Mechanical Properties of Polymer Films Assessed by Molecular Dynamics Simulations

聚合物复合材料可以在各种实际应用中取代金属，从发动机到管道。最近的例子是航空领域使用的复合材料，由于这些材料比钢轻得多，因此大大减少了碳排放。为了在能源行业发挥作用，聚合物复合材料必须是安全的，特别是当它们暴露在复杂的流体环境中时，这些环境可能含有原油、天然气、酸性气体（如CO2和H2S）、盐水和生产化学品。当暴露在这些恶劣的环境中，在广泛的温度范围内（0-180℃），准确预测复合材料的耐久性至关重要，因为预测使用寿命将允许计划维护和防止事故。为此，该项目试图在分子水平上研究暴露于与BP相关的复杂流体混合物中可能影响聚合物复合材料机械完整性的现象。该项目将沿着三个主要步骤发展，每个步骤将持续约1年。高分子复合膜的制备。将创建BP感兴趣的多达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根源，因此分子量将高达5KDa。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。肿胀的预测。在第1阶段制备的薄膜将暴露于上述成分的流体中，有时存在生产化学品（例如，缓蚀剂、抗团聚剂、H2S清除剂）。这些模拟将在原子分辨率下进行，从低于环境条件到实际应用中通常使用的高压。模拟将确定那些被认为有可能膨胀聚合物薄膜的化学物质，这些化学物质可能会穿透材料，从长远来看，可能会损害它们的机械完整性。模拟结果将与BP的实验数据进行比较。阶段3。机械性能预测。对于第1阶段生产的原始薄膜和第2阶段生产的膨胀薄膜，我们将模拟两种类型的机械测试：抗拉力和抗压缩。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，结果将与宏观尺度下的实验进行比较。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个月的学生将致力于撰写论文和捍卫博士学位。

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.