nature materials SUPPLEMENTARY INFORMATION D0h:10.1038/NMAT3228 Wetting Transparency of Graphene Javad Rafiee',Xi Mi,Hemtej Gullapalli,Abhay V.Thomas,Fazel Yavari, Yunfeng Shi2,Pulickel M.Ajayan3and Nikhil A.Koratkar. Department of Mechanical.Aerospace and Nuclear Engineering. Department of Materials Science and Engineering. Rensselaer Polytechnic Institute,Troy.New York,USA Department of Mechanical and Materials Engineering. Rice University,Houston,Texas,USA NATURE MATERIALS www.nature.com/naturematerials 1 2012 Macmillan Publishers Limited.All rights reserved
Supplementary Information Wetting Transparency of Graphene Javad Rafiee1 , Xi Mi2 , Hemtej Gullapalli3 , Abhay V. Thomas1 , Fazel Yavari1 , Yunfeng Shi2 , Pulickel M. Ajayan3* and Nikhil A. Koratkar1, 2* 1 Department of Mechanical, Aerospace and Nuclear Engineering, 2 Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, USA 3 Department of Mechanical and Materials Engineering, Rice University, Houston, Texas, USA SUPPLEMENTARY INFORMATION DOI: 10.1038/NMAT3228 NATURE MATERIALS | www.nature.com/naturematerials 1 © 2012 Macmillan Publishers Limited. All rights reserved
SUPPLEMENTARY INFORMATION D0:10.1038/NMAT3228 (1)Advancing and receding contact angles In addition to the sessile drop (as in Fig.2a in manuscript),we also studied the wetting transparency with respect to the advancing and receding contact angles.Typical results are shown below for baseline silicon and silicon with monolayer graphene coating.The measured advancing contact angle for silicon(~36 deg:Fig.Sla)was very similar to monolayer graphene coated silicon(~35 deg:Fig.SIb).Similarly the receding water contact angle on silicon(~30 deg: Fig.S1c)was also similar to that of monolayer graphene coated silicon(~31 deg:Fig.S1d).The difference between the advancing and receding contact angles(i.e.the contact angle hysteresis) for the samples were in the range of 4 to 6 degrees. (a) (b) Figure S1:Advancing water front for baseline silicon(a)and the monolayer graphene coated silicon (b).Corresponding images for the receding water front for silicon(c)and monolayer graphene coated silicon(d). 2 NATURE MATERIALS www.nature.com/naturematerials 2012 Macmillan Publishers Limited.All rights reserved
(1) Advancing and receding contact angles In addition to the sessile drop (as in Fig. 2a in manuscript), we also studied the wetting transparency with respect to the advancing and receding contact angles. Typical results are shown below for baseline silicon and silicon with monolayer graphene coating. The measured advancing contact angle for silicon (~36 deg: Fig. S1a) was very similar to monolayer graphene coated silicon (~35 deg: Fig. S1b). Similarly the receding water contact angle on silicon (~30 deg: Fig. S1c) was also similar to that of monolayer graphene coated silicon (~31 deg: Fig. S1d). The difference between the advancing and receding contact angles (i.e. the contact angle hysteresis) for the samples were in the range of 4 to 6 degrees. (a) (b) (c) (d) Figure S1: Advancing water front for baseline silicon (a) and the monolayer graphene coated silicon (b). Corresponding images for the receding water front for silicon (c) and monolayer graphene coated silicon (d). 2 NATURE MATERIALS | www.nature.com/naturematerials SUPPLEMENTARY INFORMATION DOI: 10.1038/NMAT3228 © 2012 Macmillan Publishers Limited. All rights reserved
DOE:10.1038/NMAT3228 SUPPLEMENTARY INFORMATION (2)Molecular Dynamics(MD)simulation approach: MD simulations are generally limited to nanometer-sized water droplets,which leads to non-negligible line tension force at the tri-phase junction.Therefore the apparent contact angle is usually system-size dependent.Werder et al'used MD simulations to calculate the contact angles of water on graphite with water droplets of different radii.Thus,by fitting the apparent contact angle as a function of droplet base radius to the modified Young's equation,they obtained the contact angle of a macroscopic water droplet through extrapolation to infinite