PMMA微流控芯片最佳注射成型工艺的实验研究

以聚甲基丙烯酸甲酯(PMMA)为原料,通过注塑加工的方式制备微流控芯片,经过多次注塑实验得出影响PMMA微流控芯片成型质量的主要因素是:模具温度、保压压力、熔体温度和注射速度.在其他参数不变的情况下,通过正交实验和极差分析确定了PMMA微流控芯片注射成型的最佳工艺:熔体温度260℃,模具温度50℃,保压压力60 MPa...     

基于PMMA材料的微通道快速加工技术

近年来,基于聚合物的微加工制造技术已经成为微细加工领域的研究热点,已广泛应用于制备芯片实验室和微流控芯片。以热压技术为基础,研究利用加热电阻丝制备微流控芯片微通道的快速加工技术,并最终实现了基于聚甲基丙烯酸甲酯(PMMA)材料的微通道快速加工,获得了电阻丝压印微通道的最优条件,在电流1. 8 A、时间5s、压力为44. 59 N条件下获得的微通道宽度变形率约为8. 5%,深度变形量约为8. 9%,可以在2 h左右制备完成PMMA微流控芯片。最后,利用该加工技术制作了十字型流动聚焦型微流控芯片,可稳定生成34～74 nL范围内的微液滴,实验结果显示利用本快速加工技术所获得的微通道圆润光滑、性能稳定、键合密封牢固。     

PMMA微流控芯片高效键合工艺研究

利用有限元软件对聚甲基丙烯酸甲酯(PMMA)微流控芯片键合过程进行仿真分析,而后以缩短键合时间为目的,针对键合温度、键合压力进行了相应的实验研究。结果表明,当键合温度低于聚合物材料的玻璃化转变温度时,芯片易产生未键合区域,当键合温度高于玻璃化转变温度时,微通道随温度的升高发生严重变形,最佳键合温度值应在材料玻璃化转变温度附近进行选取;键合温度105℃,键合压力1.0 MPa时,可在5 min的键合时间内得到微通道变形较小且完全键合的微流控芯片,满足模内键合的需求,大大缩短了芯片的制造周期。     

基于PMMA材料的键合封装技术研究

聚甲基丙烯酸甲酯(PMMA)作为微流控芯片研制中常用的高分子材料,其键合封装工艺是制作微流控芯片的重要组成部分。为了简捷有效地实现PMMA间的键合封装,研究了一种可在普通实验室开展的便捷、低成本且高效的PMMA键合封装方法。通过正交试验设计深入研究了键合时间、温度以及压力对PMMA键合强度的影响,从而确定最优工艺参数组合。实验结果表明,在115℃,70 min,60 N条件下可实现4.44 MPa的键合强度,且微流路通道变形较小(小于10%),可满足常规PMMA微流控芯片键合封装的要求,并可在普通微流控实验室有效开展。     

基于CAE分析的工艺参数对微结构复制程度的影响

针对注射成型中微流控芯片中微结构复制不完全的情况,采用单因素法,利用Moldflow软件对微流控芯片抽象物理模型进行仿真分析,考察熔体温度、模具温度、保压压力、注射压力等4个工艺参数对微结构复制情况的影响。结果表明,熔体温度与模具温度的影响较大,保压压力的影响次之,注射压力的影响不显著。     

工艺条件对聚碳酸酯微针成型的影响

通过模具上下模板差温的方法,以聚碳酸酯(PC)片材为基板,在热压印过程中制备了聚合物微针,研究了制备过程中,模具上下模板温度、热压印压强、热压印时间等工艺参数对微针平均长度和微结构复制率的影响。结果表明:模具上模板的合理温度(80℃左右)有助于减少压印时间和降温时间;下模板温度对微结构成型具有决定性的作用,只有在下模板温度大于154℃的条件下,才能压印出符合要求的聚合物微针;热压印压强在8～12 MPa的范围内与微针成型效果的关系呈正相关;随着压印时间的增加,微针的平均长度变长,通过控制合理的时间,微针的平均长度基本上能够达到模具上微针的长度,复制率大于95%。     

