Superstretchable and Processable Silicone Elastomers by Digital

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Applications of Polymer, Composite, and Coating Materials

Super-stretchable and processable silicone elastomers by digital light processing 3D printing Tingting Zhao, Ran Yu, Shan Li, Xinpan Li, Ying Zhang, Xin Yang, Xiaojuan Zhao, Chen Wang, Zhichao Liu, Rui Dou, and Wei Huang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 26 Mar 2019 Downloaded from http://pubs.acs.org on March 27, 2019

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ACS Applied Materials & Interfaces

Super-Stretchable and Processable Silicone Elastomers by Digital Light Processing 3D Printing Tingting Zhao1,2, Ran Yu1,*, Shan Li3, Xinpan Li1,2, Ying Zhang1, Xin Yang1, Xiaojuan Zhao1, Chen Wang1,2, Zhichao Liu3, Rui Dou3,*, Wei Huang1,2,* 1Institute

of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s

Republic of China 2University

of Chinese Academy of Sciences, Beijing 100049, People’s Republic of

China 3Technology

and Engineering Center for Space Utilization, Chinese Academy of

Sciences, Beijing 100094, People’s Republic of China *To

whom

correspondence

should

be

addressed.

E-mail:

[email protected];

[email protected]; [email protected] KEYWORDS: silicone elastomers, super-stretchable, digital light processing, 3D printing, thiol-ene click reaction

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ABSTRACT: A series of photosensitive resins suitable for the production of silicone elastomers through digital light processing 3D printing are reported. Based on thiol-ene click reaction between a branched mercaptan functionalized polysiloxane and different molecular weight vinyl terminated polydimethylsiloxane, silicone elastomers with tunable hardness and mechanical properties are obtained. Printed elastomeric objects show high printing resolution and excellent mechanical properties. The break elongation of the silicone elastomers can get up to 1400%, which is much higher than the reported UV cured elastomers and is even higher than the most stretchable thermocuring silicone elastomers. The super-stretchable silicone elastomers are then applied to fabricate stretchable electronics with carbon nanotubes-doped hydrogel. The printable and processable silicone elastomers have great potential applications in various fields including soft robotics, flexible actuators and medical implants. INTRODUCTION Three-dimensional (3D) printing, which refers to any of various processes to create three dimensional objects under computer control, has attracted great attention from researchers and industries in recent years.1-6 Due to its various advantages, including flexibility and high efficiency when small quantities of parts are needed, capability to produce objects with almost any shape or geometry, the technology developed very quickly. Many different 3D printing technologies, including fused deposit modeling, selective laser sintering, inkjet 3D printing, stereolithography (SLA), digital light processing (DLP), have been developed.7-13 SLA and DLP, which are based on the polymerization of photopolymer resin under UV illumination, display much higher printing resolution compared to other technologies. Moreover, in DLP 3D printing 2 ACS Paragon Plus Environment

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technology, UV light is projected from a DLP system, and an entire layer can be cured at once exposure, resulting in its distinct advantage on the high printing speed. However, mainly stiff networks are created through SLA or DLP technologies basing on free radical or cationic photopolymerization mechanisms, usually acrylate or epoxy functionalized photopolymers.14-18 The uncontrolled propagation reaction of these photoresins coupled with the high crosslinking density of the printed objects lead to dense and stiff networks. So far, the studies on developing high-performance elastomeric materials through SLA or DLP technologies are very limited. Due to their great properties of softness, elasticity, resilience, high deformability, elastomeric materials have been widely applied in many areas, like seals, damping elements, flexible parts and many others.19-22 Recently, the new emerging fields, such as soft robots, medical implants, simulated human tissues trigger the urgent demanding of high-performance elastomeric materials. Silicone elastomers are the most widely used materials in these applications for its biocompatibility and low or nearly none cytotoxicity.23-26 Silicone

elastomers

are

generally

fabricated

through

platinum-catalyzed

hydrosilylation, condensation or peroxide-initiated radical reactions. They are all thermocuring and rigid molds are generally needed to fabricate final products. Such traditional manufacturing technology is high-cost and time-consuming and moreover, it is unable to fabricate objects with complicated structures. If silicone elastomers can be fabricated with 3D printing technology, objects with complex structures can be easily obtained. Many researchers have tried to prepare silicone elastomers through inkjet,27 direct writing,28 extrusion29 and embedded 3D printing technologies.30 However, all these printing methods have the defect of limited printing resolution. There are also studies on



