What makes katsura mono unique

In this study, we measure the surface morphology and wettability of Katsura leaves from the summer to winter, and reveal how leaf structural changes lead to wettability changes. Due to such wettability changes, fall brown leaves support approximately 17 times greater water volume than summer leaves.

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The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. Leaves are an important part of a tree for photosynthesis, respiration, transpiration, and storage of chemical energy and water [ 1 — 3 ].

However, deciduous trees survive dry and cold winters most notably by shedding their leaves in fall [ 4 ]. To lose their leaves, trees undergo a number of physiological and morphological changes in the leaves, stems, and roots [ 5 , 6 ].

The formation of the abscission layer during the fall cuts off water and nutrient transport through the xylem and phloem [ 5 — 8 ], which expedites the dehydration in the leaf [ 6 ].

This dehydrated abscission layer weakens cell adhesion between the leaf and stem, causing the leaf to fall from the tree more easily by wind or rain [ 6 ]. Additionally, leaves are found to be less hydrophobic in the fall [ 9 ].

The hydrophobic property of tree leaves has been studied extensively [ 10 — 13 ]. Hierarchical, two-tier roughness is a typical structure of hydrophobic leaf surfaces e. Lotus leaf. The first tier is composed of epidermal cells that form convex bumps at the microscale and the second tier is tubular wax-nanocrystals.

Leaf wettability could affect the dynamics of an elastic leaf upon rain droplet impact. Droplet-impact experiments with an elastic structure similar to a leaf cantilever beam beam [ 14 , 15 ], fiber [ 16 ] and butterfly wing [ 17 ] showed that the elastic structure vibrates and its initial displacement is roughly the same regardless of wettability.

However, a higher torque is triggered at the base of a hydrophilic beam than that of a hydrophobic beam due to the adhered liquid [ 14 ]. Then, a combined Wenzel and Cassie-Baxter contact-angle model is proposed to take into account an inhomogeneous eroded area on a leaf surface, which is only observed in fall leaves.

To further correlate different configurations of micro- and nano- structures to the surface wettability, Katsura leaves are treated in various conditions vacuum, heat, and chloroform. We discuss the effect of low contact angle and high contact-angle hysteresis on a leaf, and a potential application to use the nano-wax tubules from leaves as a coating material. We selected the Katsura tree, Cercidiphyllum japonicum , for this study. Katsura trees are deciduous, which are native in China and Japan [ 18 ].

The leaves are heart-shaped and approximately 8 cm long and 6 cm broad when mature. The leaf petioles are short, only about 3 cm long. Generally, the leaves grow closely packed together. SEM observations confirm that the tree is hypostomatous i. Blacksburg is in a humid continental climate zone with an average temperature range from 4. For the purposes of this study, we classified the morphological phases of the leaves based on the season.

Here, the spring leaves are the ones taken from April to May, spanning the time from when the leaves first begin to appear on the tree until the leaves lose their reddish-green color. The summer leaves are taken approximately from June to September. During the summer, the leaves are fully grown and dark green. The fall leaves are samples taken from October to November, and have either a yellow or brown color. Then, the sample with a water droplet was tilted by the goniometer to determine the advancing and receding contact angles as well as the critical tilting angle.

The advancing and receding contact angles were measured just prior to the movement of the droplet. First, a leaf was cut to exclude regions containing the midrib and veins.

Then, the leaf sample was mounted to a plate using a double-sided carbon tape. Top-view images were taken at various magnifications. To measure the cross-sectional view, the leaves were immersed in liquid nitrogen for 10 sec and broken between two grips. Then, the sample plate was loaded into the SEM chamber. The samples were mounted using a double-sided copper tape for high heat conduction. The chamber pressure condition for sublimation was over Pa.

We used image analysis methods to analyze SEM images of various leaf conditions. The images were converted into black and white images for the Matlab edge-detection algorithm. The image analysis results show the tracked boundary of the eroded regions as blue lines in S2 c and S2 d Fig. Leaf samples were attached onto petri dishes with a double-sided adhesive tape prior to vacuum, heat, or chemical treatments. For the vacuum treatment, we placed leaf samples in a vacuum desiccator at 20 kPa for 24 hours.

