Thermally Fast-Curable, âStickyâ Nanoadhesive for Strong Adhesion

Subscriber access provided by READING UNIV

Article

Thermally Fast-Curable, “Sticky” Nano-Adhesive for Strong Adhesion on Arbitrary Substrate Munkyu Joo, Moo Jin Kwak, Heeyeon Moon, Eunjung Lee, Siyoung Q. Choi, and Sung Gap Im ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b13298 • Publication Date (Web): 01 Nov 2017 Downloaded from http://pubs.acs.org on November 3, 2017

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 free 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 accessible to all readers and 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.

ACS Applied Materials & Interfaces 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 13

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

ACS Applied Materials & Interfaces

Thermally Fast-Curable, “Sticky” Nano-Adhesive for Strong Adhesion on Arbitrary Substrate Munkyu Jooa†, Moo Jin Kwaka†, Heeyeon Moona, Eunjung Leea, Siyoung Q. Choia, and Sung Gap Ima,b* a

Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, KOREA

b

KAIST Institute for NanoCentury, Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, KOREA KEYWORDS: nano-adhesive, thermal cross-linking, stick, ionic polymer, initiated chemical vapor deposition (iCVD)

ABSTRACT: Demand of adhesives that are strong but ultra-thin with high flexibility, optical transparency, and long-term stability is rapidly growing recently. Here, we suggest a thermally curable, “sticky” nano-adhesive with outstanding adhesion strength accomplished by single-side deposition of the nano-adhesive on arbitrary substrates. The “sticky” nanoadhesive is composed of an ionic copolymer film generated from two acrylate monomers with tertiary amine and alkyl halide functionalities, formed by a solvent-free method, initiated chemical vapor deposition (iCVD). Due to the low glass transition temperature (Tg) of the copolymer (-9 °C), the ionic copolymer shows a viscoelastic behavior that makes the adhesive attachable to various substrates, regardless of the substrate materials. Moreover, the copolymer film is thermally curable via a cross-linking reaction between the alkyl halide and tertiary amine functionalities, which substantially increased the adhesion strength of the 500 nm-thick nano-adhesive greater than 25 N/25mm within 5 min curing at 120 °C. The adhesive thickness can further be reduced to 50 nm to achieve greater than 35 N/25mm within 30 min at 120 °C. The nano-adhesive layer can form uniform adhesion in a large area substrate (up to 130 × 100 mm2) with the deposition of the adhesive only on one side of the substrates to be laminated. Thanks to its ultra-thin nature, the nano-adhesive is also optically transparent as well as highly flexible, which will play a critical role in fabrication and the lamination of future flexible/wearable devices.

ever, the thickness of most of the conventional adhesive materials prepared are commonly tens of microns or higher because of their viscous nature for the stickiness.1920 The thick nature of the conventional adhesive is quite problematic because the flexibility of the device is highly sensitive to the total thickness of the product and thus the required total thickness of flexible/stretchable devices is typically considered to be less than 20 μm to guarantee reliable flexibility.21-22 Therefore, reducing the adhesive layer thickness is pivotally important.

INTRODUCTION Adhesive is one of the most common materials in our daily life. The material is mostly used as a form of tape or liquid-type glue and a variety of new adhesive products with improved features have been developed continuously in order to meet the increasing demands from diverse industrial applications, such as electronic devices,1-4 microfluidic devices,5-7 encapsulations,8-10 biomedical products,11 and sensor technologies.12-13 Recently, huge research efforts have been made to produce light-weight, flexible/wearable electronic devices and biomedical products compatible with various form factors, which critically requires a new type of adhesive with high flexibility and optical transparency without compromising the strong adhesion.14-16 Especially, to make the adhesive more flexible, the adhesive itself must be sufficiently thin.17-18 How-

Several attempts have been made to reduce the adhesive thickness while maintaining the high adhesive strength by surface modification, such as pre-treatment of target substrate with e-beam or gamma radiation or chemical modification.23-26 However, the effect of such treatments is temporary in most cases. The chemical modification of substrate often requires specific surface

1

ACS Paragon Plus Environment


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 13

25 N/25mm by additional post-curing of the adhesive at 120 oC just within 5 min. Greater than 35 N/25mm of peel adhesion could also be achieved only with 50 nm-thick nano-adhesive in 30 min at 120 oC. Furthermore, the

functionalities on the substrate and the modification procedure might be quite complicated, which substantially limit its applicability to various kinds of substrate materials. Another route to reduce the adhesive thickness is the use of organic solvents. However, it might give rise to many problems. It often causes the outgassing problem, leaving unwanted bubbles, which leads to the serious adhesion failure. Moreover, direct application of solvent-based adhesive onto electronic devices may damage the substrate materials, resulting in device failure/degradation.27 The solvent-based adhesives may also cause environmental problems such as the generation of volatile organic solvents (VOCs) and unreacted monomers. Therefore, solvent-free type of adhesive is highly desirable to minimize such solvent-related problems.28-29 Solvent-free, hot-melt adhesive is also used widely,30 but the high process temperature must be overcome to minimize the thermal deformation of flexible/stretchable substrates.31 Previously, we had developed thin, solvent-free adhesive materials in damage-free manner via initiated chemical vapor deposition (iCVD) process.5, 7 The vapor phase polymerization process enables the formation of ultrathin but defect-free films on arbitrary substrates with excellent uniformity and conformal coverage.32-34 In addition, the solventless, eco-friendly process can eliminate many problems originated from the use of solvent as noted above. Our previous works, however, also have some drawback such as inevitable use of additional posttreatment to bind two substrates and long curing time – longer than 8 hrs – to ensure an intact adhesion between the two substrates.5, 7 In this study, we addressed such issues by proposing a new type of ultra-thin, solvent-free, thermally curable “sticky” adhesive. The thermally curable “stick” nano-adhesive developed in this work can laminate two arbitrary substrates by using only one-side deposition of adhesive thanks to the inherently “sticky” nature of the adhesive materials with low glass transition temperature (Tg) and characteristic viscoelastic rheological properties. The curing time for the nano-adhesive layer here is very short – less than 30 min. The adhesive applied on a single side could form a conformal adhesion with a decent level of adhesion strength only with the thickness less than 500 nm. Importantly, the nano-adhesive system was designed to be capable of cross-linking by thermal treatment, which could increase the adhesion strength substantially by thermal curing under relatively low curing temperature compared with conventional hot-melts.31 We achieved a strong peel adhesion strength larger than

Figure 1. (a) The overall adhesion scheme with the TCIPbased nano-adhesive, p(CEA-co-DMAEMA) and (b) the reaction scheme of the iCVD polymerization and cross-linking reaction by thermal post-treatment.

thermally cross-linked adhesive was optically transparent and highly resistant against various mechanical and chemical stresses. No apparent peel strength degradation was observed in the adhesive even after flexing and bending tests in hot and humid conditions. Moreover, the developed nano-adhesive maintained strong adhesion even after the exposure to various chemicals including water, isopropanol (IPA), toluene, and tetrahydrofuran (THF) for more than 20 hrs. The ultra-thin, “sticky” nanoadhesive with high flexibility, chemical stability, and strong adhesion is expected to play an important role as a component of flexible electronic devices and wearable medical products in near future.

