@article{seed_acharya_nunn_smirnov_krim_2023, title={Tribotronic and electrochemical properties of platinum-nanofluid interfaces formed by aqueous suspensions of 5 and 40 nm TiO<sub>2</sub> nanoparticles}, volume={159}, ISSN={["1089-7690"]}, url={https://doi.org/10.1063/5.0155504}, DOI={10.1063/5.0155504}, abstractNote={Nanoparticles (NPs) can be highly beneficial as additives to lubricating fluids, and the tribotronic response of charged NPs tuned by external fields represents an area of great technological potential. Tribotronic response, however, is expected to be highly size dependent, which represents a significant design challenge. To explore this issue, quartz crystal microbalance and cyclic voltammetry were employed to characterize nanotribological and electrochemical behavior of platinum–nanofluid interfaces formed by aqueous suspensions of different-sized negatively charged titanium dioxide (TiO2) NPs. Suspensions of 5, 40, and 100 nm NPs were all observed to reduced interfacial frictional drag forces upon introduction into pure water in zero field conditions, with reductions for the 40 nm NPs about twice those of 5 nm particles at comparable concentrations. Suspensions of 100 nm NPs produced even greater reductions, but rapidly precipitated from the suspension when left unstirred. NPs were also driven to and from Pt electrode surfaces by applying external electric fields with varying amplitudes and modulation frequencies. For electric fields of sufficient amplitude and duration, the 40 nm TiO2 nanosuspension exhibited tribological properties consistent with a reversible electrophoretic deposition of the NPs, accompanied by changes in the electrochemical attributes and increasing interfacial drag. The 5 nm NP properties were consistent with progressive reductions in interfacial drag forces at the NP–suspension interface linked to field-induced increases in concentration.}, number={11}, journal={JOURNAL OF CHEMICAL PHYSICS}, author={Seed, C. M. and Acharya, B. and Nunn, N. and Smirnov, A. I. and Krim, J.}, year={2023}, month={Sep} }
 @article{acharya_seed_krim_2022, title={Shear activation of ZDDP reaction films in the presence and absence of nanodiamonds}, volume={7}, ISSN={["2666-5239"]}, DOI={10.1016/j.apsadv.2022.100214}, abstractNote={We explore the impact of shear stress and nanodiamond (ND) additives on the formation temperatures of thermal- and tribo- reaction films of steel samples immersed in basestock oils containing zinc dialkyl dithio-phosphate (ZDDP) additives. The measurements were performed in-situ using a quartz crystal microbalance (QCM) immersed in oil, oil plus ZDDP, and oil plus ZDDP-ND blends over the temperature range 25 200 °C. ZDDP reaction film formation temperatures were observed to decrease with contact stress and be similar in value to ZDDP-ND blends. ND were observed to be embedded in the reaction films, consistent with prior observations for Tricresyl phosphate (TCP) ND blends, and also consistent with the presence of both primary and secondary reaction products in the films. In addition, the ZDDP+ND reaction tribofilms were observed to be thicker, rougher and more adhesive than those formed with only ZDDP.}, journal={APPLIED SURFACE SCIENCE ADVANCES}, author={Acharya, Biplav and Seed, Caitlin M. and Krim, Jacqueline}, year={2022}, month={Feb} }
 @article{seed_acharya_krim_2021, title={QCM Study of Tribotronic Control in Ionic Liquids and Nanoparticle Suspensions}, volume={69}, ISSN={["1573-2711"]}, DOI={10.1007/s11249-021-01461-7}, number={3}, journal={TRIBOLOGY LETTERS}, author={Seed, C. M. and Acharya, B. and Krim, J.}, year={2021}, month={Sep} }
 @article{seed_acharya_perelygin_smirnov_krim_2021, title={Tribotronic control and cyclic voltammetry of platinum interfaces with metal oxide nanofluids}, volume={566}, ISSN={["1873-5584"]}, DOI={10.1016/j.apsusc.2021.150675}, abstractNote={Nanotribological and electrochemical behavior of platinum-nanofluid interfaces are reported for aqueous suspensions of positively charged Al2O3 and negatively charged TiO2 nanoparticles, employing Quartz Crystal Microbalance (QCM) and cyclic voltammetry (CV) techniques. Tribotronic methods were employed to adjust the nanoparticles’ positions relative to Pt surface electrodes, and both voltammetry and tribological performance measures were observed to be highly sensitive to the adjustments. Interfacial friction levels were observed to be higher for both types of nanoparticles when electrostatically driven towards the surface. For electric fields of sufficient amplitude and duration, the TiO2 nanosuspension exhibited properties consistent with reversible electrophoretic deposition of the nanoparticles, accompanied by changes in the electrochemical attributes of the electrode itself. Overall, the study suggests a method for active tribological control and optimization of device performance in applications where suspensions of charged nanoparticles are present and can be exposed to external fields.}, journal={APPLIED SURFACE SCIENCE}, author={Seed, C. M. and Acharya, B. and Perelygin, V and Smirnov, A. and Krim, J.}, year={2021}, month={Nov} }
