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Jena R.K.,Alliance for Manufacturing and Technology | Jena R.K.,Nanyang Technological University | Yue C.Y.,Alliance for Manufacturing and Technology | Yue C.Y.,Nanyang Technological University | And 2 more authors.
Sensors and Actuators, B: Chemical | Year: 2011

This paper reports on the development and application of a permanent surface modification technique (photo-grafting) as an improved method for bonding COC (TOPAS) microfluidic substrates with a cover plate without affecting the channel integrity. This technique not only helps to increase the bond strength of the original device but also makes the surface hydrophilic which is essential for quick fluid flow while passing analytes through the device. The bond strength of the modified and unmodified chips was measured using the tensile and peel tests. It was observed that the bond strength of the modified chips has increased approximately 6 times to 1.18 (±0.08) MPa compared to 0.21 (±0.05) MPa for the unmodified chip. The modified surface was evaluated using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and water contact angle measurement. The contact angle of the modified surface decreased to 20 ± 5° from 85 ± 3° for the untreated substrate. Scanning electron microscope and confocal microscope examinations of cross-sectional profiles of the bonded chips indicated that the integrity of the channel features was successfully preserved. © 2011 Elsevier B.V.


Jena R.K.,Alliance for Manufacturing and Technology | Jena R.K.,Nanyang Technological University | Chester S.A.,Alliance for Manufacturing and Technology | Chester S.A.,Massachusetts Institute of Technology | And 8 more authors.
Sensors and Actuators, B: Chemical | Year: 2011

Amorphous cyclic olefin copolymers (COCs) are beginning to be used for making microfluidic devices for life science applications. Typically, both micro-scale and nano-scale channels are imprinted onto the copolymer by hot embossing. However, optimal manufacturing process conditions will only be possible if the COCs thermo-mechanical behavior is experimentally well characterized, mathematically modeled, and implemented in a numerical simulation. We have conducted large-strain compression experiments on two commercial grades of COCs: TOPAS-8007, and TOPAS-6015 in a wide temperature, and strain rate range. A constitutive theory and numerical implementation developed by Srivastava et al. [1] was applied to model the behavior of TOPAS. We have employed that numerical implementation, together with the material parameters for TOPAS determined here, to predict the response of TOPAS in the following microfluidic fabrication operations: (i) micro-scale hot embossing on TOPAS-8007 to replicate a micro-chip; and (ii) for sealing the channels in the micro-chip: (a) thermal bonding of an embossed chip of TOPAS-8007 with a cover plate of TOPAS-8007; and (b) thermal bonding of an embossed chip of TOPAS-6015 with a cover plate of TOPAS-8007. We show that the model can provide a simulation capability for estimation of the processing parameters for hot embossing and thermal bonding. © 2010 Elsevier B.V. All rights reserved.


Jena R.K.,Alliance for Manufacturing and Technology | Jena R.K.,Nanyang Technological University | Chen X.,Alliance for Manufacturing and Technology | Chen X.,Nanyang Technological University | And 3 more authors.
Journal of Micromechanics and Microengineering | Year: 2011

Transparent, amorphous cyclic olefin copolymers (COCs) have been frequently used for the fabrication of microfluidic devices using a hot embossing technique for numerous applications. In hot embossing, the polymer is deformed near its glass transition temperature (Tg), i.e. between Tg and Tg + 60 °C where the viscoelastic properties of the material are dominant. The proper characterization of the viscoelastic properties is of interest as this can lead to a better understanding of polymer flow behaviour during microfabrication. Furthermore, the ability to model its rheological behaviour will enable the prediction of the optimal hot embossing processing parameters. We performed small amplitude oscillatory shear experiments on four grades of COCs, TOPAS-8007, TOPAS-5013, TOPAS-6015 and TOPAS-6017, in order to characterize their flow behaviour. The experiments were conducted within the frequency range from 0.01 to 500 Hz at between Tg + 20 and Tg + 60 °C. The flow properties could be represented using a generalized Maxwell viscoelastic constitutive model with Williams-Landel-Ferry-type temperature dependence. Good fit of the experimental data was obtained over a wide range of temperatures. The model could be coupled with ABAQUS finite element software to predict the optimal conditions for fabricating a capillary electrophoresis micro-chip on a TOPAS-5013 substrate by hot embossing. © 2011 IOP Publishing Ltd.


