Advances in Liquid Crystal Epoxy:Molecular Structures,Thermal Conductivity,and Promising Applications in Thermal Management

Traditional heat conductive epoxy composites often fall short in meeting the escalating heat dissipation demands of large-power,high-frequency,and highvoltage insulating packaging applications,due to the challenge of achieving high thermal conductivity(k),desirable dielectric performance,and robust thermomechanical properties simultaneously.Liquid crystal epoxy(LCE)emerges as a unique epoxy,exhibiting inherently high k achieved through the self-assembly of mesogenic units into ordered structures.This characteristic enables liquid crystal epoxy to retain all the beneficial physical properties of pristine epoxy,while demonstrating a prominently enhanced k.As such,liquid crystal epoxy materials represent a promising solution for thermal management,with potential to tackle the critical issues and technical bottlenecks impeding the increasing miniaturization of microelectronic devices and electrical equipment.This article provides a comprehensive review on recent advances in liquid crystal epoxy,emphasizing the correlation between liquid crystal epoxy’s microscopic arrangement,organized mesoscopic domain,k,and relevant physical properties.The impacts of LC units and curing agents on the development of ordered structure are discussed,alongside the consequent effects on the k,dielectric,thermal,and other properties.External processing factors such as temperature and pressure and their influence on the formation and organization of structured domains are also evaluated.Finally,potential applications that could benefit from the emergence of liquid crystal epoxy are reviewed.

Transient liquid phase bonding of DD5 superalloy using a designed interlayer: microstructure and mechanical properties

Nickel based single crystal superalloy is currently widely used as the material for turbine blades in aerospace engines.However,metallurgical defects during the manufacturing process and damage during harsh environmental service are inevitable challenges for turbine blades.Therefore,bonding techniques play a very important role in the manufacturing and repair of turbine blades.The transient liquid phase(TLP)bonding of DD5 Ni-based single crystal superalloy was performed using the designed H1 interlayer.A new third-generation Ni-based superalloy T1 powder was mixed with H1 powder as another interlayer to improve the mechanical properties of the bonded joints.The res-ults show that,such a designed H1 interlayer is beneficial to the improvement of shear strength of DD5 alloy bonded joints by adjusting the bonding temperature and the prolongation of holding time.The maximum shear strength at room temperature of the joint with H1 interlayer reached 681 MPa when bonded at 1260℃for 3 h.The addition of T1 powder can effectively reduce holding time or relatively lower bond-ing temperature,while maintaining relatively high shear strength.When 1 wt.%T1 powder was mixed into H1 interlayer,the maximum room temperature shear strength of the joint bonded at 1260℃reached 641 MPa,which could be obtained for only 1 h.Considering the bonding temperature and the efficiency,the acceptable process parameter of H1+5 wt.%T1 interlayer was 1240℃/2 h,and the room tem-perature shear strength reached 613 MPa.

Time-dependent effects in transient liquid phase bonding of 304L and Cp-Ti using an Ag-Cu interlayer

One of the challenges for bimetal manufacturing is the joining process.Hence,transient liquid phase(TLP)bonding was performed between 304L stainless steel and Cp-Ti using an Ag-Cu interlayer with a thickness of 75μm for bonding time of 20,40,60,and 90 min.The bonding temperature of 860℃ was considered,which is under the β transus temperature of Cp-Ti.During TLP bonding,various intermetallic compounds(IMCs),including Ti_(5)Cr_(7)Fe_(17),(Cr,Fe)_(2)Ti,Ti(Cu,Fe),Ti_(2)(Cu,Ag),and Ti_(2)Cu from 304L toward Cp-Ti formed in the joint.Also,on the one side,with the increase in time,further diffusion of elements decreases the blocky IMCs such as Ti_(5)Cr_(7)Fe_(17),(Cr,Fe)_(2)Ti,Ti(Cu,Fe)in the 304L diffusion-affected zone(DAZ)and reaction zone,and on the other side,Ti_(2)(Cu,Ag)IMC transformed into fine morphology toward Cp-Ti DAZ.The microhardness test also demonstrated that the(Cr,Fe)_(2)Ti+Ti_(5)Cr_(7)Fe_(17) IMCs in the DAZ on the side of 304L have a hardness value of HV 564,making it the hardest phase.The maximum and minimum shear strength values are equal to 78.84 and 29.0 MPa,respectively.The cleavage pattern dominated fracture surfaces due to the formation of brittle phases in dissimilar joints.

