Abstract Grease compatibility is an important consideration for end-users and grease suppliers. In the process of replacing lubricating greases, the issue is whether two greases can safely be combined or whether mixing them will decrease performance and even damage equipment. Almost 60% of global grease consumption is based on lithium soap thickener chemistry, so finding alternatives and determining their compatibility is imperative. The experimental compatibility limits of different greases in the current work were examined by preparing binary blends of a reference lithium complex grease (LiX) with three possible substitute thickener types: aluminum complex (AlX), polyurea (PU), and calcium sulfonate complex (CaSX) greases. Three blending ratios (10:90, 25:75, 50:50) for each couple were used to model partial or near-complete grease substitution. In total, nine mixed samples and four unmixed samples were tested in accordance with the ASTM D6185 standard for grease compatibility. First-order test criteria of importance were dropping point, shear stability, and high-temperature storage stability, and secondary tests included windfall storage stability and antiwear performance. The results showed that the lithium complex–polyurea combination achieved the highest compatibility score overall, while the lithium complex–calcium sulfonate complex blends were the least compatible by ASTM criteria.

This study aims to develop intelligent microcapsules to address the challenge of detecting and suppressing early-stage fires in small, enclosed spaces. Polyurea (PU) microcapsules encapsulating the fire-extinguishing agent perfluoro(2-methyl-3-pentanone) (CFO) were prepared via interfacial polymerization using isophorone diisocyanate (IPDI) and diethylenetriamine (DETA). To achieve simultaneous fire extinguishing and flame retardancy, dual-coated microcapsules were synthesized by applying an outer shell of flame-retardant melamine formaldehyde (MF) resin. The surface morphology, encapsulation efficiency, chemical structure, thermal stability, and storage stability of the synthesized microcapsules were analyzed via optical microscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The experimental results show that the process parameters have a significant effect on the preparation of microcapsules. After 10 min of emulsification at a speed of 3000 rpm, the obtained emulsion has a uniform droplet size and good dispersibility. The encapsulation efficiency of the prepared PU@CFO microcapsules and MF@PU@CFO microcapsules reached 42.5% and 41.7%, respectively, which proved the successful encapsulation. The microcapsules can release CFO by gasification when reaching the thermal response temperature and have good storage stability. Fire extinguishing experiments demonstrated the effectiveness of the dual-coated microcapsules, which reduced the peak temperature of an n-heptane flame by 255.6 °C and shortened the self-extinguishing time by 36 s. Under early fire conditions, these microcapsules release CFO for cooling, while the outer flame-retardant coating provides additional inhibition, thereby achieving dual fire-extinguishing and flame-retardant effects. These results provide an effective solution for early fire suppression and the microencapsulation of thermosensitive materials.

A novel microfluidic multichannel (4×) electrochemical cell (MMEC) was developed and used for multiplexed determination of compounds related to water quality. These include heavy metals (lead and mercury ions), catechol and hydrogen peroxide. No crosstalk between the channels of the MMEC was observed. This enabled the specific and independent modification of each MMEC channel with respect to the targeted analyte. Namely, the mercury ions were determined at the bare gold (Au) electrode, lead ions were determined at the Au electrode coated with a thin mercury film (MF), H2O2 was determined at the Au electrode electrodeposited with gold nanostructures (AuNS), and catechol at the Au electrode modified with polyurea (PU) and AuNS. The limits of detection (LODs) were determined and found to be 0.9 ppb, 0.1 ppb, 0.4 μM, and 1.6 μM for lead and mercury ions, catechol, and hydrogen peroxide, respectively. The MMEC was applied for the detection of the analytes in river water samples and in industrial wastewater and good recovery rates were obtained: from 91.8% to 109% in river water samples and 81.8% to 111.6% in industrial wastewater. In addition, comparison with the reference method (ICP-OES) was performed for the determination of Pb2+ ions and the relative error was found to be smaller than 5%. This allows the MMEC to be used for the multiplexed detection of analytes at concentrations relevant to the monitoring of the quality of water resources.

