Mechanical Properties of Polymer Films Assessed by Molecular Dynamics Simulations

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.