Numerical Optimization by Finite Element Method of Stainless Steel/Glass-Epoxy Composite Bolted Joint under Tension and Compression

The aim of this study was to optimize the geometry and the design of metallic/composite single bolted joints subjected to tension-compression loading. For this purpose, it was necessary to evaluate the stress state in each component of the bolted join. The multi-material assembly was based on the principle of double lap bolted joint. It was composed of a symmetrical balanced woven glass-epoxy composite material plate fastened to two stainless sheets using a stainless pre-stressed bolt. In order to optimize the design and the geometry of the assembly, ten configurations were proposed and studied: a classical simple bolted joint, two joints with an insert (a BigHeadR insert and a stair one) embedded in the composite, two “waved” solutions, three symmetrical configurations composed of a succession of metallic and composites layers, without a sleeve, with one and with two sleeves, and two non-symmetrical constituted of metallic and composites layers associated with a stair-insert (one with a sleeve and one without). A tridimensional Finite Element Method (FEM) was used to model each configuration mentioned above. The FE models taked into account the different materials, the effects of contact between the different sheets of the assembly and the pre-stress in the bolt. The stress state was analyzed in the composite part. The concept of stress concentration factor was used in order to evaluate the stress increase in the highly stressed regions and to compare the ten configurations studied. For this purpose, three stress concentration factors were defined: one for a monotonic loading in tension, another for a monotonic loading in compression, and the third for a tension-compression cyclic loading. The results of the FEM computations showed that the use of alternative metallic and composite layers associated with two sleeves gived low values of stress concentration factors, smaller than 1.4. In this case, there was no contact between the bolt and the composite part and the most stressed region was not the vicinity of the hole but the end of the longest layers of the metallic inserts.

基于二维液相色谱法测定关节假体周围感染患者关节液中万古霉素的质量浓度

目的基于二维液相色谱法(two-dimensional liquid chromatography,2D-LC)建立检测关节假体周围感染(prosthetic joint infection,PJI)患者关节液中万古霉素质量浓度的方法。方法采用FLC2701型2D-LC系统对万古霉素进行2D分离,第一维液相色谱系统采用Aston SC2-1A色谱柱(3.5 mm×25 mm,5μm),流动相为甲醇-乙腈-10 mmoL·L^(−1)磷酸铵水溶液(1∶1∶10),流速为0.6 mL·min^(−1);第二维液相色谱系统采用Aston SCB色谱柱(4.6 mm×125 mm,5μm),流动相为1.0 mmoL·L^(−1)磷酸氢二铵水溶液(pH=7.4)-1.0 mmoL·L^(−1)磷酸氢二铵水溶液(pH=3.0)-乙腈(52∶37∶11),流速为1.2 mL·min^(-1);柱温为45℃;检测波长为232、279 nm;进样量为50μL。结果关节假体周围感染患者关节液中万古霉素的质量浓度在1.01~50.28μg·mL^(−1)范围内线性关系良好(r=0.9998),该方法日内、日间精密度RSD值均<2.26%,平均回收率为93.83%~100.16%,样品提取回收率为100.76%~103.01%,样品稳定性RSD值<2.28%。结论基于2D-LC建立的关节假体周围感染患者关节液中万古霉素质量浓度测定方法简便、准确、高效,可用于临床患者关节液中万古霉素的质量浓度监测。

高压大功率IGBT用液晶环氧性能研究(一):热导率与耐热特性

随着绝缘栅双极型晶体管(IGBT)在工业应用上向高电压、大功率方向发展,对其散热、耐热、绝缘等性能提出了更高的要求,亟须研制高性能的绝缘灌封材料。该文提出利用联苯型环氧单体与联苯胺固化剂双液晶分子构筑液晶畴,着重调控材料热学及电气性能。系列论文(一)研究了其相关热性能,研究表明通过利用液晶联苯胺固化剂与联苯液晶环氧构建具有π-π堆砌液晶畴及高交联密度网络结构的固化物,其玻璃化转变温度Tg可达247℃,与传统双酚A型环氧的Tg相比提高了76.4%;热导率提升至0.351 W/(m·K),相对于双酚A型环氧提高了64.0%。此外,通过分子动力学模拟对交联聚合物的自由体积、Tg、热导率等微观参数及宏观性能进行了机理分析。

Determination of Water Diffusion Coefficients and Dynamics in Adhesive/Carbon Fiber Reinforced Epoxy Resin Composite Joints

