Phác họa cấu trúc tự nhiên

Tạp chí Khoa học - Công nghệ Thủy sản<br /> <br /> Số 1/2014<br /> <br /> THOÂNG BAÙO KHOA HOÏC<br /> <br /> NATURAL STRUCTURES DESIGN<br /> PHÁC HỌA CẤU TRÚC TỰ NHIÊN<br /> Kroisova Dora1, Ron Jiri2<br /> Ngày nhận bài: 21/8/2013; Ngày phản biện thông qua: 12/02/2014; Ngày duyệt đăng: 10/3/2014<br /> <br /> TÓM TẮT<br /> Mục đích của bài báo là nghiên cứu một số bề mặt cấu trúc tự nhiên, thiết kế thông minh và sáng tạo trên bề bặt của<br /> chúng nhằm ứng dụng chúng vào công nghiệp. Bề mặt lá sen (Nelumbo nucifera) được biết đến như một mặt phẳng không<br /> dính nước, bề mặt của rêu (Bryophyta) được xem như một bề mặt ưa nước và da cá mập (Carcharodon Carcharias) như bề<br /> mặt với các thông số rất tốt về thủy cơ đã được lựa chọn để nghiên cứu và phát họa cấu trúc. Ban đầu tất cả các mẫu được<br /> sấy khô trong không khí và sau đó phun lên bề mặt mẫu một lớp hợp kim Au-Pd. Các nghiên cứu về cấu trúc đều được thực<br /> hiện trên kính hiển vi điện tử quét VEGA\\TESCAN với độ phóng đại trong khoảng từ 200 đến 100 000 với điện áp gia tốc<br /> là 10 kV. Thông qua kính hiển vi điện tử quét để có thêm thông tin về cấu trúc của chúng. Phần mềm ImageTool phiên bản<br /> 3.0 của Trường Đại học Texas Health Science Center ở San Antonio đã được sử dụng để phân tích hình ảnh của bề mặt tự<br /> nhiên. Công ty KOH-I-NOR PONAS tại Cộng hòa Séc đã hợp tác chọn phác họa các bề mặt cấu trúc này và bây giờ nhiệm<br /> vụ của họ là thử nghiệm trong điều kiện thực tế.<br /> Từ khóa: cấu trúc tự nhiên và cấu trúc nano, thiết kế, kỹ thuật sinh học<br /> <br /> ABSTRACT<br /> The aim of this work is studying of natural surface structures, their design preparation and subsequent creation of<br /> the specific surfaces of molds for industrial applications. Lotus leaf surface (Nelumbo nucifera) as a superhydrophobic<br /> plant surface, a leaf surface of a common moss (Bryophyta) as a hydrophilic surface and a shark skin (Carcharodon<br /> carcharias) as a surface with good hydromechanical parameters were selected in order to show how to study and design the<br /> structures. At first all the samples were dried in the air and after that were sputtered by a layer of Au-Pd alloy. The studies<br /> of the natural object structures were performed on a scanning electron microscope VEGA\\TESCAN at magnifications in<br /> the range of 200 to 100000x at 10 kV accelerating voltage. Through the scanning electron microscopy it is possible to get<br /> more information about the structures in order to create their design. Software ImageTool version 3.0, The University of<br /> Texas Health Science Center at San Antonio was used for an image analysis of the selected natural surfaces. The designed<br /> structures of chosen surfaces were prepared in cooperation with KOH-I-NOR PONAS, the Czech Republic Company, and<br /> now their functions are tested in real conditions.<br /> Keywords: natural structures and nanostructures, design, bionics<br /> <br /> I. INTRODUCTION<br /> An increasing amount of researchers have<br /> been working on a study of natural plant and animal<br /> surfaces from point of view of material compositions<br /> and structures as well as processes by which are<br /> these objects created. An interest in this type of<br /> materials comes out from the fact that life on the<br /> <br /> 1<br /> <br /> 2<br /> <br /> Earth has developed for more than 3.5 billion years<br /> which has resulted in practically ideal solutions.<br /> The natural surfaces usually show multilevel<br /> structures beginning on a molecular level through a<br /> nano-scale level and ending on a micro-scale level<br /> where many different material combinations are in<br /> mutual coexistence.<br /> <br /> Assoc. Prof. Kroisova: Centre for Nanomaterials, Advanced Technologies and Innovations, Technical University of Liberec,<br /> Czech Republic, Email: dora.kroisova@tul.cz<br /> Msc. Ron Jiri: Faculty of Mechanical Engineering, Technical University of Liberec, Czech Republic<br /> <br /> TRƯỜNG ĐẠI HỌC NHA TRANG • 39<br /> <br /> Tạp chí Khoa học - Công nghệ Thủy sản<br /> Suitable examples are water repellent plant<br /> leaves surfaces created by various structures where<br /> the microstructure is formed of single surface cells<br /> and the nanostructure is formed by wax particles<br /> secreted on the cells surface. In some cases there<br /> may occurred obvious macrostructure which can<br /> even be visible by the naked eye.