非溶剂诱导聚苯乙烯超薄膜去润湿过程中不同有序表面形貌的形成

利用原子力显微镜研究了带有自然氧化层硅基底上聚苯乙烯薄膜在不同非溶剂诱导下的去润湿过程.研究发现,非溶剂是通过渗透取代机理诱导高分子薄膜发生去润湿.薄膜的形貌取决于成孔过程与孔增长过程的相对速度.当聚苯乙烯(PS)薄膜厚度为15 nm时,随着溶剂烷基链的增长,成孔数显著降低;然而孔开始合并时孔径明显地增加.当PS薄膜厚度增加到25 nm时,随着溶剂烷基链的增长,成孔数略有降低,薄膜形貌形成长程有序的双连续的结构.当PS膜厚为35 nm时,与其它2个膜厚相比,成孔数大幅下降.此外,温度和分子量能进一步降低去润湿过程中的成孔数,从而形成分形结构形貌.     

高分子量聚合物对溶剂诱导低分子量聚合物薄膜去润湿动力学的影响

采用偏光显微镜及椭偏仪等研究了单分散低分子量聚苯乙烯(PS)薄膜、 单分散高分子量PS薄膜以及将二者按不同质量比共混制备的PS薄膜, 在室温下用丙酮溶剂诱导其去润湿的过程. 实验发现, 按不同质量比共混的PS薄膜的去润湿动力学与单分散的PS薄膜去润湿动力学有较大区别. 按不同质量比共混的PS薄膜, 低分子量的PS更易于富集在薄膜的表面, 其去润湿的速度介于单分散低分子量PS薄膜与单分散高分子量PS薄膜的去润湿速度之间. 但共混薄膜的去润湿速率并非随着高分子量PS的加入呈现单调的变化, 这是由大量接触分子的形成抑制了去润湿所致.     

高分子薄膜去润湿孔增长动力学

高分子薄膜去润湿是近年国内外表界面研究领域的热点.孔增长动力学作为高分子薄膜去润湿动力学的重要组成部分,对其进行深入研究,不仅可以促进人们对高分子薄膜去润湿过程的理解,而且可为高分子表界面图案化设计提供理论依据.近年来,有关去润湿孔增长动力学的理论、实验和计算机模拟工作很多,并且取得了较大的进展.本文综述了这一领域最为重要的研究工作,分析了理论预言与现有实验结果偏离的原因以及由此而呈现的重要问题,并对这一领域的研究方向进行了展望.     

H型(PS)2PEG(PS)2嵌段共聚物在旋涂过程中的结晶行为

采用原子力显微镜和X射线衍射等手段研究了H型(PS)₂PEG(PS)2嵌段共聚物在不同溶剂和不同浓度的溶液中旋涂所得薄膜的形貌, 并与聚乙二醇(PEG)均聚物进行了比较. 虽然(PS)₂PEG(PS)₂中PS的链长很短, 但对形貌有很大影响, PS链段的存在改变了聚合物在基底上的稳定性, 使用四氢呋喃为溶剂, 当溶液浓度较小时, 在旋涂过程中发生去润湿, 然后再发生结晶, 膜厚较大时去润湿被抑止, 所得形貌与PEG均聚物类似. 以甲苯为溶剂时, 由于PEG和PS与溶剂的相互作用不同, 共聚物在溶液中形成胶束, 从而改变了聚合物的结晶形貌.     

利用薄膜去润湿行为研究线形和环形聚苯乙烯及共混薄膜的黏度

研究了线形聚苯乙烯(LPS)薄膜,环形聚苯乙烯(RPS)薄膜以及不同配比的共混薄膜在聚二甲基硅氧烷(PDMS)高分子刷上的去润湿动力学行为.研究发现,LPS薄膜的去润湿速度要快于RPS薄膜的去润湿速度,共混薄膜的去润湿速度介于LPS薄膜和RPS薄膜之间,且共混薄膜的去润湿速度随着RPS在共混薄膜中含量的增加而降低.利用水和乙二醇在薄膜表面的接触角计算得到LPS薄膜,RPS薄膜及共混薄膜的表面张力.结果发现,共混薄膜的表面张力均小于LPS薄膜和RPS薄膜的表面张力,且当RPS含量为70%时,共混薄膜的表面张力达到最小值.通过对薄膜在去润湿过程中的孔半径、去润湿速度、边宽以及后退接触角的研究,获得了LPS薄膜、RPS薄膜及共混薄膜的黏度.结果表明,LPS薄膜的黏度要低于RPS薄膜的黏度,实验得到的不同比例共混薄膜的黏度介于LPS薄膜和RPS薄膜的黏度之间,且其低于LPS和RPS的质量权重平均值.     

