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。     

The fabrication of polymer microfluidic devices using a solid-to-solid interfacial polyaddition

It is hard to permanently seal the microfluidic channels made of thermoset polymers without using conventional adhesives. Here, we reported a polyaddition-based mechanism to solve the problem. The method is based on introducing amine groups onto the surface of one material and epoxy groups on another material and enabling the amine–epoxide polyaddition reaction at their closely contacted solid-to-solid interface to establish a covalent and permanent bonding. It was successfully used to permanently seal polydimethylsiloxane (PDMS) microfluidic channels with glass in a scalable and multifunctional fashion and to seal epoxy (SU-8) microfluidic channels with PDMS. This type of interfacial polyaddition can be easily extended to other materials for microfluidic device fabrication and is expected to find some applications in specialty bonding.     

Effect of heat treatment temperature and surface roughness to the PDMS-FR4 adhesive bonding

The current work investigates the use of liquid polydimethylsiloxane (PDMS), with a 10:1 ratio of prepolymer:curing agent?=?10:1 as the intermediate layer for adhesive bonding with Flame Retardant 4 (FR4). The spin coating of liquid PDMS on FR4 allows irreversible adhesive bonding with the solid PDMS. The strength of the proposed adhesive bonding technique has been investigated under different treatment temperatures: oven-heated at 60?°C, 70?°C, and 80?°C, cooled down in the room temperature of 25?°C, and exposed to direct sunlight at 35?°C. All the samples were left for 6?h. Investigations were conducted to analyze the effect of FR4 surface roughness on the strength and quality of the adhesive bonding. The standard procedure of American Standard Test Measurement (ASTM) D1002 was followed to verify the strength of PDMS-FR4 adhesive bonding. Strongest adhesive bonding, free from air bubbles, was obtained from a sample with smooth surface of FR4 that has undergone a cooling down treatment in the room temperature of 25?°C. FR4 was coated by solder mask to obtain smooth surface. The techniques reported in this paper are simple, straightforward, and effective to be implemented with FR4 as a base material for adhesive bonding with PDMS, thus eliminating expensive and complicated operating equipment as widely used in the oxygen plasma-assisted bonding treatment. Another benefit from this adhesive bonding technique is the fact that it avoids the use of expensive oven or hot plate.     

三维复杂微流体纺丝芯片的封装研究

为了拓展微流体芯片的应用领域,以一种具有三层结构的多功能集成微流体纺丝芯片为例,利用去离子水和再生丝素蛋白水溶液,比较了环氧树脂粘合剂、硅胶粘合剂以及压敏胶对聚二甲基硅氧烷(PDMS)和纤维素膜的粘合效果,探讨了等离子处理、封装方式等三维复杂微流体芯片的封装技术,实现了多功能集成微流体纺丝芯片的有效封装,对具有类似结构的三维复杂微流体芯片的封装提供参考。     

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。     

Study on the photocatalytic activities of TiO2 films prepared by reactive RF sputtering

Titanium oxide (TiO₂) films were deposited on non-alkali glass by reactive radio frequency (RF) magnetron sputtering using a Ti metal target in this study. The deposition parameters employed to realize the photocatalytic activities of TiO₂ films include RF power, deposition time, argon–oxygen ratio (O₂/(Ar + O₂)) and substrate temperature. The orthogonal array and analysis of variance (ANOVA) were adopted to determine the effect of the deposition variables on characteristic properties and the optimal conditions. The results indicated that a higher photocatalytic activity of TiO₂ films could be achieved under RF power of 150 W, deposition time of 3 h, argon–oxygen ratio of 40% and substrate temperature of 80 °C. RF power and argon–oxygen ratio had a higher effect on the methylene blue (MB) absorbance. The validation experiments show an improved photocatalytic activities of 5% when the Taguchi method is used.     

聚(双环戊二烯-co-环辛二烯)微流控芯片的制备

本文报道了聚(双环戊二烯-co-环辛二烯)微流控芯片的制备方法。引入环辛二烯作为共聚单体,与双环戊二烯通过开环易位聚合制备得到弹性共聚物。当环戊二烯与环辛烯的质量比是1 : 1时,制得共聚物的力学性能接近于聚二甲基硅氧烷(PDMS),弹性共聚物具有较高的微尺寸结构成型精度。利用聚双环戊二烯半固化凝胶的反应特性,实现共聚物与聚双环戊二烯基底之间的稳定键合。共聚物微流控芯片可以通过类似于PDMS的连接方式,实现简单、高效的密封连接。利用共聚物微流控芯片制得单分散的微液滴,控制连续相的流速即可实现微液滴尺寸的调变。关键词：聚双环戊二烯共聚物；环辛烯；弹性体；微流控芯片；单分散液滴；中图分类号：TQ630 文献标识码： A 文章编号：1003-5214 (2020) 01-0000-00     

