CHEMICAL ROUTES TO MATERIALS Experimental and computational investigation of reduced graphene oxide nanoplatelets stabilized in poly(styrene sulfonate) sodium salt Celina M. Miyazaki1,2 , Marco A. E. Maria1,3,4 , Daiane Damasceno Borges4 , Cristiano F. Woellner4 , Gustavo Brunetto4 , Alexandre F. Fonseca4 , Carlos J. L. Constantino5 , Marcelo A. Pereira-da-Silva6,7 , Abner de Siervo4 , Douglas S. Galvao4 , and Antonio Riul Jr.4,* 1POSMAT – Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, UNESP – Univ Estadual Paulista, Bauru, SP, Brazil 2Universidade Federal de São Carlos – DFQM, Sorocaba, SP, Brazil 3Faculdade de Engenharia de Sorocaba – FACENS, Sorocaba, SP, Brazil 4Applied Physics Department, State University of Campinas, Campinas, SP 13083-970, Brazil 5UNESP – Univ Estadual Paulista, Presidente Prudente, SP, Brazil 6Centro Universitário Central Paulista – UNICEP, São Carlos, SP, Brazil 7 Instituto de Física de São Carlos – USP, São Carlos, SP, Brazil Received: 31 January 2018 Accepted: 12 April 2018 Published online: 19 April 2018 � Springer Science+Business Media, LLC, part of Springer Nature 2018 ABSTRACT The production of large-area interfaces and the use of scalable methods to build up designed nanostructures generating advanced functional properties are of high interest for many materials science applications. Nevertheless, large-area coverage remains a major problem even for pristine graphene, and here we present a hybrid, composite graphene-like material soluble in water that can be exploited in many areas such as energy storage, electrodes fabrication, selective membranes and biosensing. Graphene oxide (GO) was produced by the traditional Hummers’ method being further reduced in the presence of poly(styrene sulfonate) sodium salt (PSS), thus creating stable reduced graphene oxide (rGO) nanoplatelets wrapped by PSS (GPSS). Molecular dynamics simulations were carried out to further clarify the interactions between PSS molecules and rGO nanoplatelets, with calculations supported by Fourier transform infrared spectroscopy analysis. The intermolecular forces between rGO nanoplatelets and PSS lead to the formation of a hybrid material (GPSS) stabilized by van der Waals forces, allowing the fabrication of high-quality layer-by-layer (LbL) films with poly(allylamine hydrochloride) (PAH). Raman and electrical characterizations corroborated the successful modifications in the elec- tronic structures from GO to GPSS after the chemical treatment, resulting in (PAH/ GPSS) LbL films four orders of magnitude more conductive than (PAH/GO). Address correspondence to E-mail: riul@ifi.unicamp.br https://doi.org/10.1007/s10853-018-2325-1 J Mater Sci (2018) 53:10049–10058 Chemical routes to materials http://orcid.org/0000-0003-2583-3001 http://orcid.org/0000-0002-0986-4708 http://orcid.org/0000-0001-6572-5406 http://orcid.org/0000-0002-0022-1319 http://orcid.org/0000-0002-7260-7907 http://orcid.org/0000-0001-8413-9744 http://orcid.org/0000-0002-5921-3161 http://orcid.org/0000-0002-7197-4262 http://orcid.org/0000-0002-7192-4740 http://orcid.org/0000-0003-0145-8358 http://orcid.org/0000-0002-9760-1851 http://crossmark.crossref.org/dialog/?doi=10.1007/s10853-018-2325-1&domain=pdf http://crossmark.crossref.org/dialog/?doi=10.1007/s10853-018-2325-1&domain=pdf https://doi.org/10.1007/s10853-018-2325-1 Introduction Graphene is a milestone in carbon-based and 2D soft materials due to its unique mechanical, thermal, electrical and optical properties, which led to a myriad of experimental and theoretical studies and applications in energy [1–3], sensing [4], devices [5, 6] and the production of hybrid materials featuring new properties [7]. It is a one-atom thick sheet made of sp2 carbons arranged in a honeycomb lattice that was first obtained by mechanical exfoliation of pyrolytic graphite [8]. Even considering recent advances in chemical synthesis methods [9], the production of high-quality large-area graphene is still challenging. Chemical synthesis