Continuous Langmuir-Blodgett deposition and transfer by controlled

Subscriber access provided by AUSTRALIAN NATIONAL UNIV

Interfaces: Adsorption, Reactions, Films, Forces, Measurement Techniques, Charge Transfer, Electrochemistry, Electrocatalysis, Energy Production and Storage

Continuous Langmuir-Blodgett deposition and transfer by controlled edge-to-edge assembly of floating 2D materials Luzhu Xu, Adam R. Tetreault, Hadi Hosseinzadeh Khaligh, Irene A Goldthorpe, Shawn D Wettig, and Michael A Pope Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b03173 • Publication Date (Web): 12 Dec 2018 Downloaded from http://pubs.acs.org on December 17, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Continuous Langmuir-Blodgett deposition and transfer by controlled edge-to-edge assembly of floating 2D materials Luzhu Xu,1 Adam R. Tetreault,1 Hadi H. Khaligh,2 Irene A. Goldthorpe,2 Shawn D. Wettig,3 Michael A. Pope1,* 1 Department

of Chemical Engineering, University of Waterloo, Waterloo, ON N2L 3G1,

Canada 2

Department of Electrical & Computer Engineering, University of Waterloo, Waterloo, ON N2L

3G1, Canada 3 School

of Pharmacy, University of Waterloo, Kitchener, ON N2G 1C5, Canada

KEYWORDS: Graphene oxide, Langmuir-Blodgett films, roll-to-roll, 2D materials, aggregation, air-water interface, solvent spreading. Abstract: The Langmuir-Blodgett technique is one of the most controlled methods to deposit monomolecular layers of floating or surface active materials but has lacked the ability to coat truly large area substrates. In this work, by manipulating single layer dispersions of graphene oxide (GO) and thermally exfoliated graphite oxide (TEGO) into water-immiscible spreading solvents, unlike traditional Langmuir-Blodgett deposition which requires densification achieved by compressing barriers, we demonstrate the ability to control the 2D aggregation and densification behavior of these floating materials using a barrier-free method. This is done by controlling the edge-to-edge interactions through modified sub-phase conditions and by utilizing the distance-dependent spreading pressure of the deposition solvent. These phenomena allow substrates to be coated by continuous deposition and substrate withdrawal – enabling roll-to-roll deposition and patterning of large area substrates such as flexible polyethylene terephthalate. The aggregation and solventdriven densification phenomena are examined by in situ Brewster angle video microscopy and by Xu et al.

Page 1/25 ACS Paragon Plus Environment

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

measuring the local spreading pressure induced by the spreading solvent acting on the floating materials using a Langmuir-Adam balance. As an example, the performance of films deposited in this way are assessed as passivation layers for Ag nanowire-based transparent conductors. 1. Introduction Since the 1920s, the Langmuir-Blodgett (LB) deposition technique has proven to be one of the most controlled approaches for depositing films that are only one molecular layer thick. Classically, insoluble amphiphiles were used to create these well-ordered thin films, by one or more deposition steps. Nowadays, the technique is being used increasingly to deposit a variety of nanomaterials including graphene and graphene oxide (GO) onto a wide array of substrates.1–6 These materials have attracted considerable interest due to their potential use in a broad range of applications which include flexible and/or transparent electronic devices,7–13 molecular blocking layers,14,15 and selectively permeable membranes.16–18 LB films of micron-sized GO single layers, for example, have been used to prepare transparent conductors with optical conductivities approaching those of films grown by high vacuum, high temperature vapor deposition methods (e.g., CVD), while significantly outperforming films deposited by more common solution processing techniques such as vacuum-filtration,13,19 spay-coating,20 spin coating21,22 or electrophoretic deposition23 which all result in less uniform thin films with either lower bulk density or lower transparency. While promising, the LB approach has a critical drawback which limits its commercial application. Compressed, floating films are typically about one fifth of the area of the trough which limits how much material can be deposited onto a substrate in one batch. While typical trough setups are only capable of coating substrates with areas on the order of ~cm2, recently trough designs incorporating roll-to-roll coating equipment have been demonstrated;24 however, at maximum, the continuous films can only be as long as the trough is. Ideally, film transfer would be coupled to continuous material deposition to make the process truly roll-to-roll. Working towards this goal, Kim et al. recently presented a Langmuir–Blodgett scooping (LBS) method25,26 and suggested that the deposition of film on glass slides and membrane supports was driven by the Marangoni-effect caused by the evaporation of ethanol in the water bath. While densely packed monolayers of micron-sized spherical colloids were demonstrated, films of nanomaterials like carbon nanotubes were uniform but multi-layer in nature as the technique seems limited to films larger than 1020 nm in thickness.

Xu et al.


Page 2 of 25

Page 3 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

In order to transfer monolayers by such a method, the aggregation state of the floating nanomaterials must be considered. The colloidal stability of floating micro/nanoparticles is controlled by various interfacial phenomena such as electrostatic repulsion, van der Waals attraction and flotation forces.27 In the case of graphene oxide, it has been shown that a dominant repulsive electrostatic force exists between the floating sheets which allows them to be densified uniformly and reversibly from a dilute gas phase.1 However, for GO, the process has been complicated by the fact that water-miscible spreading solvents are used to deposit the material at the air-water interface due to the ease in which GO is dispersed in water and other polar solvents. This causes extensive mixing and results in reported losses of up to 99% of material into the subphase.28 The problem of poor transfer efficiency was recently addressed by Nie et al. by spreading GO and other nanoparticle dispersions from water using aerosols instead of macroscopic drops in order to minimize the sub-phase mixing.29 On the other hand, an easier method to improve transfer would be to make a switch to water-immiscible spreading solvents. In this work we will first present a method which enables high-yield transfer of GO onto the air-water interface by formulating dispersions in water immiscible solvents, like 1,2dichloroethane (DCE) and chloroform. We will then demonstrate a barrier-free deposition approach which is able to densify large area monolayer GO films during both batch deposition and by continuous deposition and withdrawal through forces associated with solvent spreading. This allows us to deposit dense monolayer coatings over areas as high as 400 m2 with just one gram of material and thus translates to efficient materials utilization and extremely low-cost films. Furthermore, we demonstrate that this approach can be extended to other 2D materials such as thermally exfoliated graphite oxide (TEGO). The mechanism of film densification and edge-toedge aggregation are investigated to gain insight as to how to control the film formation process. Lastly, we will present the performance of our monolayer GO film in one particular application – a passivation layer to prevent silver nanowires from degrading under current flow. The stability of the electrodes is significantly extended compared to films deposited by other solution deposition methods while retaining the high transparency of single-layer graphene.

