端基标记法研究受限体系PMMA扩散行为与基底效应的传递深度

发布时间：2018-08-31 16:19

【摘要】：聚合物薄膜材料因其性能卓越、用途广泛成为近年来纳米材料领域研究热点。当高分子薄膜厚度降低至与分子链相当尺度时,聚合物物理性质会偏离本体。分子链运动是决定聚合物纳米材料物理性能(例如热稳定性)的重要因素,研究受限聚合物薄膜的分子扩散行为可为纳米材料的加工设计以及性能调控提供理论指导。同时,高分子薄膜材料大多是附着在基底上使用,基底效应对薄膜分子运动行为造成显著影响。聚合物与基底的相互作用将导致薄膜黏度增大、玻璃化转变温度升高以及扩散系数降低。然而,迄今为止,基底界面如何影响整个聚合物薄膜分子运动行为的机理并不清楚。这一问题与基底界面效应的长程作用密切相关。直接研究基底界面对聚合物链扩散行为影响的传递深度对这一问题的解决具有重要意义。课题组发现氟功能化端基标记法是研究聚合物链松弛行为的有效途径。本文通过构筑上层为聚甲基丙烯酸甲酯(PMMA),下层为氟功能化端基标记PMMA(PMMA-ec-FMA)的双层薄膜,利用接触角(CA)以及X射线光电子能谱(XPS)监测下层氟化端基标记PMMA往上层膜表面的迁移过程,研究了聚合物薄膜分子链扩散动力学以及基底效应对分子链运动能力的影响深度。主要研究结果如下:(1)通过研究表面润湿性以及F/C的变化,可准确获得下层氟化标记PMMA(PMMA-ec-FMA)扩散至上层未标记PMMA表面所需时间(t*)。可根据Fickian方程计算PMMA-ec-FMA在上层膜中的扩散系数D。研究了上层膜厚度h对标记PMMA分子扩散行为影响,发现PMMA扩散系数与上层膜厚h存在依赖性。D随h的变化存在三个区间:i)当膜厚高于某一临界值(hup)时,D维持恒定,不随膜厚降低而变化;ii)当膜厚下降至临界厚度hup时,D开始随h降低而减小;iii)膜厚继续下降至另一临界厚度hlow时(hhlow),D达到另一恒定值。该研究表明聚合物薄膜分子运动能力随受限程度增加而减小。研究了下层标记PMMA分子量对两个临界厚度的影响。当上下两层分子量不同时,称为分子量非对称体系;当上下两层分子量相近时,称为分子量对称体系。比较两种双层膜结构,发现下临界厚度hlow不随分子量变化,基本维持为30 nm。上临界厚度hup/Rg(均方回转半径)随PMMA-ec-FMA分子量的变化趋势不同:分子量对称体系中的hup/Rg则维持恒定,表明薄膜受限对其分子链扩散行为影响程度与其分子链尺寸有密切关系。分子量非对称体系中的hup/Rg则随分子量的增加而逐渐减小,表明在该体系中除链尺寸外还存在其他的影响因素。(2)研究了分子量非对称体系中PMMA-ec-FMA的扩散系数与其分子量及温度的关系。发现PMMA-ec-FMA达到上临界平台的De与其分子量呈-0.58的幂次关系。同时,De随温度的升高逐渐增大,并得到活化能为49±3 kJ·mol-1。相较于本体中分子链的扩散,本论文测得的表观扩散系数比本体更大,与分子量的依赖性减弱且活化能偏低。原因可能是单端标记PMMA分子链受到氟化端基向上的牵引,而非整链的同步扩散。(3)基于双层膜的技术,通过固定上层膜厚,改变下层膜厚研究了基底效应在聚合物薄膜中的传递深度。通过双层膜表面物理化学性质随热处理而发生变化的临界时间(t*)来反映标记聚合物穿过上层膜迁移至表面所需的时间。降低下层膜厚h’,t*随之发生变化的临界厚度h*对应了基底可影响下层标记聚合物链运动能力的最远距离,即基底效应的传递深度。研究了不同基底表面性质对基底传递深度的影响。发现150℃时Si/SiOx与Si-H所产生的基底效应在PMMA(Mn=67 kg·mol-1)薄膜内的传递深度h*分别为69 nm与37 nm,在PS(Mn=43 kg·mol-1)薄膜中传递深度分别为27 nm与65 nm。说明基底效应的传递深度与基底表面性质密切相关。Si/SiOx与PMMA之间存在H键,相互作用强于Si-H;而Si-H与PS之间的相互作用强于Si/SiOx。表明聚合物/基底之间相互作用力强弱影响基底效应的传递深度。(4)研究了基底效应传递深度的分子量依赖性。发现Si/SiOx基底对PMMA的传递深度随着分子量的增加而逐渐增大,可归一化为9.5Rg。说明基底效应对薄膜动力学的影响具有分子链尺寸依赖性。基底效应通过分子链的缠结作用向上传递。进一步说明了分子量对聚合物运动行为存在重要作用。同时,研究了基底效应传递深度与温度的关系。发现基底效应传递的深度随温度的升高而降低,表明温度的升高减弱了基底效应对聚合物分子动力学的影响。由于基底效应抑制分子链的运动能力,而温度升高则活化了分子链的运动,二者相互竞争。因此升高温度会削弱基底效应对分子链运动能力的影响,进而减小基底效应的传递深度。
[Abstract]:Polymer film materials have been widely used in the field of nanomaterials in recent years because of their excellent properties. When the thickness of polymer film decreases to the same size as the molecular chain, the physical properties of polymer will deviate from the bulk. Molecular chain motion is an important factor determining the physical properties of polymer nanomaterials (such as thermal stability). Molecular diffusion behavior of polymer-confined thin films can provide theoretical guidance for the processing design and performance control of nano-materials. At the same time, polymer thin films are mostly used on the substrate, and the substrate effect has a significant impact on the molecular motion behavior of the films. However, so far, the mechanism of how the substrate interface affects the molecular motion behavior of the whole polymer film is not clear. This problem is closely related to the long-range effect of the substrate interface. The fluorinated end-group labeling method is an effective way to study the relaxation behavior of polymer chains. In this paper, the fluorinated end-group labeled PMMA (PMMA-ec-FMA) bilayer film was constructed by using contact angle (CA) and X-ray photoelectron spectroscopy (XPS). The migration process of PMMA labeled with fluorinated end groups from the lower layer to the upper layer was studied. The diffusion kinetics and the depth of influence of substrate effect on the mobility of molecular chains were studied. The diffusion coefficient D of PMMA-ec-FMA can be calculated from Fickian equation. The effect of the thickness h of the upper layer on the diffusion behavior of labeled PMMA molecules is studied. It is