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新型智能窗涂层材料，实现"光照即隔热"！ 2025-07-22 氧化钨亚纳米线 突破光致变色材料加工瓶颈 光致变色材料在光学存储、智能窗等领域前景广阔，但传统过渡金属氧化物虽具稳定性和成本优势，却受限于加工性差的问题。亚纳米材料（至少一维尺寸小于1纳米）因表面原子比例超高，表现出独特的电子结构和类聚合物特性，为突破无机材料加工瓶颈提供了新思路。然而，如何利用亚纳米尺度优势同步提升光致变色性能与加工性，仍是亟待解决的挑战。 清华大学王训教授、北京理工大学张思敏教授通过溶剂热法成功合成直径仅0.8纳米、长度数微米的氧化钨亚纳米线（TOSNWs）。该材料兼具>95%的可见光透过率和15秒快速光致变色特性，变色后展现强近红外吸收能力。其类聚合物的流变性能支持旋涂、刮涂等简易加工工艺，为开发光触发透明热屏蔽涂层铺平道路。 材料特性揭秘 图1 展示了TOSNWs的精细结构：透射电镜（TEM）图像揭示其单分散独立线状形态（图1a,b），球差校正电镜测得0.38纳米晶格间距（图1c），原子力显微镜（AFM）直接证实0.8纳米直径（图1d）。这种尺度与氧化钨晶胞尺寸相当，赋予材料超高柔性——电镜中可见线体自由弯曲盘绕（图1a,b）。在非极性溶剂（如辛烷）中，线体自组装成束带结构（图1e,f），而元素图谱（图1g-j）证实其纯净的钨、氧组成。 图1. TOSNWs形貌表征 (a,b) 乙醇分散液中TOSNWs的TEM图像。插图：TOSNWs乙醇分散液实物图。 (c) 乙醇分散液中TOSNWs的球差校正STEM图像。 (d) AFM图像及对应高度曲线图。 (e) 辛烷分散液中TOSNWs的TEM图像。 (f) 辛烷分散液中TOSNWs的HAADF-STEM图像。 (g-j) EDX元素分布图谱结果（W, O元素）。; 类聚合物行为 图2凸显了材料的类聚合物特性。随溶剂极性调节（乙醇/辛烷混合），TOSNWs实现从透明分散液到不透明凝胶的转变（图2a,b）：当辛烷体积比≤50%时，分散液透光率>90%（图2c）；辛烷比例增加促使线体组装成纳米带，通过物理缠结形成三维网络凝胶（图2d）。这种组装行为显著提升体系粘度——TOSNWs分散液粘度比直径10纳米的氧化钨线高数个量级（图2d）。研究进一步利用表面羟基设计交联凝胶（图2e）：添加二异氰酸酯后10分钟内即可形成自支撑透明凝胶（图2f），经超临界干燥制得的气凝胶密度仅0.031 g·cm⁻³，可承载蒲公英而不损伤（图2g）。 图2. TOSNWs溶剂响应行为与交联设计 (a,b) 不同乙醇/辛烷体积比的TOSNWs分散液状态（透光率与凝胶行为）。 (c) TOSNWs分散液透光率与溶剂组成关系（插图为实物图）。 (d) TOSNWs分散液粘度随辛烷体积比变化曲线。 (e) TOSNWs表面双分子层结构示意图及二异氰酸酯交联机制。 (f) 交联TOSNWs形成的自支撑透明凝胶实物图。 (g) TOSNWs气凝胶承载蒲公英的实物图（密度0.031 g·cm⁻³）。; 光致变色性能 图3 记录了材料卓越的光响应能力：TOSNWs乙醇分散液在100 mW·cm⁻²氙灯下15秒内由无色变为深蓝（图3a,b），其凝胶与气凝胶同样展现快速变色（图3c-f）。X射线光电子能谱（XPS）证实变色源于W⁵⁺形成（图3g,h），引发局域表面等离子共振效应，导致变色后材料在近红外区出现宽谱强吸收（图3i）。这种"体相变色"特性（图3k）得益于亚纳米尺度——所有WO₆八面体暴露于表面，显著提升变色效率（传统纳米颗粒仅表面反应）。 图3. TOSNWs光致变色性能 (a,b) TOSNWs乙醇分散液（5 mg·mL⁻¹）变色前后状态。 (c,d) TOSNWs凝胶（5 mg·mL⁻¹, V乙醇:V辛烷=1:1）变色前后状态。 (e,f) TOSNWs气凝胶变色前后状态。 (g,h) 初始态与变色态TOSNWs的XPS谱图（W 4f轨道）。 (i) 变色前后紫外-可见-近红外吸收光谱对比。 (j) 光照后不同时间点的吸收光谱变化（0-120分钟）。 (k) 亚纳米线（SNWs）与传统纳米颗粒光致变色机制对比示意图。; 智能窗应用验证 图4 演示了TOSNWs涂层的热屏蔽效能：旋涂于石英玻璃的透明涂层（0.2 mg·cm⁻²）初始透光率>90%，变色后仍保持>50%可见光透过（图4c,e）。在模拟日光照射下，涂层覆盖的玻璃温度5分钟内升高35℃，而裸玻璃温度不变（图4f），证实近红外光高效转化为局部热量。密闭箱体实验显示，涂层使箱内温升降低55%（13℃ vs 29℃）（图4g），显著阻隔热量传入。 图4. TOSNWs涂层热屏蔽性能验证 (a,b) 无涂层石英玻璃覆盖的自制装置实验起始/结束状态（标尺单位：厘米）。 (c,d) TOSNWs涂层石英玻璃覆盖装置实验状态（左下插图：涂层变色前后实物图）。 (e) TOSNWs涂层透光率光谱。 (f) 氙灯照射下（100 mW·cm⁻²）涂层/无涂层玻璃温度随时间变化曲线。 (g) 涂层/无涂层密闭箱体内温度随时间变化曲线。 前景展望 该研究通过亚纳米尺度设计，同步攻克了过渡金属氧化物光致变色材料的加工性与性能瓶颈。TOSNWs的类聚合物加工性、快速光响应及高效热屏蔽能力，为建筑/汽车智能窗提供了新材料解决方案。这种"光照即隔热"的特性有望显著降低制冷能耗，助力碳中和目标实现。
中科院海洋研究所，最新Nature系列综述：摩擦纳米发电机与场效应晶体管！ 2025-07-16 ;物联网;(IoT) 基础设施的实际部署面临着巨大的能源需求。为了应对这一需求，摩擦纳米发电机和场效应晶体管 (FET) 催生了摩擦电子晶体管和液滴发电机 (DEG)。前者通过将机械刺激转化为摩擦电势来实现主动机械感知，后者则通过受 FET 启发的架构的体效应来提高雨滴能量收集的效率。 鉴于此，中科院海洋研究所王鹏研究员探讨了摩擦电子晶体管和 DEG 的工作机制和设计原理，并重点介绍了它们无缝集成到全球物联网网络所必须克服的关键科学和技术挑战。他们重点介绍了用于物联网数据收集、存储和处理以及近乎永久的物联网网络中环境能量收集的先进设备的开发，以促进触觉传感器、人工突触、能量收集器和自供电传感器等物联网应用的进步。最后讨论了需要进一步研究的关键领域，包括理解基本机制、优化系统设计以及解决摩擦电子晶体管和;DEG 在大型物联网网络和自供电传感器中的应用所面临的实际挑战。相关论文以题为“Mutual promotion of triboelectric nanogenerators and field-effect transistors towards the IoT”发表在最新一期《Nature Reviews Electrical Engineering》上。 【概述】 物联网在智慧城市、医疗、农业与家庭中的愿景，受制于数十亿节点持续采集、存储和处理数据的能耗压力。TENG 可将触碰、振动、风或雨滴等普遍机械刺激转为电能，而低功耗 FET 则能减少数据处理能量需求。关键在于：当摩擦电荷直接加至 FET 栅极时，机械位移本身即可调制沟道导电，无需外部栅驱动；另一方面，把 FET 视作电极模板又启发了新型 TENG 几何结构，进一步提高电荷收集效率。两者互补，可同时解决物联网的“供能”与“节能”难题。 作者将两条曾经独立的研究路线——摩擦电纳米发电机（TENG）与场效应晶体管（FET）——定位为可持续、无处不在的物联网（IoT）之互补基元（图1）。作者指出，预计到 2030 年物联网终端将超过 320 亿个，若仍依赖传统电池和电网，耗电的传感器、存储与无线单元将不堪重负。TENG 能把日常机械能量转为电能，而先进 FET 能显著降低运算与存储功耗；当将 TENG 产生的高压耦合到 FET 栅极时，机械事件便可直接调控载流子传输，形成自供能逻辑与感测。反之，以 FET;为灵感的电极布局又催生了能高效收集雨滴能量的“类晶体管”TENG。综述围绕“摩擦电子学晶体管”用于主动机械感知，以及“晶体管式;TENG”用于环境能量采集这两大主题展开。 图;1. 摩擦纳米发电机与场效应晶体管相互促进，共同推进物联网发展 【FET 与 TENG 的集成】 首先是摩擦电子学晶体管基础（图2），摩擦电子学晶体管结合了 TENG 的摩擦层与电极，以及 FET 的源/漏/栅绝缘层与半导体沟道。在最早的接触起电 FET（CEFET）中，Kapton 薄膜周期性接触 Al 栅极；分离后形成表面电荷，产生的摩擦电势;Vtribo作用于栅介质，调控沟道电流 IDS 。Vtribo表面电荷密度、间隙距离及介电常数变化，可用经典 MOSFET 方程描述。设计要素主要分为三大类：（1）TENG 侧：材料——如等离子蚀刻 PTFE 具高负电性；纳米结构增强粗糙度与介电率。工作模式——接触分离模式适合垂直按压；滑动模式支持面内位移但磨损大；单电极模式封装简单但输出较低。（2）FET 侧：半导体——从 Si、IGZO 到柔性有机（P3HT、并五苯）及二维材料（石墨烯、MoS₂、InSe）。高迁移率与低阈值可扩大开关窗口并降低功耗。（3）集成方式：垂直堆叠 电荷耦合最强，但需精密对准；平面并置 制程简单，却引入附加电阻稀释电势。 图;2. 摩擦电子晶体管的基础知识 关于典型物联网器件（图3），则可以分为：触觉传感器：InSe 摩擦电子学晶体管在 0.1 V 漏极偏压下实现 10⁶;的开关比和毫秒级响应，能量仅皮至飞焦耳。阵列已达 10 × 10 像素，向高分辨率电子皮肤迈进。非易失触碰存储器：浮栅俘获摩擦注入电荷，可在无电源下保持 >6 000 s；石墨烯/hBN/MoS₂;堆栈记忆窗口达 60 V。人工突触：控制浮栅电荷衰减模拟短/长时程可塑性，实现约 165 aJ;每脉冲的体内计算。 图;3. 典型的基于摩擦电子晶体管的物联网设备的表示 【用于雨滴能量收集的类晶体管;TENG】 作者从DEG 架构与机理两个方面阐述了用于雨滴能量收集的类晶体管;TENG（图4）。雨滴发电机（DEG）将 TENG 重新构想为三端“液体栅”晶体管：PTFE 介质（栅）覆于 ITO 底电极（源），雨滴展开时在水/介质界面形成电双层；顶部悬浮电极（漏）接触液面完成回路，液滴极化驱动外部负载电流。单滴峰值功率密度达 50.1 W m⁻²。 图;4. 液滴能量发生器的基础知识 设计策略主要分为：介质层：超疏水高负电材料（仿荷叶纹理）增强电荷，植入肖特基二极管可直接输出直流，高压可超;1 kV。顶部电极：最佳垂直间隙约;0 mm，电极应接触最大扩展雨滴的边缘。多层/共面布局：降低寄生电容，便于模块化装配；高熵陶瓷介层将单滴电压推至 525 V。 面向物联网的应用则可以是（1）环境能量收集：DEG 模块可像光伏板一样铺设，但需解决大面积布线、整流损耗与机械耐久。与振动模式 TENG 叠层可提升约 30 % 的能量输出；与太阳电池共享电极能打造“全天候”混合板。（2）自供能传感：雨滴接触产生高信噪尖峰电流，用于微流控或管道流量监测；功能化电极还能检测细菌，最低可至;4.5 × 10³ CFU mL⁻¹。 图;5. 基于液滴能量发生器的典型物联网设备 【展望与结论】 本文主要从基础机制、器件设计、物联网应用进行了分析总结：固-固与液-固接触的原子级电荷转移机理及其与新兴半导体载流子输运的耦合尚待定量化，需要更精细的流体 电荷耦合模型。未来介质层应兼具高介电、高负电性、可拉伸与可回收；半导体需平衡迁移率与机械柔性；电极则要求耐腐蚀、透明且柔软。可用机器学习从原子力显微测得的黏附与摩电系数数据库中筛选最佳组合。摩擦电子学触觉传感仍受大应变线性度及高分辨率扩展限制；DEG 的高压/低流间歇输出给功率管理带来挑战。需材料、电子学和神经形态计算跨学科协作。 总而言之，TENG 与 FET 的互促协同已从实验室巧妙耦合发展为支撑下一代自供能智能物联网硬件的广泛平台。摩擦电子学晶体管可将机械刺激直接转化为计算与存储，而类晶体管 TENG 则把环境运动和降水重新定义为高密度电能来源。若能在界面物理、材料集成与系统工程层面继续突破，这些概念将加速从原型走向未来数万亿物联网边缘节点的实际部署。