<br /> These structures facilitate to leaves to stay<br /> clean because adhered dust and other impurities<br /> hinder a process of photosynthesis [1], [2].<br /> The first studied object was a superhydrophobic<br /> surface of a leaf of an Indian lotus (Nelumbo nucifera).<br /> Other surfaces inspiring to a muse may be for<br /> instance a hydrophilic moss surface ensuring water<br /> and nutrients absorption without necessity of using<br /> a root system.<br /> The structures lessening water flow resistance<br /> could be animal skins - shark skin in case of this<br /> study [3].<br /> II. EXPERIMENTS<br /> For a microscopic evaluation and following<br /> image analysis were chosen samples of the Indian<br /> lotus, the moss and the shark skin. All the samples<br /> were dried in the air and sputtered by a thin layer<br /> of Au-Pd alloy. Observations of the structures were<br /> performed on a scanning electron microscope (SEM)<br /> VEGA\\TESCAN at magnifications in the range of<br /> 200 to 100000x at 10 kV accelerating voltage.<br /> SEM images of the sample surface structures<br /> were used for the image analysis which aim was<br /> finding dimensions and geometry of the micro and<br /> nanoparticles. Software ImageTool version 3.0, The<br /> University of Texas Health Science Center at San<br /> Antonio was used for the image analysis.<br /> The images were tresholded and transferred to<br /> binary images, i.e. bright areas (peaks of the surface<br /> cells of the lotus) on the SEM images were<br /> transferred to white colour and areas among the<br /> cells to black colour. The images were purified<br /> from noise (spots and smears). Some cells on the<br /> SEM images were joined together which would be<br /> evaluated as a one cell instead of two ones. This<br /> problem was treated by a “watershed” function. After<br /> a segmentation of the epidermal cells a cell density<br /> ρcells was evaluated. Another step was a contact area<br /> ratio between liquid and solid phase fLSmicro<br /> evaluation (i.e. a sum of the white areas divided by<br /> the whole image area). The same policy was applied<br /> to get fLSnano values. A figure 1 shows the origin area<br /> from which was measured the cells density ρcells and<br /> outlines of the contact areas [4].<br /> <br /> 40 • TRƯỜNG ĐẠI HỌC NHA TRANG<br /> <br /> Số 1/2014<br /> <br /> Figure 1. Upper side of the Indian lotus leaf with the applied<br /> image analysis on the SEM image [4]<br /> The image analysis evaluated these values:<br /> Cells density:<br /> ρcells<br /> = 3205<br /> [mm-2]<br /> = 0,101 [-]<br /> Contact area ratio<br /> fLSmicro<br /> = 0,241 [-]<br /> fLSnano<br /> <br /> There can be counted which area is equal to<br /> a single cell from the cell density ρcells assuming<br /> hexagonal layout of the cells. The single cell area<br /> multiplied by fLSmicro corresponds with an area which<br /> is in contact with liquid from which was derived a<br /> contact diameter dcont written bellow:<br /> <br /> On the basis of the image analysis a model of<br /> a form for fabrication has been designed. The value<br /> of dcont from the analysis (Fig. 2 up) is adequate to<br /> a value of a formations which should be fabricated<br /> (Fig. 2 down).<br /> A density of the fabricated formations, their<br /> pitches and geometric layout should also be adequate to the studied natural surface [4].<br /> <br /> Figure 2. Models of natural surface structure (up)<br /> and its transformation to technical form (down) [4]<br /> <br /> Tạp chí Khoa học - Công nghệ Thủy sản<br /> <br /> Số 1/2014<br /> <br /> III. RESULTS AND DISCUSSION<br /> With the usage of the SEM and image analysis, the evaluation of three different types of natural objects<br /> was performed.<br /> The lotus leaf is known for its specific characteristic which is a high hydrophobicity. This characteristic<br /> is achieved by the microstructure and the nanostructure of the leaf surface which may also be increased by<br /> chemical composition of the surface waxes on the nanoscale level.