Four-dimensional (4D) printing of shape memory polymer (SMP) imparts time responsive properties to 3D structures. Here, we explore 4D printing of a SMP in the submicron length scale, extending its applications to nanophononics. We report a new SMP photoresist based on Vero Clear achieving print features at a resolution of ~300 nm half pitch using two-photon polymerization lithography (TPL). Prints consisting of grids with size-tunable multi-colours enabled the study of shape memory effects to achieve large visual shifts through nanoscale structure deformation. As the nanostructures are flattened, the colours and printed information become invisible. Remarkably, the shape memory effect recovers the original surface morphology of the nanostructures along with its structural colour within seconds of heating above its glass transition temperature. The high-resolution printing and excellent reversibility in both microtopography and optical properties promises a platform for temperature-sensitive labels, information hiding for anti-counterfeiting, and tunable photonic devices.

extracted with the help of patterned hydrophilic/hydrophobic regions present on its back. [3][4][5] Cotula fallax, a plant from South Africa efficiently collects water from fog using its hierarchical 3D layout present on its leaves. [6] Pinus radiata and Casuarina equisetifolia, the tree canopies, are also capable of extracting water from air with the help of structures present on their leaves. [7][8][9] Researchers have also demonstrated that spider silk of certain species of spider has directional water collecting ability. This is attributed to the presence of periodic spindle knots on its fibers. [10][11][12][13][14] These mechanisms of harvesting water from humid air have inspired the researchers to mimic the structural design as well as geometry of natural materials. [15][16][17][18][19] Electrostatic spinning (electrospinning) has received a great deal of attention in the last two decades for its ability to fabricate ultrafine fibers that are useful for various applications. [20][21][22][23][24][25][26] Researchers have demonstrated that electrospinning can be used to fabricate fibers that resemble the structural geometry of natural materials. [27][28][29][30] For example, electrospinning is used to Quest for efficient fog harvesting methods has drawn immense attention in recent times. In this study, electrospinning is used to fabricate three different sets of membranes that are based on pristine poly(N-isopropylacrylamide) (PNIPAM) fibers, pristine polyvinylidene fluoride (PVDF) fibers, and PNIPAM-PVDF bead-on-string fibers. The wettability of these membranes is investigated as a function of temperature and the effect of their wettability on the fog collection efficiency is determined. Membranes based on pristine PNIPAM and pristine PVDF fibers are fabricated using conventional electrospinning and are shown to have a smooth surface morphology. On the other hand, PNIPAM-PVDF bead-on-string fibers are fabricated using core-shell electrospinning. Water collection efficiency of the membranes is compared to investigate the influence of microstructures and wettability gradient on fog harvesting ability of the samples. Among the three samples, the bead-on-string hierarchical fibrous membrane demonstrates the highest fog harvesting rate of 1150 ± 28 mg cm −2 h −1 at 25 °C and 909 ± 31 mg cm −2 h −1 at 40 °C. Furthermore, the results demonstrate that the presence of microstructures on the nanofibers improve the fog harvesting efficiency of PNIPAM-PVDF bead-on-string fibers.

Electrospinning is employed to fabricate a Janus membrane that demonstrates hydrophobic behavior on one surface and hydrophilic behavior on the other. The Janus membrane is fabricated by electrospinning hydrophobic polyvinylidene fluoride (PVDF) on top of a hydrophilic membrane. The hydrophilic membrane is fabricated by electrospinning poly(N‐isopropylacrylamide) (PNIPAM) and PVDF blend solution. This Janus membrane exhibits a water separation efficiency of over 99.5% at an ultra‐low hydrostatic pressure of 0.7 kPa. The results demonstrate that the membrane can be used to separate both oil and water from oil in water and water in oil emulsions. The top layer of the Janus membrane selectively reduces the liquid entry pressure of one of the liquids in the emulsion and aids in its separation from the emulsion. When the water in oil emulsion contacts the PVDF layer of the Janus membrane, liquid entry pressure of the oil is considerably reduced compared to the liquid entry pressure of water. Thus, the membrane aids in the separation of oil from the emulsion and transmits it through the membrane. Similarly, the Janus membrane with PNIPAM/PVDF blend layer facing up, aids in separating and transmitting the water from oil in water emulsion.

Collection of clean water from humid air has attracted immense attention in recent years due to the lack of access to pure drinking water among large section of population in several parts of the world. Hence, there is a persistent demand for the fabrication of robust, scalable membranes for efficient harvesting of pure water, especially in fog‐laden areas. Herein, three different membranes based on neat nanofibers, nanofibers with microparticles, and nanofibers with hierarchical structures (nanopillars) are successfully fabricated using poly(vinylidene fluoride‐co‐hexafluoropropylene) and fluorinated polyhedral oligomeric silsesquioxane composite mixture. Neat nanofibers and nanofibers with microparticles are fabricated by employing direct electrospinning and electrospinning combined with electrospraying process, respectively. Hierarchical structured fibers are fabricated by growing nanopillars on the surface of the fibers using electrospinning combined with template‐wetting method. The wettability properties including water contact angle and hysteresis of these membranes are investigated. Due to the increased surface roughness and low surface energy, the hierarchical fibers exhibit higher contact angle (153°) and lower hysteresis (3°) compared to the neat nanofibers and nanofibers with microparticles. Furthermore, the results demonstrate that the presence of nanopillars on the surface of the nanofibers improves the membrane's water collection efficiency when exposed to humid air.

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