Efficient Flame Detection and Early Warning Sensors on Combustible

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Efficient Flame Detection and Early Warning Sensors on Combustible Materials Using Hierarchical Graphene Oxide/Silicone Coatings Qian Wu, Li-Xiu Gong, Yang Li, Cheng-Fei Cao, Long-Cheng Tang, Lianbin Wu, Li Zhao, Guo-Dong Zhang, Shi-Neng Li, Jiefeng Gao, Yongjin Li, and Yiu-Wing Mai ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.7b06590 • Publication Date (Web): 14 Dec 2017 Downloaded from http://pubs.acs.org on December 15, 2017

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Efficient Flame Detection and Early Warning Sensors on Combustible Materials Using Hierarchical Graphene Oxide/Silicone Coatings Qian Wu,† Li-Xiu Gong,† Yang Li,† Cheng-Fei Cao,† Long-Cheng Tang,*,†,# Lianbin Wu,† Li Zhao,† Guo-Dong Zhang,† Shi-Neng Li,†,‡ Jiefeng Gao,§ Yongjin Li,† Yiu-Wing Mai,*,# †

Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education,

College of Material, Chemistry and Chemical Engineering, Hangzhou Normal University, Hangzhou 311121, China ‡

Institute for Advanced Ceramics, State Key Laboratory of Urban Water Resource and

Environment, Harbin Institute of Technology, Harbin 150001, China §

College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou, Jiangsu,

225002, China #

Centre for Advanced Materials Technology (CAMT), School of Aerospace, Mechanical and

Mechatronic Engineering J07, The University of Sydney, Sydney, NSW, 2006, Australia

*Email: [email protected], [email protected]

ACS Paragon Plus Environment

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ABSTRACT Design and development of smart sensors for rapid flame detection in post-combustion and early fire warning in pre-combustion situations are critically needed to improve the fire safety of combustible materials in many applications. Herein, we describe the fabrication of hierarchical coatings created by assembling a multi-layered graphene oxide (GO)/silicone structure onto different combustible substrate materials. The resulting coatings exhibit distinct temperatureresponse electrical resistance change as efficient early-warning sensors for detecting abnormal high environmental temperature, thus enabling fire prevention below the ignition temperature of combustible materials. After encountering a flame attack, we demonstrate extremely rapid flame detection response in 2-3 s and excellent flame self-extinguishing retardancy for the multilayered GO/silicone structure that can be synergistically transformed to a multi-scale graphene/nano-silica protection layer. The hierarchical coatings developed are promising for fire prevention and protection applications in various critical fire risk and related perilous circumstances.

KEYWORDS: hierarchical coatings; graphene oxide; silicone; flame detecting/warning sensor; temperature-response resistance change; synergistic flame retardancy


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The deaths of about seventy-nine people in London’s Grenfell Tower fire that occurred midnight on June 14, 2017 have focused much attention on the high risks and rapid spreading of fire for many different combustible materials. The flammability of the combustible materials, e.g., polymer foams, woods and textiles has initiated massive fire accidents which not only cause considerable property loss and medical costs worldwide every year,1 but even detrimental impacts on the surrounding environment and global climate.2,3 Triggered by an ignition source (flame, cigarette, glow wire, etc.) in the range of ignition temperatures (600-700 K), the endothermic pyrolysis of the combustible materials releases the vaporization of decomposed products due to chain scission mechanisms,4 resulting in CO and smoke production during incomplete combustion.5 Meanwhile, a constant mass flux of combustible volatiles feeds the exothermic reaction,6 thus inducing rapid temperature rise as an effective heat flux in the flame zone. These related fire issues drive the development of fire safety strategy that can reduce fire risk to save lives and protect properties. For such purposes, two main fire detection strategies including smoke detector and infrared heat detector have been designed and installed indoor to monitor the high fire risk of the combustible materials. Normally, these detectors are activated through detecting the smoke product of a fire source after the continuation of flaming combustion of the combustible materials, thus showing a relatively long response time >100 s.7,8 However, the combustible materials usually burn rapidly once ignited, and the flame spreads very quickly (e.g., >8 m flame height in only ~80 s in a large-scale warehouse fire test),9 potentially causing fatal burns within 15 s of ignition,10,11 especially in oxygen-rich surroundings.12 The main drawback of these two types of detectors is that they are triggered in post-combustion and thus protractedly reflect the fire behaviors of materials, which cannot offer a timely and effective alarm signal to reduce or avoid the life and


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property loss in fire accidents. Therefore, a critical challenge is to develop efficient fire detecting/warning sensors that can trigger rapidly and reliably real-time signals once the combustible materials are attacked by a flame, or even activate early warning signals in precombustion when they are encountering high fire risk, e.g., heat flux or abnormal high temperature for ignition. Advanced multi-functional sensors that can meet the requirement of extraordinary rapid and reliable responses for detecting high fire risk of combustible materials are strongly needed. Herein, we describe a feasible method for fabricating hierarchical coatings onto combustible materials as efficient detecting/warning sensors including rapid flame detection in postcombustion and early fire warning in pre-combustion. The fabrication process uses a multilayered graphene oxide (GO)/silicone structure that is assembled onto the combustible substrates (see schematic representation in Figure 1a). Through a simple dip-coating-induced assembly process (Figure S1 in Supporting Information (SI)), a synthesized silicone polymer (SiP) with predesigned three-dimensional cross-linked molecular structure and GO sheets with lateral size ranging from 1-10 µm (Figure S2 in SI) are successively coated onto the substrate surface. Then, 1,1,2,2-Tetrahydroperfluorodecyltrimethoxysilane (PFDTS) molecules are grafted onto the sheets to obtain the hierarchical GO/silicone coatings on the combustible substrate with a hydrophobic surface. The optimized hierarchical coatings exhibit extraordinary rapid flame detection response time of less than 3 s and outstanding early warning for abnormal high temperatures that are below the ignition temperature of the combustible materials and excellent self-extinguishing flame retardant property. To our best knowledge, this is the most effective flame detection response in post-combustion and the most efficient early flame warning sensor in