Xu et al.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Results and Discussion Traditional vs. improved spreading solvent The significant improvement in transfer efficiency between the DCE/ethanol-based and methanol/water-based spreading solvents is shown in Figure 1a-e. Compression isotherms (Figure 1a) and in situ Brewster angle microscope (BAM) video snapshots (Figure 1b-e) are shown for experiments where the same mass and concentration (0.025 mg/mL) of GO was deposited from each spreading solvent system. The methanol/water case shows a shifted baseline from zero surface pressure due to the mixing of methanol and water that causes a decrease in the surface tension of the sub-phase (Figure 1a). In this case, compressing the film to an area of ~200 cm2 (point b) increases the density of what are observed to be discretely floating sheets and some clusters (Figure 1b). Further compression to nearly 100 cm2 (the limit of the trough, point c) resulted in a denser but incomplete monolayer (Figure. 1c). On the other hand, for the DCE case, at 625 cm2, larger mobile clusters are observed (Figure. 1d). For this case, the image is not focused because the cluster was moving rapidly across the field of view. At 475 cm2, the surface pressure increased to ~ 2mN/m and BAM imaging (Figure. 1e) revealed a fully dense film (at least to the resolution of the BAM, ~2 m) exhibiting weaker contrast between the water and floating GO because most of the water surface was covered – although the faint outline of the densely tiled sheets can still be observed. A comparison between these cases indicates two important differences: (i) the transfer efficiency using DCE as a spreading solvent is about five-fold higher than the methanol/water case (compare the final surface pressures in two cases); (ii) Large clusters of GO are observed in the DCE case compared to the isolated sheets in the methanol/water case (compare Figure 1b and 1d). -A compression-expansion isotherms using the improved spreading solvent can be found in the Supporting Information (Figure S1).

Xu et al.


Page 4 of 25

Page 5 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Figure 1. Analysis of Langmuir films deposited from the traditional and improved spreading solvent systems. a) Isotherms obtained after transferring the same amount of GO onto the air-water interface via two different spreading solvents: the traditional methanol/water (volume ratio of 5:1) system (black curve) and ethanol/DCE (volume ratio of 1:13) (red curve); b-e) In situ Brewster angle microscope (BAM) video snapshots of film morphologies with corresponding observation times labelled in (a). Scale bar in (b) is 100 m. Other images were taken with the same magnification. The dark, nearly black, contrast is the water phase while the brighter contrast corresponds to the GO. Note that compared to (c) where traditional solvent was used, a fully covered dense film was observed in (e) where the DCE/ethanol-based spreading solvent was used. In (e) the contrast is poorer because there was little exposed water surface due to the high density of the GO but the outline of the packed sheets can still be observed.

Xu et al.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Barrier-free densification of Langmuir films The air-water interface was recorded while repetitively dripping a 0.025 mg/mL dispersion at the air-water interface and snapshots are shown in Figure 2a-c (see Video S1 in supporting information). The video was paused and the screenshots presented the point when the drop of the spreading dispersion was deployed and had spread to its maximum area. A boundary between the evaporating solvent and the adjacent film-covered interface is clearly visible (marked as red arrows in Figure 2b-c). As more drops of dispersion are added to the trough, the spreading area is observed to shrink which suggests that the observed boundary moves inward as the film grows. This is more noticeable at later stages in the deposition (see Video S1 between 1:00 and 1:25min and after 1:26min which illustrates the reduced area near the end of the deposition). Continued dripping leads to a further decrease of the spreading area until the solvent could no longer spread and forms

Figure 2. Snapshots of videos taken at successive times throughout the process (a, b, c). The interface between growing GO film and solvent spreading is labelled by red arrows in (b) and (c). Note that at the early stage (a) of the deposition, the interface was poorly defined and thus not indicated. Snapshots of in situ BAM videos taken at the interface between the spreading solvent and ‘growing’ film using a typical concentration of GO dispersions at 0.025 mg/mL (d, e, f) and 0.00625 mg/mL (g, h, i). The position where in situ BAM were set is labeled as black squares in (a), (b) and (c). Scale bar in (d), which is effective for all the other BAM images (e-i), is 100 m. Note that the red dash line in (e) shows the moving sheets at the boundary between film growing front and pure water. surface.

Xu et al.


Page 6 of 25

Page 7 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

a liquid lens that sits at the interface for several seconds before evaporating. BAM was used to study this phenomenon in more detail as shown in Figure 2d-f. With each drop, material was observed to move rapidly past the fixed field-of-view but pausing to take a snapshot indicated that the water surface was free of any floating material during the early stages of deposition (Figure 2d). After 0.042 mg of GO was deposited, there was an abrupt transition from a clean interface to a densely tiled film that grew across the field of view with each additional drop (Figure 2e). Pausing the dripping to capture a focused image indicated that the film remained densely tiled but convection (likely introduced by air-currents above the trough) could induce the sheets at the boundary between the clean water and dense film to move and tumble (in 2D) rapidly past one another while seeming to maintain some attraction to the growing front (see area within the red dash line in Figure 2e and see Video S2 in supporting information). Adding more GO to the trough caused the film to move past the field of view of the BAM. This uniformly dense film remained solid even after dripping was paused to take a snapshot as shown in Figure 2f and Video S3 in supporting information. On the other hand, if a lower concentration dispersion of GO in DCE/ethanol is used, we observe a different phenomenon. Figure 2g-i show snapshots from the BAM when a 0.00625 mg/mL dispersion is continuously dripped onto the trough. After depositing 0.024 mg (Figure 2g), a low density network is observed of what appears to be a mixture of isolated sheets and small clusters of 5-10 sheets aggregated in a branched morphology. As deposition is continued, this network densifies (Figure 2h) and eventually yields what appears to be an equivalent packing density as the more concentrated case (Figure 2i), although it happens at a relatively later time during the deposition. As shown in Figure 3a and 3c, the 0.025 and 0.00625 mg/mL depositions both yield a densely tiled layer of sheets which are 0.7 - 1 nm in thickness (see Figure S2 for thickness distribution analysis), as is known to be the case for single layers of GO, with some wrinkles and occasional overlaps between adjacent sheets. Representative scanning electron microscopy (SEM) images of resulting films are shown in Figure 3b and 3d. A dense coverage (90-95%) was observed in both cases. In the 0.025 mg/ml case, the sheets are often found to be slightly overlapping at their edges as apparent in Figure 3b.

