【作者】 李晓宇；

【导师】 雷明凯； 李昱鹏；

【作者基本信息】 大连理工大学 ， 材料表面工程， 2023， 博士

【摘要】 针对可见-近红外光热转换、光催化、传感等技术对自清洁光吸收表面的需求,具有优异动态超疏水和广谱减反复合性能的聚合物表面加工研究备受关注。本文采用射频氧等离子体无掩模和金属薄膜掩模刻蚀,结合八氟环丁烷（C₄F₈）等离子体聚合的加工工艺,在聚甲基丙烯酸甲酯（PMMA）表面制备了氟碳膜（CF_x）修饰的纳米织构,通过等离子体刻蚀和聚合工艺对织构形态、结构和成分影响研究,确定了等离子体刻蚀和聚合的工艺条件,探明纳米织构的抗润湿压提高疏水作用和阶梯折射率降低反射作用机理,实现了PMMA表面纳米织构化的疏水减反复合改性。等离子体刻蚀和聚合加工PMMA工艺,采用功率200 W,频率13.56 MHz容性耦合射频氧等离子体无掩模和Au薄膜掩模刻蚀,结合C₄F₈等离子体聚合。无掩模刻蚀/聚合时间分别为5-30 min/1 min和10 min/5-30 min,两种厚度5 nm和10 nm的Au薄膜掩模刻蚀/聚合时间分别为5-30 min/1 min和20-50 min/1 min。利用SEM和XPS表征纳米织构形态、结构和成分,无掩模刻蚀5-30 min/聚合1 min加工获得的是纳米线束,线束宽度和间距分别为0.6-1.0mm和1.0-3.8mm,高度为1.6-4.8mm,线束内线间距为200-500 nm,刻蚀的纳米线束经短时等离子体聚合后形态和结构不变,聚合的CF_x膜由x=1、2、3的CF、CF₂、CF₃官能团构成。无掩模刻蚀10 min/聚合5-30 min加工获得的则是纳米锥,宽度和间距为0.6-1.5mm和0.8-0.9mm,高度为1.5-0.5mm,纳米锥间距与刻蚀的纳米线束间距相近且不随聚合时间变化,纳米锥表面的CF_x膜与纳米线束的CF_x膜官能团类型相同,但CF₂、CF₃含量增加。Au薄膜掩模刻蚀/聚合加工获得的均是线束变宽和间距增大、且线间距变窄的纳米线束,薄Au掩模刻蚀5-30 min/聚合1 min的线束宽度和间距为0.9-1.2mm和2.0-3.5mm,高度为1.8-4.5mm,线束内线间距减小至150nm,厚Au掩模需要更长刻蚀时间才能形成纳米线束,刻蚀20-50 min/聚合1 min的线束宽度和间距分别进一步增至2.2-3.8mm和4.3-5.5mm,高度2.8-6.7mm,长时间刻蚀的线束内线间距则都减小至50 nm,表面的CF_x官能团与无掩模刻蚀/聚合的纳米线束表面均相近,且不随Au薄膜掩模厚度变化。无掩模刻蚀加工过程中,源于真空工作室器壁的金属溅射粒子随机沉积在PMMA表面,对等离子体刻蚀起到机械阻挡作用,导致具有200-500 nm线束内线间距的纳米线束形成。Au薄膜掩模在等离子体刻蚀加工过程中具有相似的阻挡作用,导致50-150nm窄线间距的纳米线束形成,体现出更为有效的纳米织构调控能力。等离子体聚合加工过程中,纳米线束向纳米锥转变,归因于CF_x膜在纳米线束间横向沉积较在纳米线束表面具有更强的竞争效果。等离子体刻蚀和聚合加工PMMA表面的水滴静态接触角均大于150°,滚动角均小于10°。利用高速摄像机拍摄PMMA表面的水滴撞击过程,无掩模刻蚀/聚合加工获得的纳米线束表面水滴无法发生完全回弹的临界撞击速度为0.8-1.8m/s,纳米锥表面的临界撞击速度为1.7-1.9 m/s,Au薄膜掩模刻蚀/聚合加工获得的150 nm窄线间距纳米线束表面的临界撞击速度则可达3.9-4.5 m/s,50 nm窄线间距纳米线束表面的临界撞击速度大于4.5 m/s。纳米线束的线束内线间距和纳米锥的间距减小导致PMMA表面的抗润湿压高于水滴的润湿压,抑制了撞击过程中水滴在纳米织构上的浸润作用,促进水滴发生完全回弹。利用可见-近红外（Vis-NIR）光谱分析波长400-2000 nm的光在不同入射角和偏振方向下的PMMA表面反射率,无掩模刻蚀/聚合加工获得的纳米线束表面的反射率为0.3-4.9%,纳米锥表面的反射率为0.5-3.8%,Au薄膜掩模刻蚀/聚合加工获得的150 nm窄线间距纳米线束表面的反射率小于1.0%,50 nm窄线间距纳米线束表面的反射率小于0.5%。等离子体刻蚀和聚合加工PMMA表面的折射率从织构顶部到底部呈阶梯式降低,导致表面反射率减小。纳米线束的高度增加促进了光的吸收,也引起表面反射率减小。射频氧等离子体Au薄膜掩模刻蚀和聚合加工PMMA工艺中,Au薄膜的掩模作用可实现纳米线束内线间距的调节,等离子体刻蚀时间增加有利于纳米线束高度和宽度增大。采用厚度10 nm的Au薄膜掩模,刻蚀30-50 min/聚合1 min加工获得纳米线束的线束内线间距为50 nm,宽度和间距分别为2.2-2.4mm和4.5-5.5mm,高度为4.7-6.7mm。水滴静态接触角为157-158°,滚动角为0.9-4.3°,水滴的临界撞击速度大于4.5 m/s,Vis-NIR光反射率小于0.5%。窄线间距纳米线束的高抗润湿压抑制了水滴撞击在纳米织构间的浸润作用,导致PMMA表面水滴临界撞击速度增加,从纳米织构底部到顶部的梯度折射率降低了不同入射角和偏振方向的Vis-NIR光的反射率。更多还原

【Abstract】 The surfaces with self-cleaning and light-absorbing properties in visible-near-infrared（Vis-NIR）regions are necessary for photothermal conversion,photocatalysis,sensing,and other technologies.The modified methods of polymer surfaces with excellent dynamic superhydrophobicity and broad-spectrum antirelfection properties have attracted much attention.In this study,the poly（methyl methacrylate）（PMMA）surfaces with nanotextures and fluorocarbon（CF_x）film were prepared by using RF oxygen plasma etching with non-mask and metal film mask combined with octafluorocyclobutane（C₄F₈）plasma polymerization as a process technology.The effect of plasma etching and polymerization processes on the morphology,structure and chemical composition of nanotextures was studied.The process conditions for plasma etching and plasma polymerization were determined.The mechanisms of enhancing hydrophobicity due to high dewetting pressure and reducing reflectance due to gradient of refractive index of nanotextures were found.The combined modification of antiwetting and antireflection on the nanotextured PMMA surfaces was achieved.Plasma etching and polymerization processes using capacitively coupled oxygen plasma etching with non-mask and Au thin film mask combined with C₄F₈ plasma polymerization under plasma power of 200 