Lubrication Behavior Research Articles

Investigations on Ways to Improve the Scuffing and Wear Behavior of Oil-Free Water-Based Lubricants for Gear Applications

Abstract Today, mineral or synthetic oils that are made out of fossil raw materials are the most common lubricants in gear drive applications. Most of them are nonbiodegradable and may pose a risk to the environment. An important step to minimize the risk and the ecological footprint is the use of biodegradable and eco-friendly lubricants. Former research shows the potential of water-based lubricants in gear applications. Therefore, an oil-free, water-based lubricant was developed for this study. The base lubricant contains plant-based thickeners to generate an appropriate viscosity for a sufficient lubricant film thickness in the tooth contact. In experimental investigations, the sliding wear and scuffing performance has been examined under variation of the added polymers and additives. The scuffing tests A/8.3/RT are performed according to DIN ISO 14635-1. The wear test procedure is based on DGMK 377-01. In both scuffing tests with the sample, the failure load stage = 8 was achieved. For case-carburized gears, a “medium” to “high” amount of wear can be detected. Additional tests with nitrided gears show a “low” amount of wear. This article aims to show the great potential of water-based oils for gear lubrication and suggests operating conditions for maximum wear and scuffing carrying capacity.

Behavior of elastohydrodynamic lubricating film point contact problems in the unsteady state of reciprocating motion

Purpose In this study a numerical analysis of the elastohydrodynamic lubrication point contact problem in the unsteady state of reciprocating motion is presented. The effects of frequency, stroke length and load on film thickness and pressure variation during one operating cycle are discussed. The general tribological behavior of elastohydrodynamic lubrication during reciprocating motion is explained. Design/methodology/approach The system of equations of Reynolds, film thickness considering surface deformation and load balance equations are solved using the Newton-Raphson technique with the Gauss-Seidel iteration method. Numerical solutions were performed with a sinusoidal contact surface velocity to simulate reciprocating elastohydrodynamics. The methodology is validated using historical experimental measurements/observations and numerical predictions from other researchers. Findings The numerical results showed that the change in oil film during a stroke is controlled by both wedge and squeeze effects. When the surface velocity is zero at the stroke end, the squeeze effect is most noticeable. As the frequency increases, the general trend of central and minimum film thickness increases. With the same entraining speed but different stroke lengths, the properties of the oil film differ from one another, with an increase in stroke length leading to a reduction in film thickness. Finally, the numerical results showed that the overall film thickness decreases with increasing load. Originality/value General tribological behaviors of elastohydrodynamic lubricating point contact, represented by pressure and film thickness variations over time and profiles, are analyzed under reciprocating motion during one working cycle to show the effects of frequency, stroke length and applied load.

Dynamic performances of novel misaligned non-uniform distributed tilting-pad bearing

The non-uniform distributed tilting-pad journal bearings (NDTPJB) in large wind turbine main shafting has become an important development trend for high-power wind turbines due to the advantages of improving reliability and reducing maintenance costs. However, studies involving NDTPJB have not been reported under specific conditions such as low speed, wide range variable direction and magnitude of heavy-load in wind turbine. A new transient mixed elastohydrodynamic lubrication (mixed EHL) model for NDTPJB is established, taking into account the misalignment effect of the shaft tilt and the swinging of pads in the circumferential and axial directions, as well as the influence of pivot friction and elastic deformation effects. Based on the mathematical model, the dynamic characteristics and structural parameter effects of NDTPJB are systematically studied under low speed, wide range variable direction and magnitude of heavy-load. The results indicate that the NDTPJB exhibits a more significant sensitivity to the heavy load direction due to the different functional roles of the above distributed pads (ADP) and bottom distributed pads (BDP). The modified mixed EHL model can more accurately evaluate the lubrication performance of NDTPJB, and combine the characteristics in individual pad swing and the overall effect of the pads to comprehensively analyze the dynamic lubrication behavior of NDTPJB. By setting the pivot coefficient to 0.55, reducing the distribution angle of BDP, and increasing the distribution angle of ADP, a better load-carrying capacity can be achieved. The research results have guiding significance for further monitoring and analyzing the experimental performance of NDTPJB, as well as designing and optimizing such bearing structures.

