TEMPERATURE-DEPENDENT SURFACE ENERGY AND WETTABILITY OF POLYALPHAOLEFIN WITH ORGANIC FRICTION MODIFIERS
DOI:
https://doi.org/10.11113/jtse.v13.258Keywords:
Polyalphaolefin, Fatty Acid Methyl Ester, Glyceryl Monooleate, Temperature dependence, Surface energyAbstract
This study investigates the temperature-dependent wettability and surface energy behaviour of polyalphaolefin (PAO4) lubricants modified with renewable organic friction modifiers, namely fatty acid methyl ester (FAME) and glyceryl monooleate (GMO). While PAO exhibits excellent thermal stability, its inherently low polarity limits surface interaction and may reduce its effectiveness under boundary-dominated lubrication conditions. To address this limitation, PAO4 was blended with varying concentrations of FAME and GMO, and their interfacial behaviour was evaluated on steel and glass substrates at 25°C, 40°C, and 60°C using contact angle measurements. The results show that increasing additive concentration consistently reduces contact angle and interfacial energy, accompanied by reduced interfacial energy and improved spreading behaviour. On steel surfaces, the contact angle decreased from 34.21° for neat PAO4 to 19.71° for the PAO4–FAME 10 wt% blend at 60°C, corresponding to approximately 42% improvement in wettability. Similarly, PAO4 blended with GMO 7 wt% exhibited the lowest interfacial energy among the tested formulations. FAME (10 wt%) and GMO (7 wt%) exhibited optimal performance, indicating a concentration-dependent balance between polar interaction and dispersive spreading. Temperature further amplifies these effects, suggesting thermally activated molecular mobility enhances surface affinity. These findings demonstrate that wettability enhancement in PAO-based lubricants is governed by the interplay between additive polarity and temperature, providing a practical framework for screening sustainable friction modifiers. The study offers a surface-energy-based approach for screening lubricant–surface compatibility as a preliminary indicator for boundary lubrication applications.
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