17 results found
Puhan D, Casford MTL, Davies PB, 2023, Evaluation of Structural and Compositional Changes of a Model Monoaromatic Hydrocarbon in a Benchtop Hydrocracker Using GC, FTIR, and NMR Spectroscopy, ACS Omega, ISSN: 2470-1343
Puhan D, Jiang S, Wong J, 2022, Effect of carbon fiber inclusions on polymeric transfer film formation on steel, Composites Science and Technology, Vol: 217, Pages: 1-10, ISSN: 0266-3538
High performance polymers (HPPs) with good tribological properties are commonly used in dry contacts, wheretheir tribological performance often depends on properties of polymeric transfer materials (transfer layers) oncounterfaces. Most HPPs suffer from high temperature degradation due to frictional heating, leading to excessivedeformation and wear. Incorporating thermally conducting fillers increases their thermal conductivity andmechanical strength. The impact of these fillers on formation and properties of transfer layers, however, isunclear. In this work the effect of short carbon fiber fillers (CFs) on the nature of the transfer layers andtribological performance of polyetheretherketone (PEEK) and polyetheretherketone-polybenzimidizole (PBP)against steel were investigated at temperature up to 300 ◦C. Transfer layers of CF reinforced PEEK and PBPcontain CF-related materials, resulting in a reduction of friction as compared to neat PEEK and PBP, especiallyaround the glass transition temperature of PEEK (Tg− PEEK) when the transfer layer is relatively thick. While theinclusion of CFs increases the bulk thermal conductivity of polymer composites, the average contact temperatureis not affected. Rather, local hot spots are generated. As a result, their transfer layers may have formed morereadily and have undergone more severe degradation than those from neat polymer. At 300 ◦C, the PBP + CFtransfer layer is thin possibly due to abrasion by CFs dislodged from the matrix. The improvement in the wearresistance due to CF inclusion is observed with PBP up to 300 ◦C due to its improved mechanical strength. PEEK+ CF however suffers higher wear than PEEK below Tg− PEEK. Above Tg− PEEK, a thick transfer layer is formed andthe wear of PEEK + CF reduces.
Liu X, Ouyang M, Orzech M, et al., 2020, In-situ fabrication of carbon-metal fabrics as freestanding electrodes for high-performance flexible energy storage devices, Energy Storage Materials, Vol: 30, Pages: 329-336, ISSN: 2405-8297
Hierarchical 1D carbon structures are attractive due to their mechanical, chemical and electrochemical properties however the synthesis of these materials can be costly and complicated. Here, through the combination of inexpensive acetylacetonate salts of Ni, Co and Fe with a solution of polyacrylonitrile (PAN), self-assembling carbon-metal fabrics (CMFs) containing unique 1D hierarchical structures can be created via easy and low-cost heat treatment without the need for costly catalyst deposition nor a dangerous hydrocarbon atmosphere. Microscopic and spectroscopic measurements show that the CMFs form through the decomposition and exsolution of metal nanoparticle domains which then catalyze the formation of carbon nanotubes through the decomposition by-products of the PAN. These weakly bound nanoparticles form structures similar to trichomes found in plants, with a combination of base-growth, tip-growth and peapod-like structures, where the metal domain exhibits a core(graphitic)-shell(disorder) carbon coating where the thickness is in-line with the metal-carbon binding energy. These CMFs were used as a cathode in a flexible zinc-air battery which exhibited superior performance to pure electrospun carbon fibers, with their metallic nanoparticle domains acting as bifunctional catalysts. This work therefore unlocks a potentially new category of composite metal-carbon fiber based structures for energy storage applications and beyond.
Fellows AP, Puhan D, Casford MTL, et al., 2020, Understanding the Lubrication Mechanism of Poly(vinyl alcohol) Hydrogels using Infrared Nanospectroscopy, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 124, Pages: 18091-18101, ISSN: 1932-7447
Hu S, Cao X, Reddyhoff T, et al., 2020, Liquid repellency enhancement through flexible microstructures, Science Advances, Vol: 6, Pages: 1-7, ISSN: 2375-2548
Artificial liquid-repellent surfaces have attracted substantial scientific and industrial attention with a focus on creating functional topological features; however, the role of the underlying structures has been overlooked. Recent developments in micro-nanofabrication allow us now to construct a skin-muscle type system combining interfacial liquid repellence atop a mechanically functional structure. Specifically, we design surfaces comprising bioinspired, mushroom-like repelling heads and spring-like flexible supports, which are realized by three-dimensional direct laser lithography. The flexible supports elevate liquid repellency by resisting droplet impalement and reducing contact time. This, previously unknown, use of spring-like flexible supports to enhance liquid repellency provides an excellent level of control over droplet manipulation. Moreover, this extends repellent microstructure research from statics to dynamics and is envisioned to yield functionalities and possibilities by linking functional surfaces and mechanical metamaterials.
