@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_pardue_su_smirnov_brenner_krim_2019, title={Nanotribological Performance Factors for Aqueous Suspensions of Oxide Nanoparticles and Their Relation to Macroscale Lubricity}, volume={7}, ISSN={["2075-4442"]}, url={https://doi.org/10.3390/lubricants7060049}, DOI={10.3390/lubricants7060049}, abstractNote={Quartz crystal microbalance (QCM) measurements of nanotribological properties of statistically diverse materials combinations of nanoparticles and substrate electrodes in aqueous suspensions are reported and compared to macroscale measurements of the same materials combinations for a subset of the nanoparticle combinations. Four ceramic nanoparticles, TiO2, SiO2, Al2O3, and maghemite (γ-Fe2O3) and ten substrate materials (Au, Al, Cr, Cu, Mo, Ni, Pt, SiO2, Al2O3, and SS304) were studied. The QCM technique was employed to measure frequency and motional resistance changes upon introduction of nanoparticles into the water surrounding its liquid-facing electrode. This series of experiments expanded prior studies that were often limited to a single nanoparticle - solid liquid combination. The variations in QCM response from one nanoparticle to another are observed to be far greater than the variation from one substrate to another, indicating that the nanoparticles play a larger role than the substrates in determining the frictional drag force levels. The results were categorized according to the direction of the frequency and motional resistance changes and candidate statistical performance factors for the datasets were generated. The performance factors were employed to identify associations between the QCM atomic scale results and the macroscale friction coefficient measurements. Macroscale measurements of friction coefficients for selected systems document that reductions (increases) in motional resistance to shear, as measured by the QCM, are linked to decreases (increases) in macroscale friction coefficients. The performance factors identified in the initial study therefore appear applicable to a broader set of statistically diverse samples. The results facilitate full statistical analyses of the data for identification of candidate materials properties or materials genomes that underlie the performance of nanoparticle systems as lubricants.}, number={6}, journal={LUBRICANTS}, publisher={MDPI AG}, author={Acharya, Biplav and Pardue, Tyler N. and Su, Liangliang and Smirnov, Alex I. and Brenner, Donald W. and Krim, Jacqueline}, year={2019}, month={Jun} }
 @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={Abstract}, 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} }
 @article{acharya_pardue_avva_krim_2018, title={In situ, real time studies of thermal reaction film formation temperatures for iron and 304SS surfaces immersed in 5% tricresyl phosphate in base oil}, volume={126}, ISSN={["1879-2464"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85047256526&partnerID=MN8TOARS}, DOI={10.1016/j.triboint.2018.04.034}, abstractNote={The temperature at which TCP forms a thermal reaction film with Fe and 304SS surfaces has been measured in real time, in situ liquid environments utilizing a QCM immersed in a synthetic dibasic ester base stock containing 5% TCP, and observed to be 210 °C. The thermal reaction films were characterized by AFM, and observed to be uniform on Fe and non-uniform and nodular in nature on 304SS substrates, with the thicknesses in the range of 60–100 nm. The chemical composition of the thermal reaction films was studied with EDS. The methods employed here demonstrate an effective means for screening of reaction film formation, and are extendable to systems involving multiple additives and/or complex metal composite materials.}, journal={TRIBOLOGY INTERNATIONAL}, author={Acharya, B. and Pardue, T. N. and Avva, K. S. and Krim, J.}, year={2018}, month={Oct}, pages={106–115} }
