Anticorrosive and electromagnetic shielding response of a graphene/TiO₂–epoxy nanocomposite with enhanced mechanical properties

Abstract

The effect of TiO₂ nanoparticles (25–35 nm), graphene (GP) and the combination (TiO₂ + graphene) on anti-corrosion, EMI shielding and mechanical properties of an epoxy matrix have been studied. The nanocomposites were prepared with the help of an ultrasonic mixing process. Field Emission Scanning Electron Microscopy (FESEM) and transmission electron microscopy (TEM) were used to identify the morphology of fillers and their distribution in the epoxy matrix. The graphene/TiO₂–epoxy nanocomposite (epoxy + 0.25 wt% GP + 0.25 wt% TiO₂) showed excellent anti-corrosion performance with maximum corrosion protection increased up to 99.96% and also exhibited a total shielding effectiveness (SE_T) of −11 dB (>90% attenuation) compared to neat epoxy with SE_T ≈ −3 dB (50% attenuation). The graphene/TiO₂–epoxy nanocomposite showed maximum enhancement of about 36% and 84% in tensile strength and storage modulus respectively as compared to neat epoxy.

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1. Introduction

Graphene has been used widely used in the field of nano-electromechanical systems, nano-electronics, nano-photonics, nano-composites, batteries and hydrogen storage^1–7 due to its extraordinary mechanical, thermal, electrical and optical properties.^8–12 The development of filler materials in epoxy matrix has grown exponentially and received considerable attention due to the enhancement of properties of the composite material. Recently, the graphene has been used as an ideal filler material in the polymer matrix to make composite materials with excellent properties. Chatterjee et al.¹³ reported that the fracture toughness of an epoxy matrix increased to 82% as compared with neat epoxy and thermal conductivity was also increased with the addition of graphene nanoplatelets (2 wt% graphene nanoplatelets, dia. 25 μm). Rafiee et al.¹⁴ studied the mechanical properties of epoxy nanocomposites with low graphene content (0.1 wt%) and compared the results with same loading of single-walled and multi-walled carbon nanotubes in the epoxy matrix. They also reported that the composite with graphene showed highest tensile strength, Young's modulus and fracture toughness. Bolotin et al. carried out an electrochemical corrosion study on graphene's anti-corrosion efficiency and reported that atom-thick graphene have 5 times better corrosion protection in competition with conventional organic coatings.¹⁵ However, the main critical issue with graphene is poor dispersion due to strong van der Waals interactions, which lead to decrease in the surface area and limits its potential in the enhancement of performance properties of the polymer nanocomposites. Recently, some researchers introduced metal, metal oxide/hydroxide in between the layers of graphene to prevent the re-clusterization.^16–19 These inorganic nanoparticles enter among the graphene sheets, increase the inter planar spacing and surface area and provide both side of graphene layer for polymer matrix interaction. Several oxide like SiO₂, NiO, Al₂O₃, TiO₂, MnO₂, Fe₂O₃ and ZnO etc., which can be considered for this regard, but out of these TiO₂ is considerably more important due to the combination of its unique properties such as non-toxicity, photo stability, corrosion resistance, chemical resistance, good compatibility with various materials, high refractive index, high photo catalytic activity and ability to absorb ultraviolet (UV) light.^20–22 Moreover, the mechanical performance of polymers has been successfully improved by reinforcing TiO₂ nanoparticles into epoxy matrix.^23–25

Interstitial-free (IF) steels are extensively used in the automotive industries as prime material due to its superior property like high formability, fatigue resistance etc. IF steel in corrosive atmospheres like acid rain and ocean aerosphere, usually suffers high corrosion attack especially by the presence of the chloride ions, so in a short time it can lead to unfavorable damage.^26,27 Therefore, to protect the IF steel from high susceptibility of corrosion, an anti-corrosion protection layer on IF steel surface deserves to be developed. Graphene provides a barrier between metal surface and reacting species.²⁸ Generally, metals and their composites are considered to be effective materials in EMI shielding sector but its heavy weight, corrosion susceptibility and cumbersome processing methods confine their suitability for both users and researchers.^29,30 Polymer composite material with conductive inclusions like graphene have been identified as attractive and potential replacement of orthodox metal based alloys due to their tailor made properties, light weight, structural flexibility, resistant to corrosion and ease of processing advantages.³¹

The main aim of the current study is to develop mechanically strong, anticorrosive and EMI shielding composite material using epoxy as matrix and graphene (conducting) and TiO₂ (dielectric) as fillers. In order to ensure the use of this composite material under conditions of periodic stress, the dynamic mechanical properties were also studied.

