Thermal and Physical Characterization of PEG Phase Change Materials Enhanced by Carbon-Based Nanoparticles

At a Glance

Metadata	Details
Publication Date	2020-06-15
Journal	Nanomaterials
Authors	David Cabaleiro, Samah Hamze, Jacek Fal, Marco A. Marcos, Patrice Estellé
Institutions	Laboratoire de génie civil et génie mécanique, Universidade de Vigo
Citations	64
Analysis	Full AI Review Included

Technical Documentation & Analysis: Carbon-Enhanced Phase Change Materials

Reference Paper: Thermal and Physical Characterization of PEG Phase Change Materials Enhanced by Carbon-Based Nanoparticles (Nanomaterials 2020, 10, 1168)

Executive Summary

This research validates the use of high-purity carbon nanostructures, specifically nano-diamonds and graphite/diamond mixtures, as highly effective additives for enhancing the thermal and physical properties of Poly(ethylene glycol) (PEG400) Phase Change Materials (PCMs) for cold Thermal Energy Storage (TES).

Core Value Proposition: Carbon-based nanoparticles significantly improve the thermal performance and cycling stability of organic PCMs, addressing the low thermal conductivity bottleneck common in PEG systems.
Nucleation Enhancement: The addition of nanoparticles reduced the undesirable sub-cooling effect by up to ~2.0 K (raw graphite/diamond nanomixture, 1.0 wt.%), promoting faster and more efficient crystallization.
Thermal Conductivity Improvement: Maximum thermal conductivity enhancement reached 3.6% (purified graphite/diamond nanomixture, 1.0 wt.%), crucial for rapid charging and discharging cycles in TES applications.
Density Control: Nano-diamond suspensions (nD87 and nD97) showed the largest modifications in density, increasing by 0.64-0.66%, demonstrating precise control over volumetric properties.
Rheological Behavior: All carbon-based suspensions exhibited non-Newtonian pseudo-plastic (shear-thinning) behavior, which is important for estimating pumping power in liquid-phase TES systems.
Material Requirement: The study confirms the necessity of high-purity, ultra-small nanoparticles (average size 4 nm) for optimal performance, aligning directly with 6CCVD’s expertise in high-grade MPCVD diamond materials.

Technical Specifications

The following hard data points were extracted from the characterization of the nano-enhanced PCMs (NePCMs):

Parameter	Value	Unit	Context
Nanoparticle Average Size	4	nm	Nano-Diamonds (nD87, nD97) and G/D mixtures
Nanoparticle Concentration	0.5 and 1.0	wt.%	Mass concentration used in PEG400
Base Fluid Melting Temperature (T_melt.)	280.2	K	Neat PEG400
Maximum Sub-cooling Reduction	2.0	K	Raw G/D nanomixture (1.0 wt.%)
Maximum Thermal Conductivity Enhancement	3.6	%	Purified G/D nanomixture (1.0 wt.%)
Maximum Density Increase	0.66	%	Purified Nano-Diamond (nD97, 1.0 wt.%)
Crystallinity Degree (X_c) Range	50.5 - 54.3	%	NePCM vs. Neat PEG400
Dynamic Viscosity Temperature Range	288.15 - 318.15	K	Liquid phase characterization
Flow Behavior Index (n) Range	0.77 - 0.99	Dimensionless	Non-Newtonian pseudo-plastic behavior

Key Methodologies

The NePCMs were prepared and characterized using precise, multi-modal experimental techniques to ensure accurate measurement of thermal and physical properties across solid and liquid phases.

Material Selection: Five carbon-based nanomaterials were used, including two grades of nano-diamonds (nD87, nD97) and two grades of graphite/diamond nanomixtures (G/D-p, G/D-r), all sourced from PlasmaChem GmbH.
Nanofluid Preparation: A two-step method was employed, involving precise weighting (accuracy 1 x 10^-4 g) of the nanopowder and PEG400 base fluid, followed by mechanical shaking (30 min).
Sonication Protocol: Samples were sonicated for 200 min in an ultrasonic bath (45 kHz, 450 W power) with periodic water replacement to prevent overheating.
Solid-Liquid Phase Transition Analysis (DSC): Differential Scanning Calorimetry (DSC) was performed in the range 223.15 K to 313.15 K under nitrogen atmosphere at a constant scan rate of 0.5 K·min^-1.
Rheological Characterization: Dynamic viscosity (flow curves) was measured using a stress-controlled rheometer with a cone-plate geometry across four isotherms (288.15 K to 318.15 K). Oscillatory strain and temperature sweeps were used to define the linear viscoelastic region (LVR).
Thermal Conductivity Measurement: The transient short hot wire (THW) technique (ASTM D7896-14 standard) was used in the liquid phase (288.15 K to 318.15 K), utilizing a low thermal power (80 mW) and short input time (1.5 s) to prevent convection.
Surface Tension Measurement (SFT): SFT was determined using two methods for consistency: the pendant drop technique (DSA-30 drop-shape analyzer) and the Du Noüy ring tensiometer.
Density Measurement: Densities were determined using a vibrating tube densimeter (DMA 500) in the temperature range 288.15 K to 313.15 K.

