P(St-NIPAM) Particles and Their Switchable

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Smart Conducting PANI/P(St-NIPAM) Particles and Their Switchable Conductivity Jiawei Liu, Jiahui Liu, Feiyang Ma, and Jiguang Liu ACS Appl. Polym. Mater., Just Accepted Manuscript • DOI: 10.1021/acsapm.8b00014 • Publication Date (Web): 14 Jan 2019 Downloaded from http://pubs.acs.org on January 15, 2019

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ACS Applied Polymer Materials

Smart Conducting PANI/P(St-NIPAM) Particles and Their Switchable Conductivity Jiawei Liu, Jiahui Liu, Feiyang Ma and Jiguang Liu Department of Materials Science & Engineering, Beijing Institute of Fashion Technology, Beijing 100029, P.R. China. KEYWORDS: switchable conductivity, smart conducting particle, responsive polymer, volumetric change, smart circuit

ABSTRACT: Particles with circumstance-responsive conductivity have appealing performance in constructing sensors. Here, “smart” conducting polyaniline-doped poly(styrene-co-Nisopropyl acrylamide) composite spheres, i.e. PANI/P(St-NIPAM) particles, are reported. A series of PANI/P(St-NIPAM) particles can be prepared with different ratios of N-isopropyl acrylamide to monomers, i.e. N/M ratios. With the improved N/M ratios in polymerization, the amount of polyaniline (PANI) incorporating in the produced particles increased, resulting in an enhanced conductivity. With the improved N/M ratios, the hydrodynamic diameters of PANI/P(St-NIPAM) particles increased at low temperature whereas decreased at high temperature; resulting in the enhanced volume-change ability with the increasing poly(N

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isopropyl acrylamide) (PNIPAM) content in particles. Depending on the temperature-induced volume change, these particles exhibit “smart” conductivity in a home-made device, in which these particles can be used as a temperature-responsive conducting medium to construct a “onoff” circuit and the switch of LED lamp can be triggered by temperature. These particles with the smart conducting property provide wide potential applications in sensors, microelectronics, energy storage and other fields.

1. INTRODUCTION Conducting polymers attract huge attentions owing to their processibility, organic nature and tunable electrical conductivity. The granulation of conducting polymers provides a possibility of further constructing new structures with conducting polymer by self-assembly or locating on/into other materials. For example, the conductivity of semiconducting polymer blends could be dramatically improved by the self-assembly of polyaniline-phenolsulfonate and polystyrene particles.1 Micro/nano-sized particles with conducting polymer have played a very important role in developing electronic devices in recent years due to their processibility and have been widely used in many fields, such as biosensors,2 battery anodes,3 microbial fuel cells,4 electrochemical batteries,5 electrocataly-sis,6 and drug delivery.7 Diversified shapes of particles with conducting polymer have been developed up, such as spherical composite silica conducting particles (e.g. poly(pyrrole)-silica, PPy-Si),8 snowman-like PMMA/PANI,9 microcups of poly(pyrrole) (PPy) prepared by template method7 and the conducting core-shell particles produced by alternating electrostatic deposition of polyaniline (PANI) and poly(sodium 4-styrene sulfonate) (PSS) layers onto colloidal polystyrene (PS) particles.10 To date, most of conducting polymers, e.g. polyaniline (PANI),10 PPy11,12 or poly(3,4-


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ethylenedioxythiophene) (PEDOT) ,13,14 have been used to fabricate conducting particles with good shapes.15 Among them, polyaniline (PANI) receives much attentions owing to good environmental stability and tunable conductivity. Diversified polyaniline particles have been reported, such as polyaniline/polystyrene (PANI/PS) core-shell particles with smart electroresponsive electrorheo-logical performance,16,17 polyaniline-coated poly(methyl meth-acrylate) microspheres18 and polyaniline-graphene hollow spheres.10 The investigation on their electrical properties mainly focuses on their conductivity, cyclic voltammogram or electrorheological performance. It is well known that responsive polymers can change their molecular configurations between swelling and collapsing state, resulting in a volumetric change. Especially, poly(Nisopropylacrylamide) (PNIPAM) can swell/collapse when temperature below/above their lower critical solution temperature (LCST, approximate 32℃).19 With the help of stimuli-responsive volumetric change, the hybrid hydrogels consisting of responsive polymer and conducting polymer exhibited the “ smart ”

electrical conductivity, such as PNIPAM/PANI,20

PNIPAM/PPy20 and polypyrrole/agarose-based hydrogel.21 It can be predicted that the responsive conducting particles with good shapes should have the stronger processibility, sensitivity and wide applications in developing sensors or electronic devices. Although many hybrid particles consisting of conducting particles and stimuli-responsive polymers were reported, such as poly(N-isopropylacrylamide-co-acrylic acid) microgels binding Ag

nanoparticles,22

silver

nanoparticles/poly(N-isopropylacrylamide)-coated

polystyrene

microspheres;23 the involved conducting particles are mostly metal particles and the investigation on their properties mainly focuses on catalysis. There is less study involving in their conductivity.


