Anchor Group Bottlebrush Polymers as Oil Additive Friction Modifiers.

Surface-tethered polymers have been shown to be an efficient lubrication strategy for boundary and mixed lubrication by providing a solvated film between solid surfaces. We have assessed the performance of various graft copolymers as friction modifier additives in oil and revealed important structure-property relationships for this application. The polymers consisted of an oil-soluble, grafted poly(lauryl acrylate) segment and a polar, linear poly(4-acryloylmorpholine) anchor group. Reversible addition-fragmentation chain transfer polymerization was used to access various architectures with control of the grafting density and position of the anchor group. Macrotribological studies displayed promising results with ≈50% reduction in friction coefficient at low polymer treatment rates. QCM-D experiments, neutron reflectometry, small-angle neutron scattering, and atomic force microscopy were used to gather detailed information on these polymers' surface adsorption characteristics, film structure, and solution behavior.

Enhanced Adsorption of Epoxy-Functional Nanoparticles onto Stainless Steel Significantly Reduces Friction in Tribological Studies.

Epoxy-functional sterically-stabilized diblock copolymer nanoparticles (ca. 27 nm) are prepared via RAFT dispersion polymerization in mineral oil. Nanoparticle adsorption onto stainless steel is examined using a quartz crystal microbalance. Incorporating epoxy groups within the steric stabilizer chains results in a two-fold increase in the adsorbed amount, Γ, at 20 °C (7.6 mg m-2 ) compared to epoxy-core functional nanoparticles (3.7 mg m-2 ) or non-functional nanoparticles (3.8 mg m-2 ). A larger difference in Γ is observed at 40 °C; this suggests chemical adsorption of the nanoparticles rather than merely physical adsorption. A remarkable near five-fold increase in Γ is observed for ca. 50 nm epoxy-functional nanoparticles compared to non-functional nanoparticles (31.3 vs. 6.4 mg m-2 , respectively). Tribological studies confirm that chemical adsorption of the latter epoxy-functional nanoparticles leads to a significant reduction in friction between 60 °C and 120 °C.

Screening the Surface Structure-Dependent Action of a Benzotriazole Derivative on Copper Electrochemistry in a Triple-Phase Nanoscale Environment.

Copper (Cu) corrosion is a compelling problem in the automotive sector and in oil refinery and transport, where it is mainly caused by the action of acidic aqueous droplets dispersed in an oil phase. Corrosion inhibitors, such as benzotriazole (BTAH) and its derivatives, are widely used to limit such corrosion processes. The efficacy of corrosion inhibitors is expected to be dependent on the surface crystallography of metals exposed to the corrosion environment. Yet, studies of the effect of additives at the local level of the surface crystallographic structure of polycrystalline metals are challenging, particularly lacking for the triple-phase corrosion problem (metal/aqueous/oil). To address this issue, scanning electrochemical cell microscopy (SECCM), is used in an acidic nanodroplet meniscus|oil layer|polycrystalline Cu configuration to explore the grain-dependent influence of an oil soluble BTAH derivative (BTA-R) on Cu electrochemistry within the confines of a local aqueous nanoprobe. Electrochemical maps, collected in the voltammetric mode at an array of >1000 points across the Cu surface, reveal both cathodic (mainly the oxygen reduction reaction) and anodic (Cu electrooxidation) processes, of relevance to corrosion, as a function of the local crystallographic structure, deduced with co-located electron backscatter diffraction (EBSD). BTA-R is active on the whole spectrum of crystallographic orientations analyzed, but there is a complex grain-dependent action, distinct for oxygen reduction and Cu oxidation. The methodology pinpoints the surface structural motifs that facilitate corrosion-related processes and where BTA-R works most efficiently. Combined SECCM-EBSD provides a detailed screen of a spectrum of surface sites, and the results should inform future modeling studies, ultimately contributing to a better inhibitor design.

Nanoscale electrochemistry in a copper/aqueous/oil three-phase system: surface structure-activity-corrosion potential relationships.

Practically important metal electrodes are usually polycrystalline, comprising surface grains of many different crystallographic orientations, as well as grain boundaries. In this study, scanning electrochemical cell microscopy (SECCM) is applied in tandem with co-located electron backscattered diffraction (EBSD) to give a holistic view of the relationship between the surface structure and the electrochemical activity and corrosion susceptibility of polycrystalline Cu. An unusual aqueous nanodroplet/oil (dodecane)/metal three-phase configuration is employed, which opens up new prospects for fundamental studies of multiphase electrochemical systems, and mimics the environment of corrosion in certain industrial and automotive applications. In this configuration, the nanodroplet formed at the end of the SECCM probe (nanopipette) is surrounded by dodecane, which acts as a reservoir for oil-soluble species (e.g., O2) and can give rise to enhanced flux(es) across the immiscible liquid-liquid interface, as shown by finite element method (FEM) simulations. This unique three-phase configuration is used to fingerprint nanoscale corrosion in a nanodroplet cell, and to analyse the interrelationship between the Cu oxidation, Cu2+ deposition and oxygen reduction reaction (ORR) processes, together with nanoscale open circuit (corrosion) potential, in a grain-by-grain manner. Complex patterns of surface reactivity highlight the important role of grains of high-index orientation and microscopic surface defects (e.g., microscratches) in modulating the corrosion-properties of polycrystalline Cu. This work provides a roadmap for in-depth surface structure-function studies in (electro)materials science and highlights how small variations in surface structure (e.g., crystallographic orientation) can give rise to large differences in nanoscale reactivity.

