Prediction For Super-hydrophobic Performance And Oil/water Separation Applications For The Material Of Mesh Membrane

With the inspiration of natural phenomena and the special surface of wettability possessed by the creature,super-hydrophobic materials have a broad prospect in many fields such as oil-water separation for the theoretical research and practical application.In order to construct super-hydrophobic surface,scholars kept on exploring the theoretical models in recent years,but usually lost sight of the case of camber,however,the top of the mastoid morphology of microscopic rough surface is spherical or parabolic in most cases.Nevertheless,the previous research is lack of a more in-depth discussion on such situation,and the analysis of the oil-water separation performance of the mesh membrane with different micro-morphology have rarely discussed in the literature.Therefore,under the guidance of the basic theory of surface wettability and the theory of thermodynamics free energy,and based on the Cassie-Baxter model,this paper constructed two structural models,which one is the model of paraboloid that the top of mastoid morphology is camber,and the other is the model of frustum that the mastoid morphology is plane.The two models were compared and studied in this paper.At the same time,the hydrophobic lipophilic surfaces were prepared on the basis of copper mesh,and the two kinds of mesh membrane were characterized respectively.Moreover,the contact angle of each mesh membrane was predicted and verified.Finally,two kinds of mesh membranes were applied to the oil-water separation.The pressure-bearing capacity and oil-water separation efficiency of each mesh membrane were studied.In addition,the relationship between the contact angle of membrane surfaces and the oil-water separation efficiency were explored.The main conducted researches can be summarized as follows:(1)Two models were constructed to express the change of relationship between the contact angle and contact force,which one is the model of paraboloid that the top of mastoid morphology is camber,and the other is the model of frustum that the mastoid morphology is plane.The parameter K in the abbreviated formula of two models is related to the variables such as L0 and ?,and the value of parameter K affects the size of the actual contact angle directly.Under a fixed model,it has been found that a relatively larger K could increase the actual contact angle.According to the expression of K,reducing the angle of groove(?)canhelp to increase the value of K,which in turn increases the contact angle.When the unit size(L0)is less than 150?m,the two rough surfaces could get super-hydrophobic theoretically.When the contact angles are the same size,the unit size LP>LF,indicating that the model of paraboloid is more likely to maximize contact angle and achieve super-hydrophobic.Hence,the model of paraboloid has profound guiding significance for the construction of super-hydrophobic materials and the prediction of actual contact angle.(2)The hydrophobic-lipophilic surfaces were constructed with 200-mesh brass net as the substrate material.According to the characterization by fluorescence microscopy and SEM,it could be found that the copper mesh polished by sandpaper can form a rough structure which is similar to the shape of frustum when modified by stearic acid,and the copper mesh without polishing can form a rough structure which is similar to the shape of paraboloid when modified by stearic acid.When the oxidation corrosion time of H2O2 is 1min,it is much conductive to improve the hydrophobicity of the membrane surface,and increase the contact angle of water droplets on the surfaces of the mesh membrane.Through measuring the wettability of water droplets,machine oil and carbon tetrachloride on different membrane surfaces,it can be found that when the microstructure is paraboloid,the surface is more hydrophobic and the contact angle is bigger;as for hydrophobic grease,the affinity is larger and the contact angle is smaller.The above conclusions demonstrated that the structure of paraboloid is more favorable to gain the properties of super-hydrophobic and super-oleophilicity of materials than the structure of frustum.(3)The two models were used to predict the contact angle on the surfaces of the mesh membrane.Theoretical prediction suggested that the two rough surfaces could get super-hydrophobic when the unit size(L0)is less than 150?m.However,actual preparation process found that when the micro-structure is in the shape of paraboloid and the unit size(L0)is 32?m,the measured contact angle is 153.6° while the predicted contact angle is 152°,so the measured value and the theoretical value have all reached the super-hydrophobic state;when the micro-structure is in the shape of frustum and the unit size(L0)is 45?m,the contact angle cannot be predicted with the formula of the model cause the system did not reach a steady state,and the measured contact angle is 121.8° which did not reach the super-hydrophobic state.Therefore,the system of paraboloid is more stable than the system offrustum,and the contact angle can be more accurately predicted by the paraboloid model.(4)For two different kinds of oil-water separation membranes,the separation efficiency of the mixture with carbon tetrachloride,benzene,machine oil,edible oil and deionized water was studied respectively,and the pressure-bearing experiment of the two membranes was carried out separately.The results revealed that the surface structure of paraboloid has a superior pressure-bearing performance compared to the structure of frustum.For the same kind of oil,when the membrane is in the rough shape of paraboloid,the separation efficiency of oil-water mixture is better than the the rough shape of frustum.This may be due to the contact angle of oil droplets is smaller when the micro-structure is paraboloid,which can be concluded that the smaller the contact angle of oil droplets on the mesh membrane surfaces,the higher the efficiency of oil-water separation,and the structure of paraboloid is more advantageous to improving the efficiency of oil-water separation than the rough shape of frustum.Moreover,the study found that in the process of oil-water separation,the separation efficiency of different kinds of oil-water mixtures is also affected by parameters such as coefficient of viscosity.For the same membrane,in terms of oil-water separation efficiency,benzene is the highest,followed by carbon tetrachloride,edible oil and machine oil.