Micro- and nanopatterned star poly(ethylene glycol) (PEG) materials prepared by UV-based imprint lithography

A UV-based imprint lithography method is used for the direct surface structuring of hydrogel-based biomaterials, which are prepared from a family of tailor-made star poly(ethylene glycol) formulations. Bulk star poly(ethylene glycol) (PEG) hydrogels are fabricated by cross-linking acrylate-functionalized star PEG macromolecules. Cross-linking is achieved by radical reactions initiated by UV irradiation. This UV-curable star PEG formulation allows templating of mold structures to yield a stable, stand-alone, elastomeric replica of the mold. In particular, when a secondary, soft mold is used that consists of a perfluorinated elastomer with inherent excellent release properties, nanometer-sized features (down to 100 nm) can be imprinted without specialized equipment. The applied UV-based imprint lithography is a fast and simple technique to employ for the direct topographic structuring of bulk PEG-based biomaterials. The UV-based imprinting into the star PEG prepolymer by means of a perfluorinated, soft mold can be carried out on the bench top, while nanoscale resolution is demonstrated.     

注射成型聚碳酸酯厚度截面的残余应力分析

通过光弹法定量测量了注射成型聚碳酸酯(PC)试样在厚度截面上的残余应力,并结合模具温度的变化与不对称分布,对厚度截面上的残余应力分布进行了详细的研究.结果表明,在厚度截面上,试样边缘分布较高的流动残余应力,芯部分布较高的热残余应力,两区域界面处为流动应力与热应力相互耦合而形成的低应力过渡区;模具温度低于120?C时,PC的残余应力随模具温度的变化并不明显;模具温度高于120?C时,PC的残余应力随模具温度的升高显著降低;不对称模具温度会导致在低模温侧高热残余应力区分布宽,在高模温侧高热残余应力区分布窄.此外,试样的翘曲随模具温度的升高而逐渐增加,不对称模具温度会导致较大的翘曲.     

Electrochemical nanoimprint lithography directly on n-type crystalline silicon (111) wafer

Here we report spontaneous redox reactions at the Pt/Si/electrolyte three-phase interface and propose an electrochemical method for nanoimprint lithography on a crystalline Si wafer that does not require thermoplastic and photocuring resists. When the Pt metallized imprint mold is compacted on the n-type Si (111) wafer, electrons will transfer from the n-type Si to Pt due to their different electron work functions. At equilibrium, the Fermi levels of the electrons in each phase become equal, resulting in an electric field and a contact potential at the Pt/Si interface. When immersed in an electrolyte solution, the potentials of the Pt/electrolyte interface and the Si/electrolyte interface are observed to shift in opposite directions. Hydrogen peroxide is spontaneously reduced on the Pt surface. Meanwhile, the electrons in Si will tunnel to Pt and the residual holes will oxidize Si along the three-phase interface. In this way, the micro-/nanostructures on the Pt metallized imprint mold are transferred to the Si wafer.     

Applying magnetic soft mold imprint technology with ultraviolet light‐emitting‐diode array on the fabrication of microlens arrays

This study proposed a novel technology, which uses exposed technology with ultraviolet light‐emitting‐diode (UV‐LED) arrays and the polydimethylsiloxane (PDMS) magnetic flexible soft mold imprint technology, to develop exposed equipments with UV‐LED arrays. This study used magnetic soft mold imprint technology to replicate the structure of microlens, providing a more effective alternative for imprint technology and application. The measurement results showed that PDMS with magnetic iron powder can precisely cast mold to replicate the structures of microlens. Electromagnetic plates were used to control even imprinting with magnetic force, in order to fill the mold of micro‐structure of the photo‐resist. Magnetic iron powder was added to PDMS to produce composite material, which can effectively avoid the transformation of pure PDMS during soft mold imprinting, and increase mechanical strength. Magnetic PDMS soft mold is easy to make, and the casting time is short, so that costs can be effectively reduced. Also with advantages of less free energy on its surface, and unlikely to adhere to the photo‐resist during imprinting, it can be combined with electromagnetic plates evenly to control the magnetic soft mold. This imprinting technology is a big advantage to the production process of micro‐structures during imprinting. Copyright © 2009 John Wiley & Sons, Ltd.     

