In this study, a new strategy to achieve high-efficient heat transfer for non-Newtonian fluids with slippage using a stably prepared superhydrophobic coating is presented. A superhydrophobic coating is prepared on the inner surface of a sleeve at specific shear stress. The slippage and heat-transfer processes of the typical non-Newtonian fluid–1% carboxymethyl cellulose solutions on the superhydrophobic coating are investigated simultaneously. A novel porous spherical type of superhydrophobic coating with a contact angle of 168° is obtained. It is found that the shear stress in electrodeposition is a key parameter to control the morphology and wetting ability of the superhydrophobic coating. The slip length and enhancement factor of heat transfer for the non-Newtonian fluid on the coating are found in a range of 20–900 µm and 1.47 experimentally. A new parameter is proposed as Reynolds number Re divided by the dimensionless slip length ls* (Re/ls*) for the heat-transfer enhancement with slippage, which can be used as the guide for designing coating and selecting the operating conditions. The Re/ls* is <4, which can enhance the heat transfer via the slippage.

Syngas produced from thermochemical conversion of biomass has been given more attention because it can be converted to a variety of fuels and chemicals as substitutes for petroleum-based chemicals via the Fischer–Tropsch process. In this study, one wheat straw and its element content fluctuation in the feasible range are selected as samples first to study the effect of the biomass composition on the quality of syngas produced. Then, the thermochemical data (standard molar enthalpy of formation, standard molar entropy, and heat capacity) of samples are predicted by highly accurate prediction models. Thermochemical conversions of the samples are simulated by the Gibbs energy minimization method based on the results of thermochemical data prediction. At last, the effect of the biomass composition on the resource index (amounts of CO and H2 and ratio of H2/CO) and energy index (lower heat value) of syngas is calculated and analyzed. This study provides a method to obtain the relationship between the composition of biomass and the quality of syngas produced.

The “block‐on‐plate” nanocomposite structure material is realized with the zeolitic imidazolate framework (ZIF‐67) on graphene oxide (GO) with surface oxygen‐rich functional groups. Scanning electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffractograms, fourier transform infrared spectroscopy, and ZIF‐67/GO demonstrate a high capability of promoting the lubricating performance of [Choline][Proline] ([CH][P]) bio‐ionic liquid. Specifically, the wear volume of the disc by [CH][P]‐0.1 ZIF‐67/GO is only 52% of the one lubricated by pure [CH][P]. Moreover, ZIF‐67/GO shows a long time, high dispersion stability in [CH][P]. In addition, the combination of GO nanosheets and ZIF‐67 can make ZIF‐67/GO have better polishing effect between the steels during the friction process, which can effectively form a robust lubrication layer and improves overall lubricating properties. As a result, the interfacial lubrication can be significantly improved by these newly developed [CH][P]‐ZIF‐67/GO lubricants. This work offers a new promising application for ZIF‐67 nanocomposites with GO in advanced lubrication systems. This work also provides a new strategy of producing lubricants containing nanoparticles with high dispersion stability, which may solve the biggest challenge in this field.

High-value utilization of biomass has been driven by increasingly growing industrial demands. Herein, we offer a strategy composed of depolymerization and esterification reaction of lignin to transfer to bio-oil with high liquid yield (79.75~85.25%), which is demonstrated as a high performance lubricant. Overall, the bio-oil has the excellent lubrication properties, where a significant wear reduction of 97.6% was observed as compared with polyethylene glycol 200. Meanwhile, the more ether and less acid in bio-oil could improve the anti-wear properties. This work provides a new application of utilizing lignin in advanced lubrication systems.