结晶和去润湿竞争条件下分子结构对超薄膜表面形貌的影响

将星形支化结构的聚己内酯, 包括六臂星形聚己内酯(HPCL)和树枝状星形聚己内酯(DPCL), 以及线形聚己内酯(LPCL)室温旋涂于云母片上,通过原子力显微镜(AFM)观察分子结构对星形支化聚己内酯超薄膜的润湿-去润湿性质的影响. 在旋涂过程中, 薄膜的形成受去润湿和结晶竞争的控制. 差示扫描量热(DSC)测试结果表明, 当相对分子质量相同时, 结晶性的顺序是: DPCL最弱, HPCL次弱, LPCL最强. 依据分子结构和相对分子质量的影响, 即去润湿和结晶竞争的结果, LPCL、HPCL和DPCL的超薄膜表现出不同的表面形态, 包括尺寸不同的完整的球晶、开口的球晶、树枝状片、分散的颗粒.     

丙酮光解反应CH_3COCH_32CH_3 CO产物CO振动态分布的理论研究

用从头算方法 ,在UHF/6 311G 水平上 ,对丙酮光解反应进行了研究 ,结果表明 :基态丙酮 (S0 )不易发生解离 ;在光照下丙酮电子产生n→Π 跃迁 ,丙酮在激发态 (T1)下易发生解离 ,即CH3 COCH3 (T1) hν CH3 CH3 CO(R1) ,乙酰基可以进一步发生热解反应 ,即 :CH3 CO→CH3 CO(R2 ) .对R2 进一步获得了该反应的动态学信息(ωK,BKF,V0 (S) ) ,并据此计算了产物CO的振动态分布 ,获得了和实验值相一致的结果     

丙酮光解反应CH3COCH3hv→2CH3+CO产物CO振动态分布的理论研究

用从头算方法,在UHF/6-311G**水平上,对丙酮光解反应进行了研究,结果表明:基态丙酮(S0)不易发生解离;在光照下丙酮电子产生n→Π*跃迁,丙酮在激发态(T1)下易发生解离,即CH3COCH3(T1)→hvCH3+CH3CO(R1),乙酰基可以进一步发生热解反应,即:CH3CO→CH3+CO(R2). 对R2进一步获得了该反应的动态学信息(ωK,BKF,V0(S)),并据此计算了产物CO的振动态分布,获得了和实验值相一致的结果.     

聚甲基丙烯酸甲酯/聚醋酸乙烯酯共混相分离过程的标度行为与逾渗结构

本文用激光光散射和光学显微镜方法研究了聚甲基丙烯酸甲酯/聚醋酸乙烯酯共混体系不稳相分离过程最大散射强度I_m(t,T)和相应波矢q_m(t,T)随时间变化规律及相区的逾渗结构.实验结果表明:I_m(T,t)和q_m(t,T)与时间t满足简单的标度关系I_m(t,T)～t~β,q_m(t,T)～t~(-α),且标度关系β=3α成立.揭示了相态结构的分维特征.给出了计算相态结构分维数的简便方法,其分维数D值约为1.64±0.03.与逾渗模型给出的D值接近.     

多层碳纳米球的研究

用弧光放电法制备了碳的巴基葱.用原子力显微镜（AFM）、扫描隧道显微镜（STM）和透射电镜（TEM）研究了在高定向石墨(HOPG)和金(Au)基底上的巴基葱的行为和电学特性.扫描隧道谱表明,巴基葱的电学特性具有与单壁碳纳米管相似的非线性特性.较小尺寸的巴基葱呈半导体特性,尺寸增大倾向金属线性.AFM/STM图像显示,在HOPG和Au基底上的巴基葱能够聚集成二聚体.利用较小尺寸巴基葱的电学非线性特性,有希望构造纳米电子学的单电子器件.     