Xu et al.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3. Morphology of GO films prepared by barrier-free deposition. Representative AFM images of samples coated on mica substrates after filling the trough with different concentrations: 0.025 mg/mL (a), 0.00625 mg/mL (c) of GO in the ethanol/DCE spreading solvent and the corresponding height profile across the red line in the image. The scale bar in (a) and (c) are 2 μm. Representative SEM images of samples coated on highly oriented pyrolytic graphite substrates prepared by barrier-free deposition from GO concentration at 0.025 mg/mL (b) and 0.00625 mg/mL (d). The scale bar in (b) and (d) is 10 μm. In the SEM images, the substrate appears as darker contrast, the GO sheets can be observed as dark grey while the overlaps (observed more so in (b)) at the sheet edges are lighter contrast.

The transfer efficiency of the deposition process can be quantified by the Langmuir specific surface area (LSSA, defined in the Supporting Information). As shown in Figure 4 at dispersion concentrations between 0.003 and 0.025 mg/mL, we reproducibly observe LSSAs of 700 800 m2/g. Our estimates are close to the highest literature SSA value estimated for GO, determined using the method of methylene blue titration of stable single layer GO dispersions, which is 889 m2/g.30,31 Therefore, we conclude that by using our repetitive dripping deposition, we achieve a high efficiency, nearly 100%, in terms of transferring GO single layers onto the air-water interface to assemble into large area monolayer films. However, the LSSA values we estimate begin to drop at higher concentrations which is expected since we observe significant overlapping between sheets at high concentration conditions as shown in Figure S7. Xu et al.


Page 8 of 25

Page 9 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Figure 4. Langmuir specific surface area (LSSA) of GO Langmuir films as a function of the deposition dispersion concentration (i.e., the ethanol/DCE (1:13) mixture). The error was estimated as  the standard deviation of at least three depositions from freshly prepared GO dispersions.

By comparing the LSSA of two populations of GO with different lateral sizes (see Figure S8 for sheet size distribution), we observed 800 ± 30 m2/g from large sheet size suspension and 700 ± 80 m2/g from small sheet size suspension. This indicates no significant difference in the transfer efficiency and thus we conclude that there is no significant size selection in our deposition process as has been reported previously for the methanol/water system.32 Our results suggest that size-selection is result of solvent mixing during the deposition and not the ability of small vs. large sheets to float on water. Aggregation mechanism As shown in Figure 5, the depositions from GO dispersions at 0.025 mg/mL at various subphase pH (no additional salt was added) were monitored by in situ BAM. In the case of pH = 4, at the early stage of the deposition, when only 0.003 mg GO were transferred onto the water surface, we observed large island-like aggregates of close-packed GO sheets moving rapidly on the water (Figure 5a). In contrast, when basic sub-phase water was used, well-dispersed GO sheets were observed on the water surface (Figure 5g) even when more GO was deposited (0.013 mg) via the repetitive dripping process. In the case of pH = 7, we observed the formation of a large denselytiled island of GO when 0.042 mg of GO was deposited. However, as already discussed for the case above, the sheets were mobile and observed to tumble past one another under the influence of convection induced by solvent evaporation or air currents flowing over the trough (Figure 5d).

Xu et al.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

As more material is added, in all cases, the film is densified throughout the repetitive dripping process regardless of the sub-phase pH value, as shown in Figure 5b-c, e-f, h-i respectively.

Figure 5. Microscopic observations by in situ BAM of GO film formation via repetitive dripping process over subphase water at various pH levels: pH=4 (a-c), PH=7 (d-f), pH=10 (g-i). The scale bar in (a) is 100 μm and is valid for all other images. GO dispersion concentration of 0.025 mg/mL was used in all pH cases.

In Figure 6, we investigate the ionic strength effect on the behavior of GO sheets at 0.025 mg/ml and a sub-phase pH = 10. At the early stage of the deposition, when only 0.0070.013 mg GO were added onto the water surface, the sheets were observed to be repulsive in the case of 0 mM, 10 mM and 100 mM salt concentration. However, as more material was added we observed the formation of larger aggregates in the case of higher ionic strength. At the end of the deposition, the film achieved a similar density in all cases. When the ionic strength is as high as 1 M, the sheets formed large 3D aggregates from the beginning of the deposition which appeared as bright objects under BAM (Figure 6m-p). This is likely due to the significant decrease in electrostatic repulsion between the sheets as this high ionic strength could result in a very strong screening effect between the sheets. Moreover, this aggregation phenomenon was also supported by the fact that almost twice the amount of GO was required to deposit a film with the same area at pH 10 and 1 M ionic strength. Unfortunately, films from this case could not be deposited on

Xu et al.


Page 10 of 25

Page 11 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

substrates and further characterized by either scanning electron microscopy (SEM) or AFM, due to the high salt content that caused large crystals to form on top of and around the GO film.

Figure 6 Microscopic observations by in situ BAM of GO film formation via a repetitive dripping process over subphase water at pH = 10 but with various ionic strengths: 0 mM (a-d), 10 mM (e-h), 100 mM (i-l), 1 M (m-p). The scale bar in (a) is 100 μm and is valid for all other images. A GO dispersion concentration of 0.025 mg/mL was used in all ionic strength cases.

