苯乙烯—异戊二烯（或丁二烯）嵌段共聚物表面结构的形成及其影响因素

【作者】 赵玉荣；

【导师】 王新平；

【作者基本信息】 浙江理工大学 ， 高分子化学与物理， 2009， 硕士

【摘要】 聚合物的表面性能是由其表面结构决定的。要达到对聚合物表面结构进行设计与控制的目的,则必须对表面层分子的化学物理性质,表面层的聚集态结构及表面结构的形成等进行充分研究。苯乙烯-异戊二烯(或丁二烯)嵌段共聚物是热塑性弹性体,作为粘合剂和密封材料在日常生活中有广泛应用。由于它们各嵌段元素组成相同且技术手段的限制,目前有关它们表面化学组成的报道很少且已报道的有关它们表面化学组成的分析深度也大于几个分子层的水平。本论文利用具有准单分子层界面敏感性与获取丰富的界面分子结构信息及原位研究能力的和频振动光谱(SFG,sum Frequency Generation Vibrational Spectroscopy)技术为主要研究手段,结合其他表征手段研究成膜条件对苯乙烯-异戊二烯(或丁二烯)嵌段共聚物表面结构的形成的影响,并研究所形成的表面结构与固化过程、聚合物溶液性质之间的关系。得到以下结论:(1)成膜溶液浓度明显影响SB、SBS浇铸膜表面结构和性质。1% w/v浓度时,浇铸膜表面具有较高的PB含量,二嵌段SB浇铸膜表面基本为低表面能的PB段覆盖。随着浓度的增加,浇铸膜表面PS含量逐渐增加。浇铸成膜固化过程是从溶液无序到固态相对有序的自组装过程,最终形成的表面结构要受聚合物在溶液中聚集状态和链段活性的影响。低浓度时,聚合物链相对舒展,且甲苯溶剂分子在表面存在的时间较长,PB可能具有相对较高的迁移速率和较长的迁移时间,因而表面具有更高的PB富集度,甚至完全由PB段覆盖。(2)与浇铸成膜不同,苯乙烯/丁二烯嵌段共聚物旋涂膜表面存在高含量的PS且基本不受成膜溶液浓度的影响。旋涂成膜的过程是溶剂快速挥发的快速固化过程,不存在低表面能组分向表面的离析。甲苯蒸汽处理可使PB段向表面迁移,处理一定时间后旋涂膜和高浓度浇铸膜表面都能达到由一层纯的PB覆盖的结构。(3)研究链结构、成膜溶剂对苯乙烯/丁二烯嵌段共聚物表面结构形成的影响发现,二嵌段共聚物SB比三嵌段共聚物SBS有利于PB组分在表面富集。同时发现对于二嵌段共聚物SB只有在PB的选择性溶剂环己烷成膜时,其表面层化学结构才为是纯的PB组分。三嵌段共聚物SBS无论是PB的选择性溶剂环己烷还是PS的选择性溶剂甲苯成膜,三嵌段共聚物SBS的最表面层化学结构,都是由PB与PS组分共存。(4)利用轴称滴形分析法(ADSA-P,Axisymmetric Drop Shape Analysis-Profile)和原子力显微镜技术(AFM,Atomic Force Microscope)研究不同SIS膜表面水的前进接触角测量过程中三相线处stick-slip现象与表面粘弹性关系时发现,在一定的表面能范围内,stick-slip突变过程中水接触角的差值Δθ与膜表面F-D曲线逼近部分斜率呈线性关系。说明SIS膜表面的stick-slip现象主要是由于其表面的粘弹性引起的。更多还原

【Abstract】 Polymer surface properties depend critically upon the molecular structure at the polymer surface. Hence, to meet the challenge of designing and controlling the structure and properties of block copolymer surfaces at the molecular or nanoscale level, the relationship between the chemical structure of copolymer,film-formation methods surface structures of resulting films must be clearly understanded. Block copolymers composed of styrene and isoprene (butadiene) are thermoplastic elastomeric materials and they are widely used as adhesives and sealants. The chemical structures on these block copolymers surfaces remains largely unstudied and poorly understood because only few surface techniques are effective to probe such copolymer surface at the molecular level.In this paper, polystyrene/polyisoprene (polybutadiene) block copolymers surface structure and properties were investigated by contact angle measurement, surface tension measurements, atomic force microscopy (AFM) and sum frequency generation vibrational spectroscopy (SFG) which has unique ability to probe the molecular spectroscopy and molecular group orientation at submolecular level. The influence of film-forming methods and polymer solution properties on film surface structure formation was explored.It is found that very subtle variation in the polymer concentration of toluene solution can remarkably influence the surface structures of the cast films. At a copolymer concentration of 1% w/v, the PB segment in the polystyrene-block-polybutadiene(SB) diblock copolymer and polystyrene-block- polybutadiene-block-polystyrene(SBS) triblock copolymer were the most apt to segregate in the free surface region. Especially, the film of SB diblock copolymer was covered by pure PB segment. With increasing of the copolymer concentration, surface structures with more PS segment were visualized. During solution concentrating process, ordered microphase-separated surface structures were gradually formed and the final surface structure was affected by molecular association and the activity of polymer chains in the solution. At a relatively low copolymer concentration, the more stretched polymer chains and also the longer presented time of solvent molecular at solution surface give the polymer chain enough time and activity to segregate to the surface, resulting in a pure PB coverage on the surface.For spin-coated films, the PB content is lower on the surface, regardless of polymer concentration. Owe to the fast process for film formation, the evaporation process is too fast for PB component to segregate at the outmost surface. After annealing in toluene vapor, the surface was covered by pure PB, in order to minimize the surface energy.The surface structures of films casted from varing polystyrene/polybutadiene block copolymers solution were studied. The results showed that, the proportion of PB at the outmost surface of films is higher for SB solution cast films than that for SBS solution cast films. When the SB diblock copolymer was cast by cyclohexane solution, a PB-selective solvent, the resultant surface of SB was dominated by PB component. Cast by toluene solution, a good solvent of both PS and PB, but have a preferential affinity to PS, however, surface segregation of PB was restricted and the surface was composed of PS and PB. The SFG results showed that, both toluene and cyclohexane were used as solvents, PB coexist with PS at the outmost surface of SBS cast films.The relationship between the surface viscoelastic properties and the stick-slip of the three-phase line in measurement of dynamic contact angle with water on SIS copolymers was studied by axisymmetric drop shape analysis-profile (ADSA-P) and atomic force microscope (AFM). It is found that, in a certain surface energy range, the abrupt change of water contact angle (Δθ) in the stick-slip pattern has linear relationship with the slope of the contact region in the force curves. All of the evidence strongly suggests that stick-slip phenomenon on SIS films surface was caused by the surface viscoelasticity.更多还原