Multiscale dewetting of triblock copolymer thin film induced by solvent vapor

Multiscale dewetting of poly(styrene‐b‐ethylene/butylenes‐b‐styrene) (SEBS) triblock copolymer thin films induced by volatile solvent vapor treatment were observed in this study. Film rupture occurred at first and produced macroscopic holes. Near‐regular droplets (which represented a compromise between complete disorder and perfect order) could be formed at the last stage. The mechanism of solvent‐driven dewetting was discussed by comparing with that of thermal‐induced dewetting. Similar to thermal‐induced dewetting, the block copolymer thin films initially break up through the nucleation of holes that perforated the films. The rapid growing holes became unstable and formed nonequilibrium fingering patterns. The films exhibit autophobic or autodewetting phenomena. The velocity of the holes growth was nearly a constant (3.3 μm/min). The stages of the dewetting were quite similar to that found for homopolymer and block copolymer thin films dewetting on solid or liquid substrates under thermal treatment. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2874–2884, 2005     

The dewetting dynamics of the polymer thin film by solvent annealing

The slippage effect of the polymer chains is investigated in the dewetting process of the polymer solution film. The solvent-induced dewetting is used in our experiments to study the dynamics of hole growth in the dewetting process of the polymer solution film. Our results show that in the case of the low molecular weight polystyrene (PS) film, the slippage effect of the polymer chains is not displayed and the radius of the holes is R approximately exp(t/tau); in the case of the higher molecular weight PS film, the slippage effect of the polymer chain is not valid in the case of the thin film and that is valid in the case of the thick film, and the dynamic process of hole growth divides into three stages (R approximately t, and then R approximately t(x) (23相似文献   

Dewetting Behavior of Hydrogen Bonded Polymer Complex Film under Hydrothermal Condition

Hydrogen-bonded polymer complex films with the thickness ranging from 50 nm to 2400 nm were prepared by layer-by-layer (LbL) assembly of poly(2-ethyl-2-oxazoline) (PEOX) and poly(acrylic acid) (PAA). The dewetting behavior of PEOX/PAA films under hydrothermal condition was investigated. It was found that the dewetting occurred at solid-liquid interface, and the typical morphologies such as holes, irregular cellular structure, and droplets were observed. Atomic force microscopy (AFM) revealed the initial rupture of the film. Microscopic Raman and infrared (IR) imaging demonstrated that the PEOX and PAA chains remained association during the dewetting process.     

Hole‐growth instability in the dewetting of evaporating polymer solution films

We investigate the dewetting of aqueous, evaporating polymer [poly(acrylic acid)] solutions cast on glassy hydrophobic (polystyrene) substrates. As in ordinary dewetting, the evaporating films initially break up through the nucleation of holes that perforate the film, but the rapidly growing holes become unstable and form nonequilibrium patterns resembling fingering patterns that arise when injecting air into a liquid between two closely spaced plates (Hele–Shaw patterns). This is natural because the formation of holes in thin films is similar to air injection into a polymer film where the thermodynamic driving force of dewetting is the analogue of the applied pressure in the flow measurement. The patterns formed in the rapidly dewetting and evaporating polymer films become frozen into a stable glassy state after most of the solvent (water) has evaporated, leaving stationary patterns that can be examined by atomic force microscopy and optical microscopy. Similar patterns have been observed in water films evaporating from mica substrates, block copolymer films, and modest hole fingering has also been found in the dewetting of dry polymer films. From these varied observations, we expect this dewetting‐induced fingering instability to occur generally when the dewetting rate and film viscosity are sufficiently large. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2825–2832, 2002     