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3D printing of silicone elastomer based on UV curing mechanism.31-32 But, the limited tensile strength and elongation restrict their advanced applications where large deformation is needed. Several commercial UV curable elastomers, which are widely used in SLA or DLP 3D printing technologies, are also available, like EPU 40 from Carbon, Tangoplus and Agilus30 from Stratasys. However, they are mainly acrylate or polyurethane-based materials and the break elongation of these elastomers is very limited. Furthermore, it is impossible for users to tune their properties in according to the requirements for applications. Here, a type of branched mercaptan functionalized polysiloxane (MPS) is synthesized and then compounded with different molecular weight vinyl terminated polydimethylsiloxane (VPS) and different content of reinforcing filler silica particles as well as photoinitiators and then a series of photoresins for silicone elastomers are obtained. With the high UV-curing rate, the photoresins have been applied in DLP 3D printing technique and a series of silicone elastomers with tunable hardness and mechanical properties have been fabricated. EXPERIMENTAL SECTION Materials. Hexamethyldisiloxane and dimethoxydimethylsilxane were commercial products

of

Beijing

Kehua

new

material

technology

Co.,

Ltd.

Trimethoxysilylpropanethiol was supplied by Shanghai Chuqing new materials technology Co., Ltd. Hydrochloric acid and toluene were purchased from Aldrich Chemical and used as received. Vinyl- terminated polydimethylsiloxane (VPS) (with molecular weight of 22000 and 4300) were obtained from Beijing Kehua new material technology Co., Ltd. 2-Hydroxy-2-methyl-phenyl-propane-1-one (PI 1173) and phenyl 4 ACS Paragon Plus Environment

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bis (2,4,6-trimethylbenzoyl) phosphine oxide (PI 819) as photo-initiators were obtained from Sigma-Aldrich. Octabenzone was provided by Dalian Rich fortune Chemicals Co., Ltd and applied as UV absorber. Precipitated silica (PSi, 6 ~ 10 µm, SAI-779) and fumed silica (FSi, 6 ~ 12 nm, Aerosil R974) from Fujian Zhengsheng Inorganic Materials and Evonik Degussa were used as reinforcing fillers. Poly (vinyl alcohol) 1799 as a basis for PVA hydrogel, was purchased from Rhawn with the alcoholysis degree 98 %. Ethylene glycol was supplied by Sigma-Aldrich and carbon nanotubes in aqueous solution (8 wt%) were obtained from Nanjing XFNANO Materials Tech Co., Ltd. Preparation of poly ((mercaptopropyl) methylsiloxane) (MPS). A mixture of hexamethysilane (2.43 g, 0.015 mol), dimethoxydimethylsilane (144 g, 1.2 mol), trimethoxysilypropanethiol (54 g, 0.3 mol) and toluene (195 g) was firstly added into a three-necked round bottom flask equipped with a stirrer, a thermometer and a dropping funnel. Hydrochloric acid (285 g, 37 wt%) was added dropwise into the flask while keeping the temperature of the mixture at 40 °C. After dropping finished, the mixture was stirred for another 27 hours. The temperature was then raised to 120 °C and methanol and water were removed via azeotrope separation. Afterwards, the polymer was washed with deionized water for three times. Finally, toluene was removed by rotor evaporator and MPS was obtained (yield: 91 %). Preparation of photoresins. Three series of photoresins (H-FSi-, H-PSi- and L-PSiseries) were obtained using two types of vinyl terminated polysiloxane with molecular weight of 22000 (VPS-22000) and 5400 (VPS-5400) and two types of silica particles, fumed silica (FSi) and precipitated silica (PSi). VPS-5400 is the mixture of vinyl polysiloxane with molecular weight of 22000 and 4300 with the weight ratio of 1:3. The