RESULT AND DISCUSSION

2


Page 3 of 13

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


Figure 2. The chemical composition analysis of TCIP nano-adhesives, pC2D1, pC1D1, and pC1D2: (a) the FT-IR spectra, (b) the table of atomic fraction of elements and copolymer ratio, and (c) the XPS high resolution scans of N1s, and (d) Cl2p.

Figure 1a shows the overall scheme of the lamination of two substrates using the one-side-applicable adhesive based on thermally cross-linkable ionic polymer (TCIP). For the generation of the nano-adhesive system, a TCIP film was synthesized in vapor phase via iCVD process,32 which consists of an acrylic copolymer from two monomers of 2-chloroethyl acrylate (CEA) and 2(dimethylamino)ethyl methacrylate (DMAEMA). The synthetic preparation scheme of the TCIP adhesive polymer is also shown in Figure 1b. The CEA and DMAEMA monomers were selected to synthesize the TCIP layer, because of the low glass transition temperature (Tg) of each homopolymer of poly(2-chloroethyl acrylate) (pCEA) and poly[2-(dimethylamino)ethyl methacrylate] (pDMAEMA) (Tg,pCEA = -10 oC, Tg,pDMAEMA = -4 oC) (Figure S1 in Supporting Information). Thus the Tg of the copolymer, poly[2-chloroethyl acrylate-co-2(dimethylamino)ethyl methacrylate] [p(CEA-coDMAEMA)] (pCD) was also quite low so that the copolymer film retain the viscoelastic property, which makes the film sticky and enables the adhesive film to expand its contact area to the substrate. Unlike the nano-adhesive layers developed previously,5, 7 which requires the deposition of the adhesive layer on both substrates to laminate, the sticky surface of the copolymer adhesive layer could induce a physical bonding between the target substrates only with one-side deposition of nano-adhesive.35 Subsequent thermal treatment induced cross-linking reaction between the tertiary amine and alkyl halide functionalities in the copolymer, where the tertiary amine and alkyl

chloride moieties in the copolymer undergo a nucleophilic substitution (SN2) reaction,4 which dramatically increased the adhesion strength to laminate the two target substrates tightly, even with the adhesive thickness as low as 50 nm. In order to optimize the adhesion performance of the adhesive polymers, the composition of the copolymer was changed by adjusting the flow rate of each monomer injected into the iCVD chamber (see Table S1 in the Supporting Information). Three kinds of flow rate ratio of CEA to DMAEMA, 2: 1, 1: 1, and 1: 2 were used in this study to generate a set of copolymer films of pC2D1, pC1D1, and pC1D2, respectively. The chemical composition of each resultant film was analyzed by Fourier transform-infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) (Figure 2). Figure 2a shows the FT-IR spectra of pCEA, pDMAEMA homopolymers, and pCD copolymers. The characteristic peaks attributed to each monomer were clearly observed in the FT-IR spectra of all three kinds of copolymers. The C-Cl peak from CEA was observed at 662 cm-1 and the tertiary amine peak from DMAEMA was observed at 2764 cm-1, indicating that the key functionalities of CEA and DMAEMA monomers survived the iCVD polymerization process. In addition, the increase in the flow rate of CEA resulted in the increase of C-Cl peak intensity and the decrease in tertiary amine peak, respectively, which confirms that the relative amount of each functionality in the copolymer could be controlled systematically in accordance with the variation in the flow rate of the monomers.

3



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 4 of 13

Figure 3. Frequency-dependent viscoelastic properties of the pC2D1, pC1D1, and pC1D2: (a) storage modulus (G'), (b) loss modulus (G"), and (c) tan δ. (d) The Tg of the pDMAEMA homopolymer, p(CEA-co-DMAEMA) copolymers, and pCEA homopolymer.

such as cohesion, adhesion, and tackiness.37-38 Figure 3a and b shows the storage (elastic) modulus (G') and the loss (viscous) modulus (G") as a function of frequency, and the G' of each copolymer was lower than the corresponding G'' over the entire frequency range in all of the three copolymers. In particular, the storage modulus in the lower frequencies ( < 0.1 Hz) was about 103 - 104 Pa, which was about an order of magnitude lower than the loss modulus (~ 104 - 105 Pa) at the same frequency, indicating its viscous character rather than elastic while it has large viscosity ( > 104 Pa s). This satisfies the requirement of adhesive before cross-linking just as other conventional adhesives (e.g., epoxy resin); its large viscosity guarantees enough tackiness while its terminal behavior (G' < G" for lower frequencies) allows filling-in of the adhesive to the rough substrate, ensuring the large contact area. The terminal behavior can be more easily seen in tan δ (Figure 3c); for the entire frequency range, tan δ is greater than 1. The tan δ value of pC2D1 were the highest among the three copolymers and the values increased along with the increased fraction of CEA in the copolymer. Exactly same tendency was also observed in the Tg values of the other copolymers (Figure 3d and Figure S3 in Supporting In-

The surface chemical composition of the copolymer film was also investigated by XPS analysis. Each DMAEMA and CEA monomer contains a characteristic element of N and Cl, respectively, which was utilized to determine the copolymer ratio of the synthesized pCD films by calculating the atomic surface fraction of each element from the XPS survey scans (Figure 2b and Figure S2 in Supporting Information). The estimated surface composition ratios of DMAEMA to CEA were 1.1, 2.0, and 4.4 for pC2D1, pC1D1, and pC1D2, respectively. The surface fraction of DMAEMA was increased along with the increase of DMAEMA input ratio, which is fully consistent with the tendency observed in FT-IR analysis (Figure 2c, d). However, the quantitative surface composition of the copolymer film was somewhat different from the input monomer ratio in the iCVD process, which is due to the vapor pressure difference between CEA (~ 1500 mTorr) and DMAEMA (~600 mTorr) monomers.36 Figure 3 shows the frequency-dependent viscoelasticity and differential scanning calorimetry (DSC) results to monitor the viscoelastic properties of the synthesized copolymer films. Rheological analysis of adhesives is a useful tool to predict the final properties of the adhesives