On the mechanism of low-pressure imprint lithography: capillarity vs viscous flow

Dominant mechanisms in low-pressure imprint lithography processes have been identified for the regimes that are definable in terms of applied pressure, temperature, and mold material characteristics. Capillarity is found to be the dominant mechanism at high temperature and low pressure when stiff, hard molds are used. In the case of flexible thin-film ( approximately 20 microm) molds, both the capillarity and the viscous flow are involved. Both mechanisms are operative in the initial stage of the imprinting, but the capillarity takes over as time progresses.     

Study on residual stresses of thin-walled injection molding

The residual stresses of the thin-walled injection molding are investigated in this study. It was realized that the behavior of residual stresses in injection molding parts was affected by different process conditions such as melt temperature, mold temperature, packing pressure and filling time. The layer removal method was used to measure the residual stresses at a thin-walled test sample by a milling machine. This simple method was demonstrated to be adequate for a thin-walled part. Moldings under different conditions were investigated to study the effects of the process conditions on the residual stresses of a thin-walled product using the elastic and viscoelastic models. The mold temperature was found to affect the size of the core region and residual stress on the surface layer of a thin-walled part in our studied range. The packing pressure was insensitive to the residual stresses in the studied high-pressure range. The residual stresses predicted by the viscoelastic model are about the same level and trend as compared to the experimental measurement.     

Spatially-separated and photo-enhanced semiconductor corrosion processes for high-efficient and contamination-free electrochemical nanoimprint lithography

Free of any thermoplastic or photocuring resists, electrochemical nanoimprint lithography (ECNL) has emerged as an alternative nanoimprint way to fabricate three-dimensional micro/nano-structures (3D-MNSs) directly on a semiconductor wafer by a spatially-confined corrosion reaction induced by the metal/semiconductor contact potential. However, the consumption of electron acceptors in the ultrathin electrolyte between imprint mold and semiconductor wafer will slow down or even cease the corrosion rate. To solve this problem, we change the short-circuited corrosion cell into a spatially-separated primary cell: the imprint mold compacted gallium arsenide (GaAs) wafer in the anodic chamber while the platinum (Pt) plate connected to the imprint mold in the cathodic chamber. Thus, the GaAs corrosion rate will be stabilized in its limiting steady-state current density because of the abundant source of electron acceptors in the catholic chamber. The corrosion processes can be photo-enhanced by white-light illumination. Consequently, both the accuracy and the efficiency are promoted dramatically, which are demonstrated by the excellent performance of the fabricated binary optical elements. Moreover, the contamination problem caused by the electron acceptors is totally avoided. All the results prove that this novel ECNL mode is competitive and prospective in imprinting 3D-MNSs directly on semiconductor wafer.

     

Fluorinated organic-inorganic hybrid mold as a new stamp for nanoimprint and soft lithography

In this paper, we fabricated a fluorinated organic-inorganic hybrid mold using a nonhydrolytic sol-gel process which can produce a crack-free mold without leaving any trace of solvent. No special chemical treatment of a release layer is needed because the fluorinated hybrid mold has fluorine molecules in the backbone. The other advantages of the hybrid mold are thermal stability over 300 degrees C. The hybrid mold produced from UV nanoimprint lithography (UV-NIL) was used as a mold for the next UV-NIL and soft lithography without requiring use of an antisticking layer. Various nanometer scale patterns including sub-100 nm patterns could be obtained from the hybrid mold. Nanopatterning processes using this low-cost mold are useful because they preserve the expensive original master.     