is an alternative approach enabling a moderate fabrication of graphene-based materials under mild conditions, with added benefits of functionalization that allows the formation of hybrids or composites with polymers, nanoparticles, DNA, etc. [10]. Usually, the chemical process begins with graphite exfoliation by the Hummers’ method [11], generating graphene oxide (GO), an insulating material with functional oxygen groups on the basal planes and at the edges of the formed nanoplatelets. The oxidation process makes GO easily dissolved in water, and it can be further processed to reduced graphene oxide (rGO), which is a more conductive material resembling the graphene properties. The highest observed conductivity in rGO is explained by the partial reestablishment of the carbon sp2 network after the chemical reduction process [12, 13], and despite being less conductive than pristine graphene, rGO is an attractive material for interfacial applica- tions [14]. The use of graphene-based materials usually requires the deposition on a solid substrate such as silicon, quartz or glass. Within this context, the layer- by-layer (LbL) technique is an alternative and ver- satile way to promote graphene-functionalized sur- faces as it allows for well-defined molecular-level control over thickness, morphology and structure, designing advanced functional nanostructures in a diverse range of applications onto practically any surface [15]. LbL films of graphene derivatives have been widely used in energy [16, 17], selective mem- branes [18, 19], sensing and biosensing [4, 20, 21] applications. There is a plethora of studies with LbL films of graphene-based materials, such as composites with polymers used in electromagnetic interference shielding at GHz range [22]. Lee and co-workers [23] achieved transparent, conducting LbL films using chemically modified rGO with controlled thickness, and different three-dimensional GO structures could be formed throughout a new diffusion-driven layer- by-layer assembly process [24]. Multi-walled carbon nanotubes and rGO composites were employed in point-of-care and clinical screening of multiple dis- eases [25], and the assembly of carbon nanomaterials with conducting polymers was used to build up 3D nanoarchitectures for energy storage and sensing applications [26]. Since the LbL assembly is based on the spontaneous adsorption of material from aqueous suspensions [15, 27, 28], it is of great importance the development, synthesis and characterization of water-soluble graphene-based materials that can be further studied in distinct applications. In this work, we present the chemical synthesis and characterization of rGO nanoplatelets functionalized with sodium polystyrene sulfonate (PSS), a water- soluble material called here as GPSS. Molecular dynamics (MD) simulations were carried out to pro- vide further insights into the self-organization of GPSS structure. It forms stable suspensions in water for * 10 weeks, and it is attractive for LbL assem- blies, expanding the possibility of applications in energy conversion, barrier properties, sensing and biosensing by the fact that pristine rGO is poorly dispersed in several known solvents. Fourier trans- form infrared spectroscopy (FTIR) analysis helped to identify the role played by van der Waals interactions between PSS and rGO nanoplatelets in the formed GPSS nanostructure. Poly(allylamine hydrochloride) (PAH) was used as a positively charged polyelec- trolyte to build up both (PAH/GO) and (PAH/GPSS) LbL nanostructures with controlled thickness and morphology. Measurements taken by atomic force microscope (AFM) indicated the presence of larger GO nanoplatelets when compared to GPSS, and impedance characterization shows that the (PAH/ GPSS) film is four orders of magnitude more con- ductive than (PAH/GO), thus confirming the efficacy of the reduction process in the GPSS formation. 