Speaker:
Peyman Rostami (Leibniz-Institut für Polymerforschung Dresden)
Title:

Oscillation Dynamics of Viscous and Viscoelastic Drops

Authors:
Peyman Rostami (Leibniz-Institut für Polymerforschung Dresden), Castrejón-Pita, A.A. (Dept. of Engineering Science, University of Oxford), Auernhammer G.K. (Leibniz-Institut für Polymerforschung Dresden)

Abstact:
The characterization of viscoelastic fluids is critical for many applications such as inkjet printing. We placed a drop of a viscous or viscoelastic fluid on a partially wetted substrate (with a contact angle greater than 90°) that was vibrated vertically by a magnetic shaker. The amplitudes and frequencies of the substrate motion were controlled. The drop dynamics were recorded with a high-speed camera and analyzed with a Matlab program. Two types of fluids (glycerin as a viscous Newtonian fluid and aqueous PEO solution as viscoelastic fluids) were used. Based on the drop size, surface tension and density of the working fluid, the critical frequency can be estimated to maximize the deformation of the drop. We performed the drop oscillation experiments with different amplitudes and frequencies, including the critical frequency. We make a connection of our results with classical rheological experiments (SAOS, Small Amplitude Oscillatory Shear, and LAOS, Large Amplitude Oscillatory Shear) by estimating the strain and the inertia stress and the contact line dissipation stress. Similarities and differences of the two approaches are discussed.

Speaker:
Mohammadjavad Hajirezaei (University of Rhode Island)
Title:
Aging in natural gas activates the relaxations of polymer melts
Authors:
Rostami, R., Poling-Skutvik, R. (University of Rhode Island)

Abstract:
Although cast iron pipes carrying natural gas have been in service for several decades, they are prone to corrosion, cracks, and leaks. Polymeric materials such as polyethylene (PE), polyamide (PA) and polyvinylidene difluoride (PVDF) can serve as internal structural liners because of their high corrosion resistance, high strength-to-weight ratio, and impressive mechanical durability in hydrocarbon-rich and high-pressure environments. However, the impact of hydrocarbon environments on the properties of polymer liners is not yet fully understood. In this project, we characterize the properties of these materials after exposure to hydrocarbons at elevated temperatures and pressures, and over long periods of time to assess the stability of these liners in the presence of natural gas and contaminants. Dynamic mechanical analysis (DMA) and Fourier transform infrared spectroscopy (FTIR) were performed on both pre-aged and post-aged samples. Notably, the storage modulus indicates that the polymers generally maintain acceptable mechanical and chemical stability under typical natural gas compositions. However, using time-temperature superposition (TTS) indicates that hydrocarbon aging accelerates polymer relaxations and may lead to reduced mechanical performance. Thus, the activation energy governing polymer relaxation was identified as a sensitive indicator for benchmarking polymer performance and degradation. This minor change in polymer properties demonstrate that they are a viable alternative to cast iron for use as pipeline liners. However, hydrocarbon mixtures may contain reactive or corrosive contaminants. The next step of our study will focus on including these contaminants to observe their effects on mechanical and chemical properties and the activation energy.