Patterning of Wrinkled Polymer Surfaces by Single-Step Electron

Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE

Interface Components: Nanoparticles, Colloids, Emulsions, Surfactants, Proteins, Polymers

Patterning of Wrinkled Polymer Surface by Single-Step Electron Irradiation Hyung San Lim, Sang Yoon Lee, Na Eun Lee, and Sung Oh Cho Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b00403 • Publication Date (Web): 13 Apr 2018 Downloaded from http://pubs.acs.org on April 14, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Patterning of Wrinkled Polymer Surface by Single-Step Electron Irradiation Hyung San Lim+, Sang Yoon Lee+, Na Eun Lee+, and Sung Oh Cho+* +

Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Guseong, Yuseong, Daejeon 305-701, Republic of Korea

* Contact Author: Tel: +82-42-350-3823, Fax: +82-42-350-3810, E-mail: [email protected] (Prof. Sung Oh Cho)

A novel yet simple approach to fabricate and pattern wrinkled surfaces on polymers is presented. Only by irradiating an electron beam onto a polymer, wrinkles are created on the polymer surface. Electron irradiation produces a bilayer polymeric structure comprising a degrading upper layer and a pristine bottom layer. Electron irradiation also increases the polymer surface temperature to a point much higher than the glass transition temperature of the upper layer, leading to drastic thermal expansion of the upper layer. As a result, significant compressive force is applied to form surface wrinkles. The mechanism behind the wrinkle formation and the effects of electron irradiation parameters on the wrinkle characteristics are discussed. In addition, by this electron irradiation approach, patterned wrinkle structure is uniquely prepared.

Keywords Irradiation, Wrinkled Surface, Polymer, Patterning, Bilayer

Page 1 / 18 ACS Paragon Plus Environment

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 19

1. Introduction Surface wrinkle formation is a widely observed phenomenon that is characterized by shallow surface undulations, in the scale of micrometer or nanometer, that can take on various morphologies such as hexagonal, peanut-shaped and lamellar.1 In particular, wrinkling of polymer surface is of high interest in both the scientific and technological communities due to its potential applications that include tunable optical devices,2-5 switchable

wettability,6-9

engineering,14,

16-18

dry

adhesion,10-12

microfluidic channels,

14

biosensors,13-15

drug

delivery,14

tissue

and flexible electronics.19-23 The wrinkling

phenomenon is achieved through various methods; however, one of the core underlying mechanisms for its occurrence is through the application of stress.24 The stress can be induced through chemical, thermal or mechanical approach.1, 25 In the case of the mechanical approach, a wrinkled surface is obtained by stretching and releasing,1, 26 but this method has limitations in manufacturing wrinkled surfaces with large areas and in controlling the wrinkle morphology. As for the case of the chemical or thermal approach, the wrinkling process generally requires fabrication of a bilayer structure using a thin polymer film and applying expansion confinement stress. Specifically, with the thermal approach, this stress is derived from the difference in thermal expansion coefficient of the two layers. The chemical approach also employs a bilayer structure, but the stress is derived from swelling of one layer by solvent injection. These methods, although effective, require time-consuming and convoluted steps in preparing a bilayer structure, such as coating, thermal deposition, and sputtering. They also require additional steps, such as heat application and solvent injection, in applying stress. Furthermore, they demand the use of various materials, including both organic and inorganic materials to fabricate wrinkled surfaces and the methods seemed to be highly confined to utilizing thin films.10, 24


Page 3 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Although aforementioned techniques to prepare wrinkled polymer surfaces have been developed, fabricating patterned wrinkled surfaces where wrinkles are formed only on desired regions of a surface is still challenging. Such patterning of wrinkled surfaces is highly important in their application to tissue engineering and microfluidic channels.14, 16-18 In this paper, we propose a novel approach to fabricate wrinkled surfaces by irradiating an electron beam onto polymers. Electron irradiation creates a bilayer polymer structure and simultaneously supplies heat to the polymer surface to create stress, thus, no other steps are required for the fabrication of wrinkled surfaces. In addition, this approach allows for patterning of wrinkled surfaces by selectively irradiating areas on the polymer surface. The method also provides other highly advantageous traits, such as being able to be used on samples with complex shapes or large surface areas.