10050 J Mater Sci (2018) 53:10049–10058 Materials and methods Materials Graphite powder (98%), H2SO4 (95%), KMnO4(99%), K2S2O3 (99%), P2O5, H2O2, H6N2O4S were of analyt- ical grade and used in the synthesis processes. Poly(styrene sulfonate) sodium salt—PSS (Mw = * 70000), and poly(allylamine hydrochloride)—PAH (Mw * 15000), were purchased from Sigma-Aldrich and used as received. Ultrapure water (18.2 MX cm) acquired from a Millipore Direct Q5 system (at 25 �C) was used in all experiments. GO and GPSS nanoplatelets synthesis A pre-oxidation process of graphite was performed in accordance with Kovtyukhova et al. [29] in which graphite (10 g) was immersed in a mixture of con- centrated H2SO4 (15 mL), K2S2O8 (5 g) and P2O5 (5 g) at 80 �C, reacting for 6 h at room temperature. Water was carefully added to dilution, and the solid was washed till neutral pH. Sequentially, the Hummers’ method [11, 29] was applied by adding 10 g of pre- oxidized graphite into concentrated H2SO4 (230 mL) (cold bath at 0 �C). 30 g KMnO4 was added slowly with constant stirring with extreme caution as the temperature should not exceed 20 �C. The mixture was stirred for 2 h at 35 �C. Water (460 mL) was added and allowed to react for 15 min, and then, 1.4 L of water and 30% H2O2 (25 mL) were added to stop the reaction. The resulting yellow product was fil- tered, washed with 1:10 HCl solution and dried in vacuum oven at room temperature to produce GO. For the GPSS synthesis, PSS and GO were added according to Stankovich et al. [30]. Briefly, 50 mL of GO suspension (1 g L-1) was prepared in ultrasonic bath for 30 min and mixed with 500 mg of PSS. The mixture was kept under vigorous stirring, and hydrazine sulfate was added to a final concentration of 0.01 mol L-1. The final product (GPSS) was stirred and maintained at 90 �C for 12 h, being further washed with ultrapure water and dried at 90 �C in vacuum oven. GPSS was characterized with UV–Vis absorption spectroscopy using a Thermo Scientific Genesys 6 equipment, while Raman spectroscopy was performed with a micro-Raman Renishaw, model in-Via, laser at 633 nm. FTIR spectroscopy was acquired in a Thermo Nicolet, model Nexus 470. The chemical composition of the samples was analyzed by X-ray photoelectron spectroscopy (XPS) in a homemade setup using a vacuum chamber (10 mbar) and Mg Ka radiation (1253.6 eV) with 240 W. Shirley background was assumed to the XPS spectra fitting. Electrical measurements were acquired in a home- made four-probe setup in accordance with Ref [31], using drop-cast films of GO and GPSS deposited on quartz substrates, with film thickness measured by a Veeco Dektak 150 surface profilometer. Molecular Dynamics Simulations Molecular dynamics (MD) simulations were carried out to study the rGO nanoplatelets wrapped by PSS and water molecules. The preparation of the initial configuration of the system consisted in randomly placing PSS and water molecules around one single rGO nanoplatelet. PSS was built with 16 monomers of sulfonated styrene group (see Fig. 1). Every sulfonate group is treated as fully ionized, and Na? was added to neutralize the system. The water content is 5 water molecules per sulfonate groups. The rGO sheet has dimensions of * 40 9 40 Å (* 1600 Å2 in area), with the atomic concentration of the functional group Fig. 1 In the left side, it shows the simulation system components and, in the right, a snapshot of the thermalized GPSS structure. The PSS backbone and aromatic rings united atoms are repre- sented by black and cyan colors, while the terminated SO3 - atoms are in yellow and red colors. The rGO nanoplatelet is in brown color, and the water is represented in a continuum transparent surface. The thermalized structure clearly shows PSS being in stretched conformation with the sulfonated styrene groups ‘‘lying’’ on rGO. J Mater Sci (2018) 53:10049–10058 10051 been 2% hydroxyl, 2% epoxy, 1% carboxyl and 1% carbonyl. The functional group percentages are based on the XPS data discussed along this manuscript. The hydroxyl and epoxy groups are situated away from the edges, while