RESOURCES

Abstract
The variety of UV-curable monomers for 3D printing is limited by a requirement for rapid curing after each sweep depositing a layer. This study proposes to trigger supramolecular self-assembly during the process by a gemini imidazolium-based low-molecular-weight gelator, allowing printing of certain monomers. The as-printed hydrogel structures were supported by a gelator network immobilising monomer:water solutions. A thixotropic hydrogel was formed with a recovery time of < 50 seconds, storage modulus = 8.1 kPa and yield stress = 18 Pa, processable using material-extrusion 3D printing. Material-extrusion 3D printed objects are usually highly anisotropic, but in this case the gelator network improved the isotropy by subverting the usual layer-by-layer curing strategy. The monomer in all printed layers was cured simultaneously during post-processing to form a continuous polymeric network. The two networks then physically interpenetrate to enhance mechanical performance. The double-network hydrogels fabricated with layers cured simultaneously showed 62-147 % increases in tensile properties compared to layer-by-layer cured hydrogels. The results demonstrated excellent inter- and intra-layered coalescence. Consequently, the tensile properties of 3D printed hydrogels were close to mould cast objects. This study has demonstrated the benefits of using gelators to expand the variety of 3D printable monomers and shown improved isotropy to offer excellent mechanical performances.

Abstract
Thermal Energy Storage (TES) materials, such as Phase Change Materials (PCMs) are proven to enhance the energy efficiency in many fields, such as automotive and building sectors, which correspond to the most energy intensive ones. Shape-stabilized PCM and cascade PCM are procedures to overcome the most important barriers when PCMs are applied since PCMs need to be encapsulated for their technical use: the leakage of the liquid phase, corrosion, low heat transfer and narrow temperature of application. In the present study, a novel shape stabilized PCM with cascade performance (cascade shape stabilized phase change material, CSS-PCM) is synthesized via dissolution, which allows up to 60 wt.% of a paraffin-PCM in the final composition. The novel CSS-PCM is based on a biopolymer, the polycaprolactone (PCL), a low melting temperature polyester as polymeric matrix and RT27 and Micronal DS 5040 acting as PCM. To evaluate the performance of the new TES materials developed, several techniques have been used: Differential Scanning Calorimetry (DSC), and Fourier-Transformed Infrared (FT-IR) spectroscopy were used to evaluate the thermophysical properties and the chemical properties of the different formulations. The CSS-PCM show an increment of storage capacity by increasing the PCM content, and the thermal reliability was also tested: some of the CSS-PCM formulations were stable for up to 500 thermal cycles. Finally, as a potential application of the new polymeric-based PCM 3D, a printing attempt was performed in order to analyze the viability of the formulations to be used as 3D printing material as a first proof of concept.