基于黏弹性模型的PMMA微流控芯片模内键合微通道变形研究

针对聚合物微流控芯片模内键合过程中微通道变形的问题,采用黏弹性材料模型对聚甲基丙烯酸甲酯(PMMA)微流控芯片模内键合过程中具有梯形截面的微通道变形进行了仿真分析;研究了在105℃下,芯片微通道在不同键合压力和键合时间下微通道的变形。结果表明:微通道不能保持键合前的尺寸,温升对微通道变形影响很小;微通道顶部与两侧的黏合使得微通道顶部宽度和微通道高度变形远大于底部宽度变形,并随着键合压力的增大而增大;当键合时间超过50 s后,键合时间对微通道变形影响很小,可以采用较长的键合时间来保证键合强度而不影响微通道形貌。     

基于PMMA材料的微流控芯片批量注塑技术研究

微流控芯片可以操控微纳尺度上流体,借助尺度效应的帮助进行检测,具有检测过程迅速、检测准确、试剂消耗量小等特点,常应用于高效筛选、分析化学、食品安全、环境检测等领域。伴随微流控技术的发展,聚合物材料逐渐取代传统的玻璃、硅等材料成为微流控芯片的主流基体材料。面向聚甲基丙烯酸甲酯(PMMA)材质的微流控芯片,开展了设计、数值模拟仿真、注塑模具设计及微流控芯片注塑成型的全过程研究,对未来微流控芯片的大规模注塑制备具有一定借鉴意义,最后也对未来微流控芯片与注塑加工工艺相结合的发展趋势进行了展望。     

基于PDMS-PMMA材料的微流控芯片等离子体键合工艺研究

为了提高聚二甲基硅氧烷(PDMS)盖片和聚甲基丙烯酸甲酯(PMMA)基片的复合式微流控芯片键合的稳定性,开展了微流控芯片等离子处理特性的时间因素的研究。利用红外光谱和扫描电镜对处理前后的PMMA进行表征,确定硅烷化等离子方法的可行性;同时对PDMS、PMMA和硅烷化PMMA不同等离子处理时间的接触角及接触角恢复情况进行测量,采用正交试验法得到了最大键合力所需的最佳等离子处理时间以及有效操作时域,研究结果为确定微流控芯片的等离子体键合工艺参数提供借鉴。     

对类固态等温热压印过程中聚合物的填充分析

类固态等温热压印是一种模具保持恒温的压印工艺,对于无定型聚合物而言,温度应保持在Tg附近的类固态温度范围内。对聚甲基丙烯酸甲酯(PMMA)在类固态条件下的压印过程进行了有限元模拟分析,着重探讨了填充规律和成型形貌。模拟结果显示,PMMA在填充过程中的形貌稳定,不会出现传统工艺中的"双峰"缺陷。微结构深度是影响填充难度的主要几何因素,深度越大,结构的成型难度越高。深宽比、尺寸和形状对结构也有不同程度的影响,但作用均小于深度。在温度受限的情况下,聚合物的流动性受到制约,无法以熔体形态的均匀速率充满模腔,增加了模具结构的几何参数对制品成型质量的影响。     

聚合物热黏弹塑性变形微热压成型机理的数值模拟研究

研究了聚甲基丙烯酸甲酯（PMMA）超疏性阵列圆柱微结构特征功能表面的微热压成型技术,通过模拟研究了成型工艺参数对成型过程的影响规律,揭示了其热黏弹塑性变形充填流动机理,明晰了关键调控参数。结果表明,基片材料的弹性模量、成型温度和压力是影响充填成型的关键调控参数,成型压力和变形应力与成型温度呈负关联关系,而充填高度与成型温度呈正关联关系;提高成型温度至高于基片材料的玻璃化转变温度（Tg）,使基片处于黏弹性高弹态,易使基片快速产生明显的热黏弹塑性变形,且可使成型压力和变形应力趋于最小值,这有利于基片避免断裂损伤并加速充模流动。     

Finite element modeling of polymer hot embossing using a glass‐rubber finite strain constitutive model

