The tribological performance of two polymeric friction modifiers, one based on an ester‐based compound and another based on an ethoxylated fatty ester and an organic friction modifier, oleamide, was studied at 50, 90 and 140°C using a Mini Traction Machine equipped with optical interferometry and electrical contact resistance. The ability to form surface film is found to vary among the friction modifiers and with temperature and rubbing duration. Despite a thinner film being formed, polymeric friction modifier (PFMs) exhibited lower friction and wear than oleamide at all the studied temperatures. Further, the PFMs reduced boundary friction more effectively at higher temperature. In accordance with lower boundary friction, a smoother surface topography characterized by low wear was exhibited by PFM lubricated surfaces at higher temperatures. Scanning electron microscopy‐energy dispersive x‐ray analysis and time‐of‐flight secondary ion mass spectrometry provided insights on the tribofilm formation. The improvement in the tribological performance of PFMs is attributed to temperature‐induced conformation transition of adsorbed polymer chains on the surface. The results are corroborated by data obtained from dynamic light scattering and gel permeation chromatography.

A classical emulsion formulation based on petrolatum and mineral oil as the internal phase with emulsifier wax as a typical topical emulsion cream was investigated for the effect of process parameters on drug product quality and performance attributes. The Initial Design of Experiment (DoE) suggested that an oil phase above 15%, coupled with less than 10% emulsifying wax, resulted in less stable emulsions. Different processing parameters such as homogenization speed, duration, cooling rate, and final temperature showed minimal influence on properties and failed to improve stability. The final DoE suggested that the optimal emulsion stability was achieved by introducing a holding period midway through the cooling stage after solvent addition. Within the studied holding temperature range (25–35 °C), a higher holding temperature correlated with increased emulsion stability. However, the application of shear during the holding period, using a paddle mixer, adversely affected stability by disrupting the emulsion microstructure. IVRT studies revealed that the release of lidocaine was higher in the most stable emulsion produced at a holding temperature of 35 °C compared to the least stable emulsion produced at a holding temperature of 25 °C. This suggests that a holding temperature of 35 °C improves both the stability and active release performance. It appears that a slightly higher holding temperature, 35 °C, allows a more flexible and stable emulsifying agent film around the droplets facilitating stabilization of the emulsion. This study offers valuable insights into the relationship between process parameters at various stages of manufacture, microstructure, and various quality attributes of emulsion cream systems. The knowledge gained will facilitate improved design and optimization of robust manufacturing processes, ensuring the production of the formulations with the desired critical quality attributes.

A number of analytical procedures (Spectrum Descriptive Analysis (SDA), Quantitative Descriptive Analysis (QDA), and Check All That Apply (CATA)) are used for characterizing sensorial attributes of topical formulations. However, these techniques are evaluated by expert panels/consumers, which are subjective, expensive and time consuming. Despite widespread use of these methods, the techniques do not necessarily aid in the development of innovative formulations and understanding of consumer liking. In addition, the hedonic attributes of a product can significantly dominate the sensation. Therefore, a more rapid, quantitative, and objective approach is required for understanding the formulation factors that governs sensory perception at different points of consumer application. Rheological evaluations of topical formulations were carried out under steady and oscillatory (SAOS and LAOS) rheology using a commercial rheometer. Friction measurements were performed using an in-house built tribometer on non-biological skin model to investigate how surface properties are influenced by application of different topical formulations. Further, a broad range of instrumental texture measurements was performed to characterize the formulations. Principal component analysis was used for dimensionality reduction of the instrumental data. Supervised machine learning was performed on the closely related PCA parameters to develop predictive models. We identified physical parameters relevant to different perceptual attributes by comparing a range of commercial topical formulations with various compositions using rheological and tribological methods. Multi-variate machine learning models were developed where several key instrumental textural attributes and skin feel could be predicted from data obtained from linear and non-linear rheological measurements. Our study shows rheological analysis based on a few material parameters can be effectively used for predicting instrumental sensory attributes that is of relevance to consumer care industry. The machine learning models may benefit development of innovative formulations, valorisation of new materials and serve as a platform for mapping commercial formulations for product optimization. The models can likely shorten design cycle time by screening through large volume of formulations and short list only those with highest potential to be evaluated by a very specialized and expensive human test panel.

