【作者】 王胜；

【导师】 龚兴龙； 江万权；

【作者基本信息】 中国科学技术大学 ， 无机化学， 2017， 博士

【摘要】 近年来,全球范围内局部战争、地区冲突和恐怖袭击频繁发生,杀伤性武器性能不断提高,日益凸显人体安全防护的重要性。虽然目前轻质、高强度的纤维材料,如Kevlar纤维和聚乙烯纤维等已被开发和运用于防护材料,但这些材料的力学性能仍然有限且不可控,而且只能被动的承受外界的刺激而无法做出相关的响应,无法满足于未来智能可穿戴防护系统的需求。因此,开发防护性能更加优越,舒适度更高的新型智能人体防护材料以取代传统的硬质、厚重的材料显得越来越迫在眉睫。剪切增稠材料是应变率相关的新型智能材料,主要包括剪切增稠液和剪切变硬胶体两大类材料。剪切增稠材料的最大特点在于当外界应力的应变率超过临界剪切速率时,材料粘度或者模量可以迅速增大,呈现出由柔性态急速转变为坚硬固态的特性。而由于剪切变硬胶体材料具有无需密封,性能稳定和易于制备等特点而受到越来越多的关注。本文基于剪切变硬胶体材料,以设计新型多功能防护材料为目的,成功制备了几种新型的智能防护材料及器件,既有效提高了高分子材料的力学性能,又使得其具备多方面响应性能,实现了材料性能的智能化和可控化。具体的研究内容和成果安排如下:1、将磁性粒子均匀混合到剪切变硬胶高分子聚合物中,成功地制备了一种对外界磁场和剪切应力具有双重刺激-响应性能的新型多功能复合材料。研究结果表明该多功能材料具有优异的剪切变硬效应和磁流变性能,材料强度可以通过外界磁场和剪切应力而加以定向控制。除了含有磁控性能以外,这种材料也可以随着外界剪切应力的刺激而自动改变其流变性能,从而表现出了优异的剪切变硬(shear stiffening:S-ST)效应。这种智能材料的力学性能也可以通过改变颗粒物的种类和含量而加以调控。更重要的是,该材料的剪切变硬效应也可以通过调节磁场和剪切力的频率大小而加以精确调控。最后,多功能材料的刺激-响应性能产生的主要是由瞬间的B-O交联键和羰基铁粒子链所引起的。2、通过将钕铁硼引入到剪切变硬胶体中,成功制备出一种具有优良力学性能和预磁化增强效应的多功能剪切变硬胶体材料。研究表明除了该材料的模量随着外界剪切应力的频率增加而迅速增大以外,还具备较理想的预磁化效应,即在使用之前给予材料较小的磁场预加载,即可使其在撤除磁场的情况下模量也能表现出较大提升效应,而后续较高的力学强度不依赖于外界刺激的加载。基于其较好的剪切变硬效应,当外界剪切应力的刺激频率从0.1Hz上升到100Hz时,复合材料的储能模量可以从102增大到106Pa。同时,样品的硬度也可以通过改变剪切频率和磁场大小而加以定向控制。更重要的是,该多功能聚合物材料具有较高剩磁特性,样品在经过1200mT磁场的短暂预结构化处理之后,其储能模量能从1.64MPa上升到2.34MPa,表现出了优良的预磁化增强效应,且该增强的力学性能稳定可靠,这说明其增强的性能不依赖于外界刺激的持续加载,可以节约大量能量。另外,所形成的粒子链以及高剩余磁场导致的粒子之间相互作用是该复合材料奇特性能的主要原因。最后,材料优良的可塑性/粘附愈合性保证了其具有较可靠的力学性能和更长的使用寿命。3、通过一种简单的"浸渍与干燥"法将剪切变硬胶体引入到聚氨酯海绵中,成功制备了一种新型聚氨酯基防护复合材料。该种衬垫显示出了优良剪切变硬效应,抗蠕变性能和耐冲击性能。另外其理想的粘附性和疏水性赋予了材料被广泛使用的可能。由于聚氨酯骨架的支撑作用,复合材料表现出了理想的抗蠕变性能,且其硬度是可控的,具有理想的阻尼特性。该复合材料也表现出了较优良的抗冲击性能,可以使外界冲击力降低1个数量级,从而起到保护人体的目的。另外,测试结果表明即使在受到严重破坏后复合材料的结构和力学性能都没有显著的衰减,说明材料具有很好的稳定性。最后,该材料良好的粘附性和疏水性保证了其可靠的力学性能和更长的使用寿命。4、通过运用一种简便方法将多壁碳纳米管分散到剪切变硬聚合物基体中,从而制备了一种新型的具有应变率相关导电性和自愈性能的剪切变硬纳米复合材料。由于碳纳米管的引入,该种材料具有理想的导电性和力学强度,显示出了较好的力传感性能和抗冲击效应。当受到外界剪切刺激时,该多功能复合材料的模量能增加4个数量级,显示出优良的剪切变硬效应。另外,经研究发现,该材料在受到不同刺激时具有不同的正负压阻效应,显示其具有优良的力传感效应。其应变率相关的压阻效应也被进一步研究。良好的自愈性能确保了材料能够被反复破坏和恢复。因此,基于其剪切变硬、应变率相关的导电性等特点,该复合材料可以吸收大量冲击能量并感知外界冲击力。最后,该复合材料的机理也被提出,B-O化学键相互作用所导致的玻璃化转变温度和在外界刺激下材料微观结构的变化分别是导致其剪切变硬性能和应变率相关的导电性能的原因。5、通过将碳纳米管和剪切变硬胶附着于Kevlar纤维表面,成功制备了一种具有优良防护和力传感性能的可穿戴电子织物材料。随着剪切变硬胶体的引入,该新型电子织物材料显示出了更强的抗冲击性能,防护效应显著增大。另外,由于碳纳米管的均匀分散,该种织物表现出较理想的电学性能和传感效应。在准静态压缩和动态冲击条件下的针刺实验结果表明该复合材料能够吸收大量能量,其防护性能比纯纤维得到极大提高。复合材料的最大抗冲击力为1052 N,这比纯Kevlar高出了 190%。由于嵌入了多壁碳纳米管,从而使得其电导率降为10-2S/m,且材料对外力刺激极为敏感。特别地,该传感织物同样具有优良的力传感性能,可以被固定于人体的各个部位以监测分析人体移动和力的大小。由于具有柔顺性,对外界极高的敏感性和优良的人体防护性能,该复合纤维有望被运用于制备一种同时具有人体防护和监测人体移动等性能的多功能可穿戴织物器件。更多还原

【Abstract】 With the increasing of wars,civil conflicts,terrorist attack and as weapons improved,human security protection is an increasingly important now.Though lightweight and high-strength fibers such as Kevlar and polyethylene fibers have been developed and applied in body armors,these materials only resist mechanical punch in a passive way and cannot sense and respond to an external force which could not accommodate the demand of next generation smart wearable systems.Therefore,developing novel safe-guarding materials with enhanced mechanical performance to replace traditional rigid and heavy body armors is an urgent and important work.Shear thickening(ST)composite is a kind of rate-dependent smart materials.It contains shear thickening fluid(STF)and shear stiffening(S-ST)polymer composites.One of the main characteristics of ST composite is their viscosity and storage modulus increase sharply once the rate of shear stress is beyond a critical value which the material transformes from soft to solid state.Because of easy-fabrication,without sealing and stable