智能环氧防腐涂层：瞬间自我修复，抑制腐蚀发展！受豌豆启发 2025-07-16 ; 保护涂层下局部金属腐蚀的初步检测和即时修复对于金属材料在其生命周期中的长期应用以及减少环境影响和碳排放具有重要意义。 本文，复旦大学研究人员在《Prog Org Coat》期刊发表名为“A novel smart anti-corrosive coating based on the beanpod-inspired microcontainers with self-reporting and self-healing abilities”的论文，研究受豆荚的启发，制作了一种基于pH响应微容器的智能环氧防腐涂层。 受豆荚启发的微容器（micropod）由高容量中空介孔二氧化硅纳米颗粒/氧化石墨烯（MSN-NH2/GO微容器）和指示剂及抑制剂1,10-菲罗啉（Phen）组成。 微模块的pH响应性来自于GO静电阀与 MSN-NH2的相互作用，在不同的pH值下，MSN-NH2的表面电荷会发生变化，从而控制 Phen的释放。 当随着pH值的升高发生涂层下腐蚀时，Phen从脱离的微柱中逸出，与溶解的Fe2+配位，呈现出橘红色，并形成被动的络合物膜阻止腐蚀，从而实现腐蚀感应和抑制。 同时，GO的高宽比延长了腐蚀性介质在涂层中的扩散途径，从而增强了涂层的耐腐蚀性。Phen@micropod/epoxy防腐涂层在浸泡试验和盐雾试验中表现良好，在30天浸泡试验中保持完好，其Rc值是纯环氧涂层的1000倍。 受beanpod启发的micropods设计（MSN-NH2/GO microcontainer） 流程图 a）SEM图像和 b）MSN-NH2的TEM图像、N2吸附-解吸等温线和 c）MSN-NH2的孔分布曲线，d）Phen@MSN-NH2和e）不同pH值下水溶液中MSN-NH2和GO的Zeta电位 a) 空微柱和b) 填充微柱（蓝色代表Phen）的TEM图像；c) Phen、空微柱和填充微柱的TGA和推导 TGA 曲线；d) pH 值为7和10时Phen 从微柱中的释放曲线；e) pH值为7和10时微柱（MSN-NH2/GO 微容器）的组装和分离机制图示 a) 完整的纯 EP 涂层的奈奎斯特图和 b、c) Bode 图；d) Phen/EP 涂层的奈奎斯特图和 e、f) Bode 图；g) Phen@MSN-NH2/EP涂层的奈奎斯特图和 h、i) Bode 图；j) 浸泡在3.5wt% NaCl溶液中的填充微柱/EP涂层的奈奎斯特图和 k、l) Bode 图 a) 用于拟合不同浸泡阶段涂层EIS结果的等效电路，b) Rc、c) 吸水率和d)对数 fb随浸泡时间的变化 a) 涂层遇到膜下腐蚀或机械破坏时的自报告和自修复机制；b) 相应的拉曼光谱；c) Phen中N的高分辨率XPS结果；d) 在3.5wt% 的NaCl溶液中浸泡55小时后划痕区域的产物 在这项研究中，我们提出了一种受豆荚启发设计的具有自报告和自修复能力的智能防腐蚀涂层。带正电荷的中空介孔二氧化硅（MSN-NH2）和带负电荷的氧化石墨烯（GO）通过静电组装复制了豆荚的结构。合成的微柱（MSN-NH2/GO微容器）作为无毒指示剂和抑制剂Phen的大容量微容器，将Phen与环氧基质隔离，避免了不相容和早期泄漏。 ; 当pH值升高时，MSN-NH2的表面电荷变为与GO相同的负电荷状态，导致静电斥力剥离并释放出封装的Phen，模拟了豆荚成熟时的爆裂行为。这种触发释放模式保证了当局部pH值升高而发生腐蚀时，涂层中的微柱能释放出Phen，GO既是控制Phen释放的阀门，又是抑制腐蚀性介质扩散的屏障。 因此，在浸泡试验和盐雾试验中，Phen@微柱/EP涂层的防腐蚀性能非常出色，这得益于GO的高纵横比，浸泡30天后，涂层的耐腐蚀性能提高到1.4×1010Ω-cm2，吸水率降低到1.6vol%。一旦Phen在腐蚀现场局部释放，Phen就会与溶解的Fe2+相互配合，实现着色并形成覆盖腐蚀部位的被动膜，为报告涂层排除设备下的初步腐蚀情况提供了可视化解决方案，并能瞬间自我修复，抑制腐蚀的发展。 该生物启发多功能涂层在防腐蚀领域的应用前景广阔，具有合理的触发释放模式和较高的负载抑制剂、指示剂或修复剂的能力，对早期控制腐蚀发展和维护金属结构，减少金属腐蚀造成的环境污染和碳排放具有重要意义。 ;
Tribology in Cosmetics 2025-07-08 Table of ContentsIntroductionDifferent categories of tribological properties Examples of some advanced materials in cosmetic tribologyConclusionReferencesIntroductionTribology is the study of friction, wear, and lubrication and it also plays a crucial role in the development and optimization of cosmetic products. Tribological performance plays an important role in all aspects of cosmetics starting from skincare treatments to makeup formulations, achieving ideal tribological properties enhances product functionality, user satisfaction, and innovative material design. In cosmetics, the interaction of various materials and techniques not only influences frictional behavior but also impacts rheological properties, texture, and overall sensory perception, making tribology an essential consideration in both formulation and user experience. Different categories of tribological properties The different tribological properties required for the cosmetic applications are listed in the table-1 below.Table-1 The list of tribological properties and examples of those with cosmetic materialsCategoryFunctionTribological RoleCommon ExamplesLubricants (Friction-Reducing Agents)Enhance flow ability and provide a smooth, non-sticky feelLower the friction coefficient to ease applicationDimethicone, Cyclopentasiloxane, Mineral OilFilm-Forming Agents (Controlled Friction)Create a stable layer to protect skin and hold product in placeProvide balanced friction—neither too slippery nor too resistantChitosan, Hydroxyethyl Cellulose (HEC), Polylactic Acid (PLA)Rheological Modifiers (Viscosity Adjusters)Adjust viscosity and improve texture for better control during applicationEnable shear-thinning for reduced friction during use, with quick recovery post-applicationCarbomer, Xanthan Gum, Guar GumNatural Oils and Waxes (Dual-Function Agents)Provide lubrication and form protective films to retain moistureAct as lubricants and film-formers, ideal for enhancing occlusion and product performanceShea Butter, Jojoba Oil, Carnauba WaxExamples of some advanced materials in cosmetic tribologyThe advanced materials used in modern cosmetic formulations primarily serve to enhance hydration, improve texture, flowability, reduce friction, and strengthen barrier function. Materials like graphene oxide composites, bacterial cellulose, and self-healing polymers focus on moisture retention and structural integrity, making them ideal for anti-aging creams, sunscreens, and wound-healing products. Silk fibroin hydrogels, peptide-based systems, and nano emulsions aim to deliver smooth application and effective hydration, commonly used in moisturizers and serums. Stimuli-responsive and thermo-responsive polymers offer adaptive behavior, useful in climate-sensitive or smart skincare products, while nanoparticles and liposomes enhance absorption, uniform distribution, and UV protection, especially in sunscreens and treatment-focused cosmetics. Overall, these materials contribute to more efficient, durable, and user-friendly skincare solutions and are summarised in the table below. Table-2 The list of advance materials and their properties for cosmetics. Material TypeKey PropertiesFriction Coefficient (μ)Moisturizing CapacityViscosity (mPa·s)ApplicationsGraphene Oxide-Enhanced Biopolymer CompositesHigh structural stability, reduced friction~ 0.10–0.15~ 85%–Anti-aging creams, barrier-enhanced sunscreensSilk Fibroin-Based HydrogelsEnhanced hydration, smooth application, integrates natural oils/emulsions~ 0.12–0.18~ 90%–Skin regeneration gels, high-performance moisturizersBacterial Cellulose NanofibersDense, water-retentive network, increases viscosity–~ 92%–Wound-healing creams, hydrogel facial masksPeptide-Based Self-Assembling HydrogelsDelivers smoothness and moisture, good structural integrity~ 0.08–0.12–~ 2000–6000Anti-aging serums, hydration boostersIonic Liquid-Modified EmulsionsImproves viscosity and barrier function~ 0.10–0.16~ 87%–Lightweight moisturizers, active ingredient delivery systemsStimuli-Responsive Supramolecular PolymersAdaptive to pH or temperature via reversible host–guest interactions~ 0.09–0.14–~ 3000–10,000Climate-adaptive creams, smart delivery systemsThermo-Responsive PolymersAdjust elasticity/viscosity with temperature–––Adaptive skincare formulations based on skin temperatureSelf-Healing MaterialsCan rebuild structure after wear, durable and high-performance–~ 92%–Wound-healing creams, hydrogel facial masksNanoparticles/Nanosheets (e.g., Graphene Oxide)Enhance spreadability, UV protection, product efficacy–––Sunscreens, improved texture in various cosmetic formulationsLiposomes and NanoemulsionsImprove absorption and uniform distribution–––Serums, creams, products requiring deep delivery and uniform feelConclusionTribology plays a crucial role in the cosmetics industry by linking material science with consumer satisfaction. By focusing on key tribological properties like friction, wear, and lubrication, cosmetic products can be designed for both high performance and a pleasant sensory experience. Innovations such as silicone-based compounds, bioengineered proteins, and nanomaterials have significantly improved product functionality, durability, and comfort, resulting in smoother application and enhanced skin benefits. References[1] Randhawa, K., 2025. Tribology in Cosmetics Including Advanced Materials and Emerging Trends. Journal of Bio-and Tribo-Corrosion, 11(2), pp.1-17. [2] https://www.dhl.com/discover/en-hk/e-commerce-advice/shipping-guides-by-country/how-to-ship-cosmetics-and-beauty-products-from-hong-kong
