Scalable production of hexagonal boron nitride nanosheets by micelle assisted exfoliation for forced convection cooling

Hexagonal boron nitride (hBN) nanosheets is an effective material for thermal management applications due to its chemically stable, and very high in-plane thermal conductivity. However, for nanofluids, the key challenge is not only achieving higher thermal conductivity, but also maintaining dispersion stability and avoiding excessive pumping penalties under forced convection. In this work, hBN nanosheets were synthesized using a scalable micelle assisted liquid phase exfoliation route. Commercial hBN powder was dispersed in deionized water containing Tween 80 and subjected to high shear using a kitchen blender to promote exfoliation, followed by centrifugation to obtain the hBN nanosheets. Electron microscopy confirms that the exfoliated product is dominated by few layer and crystalline nanosheets. Visual sedimentation and UV–Vis spectra reveal gradual, size selective settling instead of sudden flocculation. Concentration was quantified using Beer–Lambert law showing that nanosheet concentration decreases from 3.03 to 0.76 µg/mL over 28 days. The measured zeta potential is ~ 12.5 mV, which is expected for a non-ionic surfactant system, indicating that steric stabilization. Rheological measurements show Newtonian behaviour across the relevant shear rate range and behaves as a viscoelastic liquid. Thermal conductivity of nanofluid is increased by 60% as compared to base fluid. The instrumented heat sink loop reveals that the hBN nanofluid enhances convective heat transfer, and reduces thermal resistance at moderate to high flow rates. The pressure drop and pumping power of hBN nanofluid is close to that of deionized water. As a consequence, the performance evaluation criterion (PEC) remains above unity. This observation confirming that the thermal gains outweigh the hydraulic penalty and that the nanofluid provides a net thermo-hydraulic benefit.