Dynamic instability of a sol-gel-derived thin film

We present a study on the dynamic instability of a sol-gel-derived (SG) thin film on a nonwettable substrate. Because of the structural instability accompanied by syneresis stress in a film deposited on the substrate, there exists a regular distribution of dewetting patterns required to relieve the in-plane stress, such as holes in the earlier stages, and droplets accompanying a regular polygonal distribution in the later stages of the dynamic instability. The characteristic length scales in each stage scaled linearly with the film thickness during the duration of dewetting. For the formation of holes during the earlier stages of rupture of the film, the dewetting velocity was analyzed with a viscous sintering theory of a SG thin film. In the earlier stages of the dynamic instability, the dewetting velocity decreases with increasing dewetting time and increases with increasing the initial film thickness, which indicates that the SG thin film behaves partially like a slipping polymer thin film. In the final times of the film rupture, the radius of the hole has a linear relationship with the film thickness, and the growth rate of the hole (dewetting velocity) is nearly constant, regardless of the film thickness. These dewetting behaviors indicate that the SG thin film in the final times of the rupture is somewhat similar to nonslipping film. From these observations, we found that the dewetting behavior of a SG thin film has ambivalent dewetting characteristics of slipping and nonslipping films and that a SG thin film is not a purely viscous film.     

Tunable instability mechanisms of polymer thin films by molecular self-assembly

Incorporation of a block copolymer into a thin polymer film is observed to alter both the rate and mechanism by which the film dewets from an immiscible polymer substrate. Films with little or no copolymer dewet by classical nucleation and growth of circular holes, and the dewetting rate decreases with increasing copolymer concentration. Increasing the copolymer content at constant film thickness generates copolymer micelles that adsorb/aggregate along the polymer/polymer interface and promote nonclassical dewetting fluctuations similar in appearance to spinodal dewetting. At higher copolymer concentrations, dewetting proceeds after a lengthy induction period by the nucleation and growth of flower-shaped holes suggestive of film pinning or viscous fingering. Atomic force microscopy of the polymer/polymer interface after removal of the top film by selective dissolution reveals substantial structural development due to copolymer self-assembly.     

Fabrication of polymersomes with controllable morphologies through dewetting w/o/w double emulsion droplets

In this work, monodisperse giant polymersomes are fabricated by dewetting of water-in-oil-in-water double emulsion droplets which are assembled by amphiphilic block copolymer molecules in a microfluidic device. The dewetting process can be tuned by solvation between solvent and amphiphilic block copolymer to get polymersomes with controllable morphology. Good solvent(chloroform and toluene) hinders dewetting process of double emulsion droplets and gets acornlike polymersomes or patched polymersomes. On the other hand, poor solvent(hexane) accelerates the dewetting process and achieves complete separation of inner water phase from oil phase to form complete bilayer polymersomes. In addition, twin polymersomes with bilayer membrane structure are formed by this facile method. The formation mechanism for different polymersomes is discussed in detail.     

Solvent-driven dewetting and rim instability

An experimental method suitable for reproducible results has been used to investigate dewetting behavior of thin films of solvent-laden polymer. This solvent-driven dewetting enables one to change spreading coefficient by an order of magnitude that is not readily realizable in thermal dewetting and to study polar interactions that have not been fully exploited experimentally. While the film instability is similar to that found in thermal dewetting, the rim instability is quite different. Two different types of the rim instability have been found. With a polar solvent, the rim instability changes from one type to another with increasing film thickness whereas the unstable rim becomes stable for an apolar solvent.     

Reversibility of pH-induced dewetting of poly(vinyl pyridine) thin films on silicon oxide substrate

Thin PVP films deposited on a silicon oxide surface have been found to form a dewetting pattern when treated with basic solutions (pH > or = 10). We studied the dependence of pattern morphology on the polymer's molecular weight and thickness of the polymer layer, and observed the formation of three distinctive structures. The structure formed by large drops of polymer is characteristic of a polymer with low molecular weight and the thinnest polymer layer, whereas other samples form holes or a weblike pattern upon dewetting. These experiments have demonstrated for the first time the reversibility of the dewetting process in a liquid environment. The polymer layer has revealed reversible behavior toward flat film when exposed to a pH 4 buffer solution. More complex structures can be obtained by consecutive treatments with acidic (pH 4) and basic (pH 10) solutions. We used atomic force microscopy (AFM) to study both the morphology and elastic properties of polymers in media with different acidity, in order to determine the mechanism behind the dewetting process.