Enhanced Condensation on Liquid-Infused Nanoporous Surfaces by Vibration-Assisted Droplet Sweeping.

Condensation is a universal phenomenon that occurs in nature and industry. Previous studies have used superhydrophobicity and liquid infusion to enable superior liquid repellency due to reduced contact angle hysteresis. However, small condensate droplets remain immobile on condensing surfaces until they grow to the departing size at which the body force can overcome the contact line pinning force. Hence, condensation heat transfer is limited by these remaining droplets that act as thermal barriers. To break these limitations, we introduce vibrational actuation to a slippery liquid-infused nanoporous surface (SLIPS) and show enhanced droplet mobility, controllable condensate repellency, and more efficient heat transfer compared to static SLIPSs. We demonstrate 39% smaller departing droplet size and 8× faster droplet departing speeds on the dynamic vibrating SLIPS compared to the nonactuated SLIPS. To understand the implications of these behaviors on heat transfer, we investigate the condensate area coverage and droplet distribution to verify enhanced dewetting on dynamic vibrating SLIPSs. Using well-validated heat transfer models, we demonstrate enhanced condensation heat transfer on dynamic SLIPSs due to the higher population of smaller condensate droplets (<100 µm). In addition to condensation heat transfer, we also show that vibrating SLIPSs can enhance droplet collection. This work utilizes the synergistic combination of surface chemistry and mechanical actuation to realize enhanced droplet mobility and heat transfer in an electrically controllable and switchable manner.

Preoperative vascular surgery model using a single polymer tough hydrogel with controllable elastic moduli.

Materials used in organ mimics for medial simulation and education require tissue-like softness, toughness, and hydration to give clinicians and students accurate tactile feedback. However, there is a lack of materials that satisfy these requirements. Herein, we demonstrate that a stretchable and tough polyacrylamide hydrogel is useful to build organ mimics that match softness, crack growth resistance, and interstitial water of real organs. Varying the acrylamide concentration between 29 or 62% w/w with a molar ratio between cross-linker and acrylamide of 1 : 10 800 resulted in a fracture energy around ∼2000 J m-2. More interestingly, this tough gel permitted variation of the elastic modulus from 8 to 62 kPa, which matches the softness of brain to vascular and muscle tissue. According to the rheological frequency sweep, the tough polyacrylamide hydrogels had a greatly decreased number of flow units, indicating that when deformed, stress was dispersed over a greater area. We propose that such molecular dissipation results from the increased number of entangled polymers between distant covalent cross-links. The gel was able to undergo various manipulations including stretching, puncture, delivery through a syringe tip, and suturing, thus enabling the use of the gel as a blood vessel model for microsurgery simulation.