A hyperelastic–viscoplastic constitutive model for amorphous polymers was used in finite element simulations of micro‐hot embossing across the glass transition. The model was selected for its ability to capture finite strain temperature and rate dependence over a wide range of temperatures, including across the glass transition. The simulations focused on the glass transition temperature regime, and particularly probed the effects of time and temperature during cooling and mold release. The results show that strong temperature sensitivity of the material across the glass transition leads to a wide range of required embossing force and springback. The interplay between changes in material properties upon cooling and stress relaxation can lead to significant increases in embossing force during the cooling stage, especially when high cooling rates are employed. The effects of thermal expansion also complicate the problem during rapid cooling. Nonlinear material behavior is shown to affect results in parametric hot embossing studies. Careful tailoring of embossing temperature, cooling rate, and demolding temperature is critical in acceptable feature replication. The best results are found for moderate cooling rates, which allow adequate time for stress relaxation in the material prior to mold release. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Rapid fabrication of microstructure on PMMA substrate by the plate to plate Transition‐Spanning isothermal hot embossing method nearby glass transition temperature

Generally, the hot embossing cycle time for fabricating microfeatures on the surface of polymer takes no <10 min because the mold needs to be firstly heated to 10–40°C above T_g and then cooled to temperature below T_g after certain time of holding pressing force. In this article, the Plate to Plate (P2P) Transition‐Spanning Isothermal Hot Embossing method was proposed, specific of which was relatively short embossing cycle time of 15–60 s by setting and holding constant mold temperature in a narrow temperature interval around T_g in whole cycle of embossing substrate of PMMA. The experiment hot embossing device satisfied the needs of isothermal embossing process was designed and built up, on which the micro V‐cut array with a pitch of 49 µm was successfully fabricated on the PMMA substrate. The experiments gave a confirmation of possibility for fabricating microfeatures by P2P Transition‐Spanning Isothermal Hot Embossing method. POLYM. ENG. SCI., 57:268–274, 2017. © 2016 Society of Plastics Engineers     

Hot embossing in microfabrication. Part I: Experimental

The relationship among processing conditions, material properties, and part quality in hot embossing was investigated for three optical polymers: polycarbonate (PC), polymethyl methacrylate (PMMA), and polyvinyl butyral (PVB). A series of systematic embossing experiments was conducted using mold inserts having either single or multiple feature depths. The feature dimensions varied from 90 to 3000 μm. The processing conditions studied include embossing pressure, thermal cycles, and heating methods. The displacement profile, replication accuracy and molded‐in stresses were measured experimentally. It was found that for isothermal embossing, both replication accuracy and birefringence pattern depend strongly on the processing conditions. For non‐isothermal embossing, the molded parts showed excellent replication as long as the feature transfer was completed. The flow pattern under isothermal embossing resembles a biaxial extensional flow. Under non‐isothermal embossing, the polymer deformation involves an upward flow along the wall of mold features, followed by downward compression and outward squeezing. Rheological characterization and hot embossing analysis are presented in Part II.     

Replication of plastic thin film by microfeature mould in large area hot embossing

Abstract

This study determines the replication property and surface roughness of microfeatures of a Ni mould that combines electroforming and large area hot embossing. The metal mould first uses a 4 in. silicon wafer to fabricate a master using the UV-LIGA method, and then applies the sputtering method to sputter the copper element as the seed layer on the surface of the master. The electroforming method is used to manufacture the Ni mould insert from the master with the seed layer. Finally, this study uses thin film of polymethyl methacrylate (PMMA) material to replicate the microfeatures of Ni mould insert by large area hot embossing. This study shows the replication properties and surface roughness of different microfeature shapes and sizes for the Ni mould insert and moulded PMMA on large area hot embossing. Experimental results show the average error in height of the microfeature is 0·61 μm for the Ni mould insert and moulded PMMA. The average error in surface roughness of the microfeature is 1·63 nm for the Ni mould insert and moulded PMMA. Experimental results show the good replication and surface roughness of moulded PMMA are replicated from the Ni mould insert by large area hot embossing.     

Analysis of laser/IR‐assisted microembossing

To shorten the cycle time in conventional hot embossing, an infrared laser (laser/IR)‐assisted microembossing process was investigated in this study. Since the laser/IR heats the substrate rapidly and locally, the heating and cooling time can be substantially reduced. Two different modes of IR embossing were tested. In one case, the polymer substrate was the IR‐transparent poly(methyl methacrylate) (PMMA) and a carbon black‐filled epoxy mold was used. In the second case, the polymer substrate was an IR‐absorbent PMMA, and an IR transparent epoxy mold was used. The experimental results showed that both a shorter cycle time and good replication accuracy could be achieved. A commercially available finite element (FEM) code, DEFORM?, was used for process simulation. The relationship between the penetration of radiation energy flux from the laser/IR heating source and temperature distribution inside the polymer substrate was considered in the simulation. The flow pattern observed in the experiments agreed well with the numerical simulation. However, the displacement curve showed a discrepancy. POLYM. ENG. SCI., 45:661–668, 2005. © 2005 Society of Plastics Engineers     