4


Page 5 of 13

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


Figure 4. (a) The degree of cross-linking of the TCIPs (pC2D1, pC1D1, pC1D2) before and after the cross-linking reaction at 90 and 120 °C for 30 min. (b) The high resolution XPS spectra of pristine (left) and thermal post-cured (right) pC2D1. (c) The DSC spectra of pC2D1 with 1st and 2nd cycle from 50 to 300 °C.

formation). In this regard, pC2D1 with the lowest G' and highest tan δ value along with large G" can provide the largest contact interface between the adhesive and substrate surface among the three copolymers, resulting in the best adhesion strength.

DMAMEA was about 1 : 1, formed the thermally crosslinked film with the highest degree of cross-linking.39 The pristine pC2D1 before post-treatment showed about 6 % degree of cross-linking. After thermal treatment at 90 °C for 30 min, the degree of cross-linking increased to about 10 %, and it also increased up to about 18 % by thermal curing at 120 °C. Similar trend was observed in pC1D1 and pC1D2, but the overall increase tendency was decreased.

It follows from the rheological analysis that the copolymer-based adhesive layer is sticky but the cohesion is not quite strong. However, the low cohesion strength could be enhanced substantially by inducing a SN2-type cross-linking reaction to generate quaternary ammonium chloride, cross-linked sites in the copolymer adhesive simply by a subsequent thermal treatment. The degree of cross-linking for each polymer before and after the thermal treatment could be estimated by checking the increased amount of newly emerged N+ or Cl- peaks in the high resolution XPS spectra, which is illustrated in Figures 4a. The pristine copolymer films mostly retain noncross-linked tertiary amine and alkyl halide functionalities, which were detected as neutral N and Cl peaks in the high resolution XPS spectra. The detection of new N+ and Cl- moieties in the thermally treated copolymer film in XPS spectra verifies the formation of quaternary ammonium sites in the copolymer adhesive (Figure 4b and Figure S4 in Supporting Information).39 The XPS analysis shows that the pC2D1 whose composition of CEA to

It is worthwhile to note that securing a method to deposit the adhesive polymer film without the loss of the key reactive functionalities is critically important, which must be consumed only by the cross-linking reaction after the adhesive deposition to maximize the curing efficiency. During the iCVD process in this study, the TCIP was successfully synthesized by a free radical polymerization, but the unwanted cross-linking reaction between the two valuable functionalities was minimized during the copolymer deposition step in the iCVD process. This phenomenon is due to the characteristics of the iCVD process that the polymerization is performed in solvent-free manner. Thus no solvent effect can be expected in the iCVD process, which is pivotal to trigger the SN2-type cross-linking reaction between the two functionalities, known as Menshutkin reaction, where polar solvents efficiently stabilize the transition state of the SN2 reaction.40 As a result, the

5



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 6 of 13

Figure 5. (a) The scheme of the lap shear strength test and the lap shear strength result of glass-glass adhered with the 500 nm-thick TCIP nano-adhesive. Afterward, the adhesive layer was cured at 120 °C for 30 min. (b) The scheme of the peel strength test and the peel strength result of PET-PET laminated with the 500 nm-thick TCIP nano-adhesive. Afterward, the adhesive layer was cured at 120 °C for 30 min. (c) Required dwell time vs the curing temperature, and (d) the peel strength result of PET-PET substrates laminated with pC2D1 nano-adhesive with the variation of the adhesive thickness from 50 to 1200 nm with the fixed curing condition at 120 °C for 30 min.

cross-linking reaction was suppressed effectively, and non-cross-linked, sticky copolymer film with a low Tg (< 0 °C) was obtained successfully.

to the substrate materials, and we decided to pick the lowest curing temperature as far as the adhesion strength is sufficiently high.

DSC analysis supports the occurrence of cross-linking of the copolymer by thermal annealing. Figure 4c show the 1st and 2nd scan DSC data of pC2D1, respectively. In 1st scan, a prominent exothermic peak was clearly observed in the range of 120 - 250 °C, well corresponding to the Menshutkin reaction between tertiary amine and alkyl halide in the side chains of the copolymer.41 However, no exothermic peak was observed in the 2nd scan, indicating that an irreversible exothermic reaction occurs in the copolymer film by the applied thermal treatment.

To evaluate the adhesion performances of the series of TCIP adhesives, lap shear strength and peel strength were estimated. The laminated glass-glass samples were used for the estimation of the lap shear strength. The thickness of the nano-adhesives was fixed to 500 nm. Figure 5a shows the result of the lap shear strength of each copolymer adhesive before and after the thermal curing. We should note that the shear strength vanishes as the shear rate goes to zero for the pre-curing samples, as expected from the rheological data (Figure S6 in supporting information), but higher shear rates give finite shear strength values. After the thermal curing, the lap shear strength was dramatically increased. The thermally cured pC2D1 showed the highest shear strength (about 260 N/cm2) and the thermally cured pC1D1 also showed high shear strength of about 240 N/cm2. The Menshutkin crosslinking reaction caused by the thermal treatment induces the formation of a network of polymer chains, which enhanced the creep stability greatly, resulting in the dramatic increase in the shear adhesion strength.42 The effect of the cross-linking reaction can be clearly observed in the case of pC1D2. The cross-linked pC1D2 exhibited the less improvement of shear strength compared with the

The curing temperature was optimized with respect to the cross-linking degree and peel strength. At higher temperature than 120 °C, 150 °C, cross-linking degree increases up to about 34 % (Figure S5). However, peel strength value was practically identical to the samples cured at 120 ºC. The DSC analysis (Figure 4c) also confirms the onset of the curing reaction, which is close to 120 ºC, which is fully consistent with the peel strength data shown in Figure S5. In other words, the curing starts at near 120 ºC or higher temperature, and once the curing reaction was completed, the adhesion strength is sufficiently high, regardless of the curing temperature. The increase of curing temperature might cause the damage