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pre-combustion. This finding provides a promising way for the development of advanced materials for fire safety application of combustible materials.

Figure 1. Fabrication of hierarchical GO/silicone coatings on combustible materials. (a) Schematic illustration of fabricating hierarchical GO/silicone coatings as efficient flame detection and early warning sensors on combustible materials. (b) Photographs of PU foam and PU-SGF samples and their water contact angles. (c-e) SEM images of PU-SGF sample coated with the multi-layered GO/silicone structure. Surface treatment of PFDTS molecules onto GO sheets provides a hydrophobic surface and a protective layer that stabilizes the GO network. (f) Photographs of the hierarchical coatings on various combustible materials: (i) polystyrene resin (PR), (ii) cotton (CN) and (iii) wood block (WB).

RESULTS AND DISCUSSION


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The photographs of commercial polyurethane (PU) foam and multi-layered SiP/GO/PFDTS coated PU (PU-SGF) samples and the surface water contact angles (WCAs) are shown in Figure 1b, in which the hierarchical GO/silicone coatings with 0.9/1.8/0.1/0.05 of PU/SiP/GO/PFDTS at the optimized weight ratio (Figure S3 in SI) produce excellent super-hydrophobicity of ~156o WCA for PU-SGF compared to ~88o WCA for pure PU foam. The organic-inorganic silicone pre-polymer synthesized by hydrolysis and condensation of silane molecules can provide a large number of silanol groups, which are expected to react covalently with the isocyanate groups on the PU foam and the hydroxyl groups of GO sheets.13 The PFDTS molecules after hydrolysis can react with the GO sheets and SiP at a low temperature of 80-100 oC,14 thus forming a stable multi-layered structure even after being squeezed into an acidic or alkaline solution for 15 days (Figure S4 in SI). We used thermogravimetric analysis (TGA) (Figure S5 in SI), Fourier transform infrared (FTIR) spectroscopy (Figure S6 in SI), and X-ray photoelectron spectroscopy (XPS) (Figure S7 in SI) to analyze different coatings of SiP, GO, SiP/GO and SiP/GO/PFDTS on PU foam surface. The characteristic curves and peaks of various materials including PU, SiP coated PU (PU-S), GO coated PU (PU-G), SiP/GO coated PU (PU-SG) and PU-SGF samples show the expected results for improved thermal stability and confirm the above proposed reaction mechanisms. The SEM images of the hierarchical GO/silicone coatings on the skeleton of PU foam are shown in Figure 1c-e. The presence of the multi-layered SiP/GO/PFDTS structure does not affect the porous structure of the foam significantly (Figure 1c), and produces a rougher surface on the skeleton surface (Figure 1d) compared to the smooth surface of the PU-G sample (Figure S8 in SI). The cross-sectional SEM image of PU-SGF in Figure 1e shows a typical multi-layered structure of SiP layer with 600-800 nm in thickness, interconnected GO layer and a thin


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hydrophobic surface which are well attached onto the PU skeleton. Such multi-layered structure can accommodate a large compressive strain of 75% for 120 cycles, yet recovering its original shape and size, indicating good structural stability, although the maximum compressive stress does exhibit a reduction from ~150 kPa for the 1st cycle to ~92 kPa for the 120th cycle (Figure S9 in SI). SEM-EDX mapping results (Figure S10 in SI) of the sample reveal the appearance of well-distributed silicon and fluorine elements on the rough surface, demonstrating the PFDTS molecules have been well grafted onto the sheets,15 which supports the super-hydrophobic surface obtained in Figure 1b due to the highly textured (rough surface in Figure 1d) combined with the extremely low water affinity.16 In fact, this multi-layered coating method can also be applied on various combustible substrate materials such as polystyrene resin (PR), cotton (CN) and wood block (WB) (Figure 1f), and obviously improved surface hydrophobicity on these substrates (Figure S11 in SI) can be achieved. For a concise and clear analysis, representative GO/silicone coated PU samples will be mainly observed and discussed below in respect of their structure and property measurements. Well-exfoliated GO sheets in liquid solution can be easily processed into a range of structures for diverse applications.17-19 Typically, GO coated polymer sponge via a facile dip-coating method produces a stable and thin conductive graphene layer on the foam skeleton after chemical reduction,20 showing potential multi-functional applications in strain sensing, oil/water separation, etc.21,22 However, for these graphene-based materials, additional fire retardant component is required to achieve efficient fire resistance because the graphene sheets tend to be completely burnt in air atmosphere.23,24 Shown in Figure S12a and Movie S1 (Supporting Information) are the burning process of GO-coated PU (PU-G) sample, which is readily and completely burnt in 30 s due to sufficient thermal degradation. Comparatively, flame attack does