2. Experimental

2.1 Materials

The raw materials, epoxy resin (Cam Coat 2051) and hardener (HY591) were obtained from Chemical Advanced Material Pvt Limited, India. The raw materials TiO₂ nanoparticles (average size 30 nm and density of 4 g cm⁻³) and graphene (purity 99.9%) were obtained from M/s Nanoshel LLC, USA. The FESEM image of used graphene and TiO₂ nanoparticles are shown in Fig. 1.

Fig. 1 FESEM images of used (a) graphene (b) TiO₂ nanoparticles.

2.2 Preparation of graphene/TiO₂–epoxy nanocomposite

Graphene/TiO₂–epoxy nanocomposite with composition 0.25 wt% of graphene and 0.25 wt% of TiO₂ in epoxy resin was prepared using ultrasonication for 30 min (Fig. 2). For ultrasonication, the Vibracell ultrasonic processor of maximum output power of 750 W with a constant frequency of 20 kHz and 13 mm diameter titanium alloy (Ti-6Al-4V) tip was used. During ultrasonication, 60% amplitude was applied with pulse (10 s on and 15 s off). After ultrasonication, the hardener (10 wt%) was homogeneously mixed by impeller to initiate the curing process. The mixture was degassed for 30 min under high vacuum to remove the air bubbles. Afterwards, the obtained graphene/TiO₂–epoxy nanocomposite was poured into silicon rubber mold to prepare tensile and dynamic mechanical analysis (DMA) specimen and placed in the oven for 12 h at 50 °C for curing. TiO₂ as well as graphene content (0.5 wt%) were also reinforced in the epoxy matrix to prepare nanocomposites followed by the same procedure.

Fig. 2 Schematic representation of preparation of graphene/TiO₂–epoxy nanocomposite.

2.3 Preparation of IF steel surface of corrosion studies

Before curing, 10 g of graphene/TiO₂–epoxy nanocomposite thoroughly mixed with 30 ml of acetone to make the suspension. IF steel sheet of 5 cm² surface area was cleaned and coated with this suspension by spray coating machine. After coating, the IF steel sheet was placed in hot air oven at 50 °C to evaporate the solvent and to complete the curing for 12 h. The thickness of the coated film was found to be 28 ± 1 μm (Fig. 3). Same process was followed for the preparation of coated surface of IF steel with other compositions of epoxy. The coated IF steel sheet was used as working electrode in corrosion studies.

Fig. 3 Cross section view of thickness of coating on IF steel after cutting by diamond cutter.

2.4 Characterization techniques

Dynamic mechanical analysis (DMA) was performed on DMA 8000 Perkin-Elmer by single cantilever bending mode from room temperature to 110 °C at heating rate of 2 °C min⁻¹. The dimensions of DMA specimens were 9.2 mm × 7.5 mm × 2.5 mm (L × W × T). The dispersion state of graphene and TiO₂ in the epoxy was investigated by field emission scanning electron microscope (FESEM-Ziess) on gold coated surface at an acceleration voltage of 15 kV. After sonication process a small drop of mixture with dispersed fillers (graphene and graphene/TiO₂) was poured over a carbon coated copper grid of 200 mess size and examined the influence of TiO₂ nanoparticles on exfoliation and dispersion of graphene by transmission electron microscopy (TEM-FEI Technai G2-20-S-Twin microscope) before curing at an accelerating voltage of 200 kV. The corrosion protection of nanocomposites for IF steel was studied by using Gamry Interface 1000 potentiostat with coated IF steel as working electrode. In this corrosion analysis exposed surface area of samples to the corrosive medium (3.5 wt% NaCl electrolyte) was 0.785 cm². The corrosion protection studies include the measurement of corrosion potential (E_corr), and corrosion current (I_corr). The room temperature EMI shielding properties were measured by recording the scattering parameters on an Agilent E8364B vector network analyzer in the frequency range of 12.4–18 GHz (Ku band). In this study samples were precisely cut into rectangular shapes of dimensions 15.8 mm (L) × 7.9 mm (W) × 2.0 mm (T).