W and radio frequency（RF）of 13.56 MHz were used to modify the PMMA surfaces.The duration time of etching/polymerization was selected in 5-30 min/1min and 10 min/5-30 min for maskless process.The duration time of etching/polymerization was 5-30 min/1 min and 20-50 min/1 min was selected for Au film mask process with thicknesses of 5 nm and 10 nm,respectively.The morphology,structure and chemical composition of the nanotextures were characterized by SEM and XPS.The bundles of nanowires were obtained under the plasma maskless etching for 5-30 min and plasma polymerization for 1 min.The width and spacing of bundles of nanowires was 0.6-1.0μm and1.0-3.8μm,respectively,and the height was1.6-4.8μm.The distance between nanowires in a bundle was 200-500 nm.The morphology and structure of bundles of nanowires achieved by plasma etching were unchanged under the following plasma polymerization in short time.And the CF_x film under plasma polymerization consisted of CF,CF₂,and CF₃ functional groups.Plasma maskless etching for 10 min and then plasma polymerization for 5-30 min resulted in the formation of nanocones with width of 0.6-1.5μm,ditance of 0.8-0.9μm and height of 1.5-0.5μm.The ditance between nanocones was similar to the bundles of nanowires under plasma etching,which did not vary with the polymerization duration time.The type of functional groups in CF_x film on the surfaces of nanocones were similar to the CF_x film on the bundles of nanowires.And the increased contents of CF₂ and CF₃ are found on the surfaces of nanocones.The plasma etching with Au thin film mask and then plasma polymerization resulted in the formation of bundles of nanowires with widened bundles,increased spacing and narrowed nanowire distance.The width and spacing of bundles under plasma etching with thin Au mask for 5-30 min and plasma polymerization for 1 min was 0.9-1.2μm and 2.0-3.5μm,repectively.The height of bundles was 1.8-4.5μm and the nanowire distance in a bundle was reduced to150 nm.The longer time of plasma etching with thick Au mask was required to fabricate the bundles of nanowires.The width and spacing of bundles under plasma etching for 20-50 min and plasma polymerization for 1 min further increased to 2.2-3.8μm and 4.3-5.5μm,respectively.The height of 2.8-6.7μm and the low nanowire distance of 50 nm is obtained under plasma etching for long duration time.The CF_x functional groups on the surfaces were similar to those on the surfaces with bundles of nanowires under plasma maskless etched and polymerization processes,and were nondependent on the thickness of Au film mask.During the plasma maskless etching processes,the metal nanoparticles sputtered from the reactor wall and electrode were randomly deposited on the PMMA surfaces,which acted as a mechanical barriers to plasma etching,leading to the formation of bundles of nanowires with the distance of 200-500 nm between nanowires.The Au thin film masks preserving the similar mechanical barriers during plasma etching resulted in the formation of bundles of nanowires with narrower distance of 50-150 nm between nanowires.The plasma etching with Au thin film masks showed the flexible control of nanotexture structure.The transferring from bundles of nanowires to nanocones during the plasma polymerization was attributed to the more competitive growth of CF_x films along horizon direction between bundles of nanowires than those on the top surfaces of bundles of nanowires.The static contact angles of water droplets on the PMMA surfaces