To determinate the water diffusion coefficients and dynamics in adhesive/carben fiber reinforced epoxy resin composite joints, energy dispersive X-ray spectroscopy analysis（EDX） is used to establish the content change of oxy- gen in the adhesive in adhesive/carbon fther reinforced epoxy resin composite joints. As water is made up of oxygen and hydrogen, the water diffusion coefficients and dynamics in adhesive/carben fiber reinforced epoxy resin composite joints can be obtained from the change in the content of oxygen in the adhesive during humidity aging, via EDX analy-sis. The authors have calculated the water diffusion coefficients and dynamics in the adhesive/carbon fiber reinforced epoxy resin composite joints with the aid of beth energy dispersive X-ray spectroscopy and elemental analysis. The de- termined results with EDX analysis are almost the same as those determined with elemental analysis and the results al- so show that the durability of the adhesive/carbon fther reinforced epoxy resin composite joints subjected to silane cou- pling agent treatment is better than those subjected to sand paper burnishing treatment and chemical oxidation treat- ment.

Laboratory-scale investigation of response characteristics of liquid-filled rock joints with different joint inclinations under dynamic loading

In underground rock engineering,water-bearing faults may be subjected to dynamic loading,resulting in the coupling of hydraulic and dynamic hazards.Understanding the interaction mechanism between the stress waves induced by dynamic loadings and liquid-filled rock joints is therefore crucial.In this study,an auxiliary device for simulating the liquid-filled layer was developed to analyze the dynamic response characteristics of liquid-filled rock joints in laboratory.Granite and polymethyl methacrylate(PMMA)specimens were chosen for testing,and high-amplitude shock waves induced by a split Hopkinson pressure bar(SHPB)were used to produce dynamic loadings.Impact loading tests were conducted on liquid-filled rock joints with different joint inclinations.The energy propagation coefficient and peak liquid pressure were proposed to investigate the energy propagation and attenuation of waves propagating across the joints,as well as the dynamic response characteristics of the liquid in the liquid-filled rock joints.For the inclination angle range considered herein,the experimental results showed that the energy propagation coefficient gently diminished with increasing joint inclination,and smaller coefficient values were obtained for granite specimens compared with PMMA specimens.The peak liquid pressure exhibited a gradually decreasing trend with increasing joint inclination,and the peak pressure for granite specimens was slightly higher than that for PMMA specimens.Overall,this paper may provide a considerably better method for studying liquid-filled rock joints at the laboratory scale,and serves as a guide for interpreting the underlying mechanisms for interactions between stress waves and liquid-filled rock joints.

CTBN-TOUGHENED EPOXY RESINS——EFFECT OF CURING MECHANISM ON NETWORK STRUCTURE OF THE RUBBER PHASE

Epoxy resins toughened with carboxyl-terminated butadieneacrylonitrile copolymers (CTBN) are two-phase thermosets. The network of the in situ formed rubber particles depends upon the curing mechanism of the resin. When a primary polyamine such as triethylene tetramine was used as curing agent, the network of the rubber phase was quite incomplete, whereas a perfect rubber network was formed with 2-ethyl-4-methyl imidazole as the curing agent.

Cure reaction and phase behavior of liquid crystalline epoxides-anhydride systems

A series of novel liquid crystalline epoxides with lateral substituents were cured with anhydrides and the cure kinetics was investigated by non-isothermal DSC technique. The results showed that the lengths of lateral substituents have great effect on the value of Ea. The curing reaction became less active, when the liquid crystalline epoxides have long lateral substituents and were controlled by diffusion at the late stage of cure. A nematic structure was observed by POM and XRD.

Method for the Determination of Sudan Dyes in Foods-High Performance Liquid Chromatography Jointly Issued by AQSIQ and SAC

Sudan Red are the chemosynthesis dyes of series of azo, which are mainly used as coloring additives in ma- nufacturing of some products, such as the wax, the oil-dyes, the petrol, and etc. In the process of food production, Sudan Dyes are banned to be used as food dyes in our country.