The observations discussed above suggest that, except at high salt concentrations of ~1 M, screening does not play a significant role in the aggregation at early stages of deposition. However, increasing the ionic strength tends to increase the density of 2D clusters as more material is added to the trough. Clustering has also been observed in several other studies. For example, Zhang et al. have found that injection of 200 L of 0.2 mg/mL GO from a 5:1 methanol:water dispersion at various sub-phase pH also leads to a clustering.33 The clusters were found to grow in size with decreasing pH. Silverberg et al. also observed clustering from partially reduced GO (C/O ~ 2.4) when deposited from 9:1 ethanol:water and the salt concentration was 1 mM.28 However, as discussed above, these cases are complicated by significant and uncontrolled loss of GO into the sub-phase water which likely impacts the physics in comparison to our approach. Before discussing the physics of aggregation in this system we will first discuss the solvent spreading

Xu et al.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

process which is often overlooked in LB film deposition and, we attest, plays a significant role in the aggregation process. Spreading-induced film densification As shown schematically in Figure 7a, a Langmuir-Adam balance34 was used to probe the force of the deposition solvent (DCE or chloroform – another common water immiscible spreading solvent) spreading on water and acting at different distances from the dripping position. As shown in Figure 7b when pure solvents (DCE and chloroform) were dripped on the water surface, the balance was unable to detect any significant force on the barrier even when drops were deployed 2.5 cm away. When ethanol was added to the solvents (1:13 ratio), the spreading force became significant and rose quickly when the dripping position was closer than 4 cm away from the float. The DCE/ethanol response was felt by the balance at slightly larger distances than the chloroform case. These results indicate that the spreading area prior to solvent evaporation is significantly enhanced with the addition of a small amount of ethanol and that the DCE/ethanol spreads over a larger area than the chloroform/ethanol case. This could be explained by two effects: 1. Adding ethanol will increase the work of adhesion between spreading solvent and sub-phase water and thus increase the spreading coefficient as well as the driving force for spreading; 2. Ethanol is less volatile than chloroform or DCE (vapor pressures are 44.03 mmHg vs. 61.68 mmHg at 20 C for ethanol vs. DCE).35 Therefore their mixture would also be less volatile and could result in a larger spreading area. These observations are also apparent on a macroscopic level as the pure solvent is observed to pool near the deposition point prior to evaporating while mixtures with ethanol clearly spread further and more rapidly across the water surface. In comparing the morphology of the films deposited from the DCE/ethanol vs. chloroform/ethanol cases (see Figure S10) the chloroform/ethanol spreading dispersion requires a lower concentration (0.00625 vs. 0.025 mg/ml) to obtain a film with discretely tiled single layers (Figure S10) without significant wrinkles and folds. This is likely due to the reduced spreading area that increased the probability of sheet-sheet overlap during deposition. Figure 7c and d show the changes of the maximum and baseline deflection measured after each drop of spreading dispersion (DCE/ethanol now containing GO) was added to the coating bath as a function of extent of deposition for GO dispersions at concentrations of 0.025 mg/mL and 0.00625 mg/mL. At an early stage of the deposition (labelled as A to B in both plots),

Xu et al.


Page 12 of 25

Page 13 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

significant changes in spreading pressure were detected (> 3 mN/m) for the dilute concentration, while no detectable change was recorded in the high concentration case over this range. The low concentration case could be explained by the observation of a repulsive network of branched aggregates as observed by BAM and discussed in the previous section (Figure 2g-h). The repulsive network is able to transmit a force to the balance with each drop. In the high concentration case, the aggregated GO are propelled to the extremities of the trough where they form islands that are far from the ~4 cm spreading front and thus no detectable deflection can be transmitted to the barrier. After this initial stage, in both cases, the spreading pressure was observed to increase (stage labelled B to C in plots) as the film grew from the edges of the trough inwards. Furthermore, we observed an increase in the baseline value of spreading pressure measured (in region D to E of the plots) in both concentration cases. The increase in baseline value is indicative of the increase in surface pressure caused by the densely tiled GO film. The early stage of this increase is likely due to GO bridges that form at the growth front as islands growing from both sides of the trough and begin to merge at the centre. These bridges prevent the film from relaxing from the solid phase. However, approaching the end of the deposition, this increase is likely more related to the spreading pressure of the remaining solvent due to the slower evaporation rate caused by the decrease in spreading area. Near the end of the deposition, the baseline and maximum surface pressure converge when the solvent can no longer spread. This final spreading pressure, measured to be 7.1 and 7.7 mN/m in high and low concentration cases, respectively, might be considered the equilibrium spreading pressure of the solvent acting on the GO. Assuming the spreading solvent was pure DCE, theoretically S = 12.1 mN/m which is higher than the measured value. The actual surface tension of our spreading solvent could be readily measured as 32.7 ± 0.2 mN/m which is similar to pure DCE (32.2 mN/m).36 However, the miscibility of ethanol with water makes an accurate measurement of the ethanol/DCE-water interfacial tension impractical along with the fact that the water phase is contaminated at the end of deposition with a small amount of ethanol and DCE which reduces the interfacial tension of the sub-phase water from 72.5 mN/m to typically ~68 mN/m. We suspect that these changes account for the difference between the measured and theoretically predicted value for pure DCE.

Xu et al.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 7. Probing the liquid-liquid spreading pressure acting on the Langmuir film. (a) Schematic illustration of the Langmuir-Adam balance used. The rigid supporting frame is not shown here. (b) Position-dependent deflection force of deposition solvents: DCE/ethanol (v:v = 13:1) (black, ), chloroform/ethanol (v:v = 13:1) (red, ),pure chloroform (green,  ) and pure DCE (magenta, ). The inset shows the position of solvent injection in relation to the float at a distance of 8 cm. It also shows the size scale between the trough area (12 cm by 17 cm) and the approximate solvent spreading areas of DCE/ethanol (outter circle, black dash line, RDCE/EtOH ~ 3.5 cm) and chloroform/ethanol (inner circle, red dash line, RChl/EtOH ~ 2.6 cm). Error bars indicate the standard deviation of at least 8 measurements. (c, d) Spreading pressure estimated during GO deposition at a concentration of 0.025 mg/mL (c) and 0.00625 mg/mL (d). In both cases the dripping position is the same as the inset indicated in Figure 7b. The green and red curves for each concentration show the maximum and minimum pressure, respectively, felt at the float for each drop of spreading solvent as a function of total deposition time. The inset in (c) shows a representative time-dependant voltage change measured by the float during the deployment of one drop of dispersion onto the air-water interface.