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not destroy the shape of the PU-SGF sample even burned for ~90 s (Figure S12b and Movie S2 in SI), indicating the multi-layered GO/silicone structure protects the combustible PU foam from fire. In fact, the SiP shows intrinsic flame retardancy,25 which is different from the combustible linear silicone elastomers that inorganic mineral fillers are usually needed as ceramisation agents to improve their flame resistance.26 We further compare the structural stability of the PU-G and PU-SGF samples before and after 10 s burning (Figure S13 in SI). Although they can endure an applied weight of 200 g, their structural stabilities after the burning tests are quite different. The PU-G sample after burning is unstable and collapses easily, while the burnt PU-SGF sample exhibits excellent structural stability, which can be used to connect directly with the alarm lamp as an efficient flame detection sensor. The hierarchical GO/silicone coatings provide extremely rapid responses for detecting flame on various combustible substrates such as PU foam, polymer resin, cotton and wood block when connected with an alarm lamp and a low-voltage DC power electrical source. As shown in Figure 2a, once the PU-SGF sample encounters a flame, the danger alarm is quickly triggered in 2-3 s, and continuous danger alarm is maintained even after removing the flame (Movie S3 in SI). Note that almost the same response time of danger alarm is retained even after dripping some water droplets onto the sample (simulating a rainy day) (Figure 2b, and Movie S4 in SI) or exposing it outdoor for 180 days, indicating the good applicability in an adverse environment. Further flame detection tests of the hierarchical GO/silicone coatings on other combustible substrate materials are shown in Figure S14 in SI. Similar rapid responses (less than 3 s) of flame detection alarm can also be triggered for PR (Movie S5 in SI), CN (Movie S6 in SI) and WB (Movie S7 in SI). These tests indicate that the hierarchical GO/silicone coatings show promising flame detection sensors for fire safety application in a building, which is proposed and


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illustrated in Figure S15 in SI. Once a fire originated from the lower floors spreads quickly to the higher floors through combustible materials, such as the exterior wall combustible foam material, the hierarchical GO/silicone coatings that are located in the high fire risk zone can provide a rapid flame detection alarm for people living in the higher floors to receive sufficient and timely notification for evacuation. We believe the idea of a “rapid flame detection” sensor can be simply, flexibly and robustly used in large-scale industrial applications where there are high fire risks which should be critically monitored. The explanation for this rapid response behavior for detecting a flame lies in the change in the electrical resistance of the multi-layered GO/silicone structure, which comes from the reduction of the GO layer during the flame attacking process (discussed later). As shown in Figure 2c, the electrical resistance of the PU-SGF sample before/after 120th cyclic compressions under an applied strain of 75% (see insets in figure) exhibits similar dramatic change in the burning process with almost the same flame detection response time (Movie S8 in SI). These results show good reliability of the hierarchical coatings as flame detection sensors, even after suffering a large compressive strain. The PR-SGF, CN-SGF and WB-SGF samples in Figure 2d also display significant change in electrical resistance during the flame detection process. The alarm response times (defined as the time that can light up the alarm lamp at a low voltage of 24 V, corresponding to about four orders of magnitude decrease in electrical resistance) of all the four samples are extremely rapid (less than 3 s, see inset in Figure 2d), which is much less than the reported response time of smoke and heat detector.7,8 Thus, monitoring the change of flameinduced electrical resistance of the hierarchical coatings is clearly much more effective than detecting the smoke product and heat flux of the traditional smoke/heat detectors, hence providing an efficient strategy for rapid flame detection.


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Figure 2. Rapid flame detection process of hierarchical GO/silicone coatings. (a, b) Flame detection processes of PU-SGF samples under different environmental conditions. Alarm device system was established by connecting the sample with an alarm lamp and a low-voltage DC power electrical source. Danger alarm was quickly triggered in 2-3 s once the sample encountered a flame, and continuous alarm was kept even after removing the flame. Almost the same rapid response of flame detection alarm of PU-SGF was retained even after dropping some water droplets (simulating a rainy day). (c) Electrical resistance change of PU-SGF samples before/after cyclic compression test during the flame detection process. After 120 compression cycles, the sample showed unchanged response time for flame detection by measuring the dramatic change in electrical resistance. Inset: the PU-SGF sample recovered the original shape after applying a compressive strain of 75%. (d) Electrical resistance change during the flame detection process for other combustible substrate materials (PR-SGF, CN-SGF and WB-SGF). Inset: the flame detection response time of all the four samples were less than 3 s.


