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Micro wetting system by controlling pinning and capillary forces
Microelectronic Engineering 83 (2006) 1280–1283 www.elsevier.com/locate/mee
Micro wetting system by controlling pinning and capillary forces Takayoshi Niiyama, Akira Kawai
*
Department of Electrical Engineering, Nagaoka University of Technology 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan Available online 20 February 2006
Abstract In the recent years, wetting micro systems acting in liquid environment have been recognized as one important technology in chemical, bio and relative fields. In this regard, the micro wetting behaviors become major factors in controlling the liquid flow artificially in the micro tube, which are mainly affected by the pinning effect, capillary force, Laplace force, convection and so on. The purpose of our study is to realize the drastic control method of the wetting processes based on pinning effect and capillary forces. In this study, in order to analyze the wetting behavior precisely, we observed the spontaneous wetting processes depending on the micro pattern arrangement. From the results, the wetting phenomena can be clearly observed due to the pinning effect and capillary force. Moreover, we also found that the deionized water (DI-water) is more likely to spread on a hydrophilic surface compared with that on a hydrophobic surface. Therefore, we discuss the wetting behavior in this investigation on thermodynamics. We can control the wetting behavior practically by designing the surface energy of the resist patterns and its arrangements. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Micro wetting; Pinning effect; Capillary force; Wetting property; Resist
1. Introduction
2. Experiment
In the recent years, wetting micro systems acting in liquid environment have been recognized as one important technology in chemical, bio and relative fields. In this regard, the micro wetting behaviors become major factors in controlling the liquid flow artificially in the micro tube, which are mainly dependent on the pinning effect, capillary force, Laplace force, convection and so on [1,2]. The purpose of our study is to realize the drastic control method of liquid flow and wetting processes based on the pinning effect, the capillary force and so on. In this study, we observed the spontaneous wetting processes depending on the micro pattern arrangement. Moreover, we also discuss the wetting process on the point of the wetting difference, hydrophilic and hydrophobic surfaces.
2.1. Sample preparation
*
Corresponding author. E-mail address: [email protected] (A. Kawai).
0167-9317/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2006.01.132
The dry film resist (DFR) patterns were used as the micro test patterns. The width and thickness of the resist patterns were 50lm. The DFR (consisting of phosphoric acid resin, negative type) was laminated on a Cu plated SUS substrate. In order to obtain the hydrophilic surface, the DFR patterns exposed to Ar (purity:99.9%) ion plasma for 10 s. The acceleration voltage and the current were 0.5 kV and 30 mA. The deionized water was used as the test liquid. In this study, the DI water was sessile dropped on the resist pattern edge by using the DI-water micro syringe. In order to observe the wetting processes on the resist pattern simultaneously, the optical microscope and the recording system were used. The goniometer made by Kyowa Interface Science Co., LTD. (CA-DT) was used to evaluate the surface energy of the sample surfaces.
T. Niiyama, A. Kawai / Microelectronic Engineering 83 (2006) 1280–1283
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2.2. Surface energy measurement In order to discuss the pinning and capillary phenomena in thermodynamics, surface energy of the samples was measured with sessile drop method [3–5]. The test liquids were DI-water (cl = 72.8 mJ/m2), diiodomethane (50.8 mJ/m2) and ethyleneglycol (47.7 mJ/m2), of which dispersion and polar components were well known [3]. In this study, surface energy of the Cu substrate and the resist film surface was evaluated. Then, both the surfaces which were exposed to Ar ion plasma were also evaluated. 3. Observation of wetting processes on hydrophilic and hydrophobic surfaces 3.1. In situ observation of wetting behaviors on various resist patterns The photomicrographs of the wetting behavior on L shaped, dot and line patterns fabricated with the DFR are summarized in Table 1. In the case of the L shaped patterns, the spreading of water meniscus is prevented at the pattern corner. Moreover, we can observe the DIwater climbing over the resist patterns, which are arranged in transverse to liquid advancing direction. In the case of the dot pattern array, the pinning effect can
Table 1 Wetting behavior on various DFR patterns
Fig. 1. Spreading distance of DI-water meniscus interposed between micro patterns.
