Supporting Information

Self-stabilized polyaniline@graphene aqueous colloids for

the construction of assemblied conductive network in rubber

matrix and its chemical sensing applicationZehang Zhou, Xinxing Zhang, Xiaodong Wu and Canhui Lu*

State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute

of Sichuan University, Chengdu 610065, China

*Corresponding author: Xinxing Zhang and Canhui LuE-mail address: xxzwwh@scu.edu.cn ; canhuilu@scu.edu.cn Tel: +86-28-85460607 Fax: +86-28-85402465

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The preparation of rGO and PANI

As a comparison experiment, GO nanosheets were reduced by hydrazine hydrate according to

previous study [1]. Specifically, GO was dispersed in deionized water (100 mg/mL) with stirring,

yielding a homogeneous light brown dispersion. Hydrazine hydrate solution (1 mL, 32 mmol) was

added into GO dispersion, and the dispersion was heated in oil bath for 6 h. The product was

separated by filtration and repeatedly washed. PANI was prepared by oxidative polymerization of

aniline. 0.57 g of aniline and 0.48 g of ammonium persulfate (APS) were separately dissolved in

two beakers containing 25 mL of 1.0 M HCl. The two solutions were mixed together under room

temperature and stirred for 2 h. The resulted mixture was isolated by filtration and repeatedly

washed.

The stabilization mechanism of PANI@rGO nanohybrids

Fig. S1a presents that although the PANI@rGO nanohybrids aqueous suspension could keep

stable for a long time, the addition of an electrolyte (NaCl) led to apparent flocculation in this

dispersion, which is the characteristic of lyophobic colloid stabilized through the electrostatic

repulsion. It could be explained by classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory

[2]. This result is further confirmed by the Tyndall effect of the dispersion (Fig. S1b).

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Fig. S1. Digital pictures of PANI@rGO nanocomposites aqueous suspension after the addition of

electrolyte (a) and a laser beam passes through PANI@rGO nanocomposites aqueous suspension

(b).

The stability of PANI@rGO nanohybrids in neutral aqueous suspension

Previous studies [3, 4] have demonstrated that although PANI and graphene are hydrophobic in

nature, they could reach stable aqueous dispersion via electrostatic repulsions without any

chemical modification or stabilizer. In order to further understand the stabilization mechanism of

PANI@rGO nanohybrids, its stability was studied in neutral aqueous suspension. The digital

camera picture of PANI@rGO nanohybrids is shown in Fig. S2. The sample (0.15 mg/mL) was

homogenized with vigorous stirring and placed under neutral condition for 24 h. A large

proportion of PANI@rGO nanohybrids agglomerated and subsided to the bottom of the bottle.

However, comparing to the rGO/PANI blend which started to precipitate almost immediately after

standing, PANI@rGO nanohybrids could stay stable much longer. Furthermore, small amount of

PANI@rGO nanohybrids could still disperse in the suspension. The stacking of PANI

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nanoparticles with rGO sheets prevented the nanohybrids from aggregation to a very limited

extent. Due to the relatively low ion concentration in neutral aqueous suspension, the ζ-Potential

of PANI@rGO nanohybrids was measured to be -7.2 ±1 mV, which is much lower than that under

alkaline condition. This result indicates that the electrostatic repulsion between PANI@rGO

nanohybrids which resist the particles from aggregating was greatly reduced, leading to impaired

stability. This study further demonstrated the stabilization mechanism of PANI@rGO

nanohybrids. As NR latex is typically preserved and used under alkaline condition in the industry

(with the addition of ammonia), the nanohybrid suspension prepared in this study is well suited for

latex assembly technique.

Fig. S2. The digital camera pictures of PANI@rGO nanohybrids under neutral aqueous suspension

(0.15 mg/mL) before and after standing for 24 h.

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The electrical conductivity of GO before and after reduction

The surface electrical resistances of both GO and rGO samples were evaluated by a two-point

measurement with a resistance meter (UT61, Uni-Trend, China). In this measurement, same

amount of original GO sheets and GO sheets after reduction were casted on glass substrates to

obtain thin films. The surface electrical resistance of the original GO sheets could not be read,

indicating that its resistance exceeded the range of this meter (200 MΩ), while the resistance of

reduced GO sheets was in a range of 0.15-1.5 kΩ. This result indicates that the electrical

conductivity of GO increased at least 6 orders of magnitude after reduction.

TEM observation of PANI@rGO/NR latex

As shown in Fig. S3, NR latex spheres with large exclusion volume expel the PANI@rGO

nanohybrids to the interstitial space between them, which prevents the microspheres from

agglomerating. In addition, the PANI@rGO nanocomposites entangled with each other and

organized into continuous network between multiple latex particles, which facilitates the

construction of valid conductive network in the NR matrix.

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Fig. S3. The TEM image of rGO/PANI/NR composite.

The mechanical properties of PANI@rGO/NR composite

The stress-strain behavior of the composites was studied and shown in Fig. S4. As carbon black

(CB) has been widely used as the reinforcement of rubber matrix, the mechanical properties of

neat NR and CB-filled NR composite were investigated for comparative study. Fig. S4 presents

that PANI@rGO/NR composite exhibits well enhanced mechanical properties. Its tensile strength

is about 5 times and 2 times higher than that of neat NR and CB-filled NR composite,

respectively. Meanwhile, its elongation at break is comparable to that of CB-filled NR composite,

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which is higher than that of neat NR. This result indicates the superior reinforcing effect of

PANI@rGO nanohybrids to NR matrix over traditional fillers (e.g. CB). On the other hand, the

samples for chemical sensing measurement in this study were unvulcanized, as crosslinking

polymer chains could damage their responsivity. As a result, the mechanical properties of these

samples are poorer than the vulcanized rGO/NR composites [5], which is in accordance with

previous study [6].

Fig. S4. The stress-strain curves of NR, CB/NR (CB loading= 7 wt%) and PANI@rGO/NR

(PANI@rGO loading = 7 wt %) composites.

Comparative study of chemical sensing performance of PANI@rGO/NR composite

The PANI@rGO/NR composite is very sensitive to chemical stimuli. It presents a remarkable

responsivity of 952.5 comparing to other reported chemical sensing materials as shown in Table

S1.

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Table S1. Comparison of chemical sensing performance of various CPCs

Samples AR (ΔR/ R0) References

PP/PCL/MWNT 0-3 7

PLA/MWNT 1.218-1.23 8

Styrene/butadiene/CB 8.4-38.4 9

PCL/PEG-g-CB 3-49 10

PP/TPU/CB 2-24 11

PDAC/rGO 0-0.6 12

PANI@rGO/NR composite 952.5 This work

(Note: polypropylene-PP, polycaprolactione-PCL, multi-walled carbon nanotubes-MWNT,

polyactic acid-PLA, carbon black-CB, thermoplastic polyurethane-TPU, polyethylene glycol-

PEG, poly(diallyldimethyl ammonium chloride)-PDAC)

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