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Especially, the influence of responsive polymer on particles conductivity is seldom reported. However, the “switchable” effect of responsive polymer on the conductivity should be paid more attentions due to their appealing performance in creating smart conducting materials or devices. In this work, responsive PNIPAM component is incorporated into spherical polystyrene particles to prepare poly(styrene-co-N-isopropylacrylamide), i.e. P(St-NIPAM), particles, and then conducting PANI is embedded into the sulfonated P(St-NIPAM), i.e. SP(St-NIPAM) particles, to produce polyaniline-doped poly(styrene-co-N-isopropyl acrylamide) composite particles, i.e. PANI/P(St-NIPAM) composite particles. The responsive PNIPAM fragment in polymer molecules plays a significant role in controlling PANI content, particles conductivity, and the "intelligence" of conductivity. The relationship between temperature-responsive smart conductivity and particles volumetrical change is built up. Finally, an “on-off” electric circuit is constructed using the conducting particles as electric medium, in which the switch of LED light could be triggered by temperature. 2. EXPERIMENTAL SECTION 2.1 Materials and Methods. Polyvinylpyrrolidone (PVP) (Beijing Tongguang Fine Chemistry) was dissolved in a mixed solvent containing ethyl alcohol (Beijing Tongguang Fine Chemistry) and deionized water with a ratio of 5:1 for using as a stabilizer. 2,2’azobobisisobutyronitrile (AIBN, 98%, Tianjin Fuchen Chemical Reagents Factory) and ammonium persulfate (APS, AR, Beijing Chemical Works) were used as initiator in polymerization. Divinylbenzene (DVB, 98% Aladdin) was used as crosslinking agent without further purification. Styrene (St, Tianjin Damao Chemical Reagents Factory) and N-isopropyl acrylamide (NIPAM, 99%, Aladdin) were uses as monomers. Styrene was purified by vacuum


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distillation after washed with 10% NaOH solution and water. NIPAM was directly used without further purification. Aniline (99%, AR, Tianjin Fuchen Chemical Reagents Factory) was used in oxidation polymerization without purification. Sulfuric acid (98%, AR, Beijing Chemical Works) and hydrochloric acid (35%, GR, Beijing Chemical Works) was respectively used in the particles sulfonation and oxidation polymerization. 2.2 Preparation of P(St-NIPAM) Particles and Sulfonated Particles. P(St-NIPAM) particles were prepared via a precipitation polymerization. A typical polymerization is as below: 7 wt% PVP solution, 0.0624 g AIBN, 0.0624 g DVB and a certain ratio of Nisopmpylacrylamide to styrene (e.g. 2mol%) were put into in a three-necked flask. The polymerization was initiated by heating to 70°C after deoxygenation with nitrogen. 24h later, the synthesized P(St-NIPAM) particles were centrifuged and washed 3 times with ethyl alcohol and deionized water, and then dried under vacuum. 0.1 g of the resulting P(St-NIPAM) particles were dispersed in 30 mL of concentrated sulfuric acid and warmed to 40°C, the sulfonation reaction was run for 6 h. The sulfonated P(St-NIPAM) particles, i.e. SP(St-NIPAM), were collected by repeated centrifuging and washing 3 times with deionized water. 2.3 Synthesis of PANI/P(St-NIPAM) Particles. The conducting PANI was introduced into the sulfonated P(St-NIPAM) interior using the following procedure: 0.1 g of the resulting sulfonated particles were dispersed in 40 mL of 1M HCl (35%) solution. Subsequently, 0.2 g of aniline monomer and ammonium persulfate were added into the above particles solution. Then the mixture was heated to 40°C for reaction 24h. The PANI/P(St-NIPAM) composite particles