under plasma etching and plasma polymerization were larger than 150°,and the roll angles were less than 10°.A high speed camera was used to observe the water droplet impacting behaviors on the PMMA surfaces.The critical impacting speed of water droplets showing the partial rebound is 0.8-1.8 m/s on the surfaces with bundles of nanowires under plasma maskless etching and plasma polymerization.The surfaces with nanocones showed is the critical impacting speed of 1.7-1.9 m/s.The critical impacting speed of water droplets on the surfaces with bundles of nanowires in the narrow distance of 150 nm between nanowires under plasma etching with Au film mask and plasma polymerization reached 3.9-4.5 m/s.The critical impact velocity on the surfaces with bundles of nanowires in the narrow distance of 50 nm between nanowires was larger than 4.5 m/s.The reduced distance between nanowires in the bundles of nanowires and spacing between nanocones resulted in higher dewetting pressure on the PMMA surfaces than wetting pressure of water droplets,which inhibited the infiltration effect of water droplets into the nanotextures during the impacting processes.It was beneficial to the complete rebound of water droplets on the surfaces.The visible-near-infrared（Vis-NIR）spectroscopy was used to detect the reflectance of the light in the wavelength reagion of 400-2000 nm at the different angles of incidence and polarization directions on the PMMA surfaces.The reflectance is 0.3-4.9%on the surfaces with bundles of nanowires under plasma maskless etching and plasma polymerization.The surfaces with nanocones showed the reflectance of 0.5-3.8%.The surfaces with bundles of nanowires in the narrow distance of 150 nm between nanowires under plasma etching with Au film mask and plasma polymerization were less than 1.0%.The reflectance on the surfaces with bundles of nanowires in the narrow distance of 50 nm between nanowires were less than 0.5%.The refractive index on the PMMA surfaces under plasma etching and plasma polymerization decreased gradually from the top to the bottom of nanotextures,resulting in a reduce of reflectance in the Vis-NIR wavelength region.The increased height of the bundles of nanowires promoted the light absorption to arouse the decreased reflectance.In the modification of PMMA surfaces under the plasma etching with Au film mask and plasma polymerisation,the distance between nanowires in bundles of nanowires was tuned due to the mask effect of Au thin film.The increased duration time of the plasma etching resuled in the increase of height and width of bundles of nanowires.The plasma etching with Au thin film mask in thickness of 10 nm for 30-50 min and plasma polymerization for 1 min were utilized to fabricate bundles of nanowires with narrow distance of 50 nm between nanowires,width of2.2-2.4μm,and spacings of 4.5-5.5μm and height of 4.7-6.7μm.The static contact angle of water droplets was 157-158°.The roll angle was 0.9-4.3°.The critical impacting speed was more than 4.5 m/s.The reflectance in Vis-NIR regions was less than 0.5%.The high dewetting pressure in bundles of nanowires with narrow distance between nanowires inhibited the infiltration of liquid into the spacing between the nanotextures,resulting in an increase in the critical impact velocity of water droplets on the PMMA surfaces.The gradient refractive index from the bottom to the top of the nanotextures decreaseed the reflectance of Vis-NIR light with different incidence angles and polarization directions.更多还原