Hu S, Reddyhoff T, Puhan D, et al., 2020, Droplet manipulation of hierarchical steel surfaces using femtosecond laser fabrication, Applied Surface Science, Vol: 521, Pages: 146474-146474, ISSN: 0169-4332
Wen J, Reddyhoff T, Hu S, et al., 2020, Exploiting air cushion effects to optimise a superhydrophobic/hydrophilic patterned liquid ring sealed air bearing, Tribology International, Vol: 144, ISSN: 0301-679X
A thrust bearing consisting of an air cushion formed within a liquid ring has been developed, which takes advantage of the Laplace pressure induced by the liquid/air surface tension. As forces induced by Laplace pressure and surface tension scales down much more slowly than gravity and inertial forces, such a bearing has great potential when scaled down to the micro-scale. The liquid ring between the rotor and the stator of the bearing is anchored there by alternating hydrophilic and superhydrophobic patterns. An important discovery is that the performance of this bearing is greatly enhanced by the sealed cushion of air within the ring. This air cushion and thin liquid ring arrangement mean that the solid/solid contact of the bearing is replaced by solid/air and solid/liquid contact which significantly reduces the friction and wear. The factors which affects the performance of the bearing have been studied both experimentally and numerically providing results that can be used to optimise the design of this new type of bearing.
Casford MTL, Puhan D, Davies PB, et al., 2020, Thermal Behaviour of Synovene and Oleamide in Oil Adsorbed on Steel, TRIBOLOGY LETTERS, Vol: 68, ISSN: 1023-8883
Hu S, Cao X, Reddyhoff T, et al., 2019, Self-compensating liquid repellent surfaces with stratified morphology, ACS Applied Materials and Interfaces, Vol: 12, Pages: 4174-4182, ISSN: 1944-8244
Artificial liquid repellent surfaces have recently attracted vast scientific attention; however, achieving mechanical robustness remains a formidable challenge before industrialization can be realized. To this end, inspired by plateaus in geological landscapes, a self-compensating strategy is developed to pave the way for the synthesis of durable repellent surfaces. This self-compensating surface comprises tall hydrophobic structural elements, which can repel liquid droplets. When these elements are damaged, they expose shorter structural elements that also suspend the droplets and thus preserve interfacial repellency. An example of this plateau-inspired stratified surface was created by 3D direct laser lithography micro-nano fabrication. Even after being subjected to serious frictional damage, it maintained static repellency to water with a contact angle above 147 and was simultaneously able to endure high pressures arising from droplet impacts. Extending the scope of nature-inspired functional surfaces from conventional biomimetics to geological landscapes, this works demonstrates that the plateau-inspired self-compensating strategy can provide an unprecedented level of robustness in terms of sustained liquid repellency.
Puhan D, Wong J, 2019, Properties of Polyetheretherketone (PEEK) transferred materials in a PEEK-steel contact, Tribology International, Vol: 135, Pages: 189-199, ISSN: 0301-679X
Polyetheretherketone (PEEK) is a high performance polymer that can be an alternative to metal for some moving components in unlubricated conditions. During rubbing, PEEK is transferred to the counterface. The formation and properties of PEEK transfer films on steel and sapphire are studied by in-situ observations of PEEK wear process, contact temperatures and triboemission, as well as FTIR and Raman spectroscopies ex situ. Our results suggest that frictional heating alone may not be sufficient to generate PEEK degradation observed in the transfer materials. Triboplasma observed during rubbing, together with the mechanical shear, may promote generations of radicals and degradation of PEEK, which subsequently influence the properties of PEEK transfer film and performance of polymer-metal tribopair.
