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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 16, Iss. 17 — Aug. 18, 2008
  • pp: 12715–12725
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Formation of superhydrophobic poly(dimethysiloxane) by ultrafast laser-induced surface modification

Tae Oh Yoon, Hyun Joo Shin, Sae Chae Jeoung, and Youn-Il Park  »View Author Affiliations


Optics Express, Vol. 16, Issue 17, pp. 12715-12725 (2008)
http://dx.doi.org/10.1364/OE.16.012715


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Abstract

The formation of hemispherical nanostructures and microscaled papilla by ultrafast laser irradiation was found to be a potential method to generate superhydrophbic surface of synthetic polymers. Irradiation of femtosecond laser creates roughened poly(dimethylsiloxane) (PDMS) surface in nano- and microscales, of which topography fairly well imitate a Lotus leaf in nature. The modified surface showed superhydrophobicity with a contact angle higher than 170° as well as sliding angle less than 3°. We further demonstrated that negative replica of the processed PDMS surface exhibit large contact angle hysteresis with a sliding angle of 90° while the positive replica maintains superhydrophobicity.

© 2008 Optical Society of America

1. Introduction

Much attention has been given to the preparation of superhydrophobic surface for the interest of fundamental research and application [1

1. A. Tuteja, W. Choi, M. Ma, J. M. Mabry, S. A. Mazzella, G. C. Rutledge, G. H. McKinley, and R. E. Cohen, “Designing superoleophobic surfaces,” Science 318, 1618–1622 (2007). [CrossRef] [PubMed]

, 2

2. A. Ressine, G. Marko-Varga, and T. Laurell, “Porous silicon protein microarray technology and ultra-/superhydrophobic state for improved bioanalytical readout,” Biotech. Ann Rev. 13, 149–200 (2007). [CrossRef]

]. The utilization of the water-repellent properties of superhydrophobic surface is a new micro- and nanoscaled approach to control wetting behavior of the micro-array substrate in bioassays performance and cell growth as well as to protect active microelectronics from detrimental effects of environmental water and moisture, and even self-cleaning surfaces and coatings [2

2. A. Ressine, G. Marko-Varga, and T. Laurell, “Porous silicon protein microarray technology and ultra-/superhydrophobic state for improved bioanalytical readout,” Biotech. Ann Rev. 13, 149–200 (2007). [CrossRef]

, 3

3. M.-F. Wang, N. Raghunathan, and B. Ziaie, “A nonlithographic top-down electrochemical approach for creating hierarchical (micro-nano) superhydrophobic silicon surfaces,” Langmuir 23, 2300–2303 (2007). [CrossRef] [PubMed]

]. Superhydrophobic surfaces, which occur naturally in some plant leaves and insect wings, eye, and leg, are characterized by a high contact angle (usually >150°) and low sliding angle less than 5° (low flow resistance). Many different type of fabrication method including lithographic and nonlithographic approaches have been used to form micro- and nanoscaled surfaces on various polymers, semiconductors, metals and ceramic substrates [1–9

1. A. Tuteja, W. Choi, M. Ma, J. M. Mabry, S. A. Mazzella, G. C. Rutledge, G. H. McKinley, and R. E. Cohen, “Designing superoleophobic surfaces,” Science 318, 1618–1622 (2007). [CrossRef] [PubMed]

]. Further, CO2 pulsed laser was also used to modify the surface of poly(dimethylsiloxane) (PDMS) to create a micro-pores to reveal superhydrophobicity [10

10. M. T. Khorasani, H. Mirzadeh, and P. G. Sammes, “Laser induced surface modification of polydimethylsiloxane as a super-hydrophobic material,” Radiant Phys. Chem. 47, 881–888 (1996). [CrossRef]

]. Femtosecond laser pulses have been recently utilized to make silicon surface hydrophobic under gaseous SF6 [11–13

11. T. Baldacchini, J. E. Carey, M. Zhou, and E. Mazur, “Superhydrophobic Surfaces Prepared by Microstructuring of Silicon using a Femtosecond Laser,” Langmuir 22, 4917–4919 (2006). [CrossRef] [PubMed]

].