季膦萘磺酸盐离子液体与甲基膦酸二甲酯协同阻燃环氧树脂

合成了一种新型季膦萘磺酸盐室温离子液体[TBP]NS,利用傅里叶变换红外光谱(FTIR)和核磁共振波谱(1H NMR和31P NMR)确定了其结构,并将其与甲基膦酸二甲酯(DMMP)复配用于制备阻燃环氧树脂.阻燃性能测试结果表明,当在环氧树脂(EP)中加入质量分数为6%的[TBP]NS和4%的DMMP时,所得阻燃环氧树脂EP/4%[TBP]NS/6%DMMP的极限氧指数达到31.2%, UL-94垂直燃烧通过V-0级别.与纯环氧树脂相比,该阻燃环氧树脂的峰值热释放速率(PHRR)降低了59%,总热释放(THR)降低了43%,峰值CO释放速率(PCOP)降低了41%,残炭率升高了97%.[TBP]NS和DMMP在氧指数、垂直燃烧和锥形量热测试中均展现出优异的协同阻燃作用,并且表现出良好的炭化能力和降热效果.在力学性能方面,与单纯加入DMMP的环氧树脂相比,EP/4%[TBP]NS/6%DMMP的拉伸强度、断裂伸长率和弯曲强度均有提高.

环氧树脂混凝土装配式桁架下弦K型节点力学试验及有限元分析

通过静力试验研究了环氧树脂混凝土装配式桁架下弦K型节点的破坏形态、承载能力和节点板的应力与应变分布情况,并进行了有限元模拟分析。结果表明:环氧树脂混凝土下弦K型节点在下弦杆靠近节点板的两侧出现5条竖直裂缝,最终节点板左侧下弦杆处的竖直裂缝前后贯通,弦杆发生拉弯破坏,节点的极限承载力为421.5 kN;有限元模拟结果与试验结果吻合较好,验证了有限元模拟的可靠性。

气-液两相流装置的控制和不确定度评定

气-液两相流具有复杂的流动状态从而导致其无法被准确地控制,针对一套气-液两相流装置,对装置的压力-流量控制进行了研究,并对气-液两相的联合控制进行了实验,结果表明压力对控制具有较大影响。在控制过程中需要保证压力的不变,而气-液两相的联合控制具有变化的一致性,可通过研究一致性实现气-液两相的准确控制。同时对该装置的气-液两相流分量分别进行不确定度评定,结果表明,装置气体流量的U_(r)(Q_(v,air))=3.8%(k=2);装置液体流量的扩展不确定度U_(r)(Q_(v,liq))=3.2%(k=2),可对气-液两相的流量进行准确显示。

应力波作用下水平倾向液体充填岩石节理动态响应规律试验

地下岩体工程中,液体充填岩石节理不可避免会受到地震、爆破等动力扰动。由于液体具有流动性,不同倾向节理中的液体呈现不同空间分布状态,受应力波扰动后液体的运动状态也相异。为阐明应力波作用下水平倾向液体充填岩石节理动态响应规律,利用辉长岩切槽试样、有机玻璃管与丙三醇制备了液体充填岩石节理试样,采用类霍普金森杆试验测试系统,开展了液体充填岩石节理试样的竖向冲击加载试验,考虑了节理匹配系数(J_(MC))、液体体积分数与黏度3个影响因素,并从应力波透射能量与液体运动2个方面分析了液体充填岩石节理动态响应规律。试验结果表明:液体充填岩石节理J_(MC)增大,应力波透射能量增大;随着液体体积分数增大,高幅低频应力波的透射能量单调增大,低幅高频应力波的透射能量先不变后增大;当液体体积分数为50%时,应力波透射能量随着液体黏度增大而减小,而当液体体积分数为100%时,应力波透射能量随着液体黏度增大呈现先减小后增大的趋势;节理边界处,液体运动方向垂直于水平节理面向上,节理排液能力和液体运动剧烈程度随液体黏度增大而减弱。

基于液体橡胶修复剂的光热响应自修复环氧涂层的制备及研究

提出了一种基于热固性树脂自修复性与热塑性液体橡胶流动性的自修复涂层结构,并通过炭黑实现其光热自修复。采用环氧树脂基体、热塑性液体丁腈橡胶(CTBN)修复剂以及光热填料炭黑(CB),制备了一种基于液体橡胶修复剂的光热响应自修复涂层。采用红外热成像仪、热重分析仪(TG)、扫描电子显微镜(SEM)、光学显微镜等对涂层进行了表征,研究了CB对涂层光热性能的影响,修复剂对涂层形态和性能的影响以及涂层的自修复行为。结果表明:在近红外光照射下,少量CB有利于提高涂层吸收率,从而大大提高光热性能。作为热塑性修复剂的CTBN在微尺度分散于环氧树脂中,流入并填充裂纹;涂层的光热性能随CTBN含量的增加而增加,添加0.08%CB、7.69%CTBN的涂层在0.8 W/cm^(2)的光功率密度下表现出优异的自修复性能。同时,裂纹修复后的涂层能够有效地恢复其耐腐蚀性。

