Fabrication And Wettability Responsive Control Of Superwetting Surface Based On Shape Memory Epoxy Resin

Surfaces with smart control of wettability can response to various stimulus,which is important in controlled drug release,microfluidic transport and droplet lossless transfer,and so on.As is well known,wettability is controlled by surface chemistry and surface microstructure.Up to now,the research on controlling surface chemistry is focused on the stimulus molecule.However,the responsive materials are usually grafted on the fixed surface,which only has a single surface microstructure,leading to the result that it’s hard to realize the fine regulation of wettability.In recent years,more and more researches have studied the wettability control by adjusting surface microstructure.Especially,smart wettability on shape memory polymer surface has drawn the most attention.As we know,most work in this area is focused on the wettability control with narrow range in air.However,there is few work about the dynamic wettability adjusting and wettability control in complex media(such as water).In this work,by utilizing epoxy-based shape memory polymer(ESMP),a series of smart surfaces with various infiltrative features were prepared via chemical modification and the design of microstructure.Furthermore,the surfaces obtained could be applied in the areas of droplet directional transportation,gradient wettabilities and lossless transportation of oil droplets,which are promising to make the wettability control more applicable.The contents are listed as follows in detail:Through template transfer method,surfaces with micro and micro/nano structures could be prepared.Then by hot-press method,various microgrooves appeared on the surfaces,which showed anisotropy wettabilities.When the width of microgroove was 260 μm,the surface would get the biggest anisotropy wettability,namely ΔCA ≈ 8°,ΔSA ≈ 9°.Based on the excellent shape memory effect,the microgrooves could be reversibly produced and wiped,leading to the smart switch of isotropy/anisotropy wettabilities of the surface.Mechanism analysis showed that anisotropy wettability came from the various energy barrier in directions of perpendicular and parallel to microgrooves.Besides,based on the anisotropy wettability,the as-prepared surface could be applied in the switch of controlling the droplet start and the platform for the rewritable droplet directional transportation.Furthermore,smart surfaces with features of superoleophobicity and low adhension underwater could be prepared by modifying the surface with(3-aminopropyl)triethoxysilane(APTES).In addition,the prepared samples kept great shape memory effect.By pressing/recovery experiment,the micropillars could be reversibly changed between collapsed and upright state.As a result,the variation of microstructure would make the wet contact model change between Cassie state and Wenzel state,leading to the invertible switch between high and low adhension.Finally,due to the convertible adhesion,surface obtained could be used to transport the droplets with lossless and storage the droplet reversibly.By atom transfer radical polymerization(ATRP),the ESMP surface with microstructure could be modified by using temperature-responsive poly(Nisopropylacrylamide)(PNIPAAm),and the smart surface with wettability controlled by adjusting testing temperature and pillars height.After the polymerization of PNIPAAm,the surface kept its original micromorphology,provided new nanostructure and maintained excellent shape memory effect.For PNIPAAm,when the testing temperature was higher than the lower critical solution temperature(LCST),the compact and collapsed conformation of PNIPAAm chains induced by intramolecular hydrogen bonding in PNIPAAm chains led to the low surface free energy and hydrophobicity;when the testing temperature was lower than LCST,the loosely coiled conformation of PNIPAAm chains and intermolecular hydrogen bonding with water molecules led to the high surface free energy and hydrophilicity.Furthermore,by coordinated regulating the pillars state and test temperature,the precise and reversible control of wettability between superhydrophilicity and superhydrophobicity could be realized.Finally,the surface displayed the application in the erasable platform for gradient wettability.Besides,the ESMP surface could be grafted by poly(2-(diisopropylamino)ethyl methacrylate(PDPAEMA)successfully via ATRP,achieving a new smart surface with wettability controlled by pH and pillars height.Similarly to the surface modified by PNIPAAm,surface modified by PDPAEMA kept unchanged microstructure,great shape memory effect of pillars and good pH-responsive ability of PDPAEMA.When an acid water droplet contacted the surface,the grafted PDPAEMA was protonated and showed the hydrophilicity;When a basic water droplet contacted the surface,the grafted PDPAEMA was deprotonated and the surface showed the hydrophobicity.Finally,by utilizing synergistic effect from adjusting pH and microarrays at the same time,the fine and reversible regulations of surface wettability from superhydrophilicity and superhydrophobicity,with the regulation accuracy was smaller than 15°,could be realized at room temperature.Contributing to the excellent wettability,the obtained surface could be used as platform with precise regulation of wettability.