Hot‐embossing experiments of polymethyl methacrylate across the glass transition temperature with variation in temperature and hold times

Hot‐embossing (HE) experiments were conducted on polymethyl methacrylate (PMMA) across its glass transition temperature from 92 to 142°C. The glass transition temperature (T_g) of the PMMA used in this study was ～ 102°C. The polymer samples were embossed to a depth of 0.8 mm (800 μm). The experiments were carried out at various temperatures for different hold times of 30, 90, and 180 sec during the embossing process. A few additional experiments were conducted at 142°C with cooling of the samples as well. The force required for embossing and the final depth of the embossed features were analyzed. Polymers, including PMMA, show significantly different material behavior around and above T_g. The same was seen in the aforementioned tests; the trends observed for the force as well as the final depth changed considerably around 122°C (T_g + 20). These findings will be used in developing material models for use in simulating the hot‐embossing process. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Enhanced polymer filling and uniform shrinkage of polymer and mold in a hot embossing process

Low filling efficiency and large thermal stress are two important problems that limit the wide use of hot embossing especially in fabricating high aspect ratio patterns. Two types of flow barriers, the first being an accessorial slot on the mold (SFB), the other was a block on the hot embossing machine (BFB), were designed to enhance polymer filling and their performances were simulated with the finite element method. The numerical simulation results show that two kinds of flow barriers can also accelerate the polymer filling speed and improve filling efficiency. The BFB has a better promoting effect and can be easily used as a quasi close‐die embossing process. The shrinkage of the polymer and mold is made uniform with a designed polymer grip holder to minimize the thermal stress. The polymer was clipped at a temperature in a cooling step and its deformation was fixed; thus, the shrinkage of the polymer can be equal to the mold at a special temperature. An improved hot embossing machine was designed and the hot embossing process was modified to satisfy these requirements. At last successful fabrication of the light guide plate verified the improvements. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Constant‐temperature embossing of supercooled polymer films

In conventional hot embossing, a thermoplastic polymer undergoes phase transitions in liquid, semi‐solid, and solid states through cyclic heating and cooling. This paper, in contrast, describes the development of a constant‐temperature embossing process and compares its characteristics against standard hot embossing. The new process utilizes the crystallizing nature of supercooled polymer films to obtain the necessary phase transitions. By softening and crystallizing the supercooled polymer at the same temperature, the embossing and solidification stages can be carried out isothermally without a cooling step. PET, due to its relatively slow crystallizing kinetics, was chosen as a model material for this study. The embossed films with microgroove patterns of different sizes and aspect ratios were characterized for their replication fidelity and accuracy. For supercooled PET films, constant‐temperature embossing with high replication quality and acceptable demolding characteristics was achieved in a large processing temperature window between T_g and T_m of PET. A parametric process study involving changes of the embossing temperature and embossing time was conducted, and the results indicated that the optimal process parameters for constant‐temperature embossing can be derived from the crystallization kinetics of the polymer. The removal of thermal cycling is a major advantage of constant‐temperature embossing over conventional hot embossing and represents an important process characteristic desired in industrial production. POLYM. ENG. SCI., 54:1100–1112, 2014. © 2013 Society of Plastics Engineers     

A two‐station embossing process for rapid fabrication of surface microstructures on thermoplastic polymers

An embossing strategy involving a hot station and a cold station for sequentially heating and cooling the embossing tool was investigated to reduce cycle times in hot embossing polymer microstructures. Experimental studies showed that aluminum stamps with a thickness of 1.4 mm can be rapidly heated from room temperature to 200°C in 3 s using contact heating against a hot station at 250°C. Microchannels and microlenses were successfully embossed onto high‐density polyethylene and acrylonitrile–butadiene–styrene substrates using a heating time less than 3 s and a total cycle time around 10 s. The two‐station embossing process for the microlens was also numerically studied. The simulated filling behavior agreed with the experimental observation and the predicted thermal and deformation history of the polymer offered a good explanation on the experimentally observed process characteristics. POLYM. ENG. SCI., 47:530–539, 2007. © 2007 Society of Plastics Engineers.