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were collected by washing with ethyl alcohol and deionized water respectively for 3 times. Finally, PANI/P(St-NIPAM) particles were dried in vacuum before characterization. 2.4 Constructing Smart Conducting Device. A smart circuit device of measuring current was constructed with a silicon tube with the inner diameter of 3 mm and the length of 5 mm, two metal electrodes attached with metal wires, a battery and an avometer or a LED lamp. Particles dispersion with a certain concentration was filled into the silicon tube as conducting medium. The switch of circuit was controlled by heating or cooling the silicon tube. 2.5 Characterizations. The morphologies of the prepared particles were observed by scanning electron microscopy, (SEM, JEM-7500F, JEOL) and transmission electron microscopy (TEM, JEM-1200EX, JEOL). SEM samples were prepared by dripping one droplet of particles solution on silicon wafer and dried; and then the silicon wafer was sputtered with platinum. The TEM samples were prepared by dripping particles solution on a copper net coated with carbon film. The chemical compositions of the prepared particles were examined by Fourier Transform Infrared Spectrometer (FTIR, NICOLET IS 10, Thermo Nicolet Corporation). Particles thermal properties were analyzed by thermogravimetry instrument (TGA, SII 6300) in nitrogen. TGA was carried out from 25°C to 700°C at a heating rate of 10°C /min in nitrogen. The hydrodynamic diameters of particles were measured by dynamic light scattering (DLS, Malvern Instruments Ltd. UK Zetasizer Nano ZS90) at 25°C and 50°C respectively. Electrical conductivity of particles solution was measured with a conductivity meter (DDS-307A, Shanghai Yoke Instrument Co. LTD, China).


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3. RESULTS AND DISCUSSION 3.1

Preparation of Responsive Conducting Particles. P(St-NIPAM) particles were

synthesized in a H2O/ethanol mixed solvent, in which styrene (St) and N-isopropylacrylamide (NIPAM) were used as monomers, divinylbenzene (DVB) and azobisisbutyronitrile (AIBN) was respectively used as cross-linking agent and initiator. P(St-NIPAM) particles were obtained after polymerization, and then they were treated with sulfonic acid for obtaining sulfonated poly(StNIPAM), i.e. SP(St-NIPAM). With a fixed DVB feed ratio, a series of particles were prepared by using different feed ratios of NIPAM to monomers, i.e. N/M ratios. As illustrated in Scheme 1, aniline can diffuse into the as-prepared SP(St-NIPAM) particles, and then an oxidation polymerization can be carried out in the inner of SP(St-NIPAM) particles for producing PANI/P(St-NIPAM) particles. These particles can be used as conductive medium to construct a circuit, and the switch of electric current can be triggered by temperature.

Scheme 1. Illustrating the synthesis of conducting PANI/P(St-NIPAM) composite particles and their responsive conductivity. Using SP(St-NIPAM) particles with different N/M ratios, a series of PANI/P(St-NIPAM) particles with different compositions can be prepared. The prepared P(St-NIPAM) particles with the N/M ratio of 2 mol% have smooth surface and a uniform size of around 800 nm, as shown in


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Figure 1a and Figure S1, which is consistent with their hydrodynamic diameter of 826 nm measured at 25oC with DLS (Figure S2), which PDI result is 0.234 indicating a uniform size. It should be noticed that the P(St-NIPAM) particles have a sticky surface and adhere to each other (Figure 1a & Figure S1), which should be ascribed to the macromolecular chains of PNIPAM. As a comparison, pure polystyrene (PS) particles were synthesized in the dispersion polymerization, which have good spherical shape and their surface is non-sticky (Figure S3a). PS particles have a mean diameter of 1.4 μm, apparently bigger than P(St-NIPAM) particles. That is, the feed of NIPAM in polymerization made the produced particles smaller than those polystyrene particles without NIPAM, and made P(St-NIPAM) particles surface sticky. This is consistent with the sticky nature of PNIPAM particles synthesized without styrene, which have a very small size of around 100 nm and stick to substrate as shown in SEM image (Figure S3b). TEM image further indicates P(St-NIPAM) particles have a smooth sticky homogeneous surface (Figure 1b). A series of particles with different PNIPAM contents were synthesized with different N/M ratios, all of them have the sticky surface (Figure S4). The composition of these P(St-NIPAM) particles is characterized with FTIR. As shown in Figure S5, the characteristic vibrations of polystyrene appear at 3081, 3063, 3027, 1601, 1490, 1450, 758, 698 cm-1 attributed to phenyl group and 2926, 2850 cm-1 assigned to CH2 asymmetric and symmetric tension. 1680 cm-1 is the characteristic absorption of C=O stretching vibration of the amide group in PNIPAM fragment, which intensity relative to the characteristic peak of styrene (1490, 1450 cm-1) enhances with the increasing NIPAM feed ratios, indicating the increasing content of PNIPAM in P(St-NIPAM) particles. The IR absorption near 3420 cm-1, resulting from either the –OH, –NH or the absorbed bound water, further implies that PNIPAM embed into particles.