6


Page 7 of 13

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


Figure 6. (a) The peel strength result of the laminated substrate pairs with various kinds of substrate materials, including glass, PET, PEN, PI, copper film, Invar sheet, latex rubber, paper, and PDMS (commonly using pC2D1 nanoadhesive with 500 nm thickness, and fixed post-curing at 120 °C for 30 min). (b) The photographic adhesion image of PET-Invar sheet in large area (130 mm by 100 mm), using pC2D1 nano-adhesive with 500 nm thickness, post-curing at 120 °C for 30 min. (c) Transmittance spectra in visible wavelength of PET/PET and PET/pC2D1 (500 nm)/PET samples.

above. The thermal post-treatment of the TCIP adhesive layer resulted in a dramatically increased peel strength.43 The peel adhesion strength of about 31 N/25mm was achieved for pC2D1. The thermally cured pC1D1 and pC1D2 showed somewhat lower peel strength than that of pC2D1 most likely due to the lower degree of cross-linking (~ 10 – 12 %) than that of pC2D1 (~ 18 %). The pC2D1with the highest degree of cross-linking showed the highest peel strength, which can be ascribed to the largest amount of polar ionic sites (-NR3+Cl--) formed by the cross-linking reaction among the three pCD adhesives. The highly polar cross-linking sites in the TCIP nanoadhesive play a crucial role to maintain high interfacial strength between the adhesive and substrate. Based on the rheological analysis and the adhesion strength estimation results, pC2D1 was considered as the optimal composition for the nano-adhesive application in that the pC2D1 with the lowest G' and Tg is the most sticky and wettable at the interface. Moreover, the pC2D1 layer showed the highest degree of cross-linking, leading to the substantial improvement in the adhesion strength.

pristine sample before thermal post-curing, even though the heat treatment was carried out. This phenomenon can be explained by the following reason. In pC1D2, the contents of tertiary amines are about 4-times higher than those of alkyl chlorides as the functional moieties for the cross-linking reaction. As a result, this imbalance of copolymer ratio is possible to limit increase of the degree of cross-linking, which leads to difficult to improve cohesive strength of pC1D2 copolymer. To measure the peel strength of the TCIP adhesives, one side of the polyethylene terephthalate (PET) film was coated with the 500 nm-thick adhesive and laminated with another bare PET film. The peel strength of each of the pre-cured adhesive was about 0.5, 0.3 and 0.2 N/25mm in pC2D1, pC1D1 and pC1D2, respectively, which is well consistent with the tendency of tan δ relate to tackiness of the adhesives (Figure 3c), where pC2D1 showed the highest tan δ, thus might provide the largest contact area between the adhesive and substrates. However, the peel strength value itself was still quite low due to the low cohesion strength of the adhesives as described

7



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 13

Figure 7. The stability test result of PET-PET substrates laminated with pC2D1 nano-adhesive, 500 nm thickness, at 120 °C for 30 min against (a) high temperature and humidity (85 °C, 85 % RH), (b) 500 times of flexing cycle with various bending radii, (c) various types of solvents (water, IPA, toluene, and THF), and (d) storage in air ambient for 30 days.

curing condition, adhesive with thinner thickness showed slightly higher adhesion strength than that with thicker one. The phenomenon is most likely due to the stress release after the thermal curing. In fact, regardless of the adhesive thickness, most of the adhesion failure after the peel test is the rupture of PET substrate, rather than the delamination between the adhesive layer, which strongly infers that the real adhesion strength of the TCIP adhesive should be higher. Considering this aspect, the thinner adhesive layer is advantageous in terms of stress release than thick one. In other words, the cross-linked, thicker adhesive might cause the PET substrate a bit more brittle than thinner one. However, difference in the adhesion strength in the range of adhesive thickness of 50 nm to 1.2 µm is not quite large. These results indicated that the inherently sticky nature of the TCIP adhesive to induce an excellent contact with the substrate, as well as the substantially enhanced cohesion strength obtained by the thermal cross-linking reaction is responsible for such

Figure 5c shows the required dwell time to bond at each temperature of 90, 100, 110, and 120 °C, where the dwell time was defined as the time required to reach the peel strength higher than 25 N/25mm. To obtain a strong adhesion, 45 min of dwell time was required at 90 °C, which could be reduced to only 5 min at the curing temperature of 120 °C due to the increased cross-linking reaction rate by elevating the curing temperature. Table S2 show the adhesion peel strength with different adhesive materials found in previous literature, thickness and target substrates. In previous works, the lowest peel strength value has 0.4 N/ 25mm and the highest peel strength value has 37 N/ 25 mm. However, all these references commonly used the adhesives with the thickness larger than a few microns. To the contrary, the sticky adhesive in this work was sub-micron-thick as well as binding two substrates with outstanding adhesion strength. The effect of the adhesive thickness on the peel adhesion strength was also examined by adjusting the pC2D1 adhesive thickness from about 50 to 1200 nm. At the same

8


Page 9 of 13

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


a high adhesion strength from ultra-thin, 50 nm-thick pC2D1 adhesive layer.

induced by bending, which might cause the adhesion failure. The stability test result clearly shows that no appreciable degradation in adhesion strength was observed (Figure 7a), verifying the excellent stability of the TCIP adhesive under high temperature and high humidity condition. The adhesion strength of the TCIP adhesive was also retained even after the 500 times of flexing cycles with the bending radius, 5 to 10 mm (Figure 7b), confirming its superior mechanical flexibility. In addition, the adhesive was intact without generating any cracks or interfacial defects even after the 500 times of flexing cycles, due to the ultra-thinness of the adhesive layer. The chemical stability of the TCIP adhesive was also estimated by soaking the bonded samples laminated with pC2D1 adhesive in various solvents such as water, IPA, toluene, and THF for 20 hrs, whose peel strengths were compared with the untreated, control sample (Figure 7c). No apparent loss of peel strength was observed, indicating that the cross-linking induced by the thermal treatment imparts effective chemical stability to the TCIP adhesive. The storage stability of the TCIP adhesive after the lamination was also checked by leaving the adhesive-coated substrate in air ambient from 3 to 30 days. More than 97 % of the initial peel adhesion strength was retained up to 15 days and larger than 80 % of adhesion was obtained even after the storage for 30 days, verifying the outstanding storage stability of the adhesive layer (Figure 7d). The ultra-thin but environmentally stable TCIP nano-adhesive with strong adhesion will be highly advantageous for the application to future flexible/stretchable devices that require the use of ultra-thin adhesive layer.