Hu S, Cao X, Reddyhoff T, et al., 2019, Three-dimensional printed surfaces inspired by bi-Gaussian stratified plateaus, ACS Applied Materials and Interfaces, Vol: 11, Pages: 20528-20534, ISSN: 1944-8244
Wettability of artificial surfaces is attracting increasing attention for its relevant technological applications. Functional performance is often achieved by mimicking the topographical structures found in natural flora and fauna; however, surface attributes inspired by geological landscapes have so far escaped attention. We reproduced a stratified morphology of plateaus with a bi-Gaussian height distribution using a three-dimensional direct laser lithography. The plateau-inspired artificial surface exhibits a hydrophobic behavior even if fabricated from a hydrophilic material, giving rise to a new wetting mechanism that divides the well-known macroscopic Wenzel and Cassie states into four substates. We have also successfully applied the plateau-inspired structure to droplet manipulation.
Geng Z, Puhan D, Reddyhoff T, 2019, Using acoustic emission to characterize friction and wear in dry sliding steel contacts, Tribology International, Vol: 134, Pages: 394-407, ISSN: 0301-679X
© 2019 Acoustic emission (AE) was recorded during tribological tests on 52,100 steel specimens under different loads. AE signals were transformed to the frequency domain using a Fast Fourier Transform and parameters such as power, RMS amplitude, mean frequency, and energy were analyzed and compared with friction coefficient and wear volume measurements. Results show that certain acoustic frequencies reflect friction while others reflect wear. If frequencies are chosen optimally, AE and friction signals are highly correlated (Pearson coefficients >0.8). SEM and Raman analysis reveal how plastic deformation and oxide formation affect friction, wear and AE simultaneously. AE recordings contains more information than conventional friction and wear volume measurements and are more sensitive to changes in mechanism. This all demonstrates AE's potential as a tool to monitor tribological behavior.
Hu S, Vladescu S-C, Puhan D, et al., 2019, Bi-Gaussian stratified theory to understand wettability on rough topographies, Surface and Coatings Technology, ISSN: 0257-8972
Hu S, Reddyhoff T, Puhan D, et al., 2019, Bi-Gaussian stratified wetting model on rough surfaces, Langmuir, Vol: 35, Pages: 5967-5974, ISSN: 0743-7463
Wetting mechanisms on rough surfaces were understood from either a monolayer or a multiscale perspective. However, it has recently been shown that the bi-Gaussian stratified nature of real surfaces should be accounted for when modeling mechanisms of lubrication, sealing, contact, friction, acoustic emission, and manufacture. In this work, a model combining Wenzel and Cassie theories was put forward to predict the static contact angle of a droplet on a bi-Gaussian stratified surface. The model was initially applied to numerically simulated surfaces and subsequently demonstrated on hydrophilic steel and hydrophobic self-assembled monolayer specimens with preset bi-Gaussian stratified topographies. In the Wenzel state, both the upper and the lower surface components are fully wetted. In the Cassie state, the upper component is still completely wetted, while the lower component serves as gas traps and reservoirs. By this model, wetting evolution was assessed, and the existence of different wetting states and potential state transitions was predicted.
Puhan D, Nevshupa R, Wong J, et al., 2019, Transient aspects of plasma luminescence induced by triboelectrification of polymers, Tribology International, Vol: 130, Pages: 366-377, ISSN: 0301-679X
Transient electric gas discharges that occur around sliding interfaces during contact electrification of polymers were studied at millisecond timescales and with micrometre resolution. Deduced vibrational temperatures indicate cold plasma resulting from positive corona discharge. At millisecond timescales, previously unseen rapid discharge events are observed, and modelling suggests that these result from streamer development, triggered by electron emission from the polymer surface. Those which occur over a period of several seconds are shown to be caused by competition between charge generation and the formation of polymer films. The findings explain the interplay between charging and plasma generation and their dependence on wear processes.
Bijwe J, Kadiyala AK, Kumar K, et al., 2015, Development of high performance poly (ether-ketone) composites based on novel processing technique, MATERIALS & DESIGN, Vol: 73, Pages: 50-59, ISSN: 0264-1275
Puhan D, Bijwe J, Parida T, et al., 2015, Investigations on Performance Properties of Nano-Micro Composites Based on Polyetherketone, Short Carbon Fibers and Hexa-Boron Nitride, SCIENCE OF ADVANCED MATERIALS, Vol: 7, Pages: 1002-1011, ISSN: 1947-2935
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