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Figure 1. Morphologies of the as-synthesized particles. a, b) SEM and TEM images of P(StNIPAM) particles; c, d) SEM and TEM images of PANI/P(St-NIPAM) particles. Particles were synthesized with 2mol% N/M ratio. In order to introduce conductive polyaniline (PANI) into particles, P(St-NIPAM) particles were sulfonated for absorbing aniline monomer easily. The sulfonated P(St-NIPAM) particles, SP(St-NIPAM) particles, still had a sticky surface after sulfonated (Figure S6). The FTIR absorption peak at 1178 cm-1 of S=O stretching vibration indicates that the sulfonation is successful (Figure S7).24 After sulfonated, aniline monomer was absorbed into SP(St-NIPAM) particles; and then PANI/P(St-NIPAM) composite particles were prepared via oxidation polymerization of aniline. After washed and centrifugation, blue colloid particles were obtained. SEM image of Figure 1c indicates that the prepared PANI/P(St-NIPAM) composite particles maintain a spherical shape,


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but have a much rougher surface than P(St-NIPAM) particles. Apparently, the rough surface on the composite particles resulted from polyaniline. More particles were shown in Figure S8, Figure S9 and Figure S10. The SEM image with the wider vision and the image of laser scanning confocal microscope further indicate that these particles have basically homogeneous size. In addition, particles are still sticky to each other, which make particles easily connect with each other for performing electrical conductivity. TEM image (Figure 1d) further indicates that PANI/P(St-NIPAM) composite spheres have a rough surface. A series of PANI/P(St-NIPAM) composite particles could be prepared by oxidation polymerization of aniline using sulfonated P(St-NIPAM) particles with different N/M ratios as seed particles. The surface of all PANI/P(StNIPAM) particles were rough and sticky (Figure S11). The composition of the PANI/P(St-NIPAM) particles can be confirmed by FTIR analysis. For comparison, FTIR spectra of P(St-NIPAM), SP(St-NIPAM) and PANI/P(St-NIPAM) particles with 10 mol% N/M ratio were put together in Figure 2a. As the FTIR analysis of P(St-NIPAM) particles, the absorption at 1490, 1450 cm-1 are assigned to aromatic group. The spectrum of SP(St-NIPAM) particles revealed a sulfuric acid (-SO3H) peak at 1180 cm-1, attributed to the ν(S=O) stretching modes of aromatic sulfonic acid.24 In the FTIR spectrum of PANI/P(StNIPAM) particles, the absorption at 1600, 1490 and 1450 cm-1 are still attributed to PS. Meanwhile, the strong peak at 1120 and 1300 cm-1 is respectively assigned to N=Q=N of PANI and the aromatic amine stretching band;25 indicating that PANI has been incorporated into P(StNIPAM) particles successfully. In the FTIR spectra (Figure 2b) of PANI/P(St-NIPAM) particles with different N/M ratios, the relative intensity of the characteristic peaks of PANI (N=Q=N) to that of PS (C=C) is obviously


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enhanced with the increasing PNIPAM content; indicating that PNIPAM is helpful for PANI to embed into the composite particles.

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Figure 2. The compositions of P(St-NIPAM), SP(St-NIPAM) and PANI/P(St-NIPAM) particles. a) FTIR spectra of particles; b) FTIR spectra of PANI/P(St-NIPAM) particles with different N/M ratios; c) TGA curves of particles; d) the residue of PANI/P(St-NIPAM) particles with different N/M ratios. The composition of particles is further investigated by thermogravimetric analysis (TGA). As shown in Figure 2c, The TGA curve of P(St-NIPAM) sample reveals a sharp weight loss near 350°C due to the thermal degradation of PS and PNIAPM. Its residue weight at 600°C is around 1 wt%, indicating an almost complete decomposition. TGA curve of SP(St-NIPAM) particles indicates a two stage decomposition: the first weight loss occurred at 280-330°C, which is


