Microencapsulated Alkane Wax Melting: Measured by ¹H NMR Relaxometry and Diffusometry

Area of Science:

• Materials Science
• Chemical Engineering
• Energy Storage

Background:

• Phase change materials (PCMs) are crucial for energy storage applications.
• N-alkane waxes, such as octadecane and eicosane, possess high latent heats, making them effective PCMs.
• Microencapsulation is a technique used to improve the stability and performance of PCMs.

Purpose of the Study:

• To investigate the molecular-level effects of microencapsulation on n-alkane waxes (octadecane and eicosane).
• To analyze the melting behavior of both unencapsulated and microencapsulated waxes using advanced NMR techniques.
• To understand how microencapsulation influences the heterogeneity and melting point range of these PCMs.

Main Methods:

• Utilized NMR relaxometry (T2 relaxation, T1-T2 correlated relaxation) and diffusometry (PGStE measurements).
• Studied octadecane and eicosane in both unencapsulated and microencapsulated forms.
• Acquired measurements across the melting point range at degree-wise temperature increments.

Main Results:

• Microencapsulation induced molecular-level disordering in the solid waxes, creating a significant intermediate mobility domain.
• This pseudo interface domain suggests disruption of long-range order and increased heterogeneity.
• NMR diffusometry confirmed literature values for diffusion coefficients in wax melts and provided insights into solid-state transport mechanisms.

Conclusions:

• Microencapsulation significantly alters the solid-state properties of n-alkane waxes, leading to increased heterogeneity.
• The observed molecular disordering and extended melting range are key consequences of microencapsulation.
• NMR techniques provide valuable molecular-level insights into the behavior of PCMs during phase transitions.