photoresins were prepared with VPS and MPS (the molar ratio of vinyl and thiol groups is 1:1) as well as photoinitiators and reinforcing filler silica particles. The photoresin with lower content of silica particles (below 15%) was prepared with a Planetary Centrifugal Mixer (Thinky Mixer ARE-300). It was firstly homogenized for three minutes at 2000 rpm, and then the photoresin was defoamed in the mixter for another two minutes at 2200 rpm. The photoresin with higher content of silica was prepared with a Three Roll Mill (S65, Changzhou Zili Huagong Co.). 3D printing of silicone elastomers. 3D printing of silicone elastomers in our research was performed with a DLP ceramic 3D printer (Spaceworks, Beijing, China). The wavelength of the UV light is 405 nm and DLP chip is 50 µm pixels. The layer thickness is set to be 100 µm and the exposure time and exposure intensity parameters are adjusted based on the polymerization ability of the photopolymer resin. In the printing process, the DLP projects patterned light that selectively exposes and hardens the resin. The cured resin is adhered to the working platform. After one layer is built, the platform ascends a distance of a single layer thickness above the photopolymer vat. Then, fresh photopolymer re-coated the bottom of the vat and UV light will solidify the subsequent layer. This process is repeated for each designed layer until the 3D objects are printed completely. Since an entire layer is exposed with a single pattern, fast build speeds are achieved. Preparation of PVA conductive hydrogel solution. A mixture of PVA (10 g), deionized water (50 mL), ethylene glycol (50 mL) and carbon nanotubes solution (10 mL) was added into a three-necked round flask. Afterwards, it was heated to 95 °C and stirred for 2h. The viscous PVA solution was then defoamed for 2 min.


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Preparation of conductive cellular. The 3D printed cellular was firstly dip-coated with a 1:4 ethyl cyanoacrylate adhesive-trimethylpentane dispersion, quickly following by PVA hydrogel coating. Then the elastomer cellular was put into refrigerator at – 20 °C for 24 h to get a soft stretchable electronics with a conformally coated CNT-doped hydrogel layer. Characterization. 1H-NMR and

29Si-NMR

spectra were performed on a 400 MHz

Brucker Advance 400 and a 300 MHz Brucker Advance 300 spectrometers, respectively, with deuterated chloroform (CDCl3) as solvent. The fracture surface morphology of cured samples was characterized by scanning electron microscopy (Hitachi S4800). The hardness (Shore A) of the elastomers was measured with a durometer of Shanghai Liuling Instrument Factory. The viscosities of samples were tested with Brookfield DV-II Pro type viscometer. The gel content was determined by extraction experiments with acetone for 48 h. The products were then dried in vacuum oven at 120 °C for 24 h. The mechanical properties of elastomers were characterized at room temperature by an Instron 5567 equipment in accordance to ASTM D68-14. Dumbbell-shaped samples (size: 50 mm × 4 mm × 2 mm) were made for the tensile tests and a deforming speed of 200 mm min-1 was employed in the test process. The results were the average of at least five measurements. Cyclic tensile test was also carried out on an Instron 5567 equipment to evaluate the resilient properties of the silicone elastomers. During the measurement, the samples were firstly stretched to 500 % of the strain with a rate of 200 mm min-1 and then it was released at the same rate to recover its original length. Such cyclic tensile tests were programmed to repeat for 100 times and the stress and strain of the samples were



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recorded. During another test, samples were stretched to the elongation of 200 %, 300 %, 500 %, 800 %, 1000 % and 1200 % and released to recover its original length. RESULTS AND DISCUSSION Me

Me

Me Si O Si Me Me

+

OCH3 H3CO Si OCH3

Me

+

Me H3CO Si OCH3 Me

Me Me Si O Me

Me O Me Si O Si Me Si O n m Me Me

(MPS) SH

O

Ph O P O

PI 819

HS

+

O Ph

OH

UV

PI 1173

PI

Me Me Me Si O Si O Si p Me Me Me

(VPS) -Si-CH2-CH2-CH2-S-CH2-CH2-Si-

Figure 1. The synthetic process and structures of MPS, VPS and obtained silicone elastomers Recently, the thiol-ene click reaction has attracted much attention for its rapid reaction rates, high conversions, oxygen resistance and fine control of structures.33-35 All these features make it an excellent candidate for 3D printing technology. Here, as shown in Figure 1, thiol-ene click reaction was applied to synthesize silicone elastomer with thiol groups from MPS and double bonds from VPS. The key factor to get highperformance silicone elastomers is the molecular structure of the MPS. The silicone elastomers obtained with the branched MPS show much higher curing rate and much better mechanical properties compared with those from linear MPS.32 The content of thiol groups in MPS is determined to be 9.54 wt% basing on NMR spectra results. The NMR spectra of MPS and VPS can be seen in Supporting Information (Figure S1-2). Two types of VPS, with molecular weight of 22000 (VPS-22000) and 5400 (VPS-5400) are 8 ACS Paragon Plus Environment

