates in the discussion of eight grand challenges across three thematic areas: ‘VD’, ‘Healing Chemistry’ and ‘AM’, that are likely to have major breakthroughs and socio/economic impact as these technologies are developed further in the next 10–15 years.
General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms Abstract. To explore the flow characteristics of healing agent leaving a vascular network and infusing a damage site within a fibre reinforced polymer composite, a numerical model of healing agent flow from an orifice has been developed using smoothed particle hydrodynamics. As an initial validation the discharge coefficient for low Reynolds number flow from a cylindrical tank is calculated numerically, using two different viscosity formulations, and compared to existing experimental data. Results of this comparison are very favourable; the model is able to reproduce experimental results for the discharge coefficient in the high Reynolds number limit, together with the power-law behaviour for low Reynolds numbers. Results are also presented for a representative delamination geometry showing healing fluid behaviour and fraction filled inside the delamination for a variety of fluid viscosities. This work provides the foundations for the vascular self-healing community in calculating not only the flow rate through the network, but also, by simulating a representative damage site, the final location of the healing fluid within the damage site in order to assess the improvement in local and global mechanical properties and thus healing efficiency.
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