The contact angle of liquid droplet can be explained in terms of not only chemical composition and its roughened surface but also local surface curvature [1

1. A. Tuteja, W. Choi, M. Ma, J. M. Mabry, S. A. Mazzella, G. C. Rutledge, G. H. McKinley, and R. E. Cohen, “Designing superoleophobic surfaces,” Science 318, 1618–1622 (2007). [CrossRef] [PubMed]

]. Two different models proposed by Wenzel [14

14. R.N. Wenzel, “Resistance of solid surfaces to wetting by water,” Ind. Eng. Chem. 28, 988–994 (1936). [CrossRef]

] and Cassie and Baxter [15

15. A. B.D. Cassie and S. Baxter S., “Wettability of porous surfaces,” Trans. Faraday Soc. 40, 546–551 (1994). [CrossRef]

], respectively, are commonly used to rationalize the effect of roughness on the apparent contact angle. The Cassie model rationalized large increase in the contact angle caused by microscopic air pockets underlying the liquid droplet. Meanwhile, the Wenzel model described the changes in contact angle due to the contact area enhancement followed by completely wetting the roughened surface by liquid. Both models highlighted that the presence of micro-and nanotopography plays an important role in forming the superhydrophobic surface.

It is valuable to extend our knowledge about a new method to realize the interesting micro- and nano composite surface to exhibit superhydrophobicity. The advent of reliable generation and amplification of the ultrafast laser enables it to be used for laser-induced microfabrication with high quality [16

16. P. P. Pronko, S. K. Dutta, J. Squier, J. V. Rudd, D. Du, and G. Mourou, “Machining of sub-micron holes using a femtosecond laser at 800 nm,” Opt. Commun. 114, 106–110 (1995). [CrossRef]

]. Further, a significant improvement in size and its dispersion reduction of a colloidal nanoparticle were reported in the case of ultrafast laser ablation over a nanosecond laser process [17–19

17. J. P. Sylvestre, A. V. Kabashin, E. Sacher, M. Meunier, and J. H. T. Luong, “Stabilization and size control of gold nanoparticles during laser ablation in aqueous cyclodextrins,” J. Am. Chem. Soc. 126, 7176–7177 (2004). [CrossRef] [PubMed]

]. T-H Her et al. [20

20. T.-H. Her, R. J. Finlay, C. Wu, and E. Mazur, “Femtosecond laser-induced formation of spikes on silicon,” Appl. Phys. A 70, 383–385 (2000). [CrossRef]

] reported that the irradiation of 500 laser pulses with 100 fs pulse width on silicon surfaces under 500 torr SF6 or Cl2 creates conical spikes capped by a 1.5 µm ball at the tops. We have also reported that under ambient condition the irradiation of an ultrafast laser on a Germanium single crystal results in the formation of Ge nanostructure which was dangled on the microstructures [21–23

21. S. C. Jeoung, H. S. Kim, M. I. Park, J. Lee, C. S. Kim, and C. O. Park, “Preparation of Room-Temperature Photoluminescent Nanoparticles by Ultrafast Laser Processing of Single-Crystalline Ge,” Jpn. J. Appl. Phys. 44, 5278–5281 (2005). [CrossRef]

]. Bulk Ge exhibits two different ablation thresholds resulting in amorphous layer on the surface of exposed area. At the second threshold fluence, especially nanoparticle dangled on irregular Ge microstructures was massively formed upon photoexciation with single fs-laser pulse. The modified surface was also found to be photoluminescent at room temperature accompanied with the encapsulation of the Ge nanostructure by ultrathin Ge oxide layer.

PDMS have several characteristics including high optical transparency to ultra-violet (UV) region, chemical and thermal resistance and mechanical elasticity for nanocasting as well as bioassays. In this report, we have demonstrated the formation of superhydrophobic PDMS surface by exposing the surface to ultrafast laser pulses. The observed high contact angle and low sliding angle of water droplet could be explained in terms of fs-laser induced formation of much roughened PDMS surface in nano- and microscales, of which topography fairly well imitate a Lotus leaf. Ultrafast laser induced surface modification is also known to have superior spatial resolution with a minimal thermal and mechanical damage. The method to create rather complex topographic patterns directly on PDMS surface with a high spatial resolution would be an important tool for both fundamental research and biomimic reproduction.