Robust and self-lubricating polyvinyl alcohol tubes with a mucosa-like hierarchical architecture for endotracheal intubation.

Mechanical mismatch between interventional intubation tubes and human tissues often triggers inevitable friction and causes secondary injury to patients during interventional therapy. Herein, we propose a fabrication strategy of a self-lubricating polyvinyl alcohol (PVA) tube by industrial extrusion technology followed by simple infiltration with water. First, biocompatible glycerin was introduced to weaken the intrinsic hydrogen interaction of PVA by new molecular complexation, broadening the gap between the melting and decomposition temperatures and enabling the stable extrusion of the PVA tube. Subsequently, the as-prepared PVA tube was infiltrated with an aqueous solution to construct a strong hydrogen bonding network between PVA and water molecules, forming a soft hydration layer similar to the upper epithelium layer of mucosa. Benefiting from the solid and liquid properties of the hydration layer as well as the small proportion relative to the whole, the infiltrated PVA tube exhibited excellent hydration lubrication behavior and robust mechanical property. The friction coefficient, tensile strength and elongation at break were measured to be 0.05, 26.2 MPa and 654%, respectively, surpassing the values of 0.5, 16.4 MPa and 240% observed in a commercial polyvinyl chloride tube. In vitro, the PVA intubation tube demonstrated significant biocompatibility, and short-term exposure exhibited minimal impacts on the morphology and proliferation of L929 cells. Ultimately, the potential of the infiltrated PVA tube for interventional intubation was demonstrated successfully using an in vivo rabbit model, providing a new idea for the follow-up development of interventional intubation tubes.

Hydrodynamic lubrication behavior under miscellaneous operational conditions via CGB numerical model

The current study is basically focused on investigating the possible ways to enhance the lubricating oil film performance and hence ship energy efficiency of marine journal bearings in general terms. For the intended purpose, a novel numerical Circumferential Grooved Bearing (CGB) model was developed to assess journal bearing operating conditions based on versatile simulation analyses. Prior to all conducted test trials, the model validation has been confirmed based on the conformity between numerical outcomes and those derived from experimental procedures depending on Universal Journal Bearing Test Rig. CGB performance was evaluated at slow speed variations from 25 rpm up to 125 rpm and different applied loads utilizing the two lubricant oil grades of 5W40 and 0W30. Reducing shaft rotational speed by 80% was found to incur a reduction in the maximum oil film pressure value by 1.17 bar and 0.97 bar for the two aforementioned lubricants respectively. Further, the increase of applied loads from 1079 N up to 1471 N at a constant speed of 75 rpm reduces the maximum oil film pressure ratio by 0.14 and 0.18 for the two oil grades subsequently.

The effects of bubble evolution and oil shear thinning on the static behavior of bubbly oil lubricated bearing

Bubble evolution and shear thinning effect are main factors affecting lubrication behavior of bubbly oil. In this study, a thermohydrodynamic lubrication model for the bubbly oil considering the bubble evolution and the shear thinning effect was established based on the multiphase mixtures theory. The influence of bubble evolution and shear thinning effect on the static behavior of bubbly oil lubricated bearing was analyzed, and an experimental study was conducted to verify the model. The result shows that the bubble radius is mainly dependent on the liquid pressure; the bearing static behavior is affected by the bubble evolution through the interface effect; the shear thinning effect of the pure oil can be enhanced with regarding the bubble evolution effect.

Tribological Properties and Lubrication Mechanisms of Water-Based Nanolubricants Containing TiO2 Nanoparticles during Micro Rolling of Titanium Foils.