carboxyl and carbonyl groups are on the boundaries of the nanoplatelets [32, 33], as shown in Fig. 1. Once the initial configuration was set, the system was equilibrated after a series of annealing and optimization runs using Berendsen thermostat and barostat [34]. After equilibration at ambient temperature and pressure (i.e., T = 300 K and P = 1 atm), canonical trajectories of 2 ns using Nosé– Hoover integrator scheme [35, 36] were generated for analysis. The pair-atom interactions were described within the classical formalism. Water molecules were described by rigid 3-sites Transferable Intermolecular Potential (TIP-3P) [37] model. To simulate the rGO nanoplatelets, all atoms were considered explicitly in the simulations (all-atom approach), whereas a mixed representation was used to describe the PSS mole- cule. The united atom model was used to describe the backbone chain, while all atomistic representation was applied to describe benzene ring and sulfonate groups. The force field parameters including bonded and non-bonded interactions for the PSS were extracted from Ref. [38], while for the rGO were extracted from Ref. [39]. The initial configuration was built using Packmol [40], and the MD simulations were carried out using LAMMPS [41]. LbL films assembly and characterization LbL films were fabricated using PAH as positive polyelectrolyte (1 mg mL-1) for both GO and GPSS, which were used as negatively charged suspensions (0.1 mg mL-1), thus forming (PAH/GO)n and (PAH/ GPSS)n multilayers, being n the number of deposited bilayers. All solutions were adjusted to pH 3.5, including those for washing. The immersion time was equal to 3 min for PAH and 5 min for GO and GPSS solutions. The LbL film fabrication was made using an automated dipper from a Langmuir trough (NIMA Technology, model 612D), with upward and downward rates of 60 and 10 mm min-1, respectively. LbL films were characterized using UV–Vis spec- troscopy (Thermo Scientific Genesys 6), AFM (Bruker Dimension ICON Nanoscope-V) at intermittent con- tact mode with a silicon cantilever (40 N/m, 330 kHz), and impedance measurements (Solartron impedance analyzer 1260A, coupled to a 1296 Dielectric Interface) were acquired from 1 MHz to 1 Hz, using 20 mV amplitude. (PAH/GO)5 and (PAH/GPSS)5 LbL films were deposited onto gold interdigitated electrodes (IDEs) having 30 pairs of digits, 3 mm long, 40 lm width and separated 40 lm each other. The IDEs were fabricated at the Brazilian Nanotechnology National Laboratory (LNNano/ CNPEM—Campinas, Brazil). Results and discussion GO and GPSS aqueous dispersions were character- ized by UV–Vis absorption spectroscopy (Figure S1), displaying bands at 229 and 282 nm, characteristic of p–p* transition of aromatic C–C bond, and n–p* transition of C=O bond, respectively [42, 43]. GPSS solution presents a band at 268 nm due to p–p* transition (shifted to higher wavelength), suggesting that the electronic sp2 conjugation was restored [42], and a band at 227 nm due to the PSS benzene group absorption [44]. The dispersions were stable for * 10 weeks, demonstrating that rGO is effectively dispersed in water with the presence of PSS. Figure 2 presents the Raman spectra of powder samples from graphite, GO, pristine rGO and GPSS. The G-band at * 1590 cm-1 from the E2g degenerate mode zone vibration [45] of the sp2 carbon network, and the D-band at * 1330 cm-1 attributed to defects 1000 1200 1400 1600 1800 2000 Graphite GO RGO GPSS Wavenumber (cm-1) Fig. 2 Raman spectra of graphite, GO, rGO and GPSS powder samples. 