活体水黾水面超大承载机制及其仿生研究

Water striders and fishing spiders are small creatures living on water. Their legs are covered by a layer of micro-setae with nanoscale texture, which renders the legs highly non-wetting or super-hydrophobic force so that these creatures can stand effortlessly on water. Moreover, they can move quickly on water by rowing their legs on the surface. This amazing ability has attracted substantial research work. The exploration of the underlying mechanism not only supplies a better understanding of nature but also has potential biomimetic applications. The problem of static standing on water is well studied, and 4 main hypotheses are presented including Surface tension theory, Vortex theory, Micro-nano Structure theory. However, the internal connection is not well interpreted among these different hypotheses, neither is the dynamic mechanism of propulsion. .Studying the mechanisms of gliding and super water-supporting force has important scientific significance for designing aquatic micro-devices. At present the studies of water-supporting force concentrate on the non-smooth morphology and wetting property of legs，maximal supporting force of a single hind leg against water in vitro and bionic micro-robot, etc. Yet the mechanism of super water-supporting force is not very clear at home and abroad. The main content of the project includes: Experimental study on contact angle of water striders；Experimental study on water-supporting and traction force of water striders in vivo；Mathematical and mechanical model of the relationship between water-supporting force and other crucial factors will be established and then simulation and optimization will be conducted；The research of capacity mechanism on water striders and bionic design on floating model with super water-supporting force will be done..Studies have shown that the supporting force of a single hind leg against water is about 15 times more than its self-weight. Water strider robot which has been developed is about 1.5 times. The research objective is to develop aquatic floating model which maximal supporting force against water is about 3 times more than its self-weight..The main characteristics of the project is that water-supporting force is be measured from a single hind leg in vitro turns to be measured in vivo. And the creative objectives of the project are to establish static model between flexible legs and supporting system of water surface, reveal the mechanical inbeings of super water-supporting force of water strider legs and design the floating model with super water-supporting force. They will have an important academic value, and the potential application of the project in designing new floating devices with super water-supporting force will improve the capicity of bionic micro-robot greatly.

研究水黾在水面上承载与滑行机制对设计超大承载微型漂浮器械具有重要科学意义。目前国内外关于水黾承载力的研究主要集中于腿部结构形态及润湿性、离体单腿承载力测定、仿水黾微型机器人等，其超大承载机制尚不十分明确。本项目主要研究内容：通过水黾腿腹部和背部微观结构观测、化学成分分析、接触角和滚动角测定，揭示其超疏水多元耦合机制；依据水黾活体承载试验和优化设计理论，构建承载力与关键因素之间的力学模型，研究其超大承载与推进机制及其耦联关系；建立水黾柔性腿与水面支撑系统力学模型，进行计算机仿真优化，并与试验结果对比验证，进而从理论层面揭示水黾超大承载的力学机制；根据理论与实验结果，设计研制超大承载微型漂浮模型。将水黾承载力研究由离体单腿测试转向活体实测、进行水黾活体承载力和推进力试验是本项目主要特色；揭示水黾超大承载机制力学本质、设计研制大承载仿生微型漂浮模型是本项目创新目标。

水黾的超疏水功能及其超大水面承载力引起了课题组成员的浓厚兴趣，依托本项目对其进行了系统性研究。实验测得水黾腿部、腹部、背部与翅膀的接触角分别为161.5°、156.3°、157.6°、156.4°，均具有超疏水性。电镜观察了水黾体表各部位的微观结构，对水黾体表化学成分进行分析，其中存在油脂层，对水黾体表超疏水性进行多元耦合分析，水黾身体各部位的微纳结构与油脂层共同作用导致其具有超疏水性。.首次试验研究了活体水黾的水面承载力，自行设计与制作了水面微力测量装置，测得活体水黾样本的最大水面承载力为8736.7μN，是其自身体重的20.9倍。建立了水黾柔性腿与水面接触系统的力学模型，研究了水黾腿刺破水面的临界条件，并进行了仿真优化分析。水黾腿的触水长度与压出水涡深度是其具有超大水面承载的主要因素。依据该承载力模型计算了水黾腿的最大水面承载力，与试验测定值进行比较，最大误差率为3.9%，验证了所建承载力模型的正确性。研究认为水黾的水面超大承载力由水的表面张力与浮力组成，浮力所占比重甚微，水的表面张力起主要作用。活体水黾具有超大水面承载的力学机制是因为其腿的微纳米结构导致的超疏水功能，充分利用水的表面张力，在水面制造水涡，增大了排水量。.研究认为微纳结构说、漩涡动力说与表面张力说都是水黾超大水面承载力的必要条件，这三个学说有其内在联系，水黾腿微纳结构导致的超疏水性是其在水面制造漩涡的必要条件，漩涡使水面产生变形而不破裂，才能有效利用表面张力。.以铜为材料制作了2个仿生水黾漂浮模型，铜表面经超疏水处理后接触角为154.5°。模型Ⅰ有4条支撑腿，支撑腿用直径为0.45mm的实心铜丝制作，测得最大水面承载力为28.5mN，是其自身体重的8.1倍。模型Ⅱ有4条支撑腿，支撑腿仿水黾腿部的空心结构，用薄铜片制作的中空管，测得其最大水面承载力为73.1mN，是其自身体重9.8倍。这些研究为水面微型漂浮装置的承载力设计提供了理论依据，具有重要的科学意义。