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ascribed to the breakdown of the sulfonate group attached to benzene ring;26 the second weight loss occurred at 360-475°C, which is the decomposition of polystyrene and poly(NIPAM) components. The final residue amount of the sulfonated sample at 600°C is 22 wt%, much higher than that of P(St-NIPAM). It is attributed to the improved carbonization of polymer composition due to the effect of sulfonic acid groups on polymer molecules. In addition, there is a slight weight loss before 120°C, which is caused by the adsorbed water in particles due to the hydrophilic effect of the sulfonated particles although they had been dried in the oven. Similarly, TGA curve of PANI/P(St-NIPAM) composite particles also has a two-stages decomposition, but has a more residue (24 wt%) than that of SP(St-NIPAM) particles, which is consistent with the 34 wt% high residue amounts of pure PANI (Figure S12). A series of PANI/P(St-NIPAM) particles with different N/M ratios were characterized with TGA. As shown in Figure 2d and Figure S13, the residual weights of PANI/P(St-NIPAM) particles gradually enhance with the improved N/M ratio, i.e. the increasing NIPAM feed in polymerization. That is, the PANI amount in the prepared composite particles closely depends on the PNIPAM content. The more PNIPAM amount in composite particles, the more polyaniline incorporated into particles, resulting in the more residue in TGA curves. The reason may be ascribed to the hydrophilic PNIPAM fragment in macromolecular chains that make particles structure loose and hydrophilic, allowing more aniline monomer to diffuse easier into particles inner. 3.2 Responsive volumetric change and Smart conductivity. Owing to the responsiveness of PNIPAM component, it is predicted that these composite particles have temperature-responsive volumetric change. Dynamic Light Scattering (DLS) results (Figure 3a) indicate that the hydrodynamic diameter of PANI/P(St-NIPAM) particles with 2 mol% N/M ratio was about 920


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nm at 25°C with a PDI of 0.273, which SEM and TEM images are shown in Figure 1c&d. When these particles dispersion were heated to 50°C, DLS result exhibits that particles size became to 710 nm, which PDI result is 0.196. That is, PANI/P(St-NIPAM) particles are responsive to temperature, which is ascribed to the collapse of PNIPAM molecular chains in particles when the circumstance temperature is above LCST. PNIPAM component brings about the “smart” change of particles volume.

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Figure 3. The size and electrical conductivity of PANI/P(St-NIPAM) particles. a) DLS curves of hydrodynamic diameters of PANI/P(St-NIPAM) particles with 2 mol% N/M ratio at different temperatures; b) The sizes of PANI/P(St-NIPAM) particles dependent on temperatures and their N/M ratios; c) conductivities of the particles with 10 mol% N/M ratio dependent on their concentrations in solution; d) conductivities of different particles in 50 wt% solution dependent on their N/M ratios and temperatures.


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The hydrodynamic diameters of PANI/P(St-NIPAM) composite particles with different N/M ratios were measured using DLS at different temperatures. Their sizes are summarized into Figure 3b. When the temperature is at 25°C, the hydrodynamic diameters of composite particles with 5 mol% N/M ratio is 960 nm, and it is 1.1 μm for particles with 10 mol% N/M ratio. The hydrodynamic diameters at 25°C gradually increase with the improved N/M ratio, i.e. the increasing PNIPAM content. The reason is attributed to the hydrophilicity of PNIPAM component at temperature below LCST, which leads that the more water was absorbed into particles with the more PNIPAM content, making particles expand more. However, the hydrodynamic diameters of all PANI/P(St-NIPAM) particles became smaller (Figure 3b) when temperature was up to 50°C due to the collapse of PNIPAM molecular configuration and the resulting particles shrink. The hydrodynamic diameter at 50°C was 620 nm and 530 nm for particles with 5 mol% and 10 mol% N/M ratio, respectively; which gradually decrease with the increasing PNIPAM content. The reason can be ascribed to the influence of NIPAM on particles size: the synthesized net PNIPAM particles are much smaller (Figure S3b) than all P(St-NIPAM) composite particles prepared in the same condition, while the synthesized pure polystyrene particles are the biggest in all particles (Figure S3a). By comparing hydrodynamic diameters of composite particles at high temperature with the data at low temperature, it can be concluded that the change range of particles volume gradually become much wider with the increasing N/M ratio, i.e. the increasing PNIPAM content in particles. The result indicates that the temperature-responsive capacity of particles can be improved by increasing the amount of PNIPAM component in the composite particles.