ABSTRACT Studying structural dynamics of polyurea (PU) is pivotal to analyze its vibration‐damping features. In this study, a graphene‐reinforced PU coating with enhanced mechanical and damping properties was developed. PU nanocomposite coating was reinforced with pristine graphene platelets (GNPs) and isophorone diamine (IPDA)‐modified GNPs (m‐GNPs) via in situ polymerization. Morphological characterization confirmed surface modification of GNPs with IPDA showing better dispersion within the PU matrix; this led to a strong interface between m‐GNPs and the PU matrix. The optimal mechanical and structural dynamic properties were achieved at only 0.1 wt% of m‐GNPs; the tensile strength of PU/m‐GNPs increased by 35% while the increment for pristine GNPs was only 11%. The vibration damping—evaluated by loss factor—improved for all four frequency modes; the loss factor increased across all four modes by 26.9%, 88.0%, 158.3%, and 5.0%, respectively. Moreover, a noise reduction of 33.1 dB was attained with PU/m‐GNPs compared to the bare aluminum. The improvements are associated with an effective friction and scattering mechanism, facilitated by an excellent filler‐matrix interface that reduces vibrations and sound waves. Additionally, finite element analysis was implemented to develop a model that describes dynamic responses of PU/m‐GnP composites; the model was validated, which is in accord with the experimental measurements. These findings highlight the potential of GNPs‐enhanced PU coatings as an effective solution for structural vibration damping and acoustic attenuation across diverse industrial applications.

Soft-hard strategy achieves self-healing and strong polymer electrolytes for long cycle all solid-state lithium metal batteries.

The rapid expansion of wearable electronics has accelerated the demand for flexible display technologies. Organic light-emitting diodes (OLEDs) are widely adopted due to their high luminance efficiency, lightweight nature, and inherent mechanical flexibility. However, OLEDs are highly susceptible to long-term degradation when exposed to oxygen and water vapor, leading to a dramatic reduction in device lifetime. Therefore, the development of effective thin film encapsulation (TFE) strategies is essential to ensure long-term device reliability and functionality.Initially, glass was the primary encapsulation material due to its moisture barrier properties. However, its rigidity poses a major limitation for applications requiring mechanical flexibility. To address this issue, alternative TFE materials such as inorganic oxides and organic polymers have been investigated. These materials are typically integrated into single-layer or layer-by-layer (LBL) structures to balance barrier performance and mechanical durability.Despite these efforts, both single-layer and LBL structures often exhibit degradation in moisture barrier performance when subjected to mechanical deformation such as tensile strain or bending. To evaluate these limitations, we fabricated and characterized three types of thin film samples: (a) single-layer polyurea (PU), (b) single-layer Al₂O₃, and (c) Al₂O₃/PU multilayer films in an LBL configuration.Al₂O₃ was deposited via atomic layer deposition (ALD) using trimethylaluminum (TMA) and H₂O, and PU was synthesized by molecular layer deposition (MLD) using 1,4-phenylene diisocyanate (PDIC) and ethylenediamine (ED). Both ALD and MLD processes were carried out at near-room temperature, making them suitable for thermally sensitive substrates. A low-temperature deposition condition is very critical for PU growth, as its growth per cycle (GPC) is known to decrease significantly at elevated temperatures. All films were deposited on flexible polyimide (PI) substrates.To investigate the effect of film structure, LBL samples were fabricated with varying numbers of Al₂O₃ and PU supercycles. The objective was to study how the distribution of organic and inorganic layers, rather than their absolute thicknesses, influences the mechanical reliability and moisture barrier performance of the encapsulation.The film structures were characterized using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The water vapor transmission rate (WVTR) was quantitatively evaluated using an electrical calcium (Ca) test under ambient conditions. Comparative measurements were performed before and after uniaxial tensile strain and cyclic bending to assess the mechanical robustness of each film.In this study, it is demonstrated that while the initial WVTR of Al₂O₃/PU LBL films is comparable to that of single-layer films, significantly improved retention of barrier performance is exhibited by the LBL configuration following mechanical deformation. In contrast, a substantial increase in WVTR is observed in single-layer PU and Al₂O₃ upon the application of mechanical stress. These findings suggest that tuning the supercycle distribution in LBL enhances mechanical reliability and provides a viable route for robust, low-temperature encapsulation of flexible OLED devices.