10052 J Mater Sci (2018) 53:10049–10058 in the sp2 carbon lattice were investigated [46, 47]. D and G peak positions were only slightly shifted to higher wavenumbers (see Table 1) comparing pris- tine rGO with GPSS, suggesting that PSS is not chemically bonded to rGO sheet, consequently not affecting the sp2 network domains. The ID/IG ratio increased after the GO reduction to form both rGO and GPSS, suggesting a decreased average size of the sp2 carbon domains [48, 49], which means that new sp2 domains were created, however, smaller in size and more numerous than those present in GO. The atomic ratio of C and O was obtained from XPS survey spectra (Figure S2) indicating a successful reduction process by the decrease in O/C ratio from 51.4 to 7% [13]. Figure 3 shows the high-resolution C1s XPS analysis of GO and GPSS, with C=C bonds increasing from 48.7 to 74.3% after the chemical reduction. The GO spectrum indicates high degree of oxidation with three main components: C–C from non-oxygenated ring (284.5 eV), C in C–O bonds (286.6 eV) and C in C=O from carbonyl groups (288.5 eV). The GPSS spectrum indicated a marked decrease in the oxygenated groups and an additional peak at * 285 eV related to C–S from PSS [50]. Table 2 presents the relative percentage of each functional group, which is an important data for the computational analysis. FTIR analysis (Figure S3) indicated typical GO bands at 1626 cm-1 (C=C stretching), and the pres- ence of oxy-groups at 1739 cm-1 (C=O stretching), 1057 cm-1 (C–O stretching), 1405 cm-1 (C=OH stretching) and 1225 cm-1 (epoxy group) [51], with a broad absorption band at * 3400 cm-1 (C–OH stretching) [52]. After the reduction process with hydrazine and PSS, the oxy-group bands disap- peared, while a comparison between PSS with GPSS spectra shows a shift in the benzene ring vibration in PSS from 1128 to 1132 cm-1, indicative of physical interactions between PSS and the rGO, hampering the vibrations of the PSS chains. The observed shift in the FTIR spectra can be related to a strong interaction between PSS molecules and rGO nanoplatelets. In order to better understand the GPSS structure, classical MD simulations were performed. Figure 1 shows a typical snapshot of the self-organized system containing PSS, water and rGO well thermalized at ambient temperature and pressure. The typical mass density is approximately 1.4 g/cm3, which is higher than 0.8 g/cm3 PSS in bulk. Figure 4a shows the radial distribution function between oxygen atoms of the sulfonate groups and hydrogen of OH and COOH functional groups. The simulations reveal that the PSS interacts with rGO mainly through the hydroxyl and carboxyl groups forming H-bonds (see Fig. 4). Moreover, the water molecules intermediate this interaction also via H-bonds as shown in RDF of water–functional group water–SO3 presented in Fig. 4b. The PSS is found in stretched conformation with the sulfonated styrene groups ‘‘lying’’ on rGO (see Fig. 1). This conformation maximizes the SO3 -– OH interactions and minimizes the electrostatic repulsion among sulfonate neighbors. This Table 1 Raman spectroscopy data for graphite, GO, rGO and GPSS powder samples D peak position G peak position ID/IG a Graphite 1335 1582 0.27 ± 0.01 GO 1336 1596 0.96 ± 0.02 rGO 1325 1596 1.34 ± 0.05 GPSS 1331 1599 1.41 ± 0.11 aID/IG calculated as average of 5 measurements 0 200 400 600 800 C=O (288,5 eV) C-C (284,5 eV) Mg Kα In te ns ity (C PS ) Binding Energy (eV) satélites C-O (286,6 eV) 290 285 280 275 295 290 285 280 0 500 1000 1500 2000 2500 C=O (286,0 eV) C-O (286,0 eV) C-N (286,8 eV) C-S (285,2 eV) Mg Kα In te ns ity (C PS ) Binding Energy (eV) C-C (284,5 eV) C 1s GPSS C 1s GO Fig. 3 XPS spectra for GO and GPSS in the region of C1s. J Mater Sci (2018) 53:10049–10058 10053 interaction should be strong enough to trap the styrene groups and, thus, hamper the vibration of PSS chain as suggested by FTIR analysis. These results are in good agreement with Raman studies [53], indicating that there is a trend to PSS accom- modation close to rGO nanoplatelet without chemical interaction. DC measurements acquired from the four-probe technique (see Figure S6) indicated conductivity values of 2.0 9 10-2 S cm-1 for GO and 6.3 9 102 S cm-1 for GPSS, similar to values in the literature [42, 54] and lower than those found for printed pristine graphene (* 2.5 9 104 S cm-1) [55]. This difference can be explained by defects and residual oxygen containing