Can we select the desirable material using AI? 2025-07-01 Table of ContentsIntroductionExample for tool wear monitoringHow does it work?ConclusionReferencesIntroductionThe selection of materials for various applications is crucial and these materials are influenced by friction and wear in distinct ways. Advances in artificial intelligence (AI) and machine learning (ML) have enabled the visualization and classification of wear particles using image identification techniques. By analyzing micrographs captured through various microscopic methods, AI can assess key characteristics such as particle size, texture, shape, and colour. This is essential in understanding where wear occurs, the nature of wear particles (metallic or oxide), and the underlying causes, such as fatigue or abrasion [1]. Example for tool wear monitoringOne of the notable applications of AI-driven image processing is in tool wear monitoring. Researchers have demonstrated how a microscopic imaging system could track wear on cutting tools used in machining processes. AI-based image processing can analyze tool wear by applying a processing parameter descriptor to microscope images. By positioning the microscope at a fixed point on a milling machine, a baseline for “new” material was established, allowing for accurate wear assessment over time. Using a tool shape descriptor (TSD), critical wear areas, particularly along the cutting edges, were identified and quantified. These studies highlight how direct sensor-based image processing offers a reliable and efficient approach for monitoring tool wear in conventional machining, improving maintenance strategies and prolonging tool lifespan. Figure-1 Extraction of the tool wear ROIs using a TSD [2]How can AI assist in material selection Optimizing Coating and Alloy Composition – AI can assist in selecting and optimizing metal alloys and vapor-deposited hard coatings based on factors like thickness, composition, and hardness to enhance wear resistance.Material Performance Prediction – Machine learning models analyze wear behavior over time, helping industries predict how different materials will perform under varying conditions, leading to better material selection.AI-Driven Wear Analysis – AI examines how materials degrade due to friction and wear, allowing for the identification of the best materials for specific applications based on real-world performance data.Reducing Experimental Costs in Material Testing – Artificial Neural Networks (ANN) can predict material wear rates without extensive physical testing, making material selection more efficient and cost-effective.Validating Material Suitability for Different Environments – ANN models can simulate how materials will behave under different loads, environments, and time frames, ensuring that selected materials meet the required durability and performance standards.How does it work?1. Data Analysis and Feature Extraction Feature engineering is one of the most challenging aspects of ML in material science. It involves selecting, constructing, and optimizing input variables to improve model accuracy. AI and ML techniques rely on materials data and informative landscapes to extract meaningful insights about material properties and wear behavior. Large datasets, such as open quantum materials databases, are used to develop predictive models. For example, researchers have used ML to predict thermodynamic stability in material composites, which helps in optimizing material composition for better wear resistance. 2. Multiscale Modelling Multiscale modelling integrates AI and ML with computational material science to study materials at different length and time scales. This allows researchers to predict how materials behave under different wear conditions. AI-driven modelling enables faster materials exploration and design, reducing reliance on time-consuming experimental testing. ML algorithms help identify key material features related to wear resistance, aiding in the selection of optimal materials for specific applications.3. Predictive Simulations for Wear and Friction ML techniques can simulate Multiphysics and multiscale interactions, offering insights into how materials respond to different loads, environments, and wear conditions. AI models can quantify and predict material wear, supporting the development of more durable and wear-resistant materials. These techniques are also useful for improving measurement devices, ensuring accurate monitoring of material wear over time. 4. Experimental and Simulation Data Integration ML can combine experimental data and simulation results to uncover relationships between material structure and wear behavior. By applying AI, industries can develop optimized coatings and alloys tailored for specific operational conditions, enhancing performance and longevity. Figure-2 Schematic representation of the necessary steps to implement a) supervised and b) unsupervised learning algorithms ConclusionAI and ML significantly improve