2. Experimental Section 2.1 Sample Preparation Four different polymers, poly(methyl methacrylate) (PMMA) (Goodfellow ME303031), polypropylene (PP) (Goodfellow PP303030), polystyrene (PS) (Goodfellow ST313200), and polyethylene (PE) (Goodfellow ET323250), were used in this study. The polymer plates with thickness of 3 mm were cut into 1 x 1 cm2 samples followed by washing with isopropyl alcohol and drying with nitrogen gas. The samples were homogeneously irradiated with an electron beam generated from a thermionic electron gun in a vacuum of 10-6 Torr. The energy of the electron beam was set to 50 keV and the diameter of the beam was 1.5 cm. The electron fluence received by the samples were changed from 8.35×1016 electrons/cm2 to 4.45×1017 electrons/cm2 by controlling the electron current density ranging from 1.41 to 5.66 µA/cm2 and irradiation time ranging from 30 to 160 min. Page 3 / 18 ACS Paragon Plus Environment

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

2.2 Characterization The morphology and the surface structure of the irradiated polymers were characterized with an optical microscope (OM, Park Systems XE-70) and an atomic force microscope (AFM, Park Systems XE-70) in tapping mode. The mean and standard deviation values of wrinkle width and height were determined by averaging 10 AFM measurements at different locations on the sample surface. The depth up to which a 50 keV electron beam affects the polymers was determined by Raman spectra of an irradiated polymer. The Raman spectra were measured at various positions on the cross-section of the irradiated polymer using a dispersive Raman spectrophotometer (HORIBA Jobin Yvon ARAMIS) equipped with an Arion laser. The spot size of the laser was 2 µm and the laser power of less than 0.5 mW was used to avoid damage to the polymer during the measurement. Temperature at the polymer surface during the electron irradiation was measured using thermo labels (Nichiyu). Glass transition temperatures of the irradiated polymers were derived using a low temperature differential scanning calorimeter (DSC, NETZSCH DSC 204 F1). Both sides of the thin (0.05 mm thickness) polymer films were irradiated and heated to 200˚ C at a rate of 10 ˚ C/min for the measurement of the glass transition temperature.

3. Results and Discussion All the pristine polymer samples had flat surfaces (Figure 1a, c, e, h). However, interestingly, when PMMA was electron-irradiated at a current density of 2.12 µA/cm2 for 60 min, a wrinkled surface was created all over the polymer surface (Figure 1b). A similar wrinkled surface, but with a smaller wrinkle width and height, was also observed on PP when Page 4 / 18 ACS Paragon Plus Environment

Page 4 of 19

Page 5 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

the polymer was irradiated at the same condition used to irradiate PMMA. In contrast, no wrinkled surfaces were formed on PS, and PE when they were irradiated at the aforementioned condition. Even irradiating at a higher current density of 4.24 µA/cm2 for 60 min, PS and PE kept their original flat surfaces without wrinkling.

Figure 1. Surface of a) pristine PMMA, b) PMMA irradiated at 2.12 µA/cm2 for 60 min, c) pristine PP, d) PP irradiated at 2.12 µA/cm2 for 60 min, e) pristine PS, f) PS irradiated at 2.12 µA/cm2 for 60 min, g) PS irradiated at 4.24 µA/cm2 for 60 min, h) Pristine PE, i) PE irradiated at 2.12 µA/cm2 for 60 min, and j) PE irradiated at 4.24 µA/cm2 for 60 min.

