Materials that can be switched between low and high thermal conductivity states would advance the control and conversion of thermal energy. Employing in situ time-domain thermoreflectance (TDTR) and in situ synchrotron X-ray scattering, we report a reversible, light-responsive azobenzene polymer that switches between high (0.35 W m−1K−1) and low thermal conductivity (0.10 W m−1K−1) states. This threefold change in the thermal conductivity is achieved by modulation of chain alignment resulted from the conformational transition between planar (trans) and nonplanar (cis) azobenzene groups under UV and green light illumination. This conformational transition leads to changes in the π-π stacking geometry and drives the crystal-to-liquid transition, which is fully reversible and occurs on a time scale of tens of seconds at room temperature. This result demonstrates an effective control of the thermophysical properties of polymers by modulating interchain π-π networks by light.
The success of gene technologies hinges on our ability to engineer superior encapsulation and delivery vectors. Cubosomes are lipid-based nanoparticles where membranes, instead of enveloping into classic liposomes, intertwine into complex arrays of pores well-ordered in a cubic lattice. These complex nanoparticles encapsulate large contents of siRNA compared to a liposomal analogue. Importantly, the membranes that form cubosomes have intrinsic fusogenic properties that promote fast endosomal escape. Despite the great potential, traditional routes of forming cubosomes lead to particle sizes too large to fulfill the state-of-the art requirements of delivery vectors. To overcome this challenge, we utilize a microfluidic nanomanufacturing device to synthesize cubosomes and siRNA-loaded cubosomes, termed cuboplexes. Utilizing cryogenic TEM and small angle X-ray scattering we elucidate the time-resolved mechanisms in which microfluidic devices allow the production of small cubosomes and cuboplexes (75 nm) that outperform commercially available delivery vectors, as well as liposome-based systems.
Frontal polymerization (FP) is a self-propagating reaction in which the reactive zone propagates through a monomer solution at a steady velocity. Using FP, polymeric materials are cured rapidly with minimal energy input. Here, we produce high-glass-transitiontemperature thermosets via frontal ring-opening metathesis polymerization (FROMP) of dicyclopentadiene (DCPD) with norbornene-based cross-linkable co-monomers that enable tuning of the cross-link density. The glass-transition temperatures of poly(DCPD) systems are systematically varied from 138 to 219 °C by altering the amount of cross-linking co-monomers in the resin. Front velocities exceeding 5 cm•min −1 enable rapid, solvent-free production of thermoset materials with a 99% degree of cure and yield strength of 57 MPa. The DCPD-norbornene co-monomer resins are cured with 6 orders of magnitude less energy than a traditional oven cure and have a T g nearly 90 °C higher than reported thermosets of DCPD prepared via FROMP.
A new methodology is developed to activate and characterize mechanochemical transformations at a solid interface. Maleimide-anthracene mechanophores covalently anchored at a fused silica-polymer interface are activated using laser-induced stress waves. Spallation-induced mechanophore activation is observed above a threshold activation stress of 149 MPa. The retro [4+2] cycloaddition reaction is confirmed by fluorescence microscopy, XPS, and ToF-SIMS measurements. Control experiments with specimens in which the mechanophore is not covalently attached to the polymer layer exhibit no activation. In contrast to activation in solution or bulk polymers, whereby a proportional increase in mechanophore activity is observed with applied stress, interfacial activation occurs collectively with spallation of the polymer film.
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