Priamine derived from vegetable oil has gradually gained attention due to its flexibility. In this study, priamine 1075 was applied to react with urea to prepare thermoplastic polyurea (PUr) and with biuret to polybiuret (PBU) elastomers via solvent-free and catalyst-free melting polycondensation. The obtained PUr and PBUs possess excellent chain flexibility. The strength of PBU00 achieves 8 MPa which is about twice that of PUr. This indicates that the introduction of biuret function in the backbone is able to enhance the mechanical properties. To further improve the strength of the elastomer, 1,10-decanediamine (DDA) was utilized to enlarge the size of the hard segment and the strength of the obtained polymer (PBU20) increases further to 21 MPa. Interestingly, these elastomers exhibit good energy dissipation efficiency (∼80%) and excellent hydrophobicity (water contact angle ∼ 110°), which makes them suitable to be applied in the fields of energy absorption and hydrophobic coatings.

ABSTRACT Composite laminates are particularly vulnerable to low‐velocity impacts, which induce internal damage and lead to significant strength reduction. This study presented the first investigation into the application of Polyisocyanate Oxazolidone (POZD) coatings on composite to enhance impact resistance. The effectiveness of POZD and Polyurea (PUA) coatings was evaluated through a series of impact tests at three energy levels (17, 32.5, and 50 J), followed by compression‐after‐impact (CAI) assessments. Both coatings significantly reduced damage area and suppressed crack propagation compared to uncoated specimens. Notably, they prevented weak zone formation at impact sites under low‐energy impacts and maintained superior CAI strength across all energy levels. Under 50 J impact conditions, the CAI strength showed the most significant variation. Compared to uncoated CFRP, the CAI strength of PUA‐CFRP specimens increased by 7.78%, while that of POZD‐CFRP increased by 15.27%. POZD‐coated laminates demonstrated optimal performance, exhibiting the smallest damage area and highest CAI strength values, establishing POZD as the superior protective coating for impact‐prone composite structures.

Effective mitigation of electromagnetic microwave (EMW) pollution requires the development of lightweight, broadband, and high-performance microwave absorbing materials. In this work, a novel Fe3SnC/Sn/CNF composite is synthesized via a combination of hydrothermal synthesis, electrospinning, and high-temperature carbonization. The optimal sample (FSC3) achieved a minimum reflection loss (RLmin) of -28.33dB and an effective absorption bandwidth (EAB) of 6.40GHz at a thickness of 2.50mm. To enhance environmental durability and broaden application potential, FSC3 is incorporated into a polyurea (PUA) matrix to fabricate a composite coating. The resulting material exhibited significantly improved microwave absorption, with an RLmin of -65.78dB and an EAB of 6.68GHz at only 2.17mm thickness. This enhancement is attributed to increased interfacial and dipolar polarization, as well as improved impedance matching due to the synergy between the filler and the elastomer matrix. Computer Simulation Technology (CST) simulations confirmed excellent Radar Cross Section (RCS)reduction performance, validating its stealth potential. Furthermore, the composite coating displayed enhanced mechanical strength and a hydrophilic surface, broadening its application prospects in harsh environments. This work presents a scalable and versatile strategy for designing multifunctional microwave absorbing coatings with outstanding performance.

Debris flow-induced abrasion severely damages concrete protective structures, reducing their durability. To enhance abrasion resistance, surface bionic treatments inspired by natural patterns are applied to mortar. Surface bionic patterns, including horizontal and vertical stripes, convex, circular and net shapes, are evaluated for their effects on strength, mass loss, abrasion depth, and surface morphology. Results show that bionic patterns improve mortar performance, with flexural strength increases by up to 69.6% and abrasion resistance significantly enhanced. Horizontal stripes distribute forces more effectively than vertical stripes, while convex and net patterns reduce mass loss by 94.6% and 90.0%, respectively, compared to untreated mortar. SEM analysis confirms the superior abrasion resistance of polyurea (PUA) material under debris flow, though weak bonding at the PUA-mortar interface leads to microcracks and detachment. Overall, surface bionic treatments, particularly convex and net patterns, offering a promising solution to improve the anti-abrasion performance of concrete protective structures.