<br /> By the surface analysis, data about the shapes, layouts, dimensions and densities of the cells and<br /> the waxes have been achieved. There is no possibility of identical structural analogy fabrication by current<br /> conventional methods.<br /> A following tab. 1 shows a contact angles and their hysteresis, the epidermal cell densities, the micro and<br /> nano contact area ratios and derived contact diameters with heights and pitches between asperities (epidermal<br /> cells) for 4 chosen hydrophobic surfaces.<br /> Tab. 1. Geometric parameters of chosen hydrophobic plants<br /> Micro<br /> Contact Epidermal<br /> contact<br /> angle<br /> cell density<br /> area ratio<br /> hysteresis<br /> ρcells<br /> fLSmicro<br /> [°]<br /> [mm-2]<br /> [-]<br /> <br /> Nano<br /> contact<br /> area ratio<br /> fLSnano<br /> [-]<br /> <br /> Contact<br /> diameter<br /> dcont [µm]<br /> <br /> Plant name<br /> <br /> Contact<br /> angle<br /> [°]<br /> <br /> Epidermal Epidermal<br /> cell height cell pitch<br /> H [µm]<br /> P [µm]<br /> <br /> Indian lotus*<br /> (Nelumbo Nucifera)<br /> <br /> 146,7<br /> ± 3,5<br /> <br /> 1,4 ±<br /> 0,9<br /> <br /> 3205<br /> <br /> 0,101<br /> <br /> 0,241<br /> <br /> 6,6<br /> <br /> 12,2<br /> <br /> 17,7<br /> <br /> Cock’s-foot*<br /> (Dactylis glomerata)<br /> <br /> 146,7<br /> ± 1,9<br /> <br /> 2,1 ±<br /> 1,3<br /> <br /> 3764<br /> <br /> 0,201<br /> <br /> 0,190<br /> <br /> 8,3<br /> <br /> 9,0<br /> <br /> 16,3<br /> <br /> St John’s wort*<br /> (Hypericum perforatum)<br /> <br /> 151,6<br /> ± 1,5<br /> <br /> 1,7 ±<br /> 1,0<br /> <br /> 1562<br /> <br /> 0,114<br /> <br /> 0,249<br /> <br /> 9,6<br /> <br /> 11,3<br /> <br /> 25,3<br /> <br /> Poinsettia*<br /> (Euphorbia Pulcherrima)<br /> <br /> 146,3<br /> ± 5,0<br /> <br /> 1,4 ±<br /> 0,9<br /> <br /> 2022<br /> <br /> 0,098<br /> <br /> 0,168<br /> <br /> 7,9<br /> <br /> 6,8<br /> <br /> 22,2<br /> <br /> * All the values were measured on the upper side of dehydrated leaves<br /> <br /> 1. Indian lotus (Nelumbo nucifera)<br /> <br /> Figure 3. Typical structure of the Indian lotus surface. Convex epidermal cells (the upper image) covered by the tiny wax rods<br /> (the lower image). SEM images [4]<br /> <br /> The Indian lotus is a thermo-philic tropic swamp plant which originates from India. Almost circular leaves<br /> emerge from swamp water as well as their blossoms. Despite growing in backwater the lotus remains perfectly<br /> clean a dried which is ensured by its hierarchic structure formed by the microscale concave cells with hollow<br /> nanoscale wax rods on the cells surfaces. The length of the wax rods is about 600 nm and its diameters (inner<br /> and outer) about 100 nm (fig. 4). Besides being clean, this structure also ensures self-cleaning ability.<br /> There was found out by the image analysis that the cell density ρcells is 3205 mm-2 and hollow rods density<br /> ρwaxes was approximately 6 mil. mm-2. This nanostructure with such a huge density and a nanoparticles shape is<br /> unfabricatable by current technologies. Fig. 4 shows the measured dimensions on models [4].<br /> <br /> TRƯỜNG ĐẠI HỌC NHA TRANG • 41<br /> <br /> Tạp chí Khoa học - Công nghệ Thủy sản<br /> <br /> Số 1/2014<br /> <br /> Figure 4. Models of the surface structure covering leaves of the Indian lotus<br /> - the documentation of the structure [4]<br /> <br /> Although the contact angles and hysteresis of<br /> four different hydrophobic leaves are very similar,<br /> geometrical parameters of the leaves vary distinctly.<br /> This variety may be caused by morphology and<br /> geometry of epidermal waxes and their chemical<br /> compositions. Wax morphology varies from tubes<br /> to platelets with different types of arrangement.<br /> Indian lotus possesses hollow tubes with irregular<br /> arrangement while St John’s wort has regular<br /> platelets with spacing which resembles stars with<br /> five tips.