Molecular level engineering of polymer or polymer blends has been recently demonstrated effective strategy to regulate thermal conductivity. Such materials are of great interest to meet critical requirements of transparent, light weight, flexible, etc for thermal management in electronic applications. In this work, modulated polymer blends with poly(vinyl alcohol) (PVA) and biopolymers (lignin, gelatin) were designed and significantly enhanced thermal conductivity was achieved by tuning the intermolecular interaction among polymer components. The hydrogen bond interaction has been revealed as the major driving force that affects the polymer coil dimension in aqueous solution, the microstructure of coil-coil interaction in solid film and thus the thermal conduction. A solid relationship across molecular level interaction to macro-scale thermal conduction is constructed via careful characterization of the coil size in liquid phase and assembled microstructure in solid phase. Appropriate integration of biopolymers and PVA is essential to achieve synergistic effect. Specifically, thermal conductivity of polymer blend with 10% lignin and 10% G90 in PVA reaches 0.71 W/m·K, which is 184% enhancement as compared to pure PVA. This work reveals the fundamental molecular origin of polymer blends in association with thermal conductivity and has great potential to guide molecular engineering for superior physicochemical properties.

Phonon transfer is greatly scattered in traditional polymer composites due to the unpaired phonon frequency at the polymer/filler interface. A key innovation of this work is to build continuous crystal network by self-organization and utilize it as “thermal highway” that circumvents the long-existing interfacial thermal barrier issue in traditional composites. By tuning the molecular diffusion rate of dicarboxylic acids (oxalic acid, malonic acid, and succinic acid), different crystal structures including skeletal, dendrite, diffusion-limited aggregates, and spherulite were synthesized in PVA film. These continuous crystal structures benefit the efficient phonon transfer in the composites with minimized interfacial scattering and lead to a significant thermal conductivity enhancement of up to 180% compared to that of pure polymer. Moreover, the transparent feature of these composite films provides additional benefits in display applications. The post heat treatment effect on the thermal conductivity of the composite films shows a time-dependent behavior. These uniquely structured polymer/crystal composites are expected to generate significant impacts in thermal management applications.

Lignin strengthened ionic liquids (ILs) have shown high potential to be used as high performance green lubricants. Strengthened lignin-ILs molecular interaction is an effective approach to improve their lubrication properties. The molecular interactions of ILs’ cation and anion containing different functional groups with lignin and efficiency on the lubricating properties have rarely been studied yet. In this work, a series of novel green lubricants with dissolved lignin in [Choline][Amino Acid] ([CH][AA]), [Tetramethylammonium][Glycine] ([N 1111 ][Gly]) and [Tetrabutylammonium][Glycine] ([N 4444 ][Gly]) ILs have been synthesized and their tribological properties were systematically investigated. The longer alkyl chain in cation without reciprocal H-bond interaction between ILs’ cation and anion has the positive effect on the anti-wear properties. In addition, the less steric effect and more negative natural charges of amino acid anion synergistically contribute to the stronger H-bond interaction between lignin and choline base ILs, which enhances lubrication film strength and thus resulting in the better tribological property of ILs/lignin green lubricants. Specifically, the wear volume loss of the steel disc lubricated by [N 4444 ][Gly] with the addition of 15% lignin is only 12% of the one lubricated by pure [N 4444 ][Gly]. This work presents a method to tune molecular interaction between lignin and ILs via the structural design of ILs’ cation and anion, which are revealed as the key factor that bridges the individual components and improves overall lubricating properties. 

Depolymerization and modification of lignin have been achieved simultaneously in a one-pot chemical reaction. Two heteroelement-rich modifiers, imidazol-1-yl phosphonic dichloride and 1H-1,2,4-triazol-1-yl phosphonic dichloride, were selected to react with lignin in this work. The modified lignin (m-lignin) is demonstrated as an effective lubricating additive for [choline][amino acid] ([CH][AA]) bioionic liquids. Different characterization techniques have been utilized to study the lignin depolymerization, reaction between lignin and modifiers and m-lignin/[CH][AA] interaction. The effect of the molecular structure of the modifiers on the rheological and tribological properties of m-lignin/[CH][AA] lubricants was systematically investigated. Density function theory is used to calculate the electronic structure of lignin, m-lignin, and [CH][AA]. The atomic natural charge analysis revealed the most negative charge on nitrogen bonded to a phosphorus atom and the strongest capability of forming hydrogen bonding with [CH][AA]. The introduced nitrogen and phosphorus elements not only increase the hydrogen bonding density in m-lignin/[CH][AA] but also enhance the polarity of the m-lignin, both of which facilitate a strong adhesion of lubricant on a metal surface and thus promote lubrication. A larger fraction of heteroatom groups in m-lignin contributes to a better lubrication property of these lubricants