The characteristics of the wrinkled surface could be changed by varying the electron irradiation conditions. Figure 2 shows OM images and the corresponding AFM images of PMMA surfaces electron-irradiated at various current densities. The current density was Page 5 / 18 ACS Paragon Plus Environment

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

gradually increased from 1.41 to 5.66 µA/cm2 while fixing the electron fluence at 1.67 × 1017 electrons/cm2, which meant that the irradiation time was decreased as the current density was increased. AFM measurements indicate that the width of the formed wrinkles grew from 8 to 25 µm with increasing current density. The height of the wrinkles also increased initially from 1 to 4 µm, but beyond the current density of 4.24 µA/cm2, it begin to decrease, reaching 3 µm at the current density of 5.66 µA/cm2.

Figure 2. OM and AFM (45µm× 45µm) (top-left) images of PMMA surface irradiated at a) 1.41 µA/cm2, b) 2.12 µA/cm2, c) 2.82 µA/cm2, d) 4.24 µA/cm2, and e) 5.66 µA/cm2 current to a fixed electron fluence value of 1.67 × 1017 electrons/cm2. f) Width and height of formed wrinkles as a

function of irradiation current value.

In contrast, Figure 3 displays OM images and the corresponding AFM images of PMMA surfaces irradiated at a fixed current density of 2.1 µA/cm2 while varying the irradiation time Page 6 / 18 ACS Paragon Plus Environment

Page 6 of 19

Page 7 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

from 30 to 160 min. As a consequence of the variation in the irradiation time, the electron fluence was changed from 8.35 × 1016 to 4.45 × 1017 electrons/cm2. AFM measurements indicate that the width of the formed wrinkles grew from 8 to 22 µm with increasing current density, but became unchanging beyond the electron fluence of 3.34 × 1017 electrons/cm2. The height of the wrinkles also exhibited a similar behavior: it increased from 1 to 4 µm with increasing current density, but became unchanging beyond the electron fluence of 3.34 × 1017 electrons/cm2.

Figure 3. OM and AFM (45µm× 45µm) (top-left) images of PMMA surface irradiated with an electron fluence of a) 8.35 × 1016 electrons/cm2, b) 1.67 × 1017 electrons/cm2, c) 2.51 × 1017

electrons/cm2, d) 3.44 × 1017 electrons/cm2, and e) 4.45 × 1017 electrons/cm2 at 2.12 µA/cm2. f) Width and height of formed wrinkles as a function of electron fluence.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 19

To elucidate the wrinkling phenomena, the effects of electron irradiation on polymers have been investigated. Firstly, it is well known that if a polymer is irradiated with an electron beam, its chains undergo crosslinking and scission. The ratio of crosslinking to scission depends on the type of polymer. When chain-scission or chain-crosslinking predominantly occurs due to irradiation, the polymer is regarded as a chain-scission or a chain-crosslinking polymer, respectively. PMMA and PP are known as chain-scission polymers while PS and PE are known as chain-crosslinking polymers.

27

One key difference

between a chain-scission polymer and a chain-crosslinking polymer is the change in the glass transition temperature after irradiation. This was confirmed in our measurement of glass transition temperatures of polymers as a function of electron fluence. Figure 4 shows that the glass transition temperature of PMMA decreases as electron fluence increases (Figure 4a), while the opposite is observable for PS (Figure 4b). The glass transition temperature of PMMA decreased from its pristine value of 115 to 55 oC after being irradiated with an electron fluence of 3.34 × 1017 electrons/cm2. The glass transition temperature of PS, on the other hand, increased from its pristine value of 106 to 163 oC after being irradiated with an electron fluence of 3.34 × 1017 electrons/cm2.

Figure 4. Glass transition temperature of a) PMMA and b) PS as a function of time.


Page 9 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Secondly, if a polymer is irradiated with an electron beam, most of the electron kinetic energy is converted into heat,

28

thereby increasing the polymer surface temperature. The

temperature increase due to electron irradiation was measured using thermo-labels. As shown in Figure 5, the polymer surface temperature was constantly elevated with increasing electron current density and rose to 145 oC at the current density of 5.66 µA/cm2 and fluence of 1.67 x 1017 electrons/cm2. Thus, electron irradiation ultimately leads to decrease (increase) in the glass transition temperature of chain-scission (crosslinking) polymer while increasing the polymer surface temperature. This fact should be noted because the surface temperature of chain-scission polymer can be increased to a point much higher than its glass transition temperature during electron irradiation. If this happens, the thermal expansion coefficient of the chain-scission polymer is drastically amplified by an order of magnitude.29

For a chain-

crosslinking polymer, the possibility that the polymer surface temperature reaches a point significantly greater than its glass transition temperature is very low because the glass transition temperature of the polymer is significantly increased during electron irradiation.

