荷叶表面的二元复合结构及其疏水性

Research for surface morphology and water repellency of Lotus leaf

荷花(Nelumbonucifera Gaertn.)是一种具有自清洁功能是水生植物,其叶表结构形态对其良好疏水性具有重要作用。通过模拟荷叶表面的结构形态可为开发与研制疏水表面仿生产品提供设计依据。本文对处于生长期和枯萎期的荷叶正反表面进行了扫描电镜(SEM)分析,并对其接触角进行了测量,结果表明:荷叶表面在干鲜状态下,与水的接触角存在不同,鲜叶的接触角由于表面水分饱满,表面蜡质含量相对较大而小于干叶的接触角(CA);对同一荷叶样本,无论是鲜叶还是干叶,背面接触角略大于正面接触角3~5;°荷叶背部表面形貌特征为一阶半球单元和其上二阶微小网格凹坑单元的半球型复合结构(SCS-Sem i-sphere Composite Structure);荷叶正面形貌特征为一阶锥型单元和其上二阶微小针形(1~3μm)单元的锥型复合结构(CCS-Cone Composite Structure);测试结果说明荷叶正反面具有的二元复合结构都表现出超疏水(Super-hydrophob ic)特性(CA】150°),并初步分析了荷叶疏水的表面形貌结构特征及疏水原因在于非光滑形貌几何单元及其分布密度。

Lotus(Nelumbo nucifera Gaertn.) flower owned self-cleaning abilities is a kind of aquatic plants.Lotus leaves keep themselves spotless because countless tiny projections,coated with water-repellent wax,cover their surface.Water cannot spread out on these leaves so it rolls around as droplets,removing dirt and grim as it goes.Chemists and engineers have attempted to copy this lotus-effect(or super-hydrophobic) for decades.The Lotus leaves divided into 2 groups,one is living samples and the other is fried samples,are analysed by SEM(Scanning Microscopy) at the up-back surfaces,and the contact angles(CAs) with water droplets are determined.The results showed that the difference between CAs of the same sample at up-back two surfaces is obvious.The back CAs are usually larger than the up face of Louts leaves at fried and living cases.The reasons of two cases mini-difference CAs may be due to surface structures and waxy contents of leaf surface layers.The higher wax content for the fried sample causes larger CAs than the living leaves sample.The back morphological characteristics of the Louts leaves possessed semi-sphere on which netted concaves composite structures(SCS).The up-surface morphological hydrophobic shapes is cone-shaped and many mini-protrusions on conical surfaces(CCS).The micro-structure unit and its distribution density on the surfaces of Louts are main factors of forming larger CAs.It is of great importance for bionics engineering surfaces design with special functional,eg.Hydrophobic or hydrophilic surfaces,to duplicate Louts leaf surface structures according to its morphological information.