The tribological behavior of traditional oil-in-water (O/W) lubricants (1.0 wt.%) and nano-TiO2 additive lubricants (1.0-9.0 wt.%) during micro rolling of titanium foils were analyzed. In this study, the surface morphologies of titanium foils under various lubrication conditions were assessed, and the corresponding lubrication mechanisms were revealed. The tribological behavior of nano-TiO2 additive lubricants during micro rolling of titanium foils was also explored through a series of characterization methods. The utilization of nano-TiO2 additive lubricants in micro rolling reduces the surface roughness of titanium foils. Moreover, it effectively inhibits the generation of indentations and cracks during rolling processes, enhancing the surface quality of rolled specimens. Additionally, owing to the synergism of rolling, tribo-film, mending and polishing effects of the nanoparticles, both the rolling force and surface roughness were minimized by using lubricants containing 3.0 wt.% TiO2 nanoparticles. Overall, an optimal concentration (3.0 wt.%) of TiO2 nanoparticles in water-based nanolubricants was obtained with enhanced tribological properties and lubrication performance during micro rolling of titanium foils.

Determining features in the wear resistance characteristics of tribocompounds with a textured hole surface under conditions of boundary friction

The influence of surface texture in the form of pits on the wear resistance of tribocompounds under conditions of limit friction was investigated. At the first stage of research, the mechanism of lubricant behavior between the contacting surfaces and inside the holes was modeled. The limiting condition of the rotation frequency of the sample (n>27) was established, under which a drop of lubricant "leaves" the hole in the upper position of the sample and remains in the space between the sample and the surface of the counterbody, ensuring the regeneration of the boundary lubricating film on the surface of the tribocontact when it is destroyed. When the rotation frequency of the sample is reduced (n<27), the lubricant droplet remains in the hole and does not affect the processes of the boundary lubricant film. At the second stage, experimental studies of tribocombinations with a textured hole surface under conditions of extreme friction were carried out. It was established that the high wear resistance of the textured hole surfaces is provided by the high protective effect of the texture, as well as the high efficiency of the marginal lubricating film. It has been proven that the strengthening of the surface texture by the method of ion-plasma thermocyclic nitriding additionally increases the wear resistance by 1.7 times due to the high protective effect of surface nitrided layers and their high hardness (up to 9500 MPa). This strengthens the effect of inhibiting the occurrence of defects in the surface layers of tribocontact, ensures a high rate of wetting of the places of actual contact of triboconnections, and speeds up the process of regeneration of the boundary lubricating film. Research results can be used to modify the surface layer of heavily loaded parts operating under extreme operating conditions with limited supply of lubricant under various types of friction and wear

Hexagonal Boron Nitride as Filler for Silica-Based Elastomer Nanocomposites.