2. Experiments

Superhydrophobic PDMS surface was prepared by femtosecond laser-induced surface modification of solid pieces of PDMS. A 150 fs laser pulse (Quantronix, USA) at the wavelength of 810 nm with a repetition rate of 1 KHz is irradiated on PDMS substrate [21–23

21. S. C. Jeoung, H. S. Kim, M. I. Park, J. Lee, C. S. Kim, and C. O. Park, “Preparation of Room-Temperature Photoluminescent Nanoparticles by Ultrafast Laser Processing of Single-Crystalline Ge,” Jpn. J. Appl. Phys. 44, 5278–5281 (2005). [CrossRef]

]. Fig. 1 shows the flowchart for creating the superhydrophobic surface and casting process of PDMS to replicate the modified PDMS surface structures (i.e., its negative and positive replica). The solid PDMS sheet was obtained by using a 10:1 mixture by weight of PDMS base/curing agent, that was degassed under vacuum and cured at 25°C for 24 h. PDMS sheets are mounted on two-axis motorized stage that is used to translate the sample at a constant speed of 4 mm/sec in x-direction. The distance between successive laser spots is 4 µm. The laser beam was focused on PDMS surface with an objective lens (N.A.=0.14) mounted on motorized linear translational stage. The laser beam diameter at PDMS surface was about 7.7 µm. The polarization of laser pulse is perpendicular to the scanning direction. Modified surface with a dimension of 10×10 mm was obtained by translating the PDMS sheet with a step size in y-direction of 5 µm.

To obtain negative and/or positive replica of the laser irradiated PDMS surface, we again cast PDMS base/curing agent on the modified PDMS sheet coated with anti-sticking layer of 1H,1H,2H,2H-perfluorooctyl-tricholrosilane. A feature size limitation that can be transferred is about 20 nm, which is considered to be an acceptable size for replicating the irradiated PDMS surface to maintaining nano- and microstrcutures, which is responsible for superhydrophobicity [24

24. X. M. Zhao, Y. N. Xia, and G. M. Whitesides, “Soft lithographic methods for nano-fabrication,” J. Mater. Chem. 7, 1069–1074 (1997). [CrossRef]

]. The difference in the size of complex topographic patterns between the sheet and its replicates is considered to be negligible because they have the same microstructure size and the similar superhydrophobicity in its positive replica.

We have characterized the surface of processed PDMS with atomic force microscopy (AFM, Agilent PicoPlus) and high-resolution scanning electron microscopy (HR-SEM). The surface roughness of the processed PDMS surface was estimated from the AFM images with SPM image processor. Water drop contact angle and sliding angle was evaluated by measuring the optical image between water drops and the surface of the samples (Dataphysics, OCA20). All the contact angles are mean values of five determinations on five different areas of the surface.

Fig. 1. Flowchart for creating the superhydrophobic surface and casting process of PDMS to replicate the fs-laser irradiated PDMS surface.

3. Results

Figures 2(a) and 2(b) show SEM images of fs-laser irradiated surface of PDMS sheet with the fluence of 4.4 J/cm2. Topography of the surface measured by atomic force microscopy (AFM) exhibit similar much roughened structures. The surface consists of an irregular three-dimensional papilla structure of an order of micrometer in addition to nanostructures with a size between 3 nm and 300 nm. It should be noted that nanostructured particles of various sizes are found on the papilla microstructure. The average diameter of the papilla in microscale and the average distance between them is about 6 µm and 10 µm, respectively. Surface examination by SEM did not reveal any presence of regular conical spikes dangled with microballs on its top in the processed layer with dimensions of micrometer scale that were previously reported for experiments with silicon processing by femtosecond laser irradiation [11–13

11. T. Baldacchini, J. E. Carey, M. Zhou, and E. Mazur, “Superhydrophobic Surfaces Prepared by Microstructuring of Silicon using a Femtosecond Laser,” Langmuir 22, 4917–4919 (2006). [CrossRef] [PubMed]

