Short Alkyl Chain Research Articles

Fluorescence study of some structural and compositional effects on the aggregation of hydrophobized hyaluronan

The aggregation behavior of four samples of hydrophobically modified hyaluronan was examined in water and in 0.15 M NaCl. The samples differed in the length of their hydrocarbon modifying chains, degree of substitution, or hyaluronan molecular weight. The critical aggregation concentration was determined by fluorescence spectroscopy using pyrene as a probe. Aggregation was observed even with hyaluronan modified by a short alkyl chain (C6). The critical aggregation concentration decreased with increasing alkyl chain length and with increasing hyaluronan molecular weight at a comparable degree of substitution. Aggregation was detected over a rather broad concentration interval, indicating a progressive formation of aggregates. Two populations of aggregates were detected for the oleyl substitution. The addition of NaCl had only minor effect on the critical aggregation concentration.

Carboxylesterase and lipase-catalyzed degradation of phthalate esters in soil and water: Congener structure selectivity and specificity

Phthalate esters (PAEs) are ubiquitous in agricultural soil and crops because of the widespread application of plastic films containing PAEs. The enzymes play critical roles in the elimination of pollutants from environmental matrices. In an attempt to evaluate the effect of enzymes on the degradation of various PAEs, this study investigated the enzyme-catalyzed reaction kinetics of seven selected PAE congeners in water and soil. Carboxylesterase and lipase catalyzed the transformation of PAEs to monoalkyl phthalate esters and phthalic acid with the half-life ranges of 4.78–126.03 h. PAEs with long-alkyl-chain were more recalcitrant to carboxylesterase and lipase-catalyzed degradation, and PAEs with short alkyl chains were relatively easier to be degraded by the two enzymes. The results indicate that the alkyl chain length had a profound effect on the enzyme-catalyzed degradation of PAEs. The reaction rates and half-lives were significantly correlated with the log Kow value ( p < 0.01), which was dominated by the molecular structure. The results obtained in this work are expected to well guide the application of carboxylesterase and lipase in the remediation of waterbody contaminated by various PAEs. With respect to soil, they can be well used in the remediation, exposure, and risk assessment of paddy soil. However, the application of the results in the remediation of other soils might lead to the risk of a low removal ratio. • PAEs can be readily degraded by carboxylesterase and lipase. • The degradation rates of PAEs are relatively higher in water than in soil. • The degradation rates of PAEs are congener structure associated. • The removal ratio of PAEs related to soil properties.

Removing per- and polyfluoroalkyl substances (PFAS) in water by foam fractionation

Treatment of large volumes of waters contaminated by per- and polyfluoroalkyl substances (PFAS) remains a challenge. This work presented a systematic study on PFAS removal by foam fractionation (FF). Experiments were conducted on both laboratory-spiked and environmental water samples containing PFASs. It is found that higher air flow, greater ionic strength, and addition of thickener boosted PFAS removal in the defoamed bottom solutions and intensified enrichment in the collected foam. FF treatments of a landfill leachate, a groundwater contaminated by aqueous film-forming foams, and a wastewater treatment plant effluent sample were evaluated. The removal reached above 70% for most monitored PFASs, except the ones of short alkyl chains. PFAS concentrations in the final collected foams were up to over 30 × than that in the original samples. Analysis using high-resolution mass spectrometry revealed enrichment of non-target PFASs by FF. The results of this study demonstrate great effectiveness of FF in removing most PFASs from waters, producing low-volume, highly concentrated solutions of PFASs in all tested environmental samples.

Structure-Stability Relationship in Aqueous Colloids of Latex Particles and Gemini Surfactants.

The influence of gemini surfactants (GSs) on the charging and aggregation features of anionic sulfate modified latex (SL) particles was investigated by light scattering techniques in aqueous dispersions. The GSs of short alkyl chains (2-4-2 and 4-4-4) resembled simple inert salts and aggregated the particles by charge screening. The adsorption of GSs of longer alkyl chains (8-4-8, 12-4-12, and 12-6-12) on SL led to charge neutralization and overcharging of the particles, giving rise to destabilization and restabilization of the dispersions, respectively. The comparison of the interfacial behavior of dimeric and the corresponding monomeric surfactants revealed that the former shows a more profound influence on the colloidal stability due to the presence of double positively charged head groups and hydrophobic tails, which is favorable to enhancing both electrostatic and hydrophobic particle-GS and GS-GS interactions at the interface. The different extent of the particle-GS interactions was responsible for the variation of the GS destabilization power, following the 2-4-2 < 4-4-4 < 8-4-8 < 12-4-12 order, while the length of the GS spacer did not affect the adsorption and aggregation processes. The valence of the background salts strongly influenced the stability of the SL-GS dispersions through altering the electrostatic interactions, which was more pronounced for multivalent counterions. These findings indicate that both electrostatic and hydrophobic effects play crucial roles in the adsorption of GSs on oppositely charged particles and in the corresponding aggregation mechanism. The major interparticle forces can be adjusted by changing the structure and concentration of the GSs and inorganic electrolytes present in the systems.