Figure 5. a) Polymer surface temperature as a function of irradiation current density at a fixed fluence of 1.67 x 1017 electrons/cm2. b) Polymer surface temperature as a function of fluence at a fixed irradiation current density of 2.12 µA/cm2


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Lastly, an electron beam with comparatively low energy of 50 keV cannot penetrate deep into a polymer. To identify the depth up to which a 50 keV electron beam has an effect, micro-Raman spectra of an irradiated polymer were measured at various depths. The results show that the chemical structure of the irradiated polymer from the surface to a depth of around 10 µm was modified by 50 keV electron irradiation (Figure 6), suggesting that irradiation-induced crosslinking or scission occurs only near the surface of the polymer. Consequently, the electron irradiation produces a bilayer structure30 comprising an upper layer where crosslinking or scission occurs and a bottom layer where the polymer maintains its pristine structure.

Figure 6. Raman spectra of PMMA irradiated with 50 keV at depths of a) 0 µm (surface), b) 10 µm, c) 20 µm, and d) 30 µm. e) Raman spectrum of pristine PMMA.

From these analyses, we can explain the phenomenon of wrinkled surfaces forming only on chain-scission polymers when electron irradiated. If a low-energy electron beam irradiates a chain-scission polymer such as PMMA or PP, not only is a bilayer polymeric structure Page 10 / 18 ACS Paragon Plus Environment

Page 10 of 19

Page 11 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

formed but also significant heat is applied to the upper layer. In particular, if the electron current density is high enough, the temperature of the upper layer can be increased to a point far greater than the polymer’s glass transition temperature, leading to a drastic thermal expansion of the upper layer. As a consequence, large compressive stress is delivered to the upper layer, resulting in surface wrinkling during irradiation-induced heating.31 On other hand, if a chain-crosslinking polymer such as PS or PE is irradiated, insufficient stress is supplied to the upper layer since irradiation-induced crosslinking increases the polymer’s glass transition temperature. In addition, to address the height and width behavior of the wrinkles formed by electron irradiation of PMMA, the visco-elastic property of a polymer must be explored. When a polymer is near its glass transition temperature, it is dominantly elastic. However, as the temperature of the polymer is increased closer to the polymer’s melting point, the polymer becomes dominantly viscous or fluid-like. If the effectively irradiated or the upper layer of the bilayer structure is purely elastic during the wrinkling process, the following equations3, 32 is applicable in finding the width and height of the resulting wrinkles. ,

(1) (2)

Where λ and H are the width and height of the formed wrinkles, respectively. Eu is the elastic modulus of the upper layer and Eb is the elastic modulus of the bottom layer. ∆ and t is the compressive stress applied to the bilayer system and the thickness of the upper layer, respectively. It can be observed from equation (1) that for an elastic system, compressive stress has no effect on the width of the formed wrinkles; only the change in elastic moduli of the system can alter the width. On the other hand, equation (2) shows that the height of the


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

wrinkle increases with increasing compressive stress. When the temperature of the polymer is increased closer to the polymer’s melting point, the polymer becomes viscous and begins to flow. If the upper layer is viscous or fluid-like, it likewise flows down, reducing the height of the formed wrinkles, but increasing the width of the wrinkles in the process. Diagram that illustrates the effects of viscous and elastic properties of a polymer on the resulting wrinkles is shown in Figure 7. It is important to note that a polymer under irradiation is neither purely elastic nor purely viscous because the surface temperature of the polymer is normally above its glass transition temperature.

Figure 7. Effects of viscous and elastic properties of a polymer on the resulting buckling wrinkles.