The manufacturing process for ointments typically involves a series of heating, cooling, and mixing steps. Precise control of the level of mixing through homogenization and the cooling rate, as well as temperature at different stages, is important in delivering ointments with the desired quality attributes, stability, and performance. In this work, we investigated the influence of typical plant processing conditions on the microstructure, stability, and sensorial properties of a model ointment system through a Design of Experiments (DoE) approach. Homogenization speed at the cooling stage after the addition of the solvent (propylene glycol, PG) was found to be the critical processing parameter that affects stability and the rheological and sensorial properties of the ointment. A lower PG addition temperature was also found to be beneficial. The stabilization of the ointment at a lower PG addition temperature was hypothesized to be due to more effective encapsulation by crystallizing mono- and diglycerides at the lower temperature. The in vitro release profiles were found to be not influenced by the processing parameters, suggesting that for the ointment platform studied, processing affects the microstructure, but the effects do not translate into the release profile, a key performance indicator. Our systematic study represents a Quality-by-Design (QbD) approach to the design of a robust manufacturing process for delivering stable ointments with the desired performance attributes and properties.

OBJECTIVE:Drawing parallels from rheotribology can be used to develop a robust instrumental protocol for non-subjective characterization, product development and design of topical dosage forms with desired sensory attributes. However, instrumental characterization of cosmetic products can be influenced by the measurement protocol, thixotropy, flow anomalies like shear banding or wall slip and nature of the film formed on the skin surface. In this study, we evaluated the influence of above parameters on the instrumental sensory evaluation of 12 topical formulations of different galenic forms.METHODS:Oscillatory strain sweep measurements (SAOS and LAOS) were performed to investigate the influence of frequency and wall slip on the material parameters. The textural attributes at different consumer touchpoints were evaluated by accounting time-dependent simulation of viscoelastic flow. Further, the influence of film thickness and sample drying on the tactile properties of the topical formulations were studied on a non-biological skin model using a sliding probe tribometer.RESULTS:The study shows that the flow properties of the semi-solid formulations depend on the timescale of the problem. A few formulations exhibited wall slip to varying degrees in the linear viscoelastic regime where the behaviour was found not to be characteristic of a particular topical dosage form. The material functions obtained from the Lissajous plots suggest that the non-linear flow behaviour of different galenic forms is least influenced by the boundary conditions imposed by the measurement geometry. The results were statistically analysed using principal component analysis where the attributes used for discriminating skin creams during pick up and rub out are found to be closely associated with non-linear rheology. The friction coefficient exhibited speed dependence where it formed different parametric group with rheological data depending on the lubrication regime.CONCLUSION:The study highlights that correlations are possible amongst rheological, tribological and instrumental textural analysis data, which can act an impetus for the development of models to predict attributes that drive perception at different consumer touchpoints. However, the choice of instrumental settings, anomalies associated with rheological measurements and friction dependence on a number of parameters can influence the model prediction.

The effect of oleic acid, oleyl alcohol and oleyl amine based organic friction modifiers (OFM), ester and ethoxylated fatty ester based di-block polymeric friction modifiers (PFM) and Zinc dialkyldithiophosphate (ZDDP) on the boundary lubrication of steel surfaces was studied using a ball-on-disc tribometer equipped with optical interferometry. Frictional performance of oil blends containing the OFM/PFM, with and without ZDDP, was investigated at a slide roll ratio (SRR) of 100% and 130 degrees C for a rubbing duration of 24 h. Surface topography measurements using 3D surface profilometer and scanning electron microscopy (SEM) were used to quantify the anti-wear performance. Comparison of optical interferograms and friction data showed that formation of a thicker tribofilm does not always translate to effective friction reduction. Our experiments showed that PFMs generally provide better friction reduction than OFMs with or without ZDDP by effectively eliminating the boundary regime. This was attributed to the ability of PFMs to form a tenacious low shear strength film on the metal surface due to its polymeric nature. In contrast, both the friction modifiers had a negative effect on the anti-wear performance of ZDDP. The observed tribological response is attributed to either preferential adsorption of the friction modifier over ZDDP or ZDDP decomposition products. This notion was further corroborated by results obtained from energy-dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS) with depth profile analysis, which showed lower concentration of ZDDP derived products for the formulation containing both the friction modifier and ZDDP.