To remove wax, we tilted a leaf sample at an angle around 30 degrees and dripped 10 mL of a chloroform solution Cambridge Isotope Laboratories Inc. Then, the collected solution of chloroform and leaf wax is gently dried with nitrogen gas as shown in S5 a Fig. To prove the Cassie-Baxter state at the nano scale, the critical height at a given spacing of nano-wax tubules to transition from the Cassie-Baxter to Wenzel states will be estimated for green and brown leaves.

The calculated depth of green leaves is 25 nm, which is significantly shorter than the height 1. It means that a droplet on green leaves stays in the Cassie-Baxter state at the nanoscale. Therefore, we can assume the Cassie-Baxter state for green leaves and the Wenzel state for brown leaves at the nanoscale.

Fig 1 a shows seasonal variations of a Katsura tree. In the spring, heart-shaped leaves emerge with a reddish-green color, later changing to green as they mature in the summer. In the fall, the leaves turn yellow and then brown. Not only does the leaf color change, the wettability also changes over the season. The maximum and minimum values of contact angles are defined as the advancing contact angle and receding contact angle , respectively. Our contact-angle measurements show that Katsura leaves change from superhydrophobic in the summer to sticky and hydrophobic in the fall as shown in Fig 1 b.

The leaf color changes to reddish green—green—yellow—yellowish brown—brown. The green leaf exhibits a superhydrophobic surface whereas the brown leaf becomes less hydrophobic. Scanning electron microscopy SEM images in Fig 2 show the hierarchical, two-tier surface structure of green leaves during the summer a-d and brown leaves during the fall e-h. On the green leaves during summer, microscale papillose epidermal cells form oblate spheroidal bumps as shown in Fig 2 b and 2 d. At the nanoscale, a dense layer of epicuticular wax tubules homogeneously covers the summer leaves as in Fig 2 c.

Optical and scanning electron microscope images of a green leaf a-d and a brown leaf e-h. The green leaf summer is covered with oblate spheroidal epidermal cells and homogeneous epicuticular waxes.

However, on the brown leaf fall , the epidermal cells are shrunk and the epicuticular waxes are eroded. In the dry fall, when the water content decreases inside the epidermal cells, the turgor pressure will be reduced [ 6 ].

Hence, the microscale epidermal cells with soft walls presumably deflate as the internal turgor pressure decreases. Accordingly, we observed shrinkage of the epidermal cells on a leaf as shown in Fig 2 f and 2 h. The coverage of epicuticular waxes is significantly reduced especially on top of epidermal bumps in the fall. The SEM image Fig 2 g of a fall leaf shows that the epicuticular wax tubules are eroded and the surface is flattened. A water droplet on a rough surface can be described by either a Wenzel or Cassie-Baxter state [ 21 , 22 ].

If a droplet wets the surface i. The roughness is calculated as the ratio of the actual surface area to the apparent projected surface area. In the Cassie-Baxter state, a droplet does not completely wet the rough surface i.

Due to geometric complexity in a leaf surface, it is difficult to predict which wetting state occurs over the epidermal bumps. To experimentally characterize the microscopic wetting state between a water interface and a leaf surface, a water droplet was frozen while sitting on the leaf see S1 Fig.

Then, the detached frozen droplet was visualized using environmental scanning electron microscopy ESEM. We found that the bottom interface of the frozen droplet follows the contours of the microscale epidermal cells the first-tier rough surface , which indicates the Wenzel state at the microscale.

It was hard to engrave the plum blossom design, requiring a lot of concentration, but he also needed to adjust how hard he hit the chisel to adjust the depth. There are about 7 different colors of metal. In the west, metals do not have this much variation in color. Chasing or metal engraving is a total of all the different techniques.

Katsura continues with his challenge in pursuit of a new expression. These are only basic characteristics of Noh theatre, and generally to the western spectator are unknown and seemingly complex, but in them is build long lasting tradition. Sign in. Log into your account. Forgot your password? Password recovery.

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