Elevating the electron current density increases the polymer surface temperature during irradiation, causing additional application of compressive stress to the upper layer. In the case of the results shown in Figure 2, the electron current density was altered while the electron fluence was kept constant. Since the electron fluence was kept uniform, the physical properties, including the elastic modulus, of the resulting irradiated PMMA samples were unchanging. Thus, the elastic element of the visco-elastic property of PMMA did not affect Page 12 / 18 ACS Paragon Plus Environment

Page 12 of 19

Page 13 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

the width of the formed wrinkles since there was no difference among the elastic moduli of the irradiated PMMA samples and the thickness of the irradiated layer remained constant as the energy of the electrons was not altered for any of the irradiation procedures. The width of the wrinkles increased when the electron current density rose solely due to the upper layer becoming more fluid-like with increasing temperature. Furthermore, the height of the wrinkles increased initially as the electron current density increased due to the upper layer being dominantly elastic at a low temperature. When the irradiated layer became more fluidlike at a higher temperature, the height reduction from the irradiated layer flowing down repressed the height increase stemming from the layer’s elastic property. In other words, beyond a certain high electron current density, height of the formed wrinkles decreased. Increasing the electron fluence decreases the glass transition temperature of the chainscission polymer irradiated. This decrease in glass transition temperature leads to an elevation in applied compressive stress to the polymer. In the case of the results shown in Figure 3, the electron fluence was altered while the electron current density was kept constant. Here, the width of the formed wrinkles initially increased when the electron fluence rose due to the upper layer becoming more fluid-like with decreasing glass transition temperature at a relatively constant polymer surface temperature. Height initially increased when the electron fluence rose also due to the elastic property of a polymer that causes the wrinkle height to increase with increasing applied compressive stress. However, molecular weight of irradiated PMMA decreases exponentially with increasing electron irradiation fluence,33-34 signifying that, scission rate of PMMA becomes insignificantly small past a certain dose. Figure 4 strongly supports this fact as it shows that the glass transition temperature of PMMA and the received dose also have a closely inversely exponential relationship. Therefore, when the irradiation current density is kept constant, greater irradiation duration causes no additional application of compressive stress to the polymer being irradiated. This is manifested in Figure Page 13 / 18 ACS Paragon Plus Environment

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

3 as both the width and the height of the formed wrinkles became relatively unchanging beyond a certain electron fluence. One of the most significant advantages of utilizing the electron irradiation process is being capable of selectively irradiating areas on the polymer surface. Figure 8 shows the OM image of irradiated PMMA surface that was masked with a copper TEM grid (300 lines/inch square mesh) prior to the irradiation procedure. The mask effectively shielded certain areas while exposing others to radiation. As a consequence, wrinkles formed only on the irradiated areas, clearly patterning the polymer surface.

Figure 8. OM image of PMMA surface irradiated at 0.14 µA/cm2 for 30 minutes while masked with a copper TEM grid (300 lines/inch square mesh).

4. Conclusion We have presented that a wrinkled surface can be fabricated on polymers by electron irradiation. Electron irradiation simultaneously produces a bilayer polymeric structure as well as apply heat near the polymer surface. As a result, significant compressive stress is delivered at the interface of the bilayer, leading to surface wrinkling. The characteristics of the formed Page 14 / 18 ACS Paragon Plus Environment

Page 14 of 19

Page 15 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

wrinkles can be controlled by changing the irradiation parameters such as current density and electron fluence. The one-step electron irradiation approach allows large-area wrinkled surfaces by increasing the electron irradiation area. Moreover, patterned wrinkle structures are also readily fabricated by the approach. Therefore, the electron irradiation approach provides an efficient tool in fabricating and manipulating wrinkled polymer surfaces for various applications including tunable optical devices, tissue engineering, microfluidic channels, dry adhesion, and flexible electronics.

Notes The authors declare no competing financial interest.

Acknowledgement This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (NRF-2017M2A2A6A02070697).