Two different heteroelement-rich molecules have been successfully grafted on graphene oxide (GO) sheets which were then used as lubricant additives in bio-ionic liquid. The grafting was processed with reactions between GO sheets and synthesized heteroelement-rich molecules (Imidazol-1-yl phosphonic dichloride and 1H-1,2,4-triazol-1-yl phosphonic dichloride, respectively). The modified GO (m-GO) was added into [Choline][Proline] ([CH][P]) bio-ionic liquid, and has been demonstrated effective additive in promoting lubrication. Different characterization techniques have been utilized to study the reaction between GO and the two modifiers. The effect of molecular structure of the modifiers on the rheological and tribological properties of m-GO/[CH][P] lubricants was systematically investigated. Both theoretical calculation and experimental results demonstrated that the introduced heteroelement-rich groups are beneficial to increase the robustness of lubrication film by intensified hydrogen bonding and enhance the lubricant/friction surface adhesion by increased polarity of the m-GO. As a result, the interfacial lubrication could be significantly improved by these newly developed m-GO/[CH][P] lubricants.

Synthetic additives are widely used in lubricants nowadays to upgrade lubrication properties. The potential of integrating sustainable components in modern lubricants has rarely been studied yet. In this work, two sustainable resources lignin and gelatin have been synergistically incorporated into ethylene glycol (EG), and their tribological properties were systematically investigated. The abundant hydrogen bonding sites in lignin and gelatin as well as their interchain interaction via hydrogen bonding play the dominating roles in tuning the physicochemical properties of the mixture and improving lubricating properties. Moreover, the synergistic combination of lignin and gelatin induces charge separation of gelatin that enables its preferable adsorption on the friction surface through electrostatic force and forms a robust lubrication layer. This layer will be strengthened by lignin through the interpolymer chain hydrogen bonding. At an optimized lignin:gelatin mass ratio of 1:1 and 19 wt % loading of each in EG, the friction coefficient can be greatly stabilized and the wear loss was reduced by 89% compared to pure EG. This work presents a unique synergistic phenomenon between gelatin and lignin, where hydrogen bonding and change separation are revealed as the key factor that bridges the individual components and improves overall lubricating properties.

Lignin, one of the most abundant natural polymers, has been successfully used as an effective lubricant additive with high value. The chemical structure of lignin is very diverse and strongly affected by both the source of lignin (i.e. plant species) and the lignin extraction process. In this work, a series of lignin from different biomass sources (hard or soft wood) and extraction process (organosolv with or without acid catalyst) has been successfully incorporated into poly(ethylene glycol) (PEG) and fortified lubricating properties were achieved. The effects of different lignin on the rheological, thermal and tribological properties of the lignin/EG lubricants were systematically investigated by different characterization techniques. Lignin in PEG significantly improves the lubricating property, where a wear reduction of 93.8% was observed. The thermal and lubrication properties of the PEG lubricants filled with different kinds of lignin are tightly related to the synergistic state of hydrogen bonding and molecular weight distribution. Lignin with broader molecular weight distribution and higher hydroxyl content shows better adhesion on metal surfaces and strengthened lubricating film, which could be used as the efficient lubricating additives. This work provides a criterion for selecting appropriate lignin as the efficient lubricant additive and accelerates the application of lignin.