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The electrical conductivity of PANI/P(St-NIPAM) composite particles was checked with a conductivity meter. The composite particles with 10 mol% N/M ratio were dispersed into deionized water to get a series of solutions with different concentrations, and then the electrical conductivity of particles solutions was measured at 25°C. As shown in Figure 3c, the conductivity of particles solution rose up with increasing particles concentrations. The solution with 10 wt% particles has a conductivity of 0.15 S/m. When the particles concentration is 50 wt%, its conductivity is up to 1 S/m. Fixing the particles concentration at 50 wt%, the electrical conductivities of particles solutions with different N/M ratios were measured at 25℃. As shown in Figure 3d, electrical conductivity was improved with increasing N/M ratios of particles; which can be attributed to the more conducting PANI amount in particles with the more N/M ratios. Similarly, the electrical conductivity measured at 50°C also increased with the more N/M ratios of particles, but, the measured conductivities at 50°C are obviously lower than the obtained data at 25°C for all of particles. It should be caused by the shrink of particles volume at high temperature, resulting in the lower volume concentration of particles in solution. The changing conductivity provides a possibility of constructing "smart" electrical switches. 3.3 "Smart" electrical circuit. The "smart" electrical conductivity was investigated in a home-made device containing PANI/P(St-NIPAM) composite particles, consisting of a silicon tube with the inner diameter of 3 mm and the length of 5 mm, two metal electrodes attached with metal wires and an avometer equipped with a 9V battery. Particles dispersion with a concentration of 50 wt% was filled into the silicon tube as conducting medium so that a circuit was constructed and the electric current could be measured. First of all, the electric current was


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tested using SP(St-NIPAM) particles as conducting medium, but the measured current was almost zero. When PANI/P(St-NIPAM) particles with 2 mol% N/M ratio were used as conducting medium, the measured electric current was 1.94 mA at 25°C (Figure 4a). The current was 2.66 mA for particles with 5mol% N/M ratio. When the N/M ratio of the composite particles increased to 10 mol%, the measured electric current was up to 3.55 mA. The enhanced current can be attributed to the more PANI in PANI/P(St-NIPAM) particles with the higher N/M ratios. However, the measured currents for all of samples are close to zero when the tube filled with particles was heated to 50°C (Figure 4a) due to the volume shrinks of PANI/P(St-NIPAM) particles under high temperature conditions and the resulting interruption of circuit. That is, the “smart” electric circuit is responsive to temperature.

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Figure 4. “Smart” switched conductivities of responsive PANI/P(St-NIPAM) particles. a) the measured currents in a home-made device dependent on particles N/M ratios at different temperatures; b) the switchable conductivities of PANI/P(St-NIPAM) particles dispersion filled


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in the silicon tube dependent on temperatures in a cycling temperatures performance; c) photograph of the device at 25°C, in which particles connect with each other in tube and LED lamp light on; d) photograph of the device at 50°C, in which the particles disconnected in tube and LED lamp light off. The particles have a 10 mol% N/M ratio. A cycling conducting test was carried out at 25°C and 50°C alternately, using 50 wt% PANI/P(St-NIPAM) particles with 10 mol% M/N ratio as conducting medium. The electric current was more than 2.5 mA (Figure 4b) when it was measured at 25°C, but became close to 0 μA at 50°C. The altered currents in the circuit were recorded, displaying a good "on-off" cycle stability. The above "on-off" conductivity can be used to develop temperature-responsive electric device. A LED lamp was connected into the above circuit and a battery with 9 Voltages was used to replace the avometer. When the temperature was at 25°C, the LED lamp turned on (Figure 4c). When particles in silicon tube were heated up to 50 ℃ ， particles shrank and the circuit disconnected. As shown in Figure 4d, the particles dispersion interrupted in tube at 50℃, making the LED light turn off. If the temperature cooled down again, the particles swell and the circuit could be connected and the LED light was on again. That is, the circuit interrupted at high temperature and connected again at low temperature, as shown in Scheme 1. LED lamp switched off again when the temperature was again up to 50°C. The electric “switch” can be triggered by temperature. In a word, PANI/P(St-NIPAM) particles can be used to create a smart chip responsive to temperatures, which have a wide potential application in developing sensors.


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4. CONCLUSIONS A series of PANI/P(St-NIPAM) particles were prepared via seeded polymerization in the sulfonated P(St-NIPAM) particles with different N/M ratios. The PANI amount incorporating into particles depends on the N/M ratio of P(St-NIPAM), i.e. the PNIPAM amount. With the improved N/M ratio, the change range of hydrodynamic diameters of PANI/P(St-NIPAM) particles under different temperatures regularly increased. With the improved N/M ratio, the conductivity of different composite particles increased. A temperature-responsive electrical circuit was constructed using PANI/P(St-NIPAM) composite particles as conducting medium, resulting in a switchable conductivity. The “smart” switch of LED lamp could be triggered by temperature. The investigation provides a new route to develop sensors and will have wide applications on creating smart chips, biosensors or microelectronics. ASSOCIATED CONTENT Supporting Information Additional experimental results are included in the support information, including more SEM images and FTIR of P(St-NIPAM) particles, SEM image and FTIR spectrum of SP(St-NIPAM) particles, SEM images and TGA curves of PANI/P(St-NIPAM) with different ratios of N/M ratios and TGA curve of polyaniline. There materials are available free of charge via the Internet at http://pubs.acs.org.” AUTHOR INFORMATION Corresponding Author *TEL: +86-10-62488178, Email: [email protected].