rheological properties,large numbers of attention has been paid to solid shear stiffening polymer composite.Based on shear stiffening composite,our research aims at designing and fabricating novel multifunctional composites and some novel smart safeguarding composites and the based deivces were developed in this work.Compared with pristine shear stiffening polymer,the strength of these novel composites were significantly increased.More importantly,they also exhibited ideal stimuli-responsvie properties which were intelligentized and precisely controlled.The detailed contents were summarized as follows:1.A novel multi-functional polymer composite(MPC)with dual-stimuli responsive properties is prepared by dispersing magnetic particles into shear stiffening polymer matrix.This novel soft material shows excellent shear stiffening(S-ST)performance and magnetorheological(MR)effect and its strength can be directionally controlled by changing external magnetic field and shear stress.Besides having the magnetically dependent mechanical properties(MR effects),this multi-functional MPC automatically changes its rheological behavior in response to external shear stimuli which exhibits excellent S-ST effect.The mechanical properties of this smart composite can also be alternatively achieved by varying the particle’s types and contents.More importantly,the S-ST effects of the MPC are also tunable by varying the external magnetic field,and the area of storage modulus(G’)could be greatly increased and precisely controlled.Based on the experimental results,a possible mechanism is proposed and discussed.It is believed that the "cross bonds" and the particle chains induced by the magnetic field are due to the excellent multi-functional stimulus-response properties.2.An innovative multifunctional shear stiffening polymer composite(SPM-PC)with excellent mechanical properties and ideal pre-magnetized enhanced(PME)effect was developed by dispersing NdFeB particles into shear stiffening(S-ST)polymer matrix.The storage modulus of the SPM-PC can increase sharply with the increasing of shear frequency,showing ideal S-ST effect.Its modulus also increases dramatically by loading magnetic field before used and the higher modulus is independent of external magnetic field which exhibits excellent pre-magnetizatiom effect.Owing to the shear stiffening characteristic,the storage modulus(G’)of SPM-PC can increase from 102 Pa to 106 Pa when the shear frequencies of applied stress vary from 0.1 to 100 Hz.Meanwhile,the stiffness of the multi-functional SPM-PC can also be precisely tunable by shear frequency and magnetic field.More importantly,SPM-PC with high remanence shows excellent pre-magnetized enhanced effect which the G’ can be directionally increased from 1.64 MPa to 2.34 MPa through 1200 mT of pre-magnetization treatment in short time and the enhanced mechanical properties of SPM-PC show ideal stability under cyclic excitations which will save plenty of electrical energy to maintain its high mechanical properties.Additionally,the mechanism of the interaction force due to high residual magnetization and particle chains movement are proposed and discussed.Finally,the ideal plastic/adhesion characteristics guarantee the composite with reliable mechanical performance and longer lifespan.3.By introducing S-ST polymer into polyurethane sponge with a simple and scalable "dip and dry" method,we successfully fabricate a novel stretchable polyurethane sponge-based safeguarding polymer