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used to get photoresins (H- and L- series) for silicone elastomers. VPS-5400 is the mixture of vinyl polysiloxane with molecular weight of 22000 and 4300 and the weight ratio is 1:3, aiming to get the photopolymer with relatively low viscosity and meanwhile relatively high mechanical properties after curing. Moreover, fumed and precipitated silica particles are added to the photopolymers to enhance the mechanical properties of the elastomers. Table 1 shows the detailed composition and the viscosity of the photoresins for silicone elastomers. The photoresins with high molecular weight VPS have higher viscosity and with the addition of reinforcing filler SiO2, the viscosity of the photopolymer increases significantly. Moreover, the addition of fumed silica has much greater influence on the viscosity of the photoresin than that of precipitated silica. With only 10 wt% of fumed silica, the photoresin gets to paste and the viscosity has already exceeded the range of the viscometer. Therefore, only 15 wt% of fumed silica and 20 wt% of precipitated silica can be added to prevent the photoresin changing to be solid. Viscosity is commonly a key factor for the photopolymer resin to be applied in 3D printing. Photopolymers with high viscosity are usually difficult to be applied in SLA or DLP 3D printing. But, due to the special design of the printer we used in the present research, in which the resin vat can rotate after curing of each layer, these photoresins with high viscosity are also printable.



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Table 1. The compositions and viscosity of the photopolymers applied in the present study.

Photoresins H-0 H-FSi-5 H-FSi-10 H-FSi-15 H-PSi-5 H-PSi-10 H-PSi-15 H-PSi-20 L-0 L-PSi-5 L-PSi-10 L-PSi-15 L-PSi-20

VPS22000 (g)

VPS5400 (g)

MPS (g)

Photoinitiators (g)

SiO2 (g)

Viscosity (cp, 25ºC)

10 10 10 10 10

0.47 0.47 0.47 0.47 0.47 0.47 0.47 0.47 1.29 1.29 1.29 1.29 1.29

0.16 0.16 0.16 0.16 0.16 0.16 0.16 0.16 0.11 0.11 0.11 0.11 0.11

0 0.77 1.55 2.32 0.77 1.55 2.32 3.1 0 0.57 1.14 1.71 2.28

3233 54800 paste paste 4651 7091 12250 20610 540.5 797.7 1235 1972 3728

15 15 15 15 15 15 15 15


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the super stretchability of the silicone elastomers (Movie S1 of the tensile test of SSSE, Supporting Information). a 1.8 1.2

H-0 H-PSi-5 H-PSi-10 H-PSi-15 H-PSi-20

2.0 Stress (MPa)

1.4 Stress (MPa)

b 2.4

H-0 H-FSi-5 H-FSi-10 H-FSi-15

1.6

1.0 0.8 0.6

1.6 1.2 0.8

0.4 0.4

0.2

0.0

0.0 200

400

600 800 Strain (%)

c 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0

100

200 300 Strain (%)

0.6

500

0.4

400

600

800 1000 1200 1400 1600 Strain (%)

1500 1000 500 3

0

2 1 0 30 20 10

1 25 50 75 100

0.5

Stress (MPa)

400

200

d

H-0 H-FSi-5 H-FSi-10 H-FSi-15 H-PSi-5 H-PSi-10 H-PSi-15 H-PSi-20 L-0 L-PSi-5 L-PSi-10 L-PSi-15 L-PSi-20 Tangoplus

e

0

1200

L-0 L-PSi-5 L-PSi-10 L-PSi-15 L-PSi-20

1.4

Stress (MPa)

1000

Hardness Stress (MPa) Elongation (%)

0

g

0.3 0.2 0.1 0.0 -0.1 0

f

100

200

300 Strain (%)

400

500

1 µm

1.2 1.0

Stress (MPa)

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

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0.8 0.6 0.4 0.2 0.0

50 µm 0

200

400

600 800 Strain (%)

1000

1200


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Figure 3. Mechanical properties of the silicone elastomers. (a, b, c) Stress-strain curves of the obtained silicone elastomers; (d) Comparison of hardness, ultimate tensile strength and break elongation of the obtained silicone elastomers with the most widely used commercial UV curable rubber-like material Tangoplus from Stratasys; (e) Cyclic tensile test of the SSSE (H-Psi-20) to the elongation of 500 %; (f) Cyclic tensile test of the SSSE to the elongation of 200 %, 300 %, 500 %, 800 %, 1000 % and 1200 %; (g) SEM micrographs of fracture surfaces of the silicone elastomers with fumed silica (upper) and with precipitated silica (lower).