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Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding Sources Fundamental Research Program of Textile Light (No. J201601) from Textile Vision Science & Education Fund and BIFT Program for Innovative Research Team (No. BIFTTD201801). Notes The authors have no competing financial interests. ACKNOWLEDGMENT The authors thank the support of the following grants: Fundamental Research Program of Textile Light (No. J201601) from Textile Vision Science & Education Fund, BIFT Program for Innovative Research Team (No. BIFTTD201801) and Open Foundation of National Laboratory from Beijing National Laboratory for Molecule Sciences. The authors also thank the support from the Institute of Chemistry, Chinese Academy of Sciences. REFERENCES (1) Mezzenga, R.; Ruokolainen, J.; Fredrickson, G. H.; Kramer, E. J.; Moses, D.; Heeger, A. J.; Ikkala, O. Templating Organic Semiconductors via Self-Assembly of Polymer Colloids. Sciences 2003, 299, 1872-1874. (2) Chen, J.; Miao, Y.; He, N.; Wu, X.; Li, S. Prospects of conducting polymers in biosensors. Biotechnol. Adv. 2004, 22, 505-518.


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(3) Wu, H.; Yu, G.; Pan, L.; Liu, N.; McDowell, M. T.; Bao, Z.; Cui, Y. Stable Li-ion Battery Anodes by In-Situ Polymerization of Conducting Hydrogel to Conformally Coat Silicon Nanoparticles. Nat. Commun. 2013, 4, 1943. (4) Hou, J.; Liu, Z.; Zhang, P. A New Method for Fabrication of Graphene/Polyaniline Nanocomplex Modified Microbial Fuel Cell Anodes. J. Power Sources 2013, 224, 139-144 (5) Wu, J.; Pan, Z.; Zhang, Y.; Wang, B.; Peng, H. The Recent Progress of Nitrogen-Doped Carbon Nanomaterials for Electrochemical Batteries. J. Mater. Chem. A 2018, 6, 12932-12944. (6) Zhou, Y.; Chen, J.; Li, J. T.; Lin, Z. B.; Sun, S. G. Onion-Like Metal-Organic Colloidosomes from Counterion-induced Self-Assembly of Anionic Surfactant. J. Mater. Chem. A 2018, 6, 14091-14102. (7) Antensteiner, M.; Khorrami, M.; Fallahianbijan, F.; Borhan, A.; Abidian, M. R. Conducting Polymer Microcups for Organic Bioelectronics and Drug Delivery Applications. Adv. Mater. 2017, 29, 1702576. (8) Balmer, J. A.; Schmid, A.; Armes, S. P. Colloidal Nanocomposite Particles: Quo Vadis? J. Mater. Chem. 2008, 18, 5722-5730. (9) Liu, Y. D.; Fang, F. F.; Choi, H. J. Core-Shell Structured Semiconducting PMMA/Polyaniline Snowman-like Anisotropic Microparticles and Their Electrorheology. Langmuir 2010, 26, 12849-12854. (10) Fan, W.; Zhang, C.; Tjiu, W. W.; Pramoda, K. P.; He, C.; Liu, T. Graphene-Wrapped Polyaniline Hollow Spheres as Novel Hybrid Electrode Materials for Supercapacitor Applications. ACS Appl. Mater. Interfaces 2013, 5, 3382-3391. (11) Khan, M. A.; Armes, S. P. Conducting Polymer-Coated Latex Particles. Adv. Mater. 2000, 12, 671-674. (12) Cairns, D. B.; Khan, M. A.; Perruchot, C.; Riede, A.; Armes, S. P. Synthesis and Characterization of Polypyrrole-Coated Poly(alkyl methacrylate) Latex Particles. Chem. Mater. 2003, 15, 233-239.