droplet size. However multiple simulations with water droplet of different sizes are required and this is computationally inefficient.We utilize a new wetting system setup,which is free of system size effect on the contact angle.A slab-like simulation box is adopted which is thin in y-direction and long in x-and z-directions.Periodic boundary conditions are applied such that the water droplet is infinite in y-direction with a truncated cylindrical cross-section,as seen in Fig.S2.The advantage of this approach is that the contact line between water and substrate is straight,thus there is no contribution of line tension due to curvature.As a consequence,the macroscopic contact angle can be directly calculated through fitting the x-z projection of a nanometer-sized water droplet. To test the system size dependency of our approach and to compare with Werder's classical approach',we simulate a series of samples with 1000,2000,4000 and 8000 water molecules on top of graphite.The interaction parameters are identical to case I as in Werder's work'.For our approach,all of these simulation boxes are about 21.3 A in y-dimension.The x- and z-dimensions are made large enough for each individual sample to prevent the interaction between the sample and its periodic images.The contact angles obtained using our method and those of Werder's(sample 1,5,6.7 and 8 in Ref.1)with similar system setup and force field NATURE MATERIALS www.nature.com/naturematerials 2012 Macmillan Publishers Limited.All rights reserved
(2) Molecular Dynamics (MD) simulation approach: MD simulations are generally limited to nanometer-sized water droplets, which leads to non-negligible line tension force at the tri-phase junction. Therefore the apparent contact angle is usually system-size dependent. Werder et al1 used MD simulations to calculate the contact angles of water on graphite with water droplets of different radii. Thus, by fitting the apparent contact angle as a function of droplet base radius to the modified Young’s equation, they obtained the contact angle of a macroscopic water droplet through extrapolation to infinite droplet size. However multiple simulations with water droplet of different sizes are required and this is computationally inefficient. We utilize a new wetting system setup, which is free of system size effect on the contact angle. A slab-like simulation box is adopted which is thin in y-direction and long in x- and z-directions. Periodic boundary conditions are applied such that the water droplet is infinite in y-direction with a truncated cylindrical cross-section, as seen in Fig. S2. The advantage of this approach is that the contact line between water and substrate is straight, thus there is no contribution of line tension due to curvature. As a consequence, the macroscopic contact angle can be directly calculated through fitting the x-z projection of a nanometer-sized water droplet. To test the system size dependency of our approach and to compare with Werder’s classical approach1 , we simulate a series of samples with 1000, 2000, 4000 and 8000 water molecules on top of graphite. The interaction parameters are identical to case 1 as in Werder’s work1 . For our approach, all of these simulation boxes are about 21.3 Å in y-dimension. The xand z-dimensions are made large enough for each individual sample to prevent the interaction between the sample and its periodic images. The contact angles obtained using our method and those of Werder’s (sample 1, 5, 6, 7 and 8 in Ref. 1) with similar system setup and force field NATURE MATERIALS | www.nature.com/naturematerials 3 DOI: 10.1038/NMAT3228 SUPPLEMENTARY INFORMATION © 2012 Macmillan Publishers Limited. All rights reserved