3. Result and discussion

3.1 Corrosion properties of coating nanocomposites

The Tafel plot was obtained for pure IF steel and IF steel with different coating materials from potential range −0.250 to +0.250 V relative to open circuit potential (E_ocp). Tafel plots of different coated samples are shown in Fig. 4. The IF steel coated with graphene/TiO₂–epoxy nanocomposite exhibits more positive corrosion potential in comparison with non-coated IF steel as well as coated with other composition. Graphene/TiO₂–epoxy nanocomposite coated IF steel have lower current density than the other coated specimens. This change in Tafel curves gives clear evidence about how different compositions of nanocomposites affect the anti-corrosion performance of coating. Graphene in combination with nanosize TiO₂ particles in epoxy matrix have relatively good anti-corrosion effect.

Fig. 4 Tafel plots of IF steel, neat epoxy and nanocomposites.

The corrosion of steel involves several oxidation and reduction steps³²

Fe → Fe²⁺ + 2e⁻

Fe²⁺ → Fe³⁺ + 1e⁻

O₂(g) + 2H₂O + 4e⁻ → 4OH⁻

2Fe²⁺(aq) + O₂(g) + 2H₂O → 2FeOOH + 2H⁺

Therefore, sufficient H₂O and O₂ are required for the corrosion of steel and any route is able to prevent the approach of H₂O and O₂ from steel surface, leading effectively good anti-corrosion behavior. In this corrosion study, the corrosion current (I_corr) was determined from Tafel plot by extrapolating a straight line along the linear portion of the Tafel curve to corrosion potential (E_corr). However for more understanding of corrosion behavior, the corrosion rate and corrosion protection efficiency (P.E.) were also calculated. For the corrosion rate the following expression was used.^33,34

where R_corr is corrosion rate in milli-inches per year (MPY), K is constant (1.288 × 10⁻⁵), E_W is equivalent weight of sample, d is density of sample and A is surface area of the sample. The corrosion protection efficiency (P.E.) was calculated by formula³⁵
where, I^o_corr (μA cm⁻²) is the corrosion current of IF steel, I^c_corr (μA cm⁻²) is the corrosion current of IF steel coated with nanocomposites. All the experimental measurements of corrosion study are mention in Table 1.

Table 1 The values of E_corr, I_corr, P.E. (%) and R_corr of uncoated as well as nanocomposites coated IF steel

Material coated on IF steel	Ecorr (mV)	Icorr (cm^−2)	P.E. (%)	Rcorr (MPY)
IF steel (uncoated)	−648	296 μA	—	15.79
Neat epoxy	−559	3.67 μA	94.36	1.95
TiO2 (0.5 wt%)–epoxy	−500	853 nA	99.71	449.5 × 10^−3
Graphene (0.5 wt%)–epoxy	−480	235 nA	99.92	125 × 10^−3
Graphene (0.25 wt%)–TiO2 (0.25 wt%)–epoxy	−360	105 nA	99.94	55 × 10^−3

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From Table 1, it is clear that the corrosion rate decreases and protection efficiency increases with reinforcement of 0.5 wt% of TiO₂ nanoparticles in epoxy. This improvement in corrosion behavior arises due to homogeneous dispersion of TiO₂ nanoparticles in the epoxy matrix (Fig. 10(c)). Similar improvement in corrosion behavior was also obtained by incorporating nanosilica³⁶ and zeolites.³⁷ The graphene 0.50 wt% reinforced epoxy nanocomposite exhibits more improved corrosion properties than TiO₂–epoxy nanocomposite because the aspect ratio of graphene is higher than TiO₂ nanoparticles³⁸ although exfoliation and dispersion of graphene are not so better (Fig. 10(d) and (f)). The corrosion rate of IF steel coated with graphene/TiO₂–epoxy nanocomposite exhibited 54% drop and protection efficiency improved by 56% in comparison of IF steel coated with neat epoxy. This superior behavior of graphene/TiO₂–epoxy nanocomposite may arise due to high aspect ratio of graphene and exfoliated dispersion of graphene assisted by the presence of TiO₂ nanoparticles in the epoxy matrix (Fig. 10(g) and (i)) which hindered and extended the diffusion path of oxygen and water molecules in the epoxy matrix. This delay of oxygen molecules for cathodic site decreases the rate of corrosion and provides protection from corrosion reaction on surface of IF steel. Fig. 5 explain a proposed mechanism for corrosion protection of neat epoxy (Fig. 5(a)), TiO₂–epoxy nanocomposite (Fig. 5(b)), graphene–epoxy nanocomposite (Fig. 5(c)) and graphene/TiO₂–epoxy nanocomposite (Fig. 5(d)) on IF steel surface, where coated materials inhibit IF steel oxidation by decreasing cathodic process of O₂ and H₂O.