be observed clearly. The water drop is prevented to spread at the edge of the dot patterns. In the case of the line patterns, the wetting phenomena due to capillary force can be observed. Meanwhile, the capillary force becomes large on the hydrophilic surface compared with
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Differential pressure ΔP [Pa]
that on the hydrophobic surface in both cases of the line and L shaped patterns. 3.2. Wetting speed analysis on various resist patterns As a quantitative analysis, Fig. 1 shows the spreading speed depending on the wetting property of the DFR patterns. The spreading distance x is defined as a distance from the pattern edge to the meniscus edge. In the L shaped and the line patterns, the spreading speed is relatively fast on the hydrophilic surfaces as compared with that on the hydrophobic surfaces. However, in the case of the dot pattern array, the wetting process on both surfaces is almost the same. 4. Thermodynamic analysis of pinning and capillary forces acting on resist patterns 4.1. Surface energy of sample surfaces The component map of surface energy evaluated by the sessile drop method is shown in Fig. 2. From the results, the DFR and Cu substrates indicate hydrophilic property by exposing to the Ar ion plasma. In this study, the differential pressure acting on the resist patterns is evaluated.
DI-water
γ d (mJ /m2)1/2
6
Cu DFR
After
5
Ar+ plasma
4 3 2 0
0
1
2
3
γ
d
Cu DFR 4
5
6
Point 1
4000 3000 2000
Capillary (hydrophilic)
1000
Capillary (hydrophobic)
0
0
5
10
Point 2
15
20
25
Contact angle θp [deg] Fig. 4. Simulation results of differential pressure DP depending on spreading distance x. Surface energy of DI-water = 72.8 mJ/m2, hC = constant, d = 50 lm.
4.2. Differential pressure acting on various resist patterns As the first thermodynamic analysis, we discuss the change of differential pressure DP due to pinning and capillary forces. The plain view of the analysis model for the pinning and capillary forces is shown in Fig. 3. Generally, in these models, the differential pressure of the pinning can be expressed as follows: DP ¼
DP ¼
Before
1
Pinning
5000
4c cos hP ½Pa; d
ð1Þ
where the symbol c is surface energy of the DI-water and hP is contact angle of the DI-water (as shown in Fig. 3a). Moreover, the symbol d represents the distance between the resist patterns. Meanwhile, the differential pressure of the capillary can be expressed as follows:
8 7
6000
7
(mJ /m2)1/2
Fig. 2. Component map of surface energy of samples obtained by sessile drop method.
4c cos hC ½Pa; d
ð2Þ
where hC denotes the contact angle at liquid capillary. The differential pressure of pinning and capillary as a function of the contact angle hP is shown in Fig. 4. From the results, as the the contact angle hP decreases, the effect of the pinning increases gradually by comparing with the capillary effect. Over the cross point, the water drop can spread drastically. 5. Conclusion
(b) Resist pattern
(a) Resist pattern
θp
DI-water ΔP
ΔP θC
d Pinning (dot pattern model) DI-water Capillary (line pattern model) Fig. 3. Simulation models for differential pressure DP.
The drastic control method of liquid flow and wetting processes based on pinning and capillary forces was studied. From in situ observation of the wetting processes, the pinning and capillary forces can be observed clearly due to pattern arrangement. Moreover, the thermodynamic analysis can explain well the wetting phenomena on the various resist patterns. Therefore, we can control the micro wetting behavior easily by designing the surface energy of the resist pattern and its arrangements. We can realize the presence of an artificial blood tube by applying the drastic control method of liquid flow in a micro tube.
T. Niiyama, A. Kawai / Microelectronic Engineering 83 (2006) 1280–1283
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Acknowledgements
References
The present work was partially supported by a Grant-inAid for Scientific Research from Japan Society for the Promotion of Science. (Scientific Research (B) 16360171). This work was also supported by a Grant-in-Aid for Scientific Research, Ministry of Education, Culture, Sports, Science and Technology (Exploratory research, 16656105).
[1] M. Yamanaka, A. Okada, A. Kawai, J. Vac. Sci. Technol. B 22 (6) (2004) 3525. [2] T. Cubaud, M. Fermigier, J. Colloid Interf. Sci. 269 (2004) 171. [3] D.H. Kaelble, J. Appl. Polymer Sci. 18 (1974) 1869. [4] T. Niiyama, A. Kawai, J. Photopolymer Sci. and Tech. 18 (2005) 373. [5] F.M. Fowks, Ind. Eng. Chem. 56 (1964) 40.