 @article{acharya_avva_thapa_pardue_krim_2018, title={Synergistic Effect of Nanodiamond and Phosphate Ester Anti-Wear Additive Blends}, volume={6}, ISSN={2075-4442}, url={http://dx.doi.org/10.3390/lubricants6020056}, DOI={10.3390/lubricants6020056}, abstractNote={Nanodiamonds are known to improve tribological performance when added to lubricants, but their impact on additives that may already be present in the lubricant is poorly documented. Here, we report on a study of their effects on thermal reaction films formed from tricresyl phosphate (TCP) on Fe substrates immersed in a dibasic ester basestock when blended with TCP. Thermal reaction film formation temperatures were recorded in-situ by monitoring the reaction film formation on both Fe and air baked Fe surfaces using a quartz crystal microbalance (QCM). The nanodiamonds were found to raise the thermal reaction film formation temperature by 18 °C, possibly by raising the activation energy for the reaction, but they were not observed to affect the thickness or rate of formation of the films. The nanodiamonds, moreover, were observed to trigger thermal reaction film formation on air baked Fe surfaces that otherwise were highly resistance to reaction film formation. The surface morphology, roughness, and thickness of the thermal reaction films, as measured by atomic force microscopy (AFM), are reported as well as their chemical compositions, as studied with Electron Dispersive X-ray Spectroscopy (EDS). The coefficients of friction measured on the thermal reaction films during dry solid–solid contact are also reported.}, number={2}, journal={Lubricants}, publisher={MDPI AG}, author={Acharya, Biplav and Avva, Keshav and Thapa, Binita and Pardue, Tyler and Krim, Jacqueline}, year={2018}, month={Jun}, pages={56} }
 @article{fredricks_stevens_kenny_acharya_krim_2018, title={Tuning Nanoscale Friction by Applying Weak Magnetic Fields to Reorient Adsorbed Oxygen Molecules}, volume={4}, ISSN={["2410-3896"]}, url={http://www.mdpi.com/2410-3896/4/1/1}, DOI={10.3390/condmat4010001}, abstractNote={Sliding friction levels of thin (1–2 monolayers) and thick (~10 monolayers) oxygen films adsorbed on nickel and gold at 47.5 K have been measured by means of a quartz crystal microbalance (QCM) technique. Friction levels for the thin (thick) films on nickel in the presence of a weak magnetic field were observed to be approximately 30% (50%) lower than those recorded in the absence of the external field. Friction levels for thin films on gold were meanwhile observed to be substantially increased in the presence of the field. Magnetically-induced structural reorientation (magnetostriction) and/or realignment of adlayer spins, which respectively reduce structural and magnetic interfacial corrugation and commensurability, appear likely mechanisms underlying the observed field-induced reductions in friction for the nickel samples. Eddy current formation in the gold substrates may account for the increased friction levels in this system. The work demonstrates the role of magnetic effects in model systems that are highly amenable to theoretical studies and modeling.}, number={1}, journal={CONDENSED MATTER}, author={Fredricks, Z. B. and Stevens, K. M. and Kenny, S. G. and Acharya, B. and Krim, J.}, year={2018}, month={Dec} }
 @article{acharya_chestnut_marek_smirnov_krim_2017, title={A Combined QCM and AFM Study Exploring the Nanoscale Lubrication Mechanism of Silica Nanoparticles in Aqueous Suspension}, volume={65}, ISSN={["1573-2711"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85026840191&partnerID=MN8TOARS}, DOI={10.1007/s11249-017-0898-5}, number={3}, journal={TRIBOLOGY LETTERS}, author={Acharya, B. and Chestnut, M. and Marek, A. and Smirnov, A. I. and Krim, J.}, year={2017}, month={Sep} }
 @article{acharya_sidheswaran_yungk_krim_2017, title={Quartz crystal microbalance apparatus for study of viscous liquids at high temperatures}, volume={88}, ISSN={["1089-7623"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85013763853&partnerID=MN8TOARS}, DOI={10.1063/1.4976024}, abstractNote={A design for a Quartz Crystal Microbalance (QCM) setup for use with viscous liquids at temperatures of up to 300 °C is reported. The system response for iron and gold coated QCM crystals to two common lubricant base oils, polyalphaolefin and halocarbon, is reported, yielding results that are consistent with theoretical predictions that incorporate electrode nanoscale surface roughness into their analysis.}, number={2}, journal={REVIEW OF SCIENTIFIC INSTRUMENTS}, author={Acharya, Biplav and Sidheswaran, Meera A. and Yungk, Ronald and Krim, Jacqueline}, year={2017}, month={Feb} }