Fig. 5 Proposed path of O₂ and H₂O molecules for corrosion protection in (a) neat epoxy, (b) TiO₂–epoxy, (c) graphene–epoxy and (d) graphene/TiO₂–epoxy nanocomposites.

3.2 EMI shielding performance

Total electromagnetic shielding effectiveness (SE_T) can be defined as the ability of a material to attenuate incident electromagnetic radiation and is given by following equation^39,40
where, P_t and P_i stands for power of transmitted and incident electromagnetic radiations respectively. As always P_t < P_i, so shielding effectiveness is a negative quantity. Electromagnetic shielding can be achieved by minimizing the propagation of electromagnetic waves either by reflection of the incident wave from surface of shield, by absorption and by dissipation of the radiations within the material i.e. multiple internal reflections. Therefore total shielding effectiveness (SE_T) can be determined by summation of shielding effectiveness due to reflection (SE_R), shielding effectiveness due to absorption (SE_A) and multiple internal reflections (SE_M) i.e. SE_T (dB) = SE_R + SE_A + SE_M. Basically shielding effectiveness due multiple reflection is ignored in case of thick samples and it is assumed that SE_T ≈ SE_R + SE_A.⁴¹ Fig. 6 shows schematic representation for EMI shielding mechanism.

Fig. 6 Schematic representation of EMI shielding mechanism.

Reflection is related to the presence of mobile charge carriers (holes or electrons) present on the shield and is given by equation⁴²

SE_R = 10 log(1 − R)

Absorption of electromagnetic radiation occurs when they interact with electric and magnetic dipoles present inside the shield. Shielding effectiveness due to absorption can be expressed as equation.⁴³

Using these equations total shielding effectiveness (SE_T) can be resolved into shielding effectiveness due to absorption (SE_A) and shielding effectiveness due to reflection (SE_R). The values obtained from SE_T, SE_R and SE_A were further explored to obtain attenuation (%), reflection efficiency (%) and absorption efficiency (%) respectively.

Fig. 7(a) shows that the value of total shielding effectiveness (SE_T) of hybrid nanocomposite of epoxy containing 0.25 wt% of TiO₂ and 0.25 wt% of graphene is found to be maximum i.e. ∼−11 dB (>90% attenuation) compared to −3 dB (∼50% attenuation) for neat epoxy. This dramatic increment in EMI shielding is attributed to proper dispersion of conducting filler (graphene) with in the epoxy matrix due to presence of TiO₂ nanoparticles which led to the formation of electrically conducting network. Presence of large number of charges that interact with incoming electromagnetic radiations (EMR) might be another reason for this monotonous enhancement.

Fig. 7 (a) Shielding effectiveness (dB) (b) % attenuation (c) reflection efficiency (%) (d) absorption efficiency (e) contribution of R.E. and A.E. to total attenation (%).

Resolved components of SE_T i.e. SE_R and SE_A were further analysed to calculate reflection and absorption efficiency of nanocomposites. Fig. 7(c) and (d) shows reflection efficiency (%) and absorption efficiency (%) of nanocomposites respectively. Reflection efficiency is found to be increased from 41% for neat epoxy to 75% for hybrid nanocomposite where as absorption efficiency increased to 16% for hybrid nanocomposite compared to only 6% for neat matrix. This significant enhancement in both reflection and absorption efficiency is accredited to synergistic effect of both conducting (graphene) and dielectric (TiO₂) filler. The conducting filler provides mobile charge carriers which can interact with electromagnetic radiations which is responsible for reflection and dielectric filler provides electrical dipoles which interacts with incident electromagnetic radiations and are responsible for absorption.⁴⁴