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Heretofore, we believe no reports have shown any early flame warning in pre-combustion because before being ignited the combustible materials hardly release smoke and heat to trigger the traditional detectors. It is well known that two key factors, i.e., ignition temperature and ventilation (oxygen) atmosphere, critically determine the onset of flame and fire growth and continuation of the combustible materials.27 Consequently, monitoring the temperature around the combustible materials (below their ignition temperature) is a promising and effective way to reduce high fire risk in some applications, such as batteries and wires/cables in public transportation. Interestingly, the hierarchical GO/silicone coatings on combustible substrates are sensitive to the environmental temperature. Shown in Figure 3a and Movie S9 (Supporting Information) are the temperature detection process of PU-SGF sample. When the sample was put onto a hot surface of ~350 oC, danger alarm was triggered in ~20 s and maintained for a long time, indicating efficient early fire warning of the hierarchical GO/silicone coatings in precombustion. A temperature oven was used to further evaluate the electrical resistance response of the coatings at different temperatures, as shown in illustrated in the inset in Figure 3b and Figure S16; and the electrical resistance changes of the PU-SGF sample as a function of time were also measured. It is observed that the change of the electrical resistance of PU-SGF samples is strongly dependent on the applied environmental temperature; the higher the temperature, the quicker and larger change are the electrical resistance. The response time (as defined before) of the hierarchical coatings exhibits dramatic reduction with increasing temperature, e.g., from ~415 s at 200 oC (Figure S17 in SI) to ~38 s at ~300 oC (Movie S10 in SI) and ~3 s for 400 oC (comparable to the response time for flame detection, see Figure 3c), showing excellent early fire warning for monitoring high fire risk of combustible materials in pre-combustion.


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Figure 3. Early fire warning response of hierarchical GO/silicone coatings. (a) Abnormal high temperature early warning of PU-SGF sample in pre-combustion. Danger alarm was triggered in 20 s at 350 oC, and continuous alarm was kept even after leaving the hot surface, indicating a good early warning for high fire risk. (b) Electrical resistance change of PU-SGF as a function of time at different temperatures. Inset is a schematic of monitoring the resistance change at different environmental temperatures below the ignition temperature of the combustible materials. (c) Alarm response time of the coatings at different temperatures. Inset: Raman spectra of PU-SGF under room temperature (trace i) and 400 oC (trace ii), indicating thermal reduction of GO sheets. (d) SEM images of surface morphologies of PU-SGF samples under different temperatures after 200 s: (i) 300 oC, (ii) 350 oC and (iii) 400 oC. The decomposition of silicone at high temperatures induced the micro-cracks and produced the porous nano-silica structure.


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The PFDTS molecules bonded on the GO sheets not only generate a hydrophobic surface that obtains rapid flame detection in both sunny and rainy days, but also provide a protective layer that stabilizes the GO network on the surface of the combustible material. Upon encountering a high temperature or flame, the decomposition of silicone molecules (PFDTS and SiP) induces micro-cracks and then produces a porous nano-silica structure as an effective protection layer (Figure S18 and S19 in SI).25, 28 It is noted that both the size of nano-silica particles and the thickness of the protective layer show distinct increases with increasing temperature (from 200 to 400 oC) (Figure 3d), and this layer inhibits effectively the thermal degradation of the GO sheets and facilitates the reduction of GO to reduced GO (RGO).29 The thermal reduction can be confirmed by the decreased intensity ratio of the D and G Raman bands of GO in the multilayered structure at ~1335 and ~1580 cm−1 (see inset in Figure 3c, and Figure S20a in SI), respectively,30,31 which is consistent with the chemical transformations of organic silicone molecules in an inorganic nano-silica porous protection layer (see FTIR results in Figure S20b in SI).28 Meantime, the graphitization and reduction of the GO sheets construct an effective conductive network for rapid flame detection and early warning. The formation of an environmental-friendly inorganic nano-silica/RGO layer also improves significantly the fire resistance of the combustible substrate materials, which is quite different from the traditional flame retardants that are halogenated or phosphorous compounds with negative impacts on the environment and health.32,33 Vertical burning tests (UL 94) disclose that the uncoated PU foam combustible material can be easily ignited (exposing the sample in a flame for only 1 s) and completely burnt in several seconds accompanied by continuous dripping and quick flame self-propagation (Figure S21a and Movie S11 in SI).34 PU foams coated with GO or SiP (PU-G or PU-S) display some flame retardancy, but still burn for a long time until


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they are completely combusted (Figure S21b and Movie S1 for PU-G and Figure S21c and Movie S12 for PU-S in SI). Comparatively, the presence of hierarchical GO/silicone coatings produces excellent self-extinguishing fire resistance (in 20 s) without dripping and selfpropagating flame phenomena (Figure 4a, and Movie S13 in SI). Similar self-extinguishing fire resistance can be also observed for other combustible materials including PR-SGF (Figure S22 and Movie S14 in SI), CN-SGF (Figure S23 and Movie S15 in SI) and WB-SGF (Figure S24 and Movie S16 in SI). Moreover, cone calorimetry tests demonstrate that, after being exposed to a fixed heat flux of 35 kWm-2, the char of PU-SGF sample shows almost unchanged shape and grey color in comparison with no char for the pure PU foam (Figure 4b). The peak heat release rate (pHRR) of the PU-SGF sample further displays obvious decrease (~78%) compared to that of pure foam, and is much lower than those of the PU-G and PU-S samples (Figure 25a in SI), albeit the weight loss ratio of the PU-S sample is almost the same as that of the PU-SGF sample (Figure S25b in SI). To understand the flame-retardant mechanisms of the hierarchical GO/silicone coatings on combustible substrate materials, the PU-SGF sample after the burning test was observed and analyzed. Figure 4c shows that the multi-layered GO/silicone structure is transformed into an inorganic protective layer in the outside zone during the burning process, similar to cellulose nanofibres/GO/sepiolite nano-rods nanocomposite foams 35 and Al2O3 nano-layer coated graphene sandwiched structure,36 which can be confirmed by the FTIR results. The intense Si-OSi band at ~1038 cm-1 in the outside surface zone and many peaks of massive organic groups in the inside zone (O-H band at 3342 cm-1, C-H band at 2960 and 2860 cm-1, C=C band at 1720 cm1

