Mechanical Properties of Polymer Films Assessed by Molecular Dynamics Simulations

聚合物复合材料可以在从发动机到管道的各种实际应用中取代金属。最近的例子是航空中使用的复合材料，这些材料比钢轻得多，从而显著减少了碳排放。为了对能源工业有用，要求聚合物复合材料被证明是安全的，特别是当它们暴露在复杂的流体环境中时，这些环境可能包含原油、天然气、酸性气体(如CO2和H2S)、盐水和生产化学品。准确地预测复合材料在广泛的温度范围(0-180摄氏度)下暴露在这些侵蚀性环境中的耐久性是至关重要的，因为预测其使用寿命将允许计划维护和防止事故。为此，该项目致力于在分子水平上研究可能影响聚合物复合材料在与BP相关的复杂流体混合物中的机械完整性的现象。该项目将沿着三个主要步骤发展，每个步骤将持续约一年：阶段1。聚合物复合膜的制备。将创建BP感兴趣的最多4种聚合物的原子模型。聚合物可以包括：聚乙烯、PA12：尼龙、PEEK和PVDF。由于模拟是在分子水平上进行的，并且预计聚合物末端可能是机械故障的来源，因此分子量将高达5 KDa。模拟将提取聚合物密度作为温度的函数，并将其与文献实验进行比较以验证模型。阶段2。溶胀预测。在第一阶段中制备的薄膜将暴露在上述组成的流体中，有时是在生产化学品(例如，缓蚀剂、防结块剂、硫化氢清除剂)存在的情况下。这些模拟将在原子分辨率下进行，从环境条件下到实际应用中通常采用的高压。这些模拟将确定那些被考虑的化学物质，它们可能会使聚合物薄膜膨胀，有可能穿透材料，从长远来看，可能会损害其机械完整性。模拟结果将与BP阶段3的实验数据进行比较。力学性能预测。对于第一阶段生产的原始薄膜和第二阶段生产的膨胀薄膜，我们将模拟两种类型的力学测试：抗拉力和抗压性。对于前者，我们将拉伸薄膜以提取应力-应变曲线；对于后者，我们将模拟纳米机械压痕实验。在这两种情况下，结果都将与宏观尺度上的实验进行比较。这些模拟将使我们能够确定所考虑的材料的失效机制；它们还将使我们能够了解流体中的不同化学物质是否会损害聚合物薄膜的机械完整性。阶段4。论文撰写。最后6个月的学习时间将致力于撰写论文和为博士辩护。

Polymer composites could replace metals in a variety of practical applications, ranging from engines to pipes. Recent examples are composites used in aviation, which led to significant reduction in carbon emission because these materials are much lighter than steel.To become useful to the energy industry, it is required that polymer composites are proven safe, especially when they are exposed to complex fluid environments that can contain crude oil, natural gas, acid gases such as CO2 and H2S, brines, and production chemicals.It is of vital importance to accurately predict the durability of the composites, when exposed to these aggressive environments, in a wide range of temperatures (0-180C), as predicting the service life expectancy will allow to schedule maintenance and prevent accidents.Towards that end, this project seeks to investigate, at the molecular level, phenomena that could affect the mechanical integrity of polymer composites exposed to complex fluid mixtures of relevance to BP.The project will develop along three main steps, each of which will last ~ 1 year:Stage 1. Preparation of polymer composite films. The atomistic models of up to 4 polymers of interest to BP will be created. The polymers may include: polyethylene, PA12:nylon, PEEK, and PVDF. The molecular weight will be up to 5KDa, as the simulations are conducted at the molecular level, and as it is expected that polymer ends could be the source of mechanical failure. The simulations will extract the polymer density as a function of temperature, which will be compared to literature experiments to validate the models.Stage 2. Swelling prediction. The films prepared in stage 1 will be exposed to fluids of composition discussed above, sometimes in the presence of production chemicals (e.g., corrosion inhibitors, anti-agglomerants, H2S scavengers). These simulations will be conducted at the atomistic resolution, from below ambient conditions to the high pressures typically employed in the practical applications. The simulations will identify those of the chemicals considered which have the potential of swelling the polymer films, potentially penetrating through the materials, and perhaps, in the long term, compromising their mechanical integrity. The simulations will be compared to experimental data from BP.Stage 3. Mechanical properties predictions. For the pristine films produced in stage 1, and the swelled films produced in stage 2, we will simulate two types of mechanical tests: resistance to tensile forces, and resistance to compression. For the former, we will stretch the films to extract stress-strain curves; for the latter, we will mimic a nano-mechanical indentation experiment. In both cases, the results will be compared to experiments at the macroscopic scale. The simulations will allow us to identify the failure mechanisms for the materials considered; they will also allow us to understand whether different chemicals in the fluids can compromise the mechanical integrity of the polymer films.Stage 4. Thesis write up. The last 6 months of the studentship will be dedicated to writing up the dissertation and defend the PhD.