Linear- and star-type quaternary ammonium salt-based trimeric surfactants: Effect of structure on adsorption and aggregation properties

Oligomeric surfactants with multiple hydrophobic and hydrophilic groups are an attractive novel surfactant with improved properties and functionalities compared with those of conventional monomeric surfactants. In this study, linear- and star-type quaternary ammonium salt-based trimeric surfactants, 3Cnlin-s-Q and 3Cntris-s-Q, were synthesized with different alkyl chain lengths (n), spacer chain lengths (s), and spacer skeletons (linear or star) and their adsorption and aggregation properties were characterized by electrical conductivity, surface tension, fluorescence, viscosity, dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS). Trimeric surfactants exhibited high water solubility despite containing three alkyl chains. Conversely, the linear-type trimeric surfactant 3C14lin-3-Q, composed of rigid short spacer chains and long alkyl chains, exhibited low water solubility. The adsorption and orientation of trimeric surfactants at the air/water interface depended on the alkyl chain length, spacer chain length, and spacer skeleton, and the effect of alkyl chain length was dominant. The star-type trimeric surfactant 3C12tris-6-Q was efficiently adsorbed and oriented at the air/water interface, despite its long spacer and bulky skeleton, which extended from the center of the amino group in the spacer. Therefore, trimeric surfactants with high performance and advanced functionalities were successfully achieved. This study provides insights into the molecular design and synthesis of trimeric surfactants for future application in various industrial fields.

Physicochemical characterization of levulinate esters with different alkyl chain lengths blended with fuel

AbstractDue to the advantages of cellulosic biomass, such as abundant reserves, renewable, and wide sources, the large‐scale development of lignocellulosic biomass fuels has the advantage of relieving energy pressure and promoting energy conservation and emission reduction, of which the levulinate esters are a potential biomass liquid fuel. In this study, different alkyl chain lengths of the levulinate esters were blended with 0# fossil diesel, and the physicochemical properties of the blended fuels, such as mutual solubility, density, distillation range, closed flash point, kinematic viscosity, cold filter plugging point, oxidation stability, and sulfur content and other physical and chemical properties were tested and investigated. The results showed that the longer the alkyl chains of the levulinate esters, the better their stability when mixed with 0# petrochemical diesel. And levulinate esters with short alkyl chains can be easily separated from blended fuels at low temperatures. The physicochemical properties of the blended fuels improved significantly with the increase of carbon chain length and levulinate esters content, low‐temperature flow characteristics, atomization characteristics of spraying, and safety of transportation and storage, and the physicochemical properties of levulinate blended fuels with long alkyl chains were more superior than shorter alkyl chains of the levulinate esters.

Design, Synthesis, Acaricidal Activities, and Structure-Activity Relationship Studies of Oxazolines Containing Ether Moieties.

To develop highly efficient and low cost acaricides, a series of 2,4-diphenyl-1,3-oxazolines containing an ether moiety at the para position of the 4-phenyl group were synthesized from different alcohols and phenols. The bioassay results showed that most of the compounds, especially the short-chain alkyl ethers, exhibited excellent acaricidal activity against both the larvae and the eggs of Tetranychus cinnabarinus. In particular, the n-propyl ether compound Ic possessed much better larvicidal activity (LC50 = 0.0015 mg/L) and ovicidal activity (LC50 = 0.0008 mg/L) than commercial acaricide etoxazole (LC50 = 0.0145 and 0.02 mg/L for larvae and eggs, respectively). In addition, some compounds also exhibited insecticidal activity, especially compound Iw (4-CF3-phenyl ether) showed higher mortality than etoxazole against Mythimna separata, Helicoverpa armigera, and Pyrausta nubilalis. Considering the high acaricidal activity and relatively low cost, Ic was worthy of further study as an acaricide agent. An alternative synthetic route for the large-scale synthesis of Ic was then studied.

