【作者】 田野；

【导师】 孙洪波；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2011， 博士

【摘要】 “微机械”的概念最早提出于上个世纪六十年代,以器件的特征尺寸或操控尺寸在微米量级为特征。直到八十年代,第一台静电驱动微马达被成功研制,微机械开始快速发展起来。迄今为止,其产品已经被广泛应用于生物医疗、环境监测、交通运输、自动化控制、航空航天和国防建设等领域。微机械的制备与驱动很大程度上依赖MEMS工艺,随着MEMS工艺的不断成熟,微米级,甚至纳米级微机械相继出现。然而,微机械尺寸的缩小为其驱动带来不便,传统的微机械驱动技术已显得有些力不从心。因此,开发一种新型微机械制备与驱动技术十分必要。近年来,聚合物微加工技术日趋成熟,这为微机械的制备提供了新的思路。本文在此背景下,提出利用飞秒激光双光子微纳加工这一强大的三维微加工平台,设计、制作了多种微机械,并着力研究、开发了微机械的磁力遥控驱动和溶剂响应驱动两种新型的驱动方式。1.磁力驱动方面磁力驱动是指利用磁场实现力或者力矩无接触传递的一种驱动方式,它具有非接触性和生物相容性等优点。磁力驱动的这些优点使其在生物医药领域显示出了广阔的应用前景。然而,对于聚合物微机械来说,磁性材料(如Fe304纳米粒子)由于存在兼容性差等问题很难大量掺入到聚合物之中。因此,磁驱动技术一直无法应用于聚合物微机械。在本论文中,我们介绍了一种利用飞秒激光加工磁流体光刻胶制备聚合物微机械的方法,并对其进行了磁遥控驱动。实验上,我们首先利用高温分解法制备出粒径均一、分散性好的Fe304磁性纳米粒子,粒子的粒径约为6nm。经过对纳米粒子进行表面改性处理,将PO3-TMPTA材料修饰在粒子表面,从而改变了纳米粒子在有机溶剂中的分散性质。实验结果表明：原本只能均匀分散在非极性溶剂中的纳米粒子,经过表面改性处理后能够长期均匀、稳定的分散在MA等极性溶剂中。将改性后的Fe304纳米粒子溶解到BMA中,与P03-TMPTA、TPO、Irgacure 819按照一定比例混合,配制成磁性光刻胶。由于纳米粒子的性能得到了改善,大大提高了微机械的加工精度。与含有共沉淀法合成的粒子的微结构27.5nm的表面粗糙度相比,含有改性后高温分解法合成的粒子的结构表面粗糙度仅为4.9nm。利用飞秒激光对该磁性光刻胶进行双光子微纳加工,制作了微弹簧结构,在磁场中对其进行了拉伸驱动。实验结果表明,弹簧结构能够敏感的对外界磁场做出响应。在磁场强度3000Gs的条件下,其形变量能够达到81μm,是其自由状态下自身长度的2.25倍,可谓驱动效果明显。随后,作者又设计、加工了结构更为复杂,功能性更强的微涡轮结构,并对其在磁场中的运动做了研究。实验结果表明：通过与含有共沉淀法合成的纳米粒子的涡轮相比,含有高温分解法合成的纳米粒子的涡轮表面更加光滑,运动时受到的阻力更小。因此,该涡轮旋转的稳定性和转速均明显优于前者。实验测得,含有高温分解法合成的纳米粒子的涡轮在旋转磁场中最高转速超过400r/min。通过飞秒激光倒置加工技术,作者成功的将磁性微涡轮生长在微流控通道内,将其作为一种高效的主动混合器件,有望解决微观领域内溶液混合困难的问题。2.溶剂响应驱动方面刺激性聚合物的响应特性为聚合物微机械的驱动提供了可行性,然而,这些具有响应性的聚合物通常与器件的制备工艺不兼容。而常规的光敏聚合物虽然可对其进行高精度微纳加工,却没有明显的响应特性。在这种器件的制备与响应特性的矛盾中,我们提出利用调控实验参数以设计器件响应特性的方法,实现了对普通光敏聚合物微结构的溶剂响应驱动。众所周知,交联的高分子聚合物材料在有机溶剂中能够发生不同程度的溶胀/收缩现象。从这一现象出发,本文研究了丙烯酸酯类光敏树脂和PDMS的宏观块体以及微观结构对不同溶剂的溶胀、收缩行为,发现激光加工出的聚合物微纳米结构有着非常明显的溶剂响应性质。以丙烯酸酯类光敏树脂为例,聚合物微结构在溶度参数与其相近的溶液中溶胀,而在溶度参数与其相差较大的溶剂中收缩。我们首先利用飞秒激光双光子微纳加工制作了微米线结构,并对其进行了溶剂响应的可靠性测试。实验结果显示：微米线在连续溶胀/收缩50次以后形变量仍然保持在17%左右,与初始时相当,具有非常高的可靠性,完全满足作为微机械驱动力的需要。作为溶剂响应驱动的展示,作者设计、加工了基于微米线收缩驱动的滑块结构。该滑块能够在正己烷的刺激下,沿着轨道向前滑行。通过调节微米线的激光扫描步长,作者有效的调控了聚合物的密度,也就调控了结构对溶剂刺激的敏感度,进而实现了对滑块结构的可控驱动。这部分还对滑块移动的距离和微米线的直径与激光扫描步长的依赖关系做了定性分析。实验结果显示：滑块移动的距离随激光扫描步长增加而增加,而微米线的直径随激光扫描步长增加而减少。在此基础上,作者根据飞秒激光加工灵活、可设计的技术特点,设计了由激光扫描步长不同而导致的内、外两层聚合物密度不同的双层结构。此种结构虽然材料相同,但由于加工条件不同,呈现出内、外两层对外界刺激响应程度不同的独特现象。当用正己烷刺激该结构时,结构能够发生定向弯曲,当用丙酮刺激时,结构能迅速恢复原状。这种弯曲／恢复动作能在外界的不断刺激下反复的进行。作者以这种双层结构为结构单元,设计、加工了能够在正己烷中“握紧”,在丙酮中张开的微机械手。通过倒置加工的方式,将其加工在光纤侧壁上,通过对光纤的三维操作,实现了对微机械手的大范围三维精确定位。最终,作者用该机械手完成了对微球的抓取、运输、释放等一系列动作,实现了其作为“手”的基本功能。本文成功制备了磁遥控驱动的聚合物微机械器件,通过对磁性纳米粒子进行表面改性处理,解决了纳米粒子与光刻胶相容性差的关键技术问题,大幅提高了其加工精度,从而使磁性微机械工作时的可靠性和稳定性显著提升。另-方面,我们首次利用高分子聚合物的溶胀／收缩现象制作了溶剂响应微机械,并对其实现了微观操控。本文在微机械驱动方面的创新性研究,开拓了微机械的制备与应用,为微机械的发展注入了新的活力。更多还原

【Abstract】 Micromachine, which has typical size or manipulation range in microns range, was proposed in the 1960s for the first time. Till 1980s, the first electrostatic micromotor was successfully fabricated, micromachines got their rapid development. Up to now, the products are widely applied in biomedical research, environmental monitoring, traffic and transportation, automatic control, aeronautics and astronautics and national defense etc. Generally, the fabrication and drive of micromachines mainly depended on MEMS technology heavily. With the development of MEMS technology, micro-and nano-micromachines appeared gradually. However, the size decrease of micromachines results in more complex driving instruments, and the traditional driving mechanisms become disabled. Therefore, it is necessary to develop novel fabrication and drive approaches of micromachines. In recent years, the raising of polymer micro fabrication technology made the fabrication of polymer-micromachines more easily. In this dissertation, by using femtosecond laser micro/nanofabrication as a powerful 3D microfabrication platform, micromachines were designed, and fabricated in a controlled manner. Two novel