References (1) Chen, C. M.; Yang, S., Wrinkling instabilities in polymer films and their applications. Polym Int 2012, 61 (7), 1041-1047. (2) Lee, S. G.; Lee, D. Y.; Lim, H. S.; Lee, D. H.; Lee, S.; Cho, K., Switchable Transparency and Wetting of Elastomeric Smart Windows. Adv Mater 2010, 22 (44), 5013-+. (3) Koo, W. H.; Jeong, S. M.; Araoka, F.; Ishikawa, K.; Nishimura, S.; Toyooka, T.; Takezoe, H., Light extraction from organic light-emitting diodes enhanced by spontaneously formed buckles. Nat Photonics 2010, 4 (4), 222-226. (4) Yoo, P. J., Invited Paper: Fabrication of Complexly Patterned Wavy Structures Using SelfOrganized Anisotropic Wrinkling. Electron Mater Lett 2011, 7 (1), 17-23. (5) Zhang, L.; Lang, X. Y.; Hirata, A.; Chen, M. W., Wrinkled Nanoporous Gold Films with Page 15 / 18 ACS Paragon Plus Environment

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Ultrahigh Surface-Enhanced Raman Scattering Enhancement. Acs Nano 2011, 5 (6), 4407-4413. (6) Lin, P. C.; Yang, S., Mechanically switchable wetting on wrinkled elastomers with dualscale roughness. Soft Matter 2009, 5 (5), 1011-1018. (7) Ohzono, T.; Monobe, H., Morphological Transformation of a Liquid Micropattern on Dynamically Tunable Microwrinkles. Langmuir 2010, 26 (9), 6127-6132. (8) Chung, J. Y.; Youngblood, J. P.; Stafford, C. M., Anisotropic wetting on tunable microwrinkled surfaces. Soft Matter 2007, 3 (9), 1163-1169. (9) Khare, K.; Zhou, J. H.; Yang, S., Tunable Open-Channel Microfluidics on Soft Poly(dimethylsiloxane) (PDMS) Substrates with Sinusoidal Grooves. Langmuir 2009, 25 (21), 12794-12799. (10) Chan, E. P.; Smith, E. J.; Hayward, R. C.; Crosby, A. J., Surface wrinkles for smart adhesion. Adv Mater 2008, 20 (4), 711-+. (11) Lin, P. C.; Vajpayee, S.; Jagota, A.; Hui, C. Y.; Yang, S., Mechanically tunable dry adhesive from wrinkled elastomers. Soft Matter 2008, 4 (9), 1830-1835. (12) Jin, C. R.; Khare, K.; Vajpayee, S.; Yang, S.; Jagota, A.; Hui, C. Y., Adhesive contact between a rippled elastic surface and a rigid spherical indenter: from partial to full contact. Soft Matter 2011, 7 (22), 10728-10736. (13) Kuwabara, K.; Ogino, M.; Motowaki, S.; Miyauchi, A., Fluorescence measurements of nanopillars fabricated by high-aspect-ratio nanoprint technology. Microelectron Eng 2004, 73-4, 752-756. (14) del Campo, A.; Arzt, E., Fabrication approaches for generating complex micro- and nanopatterns on polymeric surfaces. Chem Rev 2008, 108 (3), 911-945. (15) Delamarche, E.; Juncker, D.; Schmid, H., Microfluidics for processing surfaces and miniaturizing biological assays. Adv Mater 2005, 17 (24), 2911-2933. (16) Liu, Y. M.; Sun, S.; Singha, S.; Cho, M. R.; Gordon, R. J., 3D femtosecond laser patterning of collagen for directed cell attachment. Biomaterials 2005, 26 (22), 45974605. (17) Martina, M.; Subramanyam, G.; Weaver, J. C.; Hutmacher, D. W.; Morse, D. E.; Valiyaveettil, S., Developing macroporous bicontinuous materials as scaffolds for tissue engineering. Biomaterials 2005, 26 (28), 5609-5616. (18) Perale, G.; Hilborn, J. G., Bioresorbable polymers for biomedical applications : from fundamentals to translational medicine. Elsevier/Woodhead Publishing: Amsterdam, 2017; p xxxiv, 593 pages. (19) Khang, D. Y.; Xiao, J.; Kocabas, C.; MacLaren, S.; Banks, T.; Jiang, H.; Huang, Y. Y.; Page 16 / 18 ACS Paragon Plus Environment