Langmuir films of other 2D materials and continuous coating of TEGO film To visualize how the solvent spreading process can control film formation (densification) in a macroscopic view, we turn to other materials which are more easily seen by eye as a thin film, like thermally exfoliated graphene oxide (TEGO). Figure 9a, shows an example of TEGO films deposited from a TEGO powder dispersed in the same DCE/ethanol mixture as the GO in the same coating bath configuration at the concentration of 0.025 mg/mL. In the more concentrated case (for TEGO this is ~0.1 mg/mL) the formation of small island aggregates are visible to the naked eye upon the deposition of each drop (Figure 9b). These 2D aggregates are pushed to the extremities of the trough by the next drop as was inferred for the GO case. The initial aggregation

Xu et al.


Page 14 of 25

Page 15 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

appeared to take place during evaporation of the thin solvent film that distributes material over the air-water interface. These small islands then coalesced to form larger ones, until a uniform film began to build up from the outside of the trough inwards. The film continued to grow with each additional drop of dispersion until the entire trough was covered as was observed for the GO case above. As shown in Figure 9c, SEM imaging shows that the resulting TEGO film is composed of discretely tiled sheets similar to the GO case. However, the sheets appear wrinkled and many aggregated or unexfoliated materials appear to be present within the film. The wrinkling in TEGO flakes are frequently observed by others37 and are thought to result from the rapid thermal expansion process which produces defects and functional groups as well as by partially exfoliated, stacked materials which are not deaggregated by the ultrasonication procedure used. The LSSA estimated for this material was typically between 120 - 150 m2/g which confirms the presence of many aggregates and few layer stacks within the film as the theoretical surface area of a single layer of graphene is 2630 m2/g. While this material is not as well-defined as the mono-dispersed (in the thickness direction) GO films, the material appears to follow the same general behavior as with the GO films. However, the packing density or relative coverage is lower (~80%) compared to the GO films. In a previous work by Pope et al., Langmuir-Blodgett films of TEGO were shown to reach a relative coverage of above 90% when barrier compression was used to adjust the surface pressure to 25-30 mN/m.38 This is higher than what can be achieved by solvent spreading with the DCE/ethanol system (~8 mN/m as discussed above). A similar film growth phenomena has been recently demonstrated for another 2D material, 1T-MoS2 which suggests that this edge-to-edge aggregation and solvent-driven densification mechanism may be more generally applicable.39

Figure 9. Barrier-free deposition and continuous film coating of TEGO. Snapshots of videos recorded during TEGO deposition by setting the dripping position at the center (a) and close to one side of the trough (b) using two typical Xu et al.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

concentrations: 0.025 mg/mL (a) and 0.1 mg/mL (b). Note that the edges of the growing film are labelled by red arrows in (a) and (b). SEM image of the TEGO film coated onto silicon using a concentration of 0.1 mg/mL (c). The scale bar in (c) is 1 μm. In the SEM image, substrate is shown as light grey and TEGO sheets are shown as darker contrast with wrinkles shown as white. Schematic illustration of continuous coating setup and operation (d). Resulting PET sample coated with TEGO film in a dimension of 6.5 cm by 14 cm using TEGO dispersion concentration of 0.1 mg/mL (e).

As shown in Figure 9b, by changing the position of the dripping closer to one edge and making the bath narrower (6.5 cm) than the spreading front, the film could be selectively assembled from one side of the trough to the other, in contrast to the film growing symmetrically from both sides as for the central injection case. By placing a long piece of clean PET film beneath the sub-phase water, and withdrawing the film at a similar velocity to that of the growing front of TEGO for the concentrated case, we demonstrate the ability to continuously transfer the TEGO film to the PET during the dripping process. Using the estimated LSSA, a TEGO concentration of c = 0.1 mg/mL, a dripping rate of r = 0.13 mg/mL and the width of the continuous coating bath as d = 6.5 cm, the film growth speed can be estimated according to: 𝑣=

𝐿𝑆𝑆𝐴 ∙ 𝑐 ∙ 𝑟 2𝑑

Using this relation and an LSSA of 120 m2/g leads to v = 1.2 cm/min. A schematic of the coating bath is shown in Figure 9d. By withdrawing the flexible PET substrate at a coating speed of 1 cm/min, a 14 cm length could readily be coated (Figure 9e) indicating that the spreading pressure of the solvent is sufficient to keep the film intact during the transfer. The coating speed could foreseeably be increased by enhancing the evaporation rate of the solvent through increased temperature or gas flow. Furthermore, the system required only a water bath which means that many coating baths could be operated in parallel at negligible capital cost if increased throughput is necessary. The coating velocity can be compared to high temperature, high capital cost roll-to-roll CVD growth and transfer systems. By this method, maximum coating velocities of 10 cm/min have been achieved with graphene but at the expense of sub-micron crystallite size and poor film quality.40 While the continuous Langmuir-Blodgett method demonstrated above is likely not capable of producing films with the same electronic quality as the CVD method, it has several advantages and unique capabilities. For example, it can process monolayers of technologically important materials such as graphene oxide and other materials which cannot be grown by vapor deposition

Xu et al.


Page 16 of 25

Page 17 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

methods. In particular, GO holds promise as ultra-thin blocking layers and membranes for water filtration (see Supporting Information for an example of reduced GO films passivating Ag-NW electrodes from degrading under current flow). Furthermore, this approach can be applied to other water-stable 2D and potentially 1D nanomaterials to create single/few-layer thick film via a rollto-roll compatible method. Currently such materials must be applied by methods such as casting or spray coating which are geared to making films thicker than ~100 nm. The related Langmuir scooping technique being developed by Archer’s group,26 appears capable of producing films of intermediate thickness to ours and the aforementioned methods. The ability to continuously process monolayers enables films with improved properties such as higher optical transparency, flexibility and the ability to access the unique properties of 2D materials which typically only emerge when they are one or few-layer in thickness. Since the method only requires a syringe pump and glass/Teflon trough, we expect the procedures described to be widely accessible and enable researchers to more quickly deposit ultra-thin films of a variety of emerging nanomaterials to engineer both monolayer and heterostructure devices. Summary of Aggregation and Densification Mechanisms While we have only explored a small subset of the parameter space in terms of combinations of pH, ionic strength and deposition concentration we attempt here to make general conclusions (Figure 10) regarding the mechanisms at play that will guide further research based on current theories developed for colloidal dispersions and interfacial phenomena as discussed below.