The aim of the work was to identify the physical parameters relevant to different perceptual attributes by comparing a range of commercial skin creams with various compositions. We investigated the possibility of predicting sensory properties using rheological and tribological methods. Rheological evaluations of the skin creams were carried out using continuous shear, creep, creep recovery, rheodestruction and recovery measurements, oscillatory strain sweep measurements [small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear (LAOS)], and frequency sweep measurements. Friction measurements were performed on the nonbiological skin model to investigate how surface properties are influenced by the application of different topical formulations. Furthermore, the formulations were characterized by a broad range of instrumental texture measurements. In vivo sensory analysis based on the spectrum descriptive analysis method was performed to discriminate the skin creams during pickup, rub out, and after feel. Using principal component analysis meaningful correlation relating rheotribological properties and sensory attributes during the entire process of product application was carried out. Rheological parameters deduced from the nonlinear regime were found to be important parameters affecting the frictional response of skin creams. In addition, friction data were correlated with slipperiness and stickiness—subjective attributes used for the sensory evaluation of after feel. Furthermore, a number of key textural parameters and sensorial data showed good correlation with results obtained from linear and nonlinear rheological measurement, indicating rheological analysis can be sufficiently used as a precise and valid tool for sensorial mapping of topical formulations. Our study further suggests that objective evaluation based on the flow curve, oscillatory strain sweep (SAOS and LAOS), and friction measurements can be used for sensorial screening of large number of prototype formulations, which otherwise may be time consuming and costly using a sensory panel.

Tribofilm formation and frictional performance of lubricant additives — oleamide, ZDDP and their mixture formulated in PAO — on steel and diamond-like carbon (DLC)-coated steel surfaces was studied under severe boundary lubrication conditions. The binary additive system reduced friction to a greater extent compared to the individual additives for all the surfaces. Chemical composition analysis of the tribofilms using surface spectroscopic techniques (ToF-SIMS and EDX) revealed that the formation of tribo-reactive ZDDP film on steel surface is suppressed in the presence of oleamide. In turn, this results in lower friction. Frictional performance of the additives on diamond DLC and graphite DLC-coated steel surfaces was evaluated and correlated with their wear performance. Analysis of tribofilm thickness and chemical composition revealed that the additives did not form a cohesive film on diamond DLC surface. On the contrary, graphite DLC coating completely worn out from the substrate when additives were present singly in the formulation. However, the additives in combination prevented delamination of graphite DLC coating.

The influence of structural factors on the lubrication performance of organic friction modifiers (OFMs) formulated in Group V (polyol ester oil) base oil was studied using a ball-on-disk tribometer. The results show that OFMs can mitigate friction under heavy loads, low sliding speeds, and high temperatures. These conditions are commonly encountered in internal-combustion engines between cylinder liners and piston rings. The reduction in friction is ascribed to the boundary lubrication film containing the OFM. The chemical composition analysis of the metal disk surface using energy dispersive X-ray spectroscopy (EDS) confirmed the presence of a protective film of OFM on the wear track, albeit inconsistently deposited. Although the adsorption of the OFM on the metal surface was observed to be dependent on the chemical reactivity of the functional groups, levels of unsaturation, and hydrocarbon chain length of the OFM, the frictional performance was not always directly correlated with the surface coverage and tribofilm thickness. This implies that the friction reduction mechanism can involve other localized processes at the interface between the metal surface and lubricant oil. The occasional variation in friction observed for these OFMs can be attributed to the stability and durability of the boundary film formed during the rubbing phase.

Friction, wear and tribofilm growth of organic friction modifiers (glycerol monooleate and oleamide), anti-wear additive (ZDDP) and binary additive system comprising the organic friction modifiers and ZDDP were studied in polyalphaolefin (PAO) and ester oil. The mechanisms underlying base oil polarity-dependent frictional performance of the OFM and AW additives at high temperature (140 ℃), either singly or in combination, were investigated in the light of chemical composition analysis of the tribofilms post friction measurements using energy dispersive X-ray spectroscopy (EDX), static and dynamic time-of-flight secondary ion mass spectrometry (ToF–SIMS). Depending on the rubbing conditions, the boundary friction coefficient of the binary additive systems was found to be either lower than that of individual additives or to lay between the values for the individual additives. Chemical composition analysis of the tribofilms indicated that the nature of base oil controlled interactions between ZDDP and OFM and consequently adsorption and reactive tribofilm formation in the boundary lubrication layer. Surface roughness and wear scar width measured post tribological tests using 3D surface profiler showed improved wear performance in both PAO and ester-based additive formulations.