Jena R.K.,Alliance for Manufacturing and Technology | Jena R.K.,Nanyang Technological University | Chen X.,Alliance for Manufacturing and Technology | Chen X.,Nanyang Technological University | And 4 more authors.
Polymer Testing | Year: 2010

TOPAS is a copolymer that is commonly used for making micro fluidic devices for life science applications using the hot embossing technique. In this technique, both micro-scale and nano-scale channels are imprinted onto the copolymer at temperatures near or above its glass transition temperature (Tg). The viscosity of the polymer plays a dominant role in microchannel replication, and the ability to model the polymer rheological flow behavior will enable understanding and prediction of the hot embossing process. Typically in hot embossing, the polymer is deformed at between Tg to Tg + 50 °C and it is difficult to obtain the rheological properties within this temperature range using conventional viscometers. In this paper, the viscosity was measured for four different grades of TOPAS, a cyclic olefin copolymer (COC), namely TOPAS-8007, TOPAS-5013, TOPAS-6015 and TOPAS-6017, in a temperature range from Tg + 20 °C to Tg + 60 °C which is of most relevance to hot embossing. Measurements were made in the dynamic mode and the Cox-Merz rule was applied to obtain the shear viscosity versus shear rate data. The Carreau-Yasuda viscosity model with WLF-type temperature dependence fits the experimental data reasonably well at high shear rates in this temperature range. However, there was significant discrepancy between the model and the experimental data at low shear rates. In contrast, it was found that the Cross model can capture the experimental data reasonable well even at low shear rates. Therefore, the rheological behavior of COC can be represented using the Cross model. © 2010 Elsevier Ltd. All rights reserved.


Jena R.K.,Alliance for Manufacturing and Technology | Jena R.K.,Nanyang Technological University | Yue C.Y.,Alliance for Manufacturing and Technology | Yue C.Y.,Nanyang Technological University | And 2 more authors.
Microsystem Technologies | Year: 2012

Microfabrication of polymer using hot embossing technique are becoming increasingly important and considered as low-cost alternative to the silicon or glass-based micro-electro-mechanical systems technologies. This report is based on a parametric study on the hot embossing of cyclic olefin copolymer (COC) (Topas-6015 grade). The key process parameters in hot embossing such as the embossing temperature, load, the holding time and the demolding temperature significantly impact the quality of the embossed product. The work was performed to understand the influence of the various process parameters on the embossed micro-size patterns with the aim to develop the capability for microfluidic devices manufacturing. Microembossed polymer replicates were measured using a PLμ confocal microscope and inspected using a scanning electron microscope. It was established that the optimal embossing temperature for COC is 10°C above its T g, while an optimal embossing load of 2.94 kN and holding time of 180 s are required. We have also demonstrated the effective sealing of the microchannel without destroying the channel integrity by thermal bonding technique. © Springer-Verlag 2011.


Jena R.K.,Alliance for Manufacturing and Technology | Jena R.K.,Nanyang Technological University | Yue C.Y.,Alliance for Manufacturing and Technology | Yue C.Y.,Nanyang Technological University | And 4 more authors.
Sensors and Actuators, B: Chemical | Year: 2010

The development of a one-step process for producing high fidelity hot-embossed cyclic-olefin co-polymer (COC) based microfluidic devices without the need for pre-annealing the base polymer substrate/film is outlined. This was achieved through proper selection of the hot-embossing conditions that was based on an in-depth understanding of the fundamental factors which affect the replication accuracy of microchannels during the hot-embossing process. An important factor that is commonly overlooked in the hot-embossing of films (typically with thicknesses less than 1 mm) is the existence of polymer chain orientation. Generally, polymer films used for hot-embossing are not pre-annealed to minimize residual stresses and remove any chain orientation that may be present, and this affects the replication accuracy. In contrast, polymer substrates (typically with thicknesses more than 1 mm) that are used for hot-embossing to produce microfluidic devices need to be pre-annealed to minimize residual stresses and remove any chain orientation. Processing of the latter thus required an additional step. The avoidance of such pre-annealing may affect the replication accuracy. In the present work, it was demonstrated that microfluidic devices with high fidelity microchannels could be produced using a single-step hot-embossing process based on knowledge of the influence of embossing temperature, embossing pressure, embossing time and polymer chain orientation in the film/substrate on micro-replication. © 2010 Elsevier B.V.