Micro wetting system by controlling pinning and capillary forces Takayoshi Niiyama, Akira Kawai
*
Department of Electrical Engineering, Nagaoka University of Technology 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan Available online 20 February 2006
Abstract In the recent years, wetting micro systems acting in liquid environment have been recognized as one important technology in chemical, bio and relative fields. In this regard, the micro wetting behaviors become major factors in controlling the liquid flow artificially in the micro tube, which are mainly affected by the pinning effect, capillary force, Laplace force, convection and so on. The purpose of our study is to realize the drastic control method of the wetting processes based on pinning effect and capillary forces. In this study, in order to analyze the wetting behavior precisely, we observed the spontaneous wetting processes depending on the micro pattern arrangement. From the results, the wetting phenomena can be clearly observed due to the pinning effect and capillary force. Moreover, we also found that the deionized water (DI-water) is more likely to spread on a hydrophilic surface compared with that on a hydrophobic surface. Therefore, we discuss the wetting behavior in this investigation on thermodynamics. We can control the wetting behavior practically by designing the surface energy of the resist patterns and its arrangements. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Micro wetting; Pinning effect; Capillary force; Wetting property; Resist
1. Introduction
2. Experiment
In the recent years, wetting micro systems acting in liquid environment have been recognized as one important technology in chemical, bio and relative fields. In this regard, the micro wetting behaviors become major factors in controlling the liquid flow artificially in the micro tube, which are mainly dependent on the pinning effect, capillary force, Laplace force, convection and so on [1,2]. The purpose of our study is to realize the drastic control method of liquid flow and wetting processes based on the pinning effect, the capillary force and so on. In this study, we observed the spontaneous wetting processes depending on the micro pattern arrangement. Moreover, we also discuss the wetting process on the point of the wetting difference, hydrophilic and hydrophobic surfaces.
2.1. Sample preparation
*
Corresponding author. E-mail address: [email protected] (A. Kawai).
0167-9317/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2006.01.132
The dry film resist (DFR) patterns were used as the micro test patterns. The width and thickness of the resist patterns were 50lm. The DFR (consisting of phosphoric acid resin, negative type) was laminated on a Cu plated SUS substrate. In order to obtain the hydrophilic surface, the DFR patterns exposed to Ar (purity:99.9%) ion plasma for 10 s. The acceleration voltage and the current were 0.5 kV and 30 mA. The deionized water was used as the test liquid. In this study, the DI water was sessile dropped on the resist pattern edge by using the DI-water micro syringe. In order to observe the wetting processes on the resist pattern simultaneously, the optical microscope and the recording system were used. The goniometer made by Kyowa Interface Science Co., LTD. (CA-DT) was used to evaluate the surface energy of the sample surfaces.
T. Niiyama, A. Kawai / Microelectronic Engineering 83 (2006) 1280–1283
1281
2.2. Surface energy measurement In order to discuss the pinning and capillary phenomena in thermodynamics, surface energy of the samples was measured with sessile drop method [3–5]. The test liquids were DI-water (cl = 72.8 mJ/m2), diiodomethane (50.8 mJ/m2) and ethyleneglycol (47.7 mJ/m2), of which dispersion and polar components were well known [3]. In this study, surface energy of the Cu substrate and the resist film surface was evaluated. Then, both the surfaces which were exposed to Ar ion plasma were also evaluated. 3. Observation of wetting processes on hydrophilic and hydrophobic surfaces 3.1. In situ observation of wetting behaviors on various resist patterns The photomicrographs of the wetting behavior on L shaped, dot and line patterns fabricated with the DFR are summarized in Table 1. In the case of the L shaped patterns, the spreading of water meniscus is prevented at the pattern corner. Moreover, we can observe the DIwater climbing over the resist patterns, which are arranged in transverse to liquid advancing direction. In the case of the dot pattern array, the pinning effect can
Table 1 Wetting behavior on various DFR patterns
Fig. 1. Spreading distance of DI-water meniscus interposed between micro patterns.
