Prototyping of microfluidic systems with integrated ... - DTU Nanotech

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26 Polymer materials – mainly Topas parts are used as masks in the following etching of the silicon layer beneath. In recent years, SU-8 has been used directly for microfluidic channels and optical waveguides using multiple layers to create more complex geometries, and for closing channels [23]. Also, sensors like cantilevers have been fabricated in SU-8 [24]. 3.3 Polymers in microfluidics An ever-increasing number of polymers of all the three types listed above are being used in prototyping and manufacturing of microfluidic systems. The requirements, such as structural stability, chemical resistance, or optical transparency, for a specific application, will limit the number of polymers which are applicable in the given situation. A small number of well-known, cheap and readily available polymer materials are used in a large number of applications, especially in the prototyping phase. The advantage of using these polymers is evident: Due to the extensive documentation and experience, processing of theses polymers is less time-consuming than working with less known polymers. For a detailed comparison of these polymers, the reader is referred to [25]. These commonly used polymers include PMMA, which is typically used in all-polymer-systems, where the entire system is made in the same material. Also PDMS is widely used [26–29], due to its excellent properties in the many areas listed above. PDMS systems, however, are often bonded on top of e.g. glass substrates due to its lack of structural stability. 3.4 Cyclic Olefin Copolymer (COC)/Topas A considerable part of this thesis is centered around the cyclic olefin copolymer Topas, which is a registered trademark of, and manufactured by, Topas Advanced Polymers GmbH [30]. The reason for this fact is that Topas possesses many properties which are potentially useful in prototyping and manufacturing of microfluidic and lab-on-a-chip systems. In this section these properties will be presented, and a comparison with standard polymers like PMMA will be made. Topas is an acronym for Thermoplastic Olefin Polymer of Amorphous Structure, which is quite descriptive of the polymer in question, since Topas is an amorphous thermoplastic containing an olefin monomer (a
3.4 Cyclic Olefin Copolymer (COC)/Topas 27 monomer with a double carbon-carbon bond, also known as alkene), in this case ethylene. Topas belongs among the cyclic olefin copolymers, which is a relatively new class of thermoplastics with good optical properties [31]. Apart from Topas, cyclic olefin copolymers are commercially available from a couple of manufacturers: Zeonex (Nippon Zeon, Japan), Arton (Japan Synthetic and Rubber, Japan) and Apel (Mitsui, Japan). Topas is synthesised from ethylene and cyclopentadiene, which combine to form norbonene, one of the two monomers in the copolymer, the other being ethylene. Polymerisation takes place using metallocene catalysts [32]. The structure formula of Topas is shown in Fig. 3.1. Figure 3.1: The structure formula of the cyclic olefin copolymer Topas. The two monomers are ethylene, left, and norbonene, right. The copolymer is synthesised by metallocene catalysis. 3.4.1 Glass transition temperature and viscosity By varying the ratio between the two monomers the glass transition temperature can be varied from around 60℃ to above 160℃. The correlation between the norbonene content and the glass transition temperature is shown in Fig. 3.2. The four-digit data labels are the different grades of Topas numbered after two characteristic properties: The first two digits indicate the viscosity number VN which is related to the molecular weight, while the two last digit is an indication of the heat deflection temperature. An overview of the most common Topas grades is found in Table 3.1. The viscosity of the polymer is related to the length of the polymer backbone, so that longer chains will yield a higher viscosity of the substance. Intuitively, this seems right, since longer chains are more entangled with each other than shorter ones. The viscosity number indicated in the grade number is also referred to as the reduced viscosity, and is the ratio of the relative viscosity increment to the mass concentration of the polymer in a solution. It has the unit of inverse density, ml/g and is defined as:
Page 1 and 2: Prototyping of Microfluidic Systems
Page 3 and 4: Preface This thesis is one of the r
Page 5 and 6: joining the substrate, optical laye
Page 7 and 8: Disse metoder inkluderer: • Mikro
Page 9 and 10: Many thanks to the collaborators in
Page 11 and 12: microfluidic systems. In Klavs Jens
Page 13 and 14: Contents Preface i Abstract ii Resu
Page 15 and 16: CONTENTS xiii 5 Optical waveguides
Page 17 and 18: Chapter 1 Introduction In the last
Page 19 and 20: 1.1 Downscaling 3 Figure 1.1: Scali
Page 21: 1.2 Prototyping of microfluidic sys
Page 24 and 25: 8 Theoretical aspects - microfluidi
Page 26 and 27: 10 Theoretical aspects - microfluid
Page 38 and 39: 22 Polymer materials - mainly Topas
Page 52 and 53: 36 Fabrication methods results are
Page 54 and 55: 38 Fabrication methods An impressiv
Page 56 and 57: 40 Fabrication methods Average roug
Page 58 and 59: 42 Fabrication methods a b c d e 1m
Page 60 and 61: 44 Fabrication methods Generally, t
Page 62 and 63: 46 Fabrication methods branch. Sec-
Page 64 and 65: 48 Fabrication methods and the heig
Page 66 and 67: 50 Fabrication methods Topas on Top
Page 68 and 69: 52 Fabrication methods Table 4.2: C
Page 70 and 71: 54 Fabrication methods Figure 4.8:
Page 72 and 73: 56 Fabrication methods that the str
Page 74 and 75: 58 Fabrication methods the excimer
Page 76 and 77: 60 Fabrication methods 500 µm 500
Page 78 and 79: 62 Fabrication methods wedge tests
Page 81 and 82: Chapter 5 Optical waveguides in Top
Page 83 and 84: 5.1 Waveguide fabrication 67 It sho
Page 85 and 86: 5.2 Propagation loss measurements 6
Page 87 and 88: 5.3 Thermal treatment of the surfac
Page 93 and 94:
5.4 Optical cuvette absorbance meas
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5.4 Optical cuvette absorbance meas
Page 97 and 98:
5.5 A refractive index sensor 81 fr
Page 99 and 100:
5.5 A refractive index sensor 83 a
Page 101 and 102:
5.6 Summary 85 5.5.3 Improvements I
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Until further notice, Chapter 6 is
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96 Discussion and outlook transpare
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References [1] A. Manz, N. Graber,
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REFERENCES 101 [20] David Walton an
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REFERENCES 103 [41] Kiha Lee and Da
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REFERENCES 105 prototyping of polym
Page 117 and 118:
REFERENCES 107 [81] M. Grumann, J.
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