To expand the applicability of the TCIP adhesive, the lamination between various kinds of substrate material pairs were attempted with the nano-adhesive developed in this study. Especially, forming a good adhesion between two different substrate materials with far different surface properties such as roughness and surface energy is still not a trivial task to achieve. Various substrate materials, such as glass, PET, polyethylene naphthalate (PEN), polyimide (PI), copper foil, Invar (Fe-Ni alloy) sheet, latex, paper, and polydimethylsiloxane (PDMS) were used for this purpose. The peel strength of each laminated sample was measured. All samples were bonded well to each other with the high peel adhesion force larger than 10 N/25mm (Figure 6a). Especially, the gray arrows in Figure 6a indicate that substrate rupture occurred before the failure of the nano-adhesive (Figure S7 in Supporting Information). In other words, the adhesion strength in such cases is greater than the maximum yield stress of the substrate materials and the real peel adhesion strength should be far higher than the measured value. It is worthwhile to note that the surfaces with large difference in surface energy such as PET-metal (Invar film and copper foil) samples could be laminated strongly. Surfaces with non-flat, textured surface morphology could also be laminated, showing the wide versatility of the TCIP adhesive, enabled by the inherent stickiness of the adhesive layer. The apparent peel strength was just 4 N/25mm for the PET-paper sample, which is mainly due to the low yield stress of paper, not because of the weak adhesion – paper was torn out before the peel failure of the adhesive. The developed adhesive was capable of bonding in large area (130 by 100 mm2) using PET and Invar film (Figure 6b). The viscoelastic nature of the TCIP adhesive enables the uniform, intact lamination of surfaces with large area without additional treatment for bubble removal. Subsequent thermal curing could form a strong, uniform, and highly transparent adhesion even on large area substrates. As seen the Figure 6c, the 500 nm-thick pC2D1 adhesive showed nearly 100 % transmittance compared to bare PET sample in the wavelength of visible range from 380 to 780 nm.

CONCLUSION In summary, a novel one-side-applicable TCIP nanoadhesive was developed in this study. The ionic copolymer film was synthesized by the free radical polymerization method in the vapor phase via iCVD process. The vapor-phase method enabled the formation of a copolymer film with a precise control of the thickness and the composition of the adhesive layer on arbitrary substrates with areal uniformity. Especially, the viscoelastic nature of the low-Tg TCIP layer made the copolymer film highly sticky, which facilitated the stable contact with the target substrate and thus induced adhesion with the substrates by depositing the adhesive layer only onto one side of the substrate. The physically bonded substrates at room temperature by the inherent stickiness of the TCIP adhesive could be cured by subsequent thermal post-treatment, which dramatically increased the adhesion strength of the TCIP adhesives. The TCIP adhesive was composed of CEA and DMAEMA monomers, whose composition was optimized to maximize the adhesion performance of the copolymer layer, by controlling the input flow rate of each monomer. Importantly, the key functionalities of tertiary amine and alkyl halides were maintained mostly during the synthesis of the copolymer in the vapor-phase pro-

The environmental stability of the adhesive against various types of stresses, such as high temperature and humidity, repeated flexing cycles, and various kinds of organic solvents was assessed by checking the peel strength variation with the applied external stresses (Figure 7). The adhesive stability under high temperature and humidity was tested with the PET-PET laminated samples using pC2D1 adhesive bent with various bending radius, 5 to 10 mm exposed to a harsh condition (85 °C and 85 % relative humidity) for 24 hrs. The stability of adhesion in bent condition is of great importance since the difference in the coefficient of thermal expansion (CTE) between the flexible substrate and the adhesive will induce an additional strain to the adhesive layer coupled with the strain

9



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 10 of 13

each other. All the substrate materials used in this work except for paper and latex rubber were rinsed with sodium hydroxide (NaOH) solution (2.5 v/v %) and deionized (DI) water, and isopropyl alcohol (IPA) subsequently before the bonding process. The cleaned substrates were dried at 110 °C for 1 hr in vacuum oven. The adhesivecoated substrates, PET, Glass, PI and Copper foil (Cu) with the other bare substrates, Glass, PEN, Cu, Invar, Latex and paper were bonded together with light hand pressure to induce physical adhesion at room temperature, and then pressurized using hot press with 1 MPa at 120 °C for 30 min for curing of the adhesive. For bonding with the adhesive-coated PET and PDMS substrate, the sample was pressurized with 0.005 MPa at 80 °C for 3 hrs. To investigate the effect of adhesive thickness on the adhesion strength, PET-PET lamination was attempted with the thickness ranging from 50 to 1200 nm with the same curing condition of 1 MPa at 120 °C for 30 min using hot press with 1 MPa. To check the curing time dependency of the adhesive, the curing time was changed from 5 to 45 min with the lamination temperature range of 90 to 120 °C.

cess, to be used for the thermal cross-linking reaction afterward. As a result, the TCIP adhesive could form a strong adhesion with the peel strength larger than 35 N/25mm between two arbitrary substrates even with the 50 nm-thick, ultra-thin adhesive layer with the curing condition of 120 oC for 30 min. Up to 25 N/25mm was obtained within 5 min of curing time at 120 oC. The damagefree deposition characteristics of the iCVD process coupled with the benign curing condition will enable the direct, monolithic application of the TCIP adhesive layer to various kinds of flexible, damage-prone devices. Moreover, the adhesive layer showed outstanding environmental stability against various types of external stresses including many kinds of organic solvents, high temperature, humidity, and mechanical flexing applied to the adhesive layer. The development of ultra-thin, nanoadhesive with sub-100 nm thickness will enable the broad use of the adhesive layer for lamination of many kinds of flexible substrate materials. Especially, the adhesive requires only one-side deposition, which makes the lamination step much simpler and minimize the potential damage to the substrates, which will be one of the key requiring components for the realization of future flexible devices.

Characterization of the adhesive films. The FT-IR spectra were obtained using ALPHA FT-IR in absorbance mode (Bruker Optics). 64 scans were collected and averaged for each sample to be measured. The XPS survey scan and high resolution spectra were obtained using Sigma Probe Multipurpose XPS (Thermo VG Scientic) with a monochromatized Al Kα source. Rheological properties of p(CEA-co-DMAEMA) were investigated using a rheometer (MCR 302, Anton Paar) with parallel plate geometry (0.5 mm gap, 25 mm diameter). DSC analysis was performed in the range from -40 to 300 °C (heating rate was maintained with 50 °C/min) using Netzsch DSC 214 Polyma. The shear and peel strengths of the copolymer adhesives were estimated by using a universal testing machine (Instron 5583, Instron Inc., USA). The shear and peel strength are measured using similar to ASTM D1002 and D5170. The test was performed in tensile mode at a pulling speed of 20 mm/min. The transmittance of the pC2D1 adhesive was measured with an ultraviolet-visible (UV-vis) spectrophotometer (UV-3600, Shimadzu Co., Japan) equipped with an integrating sphere. Transmittance was averaged in visible wavelength region from 380 to 780 nm with reference to the PET substrate.