Tribological performance of an organic friction modifier (glycerol monooleate - GMO), an anti-wear additive (zinc dialkyldithiophosphate - ZDDP) and its combination was studied using a ball-on-disc tribometer equipped with optical interferometry at 90 degrees C and 140 degrees C. Higher temperatures were needed for the formation of additive layers and chemically reactive anti-wear protective layers. Comparison of Stribeck curves obtained after different rubbing durations showed that GMO reduced friction at low speed sliding-rolling contact. Despite notable decrease in the base oil viscosity with increase in temperature - in turn, increasing the severity of asperity contact - GMO exhibited enhanced frictional performance. The presence of ZDDP alone in the formulation led to significant increase in friction at both low and high temperatures, with the thickness of tribofilm unaffected after prolonged rubbing. The addition of friction modifier to ZDDP-based formulation reduced the friction in the boundary lubrication regime where longer rubbing aided in effective friction reduction at higher temperature. For the binary additive system, the friction coefficient was found to lie between the values corresponding to the single additives. The observed tribological response is attributed to preferential adsorption of the friction modifier over ZDDP and/or ZDDP decomposition products. This notion was corroborated by the results obtained from static and dynamic time-of-flight secondary ion mass spectrometry (ToF-SIMS) and energy-dispersive X-ray spectroscopy (EDX) analysis of the disc surface post tribological measurement. The concentration gradient of different chemical species detected in the tribofilm correlated with the frictional performance of the additives. Analysis of surface roughness and wear scar width showed an improvement in wear performance at higher temperature suggesting the friction modifier and anti-wear additive adsorbed on the surface providing a mechanical barrier. A synergistic effect on the wear performance was observed for GMO + ZDDP-based formulations, which resulted in a smaller wear scar compared to the individual additives.

FrictionFriction will be generated when two solid bodies are pressed over or slide against each other, and it acts opposite to the direction of relative motion. LubricantsLubricant are frequently used to reduce friction which otherwise may result in high machine wear and energy losses. Depending upon the phenomenon, lubricationLubrication can be classified into four different regimes: boundary, mixed, elastohydrodynamic and hydrodynamic. In boundary regime, the frictional response is mainly governed by the properties of the surfaces and it generally involves adsorption of lubricant molecules onto the mating surfaces. Therefore, in this regime, properties other than bulk properties of the lubricants play a significant role in determining the frictional response. Mixed or thin filmThin film lubrication (TFL) is a bridge that mark the transition from boundary to Elasto-Hydrodynamic (EHL) [or hydrodynamic (HL)] regimes. In TFL the loadLoad is partly supported by direct contact of the surface asperities and partly by the fluid. EHL regime is a type of HL regime which is characterized by the formation of sufficiently thick fluid film which fully separates the surfaces from direct contact thus reducing frictionFriction. Elastic deflections of the surfaces in contact in EHL regime influence the shape and thickness of the lubricantLubricant film significantly. HL differs from EHL due to negligible elastic deformation of the surfaces at the contact interface. In EHL/HL, loadLoad is fully supported by the lubricant where the bulk property of the lubricantLubricant and entrainment velocity of the tribo pairs determines the film thickness and frictionFriction. Transition between different lubrication regimesLubrication regimes is well described by Stribeck curve. In this chapter, the mechanism of transition between different regimes and factors influencing the frictional response, different types of lubricantsLubricant and additives types and their key features will be covered.

Sensing, gaging and locating the structural damage inside the wooden wall structure using vibration response is a proven technology and many research articles are published in this thematic area. The damage detection is usually carried out by monitoring and assessing damage-sensitive parameters such as resonant frequencies and operating deflection shapes. However, in this article we propose a novel methodology based on FRF curvature and transmissibility based on the vibration response data as a quantitative parameter to detect and locate damage inside a wall structure. Mock damage was created in one of the structural wooden partition wall of a specially built room and its vibration response was measured. Damage-sensitive factors were taken out from the frequency response data and applied for gaging the damage quantitatively. For locating the damage region, quantitative parameters method, i.e. broadband FRF curvature and transmissibility methods were utilized. These techniques if commercialized, can save billions of dollars in pest control.