Xu et al.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 10. Summary of 2D aggregation and spreading driven film densification. Increased clustering is observed at higher deposition concentrations – likely driven by immersion forces that exist during evaporation of the thin spreading solvent film (a). Aggregation of dilute dispersions at low pH and high ionic strengths which shield the repulsive electrostatic forces between the floating sheets (b). The spreading solvent applies a distance-dependant force to the floating sheets which compresses them into a densely tiled film. The force is transmitted throughout the trough differently depending on whether the sheets are repulsive or attractive (c).

There are several possible forces of interaction between charged and floating GO sheets that might be responsible for the observed aggregation states under the conditions investigated. In addition to the typical Derjaguin-Landau-Verwey-Overbeek (DLVO)-type interactions that govern aggregation behavior in bulk dispersions, at an interface, additional forces resulting from the capillarity induced by flotation and immersion, as well as longer range dipolar interactions between emergent portions of material must be considered.27 The weight of a particle floating on water is known to deform the interface and cause attraction between particles.27,41 However, for the same radius, relatively heavy spherical particles do not significantly deform the interface until they are larger than ~5-10 m.27,41 Thus lighter, atomically thin GO discs with diameters < 10 m used in this work are not expected to yield interaction potentials larger than the thermal energy, kBT. The related immersion force, which requires the GO be partially immersed in a thin liquid film, can arise when the dispersion solvent spreads and evaporates at the air-water interface. While the solvent film must be less than 0.7-1 nm to entrain the GO, immersion forces are known to be strong and capable of acting on aggregating proteins and other nanometer-sized objects within thin films like lipid bilayers.41 Thus it is possible that 2D aggregation could be caused by this thin evaporating film of spreading solvent that the GO is entrained in during deposition. In fact, we observe for other, less transparent materials (like the TEGO discussed above) the formation of 2D aggregates immediately upon evaporation of the first drop of spreading solvent when the concentration of material is high. This observation is summarized schematically in Figure 10a. While the immersion forces cannot persist after evaporation of the spreading solvent, they may provide a mechanism for assembling some sheets into close enough contact for shorter range van der Waals forces to take over. For other floating nanoparticles systems, long range dipolar interactions have been found to provide a strong stabilizing effect which makes 2D dispersions more robust to aggregation compared to bulk dispersions.27 If we consider the atomically thin nature of a GO sheet, there is little, if any, emergent material which sits above the water that might be able to participate in

Xu et al.


Page 18 of 25

Page 19 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

dipolar repulsive interactions. Thus, it seems reasonable to assume that this long range repulsive interaction is not important in the case of GO and other atomically thin 2D nanomaterials. On the other hand, the ionisable functional groups on the GO exist primarily at the edges (carboxylic acids, phenolic hydroxyls) and the strong dependence on aggregation with sub-phase pH and ionic strength indicates that the GO edges are submerged, and the resulting negative charge provides some electrostatic repulsion originating within the water phase. This is evidence that GO are submerged in the liquid and thus dipolar interactions should not significantly contribute. Upon solvent evaporation, the floating sheets contact the water sub-phase where the ionisable functional groups can deprotonate and induce electrostatic repulsion depending on the sub-phase pH and ionic strength as illustrated in Figure 10b. We attempted to use existing models of repulsive and attractive potentials for discs as was carried out by Silverberg et al.28 However, we were unable to reproduce their calculations and found that the calculated potentials quickly diverge under the dimensions and surface potentials for GO. While we cannot currently model the observed behavior, the observations are consistent with what is generally seen in 3D dispersions of spherical colloids. Finally, the force or spreading pressure exerted by solvent-water interactions act on these aggregated or dispersed floating sheets, pushing material from high pressure (near the drop deployment site) to low pressure. This acts to compress the dispersion as the film packs and grows closer to the spreading front (Figure 10c). The fact that the aggregates rearrange into a more densely tiled configuration during the repetitive dripping process suggests that the short-range edge-to-edge attraction is weak enough to be broken by the force of solvent spreading. 2. Conclusions In this work, by replacing the traditional spreading solvent for deploying GO onto the airwater interface with one that is largely water immiscible, we observe a concentration, sub-phase pH and salt dependant edge-to-edge aggregation behavior that in all cases leads to nearly 100% transfer efficiency. By continuously dripping material onto the interface, we observe that the force of the spreading solvent is capable of densifying the dispersed or aggregated 2D system into a dense layer of single sheets allowing us to measure surface coverages as high as 400 m2 per gram of GO deposited. Using in situ Brewster angle microscopy and a Langmuir-Adam balance, we study the aggregation and densification mechanism. Under conditions of weak attraction and by positioning the material injection point appropriately in the bath, we demonstrate that films can be Xu et al.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

continuously deposited and transferred to substrates such as PET. While the study focuses mainly on GO, other 2D materials such as TEGO are shown to yield qualitatively similar aggregation behavior that allow us to paint a mechanistic picture of this new film forming approach. As an example, we presented the performance of our monolayer GO film (after chemical reduction) in one particular application – a passivation layer to effectively protecting silver nanowires from degrading in ambient without sacrificing the original high transparency and conductivity. 3. Acknowledgments L.X., A.T. and M.P. acknowledge funding from the Natural Sciences and Engineering Research Council of Canada’s Discovery and Idea to Innovation Grants. We also thank Dr. Brian Pethica for his helpful suggestions with regards to designing the Langmuir-Adam balance. 4. Supporting Information Available: The Supporting Information is available free of charge on the ACS Publications website. Detailed experimental procedures and additional experimental results are presented. 5. References (1)

Cote, L. J.; Kim, F.; Huang, J. Langmuir−Blodgett Assembly of Graphite Oxide Single Layers. J. Am. Chem. Soc. 2009, 131 (3), 1043–1049.