Ethylene glycol (EG)-based lubricant was prepared with dissolved organosolv lignin from birch wood (BL) and softwood (SL) biomass. The effects of different lignin types on the rheological, thermal, and tribological properties of the lignin/EG lubricants were comprehensively investigated by various characterization techniques. Dissolving organosolv lignin in EG results in outstanding lubricating properties. Specifically, the wear volume of the disc by EG-44BL is only 8.9% of that lubricated by pure EG. The enhanced anti-wear property of the EG/lignin system could be attributed to the formation of a robust lubrication film and the strong adhesion of the lubricant on the contacting metal surface due to the presence of a dense hydrogen bonding (H-bonding) network. The lubricating performance of EG-BL outperforms EG-SL, which could be attributed to the denser H-bonding sites in BL and its broader molecular weight distribution. The disc wear loss of EG-44BL is only 45.7% of that lubricated by EG-44SL. Overall, H-bonding is the major contributor to the different tribological properties of BL and SL in EG-based lubricants.

Squalene and docosahexaenoic acid (DHA) have gained substantial market share as dietary supplements and vital nutraceuticals due to their beneficial effects on human health. Marine fish are the main commercial source of these nutraceuticals, but a growing global demand, issues of sustainability, and an expanding vegan and vegetarian population has prompted the search for alternatives. Oils obtained from oleaginous microorganisms such as microalgae, diatoms, certain fungi, and thraustochytrids are alternatives to fish oils for omega-3 fatty acids. Among these, DHA is now being mined from thraustochytrids due to its highest proportion in their lipids, however, this strategy is not cost-effective. One way to offset such elevated production costs is to simultaneously extract other high value-added biological products from these oleaginous microorganisms. Here, we propose a novel biorefinery process based on single-step purification of squalene from total lipids extracted from an oleaginous thraustochytrid cultivated on non-edible forest biomass. To render the process economically feasible and sustainable, additional squalene-free lipids were exploited for enrichment of DHA; whereas leftover lipids generated as by-product during the process were tested as a novel biolubricant.

Biolubricants refer to eco-friendly, biodegradable, and non-toxic lubricants. Their applications are still limited compared to mineral oils; however, their sustainable credentials are making them increasingly attractive. Vegetable oils are frequently used for this purpose. However, vegetable oils have issues of low lipid productivity, dependence on climatic conditions, and need for agricultural land. Microbial oils represent a more sustainable alternative. To ensure their widespread applicability, the suitability of microbial oils from a physicochemical point of view needs to be de-termined first. In this study, oils obtained from various oleagenic microbes—such as microalgae, thraustochytrids, and yeasts—were characterized in terms of their fatty acid profile, viscosity, friction coefficient, wear, and thermal stability. Oleaginous microalgal strains (Auxenochlorella protothe-coides and Chlorella sorokiniana), thraustochytrids strains (Aurantiochytrium limacinum SR21 and Au-rantiochytrium sp. T66), and yeast strains (Rhodosporidium toruloides and Cryptococcus curvatus) synthesized 64.5%, 35.15%, 47.89%, 47.93%, 56.42%, and 52.66% of lipid content, respectively. Oils from oleaginous microalgae (A. protothecoides and C. sorokiniana) and yeasts (R. toruloides and C. curvatus) possess excellent physicochemical and tribological qualities due to high amount of monounsatu-rated fatty acids (oleic acid C18:1 content, 56.38%, 58.82%, 46.67%, 38.81%) than those from oleaginous thraustochytrids (A. limacinum SR21 and Aurantiochytrium sp. T66; 0.96%, 0.08%, respectively) supporting their use as renewable and biodegradable alternatives to traditional mineral oil-based lubricants. Oil obtained from microalgae showed a lower friction coefficient than oils obtained from yeasts and thraustochytrids.

This work mainly focuses on the development and characterization of polyimide (PI) based composite coatings filled with multi‐walled carbon nanotubes (MWCNT) on a steel substrate. The tribological properties of PI/MWCNT composite coatings at different temperatures ranging from room temperature (RT) to 200°C were investigated. Also, the influence of MWCNT and thermal & mechanical properties of PI composites coatings were measured. The addition of MWCNT could reduce the friction coefficient as well as wear volume at elevated temperatures. The PI/3MWCNT composites coatings show better wear‐resistant properties as compared to other composites. Also, the PI/MWCNT composites showed improved mechanical properties such as micro‐hardness and nanoindentation. Formation of an organic‐inorganic structure due to the inclusion of MWCNT, enhance the mechanical properties and reduce the thermo‐degradation of composites coatings. The glass transition temperature (Tg) of the PI/MWCNT composites was improved as the MWCNT content increases from 0.1 to 5 wt%.

