共找到 20 条结果
We recently reported a new molecular heterocyclic friction modifier (FM) that exhibits excellent friction and wear reduction in the boundary lubrication regime. This paper explores the mechanisms by which friction reduction occurs with heterocyclic alkyl-cyclen FM molecules. We find that these chelating molecules adsorb onto (oxidized) steel surfaces far more tenaciously than conventional FMs such as simple alkylamines. Molecular dynamics simulations argue that the surface coverage of our heterocyclic FM molecules remains close to 100% even at 200 °C. This thermal stability allows the FMs to firmly anchor to the surface, allowing the hydrocarbon chains of the molecules to interact and trap base oil lubricant molecules. This results in thicker boundary film thickness compared with conventional FMs, as shown by optical interferometry measurements.
The shear thinning of a lubricant significantly affects lubrication film generation at high shear rates. The critical shear rate, defined at the onset of shear thinning, marks the transition of lubricant behaviors. It is challenging to capture the entire shear-thinning curve by means of molecular dynamics (MD) simulations owing to the low signal-to-noise ratio or long calculation time at comparatively low shear rates (104-106 s-1), which is likely coincident with the shear rates of interest for lubrication applications. This paper proposes an approach that correlates the shear-thinning phenomenon with the change in the molecular conformation characterized by the radius of gyration of the molecule. Such a correlation should be feasible to capture the major mechanism of shear thinning for small- to moderate-sized non-spherical molecules, which is shear-induced molecular alignment. The idea is demonstrated by analyzing the critical shear rate for squalane (C30H62) and 1-decene trimer (C30H62); it is then implemented to study the behaviors of different molecular weight poly-α-olefin (PAO) structures. Time-temperature-pressure superpositioning (TTPS) is demonstrated and it helps further extend the ranges of the temperature and pressure for shear-thinning behavior analyses. The research leads to a relationship between molecular weight and critical shear rate for PAO structures, and the results are compared with those from the Einstein-Debye equation.
The destabilization mechanism was investigated of a triple Janus emulsion. The inner part of the emulsion consisted of Janus drops of a vegetable oil (VO) and a silicone oil (SO) in an aqueous (W) drop, (VO+SO)/W. This drop, in turn was dispersed in a VO drop forming a double emulsion (VO+SO)/W/VO. Finally, these complex drops generated a complex Janus (SO+VO)/W/VO/SO triple emulsion by being dispersed in a continuous SO phase. The observations were limited to the time dependence of the over-all creaming/sedimentation processes, to the separation of layers of the compounds and to optical microscopy of the drop configuration with time. In the destabilization process the rise of the complex drops, (SO+VO)/W/VO, caused crowding in the upper part of the emulsion, which in turn led to enhanced coalescence, inversion and separation of a dilute vegetable oil emulsion. As a consequence of the separation of VO in the process, the remaining drops contained a greater W fraction and greater density. This change, in turn, resulted in sedimentation of the complex drops to form several high internal ratio morphologies in an SO continuous emulsion in the lower part of the test tube, among them a W/VO/SO emulsion. Finally, an inversion took place into an SO/VO/W double emulsion forming a separate bottom layer.
Ocean heat plus human-caused global warming is a grim recipe for deadly climate extremes
The Universe’s biggest black holes may not be born giants after all。 Scientists analyzing gravitational-wave signals from dozens of black hole collisions found evidence that the heaviest black holes are likely “cosmic recyclers” — formed through repeated smashups inside incredibly crowded star clusters。 These violent chain reactions appear to creat
NASA’s Psyche spacecraft is about to pull off a dramatic close flyby of Mars, skimming just 2,800 miles above the planet to get a powerful gravitational boost on its journey to the mysterious metal-rich asteroid Psyche。 The maneuver will save propellant while giving mission scientists a rare chance to test and calibrate the spacecraft’s instruments
A new quantum-inspired algorithm has cracked a problem so massive that conventional supercomputers struggle to even approach it。 Researchers used the method to simulate extraordinarily complex quantum materials known as quasicrystals, opening the door to powerful new quantum devices and ultra-efficient electronics。 The work could help scientists de
A medieval monk may have beaten Edmond Halley to one of astronomy’s greatest discoveries by nearly 700 years。 Researchers say Eilmer of Malmesbury recognized that the blazing comet seen in 1066 was the same one he had witnessed in 989。 At the time, comets were viewed as terrifying omens tied to war and royal deaths, adding even more drama to the fa
A newly discovered meteor stream may be the smoking gun of an asteroid slowly disintegrating under the Sun’s intense heat。 Scientists say these fiery streaks across the night sky could reveal hidden near-Earth asteroids that telescopes struggle to detect
A new study suggests AI chatbots may do more than spread misinformation — they can actively strengthen a user’s false beliefs。 Because conversational AI often validates and builds on what users say, it can make distorted memories, conspiracy theories, or delusions feel more believable and emotionally real。 Researchers warn that AI companions may be
Astronomers have spotted something surprising in the far outer Solar System—a faint, short-lived atmosphere clinging to a tiny icy world that shouldn’t be able to hold one at all。 The object, called 2002 XV93, is far smaller than Pluto, yet observations during a rare stellar alignment revealed its presence through a subtle dimming of starlight。 Eve
Hubble has revealed a giant planet-forming disk unlike anything astronomers have seen before。 Nicknamed “Dracula’s Chivito,” the enormous structure appears turbulent and oddly lopsided, with towering filaments visible on only one side。 The disk contains enough material to potentially create multiple giant planets, making it a fascinating new labora
A scorching, airless world just 48 light-years away is offering scientists a rare glimpse into the geology of distant planets。 Using the James Webb Space Telescope, researchers studied LHS 3844 b—a tidally locked “super-Earth” with a permanent dayside hot enough to melt metal—and discovered it’s a dark, barren rock with no atmosphere
Scientists in Japan have developed a new way to instantly detect elusive quantum “W states,” a major milestone for quantum technology。 The breakthrough could help unlock faster quantum communication, teleportation, and powerful new computing systems
For nearly 100 years, reinforced rubber has powered everything from car tires to airplanes, yet scientists never fully understood why adding tiny particles of carbon black made rubber so incredibly strong。 Now, researchers at the University of South Florida have finally cracked the mystery using massive computer simulations that took the equivalent
It's not entirely clear how the exploit works。 Microsoft says it's investigating