(2)

Zheng, Q.; Zhang, B.; Lin, X.; Shen, X.; Yousefi, N.; Huang, Z. D.; Li, Z.; Kim, J. K. Highly Transparent and Conducting Ultralarge Graphene Oxide / Single-Walled Carbon Nanotube Hybrid Films Produced by Langmuir-Blodgett Assembly. J. Mater. Chem. 2012, 22 (48), 25072.

(3)

Jia, B.; Zou, L. Langmuir–Blodgett Assembly of Sulphonated Graphene Nanosheets into Single- and Multi-Layered Thin Films. Chem. Phys. Lett. 2013, 568–569, 101–105.

(4)

Mangadlao, J. D.; Santos, C. M.; Felipe, M. J. L.; de Leon, a C. C.; Rodrigues, D. F.; Advincula, R. C. On the Antibacterial Mechanism of Graphene Oxide (GO) Langmuir– Blodgett Films. Chem. Commun. 2015, 51 (14), 2886–2889.

(5)

Li, X.; Zhang, G.; Bai, X.; Sun, X.; Wang, X.; Wang, E.; Dai, H. Highly Conducting Graphene Sheets and Langmuir-Blodgett Films. Nat. Nanotechnol. 2008, 3 (9), 538–542.

(6)

Lin, X.; Jia, J.; Yousefi, N.; Shen, X.; Kim, J.-K. Excellent Optoelectrical Properties of Graphene Oxide Thin Films Deposited on a Flexible Substrate by Langmuir-Blodgett

Xu et al.


Page 20 of 25

Page 21 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Assembly. J. Mater. Chem. C 2013, 1 (41), 6869–6877. (7)

Loh, K. P.; Tong, S. W.; Wu, J. Graphene and Graphene-like Molecules: Prospects in Solar Cells. J. Am. Chem. Soc. 2016, 138 (4), 1095–1102.

(8)

Zheng, Q.; Shi, L.; Yang, J. Langmuir-Blodgett Assembly of Ultra-Large Graphene Oxide Films for Transparent Electrodes. Trans. Nonferrous Met. Soc. China 2012, 22 (10), 2504– 2511.

(9)

Kim, K. S.; Zhao, Y.; Jang, H.; Lee, S. Y.; Kim, J. M.; Kim, K. S.; Ahn, J.; Kim, P.; Choi, J.-Y.; Hong, B. H. Large-Scale Pattern Growth of Graphene Films for Stretchable Transparent Electrodes. Nature 2009, 457 (7230), 706–710.

(10)

Akinwande, D.; Petrone, N.; Hone, J. Two-Dimensional Flexible Nanoelectronics. Nat. Commun. 2014, 5, 5678.

(11)

Bae, S.; Kim, H.; Lee, Y.; Xu, X.; Park, J.; Zheng, Y.; Balakrishnan, J.; Lei, T.; Ri Kim, H.; Song, Y. Il; Kim, Y.-J.; Kim, K. S.; Özyilmaz, B.; Ahn, J.-H.; Hong, B. H.; Iijima, S. Rollto-Roll Production of 30-Inch Graphene Films for Transparent Electrodes. Nat. Nanotechnol. 2010, 5 (8), 574–578.

(12)

Wang, X.; Xiong, Z.; Liu, Z.; Zhang, T. Exfoliation at the Liquid/Air Interface to Assemble Reduced Graphene Oxide Ultrathin Films for a Flexible Noncontact Sensing Device. Adv. Mater. 2015, 27 (8), 1370–1375.

(13)

Eda, G.; Fanchini, G.; Chhowalla, M. Large-Area Ultrathin Films of Reduced Graphene Oxide as a Transparent and Flexible Electronic Material. Nat. Nanotechnol. 2008, 3 (5), 270–274.

(14)

Petersen, S.; Glyvradal, M.; Bøggild, P.; Hu, W.; Feidenhans’L, R.; Laursen, B. W. Graphene Oxide as a Monoatomic Blocking Layer. ACS Nano 2012, 6 (9), 8022–8029.

(15)

Chen, R.; Das, S. R.; Jeong, C.; Khan, M. R.; Janes, D. B.; Alam, M. A. Co-Percolating Graphene-Wrapped Silver Nanowire Network for High Performance, Highly Stable, Transparent Conducting Electrodes. Adv. Funct. Mater. 2013, 23 (41), 5150–5158.

(16)

Zheng, Z.; Grünker, R.; Feng, X. Synthetic Two-Dimensional Materials: A New Paradigm of Membranes for Ultimate Separation. Adv. Mater. 2016, 28 (31), 6529–6545.

(17)

Nair, R. R.; Wu, H. A.; Jayaram, P. N.; Grigorieva, I. V.; Geim, A. K. Unimpeded Permeation of Water Through Helium-Leak-Tight Graphene-Based Membranes. Science (80-. ). 2012, 335 (6067), 442–444.

Xu et al.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(18)

Wang, S.; Wu, Y.; Zhang, N.; He, G.; Xin, Q.; Wu, X.; Wu, H.; Cao, X.; Guiver, M. D.; Jiang, Z. A Highly Permeable Graphene Oxide Membrane with Fast and Selective Transport Nanochannels for Efficient Carbon Capture. Energy Environ. Sci. 2016, 9 (10), 3107–3112.

(19)

Eda, G.; Lin, Y. Y.; Miller, S.; Chen, C. W.; Su, W. F.; Chhowalla, M. Transparent and Conducting Electrodes for Organic Electronics from Reduced Graphene Oxide. Appl. Phys. Lett. 2008, 92 (23), 10–13.

(20)

Pham, V. H.; Cuong, T. V.; Hur, S. H.; Shin, E. W.; Kim, J. S.; Chung, J. S.; Kim, E. J. Fast and Simple Fabrication of a Large Transparent Chemically-Converted Graphene Film by Spray-Coating. Carbon N. Y. 2010, 48 (7), 1945–1951.

