| Superhydrophobic membrane,due to its surface super anti-wettability,recently has played a unique role in self-cleaning surface,micro fluid system,membrane distillation,oil/water separation and other special separation processes.Compared with other strategies to fabricating superhydrophobic membrane,phase separation method shows outstanding advantages including simple steps,low cost,moderate operating conditions and large-scale producing.This thesis fabricates various superhydrophobic Poly(lactic acid)(PLA)membranes via making full use of its crystalline properties and by virtue of effects of various additives on the crystallization behavior and morphology evolution.The detailed results are summarized as follows:(1)By increasing the crystallinity of PLA,resulted membranes were enabled with mulstiscale microstructures.The crystallinity of PLA membrane could be greatly improved by non-equivalently mixing PLLA and PDLA and as a result plenty of microspheres were formed when PLLA/PDLA stereocomplex crystals precipitated from uniform solution.The morphology was analogous to the microstructure of rose petals,which were covered with numerous microspheres and nano-scale folds on the top of every microsphere.This rough surface enables PLA membrane surface with quasi surperhydrophobicity and high adhesion force to water droplets.Further,the diameter and densiy could be regulated by controlling the thickness of primary membrane and the adhesive force was between 132 ?N~74 ?N.(2)Effects of in situ polymerization of fluorinated olefin on the morphology and superhydrophobicity were investigated.Results showed that in situ polymerized Perfluoro-1-decene(PFD)has involved in the phase separation procedure of PLLA/PDLA stereocomplex system broughting about suppresive effect on both homo-crystallinity and stereocomplex crystallinity,which resulting in the microstrure on bottom surface envolving from bud-like spheres to blooming state.The porosity,specific surface area,average roughness,contact angle,rolling angle and surface adhesion force would be tunable with the variation of PFD contents.The obtained superhydrophobic PLA membrane with low adhesion can be used for controlled release of oil-soluble drugs.(3)In order to further understand the function of additives on morphology and crystallization behavior of PLLA/PDLA membrane,a series of multi-armed star-shaped PLA macromolecules were synthesized by the ring-opening reaction of lactide monomers using polyhydric alcohols as initiator and then blended with PLLA/PDLA stereocomplex system.Results showed that the stereocomplex crystallinity would be inhibited while the ?-form crystallinity would be enchanced.The crystal lamellar of ?-form stacked with sheet structure near the membrane bottom.The connect stability between stacked crystalline lamellar and support layer was very poor resulting the easily wiping off of bottom layer.Therefore,finger-like pores in support layer were exposed to forming cavities on surface which supply air pocket for superhydrophobicity.(4)In order to fabricate superhydrophobic membrane using single PLLA component,the non-solvent isopropanol(IPA)was used as additives.Before inmmersed into coagulation bath,the phase equilibrium of PLLA uniform solution was broken by the volatilization of IPA.Partial PLLA chains precipitated to form crystal nucleuses promoting the crystalline behavior of PLLA.After solidification,the bottom surface was covered with microspheres with plenty of branch-like fibers on the top of microspheres,which was analogous to the microstructure of sea urchin.Final PLLA membrane exhibited self-cleaning property with superhydrophobicity and ultralow adhesion force.This thesis puts forward a series of new methods for preparing superhydrophobic PLA membranes and a further understanding on how to achieve the tunability of microstructures and adhesion force when phase separation method is adopted. |
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