The operational life of bearings is often determined by the performance of the lubricating grease. The consistency of the grease prevents it from leaking out of the bearing and provides good sealing properties. The possible ingress of water into the bearing will have a considerable impact not only on this consistency but also on the lubricating ability of the grease. There are numerous applications where water ingress may occur, such as in the steel, food, pulp, and paper industries. Some greases are less sensitive to water than others. No specific guidelines are available to select the proper grease for bearings subjected to water ingress. The goal of the article is to contribute to the development of such guidelines for greases subjected to water ingress by studying the impact of water on grease rheology. Fully formulated, commercially available greases with the most common thickeners and base oils are used as model greases. It will be shown that water strongly influences rheological properties such as zero-shear viscosity, yield stress, and storage modulus. Calcium sulfonate greases were found to become stiffer after absorbing a considerable amount of water, leading to an increase in zero-shear viscosity and yield stress. However, lithium, lithium complex, and polyurea greases were found to soften, with appreciable changes in measured rheological properties.

Water is one of the most common contaminants in grease lubrication. There are numerous applications where bearings are susceptible to water ingresses such as in the steel, food, and pulp and paper industries. A grease can absorb water to different degrees depending upon the type of grease. The ability of a grease to either absorb or reject water can influence the service life of rolling bearings. Two parameters that determine the performance of a grease at very low temperature are the yield stress and startup torque. Water was found to influence the yield stress and startup torque depending on the operating temperature, grease type, and percentage water in the grease.

A comprehensive study of the yield stress and start-up torque for six commonly used rolling bearing greases is presented. Both parameters were found to depend exponentially on temperature where the exponent changes below a low-temperature “break point.” This break point was found to be related to the pourpoint of the base oil, although the start-up torques of the greases were an order higher in magnitude than that of their corresponding bled oils. The start-up torque is mostly used to measure the low-temperature limit of a grease. It was found here that this temperature is much lower than the break point. The start-up torque criterion is measured using a particular bearing type and conditions. The low-temperature break point for the yield stress is a more universal grease parameter that gives useful information about the behavior of a grease at low temperatures and can be used as one of the guidelines for grease selection for low-temperature applications.

The aim of this paper was to understand the parameters influencing the grease film thickness in a rolling elastohydrodynamically lubricated contact under fully flooded conditions at medium speeds. Film thickness measurements were taken under pure rolling for six commercial greases and their bled oils. The grease film thickness was found to be higher than corresponding bled oil, suggesting the presence of thickener in the contact. No rheological properties (characterized by steady and dynamic shear) showed any direct relation to the film thickness of the studied greases. AFM measurements of the thickener microstructure, from which the dimensional properties of the thickener particles (fibers/platelets/spheres) were estimated, showed that the relative increase in the film thickness due to entrainment of the thickener was proportional to the ratio of thickener volume fraction to the size of the fibers/platelets/spheres. Hence, with the same concentration, smaller thickener particles lead to the generation of thicker films than larger thickener particles. Next, this relation was used to establish the percentage of the thickener particles passing through the contact. Depending on the grease type, between about 1 and 70 % of the thickener particles were found to travel through the contact.

This paper investigates the influence of water on the EHL film thickness of six commercial lubricating greases under fully flooded and starved conditions. Although grease can absorb large quantities of water, separation occurs due to pressure and shear, leading to free water. This does not have an impact on the film thickness under fully flooded conditions. However, water does have an effect on the film thickness under starved conditions where the differences are related to the change in oil bleed. In the presence of water, an increase in oil bleed was found for lithium, lithium complex and polyurea grease. These greases showed a reduction in the levels of starvation and, therefore, thicker films. Water contamination led to lower oil bleed for calcium sulfonate complex greases, which led to an increase in starvation, and therefore, thinner films compared to their uncontaminated counterparts.

An experimental study using both a controlled stress and a controlled strain rheometer has been undertaken to characterize lubricating grease in shear, creep, stress relaxation, and oscillatory flow, with a main focus on determining the yield stress. The yield stress was examined using a cone-plate and parallel-plate system with smooth and rough surfaces. Clear discrepancies were observed in the yield stress values obtained using different techniques where oscillatory strain sweep measurements seem to be the best choice. This technique is less sensitive to wall slip, shows good reproducibility, and is relatively easy to perform. The method also shows that the yield stress is a function of the imposed frequency and therefore of the time domain. At lower values of shearthat is, in the linear viscoelastic regimethere is no structural breakdown and the rheology of the grease can be described by the Maxwell model where the stress and the strain are almost proportional to each other. Based on this observation, a novel method to determine the yield stress is proposed: The yield stress can be determined from the point where this linearity no longer applies. This method is compared to those that are commonly used. The yield stress was found to depend exponentially on temperature and linearly on frequency.