friction, lubrication, and wear modelling, enabling precise material selection and surface engineering. These advanced predictive tools help optimize material performance, ensuring durability and efficiency in complex systems. By accurately predicting wear and maintenance needs, AI and ML reduce unexpected failures and downtime. This proactive approach enhances productivity and lowers costs, benefiting industries through better maintenance planning and resource optimization. References[1] Shah, R., Jaramillo, R., Thomas, G., Rayhan, T., Hossain, N., Kchaou, M., Profito, F.J. and Rosenkranz, A., Artificial Intelligence and Machine Learning in Tribology: Selected Case Studies and Overall Potential. Advanced Engineering Materials, p.2401944. [2] Pimenov, D.Y., da Silva, L.R., Ercetin, A., Der, O., Mikolajczyk, T. and Giasin, K., 2024. State-of-the-art review of applications of image processing techniques for tool condition monitoring on conventional machining processes. The International Journal of Advanced Manufacturing Technology, 130(1), pp.57-85. [3] https://www.jhuapl.edu/news/news-releases/240806-ai-driven-materials-discovery-national-security
Thin Film Deposition of Tribological Coatings 2025-06-25 coatingsdip coatingspin coatingthin filmArticle provided by Caitlin Ryan. Thin film tribological coatings are important for reducing friction, minimising wear, and increasing the lifespan of mechanical components in a variety of industries. These coatings can be applied using different deposition techniques which each offer their own advantages based on cost, scalability, and material shape. Creating the optimal coating depends on several factors, and extends beyond the coating process and into the drying dynamics that occur as well. This article explains the key thin film deposition methods that are used to create tribological coatings, applications of each, and the overall factors that must be considered to achieve optimal coating performance.Choosing a Deposition MethodChoosing the most appropriate deposition technique for tribological coatings depends on several considerations. Firstly, the desired thickness of the tribological coating must be considered. Different coating methods can create thin layers of different thicknesses, from the nanometre to micrometre range. Additionally, how uniform the thin film is will depend on what technique is used. Some methods offer greater control over important factors such as the fluid properties, making it easier to get consistently uniform coatings. The next thing to think about is the scale of the application – is the work being carried out in a lab or on an industrial scale? Is a single item being coated, or is it part of a roll-to-roll continuous process? Some coating methods are not suitable for scaling up to an industrial level, or can only be used for batch processing. The shape of the object that is being coated is another important consideration. Some coating techniques, such as dip coating, can be used to coat complex shapes such as tubes whereas others, such as spin coating, are limited to coating small, flat surfaces only. Quite often, environmental and sustainability considerations must also be factored in when choosing a technique. For example, some coating methods waste a high amount coating solution which may be an issue if the solution is costly or environmentally harmful. As well as this, different coating methods apply coatings at different speeds and with varying levels of complexity. This impacts overall energy consumption, which can be a key consideration during the scaling up process.Thin Film Tribological Coating TechniquesThere are several thin film deposition techniques that are currently used in industry to produce uniform tribological coatings for a range of applications. The most common of these are spin coating, dip coating, and slot die coating. Each of these techniques has its own advantages and limitations, as well as a range of parameters that must be adjusted to achieve an optimal, uniform coating. Other common thin film deposition methods, such as doctor blade coating and bar coatings, are not frequently used in industry for tribological coatings specifically and are therefore not discussed. Spin CoatingSpin coating works by depositing a solution onto the substrate that you wish to coat, then rotating it at a high speed. The constant acceleration creates centrifugal force which, in combination with viscous drag and surface tension effects, causes the solution to spread evenly across the substrate. The rate that the substrate is rotated at is what determines the thickness of the film – a faster rotation results in a thinner film. Spin coating is a simple technique that works very well to create uniform coatings on a small scale. Due to the nature of the process, it does not scale very well and so it is limited to batch processing of small components, typically within the research and development period of competent development. Though limited to small, flat surfaces, there are several applications of spin coating for tribological thin films: Hard disk drives (HDDs): Spin coating can be used to apply ultra-thin layers of perfluoropolyether (PFPE) lubricant onto HDDs to reduce the friction between the read/write head and the disk surface.Micro-electromechanical systems (MEMS): The performance of MEMS can be improved by spin coating thin layers onto the surface, such as self-assembled monolayers and silicon dioxide layers. These layers reduce static friction by creating low-energy surfaces that minimise adhesion forces.Optical coatings: Sol-gel derived coatings can be spin coated onto optical surfaces such as lenses and displays to protect them from scratches and environmental degradation.Dip CoatingDip coating works as the name suggests. A substrate is immersed in a coating solution and as