Figure 3 shows the mechanical properties of the silicone elastomers. The gel content of all the printed elastomers is determined to be higher than 90%, indicating the high curing extent of the obtained silicone elastomers. The printed silicone elastomers have a wide range of Shore A hardness from 11 to 33 and the hardness is tunable within this range. Tensile tests show that the molecular weight of the polysiloxane segments in the crosslink network, that is the crosslink density, as well as the size distribution of the silica and silica concentration significantly influence the tensile properties of the composites. For H-series, in which the molecular weight of VPS is 22000, as the amount of silica in the composites increases, the elastomers display substantial improvement in all properties, including hardness, tensile strength as well as elongation at break. The ultimate tensile strength and break elongation of the unfilled silicone elastomer, H-0 are 0.30 MPa and 311.4 % and with the addition of 15 wt% fumed silica, they get to 1.69 MPa and 1107.3 %. For composites filling with 20 wt% precipitated silica, the tensile strength and elongation are 2.59 MPa and 1403.2 %. On the other hand, the composites based on



lower molecular weight polysiloxane segments show an increase in tensile strength, but a decrease in break elongation at higher silica concentration. For L-series, as the amount of silica fillers increase, the tensile strength increases from 0.21 to 1.43 MPa and the break elongation first increases from 138.4 % to 322.3 % and then decreases to 291.5 %. Comparison of the hardness, ultimate tensile strength and break elongation of the printed silicone elastomers with the most widely used commercial UV-curable rubberlike material in 3D printing, Tangoplus from Stratasys, illustrates that the break elongation of SSSE is more than seven times and the ultimate tensile stress is two times of Tangoplus. Cyclic tensile test results prove the great fatigue resistance of the printed SSSE. Figure 3g presents the morphologies of fracture surfaces of the fumed silica and precipitated silica filled elastomers. In both systems, the dispersion of the silica particles in the elastomers is quite homogeneous and bright domains due to the aggregation of silica particles are very rare, which demonstrates the good compatibility and strong interaction between the elastomer matrix and silica particles. The microstructure of the network has a significant influence on the mechanical properties of the silicone elastomers. In our research, branched mercaptan functionalized polysiloxane and vinyl terminated polydimethysiloxane with different chain length have been adopted to get silicone elastomers with suitable crosslink density. With too high or too low crosslink density, the elastomers will become too brittle or too weak. But, due to the very weak intermolecular interactions among polysiloxane chains, the silicone rubber with suitable crosslink density still exhibit relatively low mechanical properties. Therefore, various fillers have been applied to enhance the performance of silicone


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rubbers. The reinforcing mechanism of filled silicone elastomers is rather complex and strongly dependent on many parameters, including molecular weight of polysiloxane chains in the crosslinking network, size distribution and fractal character of silica, silica surface chemistry, silica concentration, etc.36-37 Studies show that dispersed filler particles are capable of enhancing the ability of the polymer matrix to dissipate energy, mainly through changes in the polymer microstructure or through interfacial stress transfer.38 In our research, two types of silica are used, fumed silica, made through hydrolysis of silicon tetrachloride in a flame and followed by modification with dihydrodichlorosilane and precipitated silica, getting from acid precipitation of sodium silicate. For systems with fumed silica, high surface area compounded with grafted organic moieties after modification enhance their compatibility and interaction between rubber matrix, while in the case of precipitated silica, strong bonding formed between hydroxyl groups on the silica particles and siloxane bonds in the PDMS backbone.37-40 Therefore, in both systems good compatibility and strong interactions between elastomer matrix and silica particles facilitate transferring of the stress from the elastomers to rigid fillers. The presence of filler particles can disturb or stop the propagation of a crack, so the fracture of the elastomers shift to higher tensile stress and larger elongation.36