Room Temperature Dye Glasses: A Guideline Toward the Fabrication of Amorphous Dye Films with Monomeric Absorption and Emission

The morphology of films containing photoactive materials is crucial for the performance of solid-state dye applications. Organic dyes tend to crystallize due to their usually planar molecular structure and the resulting intermolecular interactions. This leads to inhomogeneous films with crystalline, aggregated, and amorphous regions, decreasing device efficiency and complicating spectral analysis. Improving the glass-forming ability of organic dyes therefore presents a major challenge for solid-state dye applications. Here, we present a guideline to create organic dye glasses using BODIPY as a model dye. The method is based on the strategic design of BODIPY derivatives, equipped with short alkyl chains, in combination with blending of two or more derivatives. Mixing increases the entropy of the liquid state and lowers the thermodynamic driving force for crystallization as well as the kinetic fragility of the system. This enables the fabrication of homogeneous thin films without any additives. In these films, the dye molecules are trapped in a glassy state, featuring monomeric absorption and emission. This strategy leads to a BODIPY material with an amorphous character in thin films, dropcast films, and bulk. Further, the strategy is based on thermodynamics and is therefore expected to be general, enabling the transformation of any dye molecule into a glass former.

Effect of Alkyl Chain Length on the Phase Situation of Glass-Forming Liquid Crystals

The phase behaviour of the latest synthesised compound belonging to a family of (S)-4′-(1-methyloctyloxycarbonyl) biphenyl-4-yl 4-[‘m’-(2,2,3,3,4,4,4-heptafluorobutoxy) ‘m’alkoxy]-benzoates (where ‘m’ means 3, 5 or 7 methylene groups) is described by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and Fourier-transform infrared absorption spectroscopy. It has been shown that as the length of the alkyl chain increases, a given liquid crystal possesses a greater number of mesophases and at a higher temperature it goes into the isotropic liquid phase. All examined compounds form a chiral smectic phase with antiferroelectric properties (SmCA* phase), in which the temperature range of occurrence increases with the length of the molecule. The number of methylene groups also affects the glass transition. The compound with the shortest alkyl chain (‘m’ = 3) is vitrified from the conformationally disordered crystal phase. For the compound with five -CH2- groups (‘m’ = 5), a glass transition from the monotropic high-order hexatic smectic SmXA* phase is observed. In the case of the liquid crystal with the longest carbon chain (‘m’ = 7), the vitrification from the less ordered SmCA* phase is visible. Differences in the crystallization kinetics, e.g., the nucleation-controlled mechanism for the compound with the shortest carbon chain vs. the complex phenomenon for its longer homologs, are discussed.

Mechanism responsible altering in interfacial tension and emulsification of the crude oil-water system with nano Gemini surface active ionic liquids, salts and pH

Gemini surface active ionic liquids (GSAILs) exhibit desired activities for enhanced oil recovery (EOR). This study explores the simultaneous effects of homologous series of imidazolium nano GSAILs, [Cnim-C4-imCn][Br2], n = 4, 8, and 12 with individual and mixture of NaCl, MgCl2 salts and also with aqueous phase pH on the crude oil–water system. In the presence of the medium and long alkyl chain GSAILs, electrolytes can establish extra 93.1 and 52.6% reductions in interfacial tension (IFT) and the critical micelle concentration (CMC), compared to the salt-free system, respectively. These were while, the IFT and the CMC were initially decreased with the concentration of electrolytes and then a slight increase was corresponding with the short alkyl chain GSAIL. Results also revealed 79.2% more IFT reductions under pH 9.5 compared to the natural pH as well as high stability of GSAILs within the wide pH range of (2.5–9.5). Meanwhile, crude oil and electrolyte aqueous solutions showed one day emulsification indices within (40–85)% with little decrease after one week. Remarkably, an emulsification index of more than 90% could be achieved at pH 9.5.