 @article{seed_acharya_krim_2020, title={Continuum Model Analysis of QCM Nanotribological Data to Obtain Friction Coefficients for 304SS Contacts Lubricated by Water and TiO2 Nanoparticle Suspensions}, volume={6}, ISSN={["2297-3079"]}, DOI={10.3389/fmech.2020.00072}, abstractNote={We report a study of the response of a Quartz Crystal Microbalance (QCM) to rubbing contacts in air, water and aqueous suspensions of 40 nm TiO2 nanoparticles. Measurements were performed with a contact comprised of 3 close-packed 304SS ball bearings situated symmetrically about the center of a 304SS QCM electrode with 2 nm rms roughness. Two continuum methods were employed to infer macroscale friction coefficients μ employing QCM nanotribological data recorded in the Cattaneo-Mindlin (CM) slip regime at vibrational amplitudes that varied between 1 and 17 nm. The “slope” Method 1 involved sweeps of the QCM amplitude of vibration as ball bearings were held in continuous contact with the oscillating electrode. The “contact” Method 2 obtained μ by analyzing the shifts in frequency and bandwidth that occur at a fixed uo to solve for μ. when ball bearings were brought in and out of contact with the QCM's electrode. The results for dry and water lubricated contacts compared favorably with macroscale friction coefficients reported in the literature. The model failed to adequately describe contacts lubricated with the NP suspension, but its continuum nature did not appear to be the dominant factor underlying failure. The failure was more likely attributable to either a lack of a CM slip regime when NP were present at the interface and/or the fact that the amplitude of vibration was close in size to the individual NP contacting regions, in violation of a key underlying assumption of the model.}, journal={FRONTIERS IN MECHANICAL ENGINEERING-SWITZERLAND}, author={Seed, Caitlin M. and Acharya, Biplav and Krim, Jacqueline}, year={2020}, month={Sep} }
 @article{seed_acharya_andrus_krim_2020, title={Correlation of high frequency QCM sphere-plate stiffness measurements with macroscopic frictional contacts in thin film and bulk stainless steel materials}, volume={306}, ISSN={["1873-3069"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85082119223&partnerID=MN8TOARS}, DOI={10.1016/j.sna.2020.111913}, abstractNote={We compare friction coefficient values μ for stainless steel contacts, obtained directly using a ball on disk tribometer and/or a basic “da Vinci” method, with values inferred from two microscale analysis methods reported in the literature that treat the response of a Quartz Crystal Microbalance (QCM) to rubbing contacts with one or more ball bearings. The microscale analysis methods both employ a Cattaneo-Mindlin slip scenario to relate contact stiffness to QCM response. Analysis Method 1 involves sweeps of the QCM amplitude of vibration while ball bearings are held in continuous contact with the oscillating electrode. It obtains μ from the slope of the associated frequency or bandwidth shift trace. We find that this method yields values for μ that compare favorably with macroscale values when the bandwidth dependence on vibrational amplitude is utilized. Method 2 obtains μ by analyzing the shifts in frequency and bandwidth that occur when ball bearings are brought in and out of contact with a QCM’s oscillating electrode at a fixed vibrational amplitude. We find that this method yields values for μ that compare favorably with macroscale values when the measurements are performed with a contact comprised of 3 close-packed ball bearings situated symmetrically about the center of the QCM electrode. Overall, the results validate the combination of assumptions employed in the analysis methods, and support the methods as a viable means for linkage of macro and nanoscale tribological measurements.}, journal={SENSORS AND ACTUATORS A-PHYSICAL}, author={Seed, Caitlin M. and Acharya, Biplav and Andrus, Rachel and Krim, Jacqueline}, year={2020}, month={May} }
 @article{acharya_seed_brenner_smirnov_krim_2019, title={Tuning friction and slip at solid-nanoparticle suspension interfaces by electric fields}, volume={9}, ISSN={["2045-2322"]}, url={http://dx.doi.org/10.1038/s41598-019-54515-1}, DOI={10.1038/s41598-019-54515-1}, abstractNote={AbstractWe report an experimental Quartz Crystal Microbalance (QCM) study of tuning interfacial friction and slip lengths for aqueous suspensions of TiO2 and Al2O3 nanoparticles on planar platinum surfaces by external electric fields. Data were analyzed within theoretical frameworks that incorporate slippage at the QCM surface electrode or alternatively at the surface of adsorbed particles, yielding values for the slip lengths between 0 and 30 nm. Measurements were performed for negatively charged TiO2 and positively charged Al2O3 nanoparticles in both the absence and presence of external electric fields. Without the field the slip lengths inferred for the TiO2 suspensions were higher than those for the Al2O3 suspensions, a result that was consistent with contact angle measurements also performed on the samples. Attraction and retraction of particles perpendicular to the surface by means of an externally applied field resulted in increased and decreased interfacial friction levels and slip lengths. The variation was observed to be non-monotonic, with a profile attributed to the physical properties of interstitial water layers present between the nanoparticles and the platinum substrate.}, number={1}, journal={SCIENTIFIC REPORTS}, author={Acharya, B. and Seed, C. M. and Brenner, D. W. and Smirnov, A. I. and Krim, J.}, year={2019}, month={Dec} }