Two-dimensional hexagonal boron nitride (hBN) has attracted tremendous attention over the last few years, thanks to its stable structure and its outstanding properties, such as mechanical strength, thermal conductivity, electrical insulation, and lubricant behavior. This work demonstrates that hBN can also improve the rheological and mechanical properties of elastomer composites when used to partially replace silica. In this work, commercially available pristine hBN (hBN-p) was exfoliated and ball-mill treated in air for different durations (2.5, 5, and 10 h milling). Functionalization occurred with the -NH and -OH groups (hBN-OH). The functional groups were detected using Fourier-Transform Infrared pectroscopy (FT-IR) and were estimated to be up to about 7% through thermogravimetric analysis. The presence of an increased amount of oxygen in hBN-OH was confirmed using Scanning Electron Microscopy coupled with Energy-Dispersive X-ray Spectroscopy. (SEM-EDS). The number of stacked layers, estimated using WAXD analysis, decreased to 8-9 in hBN-OH (10 h milling) from about 130 in hBN-p. High-resolution transmission electron microscopy (HR-TEM) and SEM-EDS revealed the increase in disorder in hBN-OH. hBN-p and hBN-OH were used to partially replace silica by 15% and 30%, respectively, by volume, in elastomer composites based on poly(styrene-co-butadiene) from solution anionic polymerization (S-SBR) and poly(1,4-cis-isoprene) from Hevea Brasiliensis (natural rubber, NR) as the elastomers (volume (mm3) of composites released by the instrument). The use of both hBNs in substitution of 30% of silica led to a lower Payne effect, a higher dynamic rigidity, and an increase in E' of up to about 15% at 70 °C, with similar/lower hysteresis. Indeed, the composites with hBN-OH revealed a better balance of tan delta (higher at low temperatures and lower at high temperatures) and better ultimate properties. The functional groups reasonably promote the interaction of hBN with silica and with the silica's coupling agent, sulfur-based silane, and thus promoted the interaction with the elastomer chains. The volume of the composite, measured using a high-pressure capillary viscometer, increased by about 500% and 400% after one week of storage in the presence of hBN-p and hBN-OH. Hence, both hBNs improved the processability and the shelf life of the composites. Composites obtained using hBN-OH had even filler dispersion without the detachments of the filler from the elastomer matrix, as shown through TEM micrographs. These results pave the way for substantial improvements in the important properties of silica-based composites for tire compounds, used to reduce rolling resistance and thus the improve environmental impacts.

Thermosensitive Triblock Copolymer for Slow-Release Lubricants under Ocular Conditions.

The ocular environment is crucial for a biological lubrication system. An unstable condition of tear film may cause a series of ocular diseases due to serious friction, such as dry eye syndrome, which has drawn extensive attention nowadays. In this study, an in vitro biocompatible superlubricity system, containing thermogelling copolymers (PCGA-PEG-PCGA) and slow-release lubricant (PEG 300/Tween 80), was constructed. First, the sol-gel transition temperature and gel strength of PCGA-PEG-PCGA were adjusted based on the ocular environment by regulating the length of PCGA blocks. Furthermore, the copolymer hydrogel exhibited a reliable slow-release property within 10 days and showed low cytotoxicity. Then, the superlubricity (coefficient of friction of approximately 0.005) was achieved with its released PEG 300/Tween 80 aqueous solution at the sliding velocity range of 1-100 mm s-1 and pressure range of 10-22 kPa. However, the lubrication behaviors varied, while PEG 300 chains and Tween 80 micelles were demonstrated to form a multilayer and a single layer adsorption structure on the sliding surface, respectively. On the whole, the composite lubrication systems, especially the one composed of Tween 80, showed excellent tribological properties owing to the stable slow-release and full hydration effects under ocular conditions, which hold great potential for improving ocular lubrication and maintaining human visual health.

Simultaneous enhancement of hardness, lubrication and corrosion resistance of solid solution Zr-Y-N film

Transition-metal nitrides (TMNs) can be widely applied as protective coatings for precision parts, and improving their key performance characteristics is essential to make them more robust and durable in harsh environments. High-performance TMNs require establishing the structure-property relationship, and structural modulation is an effective procedure for optimizing their properties. Herein, high hard Zr-Y-N solid solution structure film with trace of solute Y atom fabricated by reactive magnetron sputtering and demonstrated excellent lubricating behavior under the condition of based oil, as well as superior corrosion resistance in a 3.5 wt% NaCl solution. It should be noted that the solid solution Zr-Y-N film is 40.1 % harder than pure ZrN film due to solid solution strengthening, resulting in a hardness of 29.0 GPa. During the sliding process of tribological behavior, the synergistic effect of in-situ formation Y2O3 and ZrO2 lubricating phase on the Zr-Y-N worn surface would significantly reduce the friction coefficient to 0.019. Additionally, based on the results obtained from the impedance spectrum and polarization curve, solute Y can enhance the corrosion resistance of ZrN by its compact solid solution structure, resulting in a corrosion current of S1 (1.71 E−05 A/cm2) that is much lower than that of ZrN (1.05 E−04 A/cm2), which is an important factor in optimizing the comprehensive performance of ZrN films. The novel strategy would be to open a window for more significantly improving the hardness of TMNs-based film by incorporating solute Y atoms, thereby further improving lubricating behavior and corrosion resistance.