The imperative for high-performance protective materials has catalyzed the rapid evolution of polyurea (PUA) coatings, widely recognized for their mechanical robustness, chemical resistance, and rapid-curing properties. However, their inherent flammability and harmful combustion byproducts pose significant challenges for safe use in applications where fire safety is a critical concern. In response, significant efforts focus on improving the fire resistance of PUA materials through chemical modifications and the use of functional additives. The review highlights progress in developing flame-retardant approaches for PUA coatings, placing particular emphasis on the underlying combustion mechanisms and the combined action of condensed-phase, gas-phase, and interrupted heat feedback pathways. Particular emphasis is placed on phosphorus-based, intumescent, and nano-enabled flame retardants, as well as hybrid systems incorporating two-dimensional nanomaterials and metal–organic frameworks, with a focus on exploring their synergistic effects in enhancing thermal stability, reducing smoke production, and maintaining mechanical integrity. By evaluating current strategies and recent progress, this work identifies key challenges and outlines future directions for the development of high-performance and fire-safe PUA coatings. These insights aim to guide the design of next-generation protective materials that meet the growing demand for safety and sustainability in advanced engineering applications.

Optimization of Preparation Technology and Quality Assessment of Polyurea (PUA) Modified Asphalt

Li-metal batteries (LMBs) and Na-metal batteries (NMBs) are considered as the promising next-generation battery systems to replace conventional Li-ion batteries (LIBs) due to their high theoretical energy density [1]. For LMBs and NMBs, Li metal and Na metal are the ultimate choices to achieve their high energy density due to their high specific capacity, low electrochemical potential, and lightweight. However, as alkali metals, both Li and Na metal anodes suffer from serious challenges including 1) Li/Na dendrite formations and short circuits; 2) Low Coulombic efficiency and poor cycling performance; and 3) Infinite volume changes. In this presentation, I will introduce our research that contributed to the design of artificial interfaces for Li and Na metal anode using atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques [2-3]. i) Developing ionic conductive protective layers for Li and Na metal anodes. A two-step strategy is developed to obtain the smooth and stable LiAlOx and NaAlOx artificial layer for Li and Na metal anodes by the post-lithiation process, respectively. The substrate of Li and Na metals are the Li and Na resources during post-treatment [4]. ii) Nano-alloy structure to the nano-laminated structure for Li and Na metal anodes. Through tailoring the compositions of the hybrid interfaces, we realize the nano-alloy structure to the nano-laminated structure. As a result, the nano-alloy interface (1Al2O3-1alucone or 2Al2O3-2alucone) presents the most stable electrochemical performances for both Li and Na metal anodes [5]. iii) An organic-rich or an inorganic-rich interface? We demonstrate the controllable fabrication of the hybrid artificial SEI for Li metal anode with different organic-inorganic ratios. Three typical compositions were realized: organic-rich interface, organic-inorganic-balanced interface and inorganic-rich interface. The different organic-inorganic ratios of the hybrid interfaces result in the tuning of the mechanical properties, lithiophilicity, diffusion kinetics and Li dendrite formation of the Li metal anode [6]. iv) A new hybrid protective layer for the Na metal anode. A metal-doped hybrid polyurea (PU) film with tunable composition, sodiophilic sites and improved stiffness was fabricated by introducing Zn or Al as crosslinkers into the polymer chains and adopted as an artificial SEI for Na metal. Compared to bare Na and pure PU-coated Na, the Na metal anode coated with the metal-doped PU film exhibits significantly improved electrochemical performance [7]. All these ideas have been also further applied to solve the practical issues for different Li and Na metal battery systems.[1] Energy & Environmental Science, 2024, 17, 442-496[2] Chemical Society Reviews, 2024,53, 5428-5488[3] Chemical Society Reviews, 2021, 50, 3889-3956[4] Small, 2022, 18, 2203045[5] Advanced Materials, 2023, 35, 2301414[6] Advanced Functional Materials, 2024, 2406426[7] Advanced Materials, 2024, 2406837