This paper focuses on developing a polyamic acid (PAA) of polyimide (PI) and PI filled with graphene (PI/GP) on 100CR6 ESU hardened steel. The tribological testing result of the pure PI and PI/GP against 100Cr6 steel ball at room temperature (RT) and elevated temperatures (50 °C, 100 °C, 150 °C, 200 °C) exhibits that the addition of GP clearly enhances the friction reduction and wear-resistant properties of PI, due to the excellent lubricating properties of GP. The 3 wt % of GP content in the PI is the optimum loading for the lowest friction and wear at RT and elevated temperatures. The SEM analysis of the worn surfaces showed that the high wear-resistant of the PI/GP composite is due to the generation of the loose particles from the coating surfaces which could be embedded on the friction pairs and rolled over there as a lubrication film. Also, at 60 % weight residue the PI/3 G P showed the high decomposition temperature.

Water-based lubricants are thought to be the next generation green lubricants, however, there are very few developments of aqueous grease lubricants. Here, water-based grease lubricants were developed using the food fat replacers. The concept of using fat replacers was inspired by the historical usage of fat as a lubricant. Dextrins were chosen as the fat replacers and mixture of water and PEG as the base fluid. Dextrins with different molecular weights were selected to study its effect on the rheological, tribological and thermal behavior of the gels. It was found that only higher molecular weight dextrins will form the colloidal gels, whereas low molecular weight dextrins will form the colloidal solution. The SEM images of the dried samples showed the agglomerated micro-spherical network with the void to hold the base fluid. It was found that, at an optimum concentration, the fat replacers showed 35–58% lower friction and 29–41% lower wear than the pure PEG200/water solution regardless of their molecular weight. The spherical shaped colloidal particles will form the film over the metal surface by nano-filling and these particles will act as nano-bearings which will reduce the wear and friction. These gel lubricants can be used where the highly biodegradable and bio-compatible green lubricant is needed.

Developing a fully green lubricant is an urgent need due to the growing consciousness of environmental protection and dwindling resources. In this work, fully green gel lubricants were developed out of cellulose derivatives as gelator and mixture of water and poly(ethylene glycol) 200 (PEG 200) as the base fluid. The non-ionic hydroxyethyl cellulose (HEC) and anionic sodium carboxymethyl cellulose (NaCMC) were chosen to understand the effect of ionic and non-ionic gelators on the thermal, rheological and the tribological properties of the gel lubricant. HEC or NaCMC is demonstrated as effective additive to reduce wear, stabilize friction coefficient and enhance the thermal stability of developed lubricants. It is shown that anionic gelator will result in producing lower friction and wear in comparison to non-ionic gelator, which may be attributed to the possible tribo-film formation due to the negative charge in the NaCMC molecules and its larger molecular weight.

The capability of sensor systems to efficiently scavenge their operational power from stray, weak environmental energies through sustainable pathways could enable viable schemes for self‐powered health diagnostics and therapeutics. Triboelectric nanogenerators (TENG) can effectively transform the otherwise wasted environmental, mechanical energy into electrical power. Recent advances in TENGs have resulted in a significant boost in output performance. However, obstacles hindering the development of efficient triboelectric devices based on biocompatible materials continue to prevail. Being one of the most widely used polymers for biomedical applications, polyvinyl alcohol (PVA) presents exciting opportunities for biocompatible, wearable TENGs. Here, the holistic engineering and systematic characterization of the impact of molecular and ionic fillers on PVA blends’ triboelectric performance is presented for the first time. Triboelectric devices built with optimized PVA‐gelatin composite films exhibit stable and robust triboelectricity outputs. Such wearable devices can detect the imperceptible skin deformation induced by the human pulse and capture the cardiovascular information encoded in the pulse signals with high fidelity. The gained fundamental understanding and demonstrated capabilities enable the rational design and holistic engineering of novel materials for more capable biocompatible triboelectric devices that can continuously monitor vital physiological signals for self‐powered health diagnostics and therapeutics.