groups remaining in the rGO nanoplatelets from the chemical reduction pro- cess [14], remarkably impacting the electrical prop- erties of GPSS when compared to pristine graphene. Nevertheless, our results corroborate the information of better electronic properties for GPSS when com- pared to GO [56] due to a better reestablishment of the sp2 carbon network in the formed rGO nanopla- telets, which is not disturbed owing to the non-co- valent interactions between PSS molecules, in close agreement with the MD simulation, Raman and FTIR analysis. After characterization of GPSS and GO, PAH polyelectrolyte was used to build up both (PAH/GO) and (PAH/GPSS) LbL nanostructures. LbL film growth was investigated using UV–Vis absorption spectroscopy, as shown in Fig. 5. It was initially determined the best immersion time in each poly- electrolyte (results not shown), with both LbL archi- tectures (PAH/GO)n and (PAH/GPSS)n displaying a linear rise in absorbance with increasing n, suggest- ing that the same amount of material was adsorbed at each deposition step in the LbL film formation. Figure S4 shows the AFM analysis for the LbL films. (PAH/GO)5 presented platelets with lateral dimensions ranging from 10 to 30 lm, while it was observed smaller platelets with lateral dimensions ranging from 1 to 5 lm in the (PAH/GPSS)5 film, as already predicted by ID/IG ratio in Raman spec- troscopy. The height profile (Figure S4a) displays a large fragment of a wrinkled GO platelet in the film surface (* 50 nm), where apparently all the back- ground surface is covered with thin GO layers, with Table 2 Relative percentage of functional groups to GO and GPSS samples Sample Functional group % Sample Functional group %a GO C=C (sp2 network) 48.7 GPSS C=C (sp2 network) 74.3 C-O 44.9 C-S 11.8 C=O 6.5 C-O 5.2 O-C=O 1.3 C=O 1.2 aGPSS spectrum presented 2.8% signal from C in impurities and 3.4% from p–p* satellite Fig. 4 Radial pair distribution function, g(r), of oxygen atoms in the PSS molecule (a) and hydrogen atoms in carboxylic groups (b) of the rGO nanoplatelet. 10054 J Mater Sci (2018) 53:10049–10058 smaller platelets for GPSS (* 10 nm height) (see Fig. S4b). LbL film thickness analysis was performed scratching both (PAH/GO)5 and (PAH/GPSS)5 films (topography images and height profile shown in Figure S5), indicating an average thickness of * 2 nm per deposited PAH/GO bilayer and * 4 nm per deposited PAH/GPSS bilayer, reinforcing the rGO wrapping by PSS molecules and also monolayer thickness values comparable to those reported in the literature [57]. The electronic properties of the films were investigated by impedance measurements taken from 1 Hz to 1 MHz (Fig. 6). Figure 6a shows the impedance modulus analysis with (PAH/GO)5 film presenting a dielectric material profile as expected, with higher impedance in the low-frequency region ([ 108 X) followed by a capacitive behavior[ 100 Hz (see phase angle analysis in Fig. 6b). (PAH/GPSS)5 LbL film displayed a more conductive behavior with impedance values * four times lower than those presented by (PAH/GO)5. An increase in the film conductivity is expected with the restorage of the sp2 network after the chemical reduction process; however, one must have in mind the formation of defective rGO nanoplatelets wrapped by PSS (insulating material) molecules. GPSS was also alternately deposited with a non- conductive material (PAH) to form multilayered (PAH/GPSS) nanostructures; therefore, a 7000-fold decrease in the overall resistance, from * 300 MX of (PAH/GO)5 to 39 kX of (PAH/GPSS)5, respectively, was observed. In a seminal paper, Kotov et al. [58] demonstrated the assembly of (polyelectrolytes/GO) films followed by an in-situ chemical reduction, immersing the LbL (polyelectrolytes/GO) films into aqueous hydrazine solution. They observed a 2700-fold decrease in the overall resistance, changing from 32 MX to 12 kX after the chemical treatment. Rani et al. [50] fabricated multilayered films using cationic and anionic