<br /> St John´s wort microstructure seems to be the<br /> most profitable because it has the highest contact<br /> angle (151,6 ± 1,5) with the largest dimensions of<br /> asperities which is less difficult for fabrication and<br /> also cheaper. Due to the fineness, variety and wide<br /> morphology of waxes which is currently inimitable<br /> it would be useful to choose St John´s wort<br /> microstructure<br /> dimensions<br /> as<br /> a<br /> default<br /> microstructure and try to deposit nanoasperities<br /> (PECVD) with varying dimensions and find out the<br /> best combination of micro and nanostructure to get<br /> the highest contact angle value experimentally.<br /> 2. Moss (Bryophyta)<br /> Mosses are green nonvascular plants of a<br /> small growth with a distinct ability to retain water.<br /> The mosses accept water by the whole surface of<br /> thallus and distribute it by their water conducting<br /> tissues or easily by wettable surfaces. The way how the<br /> mosses manage water enables them to use even<br /> very little amount of rainfall.<br /> <br /> 42 • TRƯỜNG ĐẠI HỌC NHA TRANG<br /> <br /> Figure 5. SEM image of the moss with the obvious<br /> structured surface<br /> <br /> The image analysis showed an elongated<br /> hexagonal alignment of the structure. Dimensions<br /> gained from the real structure were used for a fabrication<br /> of a form for plastic material injection. The form has<br /> been fabricated in many dimensional variations with<br /> maintenance of a dimensions ratio and its function<br /> has been currently tested in real conditions.<br /> <br /> Figure 6. Model of the moss surface for the form fabrication<br /> <br /> Tạp chí Khoa học - Công nghệ Thủy sản<br /> <br /> Số 1/2014<br /> <br /> Figure 7. SEM image of the form surface for the moss<br /> structure fabrication.<br /> Fabricated by KOH-I-NOOR PONAS s.r.o<br /> <br /> The mosses are interesting for their ability of<br /> surface water absorption. The model created according<br /> to the SEM images of original moss structure was<br /> served for the form surface fabrication. The form<br /> has been fabricated in cooperation with Department<br /> of Engineering Technology TUL and KOH-I-NOOR<br /> PONAS s.r.o. The function of the form has been<br /> currently tested in real conditions.<br /> 3. White shark (Carcharodon carcharias)<br /> A specific shark skin structure is covered by firm<br /> tooth-like scales lessening water flow resistance.<br /> Figure 8 shows the SEM image of shark skin scales<br /> and there are scales dimensions in figure 9. A<br /> scale width varies from 150 to 200 µm, a distance<br /> between longitudal flutes is about 40 µm and a<br /> height of the flutes varies from 10 to 20 µm.<br /> The shark skin surface was characterised on<br /> the basis of the image analysis. A new structure<br /> (figure 10) was fabricated according to the model<br /> but regarding to the large difference from its original<br /> the new structure hasn´t been tested.<br /> <br /> Figure 8. SEM image of the shark skin surface<br /> with the obvious scale structure [3]<br /> <br /> Figure 9. Model of the shark skin scale as a basis for the<br /> form fabrication<br /> <br /> Figure 10. SEM image of the new form surface fabricated<br /> on the basis of the derived dimensions. Fabricated by<br /> KOH-I-NOOR PONAS s.r.o<br /> <br /> The shark skin was used for modelling of the<br /> surface with low resistance against the flow in the<br /> water environment. The model with the dimensions<br /> achieved from the SEM images was used to design<br /> of the surface of the fabricated form. From the image<br /> above it is obvious that it was not possible to<br /> fabricate the form surface on a required level<br /> regarding the shape, structure and dimensions.<br /> IV. CONCLUSION<br /> The described image analysis applied to the<br /> images of the natural objects achieved from the<br /> scanning electron microscopy turned out to be a<br /> suitable method to determination of the surface<br /> characteristic parameters such as the size, the<br /> shape and the layout of the cells and the waxes.<br /> The parameters achieved by the image analysis<br /> are sufficient for models design of the form surfaces<br /> fabrication.<br /> <br /> TRƯỜNG ĐẠI HỌC NHA TRANG • 43<br /> <br />