Versatile Polymer-Free Graphene Transfer Method and Applications.

A new method for transferring chemical vapor deposition (CVD)-grown monolayer graphene to a variety of substrates is described. The method makes use of an organic/aqueous biphasic configuration, avoiding the use of any polymeric materials that can cause severe contamination problems. The graphene-coated copper foil sample (on which graphene was grown) sits at the interface between hexane and an aqueous etching solution of ammonium persulfate to remove the copper. With the aid of an Si/SiO2 substrate, the graphene layer is then transferred to a second hexane/water interface to remove etching products. From this new location, CVD graphene is readily transferred to arbitrary substrates, including three-dimensional architectures as represented by atomic force microscopy (AFM) tips and transmission electron microscopy (TEM) grids. Graphene produces a conformal layer on AFM tips, to the very end, allowing easy production of tips for conductive AFM imaging. Graphene transferred to copper TEM grids provides large-area, highly electron-transparent substrates for TEM imaging. These substrates can also be used as working electrodes for electrochemistry and high-resolution wetting studies. By using scanning electrochemical cell microscopy, it is possible to make electrochemical and wetting measurements at either a freestanding graphene film or a copper-supported graphene area and readily determine any differences in behavior.

Prognostic utility of cardiovascular magnetic resonance upright maximal treadmill exercise testing.

BACKGROUND: Left ventricular wall motion abnormalities (LVWMA) observed during cardiovascular magnetic resonance (CMR) pharmacologic stress testing can be used to determine cardiac prognosis, but currently, information regarding the prognostic utility of upright maximal treadmill induced LVWMA is unknown. Our objective was to determine the prognostic utility of upright maximal treadmill exercise stress CMR. METHODS: One hundred and fifteen (115) men and women with known or suspected coronary arteriosclerosis and an appropriate indication for cardiovascular (CV) imaging to supplement ST segment stress testing underwent an upright treadmill exercise CMR stress test in which LVWMA were identified before and immediately after exercise. Personnel blinded to results determined the post-test incidence of cardiac events (cardiac death, myocardial infarctions [MI], and unstable angina warranting hospital admission or coronary arterial revascularization). RESULTS: All participants completed the testing protocol, with 90% completing image acquisition within 60 s of exercise cessation. MI or cardiac death occurred in 3% of individuals without and 17% of individuals with inducible LVWMA (p = 0.024). The combination of MI, cardiac death, and unstable angina warranting hospitalization occurred in 14% of individuals without and 47% of individuals with inducible LVWMA (p = 0.002). The addition of CMR imaging identified those at risk for future events (p = 0.002), as opposed to the electrocardiogram stress test alone (p = 0.63). CONCLUSIONS: In patients with or suspected of coronary arteriosclerosis and appropriate indication for imaging to supplement ST segment analysis during upright treadmill exercise, the presence of inducible LVWMA during treadmill exercise stress CMR supplements ST segment monitoring and helps identify those at risk of the future combined endpoints of myocardial infarction, cardiac death, and unstable angina warranting hospitalization.

Nucleation, aggregative growth and detachment of metal nanoparticles during electrodeposition at electrode surfaces.

The nucleation and growth of metal nanoparticles (NPs) on surfaces is of considerable interest with regard to creating functional interfaces with myriad applications. Yet, key features of these processes remain elusive and are undergoing revision. Here, the mechanism of the electrodeposition of silver on basal plane highly oriented pyrolytic graphite (HOPG) is investigated as a model system at a wide range of length scales, spanning electrochemical measurements from the macroscale to the nanoscale using scanning electrochemical cell microscopy (SECCM), a pipette-based approach. The macroscale measurements show that the nucleation process cannot be modelled as either truly instantaneous or progressive, and that step edge sites of HOPG do not play a dominant role in nucleation events compared to the HOPG basal plane, as has been widely proposed. Moreover, nucleation numbers extracted from electrochemical analysis do not match those determined by atomic force microscopy (AFM). The high time and spatial resolution of the nanoscale pipette set-up reveals individual nucleation and growth events at the graphite basal surface that are resolved and analysed in detail. Based on these results, corroborated with complementary microscopy measurements, we propose that a nucleation-aggregative growth-detachment mechanism is an important feature of the electrodeposition of silver NPs on HOPG. These findings have major implications for NP electrodeposition and for understanding electrochemical processes at graphitic materials generally.