composite.The pad shows excellent shear stiffening effect,creep resisting and impact resistant properties.Additionally,its ideal adhesion property and hydrophobicity endow its wider engineering applications.Due to the incorporation of skeleton of PU sponge,the composite showed ideal creep resistant property.The stiffness was tunable and the composite with ideal damping capacity could reduce the impact force by 1 orders of magnitude even under cycles of consecutive dynamic impact loading with no obvious mechanical degradation.Finally,the excellent adhesion ability and hydrophobicity guarantee the composite with reliable mechanical performance and longer lifespan.4.A novel rate-dependent and self-healing conductive composite with a well-defined shear stiffening(S-ST)effect was facilely fabricated by dispersing multi-walled carbon nanotubes(MWCNTs)into shear stiffening polymer matrix.Due to the incorporation of MWCNTs,the mechanical and conductive properties of the composite is significantly enhanced which shows excellent impact resistant peoperty and force-sensing effect.The G’ of the multi-functional composite automatically increased 4 orders of magnitude when encountering external shear stimuli,demonstrating an obvious shear stiffening effect and good safe-guarding performance.Additionally,it was found that it shows different positive and negative piezoresistance effect under various external excitations which proves its ideal force-sensing characteristic.The rate-dependent piezoresistance effect of the composite was further investigated.Self-healing properties guarantee its repeating destructions and recoveries.Owing to the shear stiffening performance,the rate dependent conductive composite could both absorb impact energy and sense the attacking forces.Finally,a mechanism was proposed and it was believed that the glass transition induced by B-O interactions and the changes in the microstructure during the external action can be attributed to the S-ST performance and rate dependent electrical conductivity,respectively.5.A novel S-ST/MWCNT/Kevlar-based wearable electronic textile(WET)with enhanced safe-guarding performance and force-sensing effect has been fabricated by homogeneously dispersing MWCNT and S-ST polymer on the surface of Kevlar fabric.The safeguarding performance of the composite is significantly increased due to the introduction of S-ST polymer.Additionally,it also shows ideal force-sening and monitoring properties.Stab resistance performance tests under quasi-static and dynamic conditions show the fiber composite could absorb large numbers of energy and show dramatic increment in safeguarding property than the neat Kevlar.Dynamic impact resistance tests show the maximum resistance force of WET is 1052 N,which is about 190%improvement than neat Kevlar.Due to the incorporation of multi-walled carbon nanotubes(MWCNTs),the WET obtains a stable electrical conductivity of～10-2 S/m and the conductivity is fast sensitive to the external mechanic forces.Notably,the sensor fabric also offers outstanding multiple sensing performance to detect and analyze external force,thus it can be fixed at every position of human body and exhibits ideal monitoring performance.Because of the flexibility,high sensitivity to various deformations and excellent safe-guarding performance,WET has a strong potential for wearable monitoring textile to simultaneously protect human beings and detect the movements of the human body under various conditions.更多还原