graphene-based polyelectrolytes that presented 5000 MX resistance with six deposited bilayers, which was further dropped to 30 kX after 2-h annealing at 250 �C under a nitrogen atmosphere. Kim and Min [59] observed a decrease in the sheet 200 400 600 800 1000 0.0 0.1 0.2 0.3 0.4 A bs or ba nc e Wavelength (nm) 268 nm 200 400 600 800 1000 0.0 0.1 0.2 0.3 0.4 A bs or ba nc e Wavelength (nm) 229 nm 282 nm 0 2 4 6 8 10 0.0 0.1 0.2 0.3 0.4 0.5 Ab s ( λ 22 9 nm ) Bilayers deposited 0 2 4 6 8 100.0 0.1 0.2 0.3 A bs (λ 26 8n m ) Bilayers Deposited (a) (b) Fig. 5 UV–Vis absorption spectra of the LbL films growth onto quartz plates: a (PAH/GO)10; b (PAH/GPSS)10. 100 101 102 103 104 105 106103 104 105 106 107 108 (PAH/GO) 5 film (PAH/GPSS)5 filmIm pe da nc e M ag ni tu de ( Ω ) Frequency (Hz) 100 101 102 103 104 105 106 -120 -100 -80 -60 -40 -20 0 20 40 (PAH/GO) 5 film (PAH/GPSS)5 film P ha se (d eg re es ) Frequency (Hz) (a) (b) Fig. 6 a Impedance modulus and b phase angle spectra of (PAH/ GO)5 and (PAH/GPSS)5 LbL films. J Mater Sci (2018) 53:10049–10058 10055 resistance of graphene oxide layers with the adsorp- tion of multi-walled carbon nanotubes (MWCNTs). A graphene oxide/aminated MWNTs bilayer was self- assembled and chemically reduced by immersion into aqueous hydrazine solution, presenting a sheet resistance of * 1.0 MX/sq. The film was annealed 1 h at 500 �C under argon atmosphere, changing the sheet resistance to 100 kX/sq. In general, an addi- tional processing (in situ reduction or annealing) is necessary after the LbL film fabrication to achieve kX- order resistance. Here, that was achieved from aqueous suspensions of GPSS straightforward in the LbL assembly, which can be easily explained by the non-covalent interactions between rGO and PSS molecules, thus enabling a more conductive state to the GPSS nanoplatelets. In addition, this composite material can be easily processed without further processing to tune charge transport and carrier mobility at interfaces [60], highly keen in electronic applications. Conclusions The present work demonstrated a successful syn- thesis of GPSS nanoplatelets that easily form stable water suspensions. MD simulations elucidated the driven force involved in the GPSS formation. The presence of functional groups in the rGO favors physical interactions with the PSS molecules, thus creating a composite, hybrid material with interesting electrical properties. The atomic structure of the materials forming the GPSS structure is essentially attributed to H-bond formation between oxygen groups in PSS with hydrogen from hydroxyl and carboxyl groups in rGO. Those interactions are favored even in the presence of water, forming an interesting system to build up ordered multilayer nanostructures using the LbL assembly. (PAH/GO) and (PAH/GPSS) LbL films displayed a good linear growth, with the GO film presenting larger nano- platelets when compared to GPSS due to the chemical attack during the chemical reduction in the GPSS formation. The non-covalent interactions between PSS and rGO endow interesting electrical properties to GPSS, which is four orders of magnitude more conductive than GO. Supplementary material See supplementary material for UV–Vis, XPS survey and FTIR spectra. Also, AFM morphology images, height profile and E versus i plots. Acknowledgements Authors are grateful to FAPESP (2010/13033-6, 2012/01484-9, 2015/14703-9, 2016/00023-9, 2014/24547-1 and 2014/11410-8), INEO (CNPq) for financial support, and also Bernhard Gross Polymer Group (IFSC–USP), Ângelo L. Gobbi and Maria Helena O. Piazzetta at Laboratory of Microfabrication (LNNano/CNPEM) for the cooperation in micro- electrodes fabrication. This research also used the computing resources and assistance of the John David Rogers Computing Center (CCJDR) in the Institute of Physics ‘‘Gleb Wataghin,’’ University of Campinas. Compliance with ethical standards Conflicts of interest No conflicts of interest. 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