be observed clearly. The water drop is prevented to spread at the edge of the dot patterns. In the case of the line patterns, the wetting phenomena due to capillary force can be observed. Meanwhile, the capillary force becomes large on the hydrophilic surface compared with
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T. Niiyama, A. Kawai / Microelectronic Engineering 83 (2006) 1280–1283
Differential pressure ΔP [Pa]
that on the hydrophobic surface in both cases of the line and L shaped patterns. 3.2. Wetting speed analysis on various resist patterns As a quantitative analysis, Fig. 1 shows the spreading speed depending on the wetting property of the DFR patterns. The spreading distance x is defined as a distance from the pattern edge to the meniscus edge. In the L shaped and the line patterns, the spreading speed is relatively fast on the hydrophilic surfaces as compared with that on the hydrophobic surfaces. However, in the case of the dot pattern array, the wetting process on both surfaces is almost the same. 4. Thermodynamic analysis of pinning and capillary forces acting on resist patterns 4.1. Surface energy of sample surfaces The component map of surface energy evaluated by the sessile drop method is shown in Fig. 2. From the results, the DFR and Cu substrates indicate hydrophilic property by exposing to the Ar ion plasma. In this study, the differential pressure acting on the resist patterns is evaluated.
DI-water
γ d (mJ /m2)1/2
6
Cu DFR
After
5
Ar+ plasma
4 3 2 0
0
1
2
3
γ
d
Cu DFR 4
5
6
Point 1
4000 3000 2000
Capillary (hydrophilic)
1000
Capillary (hydrophobic)
0
0
5
10
Point 2
15
20
25
Contact angle θp [deg] Fig. 4. Simulation results of differential pressure DP depending on spreading distance x. Surface energy of DI-water = 72.8 mJ/m2, hC = constant, d = 50 lm.
4.2. Differential pressure acting on various resist patterns As the first thermodynamic analysis, we discuss the change of differential pressure DP due to pinning and capillary forces. The plain view of the analysis model for the pinning and capillary forces is shown in Fig. 3. Generally, in these models, the differential pressure of the pinning can be expressed as follows: DP ¼
DP ¼
Before
1
Pinning
5000
4c cos hP ½Pa; d
ð1Þ
where the symbol c is surface energy of the DI-water and hP is contact angle of the DI-water (as shown in Fig. 3a). Moreover, the symbol d represents the distance between the resist patterns. Meanwhile, the differential pressure of the capillary can be expressed as follows:
8 7
6000
7
(mJ /m2)1/2
Fig. 2. Component map of surface energy of samples obtained by sessile drop method.
4c cos hC ½Pa; d
ð2Þ
where hC denotes the contact angle at liquid capillary. The differential pressure of pinning and capillary as a function of the contact angle hP is shown in Fig. 4. From the results, as the the contact angle hP decreases, the effect of the pinning increases gradually by comparing with the capillary effect. Over the cross point, the water drop can spread drastically. 5. Conclusion
(b) Resist pattern
(a) Resist pattern
θp
DI-water ΔP
ΔP θC
d Pinning (dot pattern model) DI-water Capillary (line pattern model) Fig. 3. Simulation models for differential pressure DP.
The drastic control method of liquid flow and wetting processes based on pinning and capillary forces was studied. From in situ observation of the wetting processes, the pinning and capillary forces can be observed clearly due to pattern arrangement. Moreover, the thermodynamic analysis can explain well the wetting phenomena on the various resist patterns. Therefore, we can control the micro wetting behavior easily by designing the surface energy of the resist pattern and its arrangements. We can realize the presence of an artificial blood tube by applying the drastic control method of liquid flow in a micro tube.
T. Niiyama, A. Kawai / Microelectronic Engineering 83 (2006) 1280–1283
1283
Acknowledgements
References
The present work was partially supported by a Grant-inAid for Scientific Research from Japan Society for the Promotion of Science. (Scientific Research (B) 16360171). This work was also supported by a Grant-in-Aid for Scientific Research, Ministry of Education, Culture, Sports, Science and Technology (Exploratory research, 16656105).
[1] M. Yamanaka, A. Okada, A. Kawai, J. Vac. Sci. Technol. B 22 (6) (2004) 3525. [2] T. Cubaud, M. Fermigier, J. Colloid Interf. Sci. 269 (2004) 171. [3] D.H. Kaelble, J. Appl. Polymer Sci. 18 (1974) 1869. [4] T. Niiyama, A. Kawai, J. Photopolymer Sci. and Tech. 18 (2005) 373. [5] F.M. Fowks, Ind. Eng. Chem. 56 (1964) 40.