it is withdrawn, a thin layer of the coating solution forms on the substrate. Once the solvent within the coating solution is evaporated from the substrate’s surface, a dry thin film will remain. The thickness of the thin film is hardest to control with dip coating, and it is based on several factors including withdrawal speed, air flow, viscosity, and evaporation rate.Despite this, dip coating is very commonly used to deposit thin tribological coatings across a range of industries: Biomedical implants: Biomedical implants such as titanium alloy joint replacements can be dip coated with polymers including ultra-high molecular weight polyethylene (UHMWPE). In doing so, load bearing and wear resistance are increased, leading to better patient outcomes.Automotive engine components: Dip coating is often used for engine components such as pistons and shafts because the immersion-based technique means that entire complex geometries can be coated in one process. E-coating, a form of dip coating that also includes an electric field, is sometimes used to apply even layers of anti-corrosion films to components.Slot Die CoatingIn slot die coating, a solution flows through a ‘head’ at a determined rate and directly onto a substrate, which moves relative to the head. The thickness of the deposited film is determined by how much solution is placed onto the substrate. Other factors, such as the solution flow rate and substrate movement speed, must be optimised to improve how uniform the thin film deposition is. Slot die coating scales very easily and is the most commonly seen thin film deposition technique within the large-scale manufacturing industry. A big benefit over dip coating is that the solution is directly coated onto the substrate, which means there is very little waste.It is, however, the most complex coating technique and a lot of optimisation work is required to ensure that tribological coatings are consistent, stable, and uniform. As previously mentioned, slot die coating is often used to create tribological thin films on an industrial scale: Turbine blades: Slot die coating is compatible with roll-to-roll processes meaning it can be used to create large-area tribological coatings for parts such as turbine blades.Energy applications: Slot die coating is used to create protective components on battery electrodes and fuel cell membranes to increase durability. The advantage of this technique is that, once optimised, tribological coatings are consistently defect-free which is particularly important for energy applications.Industrial machinery: Precise thickness lubricant films can be deposited onto industrial machinery using slot die coating to reduce friction and wear during operation.Drying and Film UniformityThe drying stage is a very important aspect of the deposition of the tribological thin film process. The way that a coating is dried can impact the morphology, uniformity, and therefore its subsequent performance. For that reason, the suitable drying method for both the coating type and technique must be determined to prevent defects from occurring. The formation of thin films is heavily influenced by the evaporation of the solvent within the coating solution. Once a substrate has been coated and the solvent begins to evaporate, the solid materials in the wet coating become increasingly concentrated until the final dry layer is formed. Therefore, the evaporation process determines how the solid materials organise to create the finished dry layer. The drying method used is an important consideration, as different techniques can change the final morphology of the film without changing the coating’s chemical composition. Commonly, thin film tribological coatings are thermally dried for example in a furnace or on a hotplate. A higher temperature results in a faster evaporation rate and a reduced drying time. Drying of Dip Coated Thin FilmsThe dynamics that occur during the drying of a dip coated thin film depend on the speed that it is withdrawn from the coating solution. When the withdrawal speed is fast enough, the drying dynamics are dominated by the constant rate period in which solvent evaporation happens uniformly across the surfaces of the wet film. The only exception is at the edge of the coated substrate, where a drying front occurs. In this scenario, the final film thickness is dependent on the initial wet film thickness. If the withdrawal speed is slow, the drying dynamics become dominated by the drying front period instead. At the drying front, there is a greater surface-to-area volume which causes evaporation to occur much faster, leading to the formation of a wet film with a higher concentration of solid particles. A combination of surface-tension driven effects and capillary forces results in a thickening of the deposited film. Drying of Spin Coated Thin FilmsThe rate of evaporation is typically fastest in a spin coated wet film compared to a dip coated or slot die coated wet film. This is because the spinning environment causes the surrounding atmosphere to be less vapour-saturated, which drives more rapid evaporation. For that reason, the rate of evaporation can be slowed down by spin coating in an environment that is vapour saturated. Additionally, the speed of rotation has an impact on the evaporation rate. Spinning faster results in faster evaporation, but will also create a thinner tribological coating meaning some optimisation between the two is required. Different evaporation rates can sometimes lead to complex behaviours occurring. For example, if the evaporation rate is too high, it can lead to the formation of a top layer that has a higher concentration. This so-called ‘crust’ can prevent evaporation from within the coating, trapping solvent there. Often, this leads to defects arising such as wrinkling in the final film. Drying of Slot Die