Jena R.K.,Alliance for Manufacturing and Technology | Jena R.K.,Nanyang Technological University | Yue C.Y.,Alliance for Manufacturing and Technology | Yue C.Y.,Nanyang Technological University | And 5 more authors.
Sensors and Actuators, B: Chemical | Year: 2012

In the fabrication of microfluidic devices by hot embossing, secondary molds made from epoxy and other polymeric materials with high T g are commonly used in lab-scale research and for short production runs of several hundred products. However, few studies have been conducted to compare the performance and efficacy of such molds compared to the master silicon mold. To allow such molds to be exploited fully, this study investigates the performance of silicon, epoxy and COC (TOPAS-6017 grade) molds to fabricate microchannels on COC (TOPAS-8007 grade) substrate using hot embossing. The degree of filling of the mold cavity during microfabrication was assessed. At the optimum embossing conditions (i.e. 100 °C, 2.94 kN load and 5 min loading time), all three molds had similar performance in terms of replication fidelity. However, at sub-optimum conditions (e.g. 80 °C), the silicon mold was the best in terms of mold cavity filling followed by COC and epoxy. For surface roughness and friction coefficient which are important factors affecting tool life, it was found that epoxy mold gives the lowest values followed by COC and silicon. The surface energy determined using contact angle measurements gave a similar trend with epoxy having the lowest surface energy (28 dyne/cm), followed by COC (33.52 dyne/cm) and silicon (71.63 dynedyne/cm). A lower surface energy will result in lower adhesion and friction coefficient between the polymer and mold, resulting in easier demolding. © 2012 Elsevier B.V. All rights reserved.


Rosli S.E.,Alliance for Manufacturing and Technology | Mohd-Norddin M.N.A.,Alliance for Manufacturing and Technology | Jaafar J.,Alliance for Manufacturing and Technology | Sudirman R.,UniversitiTeknologi Malaysia
Proceedings of the 2013 IEEE 7th International Power Engineering and Optimization Conference, PEOCO 2013 | Year: 2013

The purpose of this research is to develop an optimum of anode catalyst loading based on modified sulfonated poly(ether ether ketone) (SPEEK) with charged surface modifying macromolecules (cSMM) membrane. The preparation method of catalyst ink and membrane electrode assembly (MEA) was based on Dr. Blade method and hot pressing by using catalyzed diffusion media (CDM) method. The effect of 30% and 40% PtRu in 2, 4 and 6 mgcm-2 of catalyst loading has been investigated with a fuel cell assembly. The optimization of anode catalyst loading will enhance the DMFC performance. It was found, the best optimal anode catalyst loading was 4 mgcm-2 for this application. Therefore, 4 mgcm-2 is the best catalyst loading. © 2013 IEEE.


PubMed | Alliance for Manufacturing and Technology
Type: | Journal: Health care management science | Year: 2016

This paper considers how to schedule appointments for outpatients, for a clinic that is subject to appointment lead-time targets for both new and returning patients. We develop heuristic rules, which are the exact and relaxed appointment scheduling rules, to schedule each new patient appointment (only) in light of uncertainty about future arrivals. The scheduling rules entail two decisions. First, the rules need to determine whether or not a patients request can be accepted; then, if the request is not rejected, the rules prescribe how to assign the patient to an available slot. The intent of the scheduling rules is to maximize the utilization of the planned resource (i.e., the physician staff), or equivalently to maximize the number of patients that are admitted, while maintaining the service targets on the median, the 95th percentile, and the maximum appointment lead-times. We test the proposed scheduling rules with numerical experiments using real data from the chosen clinic of Tan Tock Seng hospital in Singapore. The results show the efficiency and the efficacy of the scheduling rules, in terms of the service-target satisfaction and the resource utilization. From the sensitivity analysis, we find that the performance of the proposed scheduling rules is fairly robust to the specification of the established lead-time targets.


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