6CCVD Solutions & Capabilities

The successful enhancement of PEG400 PCMs relies on the precise control of nanoparticle purity, size, and morphology—areas where 6CCVD’s expertise in MPCVD diamond materials provides a critical advantage for researchers and engineers developing next-generation TES systems.

Applicable Materials for NePCM Research

The paper highlights the superior performance of high-purity nano-diamonds (nD97, 4 nm). 6CCVD offers the foundational materials necessary to replicate, optimize, and scale this research:

Polycrystalline Diamond (PCD) Precursors: 6CCVD supplies high-purity PCD plates and wafers (up to 125mm in size) which can be processed into highly uniform, high-grade nano-diamond powders, ensuring superior purity control compared to commercial grades.
Single Crystal Diamond (SCD) Material: For integration studies requiring extreme thermal stability and purity, 6CCVD offers SCD material up to 500µm thick, ideal for use as high-conductivity heat spreaders or thin-film supports.
Boron-Doped Diamond (BDD): The introduction mentions integrated PV/TES systems. BDD offers tunable electrical conductivity alongside excellent thermal properties. 6CCVD provides custom BDD materials to explore electro-thermal coupling and active thermal management within NePCMs.

Customization Potential for Advanced TES Integration

The future direction of NePCM research involves integration into complex systems (e.g., micro-channels, encapsulated PCMs). 6CCVD’s custom fabrication capabilities directly support these advanced engineering requirements:

Research Requirement	6CCVD Customization Service	Technical Specification
High-Density Integration/Encapsulation	Custom Dimensions & Substrates	Plates/wafers up to 125mm (PCD); Substrates up to 10mm thick.
Interface Optimization & Thin Films	Custom Metalization	Internal capability for Au, Pt, Pd, Ti, W, Cu deposition for optimal interface bonding or electrical contact.
Micro-Channel Heat Sinks	Ultra-Smooth Polishing	SCD surfaces polished to Ra < 1nm; Inch-size PCD polished to Ra < 5nm, minimizing flow resistance and maximizing heat transfer area.
Tailored Thermal Management	Custom Thickness Control	SCD and PCD layers available from 0.1µm to 500µm, allowing precise control over thermal resistance in multi-layer devices.

Engineering Support

6CCVD’s in-house PhD team can assist with material selection and optimization for similar Thermal Energy Storage (TES) and Phase Change Material (PCM) projects. We provide consultation on:

Optimizing diamond purity and morphology for maximum sub-cooling reduction and thermal conductivity enhancement.
Designing diamond substrates for use in high-efficiency heat exchangers or structural supports within NePCM systems.
Developing custom BDD materials for active thermal control applications.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

This paper presents the preparation and thermal/physical characterization of phase change materials (PCMs) based on poly(ethylene glycol) 400 g·mol−1 and nano-enhanced by either carbon black (CB), a raw graphite/diamond nanomixture (G/D-r), a purified graphite/diamond nanomixture (G/D-p) or nano-Diamond nanopowders with purity grades of 87% or 97% (nD87 and nD97, respectively). Differential scanning calorimetry and oscillatory rheology experiments were used to provide an insight into the thermal and mechanical changes taking place during solid-liquid phase transitions of the carbon-based suspensions. PEG400-based samples loaded with 1.0 wt.% of raw graphite/diamond nanomixture (G/D-r) exhibited the lowest sub-cooling effect (with a reduction of ~2 K regarding neat PEG400). The influences that the type of carbon-based nanoadditive and nanoparticle loading (0.50 and 1.0 wt.%) have on dynamic viscosity, thermal conductivity, density and surface tension were also investigated in the temperature range from 288 to 318 K. Non-linear rheological experiments showed that all dispersions exhibited a non-Newtonian pseudo-plastic behavior, which was more noticeable in the case of carbon black nanofluids at low shear rates. The highest enhancements in thermal conductivity were observed for graphite/diamond nanomixtures (3.3-3.6%), while nano-diamond suspensions showed the largest modifications in density (0.64-0.66%). Reductions in surface tension were measured for the two nano-diamond nanopowders (nD87 and nD97), while slight increases (within experimental uncertainties) were observed for dispersions prepared using the other three carbon-based nanopowders. Finally, a good agreement was observed between the experimental surface tension measurements performed using a Du Noüy ring tensiometer and a drop-shape analyzer.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano10061168

References

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2019 - A review on potentials of coupling PCM storage modules to heat pipes and heat pumps [Crossref]