, C-C band at 1597 cm-1, Si-C band at 1265 and 783 cm-1, Si-O-C band at 1088 cm-1, and Si-O-

Si band at 1597 cm-1) indicate that the protective silica-rich surface layer inhibits effectively the


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thermal degradation of the inside GO/silicone coating. The decreased intensity ratio of the D and G Raman bands of GO (ID/IG) after burning (Figure S20a in SI) suggests a reduction of GO to RGO in the flame 37 and transformation of GO sheets into char.38 SEM images in Figure 4d demonstrate that the porous nano-silica protective crust is formed on the RGO network in the outside zone, and the hierarchical GO/silicone structure in the inside zone does not show obvious thermal decomposition (Figure S26 in SI). Once encountering an abnormal high temperature or flame attack, thermal degradation of surface PFDTS molecules transforms into a nano-silica protective layer to inhibit the decomposition of GO sheets but rapidly reduce them for efficient fire detection and early warning. For a continuous flame, the inside SiP polymer would also decompose through the micro-cracks on the surface (as shown in Figure 3d) to form the porous nano-silica layer. As a result, the formation of multi-scale porous nano-silica and RGO char as an effective protective layer can synergistically suppress the transport of heat and oxygen (Figure 4e),39,40 thus showing an “environmentally friendly” alternative for protecting foams and many other complex substrates (e.g., fabrics) without altering their processing and desirable mechanical behavior.41 Indeed, analysis of the chemical and structural transformations of hierarchical GO/silicone coatings shows that the porous nanosilica structure produced by the silicone polymer at the high temperature effectively suppresses the transport of heat (Figure S27 in SI) and thus promote the graphitization of GO and the formation of RGO conductive network (Figure S28 in SI), providing excellent flame retardancy and flame rapid detection for the combustible substrate materials.


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Figure 4. Flame resistant properties and mechanisms of hierarchical GO/silicone coatings on combustible substrate materials. (a) Vertical burning test (UL94) of a PU-SGF sample. The images show the sample before the test, after applying an alcohol flame for 10 s, and the sample after the test demonstrating excellent self-extinguishing characteristics and high fire retardancy. (b) Photographs of pure PU and PU-SGF char after the cone calorimetry test together with the corresponding peak heat release rates (pHRR). The results reveal high fire resistance and char for the hierarchical coatings on the PU foam. (c) Infrared spectra and corresponding photograph of a PU-SGF sample after burning observed at different zones. (d) SEM images of the PU-SGF sample after burning. (e) Schematic illustration of the burning process of multilayered GO/silicone structure on the PU skeleton (not drawn to scale). Both silicone decomposition and GO graphitization during the burning process induce the formation of a


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multi-scale nano-silica/RGO protective crust, which inhibits the pyrolytic degradation of the inside RGO network, providing efficient flame detection and synergistic flame retardant effect on the combustible substrate materials.

CONCLUSIONS In summary, the hierarchical GO/silicone coatings show that an extremely rapid response (less than 3 s) to flame detection and an ideal early warning to the environmental temperature (below ignition temperature of the combustible materials) in pre-combustion and ease of applicability can be achieved by the simple and feasible dip-coating method. Various potential fire safety applications of the hierarchical GO/silicone coatings as efficient flame detection and early fire warning sensors are supported by our results through detecting temperature-dependent electrical resistance change. The coatings can also be readily implemented on different combustible substrate materials that fire safety is critically required. In addition, the porous nano-silica structures as an effective protective layer transformed from silicone polymer during burning protect the degradation of GO from fire and promote the formation of a RGO conductive network, thus yielding excellent flame retardancy. Our results provide substantial motivation and opportunity to develop advanced multi-functional sensors for fire prevention and protection applications in buildings, transportation and public security where combustible materials are widely used.

METHODS Materials and preparation. Materials and detail synthesis of GO and silicone polymer were given in Supporting Information. PU-SGF sample was prepared as follows. Synthesized silicone pre-polymer (50 g), alcohol (50 g) and polyetheramine D230 (0.6 g) were mixed at 1000 rpm for


