Friction and wear are unavoidable problems that affect moving workpieces in all machines, resulting in significant energy and lifespan losses. Researchers have estimated that almost 23% of the world’s total energy consumption is generated from friction and wear in mechanical moving parts. The aforementioned energy loss could be reduced by up to 62% when employing advanced lubricants between the contacting surfaces to increase the durability and efficiency of working components. In the recent decade, ionic liquids have shown great potential as high-performance lubricants and “tailor-made” lubricating additives across different tribological systems due to their unique properties such as nonvolatility, excellent thermal stability, and electrical conductivity. However, the study of ILs in lubrication is mainly focused on aprotic ionic liquids, which are too expensive to be widely used in industry. Also, most of them contain halogen elements which are toxic to the environment. On the contrary, the synthesis route of protic ionic liquids is simple and controllable to avoid halogens in their molecular components. The core of this work is to provide fundamental knowledge for the molecular design of more effective and low toxic protic ionic liquids as neat lubricants and lubricant additives. Taking account of the induced stress and activated thermal energy at sliding interfaces, the dependence of tribological performance on the chemistry of protic ionic liquids is systematically investigated. protic ionic liquids with different molecular structures and ionicities are synthesized and evaluated at different material interfaces. The ionic conductivity of each protic ionic liquid and the chemistry of the resulting surface reaction film are characterized to elucidate the chemical changes in protic ionic liquids and their chemical reactivity at different material surfaces. The varying hydrogen bond strength, ionicity, and molecular structure of a protic ionic liquid are found to affect its rheological properties and thermal behaviors, as well as the solubility in base lines with different polarities. Specifically, the ionicity and ion-pairing effect of a protic ionic liquid are demonstrated to impact its tribological properties.

Library of Congress Subject Headings

Lubrication and lubricants; Ionic solutions; Surfaces (Technology)

Publication Date


Document Type


Student Type


Degree Name

Engineering (Ph.D.)

Department, Program, or Center

Engineering (KGCOE)


Patricia Iglesias Victoria

Advisor/Committee Member

Thomas W. Smith

Advisor/Committee Member

Alfonso Fuentes Aznar


RIT – Main Campus

Plan Codes