Programming Shape Memory Hydrogel to a Pre‐Encoded Static Deformation toward Hierarchical Morphological Information Encryption

AbstractMorphological information encryption such as gesture and sign language is a traditional but efficient way of information storage and communication. However, due to the limited deformability, almost all of the existing information encryption materials store and deliver information via the pattern or color changes on the 2D plane. Herein, a thermo and ion dual‐responsive shape memory hydrogel containing short alkyl chains modified polyvinyl alcohol (PVA‐C6) and polyacrylamide‐co‐polyacrylic acid [P(AAm‐co‐AAc)], is prepared. In this system, the ion‐responsive shape memory process of P(AAm‐co‐AAc) provides the preprogrammed morphological information and actuating force while the thermo‐responsive hydrophobic clusters of PVA‐C6 are utilized as a molecular switch to control the deformed posture within the deformation process. Incorporated with a photothermal particle, Fe3O4, the photothermal PVA‐C6 hydrogel is capable of generating diverse configurations that can be encoded as the corresponding information. With the assistance of the programmable NIR, the hydrogel can transfer to the encoded configuration and decrypt the information. Besides, the obtained morphological information can also be erased by immersing the hydrogel in hot water, in order to avoid the leakage of information. This study motivates the design and fabrication of deformable materials and provides a new insight into the information encrypt materials.

Role of C2 methylation and anion type on the physicochemical and thermal properties of imidazolium-based ionic liquids

This study focused on the effects of methylation and different anions (Br − and Cl − ) on the physicochemical and thermal properties of [C 16 MIM]X and [C 16 MMIM]X, belonging to the imidazolium-based ionic liquid (IL) family. The effect of methylation on the transmittance in the fingerprint region of the Fourier transform infrared (FT-IR) spectrum was observed as a blue shift, and a new peak associated with the C-N stretching bond was obtained. In contrast, in the functional group region, the frequency shift was related to the change in the vibrational mode from C2-H-X to C2-methyl-X. In general, methylation resulted in an increase in decomposition temperature, an increase in melting temperature, and a decrease in melting enthalpy, leading to a reduction in entropy. The trends observed for the decomposition temperature, melting temperature, and melting enthalpy with different anions depended on the strength of the Brønsted acids and hydrogen bonds of the Br − and Cl − based anions. The thermal conductivity of the methylated ILs increased with an increase in temperature. In contrast, for the non-methylated (protonated) ILs, the thermal conductivity of [C 16 MIM]Br decreased with an increase in temperature, while the opposite trend was observed for [C 16 MIM]Cl. The data were compared with those of the short alkyl chain and weakly coordinating anion of NTf 2 . The analysis was performed considering different phases, the prominent role and different behaviour in the hydrogen bonding at the C2 position of the imidazolium ring upon methylation, and the significant change in viscosity, which can influence the IL structure.

Effects of Surface Hydrophobicity on Catalytic Transfer Hydrogenation of Styrene with Formic Acid in a Biphasic Mixture.

Transfer hydrogenation (TH) of unsaturated hydrocarbons with formic acid (FA) is an attractive processing pathway for the reduction of lignocellulosic pyrolysis oils. The low solubility of hydrophobic bio-oil species in water and FA in oil necessitates the use of a biphasic system as the reaction environment. Here, we report the effects of Pd/silica catalyst surface wettability on the TH reaction rate. Modification of the surface with short chain (C1-C4) alkyl silanes resulted in an increase in the reaction rate as compared to the unmodified catalyst. In contrast, modification of the surface with sulfonate (hydrophilic) and C18 alkyl silanes (hydrophobic) resulted in a decrease in the reaction rate as compared to the unmodified catalyst. The results are discussed in terms of the catalyst interfacial activity and relative affinity of the reagents to the Pd active sites. An observed change in the apparent reaction order in styrene for a hydrophilic catalyst suggests that changing catalyst surface wettability from hydrophilic to hydrophobic resulted in a switch from a transport-limited to a kinetic-limited reaction regime.

A Supramolecular Hydrogel Based on Copolymers of Acrylic Acid and Maleic Anhydride Derivatives with Terpyridine Motifs.

A kind of terpyridine derivative (NH2-Tpy) in which the amino was incorporated by a short alkyl chain was synthesized. Through grafting of terpyridine units into the hydrophilic copolymers of maleic anhydride and acrylic acid PAAMa via the reaction of the amino groups in NH2-Tpy and the maleic anhydride units, a series of gelator polymers—P1, P2, and P3—containing different contents of terpyridine units was synthesized. Under coordination of Ni2+ and terpyridine ligands in linear polymers, the supramolecular hydrogels H1, H2, and H3 with different cross-linking degrees were prepared. The linear polymers P1–P3 had a strong absorption peak at about 290 nm in the UV-vis spectra which was attributed to π–π* transition, and there was a new peak at about 335 nm led by the metal-to-ligands charge transfer (MLCT) when coordinated with Ni2+ ions. According to the rheological behaviors, the storage modulus (G′) was larger than the loss modulus (G′′). These hydrogels showed typical gel-like characteristics when the terpyridine content of the hydrogels exceeded 10%, and the hydrogels showed liquid-like characteristics when the terpyridine content of the hydrogels was less than 7%. The results of the micromorphological investigation of the xerogels from SEM illustrated the metal–terpyridine coordination cross-linking could have an important influence on the microstructures of the resulting hydrogels. Furthermore, these hydrogels based on supramolecular cross-links exhibited reversible solution–gel transition at different environmental temperatures. At the same time, the equilibrium swelling of the supramolecular hydrogels was 8.0–12.3 g/g, which increased with the decrease in the content of the terpyridine units in the resulting hydrogels.