(21)

Becerril, H. A.; Mao, J.; Liu, Z.; Stoltenberg, R. M.; Bao, Z.; Chen, Y. Evaluation of Solution-Processed Reduced Graphene Oxide Films as Transparent Conductors. ACS Nano 2008, 2 (3), 463–470.

(22)

Lee, D. W.; Hong, T.-K.; Kang, D.; Lee, J.; Heo, M.; Kim, J. Y.; Kim, B.-S.; Shin, H. S. Highly Controllable Transparent and Conducting Thin Films Using Layer-by-Layer Assembly of Oppositely Charged Reduced Graphene Oxides. J. Mater. Chem. 2011, 21 (10), 3438.

(23)

An, S. J.; Zhu, Y.; Lee, S. H.; Stoller, M. D.; Emilsson, T.; Park, S.; Velamakanni, A.; An, J.; Ruoff, R. S. Thin Film Fabrication and Simultaneous Anodic Reduction of Deposited Graphene Oxide Platelets by Electrophoretic Deposition. J. Phys. Chem. Lett. 2010, 1 (8), 1259–1263.

(24)

Parchine, M.; McGrath, J.; Bardosova, M.; Pemble, M. E. Large Area 2D and 3D Colloidal Photonic Crystals Fabricated by a Roll-to-Roll Langmuir-Blodgett Method. Langmuir 2016, 32 (23), 5862–5869.

(25)

Kim, M. S.; Ma, L.; Choudhury, S.; Archer, L. A. Multifunctional Separator Coatings for High-Performance Lithium–Sulfur Batteries. Adv. Mater. Interfaces 2016, 3 (22), 1600450.

(26)

Kim, M. S.; Ma, L.; Choudhury, S.; Moganty, S. S.; Wei, S.; Archer, L. A. Fabricating Multifunctional Nanoparticle Membranes by a Fast Layer-by-Layer Langmuir–Blodgett Process: Application in Lithium–Sulfur Batteries. J. Mater. Chem. A 2016, 4 (38), 14709– 14719.

(27)

Bresme, F.; Oettel, M. Nanoparticles at Fluid Interfaces. J. Phys. Condens. Matter 2007, 19 (41), 413101.

Xu et al.


Page 22 of 25

Page 23 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(28)

Silverberg, G. J.; Pearce, P.; Vecitis, C. D. Controlling Self-Assembly of Reduced Graphene Oxide at the Air-Water Interface: Quantitative Evidence for Long-Range Attractive and Many-Body Interactions. ACS Appl. Mater. Interfaces 2015, 7 (6), 3807–3815.

(29)

Nie, H. L.; Dou, X.; Tang, Z.; Jang, H. D.; Huang, J. High-Yield Spreading of WaterMiscible Solvents on Water for Langmuir-Blodgett Assembly. J. Am. Chem. Soc. 2015, 137 (33), 10683–10688.

(30)

Bradder, P.; Ling, S. K.; Wang, S.; Liu, S. Dye Adsorption on Layered Graphite Oxide. J. Chem. Eng. Data 2011, 56 (1), 138–141.

(31)

Montes-Navajas, P.; Asenjo, N. G.; Santamaría, R.; Menéndez, R.; Corma, A.; García, H. Surface Area Measurement of Graphene Oxide in Aqueous Solutions. Langmuir 2013, 29 (44), 13443–13448.

(32)

Kim, J.; Cote, L. J.; Kim, F.; Yuan, W.; Shull, K. .; J. Huang, J. Graphene Oxide Sheets at Interfaces. J. Am. Chem. Soc. 2010, 132 (14), 8180–8186.

(33)

Zhang, X.; Sun, H.; Yang, S. Self-Limiting Assembly of Two-Dimensional Domains from Graphene Oxide at the Air/Water Interface. J. Phys. Chem. C 2012, 116 (35), 19018–19024.

(34)

Transue, L. F.; Washburn, E. R.; Kahler, F. H. The Direct Measurement of the Spreading Pressures of Volatile Organic Liquids on Water. J. Am. Chem. Soc. 1942, 64 (2), 274–276.

(35)

Reid, R. C.; Prausnitz, J. M.; Poling, B. E. The Properties of Gases and Liquids, 3rd ed.; McGraw Hill Book Co.,New York, NY: United States, 1977.

(36)

Dean, J. A. Lange’s Handbook of Chemistry; McGraw-Hill, inc.: New York, 1999.

(37)

Schniepp, H. C.; Li, J.-L.; McAllister, M. J.; Sai, H.; Herrera-Alonso, M.; Adamson, D. H.; Prud’homme, R. K.; Car, R.; Saville, D. A.; Aksay, I. A. Functionalized Single Graphene Sheets Derived from Splitting Graphite Oxide. J. Phys. Chem. B 2006, 110 (17), 8535–8539.

(38)

Pope, M. A.; Aksay, I. A. Four-Fold Increase in the Intrinsic Capacitance of Graphene through Functionalization and Lattice Disorder. J. Phys. Chem. C 2015, 119 (35), 20369– 20378.

(39)

Zhang, Y.; Xu, L.; Walker, W. R.; Tittle, C. M.; Backhouse, C. J.; Pope, M. A. Langmuir Films and Uniform, Large Area, Transparent Coatings of Chemically Exfoliated MoS2 Single Layers. J. Mater. Chem. C 2017, 5 (43), 11275–11287.

(40)

Kobayashi, T.; Bando, M.; Kimura, N.; Shimizu, K.; Kadono, K.; Umezu, N.; Miyahara, K.; Hayazaki, S.; Nagai, S.; Mizuguchi, Y.; Murakami, Y.; Hobara, D. Production of a 100-

Xu et al.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

m-Long High-Quality Graphene Transparent Conductive Film by Roll-to-Roll Chemical Vapor Deposition and Transfer Process. Appl. Phys. Lett. 2013, 102 (2), 023112. (41)

Kralchevsky, P. A.; Nagayama, K. Capillary Interactions between Particles Bound to Interfaces, Liquid Films and Biomembranes. Adv. Colloid Interface Sci. 2000, 85 (2), 145– 192.

Xu et al.


Page 24 of 25

Page 25 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Table of contents

Xu et al.


Continuous Langmuir-Blodgett deposition and transfer by controlled

Recommend Documents