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(13) Culebras, M.; Serrano-Claumarchirant, J. F.; Sanchis, M. J.; Landfester, K.; Cantarero, A.; Gomez, C. M.; Muñoz-Espí, R. Conducting PEDOT Nanoparticles: Controlling Colloidal Stability and Electrical Properties. J. Phys. Chem. C 2018, 122, 19197-19203. (14) Muro, K.; Watanabe, M.; Tamai, T.; Yazawa, K.; Matsukawa, K. PEDOT/PSS Nanoparticles: Synthesis and Properties. RSC Adv. 2016, 6, 87147. (15) Fielding, L. A.; Hillier, J. K.; Burchell, M. J.; Armes, S. P. Space Science Applications for Conducting Polymer Particles: Synthetic Mimics for Cosmic Dust and Micrometeorites. Chem. Commun. 2015, 51, 16886-16899. (16) Liu, Y. D.; Park, B. J.; Kim, Y. H.; Choi, H. J. Smart Monodisperse Polystyrene/Polyaniline Core-Shell Structured Hybrid Microspheres Fabricated by a Controlled Releasing Technique and Their Electro-Responsive Characteristics. J. Mater. Chem. 2011, 21, 17396. (17) Piao, S. H.; Gao, C. Y.; Choi, H. J. Sulfonated Polystyrene Nanoparticles Coated with Conducting Polyaniline and Their Electro-Responsive Suspension Characteristics Under Electric Fields. Polymer 2017, 127, 174-181. (18) Lee, I. S.; Cho, M. S.; Choi, H. J. Preparation of Polyaniline Coated Poly(methyl methacrylate) Microsphere by Graft Polymerization and Its Electrorheology. Polymer 2005, 46, 1317-1321. (19) Fujishige, S.; Kubota, K.; Ando, I. Phase Transition of Aqueous Solution of Poly(Nisopropylacrylamide) and Poly(N-isopropylmethacrylamide). J. Phys Chem. 1989, 93, 33113313. (20) Shi, Y.; Ma, C.; Peng L.; Yu, G. Conductive “Smart” Hybrid Hydrogels with PNIPAM and Nanostructured Conductive Polymers. Adv. Funct. Mater. 2015, 25, 1219-1225. (21) Hur, J.; Im, K.; Kim, S. W.; Kim, J.; Chung, D. Y.; Kim, T. H.; Jo, K. H.; Hahn, J. H.; Bao, Z.; Hwang, S.; Park, N. Polypyrrole/Agarose-based Electronically Conductive and Reversibly Restorable Hydrogel. ACS Nano 2014, 8, 10066.


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Scheme 1. Illustrating the synthesis of conducting PANI/P(St-NIPAM) composite particles and their responsive conductivity. 418x97mm (72 x 72 DPI)



Figure 1. Morphologies of the as-synthesized particles. a, b) SEM and TEM images of P(St-NIPAM) particles; c, d) SEM and TEM images of PANI/P(St-NIPAM) particles. Particles were synthesized with 2mol% N/M ratio. 452x351mm (72 x 72 DPI)


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Figure 2. The compositions of P(St-NIPAM), SP(St-NIPAM) and PANI/P(St-NIPAM) particles. a) FTIR spectra of particles; b) FTIR spectra of PANI/P(St-NIPAM) particles with different N/M ratios; c) TGA curves of particles; d) the residue of PANI/P(St-NIPAM) particles with different N/M ratios. 757x541mm (72 x 72 DPI)



Figure 3. The size and electrical conductivity of PANI/P(St-NIPAM) particles. a) DLS curves of hydrodynamic diameters of PANI/P(St-NIPAM) particles with 2 mol% N/M ratio at different temperatures; b) The sizes of PANI/P(St-NIPAM) particles dependent on temperatures and their N/M ratios; c) conductivities of the particles with 10 mol% N/M ratio dependent on their concentrations in solution; d) conductivities of different particles in 50 wt% solution dependent on their N/M ratios and temperatures. 757x541mm (72 x 72 DPI)


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Figure 4. “Smart” switched conductivities of responsive PANI/P(St-NIPAM) particles. a) the measured currents in a home-made device dependent on particles N/M ratios at different temperatures; b) the switchable conductivities of PANI/P(St-NIPAM) particles dispersion filled in the silicon tube dependent on temperatures in a cycling temperatures performance; c) photograph of the device at 25°C, in which particles connect with each other in tube and LED lamp light on; d) photograph of the device at 50°C, in which the particles disconnected in tube and LED lamp light off. The particles have a 10 mol% N/M ratio. 757x541mm (72 x 72 DPI)



262x159mm (72 x 72 DPI)


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P(St-NIPAM) Particles and Their Switchable

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