Study On Superhydrophilic Mechanism Of Sphagnum

Superhydrophilic surface is a special wetting surface,with the characteristics of ultra-infiltration.Superhydrophilic surface have extensive applications in self-cleaning,anti-fogging,oil-water separation,high-negative liquid transport,blood compatibility materials and bone affinity materials.Searching for natural superhydrophilic surface is one of important way to study superhydrophilic surface.Sphagnum moss has been described as the plant with superhydrophilic surface in many literatures.However,less systematic study on its hydrophilicity has been found.Therefore,in this paper,sphagnum moss,a natural superhydrophilic plant,was studied as the object.The structure of sphagnum leaves,microscopic morphology and surface chemical composition were characterized,and the wettability of liquid on the sphagnum surface was studied through high-speed camera.First of all,maximum water absorption mass,water absorption velocity,dehydration velocity,dehydration rate on the sphagnum have carried on the detailed study,the results show that the maximum water absorption mass is 22.5 times of its own drying mass,After studying the relationship between time and water absorption mass or water absorption velocity,water absorption mass has natural logarithmic function relationship:m_absorb=alnt_absorb+b,water absorption velocity has power function relationship:v_absorb=at^b_absorb.Then,the microscopic morphology of sphagnum has been observed.It was found that sphagnum leaf was half gourd shape,with sharp front and protruding outside.Thus,a large amount of water could be stored inside the leaf.The sphagnum moss leaf consists of a single layer of hollow cells.The sphagnum structures were further characterized by fractal dimension,surface roughness,etc.Finally,three-dimensional model reconstruction of sphagnum was carried out according to the geometrical dimensions of the obtained sphagnum plants,and maximum water absorption and porosity of sphagnum leaves were calculated according to the three-dimensional model.The spreading process of liquid in sphagnum peat was studied by using high speed camera.The influences of different surface tension and viscosity on spreading distance and spreading speed of sphagnum peat were studied.According to the traditional wet theory of superhydrophilic surface,the equation of water contact angle of sphagnum leaf was modified.The superhydrophilic mechanism on the sphagnum moss is that the rough structure of the hollow cell surface and the high porosity work together to make the sphagnum leaf surface superhydrophilicity.Liquid spreading process in sphagnum hollow cells was studied.Because the hollow cell wall is not smooth,the hollow cell were divided into small cubicle by ribs.The flow of liquid inside a hollow cell is to fill each compartment in turn.According to measurement data,spreading distance and the corresponding time data fitting equation for l_spread=202 t^0.53_spread,spreading velocity equation for v_spread=107t^-0.47_spread.The macroscopic and microscopic processes of sphagnum absorbing fog water were observed.From the actual observation,it can be found that in the early period of the mist,bump structure can expand real contact area between the peat moss surface and mist water,so that peat moss can absorb more fog.With the increasing of absorbing water mass,the hollow cells and the inner space of sphagnum leaf were filled with fog water to meet the needs of sphagnum for water.Finally,in order to know how the sphagnum absorbs rain water in rainy days,the interaction between falling drops and the sphagnum stem leaves was studied.The study showed that the elasticity of the sphagnum leaves would increase the critical separation velocity of the impact of water droplets,which could make the sphagnum leaves absorb falling drops at a faster velocity.Thus,sphagnum leaves can absorb more rain in the rainy environment.