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20 min to obtain a homogenous solution. Pure PU foam was then fully immersed into the above mixture under vacuum for 15 min, and then centrifuged at 600 rpm for 5 min to remove the extra silicone pre-polymer. The sample was then cured by D230 at 90 oC for ~4 h to obtain the PU-S sample. After that, the PU-S sample was fully immersed into the GO aqueous solution aided by a vacuum pump and centrifugation, and then dried at 70 oC for 4 h to obtain the PU-SG sample. Finally, PFDTS (1 g) and DI water (0.5 mL) were dispersed in 250 mL of alcohol and ultrasonicated for 10 min, and then the above PU-SG sample was fully immersed into the above PFDTS mixture at 60 oC for 5 min and dried at 70 oC for 2 h. Similarly, various combustible materials coated by the silicone polymer, GO and silicone/GO were fabricated according to the above process. Further detailed information was provided in Supporting Information. Characterization. Raman spectra of various samples were performed from 200 to 4000 cm-1 using a SENTERRA Micro Raman Spectrometer (Bruker Instruments, Germany) with a 633 nm He-Ne laser beam. The morphology and structure of the GO sheets were analyzed by transmission electron microscopy (TEM, HITACHI H- 7650) and atomic force microscopy (AFM, Digital Instrument D3100). The surface morphologies of various samples before or after flame burning tests were examined by and scanning electron microscopy (SEM, Zeiss ultra plus and HITACHI S-4800) with an energy dispersive X-ray spectroscopy (EDS) detector. X-ray diffraction (XRD) was performed using a diffraction technology mini-materials analyzer on the samples with a D/Max2550 V X-ray diffractor (Rigaku, Japan), and the diffraction patterns were recorded in the 2θ range from 5 to 40° with a scan rate of 5° min−1. Fourier transform infrared (FTIR) spectra were obtained using a Nicolet 7000 FTIR (Nicolet Instrument Company, USA) between 600 and 4000 cm−1. High-resolution X-ray photoelectron spectra (XPS) measurements were obtained using the VG scientific ESCALab 220I-XL equipped with Mg Kα X-ray source


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ACS Nano

and a hemispherical electron analyzer. Themogravimetric analysis (TGA) was performed by a TA Instruments Q500 in air/nitrogen atmospheres at a heating rate of 10 oC min-1 between room temperature and 800 oC. Compression tests were performed using an AMETEK Ls 100Plus (100N load cell) at a speed of 1.0 mm/min at room temperature, and the samples size was 20.0 mm long × 20.0 mm wide × 10.0 mm thick. Electrical resistance of various samples was monitored with a two-electrode method (ESCORT 3146A Multimeter); and each end of the samples was carefully affixed to copper sheets as electrodes. A vertical flame test was performed on uncoated and coated combustible samples. The fire from a gas burner was applied on the tested fabric for 10 s and then removed; and before testing, the specimens were conditioned at 25±1 oC and 50±2% relative humidity for 72 h. PU, PU-G, PU-S and PU-SGF samples were characterized using a cone calorimeter performed in an FTT, UK device according to ISO 5660; and samples with dimensions of 100 mm long × 100 mm wide × 10 mm thick were exposed to a heat flux of 35 kW m-2, and the data reported in this work were the averages of three experiments.

AUTHOR INFORMATION Corresponding Author *Email: [email protected], [email protected] ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (Grants 51203038 and 51403047), the Zhejiang Provincial Natural Science Foundation (Grants LY15E030015 and LY18E030005) and the Project for the Innovation of High Level Returned Overseas Scholars in Hangzhou. The authors thank Y. Wang, F. Qiang and Y.J. Wan for AFM


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and SEM characterizations. The authors also thank Dr. Y.B. Pei for discussions of possible fire retardant mechanisms.

ASSOCIATED CONTENT Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org. Figures (1-28) and Movies (1-16) showing the structural characterizations of hierarchical coating, performance of the hierarchical coating on various combustible materials, demo movies of flame detecting/warning sensor and flame resistance, investigation on the working principle of the hierarchical coating and experiment on synergistic flame retardant effect.

REFERENCES 1.

International Association of Fire and Rescue Services: World Fire Statistics.

http://www.ctif.org/. (accessed April 2017). 2.

Randerson, J. T.; Liu, H.; Flanner, M. G.; Chambers, S. D.; Jin, Y.; Hess, P. G.; Pfister,

G.; Mack, M. C.; Treseder, K. K.; Welp, L. R.; Chapin, F. S.; Harden, J. W.; Goulden, M. L.; Lyons, E.; Neff, J. C.; Schuur, E. A. G.; Zender, C. S., The Impact of Boreal Forest Fire on Climate Warming. Science 2006, 314 , 1130-1132. 3.

Bowman, D. M. J. S.; Balch, J. K.; Artaxo, P.; Bond, W. J.; Carlson, J. M.; Cochrane, M.

A.; D’Antonio, C. M.; DeFries, R. S.; Doyle, J. C.; Harrison, S. P.; Johnston, F. H.; Keeley, J. E.; Krawchuk, M. A.; Kull, C. A.; Marston, J. B.; Moritz, M. A.; Prentice, I. C.; Roos, C. I.; Scott, A. C.; Swetnam, T. W.; et al., Fire in the Earth System. Science 2009, 324 , 481-484.


20

Page 21 of 25 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 Nano

4.

Erickson, K. L., Thermal Decomposition Mechanisms Common to Polyurethane, Epoxy,

Poly(diallyl phthalate), Polycarbonate and Poly(phenylene sulfide). J. Therm. Anal. Calorim. 2007, 89 , 427-440. 5.

Schartel, B.; Hull, T. R., Development of Fire-Retarded Materials-Interpretation of Cone

calorimeter Data. Fire Mater. 2007, 31 , 327-354. 6.

Schartel, B.; Weiß, A., Temperature Inside Burning Polymer Specimens: Pyrolysis Zone

and Shielding. Fire Mater. 2010, 34 , 217-235. 7.

