Compositional Complexity in High-Entropy Oxides Optimizes Colloidal Stability and Pool Boiling Heat Transfer

High-entropy oxides (HEOs) represent a class of functional materials whose interfacial chemistry and colloidal behavior remain poorly understood, limiting their development for demanding applications. This work establishes how compositional complexity in multielement oxide systems governs both colloidal stability and functional performance through a systematic investigation of eight HEO compositions in pool boiling experiments, where thermal gradients and active nucleation simultaneously test these properties under demanding conditions. Results demonstrate that HEOs with five or more equimolar elements exhibit enhanced dispersion stability compared to lower-entropy oxide systems due to configurational entropy effects, providing thermodynamic resistance to particle aggregation. Configurational entropy values of 13.38–14.90 J/mol·K exceed the critical 1.5R threshold for entropy-stabilized phases. Y-HEO, featuring yttrium combined with equimolar Co, Cr, Fe, Mn, and Ni, achieved superior performance with a 63% critical heat flux enhancement and a 135% heat transfer coefficient improvement relative to the deionized water baseline at 0.05 wt % concentration. Comprehensive surface characterization revealed that multielement oxide composition creates unique interfacial properties: contact angle reduced from 96° to 62°, minimal hysteresis of ∼12° enabling rapid rewetting, and surface roughness increased by 170%, establishing abundant nucleation sites with dramatically reduced superheat requirements. These combined effects─enhanced colloidal stability from configurational entropy, superior interfacial chemistry from compositional heterogeneity, and optimized wettability from multielement cation coordination─synergistically produced exceptional thermal performance. This work demonstrates that the precision design of multielement oxide composition directly translates fundamental materials chemistry principles into functional advantages in thermal applications.