3.3 Tensile properties

Any anticorrosive shielding material should be structurally strong in desired application range therefore effect of nanofillers on mechanical properties of epoxy were also investigated. The stress–strain curves of different composition are shown in Fig. 8. These stress–strain curves are an average of five samples as per ASTM D-638 standard that are used to calculate the tensile strength and area under the curves. The area under the curve is an indication of toughness of materials (Fig. 9). When epoxy reinforced with 0.5 wt% of TiO₂ nanoparticles, there is no momentous improvement in tensile strength (Fig. 8) and area under the curve (Fig. 9). This indicates that a very low wt% of TiO₂ does not significantly enhance the tensile performance of nanocomposite.⁴⁵ Graphene with 0.5 wt% in epoxy matrix improves the tensile strength by 18% and area under the curve by 22%. The tensile strength and toughness (area under the curve) of epoxy increased maximum by 36% and 55% respectively, when reinforced with 0.25 wt% of graphene in presence of 0.25 wt% of TiO₂ nanoparticles. This may primarily happened due to exfoliation and homogeneous dispersion of graphene assisted by TiO₂ nanoparticles as shown in Fig. 10(g) and (i). The homogeneous dispersion and exfoliation of graphene considerably extend interfacial contact area which improve adhesion with host matrix and lead to enhance the mechanical properties of nanocomposite.

Fig. 8 Stress–strain curves of the neat epoxy and nanocomposites.

Fig. 9 Area under the curve (toughness) of (a) neat epoxy, (b) TiO₂–epoxy, (c) graphene–epoxy and (d) graphene/TiO₂–epoxy nanocomposites.

Fig. 10 FESEM images of tensile fracture surface of neat epoxy (a), TiO₂–epoxy nanocomposite at low (b) and high (c) magnifications (50KX), graphene–epoxy nanocomposite at low (e) and high (f) magnifications (50KX), graphene/TiO₂–epoxy nanocomposite at low (h) and high (i) magnifications (25KX), TEM image of graphene before curing of epoxy resin (d) and TEM image of graphene/TiO₂ before curing of epoxy resin (g).

3.4 FESEM and TEM analysis

As shown in Fig. 10(a), the tensile fracture surface of the neat epoxy exhibits very smooth and river patterns. In addition, the cracks propagated freely and randomly, revealing neat epoxy's nature of weak resistance to crack initiation and transmission. The neat epoxy matrix shows typical brittle fracture pattern. However, with the addition of TiO₂ nanoparticles, graphene and TiO₂ + graphene, the fracture surface exhibits more roughness as seen in Fig. 10(b), (e) and (h) respectively, and numerous circuitous, deep cracks can be identified in the fracture surface. These findings indicate that TiO₂ nanoparticles, graphene and TiO₂ + graphene have induced the deflection of propagating crack fronts and hence generated a new fracture surface.^14,46 The single headed white arrows indicate the direction of crack propagation. Generally, more fracture energy is dissipated if roughness of fracture surface is higher.⁴⁶ As shown in FESEM image Fig. 10(c) at higher magnification, when 0.50 wt% of TiO₂ loaded in the epoxy, TiO₂ particles are uniformly dispersed in the epoxy matrix upto single particle without formation of any agglomerate at applied processing condition. This homogeneous dispersion of TiO₂ nanoparticles arises due to weak inter-particle interaction.⁴⁷ TEM and FESEM studies also confirmed that in the absence of TiO₂ particles, with 0.50 wt% loading of graphene, the dispersion and exfoliation of graphene tended to worsen and some clusters of graphene stacks were formed in epoxy (Fig. 10(d) and (f)). So the used parameters of the ultrasonication are not sufficient for complete exfoliation and dispersion of graphene sheets. So the used parameters of the ultrasonication are not sufficient for complete exfoliation and dispersion of graphene sheets. When TiO₂ particles (0.25 wt%) were added to graphene (0.25 wt%)/epoxy, both dispersion and exfoliation of graphene were enhanced significantly (Fig. 10(g) and (i)). From TEM image as shown in Fig. 10(g), it is much clear that the TiO₂ nanoparticles cover the surface of graphene. This intrinsic interaction between graphene surface and TiO₂ nanoparticles generates a new hybrid structure of filler which makes weak electrostatic interactions between graphene sheets for re-agglomeration due to the less availability of the free surface area of graphene sheets. So TiO₂ nanoparticles act as spacer which suppresses the re-agglomeration of graphene. Yang et al. and Kedem et al. also reported the strong affinity of TiO₂ particles to planer hexagonal ring of carbon atoms.^48,49 One important factor that explained the interaction between TiO₂ particle and graphite-like structure is negative and positive zeta-potential.^50–54 TiO₂ assisted exfoliation and dispersion of graphene sheets may be explained by the formation of hybrid structure due to attachment of TiO₂ nanoparticles at the surface of graphene, which leads to enhancement in the properties of graphene/TiO₂–epoxy nanocomposite.