Investigation of Polyimidesiloxanes for Use as Adhesives by Electron Spectroscopy for Chemical Analysis

Angle-dependent electron spectroscopy for chemical analysis (ESCA) was used to examine the air facing surface (20–100 Å thick) composition of polyimidesiloxanes with different processing variations, and of varying polydimethylsiloxane (PDMS) content and block length (number of PDMS repeat unit varies from 1 to 9). Polyimide was clearly detected (due to the nitrogen content) in the 20–100 Å surface regions. This shows that a small amount of PDMS and short PDMS segment lengths in polyimidesiloxanes give a surface region with both PDMS and polyimide present. The surface composition, particularly that in the ca. 100 Å region, was correlated to the peel strength of polyimidesiloxane melt pressed to a metal substrate. Our results suggest that both PDMS and polyimide are essential components to rendering a needed peel strength. PDMS, having a good diffusive ability, readily reaches the substrate upon being pressed, achieving intimate contact, while imide groups interact with the substrate, presumably through chemical bonding; these two factors act synergistically to result in a high peel strength. In addition, the interaction mechanism and the failure mechanism involved in bonding polyimidesiloxane and metal substrate were also elucidated based on the ESCA results.     

Evaluation of Polymethylmethacrylate Cohesion Behavior with a Gas-Assisted Thermal Bonding Method

By applying heat and pressure to thermoplastic materials, the overlap of the two pieces can be bonded to form hermetic systems. Polymethylmethacrylate (PMMA) is a thermoplastic used in commercial microfluidic devices; its advantages include low cost, ready fabrication, and high transparency. In order to gain an understanding of PMMA's relevant characteristics (thermal behavior, material strength, and hermetic sealing strength), we study its bulk properties and mechanical behavior. Experimental results of the cohesion behavior of PMMA sheets were collected and are presented here. Samples were bonded by subjecting a sample to elevated pressure and temperature in the glass transition range (85°C–165°C), which was determined beforehand by differential scanning calorimetry and literature. Five different bonding temperatures (140°C, 150°C, 160°C, 170°C, and 180°C) and three bonding pressures (1.2, 1.4, and 1.6 MPa) were applied for making samples; mechanical strength tests were then carried out to understand separately the bulk mechanical strength and the interfacial properties (shear strength and bonding strength) of a cohesive laminate at the temperatures near the glass transition range. POLYM. ENG. SCI., 60:161–167, 2020. © 2019 Society of Plastics Engineers     

等离子体射流载气流量大小对玻璃纤维改性效果影响的研究

通过大气压等离子体射流在玻璃纤维（GF）表面沉积氧化硅（SiOx）纳米颗粒的方法改善玻璃纤维增强聚丙烯（GFRP）复合材料的界面结合性能,利用扫描电子显微镜、原子力显微镜和X射线光电子能谱等表征分析了改性纤维的表面形貌、化学成分、润湿性能和复合材料的界面结合性能,并考察了等离子体射流载气流量大小对GF改性效果的影响。结果表明,当载气流量为40 mL/min时,GF的改性效果最好,且此时GF的表面能相比对照组提高了43.18%,GFRP复合材料的层间剪切强度提高了30.79%;经过等离子体处理后,GF的表面粗糙度增大,极性官能团增多,复合材料的界面结合性能提升。     

Effect of the type of plasma on the polydimethylsiloxane/collagen composites adhesive properties

Polydimethylsiloxane (PDMS) films were treated with either oxygen (O₂), nitrogen (N₂) or argon (Ar) plasma between 40 W and 120 W for 5–15 min and their surface properties studied by contact angle measurements, infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Lower contact angles and increases in surface roughness, assessed by SEM and AFM, were observed for all used gases when plasma power and time increased, with argon treatment being the one that showed the most significant change in roughness.PDMS/collagen type I composites obtained after treating PDMS with oxygen at 80 W for 13 min or nitrogen and argon at 80 W for 14 min showed a peel strength of 0.1N/mm (oxygen plasma), 0.08 N/mm (nitrogen plasma) and 0.09 N/mm (argon plasma). In all cases, peel strength was higher than that measured for the untreated bilayer composite. An increase in adhesion strength, after oxygen and nitrogen plasma, was mostly attributed to chemical interaction between functional groups introduced on the PDMS surface and the functional groups on collagen as detected by FTIR. In contrast, the high peel strength observed on PDMS treated with argon plasma was attributed to its increased roughness which in turn increased mechanical interlocking. The properties of these composites render them suitable for adhesive free skin substitutes.     