Page 16 of 19

Page 17 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Rogers, J. A., Molecular scale buckling mechanics in individual aligned single-wall carbon nanotubes on elastomeric substrates. Nano Lett 2008, 8 (1), 124-30. (20) Kim, D. H.; Ahn, J. H.; Choi, W. M.; Kim, H. S.; Kim, T. H.; Song, J. Z.; Huang, Y. G. Y.; Liu, Z. J.; Lu, C.; Rogers, J. A., Stretchable and foldable silicon integrated circuits. Science 2008, 320 (5875), 507-511. (21) Tahk, D.; Lee, H. H.; Khang, D. Y., Elastic Moduli of Organic Electronic Materials by the Buckling Method. Macromolecules 2009, 42 (18), 7079-7083. (22) Lipomi, D. J.; Bao, Z. A., Stretchable, elastic materials and devices for solar energy conversion. Energ Environ Sci 2011, 4 (9), 3314-3328. (23) Wu, H. S.; Kustra, S.; Gates, E. M.; Bettinger, C. J., Topographic substrates as strain relief features in stretchable organic thin film transistors. Org Electron 2013, 14 (6), 1636-1642. (24) Yoo, P. J.; Lee, H. H., Morphological diagram for metal/polymer bilayer wrinkling: Influence of thermomechanical properties of polymer layer. Macromolecules 2005, 38 (7), 2820-2831. (25) Yang, S.; Khare, K.; Lin, P. C., Harnessing Surface Wrinkle Patterns in Soft Matter. Adv Funct Mater 2010, 20 (16), 2550-2564. (26) Schweikart, A.; Horn, A.; Boker, A.; Fery, A., Controlled Wrinkling as a Novel Method for the Fabrication of Patterned Surfaces. Complex Macromolecular Systems I 2010, 227, 75-99. (27) Makuuchi, K.; Cheng, S., Radiation processing of polymer materials and its industrial applications. Wiley: Hoboken, N.J., 2011; p xxviii, 415 p. (28) Long, B. W.; Frank, E. D.; Ehrlich, R. A., Radiography essentials for limited practice. 3rd ed.; Saunders/Elsevier: St. Louis, Mo., 2010; p xi, 642 p. (29) Mark, J. E., Polymer data handbook. Oxford University Press: New York, 1999; p xi, 1018 p. (30) Stenberg, H.; Maaranen, J.; Suvanto, M.; Pakkanen, T. T., Solvent-assisted and thermal wrinklings of argon plasma treated polystyrene coatings on silicon substrate. Surf Coat Tech 2014, 238, 133-138. (31) Chan, E. P.; Page, K. A.; Im, S. H.; Patton, D. L.; Huang, R.; Stafford, C. M., Viscoelastic properties of confined polymer films measured via thermal wrinkling. Soft Matter 2009, 5 (23), 4638-4641. (32) Bowden, N.; Brittain, S.; Evans, A. G.; Hutchinson, J. W.; Whitesides, G. M., Spontaneous formation of ordered structures in thin films of metals supported on an elastomeric polymer. Nature 1998, 393 (6681), 146-149.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(33) Sayyah, S. M.; Khaliel, A. B.; El-Salam, H. M. A., Molecular weight studies of the gamma-irradiation degradation of poly(methyl methacrylate) doped with poly(psulfanilamide). J Appl Polym Sci 2007, 106 (2), 1294-1300. (34) Lu, C. I., Electron degradation of poly(methyl methacrylate). International Nuclear Information System 1981, 15 (5).


Page 18 of 19

Page 19 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Table of Contents/Abstract Graphic


Patterning of Wrinkled Polymer Surfaces by Single-Step Electron

Recommend Documents