Evans, D. D.; Stroup, D. W., Methods to Calculate the Response Time of Heat and

Smoke Detectors Installed Below Large Unobstructed Ceilings. Fire Technol. 1986, 22 , 54-65. 8.

Qualey, J. R., Fire Test Comparisons of Smoke Detector Response Times. Fire Technol.

2000, 36 , 89-108. 9.

Overholt, K. J.; Gollner, M. J.; Perricone, J.; Rangwala, A. S.; Williams, F. A.,

Warehouse Commodity Classification from Fundamental Principles. Part II: Flame Heights and Flame Spread. Fire Safety Journal 2011, 46 , 317-329. 10.

You, F.; Hu, Y., Reaction-to-Fire Properties and Fire Spread Properties of Metal-Skinned

Expanded Polystyrene Foam Sandwich Panel. J. Combust. Sci. Technol. 2012, 18 , 228-236. 11.

Li, Y. C.; Schulz, J.; Mannen, S.; Delhom, C.; Condon, B.; Chang, S.; Zammarano, M.;

Grunlan, J. C., Flame Retardant Behavior of Polyelectrolyte-Clay Thin Film Assemblies on Cotton Fabric. ACS. Nano. 2010, 4 , 3325-3337. 12.

Denison, D. M.; Ernsting, J.; Tonkins, W. J.; Cresswell, A. W., Problem of Fire in

Oxygen-Rich Surroundings. Nature 1968, 218 , 1110-1113. 13.

Xiong, S.; Zhong, Z.; Wang, Y., Direct Silanization of Polyurethane Foams for Efficient

Selective Absorption of Oil from Water. AIChE J. 2017, 63 , 2232-2240.


21

ACS Nano 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

14.

Page 22 of 25

Wan, Y. J.; Gong, L. X.; Tang, L. C.; Wu, L. B.; Jiang, J. X., Mechanical Properties of

Epoxy Composites Filled with Silane-Functionalized Graphene Oxide. Compos. Part. A. 2014, 64 , 79-89. 15.

Guan, L. Z.; Gao, J. F.; Pei, Y. B.; Zhao, L.; Gong, L. X.; Wan, Y. J.; Zhou, H.; Zheng,

N.; Du, X. S.; Wu, L. B., Silane Bonded Graphene Aerogels with Tunable Functionality and Reversible Compressibility. Carbon 2016, 107, 573-582. 16.

Hua, Z.; Wang, H.; Niu, H.; Gestos, A.; Wang, X.; Tong, L., Fluoroalkyl Silane Modified

Silicone Rubber/Nanoparticle Composite: A Super Durable, Robust Superhydrophobic Fabric Coating. Adv. Mater. 2012, 24 , 2409-2412. 17.

Stankovich, S.; Dikin, D. A.; Dommett, G. H. B.; Kohlhaas, K. M.; Zimney, E. J.; Stach,

E. A.; Piner, R. D.; Nguyen, S. T.; Ruoff, R. S., Graphene-Based Composite Materials. Nature 2006, 442 , 282-286. 18.

Nicolosi, V.; Chhowalla, M.; Kanatzidis, M. G.; Strano, M. S.; Coleman, J. N., Liquid

Exfoliation of Layered Materials. Science 2013, 340 , 1226419. 19.

Boland, C. S.; Khan, U.; Ryan, G.; Barwich, S.; Charifou, R.; Harvey, A.; Backes, C.; Li,

Z.; Ferreira, M. S.; Möbius, M. E.; Young, R. J.; Coleman, J. N., Sensitive Electromechanical Sensors Using Viscoelastic Graphene-Polymer Nanocomposites. Science 2016, 354 , 1257-1260. 20.

Yao, H. B.; Ge, J.; Wang, C. F.; Wang, X.; Hu, W.; Zheng, Z. J.; Ni, Y.; Yu, S. H., A

Flexible and Highly Pressure-Sensitive Graphene-Polyurethane Sponge Based on Fractured Microstructure Design. Adv. Mater. 2013, 25 , 6692-6698. 21.

Du, X.; Liu, H. Y.; Mai, Y-W., Ultrafast Synthesis of Multifunctional N-Doped Graphene

Foam in An Ethanol Flame. ACS. Nano. 2015, 10 , 453-462.


22

Page 23 of 25 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 Nano

22.

Ge, J.; Shi, L. A.; Wang, Y. C.; Zhao, H. Y.; Yao, H. B.; Zhu, Y.-B.; Zhang, Y.; Zhu, H.

W.; Wu, H.-A.; Yu, S. H., Joule-Heated Graphene-Wrapped Sponge Enables Fast Clean-Up of Viscous Crude-Oil Spill. Nat Nano 2017, 12 , 434-440. 23.

Fang, B.; Peng, L.; Xu, Z.; Gao, C., Wet-Spinning of Continuous Montmorillonite-

Graphene Fibers for Fire-Resistant Lightweight Conductors. ACS. Nano. 2015, 9 , 5214-5222. 24.

Dong, L.; Hu, C.; Song, L.; Huang, X.; Chen, N.; Qu, L., A Large‐Area, Flexible, and

Flame‐Retardant Graphene Paper. Adv. Funct. Mater. 2016, 26 , 1470-1476. 25.