driving mechanisms named magnetically remote driving (MRD) and solvents response driving (SRD) were developed for micromachine manipulation.1. Magnetically remote drivingMagnetically remote drive is a noncontact driving manner which transmits force and moment by using magnet field. This drive mechanism shows great prospects in the biomedical use due to its advantages of its noncontacting and biocompatibility. However, magnetic materials (such as Fe3O4 nanoparticles) are difficult to dope into polymer homogeneously due to their poor compatibility. So, magnetic drive technology has not yet been applied to polymer micromachines. In this dissertation, we represent a fabrication of magnetic polymer micromachines by femtosecond laser processing of ferrofluid photoresists. Subsequently, the micromachines were remotely manuplated in magnetic field.Experimentally, well dispersived Fe3O4 magnetic nanoparticles with uniform diameter of～6 nm were prepared by thermal-decomposition method. After surface modification, PO3-TMPTA was modified on the surface of nanoparticles, and then the surface property of nanoparticles was changed. Experimental results showed that the surface modified nanoparticles could be dispersed in polar solvents (such as MA) uniformly and steadily for a long time.Magnetic photoresists were achieved by dispersing the Fe3O4 nanoparticles into the conventional photoresists which consisted of butyl methacrylate as monomer, PO3-TMPTA as crosslinker, TPO and Irgacure 819 as photoinitiators. In order to obtain high fabricative precision, surface quality of micromachines was significantly improved by using optimizated Fe3O4 nanoparticles as doping agents. Compared with the microstructure containing coprecipitation-synthesized nanoparticles whose surface roughness was 27.5nm, the surface roughness of this optimizated microstructure was only 4.9nm.As a typical illustration, microsprings were fabricated by femtosecond laser two-photon photopolymerization (TPP) of the magnetic photoresists. Experimental results showed that the microsprings could respond sensitively to external magnetic fields. When the intensity of magnetic field was 3000Gs, the deformation of microsprings could reach 81μm, which was 2.25 times of their original lengths. Obviously, the driving effect was significant.Subsequently, a more complex and functional microturbine was designed and fabricated through the same method. In our work we also studied their movements in magnetic field. Experimental results showed that compared with the microturbines containing coprecipitation Fe3O4 nanoparticles, the surfaces of microturbines containing thermal-decomposition Fe3O4 nanoparticles were much smoother. Moreover, the stability and speed of their rotation were better than those containing coprecipitation Fe3O4 nanoparticles due to the much little friction in surface. The maximum rotating speed of the microturbines containing thermal-decomposition Fe3O4 nanoparticles was as high as 400r/min.Through femtosecond laser invert fabrication technology, the microturbines were prepared in microfluidic channel successfully. As effectively active mixing devices, they could be used to solve the problems of solvents mixing in micro scales.2. Solvents response drivingThe responsive features of stimuli-responsive polymer provide the possibility of driving polymer micromachines in a controlled fashion. However, the stimuli-responsive polymers are usually not compatible with microfabrication technology. Although the conventional photoresists could be fabricated with high precision, there are no obvious responsive features of them. In the conflict of device fabrication and responsive properties, we propose a solvents