Solubility and adhesion characteristics of plasma polymerized thin films derived from Lavandula angustifolia essential oil

Integration and implementation of organic polymer thin films often require knowledge of the stability when in contact with solvents and the adhesion quality when applied to different substrates. This article describes the solubility and adhesion characteristics of organic polymer thin films produced from Lavandula angustifolia essential oil, using radio frequency plasma polymerization at four RF power levels. Contact angle data was obtained for various solvents and used to determine the surface tension values for the polymer by using three established methods. A relatively strong electron–donor component and a negligible electronic acceptor component for the polymers indicate that they are monopolar in nature. Solubility data derived from interfacial tension values suggest that the polymers would resist solubilization from the solvents explored. The strongest solvophobic response was assigned to water, whereas diiodomethane demonstrated the weakest solvophobic response, with ΔG₁₂₁ > 0 in some instances depending on the surface tension values used. The adhesion tests of the polymers deposited on glass, PET, and PS indicated that the adhesion quality of the thin film improved with RF power, and it was associated with an improvement in interfacial bonding. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fabrication and characterization of a flow-through PCR device with integrated chromium resistive heaters

A flow-through PCR device with integrated chromium resistive heaters was developed. The PCR device was composed of a polydimethylsiloxane flow channel chip fabricated using soft lithography and a glass heating chip produced by standard photolithography. PDMS bonding layers were used to assemble the device instead of oxygen plasma treatment. The formation of air bubbles within the device was suppressed by treating the flow channel with 20% (v/v) Tween 20. DNA fragments with different lengths (219, 298, and 842 bp) were successfully amplified with the device. For the 298 bp fragment, 30 thermal cycles were completed in 23 min and a clear product band was observed after gel electrophoresis. The device showed no cross contamination after appropriate washing. Two commonly used PCR additives, bovine serum albumin and polyethylene glycol, showed inhibitory effect in the Tween 20 treated PCR device.     

A Parametric Study of a Monolithic Microfluidic System for On-Chip Biomolecular Separation

A microfabricated poly(dimethylsiloxane) (PDMS) chip containing channel filled with polymer monolith has been developed for on-chip biomolecule separation. Methacrylate monolithic polymers were prepared by photo-initiated polymerization within the channel to serve as a continuous stationary phase. The monolithic polymer was functionalized with a weak anion-exchange ligand, and key parameters affecting the binding characteristics of the system were investigated. The total binding capacity was unaffected by the flow rate of the mobile phase but varied significantly with changes in ionic strength and pH of the binding buffer. The binding capacity decreased with increasing buffer ionic strength, and this is due to the limited available binding sites for protein adsorption resulting from cationic shielding effect. Similarly, the binding capacity decreased with decreasing buffer pH towards the isoelectric point of the protein. A protein mixture, BSA and ovalbumin, was used to illustrate the capacity of the methacrylate-based microfluidic chip for rapid biomolecule separation.     

Capillary driven flow in wettability altered microchannel

The capillary driven flow of water inside a microchannel with altered wettabilities is experimentally investigated and modeled theoretically. The surfaces of the PDMS made microchannel are exposed to oxygen plasma, rendering the surfaces increasingly hydrophilic, which provides the driving force for the flow. The plasma treated surfaces are characterized using topography and phase imaging of AFM scanning, as well as nano‐indentation, to correlate the distinct structural changes to the hydrodynamic profiles of the advancing meniscus. The experimental results are further analyzed using a newly proposed slip velocity model. The aim is to obtain a qualitative relationship between the surface properties and the flow parameters, namely the advancing meniscus velocity and pressure drop inside the channel. The insights are of fundamental importance in diverse fields, such as enhanced oil recovery, microfluidic devices, cell separation, and pathology. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4616–4627, 2017     

Steady microfluidic measurements of mutual diffusion coefficients of liquid binary mixtures

We present a microfluidic method leading to accurate measurements of the mutual diffusion coefficient of a liquid binary mixture over the whole solute concentration range in a single experiment. This method fully exploits solvent pervaporation through a poly(dimethylsiloxane) (PDMS) membrane to obtain a steady concentration gradient within a microfluidic channel. Our method is applicable for solutes which cannot permeate through PDMS, and requires the activity and the density over the full concentration range as input parameters. We demonstrate the accuracy of our methodology by measuring the mutual diffusion coefficient of the water (1) + glycerol (2) mixture, from measurements of the concentration gradient using Raman confocal spectroscopy and the pervaporation‐induced flow using particle tracking velocimetry. © 2017 American Institute of Chemical Engineers AIChE J, 63: 358–366, 2018     