, 20

20. T.-H. Her, R. J. Finlay, C. Wu, and E. Mazur, “Femtosecond laser-induced formation of spikes on silicon,” Appl. Phys. A 70, 383–385 (2000). [CrossRef]

]. Furthermore, we did not observe any evidence on the presence of micro-pores, which was reported on the basis of CO2 laser irradiation on PDMS [10

10. M. T. Khorasani, H. Mirzadeh, and P. G. Sammes, “Laser induced surface modification of polydimethylsiloxane as a super-hydrophobic material,” Radiant Phys. Chem. 47, 881–888 (1996). [CrossRef]

]. Figures 2(c) and 2(d) shows SEM micrographs for the negative replica of the irradiated PDMS surface. The SEM image highlights the complementary pores in micro- and nanometer scale on PDMS surface compared to fs-laser irradiated PDMS surface. Microscaled papilla structure with nanostructures was partly recovered in the positive replicates (Figs. 2(e) and 2(f)). This is consistent with that a feature size limitation that can be transferred by casting of PDMS is about 20 nm [24

24. X. M. Zhao, Y. N. Xia, and G. M. Whitesides, “Soft lithographic methods for nano-fabrication,” J. Mater. Chem. 7, 1069–1074 (1997). [CrossRef]

]. Thus, we could see that the surface structures of fs-laser irradiated PDMS surface have been replicated with high fidelity by two successive replications.

Raman spectral features of fs-laser irradiated PDMS surface exhibited a remarkable reduction of Raman intensity of –Si-O-Si- skeletal deformation band at 489 cm-1 but an enhancement of the intensity for the Raman band at 1746 cm-1 which could be assigned to carbonate groups (-O-COO-). (Data have been not shown.) We measured a contact angle of water droplet on the surface of the positive and the negative replica as well as on laser irradiated PDMS sheet (Table 1). Figure 3 shows microscopic images of the water drops on the three types of surfaces. The fs-laser modified surface of PDMS shows the average contact angle of 165°. The average contact angle on the positive replica is 150°, whereas the negative replica has a contact angle of only 136°. For reference, intact PDMS surface shows a contact angle of 105°. It should be notified that the contact angle increases by 60° upon surface modification of PDMS. Superhydrophobic surfaces exhibit not only large contact angles higher than 150° but also small rolling-off angle (i.e., low sliding angle).

Fig. 2. SEM images of PDMS sheet exposed to fs-laser pulses with a fluence of 4.4 J/cm2: (a) low magnification and (b) high magnification. SEM micrographs for the negative replica ((c) and (d) as well as the positive ones ((e) and (f)) of the irradiated PDMS surface are also shown.

Fig. 3. Microscopic images of the water drops on the three types of surfaces of laser irradiated PDMS (a), its negative replica (b) and positive replica (c).

Table 1. Contact angle and sliding angle of the water drops on the three types of PDMS surfaces. The laser fluence to modify the PDMS surface is 4.4. J/cm2. All the angles are the average values of five determinations on five different areas of the surface.

table-icon
View This Table

Figure 4 shows the contact angle and sliding angles of water droplet on laser irradiated PDMS sheet as a function of fs-laser fluence used in surface modification. The translation speed of PDMS and the line spacing are kept to be 4 mm/s and 5 µm, respectively. The contact angle of water droplet increases with increasing the laser fluence. For the laser fluence of 4.9 J/cm2, the contact angle is about 175°, which is almost invariable even further increase in the fluence. While the water droplet does not roll off from the PDMS sheet processed with the laser fluence less than 3.4 J/cm2, the sliding angle of the water drop abruptly decreases for PDMS surface modified with the fluence higher than 3.8 J/cm2. These observations strongly suggest that a direct surface modification based on fs-laser microprocessing results in superhydrophobicity of PDMS surfaces. We have estimated the roughness, defined by the ratio of actual area of the solid surface to the projected area, of laser irradiated PDMS surface by using AFM topography as shown in Fig. 5. As shown in Fig. 4(b), the roughness exhibits quite strong correlation with the changes in the surface wetting property. The roughness of laser irradiated PDMS surface is 2.5 at the laser fluence of 3.8 while the value is only 1.3 at 3.0 J/cm2. This abrupt increase in the roughness caused by fs laser surface modification plays an important role in alteration of the surface wetting property of PDMS.