The application of elastic auxiliary air bag imprinting technology to the development of linear gradient micro‐structure replication processes

This study proposed an innovative imprinting process technology using an elastic auxiliary air bag imprinting mechanism, combined with poly(dimethylsiloxane) (PDMS) soft mold and UV–LED array photocuring equipment, to evenly imprint and reproduce a micro‐lens mold into a gradient micro‐lens structure in order to achieve linear gradient in micro‐structures. The structure defined by the proposed process technology is more continuous and smoother than that of the current semi‐conductor gray scale photomasking process technology. The process is simpler, faster, and less expensive and is a more effective option for satisfying the formation requirements of different structural heights. This study used pressure‐sensitive film to test and discuss gradient imprint force distribution. The test results suggested that different spring constants led to tilt impressions, which caused the PDMS soft mold to contact with the substrate surface at different pressures. The color depth distribution of the pressure‐sensitive film testing results indicated that the spring constant and pressure distribution were somewhat correlated. Hence, the height of structural formation can be controlled by different spring constants. Finally, SEM and surface profiler measurements suggested that different spring constants can result in different tilt degrees of the imprinting platform of air bag imprinting applications for the imprinting and reproduction of smooth, continuous micro‐lens array structures of different heights. Copyright © 2012 John Wiley & Sons, Ltd.     

A bio-imprinted ascorbate oxidase biosensor

Interest in bio-imprinting techniques has increased because it allows some stability characteristics of enzymes to be improved. In this study, we developed a simple way to improve the thermal and pH stabilities of ascorbate oxidase biosensor. The membrane of a Clark oxygen electrode was coated by a bioactive layer containing ascorbate oxidase and gelatin cross-linked by glutaraldehyde. Citrate was used to imprint the ascorbate oxidase molecularly. The optimum temperature and pH of both unmodified and citrate modified biosensors were investigated, by comparing their resulting stability. Also, calibration graphs and operational stabilities were compared with each other. The results showed that this simple way should be used to improve the stabilities of a biosensor.     

Fabrication of optical waveguide devices using gas‐assisted UV micro/nanoimprinting with soft mold

Wavelength limitation and diffraction of light are the bottlenecks encountered in the production of structures by conventional lithography. Nano‐imprinting has been a potential process for mass production of nanometer structures at low cost. This paper reports an innovative process to replicate the ridge‐shaped microstructures on the silicon mold onto the photoresist using gas‐assisted pressing mechanism and soft mold. The microstructures on the silicon mold are replicated unto PC films. The soft mold is obtained by casting the PDMS with the PC film as templates, PDMS mold and UV‐curable photoresist are brought into contact, and are pressurized by gas and cured by UV‐light at the same time. After curing, structures for optical wave guilding can be obtained, In this process, through the control of gas pressure, the residual layer of the ridge‐shaped component for light guilding can eliminated. Etching is no longer needed to get rid of the residual layer. This process is effective for mass production for replication of microstructures at low cost. Copyright © 2007 John Wiley & Sons, Ltd.     

Characterization of deformation in injection molded parts after packing and cooling

Residual stresses which are developed in injection molded parts affect dimensional accuracy and mechanical properties of the final products. To predict the residual stresses in injection molded parts, three stages of injection molding, i. e., filling, packing, and cooling, must be taken into consideration for the thermal and flow analyses. Flow field anaysis for filling and postfilling stages has been carried out by using the control volume based FEM/FDM hybrid method. The generalized Hele-Shaw flow is assumed. Compressibility of the Polymer melt is considered during packing and cooling stages. Modified Cross model is employed to reflect the dependency of the viscosity upon shear rate and temperature. An equation of state proposed by Tait offers an efficient means to describe pvt-relationship of the polymer. Variations in temperature and pressure fields are obtained over all stages by the numerical flow analysis and used as input data for the stress analysis of the part. Plane stress elements, such as shell elements, are used for finite element stress analysis of injection molded parts with appropriate boundary conditions both in the mold and after ejected from the mold. The numerical analysis yields useful information which is relevant to the mechanical properties of the final products, e. g., residual stress distribution, shape of deformation, displacement field, and strain distribution.     