found that the diffusion coefficient of PMMA is dependent on the thickness h of the upper layer. There are three intervals of D with the change of h: i) when the film thickness is higher than a certain critical value (i). When the film thickness drops to the critical thickness hup, D begins to decrease with the decrease of h; when the film thickness drops to the critical thickness hup, D begins to decrease with the decrease of h; when the film thickness continues to drop to another critical thickness hlow (h hlow), D reaches another constant value. When the molecular weight of the upper and lower layers is different, it is called molecular weight asymmetry system; when the molecular weight of the upper and lower layers is similar, it is called molecular weight symmetry system. The change trend of the molecular weight of PMMA-ec-FMA is different: the hup/Rg in the molecular weight symmetric system keeps constant, which indicates that the influence of membrane confinement on the diffusion behavior of the molecular chain is closely related to the molecular size of the chain. (2) The relationship between the diffusion coefficient of PMMA-ec-FMA and its molecular weight and temperature in the asymmetric system was studied. It was found that the molecular weight of PMMA-ec-FMA reached the upper critical platform in a power relationship of - 0.58. At the same time, the activation energy of De increased gradually with the increase of temperature and the activation energy was 49 3 kJ 65 1. The apparent diffusion coefficients measured in this paper are larger than those in bulk, less dependent on molecular weight and lower activation energies. The reason may be that the single-ended labeled PMMA chains are pulled upward by the fluorinated end group rather than the whole chain synchronously diffused. (3) Based on the double-layer membrane technology, the thickness of the upper layer is fixed and the activation energy is lower. The transfer depth of substrate effect in polymer film was studied by changing the film thickness. The critical time (t *) of the surface physical and chemical properties of the bilayer film changing with heat treatment was used to reflect the time needed for the labeled polymer to migrate through the upper film to the surface. It is found that the transfer depths of Si/SiOx and Si-H in PMMA (Mn=67 kg.mol-1) films are 69 nm and 37 nm, respectively, and in PS (Mn=43.3 nm) at 150 C. The transfer depths of Si/SiOx and PMMA are 27 nm and 65 nm, respectively. It shows that the transfer depth of substrate effect is closely related to the substrate surface properties. There is H bond between Si/SiOx and PMMA, and the interaction between Si-H and PS is stronger than that between Si/SiOx. Depth. (4) Molecular weight dependence of the transfer depth of the substrate effect was studied. It was found that the transfer depth of the Si/SiOx substrate to PMMA increased gradually with the increase of the molecular weight and could be normalized to 9.5Rg. It was shown that the effect of the substrate effect on the film dynamics was dependent on the molecular chain size. It is found that the depth of substrate effect transfer decreases with the increase of temperature, indicating that the increase of temperature weakens the effect of substrate effect on the molecular dynamics of polymers. Chain motility is activated by increasing temperature, which competes with each other. Therefore, increasing temperature will weaken the influence of substrate effect on chain motility and thus reduce the depth of transfer of substrate effect.
【学位授予单位】：浙江理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O632.52;TB383.2

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