Fig. 4. (a). Contact angle (open circle) and sliding angle (closed circle) of PDMS surface as a function of the laser fluence. (b) and (c) shows the roughness (solid rectangular) and laser spot diameter (open triangle) as a function of the laser fluence, respectively. The roughness is defined by the ratio of actual area of the solid surface to the projected area.
Fig. 5. AFM topographic images of PDMS surface irradiated with laser fluence of 3.0 J/cm2 (a), 3.4 J/cm2 (b), 3.8 J/cm2 (c), and 6.3 J/cm2 (d), respectively. The lower part of each image displays the cross-sectional profiles observed in the depicted dotted line. It should be noted that the surface of the papilla as well as the valley of modified PDMS sheet are covered with almost hemispherical structures. The height of papilla increased with increasing laser fluence. The presence of roughened region between the papilla is also clearly seen in the cross-sectional profiles of (c) and (d).

4. Discussions

COSθCB=ΦsCOSθY(1Φs)
(1)

in which θC-B and θY are the C-B contact angle of a roughened surface and the Young contact angle (i.e., the contact angle measured on the equivalent flat surface), respectively. Φ s is the fraction of the project area of the solid surface in contact with liquid [15

15. A. B.D. Cassie and S. Baxter S., “Wettability of porous surfaces,” Trans. Faraday Soc. 40, 546–551 (1994). [CrossRef]

]. Since Φ s is always less than 1, the contact angle of roughened surface is always greater than that of flat surface. On the other hand, the liquid droplet fills up the rough surface to form a completely wetted contact with the surface as shown in Fig. 5(b), which is also known as the Wenzel model formulated as the fraction of the solid in contact with the equation [14

14. R.N. Wenzel, “Resistance of solid surfaces to wetting by water,” Ind. Eng. Chem. 28, 988–994 (1936). [CrossRef]

]:

COSθW=rCOSθY
(2)

in which θW and θY are the contact angle of the Wenzel mode and the Young contact angle, respectively. r is the surface roughness defined as the ratio of actual area of the solid surface to the projected area.

There exists a transition between the Wenzel and C-B states. The roughness at the transition point, rc, can be determined by equating θC-BW [27

27. K. -Y. Yeh, L.-J. Chen, and J. -Y. Chang, “Contact Angle Hysteresis on Regular Pillar-like Hydrophobic Surfaces,” Langmuir 24, 245–251 (2008). [CrossRef]

]:

rc=Φs(1Φs)COSθY
(3)

When r<rc, water penetrates to fully wet the surface; i.e., the system belongs to the Wenzel state. On the other hand, when r>rc, a water droplet suspends on a composite surface of air and solid; i.e., the system belongs to the C-B state. The sliding angle can be used to conclude the state of a liquid droplet. If the sliding angle is small, then the droplet would be at the C-B state. On the other hand, if the sliding angle is large, then the droplet would be at the Wenzel state. For a superhydrophobic surface, the sliding angle must be small, and a water droplet rolls off spontaneously on slightly inclined surface.

Fig. 6. Illustrations of the roughened surface to explain the C-B model (a), Wenzel model (b), and a proposed model to describe the wetting nature of negative replica sheet (c). PDMS solid, water, and air are depicted with yellow, blue, and white colors, respectively.

Since contact angle of fs-laser irradiated PDMS is about 165°, and also the sliding angle is less than 3°, this lotus-like PDMS sheet could be described with C-B model as shown in Fig. 6(a). Meanwhile, the sliding angle of negative replica of irradiated PDMS is large while the advancing contact angle is larger than 136° even if the roughness, r, of two samples should be almost same. But, Φ s of negative replica is much larger than that of directly irradiated PDMS sheet since the flat part of the replica is fronted to the water droplet while the flat part of irradiated PDMS sheet should be underlying the water droplet. Therefore, the transition roughness between the Wenzel state to the C-B state for negative replica, rc,neg, should be larger than that for directly formed PDMS sheet, rc,syn. It is reasonable to suppose that water might fully wet the surface of the negative replica, and its surface could be described with the Wenzel model. We have illustrated the state of the water droplet on negative replica sheet in Fig. 6(c). This supposition was further supported by the observation of large sliding angle from the negative replica. (Table 1)