Grease compatibility is an important consideration for both grease manufacturers and end-users. When switching from one lubricating grease to another, the concern is whether the two greases can safely coexist or if mixing them will degrade performance and potentially harm equipment. Almost 60% of the global grease demand is based on lithium soap thickener chemistry, so finding viable alternatives and understanding their compatibility is vital. In this study, the compatibility limits of different greases were experimentally examined by preparing binary blends of a conventional lithium complex grease (LiX) with three alternative thickener types: aluminum complex (AlX), polyurea (PU), and calcium sulfonate complex (CaSX) greases. Three mixing ratios (10:90, 25:75, 50:50) were tested for each combination to simulate partial or nearly complete grease replacement. A total of nine blended samples, along with the four neat (unmixed) greases, were evaluated according to the ASTM D6185 protocol for grease compatibility. Primary test criteria included dropping point, shear stability, and high-temperature storage stability, while secondary evaluations covered oxidation stability and anti-wear performance. The results revealed that the lithium complex–polyurea combination achieved the highest compatibility score overall, while the lithium complex–calcium sulfonate complex blends were the least compatible by ASTM criteria. The study demonstrates the importance of both standardized tests and practical performance limits in judging grease pair compatibility.

Microplastics (MPs) in soil are an emerging environmental concern due to their widespread distribution, persistence, potential toxicity to soil organisms, possible transfer into crops and groundwater as well as their potential ability to alter soil functions. MP polymers, such as linear low-density polyethylene (LLDPE) and polyurea (PUA) are commonly applied to soils for mulching and pesticide application and their fate needs to be better understood. For qualitative and quantitative analysis, MPs need to be efficiently isolated from soils using suitable extraction methods. Therefore, we developed a modified oil extraction method using n-octanol and compared it with the widely used density extraction method, both preceded by a potassium hydroxide (KOH) extraction step. Pristine and artificially weathered (light-irradiated) small-sized LLDPE mulch film particles (cryo-milled to a median size of 147 µm) and PUA microcapsules used for pesticide applications (median diameter of 2 µm) were spiked into 25 g samples of two standard agricultural soils. Both MP types differed in size, shape, density and especially their composition, as the PUA microcapsules predominantly consisted of oil. After MP isolation, precise MP quantification was facilitated by 14C-radiolabelling of the polymers, which enabled accurate mass balancing while eliminating potential interferences from background polymers. The modified oil extraction method, achieved extraction efficiencies of up to 75% of the applied radioactivity (AR), compared to a maximum efficiency of 62%AR using the conventional density extraction method combined with KOH.Graphical

To counteract microplastic (MP) pollution the European Commission adopted a restriction of intentionally adding synthetic polymer microparticles to products, such as detergents, rinse-off cosmetics, controlled-release fertilizers or pesticides. Exempted are particles consisting of polymers that, e.g., meet the (bio)degradability pass criteria of the available test methods. The main criterion for proving biodegradability is the particle’s mineralization rate, as set out, amongst others, in OECD testing guidelines 301B referenced by the REACH regulation of the European Union. Since present test methods are designed and validated to test low-molecular, soluble compounds adaptations regarding MP biodegradability testing are of high interest. In this study, the biodegradability of a polyurea (PUA) microcapsule suspension was tested using a standard degradation test method (OECD test guideline (TG) 301B). Since the polymeric component comprised less than 1% of the suspension, besides the aromatic solvent inside the microcapsule (8.6%) and water (90.9%), 14C-labeling of the polymer was essential for specific detection throughout the experiments. Particle size determination of the tested PUA microcapsules indicated a bias in the test results due to the presence of a soluble 14C-compound, a byproduct of synthesis, identified using ultra-high performance liquid chromatography–high resolution mass spectrometry (UHPLC–HRMS) coupled with radioactivity detection. This study highlights the need for proper characterization and purification of the tested particles prior to biodegradation testing and suggests how to diversify future regulatory testing for a comprehensive assessment of the biodegradation of MPs.Graphical abstract

Abstract Polyurea (PUA) resin exhibits excellent flexibility and stress dispersion, and its application has been widely explored across various fields in recent years. To assess the potential of PUA materials in asphalt binder pavement applications, both the PUA modifier and the modified asphalt binder were prepared in this study. The interactions between PUA and asphalt binder were investigated using scanning electron microscopy and storage stability tests, focusing on the interaction effects and segregation phenomena. The optimal particle size of the PUA modifier for use in asphalt binder was identified. Rheological models, including the Han curve and Cole-Cole plots, were employed to examine the phase separation behavior of PUA-modified asphalt binder. Additionally, the compatibility of the modified binder was analyzed in relation to its thermal properties. The correlation between the mechanical properties and the compatibility of the PUA-modified asphalt binder was explored. The results demonstrated that PUA modifiers with smaller particle sizes exhibited stronger integration with the base asphalt binder, showing improved compatibility. Increasing the particle size and content of the modifier exacerbated phase separation and segregation phenomena in the asphalt binder system. A strong correlation was observed between the macroscopic properties and the compatibility of the PUA-modified asphalt binder. To achieve favorable macroscopic mechanical properties while minimizing segregation, comprehensive consideration of the particle size and dosage parameters of PUA is necessary for optimizing the compatibility and performance of modified asphalt binders.