Investigation of Mineral Oil and CuO Mixed Synthetic Oil in Compression Ignition Engines: A Comparison of Physicochemical Attributes

Mineral oil resources are depleting rapidly, and the slower conventional oil biodegradation process results in environmental pollution. To resolve this issue, cupric oxide (CuO) nanoparticles (1% wt) were introduced into a base oil to improve the lubricating capability of castor oil. In addition, 1% wt. sodium dodecyl sulfate was also blended with the base oil in order to attain the maximum dispersion stability of CuO nanoparticles in the castor oil. Afterward, thermophysical property, atomic absorption spectroscopy, and Fourier transform infrared radiation (FTIR) testing of the lubricant oil sample were performed before and after 100 h of engine operations at 75% throttle and 2200 rpm for each lubricant sample in order to check the capability of the novel oil with mineral oil. Compared with the natural mineral oil, the behavior of the CuO-based lubricant has essentially the same physical features, as measured according to ASTM standard methods. The physicochemical properties like (KV)40 °C, (KV)100 °C, FP, ash, and TBN decrease more in the case of the synthetic oil by 1.15, 1.11, 0.46, 1.1, and 1.2% than in the conventional oil, respectively. FTIR testing shows that the maximum peaks lie in the region of 500 to 1750 cm−1, which shows the presence of C=O, C-N, and C-Br to a maximum extent in the lubricant oil sample. AAS testing shows that the synthetic oil has 21.64, 3.23, 21.44, and 1.23% higher chromium, iron, aluminum, and zinc content. However, the copper and calcium content in the synthetic oil is 14.72 and 17.68%, respectively. It can be concluded that novel bio-lubricants can be utilized as an alternative to those applications that are powered by naturally produced mineral oil after adding suitable additives that further enhance their performance.

Rheological Characterization and Tribological Evaluation of Water-Based Lubricants in AISI 52100 Bearing Steel

This study explores the rheological and tribological behavior of water-based lubricants (WBLs) as potential alternatives for electric vehicle (EV) applications. As the transportation sector increasingly shifts towards EVs to reduce carbon emissions, the demand for efficient lubricants becomes critical. WBLs here are defined as fluids containing a minimum of 50 wt% water mixed with glycerol, ethylene glycol (MEG), polyethylene glycol (PEG), or one of two polyalkylene glycols (PAGs). Rheological properties were investigated and compared with traditional lubricating oils. Results demonstrate distinctive rheological characteristics in WBLs, with viscosity–temperature responses resembling traditional oils with lowered pressure–viscosity coefficients. Nevertheless, WBLs exhibit promising film-forming capabilities in highly loaded contacts. Additionally, in sliding contacts, WBLs generally display lower friction coefficients compared to traditional oils, with PEG exhibiting the lowest value near 0.1. These findings suggest that WBLs may offer advantages in reducing friction and energy loss in EV applications. Furthermore, sliding wear tests indicate low wear rates in WBLs such as PEG, PAG, and glycerol, supporting their potential as viable lubrication options. The study highlights the importance of high-pressure rheology and tribochemistry in wear mechanisms among the different lubricants.