Analysis of mold insert fabrication for the processing of microfluidic chip

The microfluidic chip has been used as an example to discuss different mold insert materials by micro hot‐embossing molding. For the mold insert, this study uses the SU‐8 photoresist to coat on the silicon wafer, then uses UV light to expose the pattern on the surface of SU‐8 photoresist, and coat the seed layer on the SU‐8 structure using thermal evaporation. The micro electroforming technology has been combined to fabricate the mold inserts (Ni, Ni‐Co) followed by replicating the microstructure from the metal mold insert by micro‐hot embossing molding. Different processing parameters (Embossing temperature, embossing pressure, embossing time, and demolding temperature) for the properties of COP film of microfluidic chip have been discussed. The results show that the most important parameter is the embossing temperature for replication properties of molded microfluidic chip. The demolding temperature is the most important parameter for surface roughness of the molded microfluidic chip. The Ni‐Co mold insert is the most suitable mold material for molded microfluidic chip by microhot embossing molding. The bonding temperature is the most important factor for the bonding strength of sealed microfluidic chip by tensile bonding test. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Characterization of fracture energy and toughness of air plasma PDMS–PDMS bonding by T-peel testing

The fracture energy, toughness and failure modes of air plasma oxidized polydimethylsiloxane (PDMS) bonding are evaluated in this paper. Each PDMS–PDMS bonded specimen was subjected to T-peel testing at a constant-displacement rate. The load–extension curve from each test was analyzed by the principle of energy balance in linearly elastic fracture mechanics, to calculate the fracture energy (critical strain energy), which is the maximal strain energy a bonded specimen can withstand without losing its assembly integrity, and toughness (surface energy), which is the bonding energy at the interface. A distribution of calculated values against the air plasma treatment parameters shows the predominant range of 0.1 to 0.4 N/mm for fracture energy and 0.1 to 0.2 N/mm for toughness. Together with an analysis of three failure modes (cohesive, adhesive, and mixed), the results suggest 0.1 N/mm as the threshold of the fracture energy for weak bonding, below which a specimen will be likely to fail through debonding. A set of treatment parameters are recommended for using air plasma to achieve strong bonding.     

Glass forming region and bonding mechanism of low-melting V2O5–TeO2–Bi2O3 glass applied in vacuum glazing sealing

As a new kind of energy-saving glass, vacuum glazing has excellent thermal and sound insulation properties and is widely used in building, household appliances and solar photovoltaic. The edge sealing material, along with sealing method, is key to the fabrication of vacuum glazing. Low transition temperature (T_g) and good fluidity at sealing temperature (T_s) make low-melting glass of V₂O₅–TeO₂–Bi₂O₃ (VTB) system perfect to be the edge sealing material for vacuum glazing. The glass forming region of VTB ternary system was mapped for the first time in this work. Low-melting VTB glass of 40V₂O₅–50TeO₂–5Bi₂O₃–3ZnO–2Na₂O (wt%) was optimized to be the sealing material. Glass powder of this composition could be used to seal the edges of vacuum glazing at an extremely low temperature of 360°C. With the assistance of anodic-bonding method, the bonding strength of vacuum glazing was dramatically enhanced. Vacuum glazing fabricated under the optimized process parameters of 420°C, 600 V, and 60 min possesses a highest bonding strength of 4.31 MPa. Furthermore, anodic-bonding mechanism of low-melting VTB glass applied in vacuum glazing sealing has been thoroughly researched.     

Hydrogen Oxidation Catalyzed by Pt Supported on Carbon Nanofibers with Different Graphite Sheet Orientations

The kinetic study of hydrogen oxidation with or without the presence of CO has been used as a tool to study the relative oxygen and CO adsorption strength on Pt nanoparticles, which are important parameters for fuel cell catalysts. It was found that the activation energy, which is determined by the oxygen binding energy, is influenced by the CNF graphite sheet orientation, CNF oxygen groups and catalyst preparation method. A weaker bonding of oxygen was indicated for Pt nanoparticles supported on platelet compared to Pt on fishbone CNFs. Moreover, oxygen seemed to be more strongly bonded to Pt particles on CNFs prepared by deposition–precipitation compared to those prepared by incipient wetness impregnation and a metal-oxide colloid method. Enhanced CO-adsorption was indicated for Pt supported on carbon nanofibers with introduced oxygen groups.