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The surface of the models is very smooth and the features of the cat are very clear, indicating the high printing resolution and accuracy. Overall, a series of photoresins for silicone elastomers, which are composed of mercaptan functionalized polysiloxane and vinyl terminated polydimethylsiloxane, have been developed in our research. Due to the high curing rate of thiol-ene click reaction, the photoresins have been applied in DLP 3D printing. The silicone elastomers with tunable hardness and mechanical properties have been obtained and the break elongation of SSSE can get up to 1400 %. In the following part, the printed silicone elastomers with excellent stretchability are applied to fabricate stretchable electrical devices.

a

c

b

CNT-doped hydrogel Instant tough bonding Silicone elastomer

d

h

e

g

f

i

j

Figure 5. Stretchable electrical devices developed with silicone elastomers and CNTdoped hydrogels. (a) The printed silicone elastomer with honeycomb shape (the bar indicates 1 cm); (b) After coating with CNT-doped hydrogel layer; (c) Schematic



illustration of the structure of the stretchable electronics; (d-j) Photos illustrating the electrical conductivity of the elastomer-hydrogel heterostructures. Stretchable electronics has great potential applications in many fields, such as human wearable sensors, soft robotics, flexible actuators and so on. Therefore, the preparation of conductive elastomers with excellent properties of elasticity, resilience, and conductivity has attracted tremendous interests in recent years. Conductive elastomers can be generally obtained through incorporation of metallic components into the elastomers.28 Recently, the use of hydrogels as conductors has gained great popularity.41 Stretchable electronics can be fabricated through integrating conductive hydrogels with stretchable elastomers. In the conductive hydrogels, charge carriers can be ions, like solvated salts or ionic liquids, as well as carbon nanomaterials, like graphene, carbon nanotubes (CNTs).41-43 CNTs, one dimensional nano-sized carbon with high aspect ratio, favorable mechanical and electrical properties, are promising candidate to enhance the electrical conductivity of polymers.44-47 Here, stretchable electronics was obtained through coating the printed silicone elastomers with CNT-doped conductive hydrogels. The 3D printed cellular was firstly dip-coated with a 1:4 ethyl cyanoacrylate adhesive-trimethylpentane dispersion and followed by PVA conductive hydrogel coating (CNTs, 0.67 wt%). The dispersion of cyanoacrylate monomer and trimethylpentane dispersion ensures the formation of instant tough bonding between silicone elastomers and hydrogels, because the adhesive can diffuse into hydrogel and elastomers during the polymerization process.48 Finally, a soft stretchable electronic with a conformally coated CNT-doped hydrogel layer was obtained.


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The stretchable electrical devices were connected to a LED and a power supply. Figure 5 clearly shows the electrical conductivity of the obtained elastomer-hydrogel heterostructures in the original shape as well stretchable and compressed states (Movie S2 and Movie S3, Supporting Information). Actually, the conductivity of the heterostructures can be readily enhanced by increasing the content of CNTs in the hydrogel. CONCLUSION In the present research, a series of silicone elastomers with tunable mechanical properties has been printed by DLP 3D printing. By controlling the thiol content of MPS and the molecular weight of VPS and the content of silica filler, the silicone elastomers with super-stretchability have been developed. The SSSE can be stretched up to 1400 %, which is much higher than the reported UV cured elastomers and is even higher than the most stretchable thermocuring silicone elastomers. With the excellent mechanical and resilient properties, the printed silicone elastomers have been applied to fabricate stretchable electronics with CNT-doped hydrogel. The super-stretchable 3D printed silicone elastomers have widely potential applications in areas like soft robotics, flexible actuators and medical implants.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website.



Tensile test video of the printed super-stretchable silicone elastomers (AVI) Conductive test video of the stretchable electrical devices developed through the printed silicone elastomers and CNTs-doped hydrogels (AVI) 1H-NMR

and 29Si-NMR spectra of the poly ((mercaptopropyl) methylsiloxane) and

vinyl terminated polydimethylsiloxane, a table lists the tensile strength, break elongation and hardness of the printed silicone elastomers (DOCX)

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]; [email protected]; [email protected] ORCID Ran Yu: 0000-0001-6785-3209 Wei Huang: 0000-0003-4513-8735 Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This study is financially supported by the National Natural Science Foundation of China (No. 51573189 and No. 51603208) and the National Key Research and Development Program of China (No. 2017YFB0404800).


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TOC 161x152mm (96 x 96 DPI)


Superstretchable and Processable Silicone Elastomers by Digital

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