Molecular functionalization of graphite surfaces: basal plane versus step edge electrochemical activity.

The chemical functionalization of carbon surfaces has myriad applications, from tailored sensors to electrocatalysts. Here, the adsorption and electrochemistry of anthraquinone-2,6-disulfonate (AQDS) is studied on highly oriented pyrolytic graphite (HOPG) as a model sp(2) surface. A major focus is to elucidate whether adsorbed electroactive AQDS can be used as a marker of step edges, which have generally been regarded as the main electroactive sites on graphite electrode surfaces. First, the macroscopic electrochemistry of AQDS is studied on a range of surfaces differing in step edge density by more than 2 orders of magnitude, complemented with ex situ tapping mode atomic force microscopy (AFM) data. These measurements show that step edges have little effect on the extent of adsorbed electroactive AQDS. Second, a new fast scan cyclic voltammetry protocol carried out with scanning electrochemical cell microscopy (SECCM) enables the evolution of AQDS adsorption to be followed locally on a rapid time scale. Subsequent AFM imaging of the areas probed by SECCM allows a direct correlation of the electroactive adsorption coverage and the actual step edge density of the entire working area. The amount of adsorbed electroactive AQDS and the electron transfer kinetics are independent of the step edge coverage. Last, SECCM reactive patterning is carried out with complementary AFM measurements to probe the diffusional electroactivity of AQDS. There is essentially uniform and high activity across the basal surface of HOPG. This work provides new methodology to monitor adsorption processes at surfaces and shows unambiguously that there is no correlation between the step edge density of graphite surfaces and the observed coverage of electroactive AQDS. The electroactivity is dominated by the basal surface, and studies that have used AQDS as a marker of steps need to be revised.

Spatial and temporal control of the diazonium modification of sp2 carbon surfaces.

Interest in the controlled chemical functionalization of sp(2) carbon materials using diazonium compounds has been recently reignited, particularly as a means to generate a band gap in graphene. We demonstrate local diazonium modification of pristine sp(2) carbon surfaces, with high control, at the micrometer scale through the use of scanning electrochemical cell microscopy (SECCM). Electrochemically driven diazonium patterning is investigated at a range of driving forces, coupled with surface analysis using atomic force microscopy (AFM) and Raman spectroscopy. We highlight how the film density, level of sp(2)/sp(3) rehybridization and the extent of multilayer formation can be controlled, paving the way for the use of localized electrochemistry as a route to controlled diazonium modification.

Argon beam coagulation versus fibrin sealant for hemostasis following liver resection: a randomized study in a porcine model.

BACKGROUND/AIMS: Bleeding from the raw liver surface represents a significant surgical complication after elective liver resection or hepatic trauma. The application of argon beam coagulation (ABC) has been proposed to improve hemostasis, but is associated with significant necrosis of the liver parenchyma. Topical hemostatic agents, i.e. fibrin sealant (FS), have also been recommended, yet the optimal management is under debate. This study compares the efficacy and safety of both methods following liver resection in an animal model. METHODOLOGY: Twenty pigs underwent liver resection, and were then randomized into ABC or FS group for treatment of raw liver surfaces. Intraoperative and postoperative parameters were studied. Animals were sacrificed at day 12, and extent of necrosis was assessed using a scoring system and morphometry. RESULTS: Intraoperative parameters did not show any significant difference between two groups except for shorter time of application in the FS group. Postoperatively, animals in the FS group showed significantly higher hemoglobin levels (p=0.0001). Histologically, FS showed a smaller depth of necrosis than ABC (p=0.022). CONCLUSIONS: The use of FS is superior to ABC for management of the raw liver surface after liver resection, in terms of application time, postoperative bleeding and the extent of liver tissue necrosis.

Neointimal hyperplasia on a cell-seeded polytetrafluoroethylene graft is promoted by transfer of tissue plasminogen activator gene and inhibited by transfer of nitric oxide synthase gene.