Fabrication of starch-based oleogels using capillary bridges: Potential for application as edible inks in 3D food printing

Food-grade oleogels may be used as edible inks in 3D food printing applications. However, there is currently a lack of simple and robust methods of fabricating oleogel-based edible inks with tunable printing properties. In this study, native starch-based oleogels were prepared from starch, oil, and water. Initially, powdered starch was dispersed into soybean oil and then water was added to promote starch aggregation through capillary attraction. The impact of adding xanthan gum to the water was also investigated, as it is known to greatly impact its rheology. The impact of starch, water, and xanthan gum content on the structure, rheology, and stability of the oleogels was then evaluated using magnetic resonance imaging, dynamic shear rheometry, and confocal scanning laser microscopy. The properties of the oleogels could be modulated by altering the starch and water content, as these parameters influenced the formation of a space-spanning particle network held together by capillary forces. Adding xanthan gum to the water had little impact on oleogel properties, which was attributed to the dominance of capillary forces in oleogel formation. The starch oleogels exhibited physicochemical characteristics that made them suitable as edible inks in 3D food printing applications, including high printing accuracy and the ability to maintain their shape after printing. Tribology analysis showed that the oleogels exhibited mixed lubrication behavior, with the lowest lubricity being observed at S = 0.2, φP = 0.38. In conclusion, this study shows that starch oleogels with controllable properties may be suitable as edible inks for food applications.

Relationships between crystallization behavior and application properties of chemically coupled PAI-PTFE coatings

AbstractPoly(tetrafluoroethylene) (PTFE) is well known for its very low friction coefficient and thus widely used for antifriction applications, e.g., sliding lacquers, for many years. Because of the high wear rate and cold flow of the original polymer, PTFE is usually added in higher amounts to other polymer matrices as a lubricant. However, the incompatibility of PTFE requires lots of efforts to perform a homogeneous breaking down of agglomerates and particle distribution as well as dispersion stabilization of the physical mixtures during application and curing. PTFE can be functionalized by high energy irradiation and subsequently compatibilized with a polymer matrix by reactive extrusion resulting in chemical bonding of both polymers via suitable reactive groups. In this manner, poly(amide imide) (PAI) was coupled to γ-radiation modified PTFE micro-powder prior to the dispersion procedure. This study deals with the thermal and crystallization behavior of the PTFE lubricant in chemical bonded (cb) PAI-PTFEcb compound thin layers in comparison with those of the plain radiation modified PTFE depending on the cooling rate by DSC, Flash-DSC and WAXS. A morphological characterization of the extrudate as well as the coating gives information about the fragmentation and distribution of the PTFE phase in the PAI matrix. Furthermore, mechanical and surface properties of sliding lacquer films were analyzed after application on steel substrates by varying dry film thickness and curing. Graphical Abstract

Adsorption-induced transient friction of hydrogels on hydrophilic countersurfaces

Soft hydrated permeable surfaces of hydrogels exhibit unique lubrication behaviors, including frictional hysteresis found in tribo-rheometry measurements. A hydrogel lubrication model that describes the transient behavior was previously developed using the structure kinetics model in the field of rheology and rate-and-state friction model, where the friction change is described as a competition between buildup and breakdown rates. In this study, the model is further modified to include the effect of hydrophilicity of a countersurface. Ultraviolet (UV)/ozone treatment on an aluminum surface significantly removes organic materials, resulting in extremely hydrophilic surface. Friction response of a polyacrylamide hydrogel against untreated and UV/ozone-treated aluminum exhibited noteworthy difference in the trajectory of hysteresis. Model fits were conducted using the modified lubrication model on both hystereses, and the fitting parameters of both hystereses are compared with each other to identify a parameter addressing hydrophilicity. Based on the model fits, we suggest that the hydrophilicity of the countersurface initially prevents the adsorption on the hydrogel surface because it holds water better. However, once water goes out of the contact due to contact pressure, a stronger adsorption occurs, which increases friction and decreases the speed dependence of friction.

Study on pH-dependence of electroosmosis effect and tribological behavior of water-based lubricants at friction interfaces

pH is usually used to assess the corrosion resistance and bacteriostasis of lubricants. In this paper, the electroosmotic and tribological characteristics of water-based lubricants at AISI 52100 steel/alumina ceramic friction interfaces are evaluated as an effect of pH value. A self-excited electric field (SEEF) generated by interface material frictional electrification induces the lubricant electroosmosis. Appropriately increasing the pH can improve the electroosmotic abilities of lubricants by changing the electrical double layer (EDL) structures at the friction material/lubricant interfaces. The lubricant tribological performance and penetrability are improved upon increasing the pH from 7 to 10. This is attributed to the fact that the lubricant with favorable electroosmotic performance shows a better penetrability, thus exerting an excellent effect of anti-friction and anti-wear.