Finally, it should be interesting to discuss about the underlying mechanism to form a roughened surface with superhydrophobicity by exposing intact PDMS surface to ultrafast laser pulses under ambient condition. The changes in chemical composition of PDMS due to ultrafast laser irradiation could be conjectured to be responsible to increase the contact angle. However, the Raman spectral features on modified surface clearly shows that fs-laser irradiation on PDMS surface results in the enhancement of more hydrophilic moieties of carbonate functional groups accompanied with a remarkable reduction of hydrophobic ones of –Si-O-Si- skeletal structures. As a result, it is not reasonable to explain the formation of superhydrophobic surface in terms of fs-laser induced photochemical reactions of intact PDMS.

It is of fundamental interest to learn whether and how strain-induced microstructural changes and phase transitions occur if fs-laser irradiation induces high-strain-rate disturbance in solid materials. The disturbances can be referred to as ‘shocks’ as is common in the literature [30

30. L. Phillips, R. S. Sinkovits, E. S. Oran, and J. P. Boris, “The interaction of shocks and defects in Lennard-Jones crystal,” J. Phys.: Condens. Matter , 5, 6357–6376 (1993). [CrossRef]

]. In fact, nonhomogeneous inelastic deformation is often observed during high-strain-rate loading of many materials like metal alloys. Generation of disorder and free volume in the materials is the only mechanism of plastic deformation in amorphous solids. While localized deformation can induce amorphous-to-nanocrystalline phase transitions in amorphous materials, crystalline-to-amorphous phase transition has also been observed during shock compression [31

31. P. Erhart, E. M. Bringa, M. Kumar, and K. Albe, “Atomistic mechanism of shock-induced void collapse in nano-porous metals,” Phys. Rev. B. 72, 052104(1)–052104(4) (2005) [CrossRef]

]. We supposed that the shock generated by fs-laser irradiation in PDMS initiates detonation through the generation of scission forces on the molecules comprising the solid PDMS, breaking chemical bonds, creating a distribution of free radicals, and supplying the kinetic energy required to initiate the formation of nano- and microstructures.

Fig. 7. AFM images of the PDMS surface irradiated with fs-laser pulses by using a telecentric lens (N.A. ~0.035) at a repetition rate of 1 KHz. To make overlapping between the successive laser pulses, the scanning speed is fixed into about 10 mm/sec.

While a direct interband transition is not allowed in PDMS at the wavelength of 810 nm by linear absorption, multiphoton absorption process caused by delivering high laser energy into PDMS may result in high-strain-rate disturbance if there is considerable density of defects inside the materials. In fact, the irradiation of fs-laser scarcely induces irregular structure inside laser spot when only single pulse of fs laser is irradiated, while in the overlapped area between successive laser spots much roughened surface could be observed (Fig. 7). This observation can be explained to propose the generation of a defect site like void in PDMS by the first laser pulse. If this is the case, the successive laser pulse occur a high-strain-rate disturbance, which should highlight the amorphization to results in a detonation of PDMS to form much roughened PDMS surface. The current supposition on the underlying mechanism for the formation of much roughened PDMS surface might be also strengthened by the observation of the correlation between the ablation diameter with the roughness as well as the wetting properties of the PDMS surface as shown Fig. 4.

In summary, we have demonstrated that fs-laser surface modification of PDMS under ambient condition should be a promising optical method for the formation of superhydrophobic surface with both high contact angle and low sliding angle. The morphology of the irradiated PDMS surface is to imitate natural Lotus leaf both on micro- and nanoscales. We found that its negative replica, which was obtained by casting the irradiated PDMS sheet, are belongs to the Wenzel state, which has high sliding angle. Since PDMS have several benefit characteristics in bioanalysis as a raw material, ultrafast laser induced surface modification, which is well known to have superior spatial resolution and minimal damage, should provide a unique and powerful method for changing local hydrodynamic properties of PDMS.

