Fabrication Of Superhydrophobic PLLA Materials With Controllable Adhesion And Their Application

The wetting property of liquid to solid is an important research topic,especially superhydrophobicity.Droplets are bead-like state on lotus surfaces,when lotus surface is slightly inclined,droplets will roll off naturally due to gravity;while droplets on rose surfaces can be firmly fixed in the opposite state.Inspired by the nature,we choose biodegradable poly(L-lactic acid)(PLLA)as substrate,and porous PLLA surfaces with micro/nano-scale structures can be successfully prepared by using non-solvent-induced phase separation(NIPS)technique,showing superhydrophobic property with controllable adhesion.In this work,the basic principle of NIPS is analyzed according to thier structural characterization and morphological observation,further building PLLA-solvent-non-solvent ternary phase diagram,and we also study their application in the fields of transferring micro-droplet array,self-cleaning,and oil-water separation.It is summarized as follows:(1)Study on superhydrophobic PLLA film with controllable adhesion and their application of high-through transferring microdroplet arrays on homozygous surfaces.By changing the content of non-solvent in the system,we can fabracate heirarchical PLLA micro/nano-scale structures.NIPS method with combination of peeled-off process is used to prepare the superhydrophobic surface with controllable adhesion.The contact angle values are more than 150~o,and adhesive force ranges from 62 to 144?N,the sliding angle changes from high to low one.For high adhesion,droplets are fully attached into the PLLA surfaces even the surfaces are inverted 180~o,while droplets can roll off at slope of 24~o for low adhesion.This can meet the need of low-surface-energy-free modification for superhydrophobic surfaces with controllable adhesion,which can be applied in transferring 1~10?L microdroplet arrays(>7×7).(2)Study on control of water-repelling performance on PLLA surfaces and its application of high-efficiency self-cleaning effect.Because different kinds of non-solvents have their own solubility parameters(?)and polarity(?),?and?can determine the compatibility between non-solvent and polymer,which influences the preparation of different micro/nano-scale structures in phase separation process.The superhydrophobic surface with lotus effect is prepared by changing the kinds of non-solvent(n-butyl alcohol,isobutanol,n-propanol,isopropanol,ethanol,methanol,etc).The self-cleaning experiment shows that both soluble and insoluble contaminants(salt particles or graphite)can be washed off completely on the surface,showing good self-cleaning effect.(3)Study on fabracation of PLLA cluster crystal structure and its application in oil-water separation.By regulating the number,content and proportion of non-solvent to PLLA solution,different PLLA microstructures can be prepared.For example,1-dimensional(1D)fibers appear for the first adding non-solvent,while the second adding non-solvent will generate 2D or 3D clusters.The cluster effect is significantly related to the ratio of two addition of non-solvent,and the cluster effect is more obvious when the second addition of non-solvent is more.Contact angle to water is up to 158~o,and sliding angle is only 4~o;while contact angle to oil is 0~o,and absorption is up to 21 times,showing excellent oil-water separation ability.The PLLA superhydrophobic materials prepared by non-solvent-induced micro-phase separation can not only avoid the environmental pollution due to the addition of low-surface-energy materials,but also have the characteristics of preparation-simple process and low cost.The superhydrophobic materials can be widely used in microfluidics,biomedicine,intelligent bionics and new energy fields.In addition,the preparation process proposed in this work can provide a new design idea for preparation of multi-dimensional materials,which will also have significantly potential application in new material preparation and structural innovation.