Benchtop micromolding of polystyrene by soft lithography

Polystyrene (PS), a standard material for cell culture consumable labware, was molded into microstructures with high fidelity of replication by an elastomeric polydimethylsiloxane (PDMS) mold. The process was a simple, benchtop method based on soft lithography using readily available materials. The key to successful replica molding by this simple procedure relies on the use of a solvent, for example, gamma-butyrolactone, which dissolves PS without swelling the PDMS mold. PS solution was added to the PDMS mold, and evaporation of the solvent was accomplished by baking the mold on a hotplate. Microstructures with feature sizes as small as 3 μm and aspect ratios as large as 7 were readily molded. Prototypes of microfluidic chips made from PS were prepared by thermal bonding of a microchannel molded in PS with a flat PS substrate. The PS microfluidic chip displayed much lower adsorption and absorption of hydrophobic molecules (e.g. rhodamine B) compared to a comparable chip created from PDMS. The molded PS surface exhibited stable surface properties after plasma oxidation as assessed by contact angle measurement. The molded, oxidized PS surface remained an excellent surface for cell culture based on cell adhesion and proliferation. To demonstrate the application of this process for cell biology research, PS was micromolded into two different microarray formats, microwells and microposts, for segregation and tracking of non-adherent and adherent cells, respectively. The micromolded PS possessed properties that were ideal for biological and bioanalytical needs, thus making it an alternative material to PDMS and suitable for building lab-on-a-chip devices by soft lithography methods.     

Thermal degradation of environmentally degradable poly(hydroxyalkanoic acid)s

Aliphatic polyesters have attracted industrial attention as environmentally degradable thermoplastics to be used for a wide range of applications. Besides intensive studies on the biodegradability of aliphatic polyesters, understanding of the thermal stability has importance for processing, application, and recycling. The details of thermal degradation processes of five types of aliphatic polyesters; namely, poly(L-lactide), poly(3-hydroxybutyric acid), poly(4-hydroxybutyric acid), poly(delta-valerolactone), and poly(epsilon-caprolactone), were investigated by means of several thermoanalytical techniques under both isothermal and non-isothermal conditions. In this feature article, the thermal degradation behaviors of aliphatic polyesters with different numbers of carbon atoms in the main chain of the monomeric unit are reviewed. In addition, the effects of chain-end structure and residual metal compounds on the thermal degradation processes of aliphatic polyesters consisting of hydroxyalkanoic acid monomeric units are presented. Schemes of thermal degradation reaction of poly(hydroxyalkanoic acid)s.     

Thermal behavior of iminodiacetic acid and its disodium salt

The thermal properties of iminodiacetic acid (IDA) and its disodium salt were investigated by DTA, TG and static heating. The gaseous evolved products were analysed by chromatography in order to follow the thermal process. The heating of the samples was stopped at characteristic decomposition steps and the residual substances were investigated by IR spectroscopy. The obtained data suggest the processes of decomposition for these compounds.     

Research and application of a new rapid heat cycle molding with electric heating and coolant cooling to improve the surface quality of large LCD TV panels

The usage of rapid heat cycle molding (RHCM) has gained increasing attention in overcoming the limits of conventional injection molding (CIM) and improving the surface quality and mechanical properties of molded plastic products. In RHCM, the vario‐thermal mold temperature control system is the key technique because it directly affects the molding cycle time and the final part quality. In this study, a new RHCM technology with electric heating and coolant cooling was studied in detail. Two different RHCM mold structures for a large LCD TV panel were proposed and designed. The numerical simulation method was used to analyze the thermal response of the mold cavity surface at the heating stage and the thermal response of the resin melt at the cooling stage. The heating/cooling efficiency of the proposed electric heating RHCM system was evaluated. The thermal expansion analysis of mold cavity was implemented and the fixation of the cavity in molds was also optimized. The results showed that the electric‐heating mold with a separate cooling plate can efficiently enhance the heating efficiency. The thermal expansion of the cavity surface can be reduced by increasing the alleviating‐gap between the cavity and the cavity‐retainer plate. Then, the service lifetime of the electric‐heating mold can be improved. A RHCM production line with electric heating for the large LCD TV panel was constructed. Both the simulation and test production results indicate that the proposed electric heating RHCM technique can realize high‐temperature injection molding without increasing the molding cycle time. The surface appearance of the LCD TV panels was dramatically improved and the surface marks that usually occur in CIM process were eliminated completely. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal and photochemical oxidation of polypropylene. Influence of residual catalyst levels in unstabilised diluent and gas phase polymers