Polymers prepared from ionic liquids are widely called polymerized ionic liquids (PILs). Compared to monocationic and dicationic ILs, PILs have higher molecular weights, charge, and greater intermolecular interactions, which make PILs have a higher possibility to generate better lubricity. PILs of poly‐alkylimidazolium bis(trifluoromethylsulfonyl)imide (PImC6NTf2) is studied herein. Dicationic ILs of 1,1′‐(pentane‐1,5‐diyl)‐bis(3‐butylimidazolium) bis(trifluoromethylsulfonyl)imide (BIm5‐(NTf2)2) is used as additive to decrease the crystallization temperature of PImC6NTf2. Lubricity of PImC6NTf2 and PImC6NTf2+BIm5‐(NTf2)2, as well as BIm5‐(NTf2)2 for comparison is evaluated under severe conditions, i.e., 3.0 to 3.5 GPa and 200 °C. The rheological study suggests that PImC6NTf2 can be classified into grease. Tribological test results show that PImC6NTf2 has much better antiwear property than BIm5‐(NTf2)2, especially at 3.5 GPa. Adding 4% BIm5‐(NTf2)2 to PImC6NTf2 is able to reduce friction under high pressure. At 200 °C, PImC6NTf2 exhibits excellent lubricity. The mixture of 96%PImC6NTf2+4%BIm5‐(NTf2)2 shows even better antiwear property than neat PImC6NTf2 and exhibits the highest friction reducing property among the ILs at 200 °C. It is speculated that the robust strength of PILs and strong adhesion between PILs and solids are key factors in achieving the excellent antiwear property.

Polyimide (PI) is one of the most excellent polymers for coating. However, the high friction coefficient and the high wear rate of pure PI limit its further applications. In this work, the hollow inorganic fullerene-like MoS₂/reduced graphene oxide (HIF-MoS₂/r-GO) nanocomposite filled PI coating is prepared by in situ polymerization. Reinforcement in mechanical strength and thermal stability is realized on the PI composite coating with incorporation of HIF-MoS₂/r-GO, which performs better than carbon nanofiber (CNF). Reduced elastic modulus and hardness of HIF-MoS₂/r-GO/PI coating is increased by 8.3% and 4.8%, respectively. The addition of HIF-MoS₂/r-GO also results in 24% higher residual mass at 800 °C than CNF. Tribological study indicates that, HIF-MoS₂/r-GO/PI achieves a wear rate reduction of 79% compared with pure PI under dry sliding condition, which is much more effective than other nanofillers including CNF, r-GO nanosheets and MoS₂ nanoparticles. Under ionic liquid-lubricated condition, the presence of HIF-MoS₂/r-GO in PI results in a 30% reduction in wear rate and 10% reduction in friction coefficient as compared to pure PI. It is thought that the HIF-MoS₂/r-GO in PI can be slowly released to the frictional interface and form a protective film during sliding, in this way the aggregation problem is successfully solved.

From one to more, the same raw materials giving rise to multifarious products is one of the goals of researchers to pursue industrial efficiency. Herein, we designed a formula (controlling the content of the matrix) to prepare two functional ionic gels, integrating the excellent lubrication, thermal conductivity, and self-healing ability to meet different industrial demands of the lubrication and biomedical fields. Deep eutectic solvents (DESs) of urea/choline chloride (UCC) and glycerol/choline chloride (GCC) were locked in polyacrylamide (PAM) ionic gel formed by acrylamide (AM) and a photoinitiator by freer-adical polymerization. The unique dual hydrogen bond network in the ionic gel causes the material to exhibit a low wear rate, which can effectively reduce the wear of metal contact. With the addition of PAM, the ionic gel has excellent mechanical strength and good recovery performance. Unexpectedly, this dense hydrogen bond network enhances thermal conductivity by optimizing phonon and electron transfer. The versatile ionic gel has a good application prospect as a substitute for industrial lubricants and medical device materials.