Coated Thin FilmsSlot die coating is the most frequently used thin film deposition method in industry, but the drying phase can cause several complications if not properly optimised. This is because the surface tension and viscoelastic properties of the coating solution can cause the coating to expand or recede whilst it is still wet. Naturally, this causes the coating to dry differently than the way it was applied, resulting in variations in the thickness and width than expected. As well as this, the increased surface area at the edge causes the edge of the coating to dry faster than the centre. This creates capillary forces that result in a flow of coating to move towards the edge of the film where the concentration of solids increases. This is known as the ‘coffee ring’ effect as the edge of the film ends up being thicker, leading to a pattern that looks like the ring left behind by a mug of coffee. Slot die coating is also fairly unique in that there is a delay between the application of the first and last regions of the coating, due it passing underneath the coating head. This results in a drying front, which is the point where the wet and dry coating meet. The rate that this front moves across the surface as it dries can be an issue if it moves at a different speed to the solution deposition. The drying conditions need to be optimised to ensure that the movement of the drying front is consistent, and to prevent defects such as cracks and pinholes.
Antioxidants for Lubricants 2025-06-03 Table of ContentsIntroductionNeed for AntioxidantsClassification of Antioxidants Future for AntioxidantsReferenceIntroductionThe addition of lubricants in mechanical systems helps to reduce or eliminate friction which is crucial for their proper functioning and longevity. Early lubricants primarily relied on viscosity to create an oil film between frictional surfaces, preventing direct contact and minimizing wear. However, these lubricants often struggle to perform effectively in high-temperature and/or high-pressure environments, as such harsh conditions can destroy the oil film, resulting in increased friction and diminished mechanical efficiency. Consequently, the development of high-performance lubricants has become a pressing need in the machinery industry and for the manufacturing of advanced equipment [1]. Need for AntioxidantsThe performance of lubricating oils can be severely affected by oxidative degradation triggered by various factors, including internal oxygen, environmental conditions (temperature, pressure, and friction), and metals in mechanical components. This degradation results in the formation of oxidation products such as acids, esters, alcohols, and hydroxyl acids, which can condense into high molecular compounds, increasing viscosity and friction in mechanical systems. Antioxidants are vital additives in lubricating oils, helping to improve their thermal stability and extend their service life. By slowing or eliminating oxidation processes, antioxidants prevent the formation of harmful oxidation products that can cause corrosion, wear of metal parts, and loss of lubrication effectiveness, thus ensuring the continued optimal performance of mechanical equipment [1, 2]. Classification of Antioxidants CategoryAntioxidant TypesDescriptionTraditional AntioxidantsSulfur compounds, Phosphorus compounds, Sulfur–Phosphorus compounds, Sulfur–Nitrogen compounds, ZDDP (Zinc dialkyldithiophosphate)These compounds have excellent antioxidant properties but may cause harm to mechanical equipment, catalysts, and the environment when used in high concentrations.Radical ScavengersHindered phenols, Aromatic aminesThese antioxidants are gaining attention for creating “green” lubricants. However, their thermal stability and antioxidant properties may need further enhancement.Advanced AntioxidantsPhenolic amine complexesA combination of hindered phenol and aromatic amine structures within a single molecule, designed to offer synergistic antioxidant effects.Innovative AntioxidantsMolecules with multiple phenolic hydroxyls or imine groups, surface-functionalized inorganic particles, polymerized moleculesThese antioxidants are synthesized using strategic approaches such as chemical bonds, bridged centers, or polymerization, exhibiting outstanding high-temperature stability.Future for AntioxidantsThe future of antioxidant development in lubricating oils should focus on several key advancements. One major direction is the shift toward ashless antioxidants that are free from sulfur and phosphorus, aiming to reduce pollution and oil ash formation, thereby promoting more environmentally friendly lubricants. Another promising area is the development of multi-phenol antioxidants, which offer enhanced antioxidant properties compared to single phenolic compounds, providing more effective protection against oxidative degradation. Additionally, macromolecular antioxidants are being explored, including the alkylation and aromatization of multi-phenols and alkylated aromatic amines, which can offer improved stability and high-temperature performance. Finally, composite antioxidants are gaining attention for their ability to combine various antioxidant materials, improving oxidation resistance, especially at high temperatures, and ensuring the longevity and efficiency of lubricating oils in demanding conditions. These innovations collectively promise to create more sustainable, efficient, and high-performing lubricants for the future [1].Reference[1] Xia, D., Wang, Y., Liu, H., Yan, J., Lin, H. and Han, S., 2024. Research progress of antioxidant additives for lubricating oils. Lubricants, 12(4), p.115. [2] Soleimani, M., Dehabadi, L., Wilson, L.D. and Tabil, L.G., 2018. Antioxidants classification and applications in lubricants. In Lubrication-tribology, lubricants and additives. IntechOpen.