OBJECTIVE: The objective of this study was to examine the effect of tissue plasminogen activator (tPA) and endothelial nitric oxide synthase (eNOS) on thrombosis and neointimal hyperplasia on a polytetrafluoroethylene (PTFE) graft seeded with smooth muscle cells (SMCs). METHODS: SMCs retrovirally transduced with tPA and eNOS genes were seeded on PTFE grafts and then implanted into the infrarenal rabbit aorta. Thrombosis and neointimal hyperplasia on the grafts were examined after 30 and 100 days of implantation. RESULTS: At 30 days of implantation, thrombus was observed on the luminal surface of both unseeded and SMC seeded control grafts, whereas grafts seeded with SMCs secreting tPA were nearly free of thrombus. At 100 days, the neointima on grafts seeded with tPA transduced SMCs was significantly thicker (925 +/- 150 microm, n = 5) than neointima on the other grafts (range, 132 to 374 microm; P < .001). Neointima thickness on grafts seeded with eNOS transduced SMCs (154 +/- 27 microm) was similar to that of unseeded grafts (132 +/- 16 microm, P > .05); both were thinner than those on grafts seeded with SMCs transduced with only lacZ gene (287 +/- 35 microm). The ratio of seeded cells in the neointima was significantly higher on SMC/tPA grafts (46% +/- 8%) than SMC/NOS grafts (21% +/- 6%, P < .05), indicating tPA transduced cells proliferated more than eNOS transduced cells. CONCLUSIONS: Engineered tPA expression in seeded SMCs causes significantly more neointimal hyperplasia, despite the favorable inhibition of luminal thrombus. eNOS expression in the seeded cells inhibits neointimal hyperplasia.

Smooth muscle cells improve endothelial cell retention on polytetrafluoroethylene grafts in vivo.

OBJECTIVE: We investigated the influence of smooth muscle cells (SMC) on endothelial cell (EC) retention on polytetrafluoroethylene (PTFE) grafts and the effect of SMC seeding on intimal hyperplasia in vivo in a rabbit model. METHODS: Fibronectin-coated PTFE grafts (4 mm diameter) were seeded with either EC alone, SMC alone, or SMC followed 24 hours later by EC. The grafts were connected to an extracorporal aortic shunt for 1 hour or were individually implanted for 1, 30, and 100 days into the infrarenal aorta as an end-to-side bypass graft. The number of retained cells was compared at 1 hour and at 1 day after implantation. Neointimal thickness was measured 30 and 100 days after implantation. RESULTS: After 1-hour exposure to blood flow, EC retention rate was greater (P <.005) if seeded on top of SMC (98% +/- 2%; n = 8) versus being seeded alone (65 +/- 11%; n = 8). SMC retention rate was 95 +/- 5% (n = 8) when seeded alone. Similar cell retention was obtained 1 day after implantation. After 30-day implantation the neointima was thicker in grafts seeded with EC and SMC (282 +/- 136 microm; n = 3) than with EC only (52 +/- 45 microm; n = 3; P <.001). However, the neointimal thickness for dual-cell-seeded grafts (126 +/- 60 microm; n = 3) was not significantly different (P =.09) from EC-seeded grafts (79 +/- 48 microm; n = 3) after 100-day implantation. CONCLUSION: EC retention on PTFE grafts in vivo is improved if seeded over a layer of SMC. Further studies are needed to determine whether overlying EC modulate proliferation of underlying SMC.

Abdominal insufflation for prevention of exsanguination.

BACKGROUND: Currently, traumatic intra-abdominal hemorrhage continues unchecked during transport and triage, and a simple technique of prehospital hemostasis might improve outcomes. The hemostatic effect of abdominal hypertension has not been studied. PURPOSE: To examine the effect of iatrogenic abdominal insufflation on blood loss and hemodynamic performance after major abdominal vascular injury. METHODS: Following laparotomy, a 2.7 mm hole was created in the inferior vena cava of 10 anticoagulated pigs and controlled with a partially occlusive, laparoscopic vascular clamp. After abdominal closure the clamp was released and the pig was randomized to either control (n = 5) or immediate abdominal CO2 insufflation at 20 cm H2O pressure (n = 5). Lactated Ringer's solution was used as needed to maintain a mean arterial pressure of 60 mm Hg. After 15 minutes of hemorrhage and hemodynamic monitoring, the animals were killed and blood loss measured. Mean blood loss was compared between groups using the Student test, as were final values for physiologic variables. Temporal changes in physiologic parameters were compared using analysis of variance. RESULTS: Mean blood loss was reduced by 61% in insufflated pigs versus controls (695 +/- 244 versus 1764 +/- 328 cc, p < 0.001). Compared with controls, insufflated pigs had significantly higher mean arterial pressure (64 versus 25 mm Hg, p < 0.001), end-tidal CO2 (40.8 versus 17.8 mm Hg, p < 0.001), and pulmonary capillary wedge pressure (10.2 versus 5.8 mm Hg, p = 0.026) immediately before the pigs were killed. CONCLUSION: Iatrogenic abdominal insufflation significantly decreased blood loss and improved hemodynamics in a porcine model of traumatic venous hemorrhage. Iatrogenic abdominal insufflation may be useful in the prehospital management of abdominal injury.