Acknowledgment

This work was financially supported from “Next Generation New Technology Development Program” by MOCIE, Korea.

References and links

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A. Tuteja, W. Choi, M. Ma, J. M. Mabry, S. A. Mazzella, G. C. Rutledge, G. H. McKinley, and R. E. Cohen, “Designing superoleophobic surfaces,” Science 318, 1618–1622 (2007). [CrossRef] [PubMed]

2.

A. Ressine, G. Marko-Varga, and T. Laurell, “Porous silicon protein microarray technology and ultra-/superhydrophobic state for improved bioanalytical readout,” Biotech. Ann Rev. 13, 149–200 (2007). [CrossRef]

3.

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11.

T. Baldacchini, J. E. Carey, M. Zhou, and E. Mazur, “Superhydrophobic Surfaces Prepared by Microstructuring of Silicon using a Femtosecond Laser,” Langmuir 22, 4917–4919 (2006). [CrossRef] [PubMed]

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16.

P. P. Pronko, S. K. Dutta, J. Squier, J. V. Rudd, D. Du, and G. Mourou, “Machining of sub-micron holes using a femtosecond laser at 800 nm,” Opt. Commun. 114, 106–110 (1995). [CrossRef]

17.

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T.-H. Her, R. J. Finlay, C. Wu, and E. Mazur, “Femtosecond laser-induced formation of spikes on silicon,” Appl. Phys. A 70, 383–385 (2000). [CrossRef]

21.

S. C. Jeoung, H. S. Kim, M. I. Park, J. Lee, C. S. Kim, and C. O. Park, “Preparation of Room-Temperature Photoluminescent Nanoparticles by Ultrafast Laser Processing of Single-Crystalline Ge,” Jpn. J. Appl. Phys. 44, 5278–5281 (2005). [CrossRef]

22.

M. A. Seo, D. S. Kim, H. S. Kim, and S. C. Jeoung, “Polarization-induced size control and ablation dynamics of Ge nanostructures formed by a femtosecond laser,” Opt. Express 14, 3694–3699 (2006). [CrossRef] [PubMed]

23.

M. A. Seo, D. S. Kim, H. S. Kim, D. S. Choi, and S. C. Jeoung, “Formation of photoluminescent germanium nanostructures by femtosecond laser processing on bulk germanium: role of ambient gases,” Opt. Express 14, 4908–4914 (2006). [CrossRef] [PubMed]

24.

X. M. Zhao, Y. N. Xia, and G. M. Whitesides, “Soft lithographic methods for nano-fabrication,” J. Mater. Chem. 7, 1069–1074 (1997). [CrossRef]

25.

W. Chen, W. A. T. Fadeev, M. C. Hsieh, D. Oner, J. Youngblood, and T. J. McCarthy, “Ultrahydrophobic and Ultralyophobic Surfaces: Some Comments and Examples,” Langmuir 15, 3395–3399 (1999). [CrossRef]

26.

D. Oner and T. J. McCarthy, “Ultrahydrophobic Surfaces. Effects of Topography Length Scales on Wettability,” Langmuir 16, 7777–7782 (2000). [CrossRef]

27.

K. -Y. Yeh, L.-J. Chen, and J. -Y. Chang, “Contact Angle Hysteresis on Regular Pillar-like Hydrophobic Surfaces,” Langmuir 24, 245–251 (2008). [CrossRef]

28.

C. V. Shank, R. Yen, and C. Hirlimann, “Time-resolved reflectivity measurements of femtosecond-opticalpulse-induced phase transitions in silicon,” Phys. Rev. Lett. 50, 454–457 (1983). [CrossRef]

29.

D. C. Sayle and S. C. Parker, “Encapsulated oxide nanoparticles: the influence of the microstructure on associated impurities within a material,” J. Am. Chem. Soc. 125, 8581–8594 (2003). [CrossRef] [PubMed]

30.

L. Phillips, R. S. Sinkovits, E. S. Oran, and J. P. Boris, “The interaction of shocks and defects in Lennard-Jones crystal,” J. Phys.: Condens. Matter , 5, 6357–6376 (1993). [CrossRef]

31.