中科大李闯AM：利用两亲性多肽纳米纤维交联剂构筑坚韧、多功能、可回收的超分子水凝胶 2025-05-22 生物体通过在不同尺度上动态重组其复杂层次结构实现能量耗散过程，并进化出具有非凡强度和韧性的多种承重组织和材料。机械强化的生物学原理为科学家开发具有仿生能量耗散结构和宏观强韧机械性能的合成材料提供了灵感和指导。为了更好地模拟生物组织中观察到的层次结构的高度有序性和动态重组，科学家们试图将高度有序的合成层次结构引入到与天然组织具有相似结构的水凝胶材料中。目前，研究者们已经实现将冷冻和盐析等方法形成的各向异性结构、芯鞘结构以及梯度胶合板结构，通过折叠蛋白、螺旋聚多肽等生物大分子实现的对隐藏长度的储存以及由短肽组装的纳米纤维交联剂等整合到水凝胶基体中实现具有仿生分级结构的强韧水凝胶。然而，上述设计中仍存在对共价交联剂维持水凝胶成形的依赖问题，这会影响水凝胶的加工和可回收性能。另外，多肽在序列特异性可编程性和结构可调性方面的固有优势并未得到开发和利用。近期，中国科学技术大学李闯教授团队提出了一种仿生分层工程策略，通过两亲性肽衍生的纳米纤维结构作为动态超分子交联剂，构建具有可编程功能的强韧可加工水凝胶。与形成均匀纳米纤维结构的序列固定亲水性肽或聚赖氨酸不同，模块化设计的两亲性肽自发自组装形成明确的1D纳米纤维结构，无论组装驱动结构域的化学结构如何，都具有可区分的疏水核心结构和亲水壳层结构（图1）。当作为超分子交联剂集成在水凝胶网络中时，这种分层结构通过涉及纤维内部单个肽分子动态分离的能量耗散机制，显著提高了机械强度和韧性，这与之前报道的弹簧状能量耗散机制不同（图2）。除了机械增强之外，肽组装交联剂的可编程两亲性结构还可以在不同的结构域（包括疏水核心、组装驱动域和亲水壳层）上进行正交官能化。这种空间控制促进了多功能定制，通过三个关键应用得到了证明：1）亲脂性荧光团的激活，2）光响应图案化，3）模拟肌肉驱动的各向异性收缩。水凝胶固有的离子导电性与其快速弹性恢复相结合，能够开发出高性能应变传感器，在监测人体运动方面表现出卓越的灵敏度、信号保真度和操作稳定性。至关重要的是，超分子设计允许通过交联剂得到可以解组装-再组装过程进行闭环回收和再加工，同时在多个再加工循环中保持结构完整性。这种分层工程范式为先进的软材料建立了一个多功能平台，该平台协同整合了传统上相互冲突的属性：强韧的机械性能、动态适应性、可定制功能和环境可持续性。所展示的材料体系在柔性生物电子学、自适应软机器人和可持续生物医学设备等的应用中显示出特别的前景。该研究成果近期以“Hierarchical Engineering of Amphiphilic Peptides Nanofibrous Crosslinkers toward Mechanically Robust, Functionally Customable, and Sustainable Supramolecular Hydrogels”为题发表在Advanced Materials上。中国科学技术大学高分子科学与工程系李闯教授为论文通讯作者。中国科学技术大学博士研究生郑一帆为论文第一作者。该工作得到国家自然科学基金、国家重点研发计划和中国科学技术大学的支持。
Dispersants for lubricants 2025-05-20 Table of Contents Introduction Need for Dispersants Mechanism of Dispersants Difference between Dispersants and Detergents Reference Introduction Dispersants are like the detergents that are used in fuels and lubricants for many years to prevent excessive viscosity in the automobile lubricants. By keeping polar debris from oxidation in suspension, dispersants prevented thickening. Today, they are widely used in various automotive fluids, including engine oils, fuels, transmission fluids, and gear oils. They help in preventing oil thickening ensures consistent flow properties and optimal lubrication. Further they contain carbon sludge, preventing blockages that could restrict oil flow and cause engine failure. Need for Dispersants Without dispersants the lubricants could not maintain engine cleanliness and performance because they prevent sludge and deposit formation by keeping contaminants suspended in the oil. In the absence of dispersants, the lubricants can accumulate on piston rings and grooves, leading to ring sticking and loss of oil control. Further, the increased oil flow into the combustion chamber, causing higher engine exhaust emissions. Also leads to greater oil consumption, requiring more frequent top-ups between oil changes. It causes valve deposits that cause sticking, leading to incomplete combustion and additional emissions. It accelerates oil degradation and necessitates more frequent oil changes due to the contaminants entering the crankcase. Finally, the lack of dispersants causes lubricants less effective at maintaining engine efficiency and longevity, leading to higher maintenance costs and environmental impact. Mechanism of Dispersants Oil dispersants are primarily composed of surfactants dissolved in solvents. Surfactants are molecules with two distinct ends: one hydrophilic (water-attracting) and one lipophilic (oil-attracting). This unique structure allows them to interact with both oil and water phases. When dispersants are applied to an oil slick on the surface of water, the surfactant molecules begin to interact with the oil-water interface. The lipophilic (oil-attracting) ends of the surfactant molecules attach to the oil, while the hydrophilic (water-attracting) ends face the water phase. The presence of surfactants reduces the surface tension between the oil and water, making it easier for the oil to break up and disperse into smaller droplets. This reduction in interfacial tension allows the oil to mix more readily with water. With the natural agitation from waves or other forces, the oil slick begins to break apart. The oil dispersant helps break the oil into small, discrete droplets, typically ranging from 1 to 70 microns in size. These droplets form and remain suspended in the top 5–10 meters of the water column. Once the droplets are formed, the surfactant molecules adsorb onto the surface of each droplet. The hydrophilic end of the surfactant faces outward toward the water, while the lipophilic end remains embedded in the oil. This stabilizes the droplets, preventing them from re-coalescing or re-forming an oil slick. The stabilized oil droplets are dispersed throughout the water column, where they are diluted. Over time, the dispersed oil in the droplets is broken down and degraded by microorganisms naturally present in the water, helping to mitigate the environmental impact of the oil spill. Figure-1 A) Working mechanism of dispersants B) Mechanism of chemical dispersion Difference between Dispersants and Detergents Property Detergents Dispersants Composition Contain metals (calcium, magnesium, sodium, barium) in the hydrophilic head. Do not contain metals; may contain amine structures (weak bases). Acid Neutralization Can neutralize oxidation products (e.g., sulfuric and nitric acids). Little to no acid-neutralizing capability. Effect on Combustion May leave