EXPERIMENTAL SECTION Preparation of polymer adhesives using iCVD process. pCEA, pDMAEMA and [p(CEA-co-DMAEMA)] (pCD) were prepared by iCVD process onto PET substrates (thickness = 188 μm, SK Chemicals). The two monomers, CEA (97 %, Sigma-Aldrich) and DMAEMA (95 %, TCI Chemicals), and initiator, tert-butyl peroxide (TBPO, 98 %, Sigma-Aldrich) were vaporized and introduced into an iCVD reactor (Daeki Hi-Tech co, Ltd). All the chemicals in this work were used as purchased without any further purification. TBPO were kept at room temperature, CEA and DMAEMA monomers were heated to 30 and 35 °C, respectively to vaporize them. The reactor pressure and the substrate temperature were kept at 300 mTorr and 30 °C, respectively. For the deposition of p(CEA-co-DMAEMA)s, the flow rates of monomers were varied to deposit the copolymers (pC2D1, pC1D1, and pC1D2) with three compositions. The filament temperature was maintained at 180 °C during the iCVD process. The thickness of the deposited film was monitored in situ by an interferometer as described previously.44-46 For the detailed information about the flow rate of each monomer and the corresponding composition of each copolymer film, see Table S1 in Supporting Information.

Stability test. Mechanical stability test in highly humid condition was executed by introducing the PET-PET samples bonded with the adhesive (pC2D1, 500 nm) and folded at the bending radius of 5 to 10 mm in a humid oven (85 °C and 85 % of humidity) for 20 hrs and then the peel strength of the thermally treated samples was measured. Flexing tests were performed by repeated flexing cycles of PET-PET samples bonded with the pC2D1 adhesives at the bending radius of 5 to 10 mm for 500 times using a bending machine (HanTech co, Ltd), followed by measuring the peel strength before and after the flexing cycles. Chemical stability of the copolymer adhesives was tested by measuring the lap shear strength of bonded

Preparation of adhesive assemblies. A substrate coated with the 500 nm-thick copolymer adhesives were stacked with various other substrates. Slide glass, PEN (100 μm, Teijin Dupont Films), PI (75 μm, Suzhou Kying Industrial Materials), copper foil (300 μm, Nilaco) and Invar (Fe-Ni alloy, 100 μm, Poongwon Precision) substrates were used as the substrates to be laminated to

10


Page 11 of 13

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

ACS Applied Materials & Interfaces (3) Kim, J. H.; Han, M. J.; Seo, S. Flexible, Stretchable, and Patchable Organic Devices Integrated on Freestanding Polymeric Substrates. Journal of Polymer Science Part B-Polymer Physics 2015, 53 (6), 453460, DOI: 10.1002/polb.23662. (4) Seo, J. W.; Joo, M.; Ahn, J.; Lee, T. I.; Kim, T. S.; Im, S. G.; Lee, J. Y. Facilitated embedding of silver nanowires into conformally-coated iCVD polymer films deposited on cloth for robust wearable electronics. Nanoscale 2017, 9 (10), 3399-3407, DOI: 10.1039/c6nr08168a. (5) Im, S. G.; Bong, K. W.; Lee, C. H.; Doyle, P. S.; Gleason, K. K. A conformal nano-adhesive via initiated chemical vapor deposition for microfluidic devices. Lab Chip 2009, 9 (3), 411-416. (6) You, J. B.; Kang, K.; Tran, T. T.; Park, H.; Hwang, W. R.; Be, J. M. K.; Im, S. G. PDMS-based turbulent microfluidic mixer. Lab on a Chip 2015, 15 (7), 1727-1735, DOI: 10.1039/c5lc00070j. (7) You, J. B.; Min, K. I.; Lee, B.; Kim, D. P.; Im, S. G. A doubly crosslinked nano-adhesive for the reliable sealing of flexible microfluidic devices. Lab on a Chip 2013, 13 (7), 1266-1272, DOI: 10.1039/c2lc41266g. (8) Weerasinghe, H. C.; Dkhissi, Y.; Scully, A. D.; Caruso, R. A.; Cheng, Y. B. Encapsulation for improving the lifetime of flexible perovskite solar cells. Nano Energy 2015, 18, 118-125, DOI: 10.1016/j.nanoen.2015.10.006. (9) Weerasinghe, H. C.; Vak, D.; Robotham, B.; Fell, C. J.; Jones, D.; Scully, A. D. New barrier encapsulation and lifetime assessment of printed organic photovoltaic modules. Solar Energy Materials and Solar Cells 2016, 155, 108-116, DOI: 10.1016/j.solmat.2016.04.051. (10) Prager, L.; Helmstedt, U.; Herrnberger, H.; Kahle, O.; Kita, F.; Munch, M.; Pender, A.; Prager, A.; Gerlach, J. W.; Stasiak, M. Photochemical approach to high-barrier films for the encapsulation of flexible laminary electronic devices. Thin Solid Films 2014, 570, 87-95, DOI: 10.1016/j.tsf.2014.09.014. (11) Lee, J. K.; Kang, S. M.; Yang, S. H.; Cho, W. K. Micro/Nanostructured Films and Adhesives for Biomedical Applications. Journal of Biomedical Nanotechnology 2015, 11 (12), 2081-2110, DOI: 10.1166/jbn.2015.2097. (12) Kang, D. Y.; Kim, Y. S.; Ornelas, G.; Sinha, M.; Naidu, K.; Coleman, T. P. Scalable Microfabrication Procedures for AdhesiveIntegrated Flexible and Stretchable Electronic Sensors. Sensors 2015, 15 (9), 23459-23476, DOI: 10.3390/s150923459. (13) Rose, D. P.; Ratterman, M. E.; Griffin, D. K.; Hou, L. L.; KelleyLoughnane, N.; Naik, R. R.; Hagen, J. A.; Papautsky, I.; Heikenfeld, J. C. Adhesive RFID Sensor Patch for Monitoring of Sweat Electrolytes. Ieee Transactions on Biomedical Engineering 2015, 62 (6), 1457-1465, DOI: 10.1109/Tbme.2014.2369991. (14) Li, Z.; Zhang, R. W.; Moon, K. S.; Liu, Y.; Hansen, K.; Le, T. R.; Wong, C. P. Highly Conductive, Flexible, Polyurethane-Based Adhesives for Flexible and Printed Electronics. Adv Funct Mater 2013, 23 (11), 1459-1465, DOI: 10.1002/adfm.201202249. (15) Miller, M. S.; O'Kane, J. C.; Niec, A.; Carmichael, R. S.; Carmichael, T. B. Silver Nanowire/Optical Adhesive Coatings as Transparent Electrodes for Flexible Electronics. Acs Applied Materials & Interfaces 2013, 5 (20), 10165-10172, DOI: 10.1021/am402847y. (16) Russo, A.; Ahn, B. Y.; Adams, J. J.; Duoss, E. B.; Bernhard, J. T.; Lewis, J. A. Pen-on-Paper Flexible Electronics. Advanced materials 2011, 23 (30), 3426-+, DOI: 10.1002/adma.201101328. (17) Siegel, A. C.; Phillips, S. T.; Dickey, M. D.; Lu, N. S.; Suo, Z. G.; Whitesides, G. M. Foldable Printed Circuit Boards on Paper Substrates. Adv Funct Mater 2010, 20 (1), 28-35, DOI: 10.1002/adfm.200901363. (18) Creton, C.; Ciccotti, M. Fracture and adhesion of soft materials: a review. Reports on Progress in Physics 2016, 79 (4), DOI: Artn 04660110.1088/0034-4885/79/4/046601.