P. Erhart, E. M. Bringa, M. Kumar, and K. Albe, “Atomistic mechanism of shock-induced void collapse in nano-porous metals,” Phys. Rev. B. 72, 052104(1)–052104(4) (2005) [CrossRef]

32.

J. Bonse, G. Bachelier, J. Siegel, J. Solis, and H. Sturm, “Time- and space-resolved dynamics of ablation and optical breakdown induced by femtosecond laser pulses in indium phosphide,” J. Appl. Phys. 103, 054910(1)–54910(6) (2008). [CrossRef]

OCIS Codes
(160.5470) Materials : Polymers
(220.4241) Optical design and fabrication : Nanostructure fabrication

ToC Category:
Materials

History
Original Manuscript: May 12, 2008
Revised Manuscript: June 22, 2008
Manuscript Accepted: August 3, 2008
Published: August 7, 2008

Virtual Issues
Vol. 3, Iss. 10 Virtual Journal for Biomedical Optics

Citation
Tae Oh Yoon, Hyun Joo Shin, Sae Chae Jeoung, and Youn-Il Park, "Formation of superhydrophobic poly(dimethysiloxane) by ultrafast laser-induced surface modification," Opt. Express 16, 12715-12725 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-17-12715


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References

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  22. M. A. Seo, D. S. Kim, H. S. Kim, and S. C. Jeoung, "Polarization-induced size control and ablation dynamics of Ge nanostructures formed by a femtosecond laser," Opt. Express 14, 3694-3699 (2006). [CrossRef] [PubMed]
  23. M. A. Seo, D. S. Kim, H. S. Kim, D. S. Choi, and S. C. Jeoung, "Formation of photoluminescent germanium nanostructures by femtosecond laser processing on bulk germanium: role of ambient gases," Opt. Express 14, 4908-4914 (2006). [CrossRef] [PubMed]
  24. X. M. Zhao, Y. N. Xia, and G. M. Whitesides, "Soft lithographic methods for nano-fabrication," J. Mater. Chem. 7, 1069-1074 (1997) [CrossRef]
  25. W. Chen, W. A. T. Fadeev, M. C. Hsieh, D. Oner, J. Youngblood, T. J. McCarthy, "Ultrahydrophobic and Ultralyophobic Surfaces: Some Comments and Examples," Langmuir 15, 3395-3399 (1999). [CrossRef]
  26. D. Oner and T. J. McCarthy, "Ultrahydrophobic Surfaces. Effects of Topography Length Scales on Wettability," Langmuir 16, 7777-7782 (2000). [CrossRef]
  27. K. -Y. Yeh, L.-J. Chen, and J. -Y. Chang, "Contact Angle Hysteresis on Regular Pillar-like Hydrophobic Surfaces," Langmuir 24, 245-251 (2008). [CrossRef]
  28. C. V. Shank, R. Yen, and C. Hirlimann, "Time-resolved reflectivity measurements of femtosecond-opticalpulse-induced phase transitions in silicon," Phys. Rev. Lett. 50, 454-457 (1983). [CrossRef]
  29. D. C. Sayle and S. C. Parker, "Encapsulated oxide nanoparticles: the influence of the microstructure on associated impurities within a material," J. Am. Chem. Soc. 125, 8581-8594 (2003). [CrossRef] [PubMed]
  30. L. Phillips, R. S. Sinkovits, E. S. Oran, and J. P. Boris, "The interaction of shocks and defects in Lennard-Jones crystal," J. Phys.: Condens. Matter,  5, 6357-6376 (1993). [CrossRef]
  31. P. Erhart, E. M. Bringa, M. Kumar, and K. Albe, "Atomistic mechanism of shock-induced void collapse in nano-porous metals," Phys. Rev. B.  72, 052104(1)-052104(4) (2005) [CrossRef]
  32. J. Bonse, G. Bachelier, J. Siegel, J. Solis, and H. Sturm, "Time- and space-resolved dynamics of ablation and optical breakdown induced by femtosecond laser pulses in indium phosphide," J. Appl. Phys.  103, 054910(1)-54910(6) (2008). [CrossRef]

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