宜州城区常见绿化树种叶表面微观结构与滞尘能力的比较

为了筛选滞尘效果较好的绿化树种,为城镇街区大气净化提供理论支持,以宜州城区13种常见绿化树种为研究对象,采用洗脱——抽滤法测定其单位叶面积滞尘量,分析其不同粒径颗粒物的占比,并利用扫描电镜(SEM)和Image J软件观测叶表面微观结构,对不同树种叶表面微观结构与单位叶面积滞尘量的相关性进行比较分析。结果表明:1) 在宜州城区被测的绿化树种中,单位面积叶表面总颗粒物滞留量表现为交通繁忙区 > 非交通繁忙区,乔木树种的滞尘能力优于灌木树种;2) 在13种被测树种中,其叶表层滞留的大颗粒物占比均超过50 %;除鹅掌柴外,其余树种单位面积叶表层滞留的颗粒物数量均超过其蜡质层;3) 被测树种叶表面微观结构与其滞尘能力密切相关,气孔导度及气孔密度增大,叶片表面(特别是气孔附近)的颗粒物滞留量增加;4) 在13种被测树种中,杧果、白兰、木樨、雅榕和海南蒲桃的综合滞尘效益排名前5,可将其可作为当地街区道路绿化的优选树种。由于不同绿化树种的叶表面微观结构具有一定的差异,其相应的滞尘能力也有不同,因此,可将叶表面微观结构作为优良绿化树种选择的参考依据。

深圳市常见园林植物滞尘效应研究

以深圳市6种常见的园林植物为对象,研究其单位面积滞尘量及其粒径组成特征,探究植物叶片表面的微观形貌结构以及滞留颗粒物的组分和分布特征,分析气象因子对植物滞尘的影响。结果表明:1)6种园林植物的单位叶面积滞尘量排序为黄金榕(0.74±0.21 g/m2)>鹅掌藤(0.42±0.26 g/m2)>对叶榕(0.24±0.26 g/m2)>龙船花(0.20±0.07 g/m2)>沿阶草(0.18±0.10 g/m2)>鸡蛋花(0.15±0.10 g/m2);2)6种园林植物滞尘以粒径α>10μm的颗粒物为主,质量占比为59.21%~88.92%(黄金榕除外),鹅掌藤对α>10μm颗粒物的滞尘能力最强(0.34±0.20 g/m2),黄金榕对3μm<α<10μm(0.51±0.15 g/m2)和0.15μm<α<3μm(0.14±0.07 g/m2)颗粒物的滞留能力最强;3)6种园林植物叶表面的气孔、褶皱、沟槽、絮状凸起和绒毛等微观形貌有利于叶片对颗粒物的截留,叶片滞留颗粒物的元素组成主要为O,Si和Al;4)6种园林植物叶表滞留的大颗粒物(α>10μm)易受风速和温度的影响。研究结果对深圳市园林植物配置具有指导意义,并可为通过植物滞尘效应改善空气质量提供一定的理论依据。

Study of dynamic hydrophobicity of micro-structured hydrophobic surfaces and lotus leaves

The dynamic wetting characteristics of water droplets on silicon wafers with microscale regular pillars structures and fresh lotus leaves are investigated experimentally.We measured the static contact angle,contact angle hysteresis,and roll-off angle of water droplets on both of these superhydrophobic surfaces with a high speed contact angle meter.The dynamic contact angles and internal velocity distribution of water droplets on superhydrophobic surfaces were studied with a high-speed camera system and a particle image velocimetry (PIV) system,respectively.We found that the acceleration of water droplets when they slide off lotus leaves is greater than that of water droplets sliding off the silicon wafers with microscale pillar structures although the static contact angles of water droplets on lotus leaves are slightly smaller than those on the silicon wafers.The reason is that water droplets sliding off lotus leaves have smaller contact angle hysteresis and larger slip velocities.These results indicate that the dynamic contact angle hysteresis and sliding acceleration of liquid droplets are more suitable for reflecting the hydrophobicity of material surfaces compared with static contact angles.Our experiments also show that lotus leaves with multiscale micro/nanostructures have stronger hydrophobicity and self-cleaning properties compared with the micro-structured superhydrophobic surfaces.