an ash residue upon combustion; calcium carbonate is often used to reduce ash. Do not leave ash residue; focus on suspending contaminants. Molecular Weight Lower molecular weight, smaller molecules. Higher molecular weight (10 times larger), with polymeric dispersants ranging from 1,000-2,000 and dispersant polymers over 25,000. Primary Function Neutralize acids, remove deposits, and prevent acid buildup. Keep contaminants suspended, prevent the formation of large aggregates. Role in Lubricants Work with dispersants to keep contaminants in suspension and prevent deposits. Prevent the formation of deposits by suspending contaminants. Use in Engine Oils Neutralize acids and prevent deposits but can leave ash. Keep oil clean by suspending contaminants, ensuring oil remains effective. Reference [1] Seddon, E.J., Friend, C.L. and Roski, J.P., 2010. Detergents and dispersants. Chemistry and technology of lubricants, pp.213-236. [2] Farahani, M.D. and Zheng, Y., 2022. The formulation, development and application of oil dispersants. Journal of Marine Science and Engineering, 10(3), p.425.
Viscosity Index Modifiers 2025-05-13 Introduction Viscosity is a fluid’s resistance to flow, influenced by temperature, pressure, and shear stress. The viscosity index (VI) describes how viscosity changes with temperature. Viscosity is measured as kinematic (without shear stress) and dynamic (under shear stress). VI is calculated using kinematic viscosities at 40°C and 100°C. A higher VI means less viscosity change with temperature, which is desirable for lubricants. However, VI calculation can be challenging for very low-viscosity oils. Dynamic Viscosity Index (DVI) and Proportional Viscosity Index (PVI) have been proposed to overcome VI calculation limitations but are not widely used. Every 15–20°C change in operating temperature requires adjusting the oil by one ISO grade. For gears operating at 65°C with 10 m/s velocity, different VI and ISO grades are recommended based on viscosity stability. Viscosity must be low enough for cold starts but high enough to maintain lubrication under heat. Controlling viscosity changes through formulation adjustments, like selecting viscosity index improvers (VII), is crucial. The most common types of VII polymer are polyisobutenes (PIB), poly (alkyl methacrylates), poly (styrene-dienes), polyisoperenes, and olefin copolymers (OCPs). Figure-1 Structures of the Viscosity Index Improvers [1] How do they work? The Figure-2 illustrates the impact of Viscosity Index Improvers (VII) on dynamic viscosity across temperature variations, based on the Selby coil expansion model. It compares three cases: high-viscosity base oil without VII, low-viscosity base oil without VII, and low-viscosity base oil with VII. As temperature increases, base oils naturally lose viscosity, with low-viscosity oil (A) dropping below the optimal lubrication range at high temperatures, while high-viscosity oil (B) remains too thick at low temperatures. Adding VII to low-viscosity oil helps stabilize viscosity by expanding polymer molecules at high temperatures, compensating for viscosity loss. This keeps the oil within an appropriate viscosity range, ensuring good lubrication at both low and high temperatures. VII allows the use of lower-viscosity base oils, improving cold-start performance while maintaining lubrication under heat, making them essential for multi-grade lubricants. Figure-2 Selby model for VI improvement [1] There are several other models that have been proposed to explain how VIIs enhance viscosity stability across temperature variations. The Entanglement Model suggests that VII polymers form entanglements in the oil at low temperatures, restricting fluidity, while at higher temperatures, the polymer chains extend but still provide thickening due to entanglement. The Hydrodynamic Volume Model explains that as temperature rises, polymer molecules expand, increasing their hydrodynamic volume and resisting viscosity loss. The Micelle Formation Model proposes that some VII molecules self-assemble into micelles at low temperatures, reducing their thickening effect, but break apart at higher temperatures, allowing better polymer interaction and viscosity control. Additionally, the Shear-Thinning and Associative Thickening Model describes how certain VIIs display shear-thinning behavior, meaning they align under mechanical stress, reducing viscosity for efficiency, while at low shear rates, they form an associative network that thickens the oil and maintains lubrication. Each of these models provides insight into the behavior of VIIs, though their effectiveness depends on the polymer type and lubricant formulation [2, 3]. Reference [1] Khalafvandi, S.A., Pazokian, M.A. and Fathollahi, E., 2022. The investigation of viscometric properties of the most reputable types of viscosity index improvers in different lubricant base oils: API groups I, II, and III. Lubricants, 10(1), p.6. [2] Martini, A., Ramasamy, U.S. and Len, M., 2018. Review of viscosity modifier lubricant additives. Tribology Letters, 66, pp.1-14. [3] Len, M., 2020. Understanding Viscosity Modifiers Using Molecular Dynamics Simulations. University of California, Merced.
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