glass slides exposed to various chemicals including DI water, IPA, toluene, and THF. Pairs of laminated glass slides with the pC2D1 adhesive were soaked in each test chemical for 20 hrs. After 20 hrs of soaking, the samples were rinsed thoroughly with DI water and dried with N2 gas for the measurement of lap shear strength.

ASSOCIATED CONTENT Supporting Information. The iCVD process condition and DSC data of pCEA, pDMAEMA homopolymers and pCD copolymers, the XPS survey scan of pCD copolymers, the XPS high resolution scan data of pCD copolymers before and after thermal post-curing, the XPS high resolution scan data of pC2D1 before and after thermal post-curing and peel strength data, the shear and peel strength data of pC2D1 pristine (non-curing) samples according to measuring speed, the image of substrate failure and peel strength data after peel test for PET-latex rubber, PET-paper, and PET-PDMS samples, and summary of the adhesion peel strength with previous works. (PDF) The simple video for the bonding process of PET-latex specimen using pC2D1 adhesive (adhesive thickness ~ 500 nm). (AVI) These materials are available free of charge on the ACS Publications website at DOI: xx.xxxx / acsami. xxxxxxx.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version † of the manuscript. These authors contributed equally.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by Wearable Platform Materials Technology Center (WMC) funded by the National Research Foundation of Korea (NRF) Grant of the Korean Government (MSIP) (No. 2016R1A5A1009926), and the Center for Advanced Soft-Electronics funded by the Ministry of Science, ICT and Future Planning as a Global Frontier Project (CASE2017M3A6A5052509). This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No.2017R1A2B3007806).

(19) Volodin, P.; Kondyurin, A. Dewetting of thin polymer film on rough substrate: I. Theory. Journal of Physics D-Applied Physics 2008, 41 (6), DOI: Artn 06530610.1088/0022-3727/41/6/065306.

REFERENCES (1) White, M. S.; Kaltenbrunner, M.; Glowacki, E. D.; Gutnichenko, K.; Kettlgruber, G.; Graz, I.; Aazou, S.; Ulbricht, C.; Egbe, D. A. M.; Miron, M. C.; Major, Z.; Scharber, M. C.; Sekitani, T.; Someya, T.; Bauer, S.; Sariciftci, N. S. Ultrathin, highly flexible and stretchable PLEDs. Nature Photonics 2013, 7 (10), 811-816, DOI: 10.1038/Nphoton.2013.188. (2) Kim, K.; Kim, S. Y.; Lee, J. L. Flexible organic light-emitting diodes using a laser lift-off method. Journal of Materials Chemistry C 2014, 2 (12), 2144-2149, DOI: 10.1039/c3tc30848k.

(20) Gu, X.; Raghavan, D.; Douglas, J. F.; Karim, A. Hole-growth instability in the dewetting of evaporating polymer solution films. Journal of Polymer Science Part B-Polymer Physics 2002, 40 (24), 2825-2832, DOI: 10.1002/polb.10347.