联苯型环氧树脂强韧化TDE-85树脂体系的制备与性能

环氧树脂因其黏结力强、热稳定性好等优点,被广泛应用于涂料、电子封装材料和胶黏剂等领域,但其高交联密度也带来了脆性大、韧性差的问题,成为制约其发展应用的主要因素。采用熔融共混的方法,以3,3′-二氨基二苯砜(3,3′-DDS)为固化剂,用联苯型环氧树脂3,3′,5,5′-四甲基联苯双酚二缩水甘油醚(TMBP)改性高性能环氧树脂(TDE-85)。研究了改性树脂体系的力学性能,偏光显微镜和扫描电子显微镜的分析表明液晶结构能良好分散在环氧树脂基体中并增强增韧。结果表明:当TMBP含量为6wt%时,固化物的力学性能明显提高,冲击强度和弯曲强度分别提高了30%和27%,韧性和强度明显提升;当TMBP含量为4wt%时,拉伸强度和拉伸模量均达到最大,分别为93.69 MPa与5.39 GPa。

儿童膝关节周围骨肉瘤灭活再植与假体置换的短期疗效对比

目的探讨儿童膝关节周围骨肉瘤瘤段灭活再植术与全膝关节肿瘤假体置换术的短期疗效差异。方法回顾性分析2019年1月至2022年1月就诊于新疆医科大学附属肿瘤医院骨与软组织肿瘤及黑色素瘤科,行保留骨骺的瘤段灭活再植术和全膝关节肿瘤假体置换术的膝关节周围骨肉瘤26例患者的临床资料,男13例,女13例;年龄8~16岁,平均(11.88±2.42)岁。其中采用瘤段灭活再植手术8例(股骨5例,胫骨3例),为灭活再植组;采用全膝关节肿瘤假体置换手术方式共18例(股骨9例,胫骨9例),为假体置换组。比较两组患者一般临床资料,功能评估采用肌肉骨骼肿瘤协会评分(musculoskeletal tumor society,MSTS),使用膝关节活动度评分(range of motion,ROM)评估膝关节活动范围,术后定期复查X线片评估双下肢长度差异,进行肿瘤学评估以及并发症评估等。结果26例膝关节周围骨肉瘤患者,随访20~56个月,平均(29.50±6.46)个月。灭活再植组中双下肢长度差异0.63~1.75 cm,平均(1.03±0.37)cm;假体置换组中双下肢长度差异0.73~4.00 cm,平均(1.96±0.88)cm,两组比较差异有统计学意义(t=2.86,P=0.009)。MSTS评分灭活再植组平均为(26.63±1.51)分,假体置换组平均为(24.50±1.89)分,两组MSTS评分比较,差异有统计学意义(t=2.81,P=0.01)。瘤段灭活再植组中末次随访膝关节屈曲角度平均为健侧的(62.13±13.78)%;全膝关节肿瘤假体置换组末次随访膝关节屈曲角度平均为健侧的(65.68±10.40)%,两组患者膝关节屈曲角度比较,差异无统计学意义(χ2=1.25,P=0.26)。结论儿童膝关节周围骨肉瘤瘤段灭活再植保留骨骺能够有效保留患肢的生长发育潜能,改善患者关节功能,植骨融合较好,并发症较少,短期随访具有较好的临床疗效。

液体丁腈橡胶增韧改性环氧树脂的研究进展

环氧树脂成本低廉、性能优异,应用范围广泛。目前研究人员多对其进行增韧改性,以弥补结构不足,进一步扩展其应用范围。其中,液体丁腈橡胶增韧改性环氧树脂是应用最成功的方法之一。本文简介了环氧树脂的增韧机理,综述了近年来各类液体丁腈橡胶,如端羧基液体丁腈(CTBN)、端羟基液体丁腈(HTBN)、无规羧基液体丁腈(XNBR)、液体丁腈(LNBR)、端胺基液体丁腈(ATBN)和端环氧基液体丁腈(ETBN)等增韧环氧树脂的研究进展,并对液体丁腈橡胶增韧环氧树脂的研究方向进行了展望。