Bio‐based glycerol plasticizers for flexible poly(vinyl chloride) blends

AbstractA series of glycerol‐based compounds were investigated for their application as plasticizers for flexible poly(vinyl chloride) (PVC) blends. The effect of plasticizer chemical structure on the performance, migration behavior, and blend morphology were evaluated and compared to blends produced using the commercial plasticizer dioctyl terephthalate (DOTP). Blends containing 40 phr (parts per hundred rubber) of glycerol‐based plasticizer showed a considerable reduction (between 54 to 86°C) in glass transition temperature (Tg) relative to neat PVC (Tg ~ 80°C). Tensile testing of samples prepared with the glycerol analogs demonstrated higher ductility (elongation at break values of up to 97%) than DOTP (elongation at break value of 75%) at identical plasticizer loadings. The surface morphologies showed excellent incorporation of the glycerol plasticizers functionalized with alkyl chains longer than four carbons in length into the PVC matrix, whereas droplet formation was observed in blends with shorter chain glycerol derivatives. Leaching behavior of the plasticized samples were evaluated into different media and showed that plasticizers comprised of branched, or longer alkyl chains produced 2‐ to 4‐fold lower migration rates compared to those with shorter alkyl chains into polar solutions.

Selection of suitable surfactants for the incorporation of organic liquids into fresh geopolymer pastes

• Torque monitoring during emulsification of OL into fresh GP allows to have one-line viscosity. • Torque evolution allows to predict if OL will be successfully incorporated in GP or not. • Quaternary ammonium salts such as CTAB are well adapted to adjust the viscosity of fresh GEOIL. • Capillary forces between OL and MK were shown using Zêta potential measurements and Washburn tests. Geopolymers (GP) have recently emerged as suitable binders for the conditioning of radioactive organic liquids (OL). The condition for suitably incorporating high amounts of OL into GP is assessed in this research. A series of OL has been selected, comprising alkanes (dodecane and 2 paraffinic mineral oils), an industrial gear oil and tributylphosphate (TBP), in order to cover a wide range of viscosities (0.0018–2.33 Pa.s). The incorporation of viscous OL (>0.2 Pa.s) into fresh GP results in a regular torque increase, indicating a suitable process with the dispersion of the OL in the form of fine micrometric droplets. When the torque remains stable, for OL of low viscosity (<0.2 Pa.s) like TBP/Dodecane mixtures, the incorporation is not possible, or only partial in the form of large droplets quickly coalescing and leading to an organic supernatant above the hardened GP. For low viscosity OL, surfactants are required. The use of quaternary ammoniums (QAs) like cetyltrimethylammonium bromide (CTAB) has been studied. Torque monitoring shows that the OL is incorporated similarly in the GP slurry, whether the surfactant is introduced at the beginning, through the course or at the end of the mixing process. The torque evolution also provides the optimum surfactant concentration, by evidencing that beyond a certain concentration, the medium hardens too quickly, preventing the incorporation of OL. Finally, torque monitoring highlights that QAs with shorter alkyl chains, such as hexamethyltrimethylammonium, are able to replace CTAB with the same efficiency. Therefore, the powerful action of CTAB on the incorporation of alkanes into GP is attributed to its positive charge rather than to its surfactant effect.

Polyethers Based on Short-Chain Alkyl Glycidyl Ethers: Thermoresponsive and Highly Biocompatible Materials.