3.5 Dynamic mechanical analysis

The dynamic mechanical properties of the nano-particulate composite materials are the important properties to consider their load bearing capacity. The variation of the different types of reinforced nano-filler TiO₂, graphene (GP) and TiO₂ + GP on storage modulus of epoxy resin has been shown in Fig. 11. The enhancement in the storage modulus of epoxy is low with reinforcement of TiO₂ and GP individually but when uses the combination of TiO₂ + GP in epoxy matrix, the storage modulus increases sharply. This sharp increase in storage modulus is due to the homogeneous distribution of GP in epoxy matrix in the presence of TiO₂ nanoparticles. TiO₂ nanoparticles support exfoliation and dispersion of graphene in the epoxy matrix during ultrasonication. The values of storage modulus for neat epoxy and TiO₂ (0.25 wt%) + GP (0.25 wt%) reinforced epoxy nanocomposite are 748 MPa and 1379 MPa respectively. The storage modulus with TiO₂ (0.25 wt%) + GP (0.25 wt%) reinforced epoxy nanocomposite shows maximum of 84% enhancement as compared to neat epoxy. This enhancement in storage modulus may be due to the restriction of molecular chain mobility of epoxy in the presence of TiO₂ and graphene nano-fillers during deformations. The better interaction between nano-fillers and epoxy matrix restricts molecular chain mobility in epoxy resin. The value of storage modulus of neat as well as nano-filler reinforced epoxy nanocomposite decreases with increase in temperature and when the temperature range goes near to glass transition temperature storage modulus decreases sharply as shown in [Fig. 11]. The decrement in storage modulus near glass transition temperature is ascribed to the enhanced molecular chain mobility.

Fig. 11 Storage modulus of TiO₂, graphene (GP) and TiO₂ + GP reinforced epoxy nanocomposite.

The damping properties of a composite material is defined as the ratio of loss modulus to the storage modulus and called as mechanical loss factor or tan δ (Fig. 12). The reinforcement of nano-fillers in epoxy matrix can affect the damping property of the epoxy matrix. Below glass transition temperature damping goes high because the molecular chain mobility in this region are in restricted state and above glass transition temperature or in rubbery state the damping goes down because molecular chain mobility are relatively high and there is no restriction to flow. The height and position of tan δ peak indicate the thermal stability and glass transition temperature respectively. Decrease in height of tan δ is clear indication of enhanced thermal stability of nanocomposites. TiO₂ (0.25 wt%) + GP (0.25 wt%) reinforced epoxy nanocomposite shows lowest peak height as shown in Fig. 12, which proves that the graphene/TiO₂–epoxy nanocomposite is more stable than others. Shifting of the tan δ peak towards right side shows that the nanocomposites have higher glass transition temperature than neat epoxy resin. TiO₂ + GP reinforced epoxy nanocomposite shows highest improvement in glass transition temperature i.e. 91 °C compared to neat epoxy i.e. 83 °C. This is due to the restriction of molecular chain mobility in epoxy matrix by better interfacial bonding between nano-filler and epoxy chains.

Fig. 12 tan δ values of TiO₂, graphene (GP) and TiO₂ + GP reinforced epoxy nanocomposite.

4. Conclusions

The graphene, TiO₂ and combined graphene/TiO₂ fillers were successfully incorporated in epoxy matrix using ultrasonic mixing process. The exfoliation and dispersion of graphene were enhanced significantly by the presence of TiO₂ nanoparticles during fabrication of nanocomposite. The experimental results demonstrate that the anti-corrosion performance, mechanical properties and EMI shielding performance of graphene reinforced nanocomposite greatly depend on the degree of exfoliation and dispersion of graphene. The characteristics of dispersion state of the graphene/TiO₂ in epoxy matrix were confirmed by FESEM and TEM studies on the composite materials. Graphene/TiO₂–epoxy nanocomposite exhibits superior anti-corrosion and EMI shielding performance in comparison to epoxy reinforced with graphene due to generation of a new hybrid filler structure between graphene and TiO₂ nanoparticles. The low wt% of TiO₂ nanoparticles in epoxy matrix was not capable to improve significantly the mechanical and anti-corrosion properties.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c6ra15273b

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