Evaporation is a ubiquitous phenomenon found in nature and widely used in industry. Yet a fundamental understanding of interfacial transport during evaporation remains limited to date owing to the difficulty of characterizing the heat and mass transfer at the interface, especially at high heat fluxes (>100 W/cm). In this work, we elucidated evaporation into an air ambient with an ultrathin (≈200 nm thick) nanoporous (≈130 nm pore diameter) membrane. With our evaporator design, we accurately monitored the temperature of the liquid-vapor interface, reduced the thermal-fluidic transport resistance, and mitigated the clogging risk associated with contamination. At a steady state, we demonstrated heat fluxes of ≈500 W/cm across the interface over a total evaporation area of 0.20 mm. In the high flux regime, we showed the importance of convective transport caused by evaporation itself and that Fick's first law of diffusion no longer applies. This work improves our fundamental understanding of evaporation and paves the way for high flux phase-change devices.

Figure 4. Optical properties of direct-write colloidal crystals. Photographs of a) small-grain and b) large-grain colloidal crystal imaged under ring lighting around the objective lens. c) Schematic depicting the characterization of optical properties by illuminating the colloidal crystal with collimated light at an angle normal to the crystal and observing the projection of diffracted colors on a hemispherical screen. Photograph of colors projected from the d) smallgrain and g) large-grain colloidal crystal. Colors from the e) small-grain and h) large-grain samples linearly mapped onto azimuthal angle φ and polar angle θ. f) Plot of radiant intensity versus θ for each of the RGB channels, obtained by averaging over all values of φ. i) Plot of radiant intensity versus azimuthal angle φ derived from the blue channel of (h), ranging φ = 0°-60° averaged over the sixfold symmetry regions, at θ = 52°. The solid blue line is the radiant intensity and the shaded region represents standard deviation. The highest peak is from the largest grain, A; the second highest peak is from the second-largest grain, B; and the lowest radiant intensity, denoted by the solid black line, is an estimate of the amount of light from various other small grains, C. The dashed line represents the background illumination of the ping pong ball, measured in a noncolored region. j) Optical image of the illuminated region, with A, B, and C grain structures identified. k) SEM image analysis confirms that the largest grain A and the second-largest grain B are relatively orientated at 19.5°. www.advancedsciencenews.com

Vaginal delivery is typically avoided in the extremely preterm breech population due to the concern of entrapment by the cervix of the aftercoming head. A mechanical device concept is presented to enable vaginal delivery by preventing retraction of the cervix against the fetus during delivery. The two-part device was designed to dilate the cervix, prevent prolapse of small fetal parts and maintain sufficient dilation during delivery. The two-part device was designed and manufactured with the following modules: an inflatable saline-filled cervical balloon for dilation and a cervical retractor composed of semi-rigid beams to stabilize the cervix and maintain adequate dilation. The device was tested using a cervical phantom designed to simulate the compressive force the cervix exerts. The cervical balloon reached a maximum dilation of 8.5 cm, after which there was leakage of saline from the balloon. While this dilation was less than the target goal of 10 cm, the leaking was attributed to prototype manufacturing defects which could be resolved with further development. The cervical retractor was able to withstand between 1 - 3 kPa. Although estimates of cervical pressures can be upwards of 30 kpa, there are no in-vivo measurements to formally identify the pressures for patients in preterm labor. This device serves as a viable proof-of-concept for utilizing an inflatable balloon device to prevent cervical retraction in the setting of extremely preterm vaginal breech delivery. Further manufacturing improvements and design changes could improve the device for continued development and testing.