The polymerization of short-chain alkyl glycidyl ethers (SCAGEs) enables the synthesis of biocompatible polyethers with finely tunable hydrophilicity. Aliphatic polyethers, most prominently poly(ethylene glycol) (PEG), are utilized in manifold biomedical applications due to their excellent biocompatibility and aqueous solubility. By incorporation of short hydrophobic side-chains at linear polyglycerol, control of aqueous solubility and the respective lower critical solution temperature (LCST) in aqueous solution is feasible. Concurrently, the chemically inert character in analogy to PEG is maintained, as no further functional groups are introduced at the polyether structure. Adjustment of the hydrophilicity and the thermoresponsive behavior of the resulting poly(glycidyl ether)s in a broad temperature range is achieved either by the combination of the different SCAGEs or with PEG as a hydrophilic block. Homopolymers of methyl and ethyl glycidyl ether (PGME, PEGE) are soluble in aqueous solution at room temperature. In contrast, n-propyl glycidyl ether and iso-propyl glycidyl ether lead to hydrophobic polyethers. The use of a variety of ring-opening polymerization techniques allows for controlled polymerization, while simultaneously determining the resulting microstructures. Atactic as well as isotactic polymers are accessible by utilization of the respective racemic or enantiomerically pure monomers. Polymer architectures varying from statistical copolymers, di- and triblock structures to star-shaped architectures, in combination with PEG, have been applied in various thermoresponsive hydrogel formulations or polymeric surface coatings for cell sheet engineering. Materials responding to stimuli are of increasing importance for "smart" biomedical systems, making thermoresponsive polyethers with short-alkyl ether side chains promising candidates for future biomaterials.

Influences of nanoparticles and chain length on thermodynamic and electrical behavior of fluorine liquid crystals

Hydrogen-bonded polar nematic liquid crystal series with the general formula nOBAF (n = 7–12) is studied. The mesomorphic characterization is demonstrated through differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The complexes with short alkyl chains (n = 7, 8) present a wide nematic range and monotropic smectic F mesophase, whereas the longer alkyl chain (n = 10–12) analogues show high melting and low clearing mesomorphic liquid crystals. The thermal range of the mesophase and the birefringence increase with chain length decreasing. Furthermore, the effect of the nanoparticles (LiNbO3) on the thermal and the electrical behavior of 8OBAF are investigated. The presence of LiNbO3 nanoparticles increases the conductivity and reduces the resistivity of the complex.

Anionic amphiphilic calixarenes for peptide assembly and delivery

Shape-persistent macrocycles enable superior control on molecular self-assembly, allowing the preparation of well-defined nanostructures with new functions. Here, we report on anionic amphiphilic calixarenes of conic shape and their self-assembly behavior in aqueous media for application in intracellular delivery of peptides. Newly synthesized calixarenes bearing four phosphonate groups and two or four long alkyl chains were found to form micelles of ∼ 10 nm diameter, in contrast to an analogue with short alkyl chains. These amphiphilic calixarenes are able to complex model (oligo-lysine) and biologically relevant (HIV-1 nucleocapsid peptide) cationic peptides into small nanoparticles (20–40 nm). By contrast, a control anionic calixarene with short alkyl chains fails to form small nanoparticles with peptides, highlighting the importance of micellar assembly of amphiphilic calixarenes for peptide complexation. Cellular studies reveal that anionic amphiphilic calixarenes exhibit low cytotoxicity and enable internalization of fluorescently labelled peptides into live cells. These findings suggest anionic amphiphilic macrocycles as promising building blocks for the preparation of peptide delivery vehicles.

The superior lubricating performance and unique mechanism of oil-soluble protic ionic liquids with short alkyl chains

HypothesisIonic liquids (ILs), as lubricant additives, can greatly improve the lubricating behavior of the frictional interfaces. However, it is urgent to explore ILs with good oil solubility in nonpolar oils, and it is necessary to further study and verify the lubrication mechanism of ILs from the perspective of alkyl chain length. ExperimentsFive protic ILs (PILs) with varying alkyl chain lengths were synthesized by proton transfer method. As additives in PAO oil, their tribological properties were investigated on SRV-V tester. Through molecular dynamics simulation, the adsorption behavior of PILs at the frictional interface was illustrated. FindingsThe tribological properties of base oil could be significantly improved by adding PIL additives, but interestingly, PILs with short-chain anions showed better lubricating performance, which contradicted most of the early findings. Further analyses revealed that PILs achieved effective lubrication by the tribochemical interaction between anions and frictional interface, and the formation of cationic protective layer. However, PILs with shorter-chain anions form a denser protective layer that can better support the interfacial anions to participate in tribochemical reactions and thus abnormally exhibit superior lubricating performance than those with longer-chain anions.