Abstract Explosive blasts are considered a distinct hazard in modern military conflicts, which cause extensive damage to buildings and people. Although conventional impact‐resistant materials, consisting of metals/ceramics and polymers, have been researched systematically, the study of lightweight polymer matrix materials on explosive blast attenuation is limited. Therefore, we designed two main structural materials to evaluate the protective ability and mechanical properties of polyurethane elastomer (PUE) and polyurea (PUA) engineering materials under explosive blast loads. The first material was obtained by doping reinforced carbon nanofibers into PUE composites, and the second material was designed based on the mechanical properties of the PUE and PUA single‐layer plates. The attenuation rate of PUE nanocomposites with different nanofiller masses was found to be reduced by 48.44%. Involving multilayers between different types of polymers, PUE/PUA composite plates exhibited an attenuation rate of 84.82% by altering the structure and materials based on their mechanical properties under explosive loads. Therefore, they can provide a favorable and practical strategy for the preparation and structural design of protection materials to withstand the shock wave in vehicle applications, gas explosions, and military events. Highlights Lightweight polymer matrix materials on explosive blast attenuation were studied systematically. Composite plates were made up of polyurea and polyurethane elastomer. Two main structural materials were designed. Carbon nanofibers were used to enhance the composites. PUE/PUA composite plates exhibited an attenuation rate of 84.82% under the explosion.

In recent years, polyurea (PUA) systems have drawn considerable attention in the coatings industry for their superior performance. Among these systems, polyaspartate ester-based polyurea (PAE-PUA) stands out for its excellent comprehensive properties, and the structure of the diamines used in polyaspartate ester (PAE) significantly influences key performance attributes, such as gel time, mechanical properties, and thermal stability. To investigate the influence of diamine structures on PAE-PUA properties, this study synthesized PAEs through ester exchange reactions involving diamines and monohydric alcohols with varied chain lengths and structural types (linear or cyclic). The effects of four diamines (D230, DMH, IPDA, PACM) and four monohydric alcohols (CA, DDA, OD, CHOL) on polyurea coating properties were systematically examined. The results demonstrated that adjusting the structural regularity of PAEs via ester exchange reactions effectively regulated their viscosity, maintaining it below 1500 mPa·s. These reactions also enabled simultaneous regulation of surface-drying time, mechanical properties, and thermal performance. Notably, introducing 1-octadecanol (OD) significantly improved surface-drying time and thermal stability, whereas cyclic structures in diamines or alcohols resulted in higher glass transition temperatures (Tg). Additionally, the mechanical properties and reaction rates of modified PAEs can be tailored to meet specific application requirements, offering an effective strategy for developing polyurea materials optimized for the coatings industry.

The protective effect of polyurea (PU) coatings on polymer matrix composite (PMC) panels subjected to high-velocity ballistic impacts, particularly as a potential replacement material for large power transformer (LPT) tanks, has not been extensively reported in the literature. This study addresses the gap by presenting a numerical investigation into the ballistic performance of PMC panels with PU coatings. Due to the complex nature and high cost of experimental testing, this research relies on finite element modeling to predict the panels' responses under impact. Glass fiber/epoxy and carbon fiber/epoxy composite panels were tested individually and in hybrid configurations while being subjected to simulated 400 m/s steel projectile impacts. This study first investigates the impact damage evolution in uncoated panels, analyzing the arrest depth as a function of the panel thickness. It then evaluates the effect of PU coatings on the ballistic response. The results demonstrate that PU coatings are three times more effective in protecting both glass and carbon fiber panels from penetration compared to simply increasing the panel thickness. Additionally, the utilization of PU coatings led to a reduction in cost, mass, and thickness while still preventing penetration of the projectile in the models.