Wu, Q.; Zhang, Q.; Zhao, L.; Li, S. N.; Wu, L. B.; Jiang, J. X.; Tang, L. C., A Novel and

Facile Strategy for Highly Flame Retardant Polymer Foam Composite Materials: Transforming Silicone Resin Coating into Silica Self-Extinguishing Layer. J. Hazard. Mater. 2017, 336, 222231. 26.

Hamdani, S.; Longuet, C.; Perrin, D.; Lopez-cuesta, J.-M.; Ganachaud, F., Flame

Retardancy of Silicone-Based Materials. Polym. Degrad. Stab. 2009, 94 , 465-495. 27.

Laoutid, F.; Bonnaud, L.; Alexandre, M.; Lopez-Cuesta, J. M.; Dubois, P., New

Prospects in Flame Retardant Polymer Materials: From Fundamentals to Nanocomposites. Mater. Sci. Eng. R 2009, 63 , 100-125. 28.

Tian, X.; Shaw, S.; Lind, K. R.; Cademartiri, L., Thermal Processing of Silicones for

Green, Scalable, and Healable Superhydrophobic Coatings. Adv. Mater. 2016, 28 , 3677-3682. 29.

Lee, W.; Lee, J. U.; Jung, B. M.; Byun, J. H.; Yi, J. W.; Lee, S. B.; Kim, B. S.,

Simultaneous Enhancement of Mechanical, Electrical and Thermal Properties of Graphene Oxide Paper by Embedding Dopamine. Carbon 2013, 65 , 296-304.


23

ACS Nano 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

30.

Page 24 of 25

Tang, L. C.; Wan, Y. J.; Yan, D.; Pei, Y. B.; Zhao, L.; Li, Y. B.; Wu, L. B.; Jiang, J. X.;

Lai, G. Q., The Effect of Graphene Dispersion on The Mechanical Properties of Graphene/Epoxy Composites. Carbon 2013, 60, 16-27. 31.

Wan, Y. J.; Tang, L. C.; Gong, L. X.; Yan, D.; Li, Y. B.; Wu, L. B.; Jiang, J. X.; Lai, G.

Q., Grafting of Epoxy Chains onto Graphene Oxide for Epoxy Composites with Improved Mechanical and Thermal Properties. Carbon 2014, 69, 467-480. 32.

Hale, R. C.; La Guardia, M. J.; Harvey, E. P.; Gaylor, M. O.; Mainor, T. M.; Duff, W. H.,

Flame Retardants: Persistent Pollutants in Land-Applied Sludges. Nature 2001, 412 , 140-141. 33.

Shaw, S. D.; Blum, A.; Weber, R.; Kannan, K.; Rich, D.; Lucas, D.; Koshland, C. P.;

Dobraca, D.; Hanson, S.; Birnbaum, L. S., Halogenated Flame Retardants: Do The Fire Safety Benefits Justify The Risks? Rev. Environ. Health 2010, 25 , 261-305. 34.

Chattopadhyay, D. K.; Webster, D. C., Thermal Stability and Flame Retardancy of

Polyurethanes. Prog. Polym. Sci. 2009, 34 , 1068-1133. 35.

Wicklein, B.; Kocjan, A.; Salazar-Alvarez, G.; Carosio, F.; Camino, G.; Antonietti, M.;

Bergstrom, L., Thermally Insulating and Fire-Retardant Lightweight Anisotropic Foams Based on Nanocellulose and Graphene Oxide. Nat. Nanotechnol. 2015, 10 , 277-283. 36.

Zhang, Q.; Lin, D.; Deng, B.; Xu, X.; Nian, Q.; Jin, S.; Leedy, K. D.; Li, H.; Cheng, G.

J., Flyweight, Superelastic, Electrically Conductive, and Flame-Retardant 3D Multi-Nanolayer Graphene/Ceramic Metamaterial. Adv. Mater. 2017, 29 , 1605506. 37.

Shi, Y.; Li, L.-J., Chemically Modified Graphene: Flame Retardant or Fuel for

Combustion? J. Mater. Chem. 2011, 21 , 3277-3279. 38.

Higginbotham, A. L.; Lomeda, J. R.; Morgan, A. B.; Tour, J. M., Graphite Oxide Flame-

Retardant Polymer Nanocomposites. ACS Appl. Mat. Interfaces 2009, 1 , 2256-2261.


24

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ACS Nano

39.

Kashiwagi, T.; Du, F.; Douglas, J. F.; Winey, K. I.; Harris, R. H.; Shields, J. R.,

Nanoparticle Networks Reduce The Flammability of Polymer Nanocomposites. Nat. Mater. 2005, 4 , 928-933. 40.

Ding, F.; Liu, J.; Zeng, S.; Xia, Y.; Wells, K. M.; Nieh, M. P.; Sun, L., Biomimetic

Nanocoatings with Exceptional Mechanical, Barrier, and Flame-Retardant Properties from Large-Scale One-Step Coassembly. Science Advances 2017, 3 , e1701212. 41.

Li, Y. C.; Mannen, S.; Morgan, A. B.; Chang, S.; Yang, Y. H.; Condon, B.; Grunlan, J.

C., Intumescent All-Polymer Multilayer Nanocoating Capable of Extinguishing Flame on Fabric. Adv. Mater. 2011, 23 , 3926-3931.

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Efficient Flame Detection and Early Warning Sensors on Combustible

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