they melt into a liquid and releasing heat as they solidify into a solid. The greater the latent heat of fusion, the greater the energy absorbed/released during these phase transitions. [5,6] As various groups have shown, by encapsulating micron to millimeter diameter droplets of a PCM, functionalities ranging from temperaturedependent permeability to enhanced solar thermal energy storage efficiency can be realized. [7,8] Once encapsulated, PCMs can be embedded in a diversity of matrices, which may enable new applications in areas ranging from thermal energy storage and conversion, electronics, [9-12] smart fibers and textiles, and thermal comfort in vehicles. [13] A conventional approach to encapsulation is through shell polymerization in oil-in-water (o/w) or water-in-oil-in-water (w/o/w) double emulsions, such as those used to prepare the self-healing microcapsules first reported by Moore et al. [14] Challenges with this approach are the generally wide size distribution of the capsules prepared, compatibility between the capsule shell polymerization chemistry and the core chemistry, and control of the synthetic parameters required to enable reproducible results. [15-17] Because the thermal transitions of PCMs are sensitive to the Microencapsulated materials are receiving broad attention for applications as diverse as energy storage and conversion, biomedicine, self-healing materials, and electronics. Here, a general microfluidic approach is presented to prepare phase-change material-infilled microcapsules with unique thermal and mechanical properties. Aqueous sodium acetate solutions are encapsulated by an acrylate-based shell via a microfluidic method. To understand and optimize microcapsule formation, flow behavior during the encapsulation is numerically simulated. When the microcapsules are embedded in an acrylate matrix (same composition as the shell wall material), the microcapsules exhibit a significant 46.6 ºC difference between the crystallization and melting temperatures as determined by differential scanning calorimetry at a rate of 10 ºC per min. Variable temperature dynamic mechanical analysis over the range of 50 to-90 ºC reveals up to a 50% change in the composite's elastic modulus at a given temperature, depending on if the sample is being cooled or heated, due to significant undercooling of the core material crystallization as shown by X-ray diffraction.

In article number 2000286, Jinyun Liu, Ting Si, Jinjin Li, Paul V. Braun, and co-workers present a phase-change material-infilled microcapsule with unique thermal and mechanical properties. Variable temperature dynamic mechanical analysis from 50 to-90 °C reveals up to a 50% change in the elastic modulus at a given temperature due to significant undercooling of the core crystallization.