Research On Fabrication Of Bio-inspired Micro/Nano Structures For Water Condensation And Collection

Efficient water condensation and collection is important for handling the water shortage in desert and reducing energy waste.It also plays important roles in spacecraft and military equipment.Filmwise condensation and dropwise condensation technique have been improved these years.However,the condensation efficiency is not high enough,not to mention water collection from the damp air.In recent years,people found some living creatures,such as cactuses,spiders and some beetles,who have special micro/nano structures,can collect water from the fog.Scientists have investigated the micro/nano structures and the collection mechanism of those living creatures.We investigated bio-inspired micro/nano stuctures for water condensation and collection imitating those typical living creatures.The main research work is as follows.Firstly,we modeled the barrel and clam-shell drop on cone based on the cactus spins.The free energy distribution and the free energy gradient distribution were obtained through theoretical calculations and simulations.The relations of the structure parameter,free energy and free energy gradient were revealed.We further modeled the drop in tube system,and revealed the drop motion rules inside the conical tubes and wedgy tubes.Planar gradient surface consisting of alternate hydrophilic and hydrophobic wedgy regions were designed by combining the gradient shapes and manufacturability.We analyzed the influence of structure shape and contact angle on the drop motion,and revealed the motion law of the drops on the bio-inspired structures,offering theoretical bases for design and fabrication of bio-inspired structures.Secondly,we investigated the surface modification process,and obtained OTS SAM,CuO/Cu(OH)2 nano structures,Si nanowires/nanocones,and Si microtubes on the substrates.Cu cones and PDMS cone arrays as well as photoresist/SiO2,Si/SiO2 and OTS/SiO2 patterns were fabricated,and modified with either nano structures or coating material,on the basis of the material properties of the gradient structures and the process compatibility.Thus the bio-inspired water condensation and collection micro/nano structures were achieved.Finally,we built condensation and water collection testing system,and tested the condensation and water collection ability of the prepared samples.The testing verified the directional drop transportation of the bio-inspired structures.It is found that hydrophilic cones are more efficient for water condensation and collection.We found the optimized half-apex angle of the cactus spin inspired structure,below which the water collection ability decreased owing to the weak driving force.The gradient surface also exhibited directional collection ability,and the width of the hydrophobic regions can be designed to control the drop diameter distribution.The branched wedgy surfaces exhibited better performance than flat surface.