11



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

(21) Sekitani, T.; Zschieschang, U.; Klauk, H.; Someya, T. Flexible organic transistors and circuits with extreme bending stability. Nature materials 2010, 9 (12), 1015-1022, DOI: 10.1038/Nmat2896. (22) Lee, S.; Reuveny, A.; Reeder, J.; Lee, S.; Jin, H.; Liu, Q. H.; Yokota, T.; Sekitani, T.; Isoyama, T.; Abe, Y.; Suo, Z. G.; Someya, T. A transparent bending-insensitive pressure sensor. Nature Nanotechnology 2016, 11 (5), 472-+, DOI: 10.1038/Nnano.2015.324. (23) Bhatnagar, N.; Pyngrope, D.; Pradhan, R.; Jha, S.; Bhowmik, S.; Poulis, H.; Bui, V. T.; Bonin, H. Electron beam modification of space durable polymeric nano-adhesive bonding of ultra-high temperature resistant polymer. Journal of Polymer Engineering 2011, 31 (4), 381-386, DOI: 10.1515/Polyeng.2011.007. (24) Bhowmik, S.; Benedictus, R.; Poulis, J. A.; Bonin, H. W.; Bui, V. T. Influence of mixed field radiation and gamma radiation on nano adhesive bonding of high performance polymer. Journal of Polymer Engineering 2008, 28 (4), 225-242. (25) Pang, B.; Ryu, C. M.; Jin, X.; Kim, H. I. Preparation and properties of UV curable acrylic PSA by vinyl bonded graphene oxide. Applied Surface Science 2013, 285, 727-731, DOI: 10.1016/j.apsusc.2013.08.117. (26) Subramanian, A. S.; Tey, J. N.; Zhang, L. Y.; Ng, B. H.; Roy, S.; Wei, J.; Hu, X. Synergistic bond strengthening in epoxy adhesives using polydopamine/MWCNT hybrids. Polymer 2016, 82, 285-294, DOI: 10.1016/j.polymer.2015.11.031. (27) Naganawa, S.; Nishijima, K.; Hagihara, Y.; Suzuki, Y.; Nagamoto, K.; Kondo, T. P-92: Encapsulation Adhesive Possessing High Water Barrier and Low Corrosive Properties for Flexible Electronic Device. SID Symposium Digest of Technical Papers 2014, 45 (1), 1332-1335, DOI: 10.1002/j.2168-0159.2014.tb00351.x. (28) Czech, Z.; Butwin, A. Development of photoreactive UVcrosslinkable solvent-free acrylic pressure-sensitive adhesives coated at room temperature and used for removable and repositionable self-adhesive materials. Polish Journal of Chemical Technology 2011, 13 (1), 31-34, DOI: 10.2478/v10026-011-0006-9. (29) Czech, Z.; Wesolowska, M. Development of solvent-free acrylic pressure-sensitive adhesives. European Polymer Journal 2007, 43 (8), 3604-3612, DOI: 10.1016/j.eurpolymj.2007.05.003. (30) Creton, C. Pressure-sensitive adhesives: An introductory course. Mrs Bulletin 2003, 28 (6), 434-439, DOI: DOI 10.1557/mrs2003.124. (31) Malysheva, G. V.; Bodrykh, N. V. Hot-melt adhesives. Polymer Science Series D 2011, 4 (4), 301-303. (32) Tenhaeff, W. E.; Gleason, K. K. Initiated and oxidative chemical vapor deposition of polymeric thin films: iCVD and oCVD. Adv Funct Mater 2008, 18 (7), 979-992, DOI: 10.1002/adfm.200701479. (33) Wang, M.; Wang, X.; Moni, P.; Liu, A.; Kim, D. H.; Jo, W. J.; Sojoudi, H.; Gleason, K. K. CVD Polymers for Devices and Device Fabrication. Advanced materials 2017, 29 (11), DOI: 10.1002/adma.201604606. (34) Lau, K. K. S.; Gleason, K. K. Initiated chemical vapor deposition (iCVD) of poly(alkyl acrylates): A kinetic model. Macromolecules 2006, 39 (10), 3695-3703, DOI: 10.1021/ma0601621. (35) Czech, Z. Synthesis and cross-linking of acrylic PSA systems. Journal of Adhesion Science and Technology 2007, 21 (7), 625-635, DOI: Doi 10.1163/156856107781192337. (36) Kwak, M. J.; Oh, M. S.; Yoo, Y.; You, J. B.; Kim, J.; Yu, S. J.; Im, S. G. Series of Liquid Separation System Made of Homogeneous Copolymer Films with Controlled Surface Wettability. Chem Mater 2015, 27 (9), 3441-3449, DOI: 10.1021/acs.chemmater.5b00842. (37) Demarteau, W.; Loutz, J. M. Rheology of acrylic dispersions for pressure sensitive adhesives. Progress in Organic Coatings 1996, 27 (14), 33-44, DOI: Doi 10.1016/0300-9440(95)00517-X. (38) Chu, S. G.; Lee, L.-H. Dynamic Mechanical Properties of Pressure Sensitive Adhesives. In Adhesive Bonding; Plenum Publishing: 1991; pp 97-115. (39) Joo, M.; Shin, J.; Kim, J.; You, J. B.; Yoo, Y.; Kwak, M. J.; Oh, M. S.; Im, S. G. One-Step Synthesis of Cross-Linked Ionic Polymer Thin Films in Vapor Phase and Its Application to an Oil/Water Separation Membrane. Journal of the American Chemical Society 2017, 139 (6), 2329-2337, DOI: 10.1021/jacs.6b11349. (40) Giri, S.; Inostroza-Rivera, R.; Herrera, B.; Nunez, A. S.; Lund, F.; Toro-Labbe, A. The mechanism of Menshutkin reaction in gas and solvent phases from the perspective of reaction electronic flux. Journal of Molecular Modeling 2014, 20 (9), DOI: ARTN 2353

Page 12 of 13

10.1007/s00894-014-2353-y. (41) Hirschl, C.; Biebl-Rydlo, M.; DeBiasio, M.; Muhleisen, W.; Neumaier, L.; Scherf, W.; Oreski, G.; Eder, G.; Chernev, B.; Schwab, W.; Kraft, M. Determining the degree of crosslinking of ethylene vinyl acetate photovoltaic module encapsulants-A comparative study. Solar Energy Materials and Solar Cells 2013, 116, 203-218, DOI: 10.1016/j.solmat.2013.04.022. (42) Peykova, Y.; Lebedeva, O. V.; Diethert, A.; Muller-Buschbaum, P.; Willenbacher, N. Adhesive properties of acrylate copolymers: Effect of the nature of the substrate and copolymer functionality. International Journal of Adhesion and Adhesives 2012, 34, 107-116, DOI: 10.1016/j.ijadhadh.2011.12.001. (43) Lu, X. C.; Cao, G.; Niu, Z. F.; Pan, Q. M. Viscoelastic and Adhesive Properties of Single-Component Thermo-Resistant Acrylic Pressure Sensitive Adhesives. Journal of Applied Polymer Science 2014, 131 (7), DOI: ARTN 4008610.1002/app.40086. (44) Lau, K. K. S.; Gleason, K. K. Initiated chemical vapor deposition (iCVD) of poly( alkyl acrylates): An experimental study. Macromolecules 2006, 39 (10), 3688-3694, DOI: 10.1021/ma0601619. (45) Moon, H.; Seong, H.; Shin, W. C.; Park, W. T.; Kim, M.; Lee, S.; Bong, J. H.; Noh, Y. Y.; Cho, B. J.; Yoo, S.; Im, S. G. Synthesis of ultrathin polymer insulating layers by initiated chemical vapour deposition for low-power soft electronics. Nature materials 2015, 14 (6), 628-35, DOI: 10.1038/nmat4237. (46) Pak, K.; Seong, H.; Choi, J.; Hwang, W. S.; Im, S. G. Synthesis of Ultrathin, Homogeneous Copolymer Dielectrics to Control the Threshold Voltage of Organic Thin-Film Transistors. Adv Funct Mater 2016, 26 (36), 6574-6582.

12


Page 13 of 13

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


TOC Graphic

13


Thermally Fast-Curable, âStickyâ Nanoadhesive for Strong Adhesion

Recommend Documents

Thermally Fast-Curable, âStickyâ Nanoadhesive for Strong Adhesion