Impact of conjugated polymer addition on the properties of paraffin–asphaltene blends for heat storage applications: Insight from computer modeling and experiment

Abstract

Adding carbon nanoparticles into organic phase change materials (PCMs) such as paraffins is a common way to enhance its thermal conductivity and to improve the efficiency of the heat storage devices. However, sedimentation stability of such blends can be low due to aggregation of aromatic carbon nanoparticles in the aliphatic paraffin environment. In this paper we explore whether this important issue can be resolved by introduction of a polymer agent such as poly(3-hexylthiophene) (P3HT) into the paraffin-nanoparticle blends: P3HT could ensure the compatibility of aromatic carbon nanoparticles with aliphatic paraffin chains. We employed a combination of experimental and computational approaches to determine the impact of P3HT addition on the properties of organic PCMs composed of paraffin and carbon nanoparticles (asphaltenes). Our findings clearly show an increase in the sedimentation stability of paraffin-asphaltene blends, when P3HT is added through a decrease in average size of asphaltene aggregates as well as in an increase of the blends' viscosity. We also witness the appearance of the yield strength and gel-like behavior of the mixtures. At the same time, presence of P3HT in the blends has almost no effect on their thermophysical properties. This implies that all properties of the blends, which are critical for heat storage applications, are well preserved. Thus, we demonstrated that adding polyalkylthiophenes to paraffin-asphaltene mixtures led to significant improvement in the performance characteristics of these systems. Therefore, the polymer additives can serve as promising compatibilizers for organic PCMs composed of paraffins and asphaltenes and other types of carbon nanoparticles.

Size matters: asphaltenes with enlarged aromatic cores promote heat transfer in organic phase-change materials

“…It has to be emphasized that such an approach is an approximation for anisotropic systems and is used here solely to link our computational results with experiments, where a single value for the thermal conductivity is normally measured. 15–17 Real systems are much larger than those considered in our simulations, so anisotropic asphaltene aggregates can be randomly oriented within a sample. This implies that a system, being anisotropic on sufficiently small scales, can be considered isotropic on larger scales, thereby justifying our approach.…”

“…38–41 In practice, to evaluate the thermal conductivity, we followed closely the Green–Kubo approach employed and validated in our previous papers. 14,17,42…”

“…14–16 Moreover, it has been established that the sedimentation stability of paraffin-based blends filled with asphaltenes can be improved using polymer compatibilizers such as poly(3-hexylthiophene). 17…”

“…[14][15][16] Moreover, it has been established that the sedimentation stability of paraffin-based blends filled with asphaltenes can be improved using polymer compatibilizers such as poly(3-hexylthiophene). 17 Most previous studies considered asphaltenes of the socalled ''island'' type, whose cores chemically resembled small ''flakes'' of graphene. 18 At the same time, ''island''-type asphaltenes can also be classified as discotic liquid crystalline molecules due to the presence of polycyclic aromatic cores in their composition.…”

“…This theoretical approach has been shown to give reliable results consistent with experiments for paraffin-asphaltene systems. 17 At the same time, unlike experiments the simulations allow us to consider asphaltene molecules of well-defined chemical structures and understand how a subtle difference in cores may affect the asphaltene behavior and system properties in real systems.…”