response driving mechanism for conventional photopolymer micromachine by adjusting the experimental parameters.It is well known that cross-linked polymer materials can swell and shrink in organic solvents. Based on this phenomenon, the swelling and shrinking behaviors of bulk materials, microstructured photopolymers, and PDMS were carefully studied. We found that the solvents response behaviors of polymer microstructures fabricated by femtosecond laser were much more obvious due to the relatively large interfacial surface area.For example, methacrylate-based photoresists swelled in solvents whose solubility parameters were similar, and shrunk in solvents whose solubility parameters were different. We first fabricate microwire structures by TPP. And then a reliability test of solvents response of microwires was applied. Experimental results showed that after swelled and shrunk for 50 times, the deformation degree of microwires remained at 17%. It was similar with the initial deformation degree, showing a great reliability, which fully met the high standard of micromachines drive.As a display of solvents response manuplation, slipping-block structures based on microwires shrinking were designed and fabricated. The devices could slip along a rail by the stimulation of n-hexane. The polymer density of the formed networks was controlled effectively by adjusting the laser scanning step length so as to tune the sensitivity of the structures to solvents. In this part, the dependence of the block moving distance and the diameters of microwires on the scanning step length of the laser was also analyzed quantitatively. Experimental results showed that the block moving distance increased with step length, and the diameters of microwires decreased with step length.On this basis, through the flexible and designable TPP fabrication, the bilayer polymer structures with different polymer density were designed and fabricated. Although the structures were consisted with the same material, the microstructure showed directional curving property, due to the different responsive degreen. When they were immersed in n-hexane, the structures could bend directionally. When they were immersed in acetone the structures restored quickly. This bending/restoring action could act repeatedly under the condition of constant external stimulation.Using this bilayer structure as a basic unit, the micromanipulators which can grip in n-hexane and open in acetone were designed and fabricated. The micromanipulators were fabricated on the cladding of fibber by inverting fabrication method. The large-scale three-dimensional precise position was achieved via the operation of fiber in three-dimensions. Finally, as the basic functions of a "microhand", a series of actions, such as capturing, transporting and releasing of microspheres were carried out.The magnetically remote polymer micromachines were fabricated successfully in this dissertation. The key technical problem of the poor compatibility between magnetic nanoparticles and photoresists was solved by successful preparation of ferrofluid photoresist containing surface modified Fe3O4 nanoparticles, which improved fabrication precision greatly. At the same time, improved reliability and stability of magnetic micromechines were obtained for subsequent manipulation. On the other hand, the solvents responsive micromachines were designed based on swelling and shrinking phenomenon of polymer networks for the first time. Controllable micromanipulation of these solvent responsive micromachines was achieved by solvents stimulation. The innovative researches in fabrication and manipulation of micromachines would promote their further developments and applications更多还原