Video_1_Hydraulic Strategy of Cactus Root–Stem Junction for Effective Water Transport.MP4

<p>Cactus roots function as a hydraulic safety valve by conducting available water quickly and preventing water loss under drought condition. In particular, the root–stem (R–S) junction is responsible for effective water transport by direct coupling of the water absorptive thin roots and the moisture-filled bulky stem. In this study, the morphological features of the R–S junction were observed by using X-ray micro-imaging technique. Their structural and functional characteristics were also elucidated according to a hydrodynamic viewpoint. With regard to the axial water transport through xylem, the R–S junction prevents water leakage by embolizing large-scale vessels with relatively high hydraulic conductivity. In addition, the axial theoretical hydraulic conductivity of xylem vessels from the roots to the stem drastically increases to facilitate water absorption and prevent water loss. The cortex cell layer of a cactus is thinner than that of other plant species. In the viewpoint of radial conductivity, this property can be the hydraulic strategy of the cactus R–S junction to transport water quickly from the root surface into the xylem. These results suggest that the R–S junction functions as a hydraulic safety valve that can maximize water uptake in axial and radial directions at limited rainfall. This junction can also prevent the stem from leaking water under drought condition.</p

Schematic diagram of surface fabrication and experimental processes.

(a) Plasma treatment of PTFE by controlling variables. (b) Measure the contact angle and sliding angle of the surface using a surface tension measuring equipment. (c) Check the self-cleaning effect of the specimen using graphite and water droplets.</p

Design of surface treatment parameters for plasma treatment.

Design of surface treatment parameters for plasma treatment.</p

Graph of contact angle and change of contact angle according to slide angle and surface treatment parameters of treated specimen.

(a) contact angle and sliding angle graph of before and after treatment (b) i) Before treatment, ii) After PE treatment, iii) After RIE treatment, the image where the droplet is located and the contact angle. (c, d) The contact angle graph according to the surface treatment parameter (RF power, exposure time). The PE-treated specimen is expressed in red and the RIE-treated specimen is expressed in black.</p

Verifying the self-cleaning effect of the produced specimen.

(a) The process of removing fine contaminants from the manufactured specimen. (b) The process of removing contaminants from the treated specimen. The water droplets repeatedly bounced off the surface. In this process, particles in the path were removed, and finally, they were off the surface of the specimen. As a result of repeating the same process for 20 seconds, almost all particles on the surface were removed, and only a few particles remained in the place where water droplets did not contact.</p

Observation and analysis of droplet collisions.

(a) Composition of experimental equipment for droplet collision observation. The needle dropped droplets at a height of 20 mm from the surface and the droplet size is 2.8±0.2 mm. The velocity of the droplet was 1.02 m/s. (b) Results of high speed cameras from contact with droplets to removal from surfaces. Compared with the specimen treated with the PE method, water droplets splashed faster on the specimen treated with RIE. (c) When water droplets bounced from the specimen treated with the PE method, small water droplets are scattered. The small droplets were between 0.4 and 0.5 mm in size.</p

Analysis of surface characteristics.

(a) FE-SEM image i) Before treatment, ii) After RIE treatment, iii) After PE treatment. More detailed structures of columnar shapes can be observed on the RIE surface, and leaf vein-like structures can be observed on the PE surface. (b) SPM images of surfaces i) pristine, ii) after PE treatment and iii) after RIE treatment. (c) FT-IR spectrum analysis confirmed no significant difference in the chemical composition of the surface before and after treatment. (d) XPS results of pristine, PE, and RIE Specimens.</p

Interface tension and <i>We</i> of the surface before and after treatment.

Interface tension and We of the surface before and after treatment.</p

S1 File -

Superhydrophobic surfaces (SHS) are attracting attention in many fields owing to their excellent advantages such as anti-freezing, corrosion prevention, and self-cleaning. However, to modify the surface structure, environmental pollution caused by complex processes and chemical treatment must be considered. In this study, the surface of polytetrafluoroethylene (PTFE) was plasma-treated using oxygen and argon plasma to change the surface structure without a complicated process. The PTFE surface was treated in two ways: plasma etching (PE) and reactive ion etching (RIE). The contact angle of the conventional PTFE surface was 113.8 ± 1.4°, but the contact angle of the manufactured surface was 152.3 ± 1.7° and 172.5 ± 1.2°. The chemical composition and physical structure of the samples produced were compared. The treated specimens had the same chemical composition as the specimen before treatment and exhibited differences in their surface structures. Therefore, it was determined that the change in the water repellency was due to the surface structure. After PE treatment, the specimen surface had a mountain range-like structure, and the RIE specimen had a more detailed structure than the PE specimen. The contact rate of water droplets decreased due to the difference in the structure of the specimen before and after treatment, and the increase in the surface contact angle was manifested. In order to confirm that the plasma treatment reduces surface energy, the shape of the liquid collision was observed using a high-speed camera, and the contact time was calculated to confirm water repellency. The contact time of the PE and RIE specimen was 24 milli-second (ms) and 18 ms, respectively. The high contact angle and low sliding angle of the RIE specimen made it easy to restore surface cleanliness in a self-cleaning experiment using graphite.</div

Development of a Desalination Membrane Bioinspired by Mangrove Roots for Spontaneous Filtration of Sodium Ions

The shortage of available fresh water is one of the global issues presently faced by humanity. To determine a solution to this problem, the survival strategies of plants have been examined. In this study, a nature-inspired membrane with a highly charged surface is proposed as an effective membrane for the filtration of saline water. To mimic the desalination characteristics of mangrove roots, a macroporous membrane based on polyethylene terephthalate is treated with polyelectrolytes using a layer-by-layer deposition method. The fabricated membrane surface has a highly negative charged ζ-potential value of −97.5 ± 4.3 mV, similar to that of the first layer of mangrove roots. Desalination of saline water using this membrane shows a high salt retention rate of 96.5%. The highly charged surface of the membrane may induce a relatively thick and stable ion depletion zone in front of the membrane. As a result, most co-ions are repelled from the membrane surface, and counterions are also rejected by virtue of their electroneutrality. The water permeability is found to be 7.60–7.69 L/m²·h, which is 10 times higher than that of the reverse osmosis desalination method. This nature-inspired filtration membrane exhibits steady desalination performance over 72 h of operation, successfully demonstrating the stable filtration of saline water. This nature-inspired membrane is applicable to the design of a small-scale, portable, and energy-free desalination device for use in third-world countries or small villages