The thermal and photochemical behaviour of several unstabilised polypropylene samples made experimentally by a gas phase (GP) process has been examined and compared with those of samples made commercially by the normal diluent phase (DP) process. Higher levels of residual catalysts are shown to have a marked effect on both the thermal and photochemical processes. The initial autocatalytic growth of hydroperoxides, observed during both oven-ageing and melt processing, is considerably suppressed in GP polymer when compared to DP polymers probably because higher levels of residual catalysts are ionically inducing the decomposition of hydroperoxides thereby accelerating the subsequent thermal and photochemical breakdown of the polymer. Pre-treatment of both types of polymers with alcoholic phosphoric acid solution or sulphur dioxide produces some interesting and markedly different effects on photostability. Of the catalyst residues present, variation in titanium levels seems to be important in controlling thermal and photochemical stability: the effect of aluminium is seen but is as yet undefined.     

Construction of Pre-Deformed Shapes for Rapid Tooling in Injection Molding

The major issues in the development of injection molding technology include the progress in CAE and the developments in tool design methodology such as rapid tooling. The applicability of rapid tooling in injection molding was examined using unbalanced cooling to analyze the warpage and shrinkage. Moldflow Plastics Insight simulation software was used for the deformation calculations with different mold thermal conductivities. It can be concluded that the decreasing mold thermal conductivity will dramatically increase the volumetric shrinkage and the warpage as well. Because of these effects, it is of fundamental importance to compensate for the shrinkage and warpage, so in the paper a new design methodology is suggested for rapid tooling, which is based on the pre-deformed model.     

A Simple Imprint Method for Multi‐Tiered Polymer Nanopatterning on Large Flexible Substrates Employing a Flexible Mold and Hemispherical PDMS Elastomer

This work reports a facile method to fabricate multi‐tiered polymer nanopatterns on SU‐8 by the combination of imprint‐ and photo‐lithography. First, SU‐8 is imprint patterned using a polymeric flexible mold with an anti‐adhesion coating that is deposited on a transparent and flexible substrate, at room temperature under low pressure. Next, the resulting SU‐8 nanopatterns are exposed to UV light through a chromium mask by a photolithographic process. Removal of the unexposed SU‐8 leaves behind multi‐tiered structures. The use of a hemispherical poly(dimethylsiloxane) pad facilitates the evacuation of trapped air during the imprinting process. Line/space patterns of 500 nm with the smallest line width of 200 nm were homogeneously imprint‐patterned on SU‐8 on a large flexible substrate, and three‐tiered structures, ranging in thickness from 300 nm to 2 µm, were successfully formed.

     

Simple,low‐cost fabrication of semi‐circular channel using the surface tension of solder paste and its application to microfluidic valves

This work presents a simple, low‐cost method to fabricate semi‐circular channels using solder paste, which can amalgamate the cooper surface to form a half‐cylinder mold using the surface tension of Sn–Pd alloy (the main component in solder paste). This technique enables semi‐circular channels to be manufactured with different dimensions. These semi‐circular channels will then be integrated with a polymethylmethacrylate frame and machine screws to create miniaturized, portable microfluidic valves for sequential liquid delivery and particle synthesis. This approach avoids complicated fabrication processes and expensive facilities and thus has the potential to be a useful tool for lab‐on‐a‐chip applications.