Dispersion stability and tribological behavior of nanocomposite supramolecular gel lubricants and molecular dynamic simulation

The poor dispersion stability of nanoparticles in oils limited their application. To address this problem, diverse of nanoparticles were introduced to supramolecular gels to fabricate a new lubricant (Nano-Gel). The results of molecular dynamics simulation show that gelators adsorbed onto the surface of nanoparticles at the non-covalent interaction. Besides, the intricate networks of supramolecular gels show spatial confinement to nanoparticles, which improved the dispersion stability of nanoparticles. Compared with supramolecular gels lubricant, Nano-Gel shows good anti-friction and anti-wear properties. The excellent tribological properties would be contributed to the self-repairing and tribo-film formed by nanoparticles and gelators. The Nano-Gels provide effective solution to the application of nanoparticles in lubricating oil, which have great values to prolong the life of mechanisms.

Influence of geometric shapes of recess on the performance of MR lubricated multi-recessed hybrid spherical thrust bearing

This paper aims to investigate the impact of different geometric shapes of recesses/pockets on the behavior of a multi-recessed hybrid spherical thrust bearing (MHSTB) configuration along with MR (magnetorheological) lubricant behavior. The analysis employs a finite element approach to assess the behavior of MHSTB configurations lubricated with MR fluids, with the MR lubricant's behavior modeled using the Herschel–Bulkley model. The governing equations are solved through Galerkin's discretization method combined with a suitable iterative technique. The study reveals significant variations in bearing performance when altering the magnetic field intensity and axial eccentricity ratio. The study explores various geometric recess shapes (i.e., elliptical, circular, triangular, and square) within the MHSTB configuration while maintaining same bearing operating and geometric parameters. Numerical simulations demonstrate that MHSTB systems operating with MR lubricant exhibit higher fluid film reaction and damping coefficients compared to Newtonian lubricant. Furthermore, it is observed that the elliptical recessed bearing configuration outperforms square, triangular, and circular recessed bearing configuration in terms of fluid film reaction and lubricant flow rate.

Lubrication behavior of mixed colloidal systems: Effect of interactions between polysaccharides and oil droplets/ protein particles

The lubrication behavior of food systems is critical for sensory perception and consumer acceptance. This behavior depends on the components present in food and their interactions. In the present study, binary systems were designed to systematically investigate the effect of the interactions (i.e. repulsive and attractive interactions) between components on lubrication properties. Whey protein-stabilized emulsion droplets or whey protein aggregates functioned as dispersed particles, while polysaccharides were present in the continuous phase. Polysaccharides with different molecular characteristics, i.e. xanthan (charged, stiff), pectin (charged, semi-flexible) and guar gum (non-charged, flexible), were selected. We observed that bridging due to attractive interactions between polysaccharides and particles (oil droplets or proteins aggregates) induced extensive particle aggregation, leading to increased friction coefficients. Such bridging was reduced as the concentration of polysaccharides increased, decreasing both cluster size and friction coefficient. In the case of systems with the same charge, weaker depletion interactions led to the formation of particle aggregates, resulting in increased friction coefficients. This was mostly observed for pectin. Conversely, addition of xanthan and guar gum did not cause extensive aggregation and a more homogeneous microstructure was observed. As a result, lower friction coefficients were obtained. The friction coefficients were reduced further when more xanthan or guar gum were added, the highly charged xanthan being more effective. Overall, for both types of interactions, systems with a more homogeneous microstructure (i.e. smaller clusters) resulted in lower friction, indicating that the microstructure of the systems was the primary determinant of lubrication behavior.