SUPPLEMENTARY INFORMATION D0:10.1038/NMAT3228 parameters have been organized in Table 1.The contact angles of our samples do not exhibit system-size dependency once the size of the droplet is larger than 2000 molecules.The contact angle is around 1099.This value is close to the macroscopic contact angle 104 by Werder et al. Note that Werder's result might be biased by the smallest droplet,for which the contact angle has the largest uncertainty. Reference: 1.Werder,T.,Walther,J.H.,Jaffe,R.L.,Halicioglu,T.Koumoutsakos,P.On the Water-Carbon Interaction for Use in Molecular Dynamics Simulations of Graphite and Carbon Nanotubes.The Journal of Physical Chemistry B 107,1345-1352 (2003). 213AJ →X Figure S2:Side(top)and top view (bottom)of the snapshots for 4000 water molecules on double graphene layers.The dimensions are 393.5 A x 21.3 A x 200 A.Only part of the simulation system is shown.Blue,red and green dots are C,O and H atoms respectively NATURE MATERIALS www.nature.com/naturematerials 2012 Macmillan Publishers Limited.All rights reserved
parameters have been organized in Table 1. The contact angles of our samples do not exhibit system-size dependency once the size of the droplet is larger than 2000 molecules. The contact angle is around 109⁰. This value is close to the macroscopic contact angle 104⁰ by Werder et al1 . Note that Werder’s result might be biased by the smallest droplet, for which the contact angle has the largest uncertainty. Reference: 1. Werder, T., Walther, J.H., Jaffe, R.L., Halicioglu, T. & Koumoutsakos, P. On the Water−Carbon Interaction for Use in Molecular Dynamics Simulations of Graphite and Carbon Nanotubes. The Journal of Physical Chemistry B 107, 1345-1352 (2003). Figure S2: Side (top) and top view (bottom) of the snapshots for 4000 water molecules on double graphene layers. The dimensions are 393.5 Å × 21.3 Å × 200 Å. Only part of the simulation system is shown. Blue, red and green dots are C, O and H atoms respectively. 4 NATURE MATERIALS | www.nature.com/naturematerials SUPPLEMENTARY INFORMATION DOI: 10.1038/NMAT3228 © 2012 Macmillan Publishers Limited. All rights reserved
DOE:10.1038/NMAT3228 SUPPLEMENTARY INFORMATION Table.1:Comparison of the contact angle predicted by Werder's approach and our approach. The system setup is water on double layer graphene.Same sets of force field parameters are used here for both approaches. H2O molecules Contact angle (deg) H2O molecules Contact angle (deg) in the system by our new method in the system by Werder's method 1000 121.1 1000 115.5 2000 109.8 2000 111.3 4000 109.2 4000 109.2 8000 110.9 8379 108.8 17576 107.7 00 103.9a Obtained through linear fitting. (3)Effect of coating layer thickness on the wetting transparency effect The continuum model(Eq.3 in manuscript)was used to predict the effect of the coating layer thickness on the wetting transparency effect.Figure S3 shows the water contact angle transition from copper to graphite for carbon film coatings on copper with thicknesses of 0.34 nm,0.7 nm and I nm.Even the ultrathin 0.7 nm or 1 nm coatings fail to provide wetting transparency.The wetting transparency effect becomes apparent only when one goes down to 0.34 nm(ie.the thickness of graphene).This highlights the importance of graphene in its ability to provide ultra-thin conformal coatings on a variety of substrates. NATURE MATERIALS www.nature.com/naturematerials 2012 Macmillan Publishers Limited.All rights reserved
Table. 1: Comparison of the contact angle predicted by Werder’s approach and our approach. The system setup is water on double layer graphene. Same sets of force field parameters are used here for both approaches. H2O molecules in the system Contact angle (deg) by our new method H2O molecules in the system Contact angle (deg) by Werder’s method 1000 121.1 1000 115.5 2000 109.8 2000 111.3 4000 109.2 4000 109.2 8000 110.9 8379 108.8 17576 107.7 ∞ 103.9 a a Obtained through linear fitting. (3) Effect of coating layer thickness on the wetting transparency effect The continuum model (Eq. 3 in manuscript) was used to predict the effect of the coating layer thickness on the wetting transparency effect. Figure S3 shows the water contact angle transition from copper to graphite for carbon film coatings on copper with thicknesses of 0.34 nm, 0.7 nm and 1 nm. Even the ultrathin 0.7 nm or 1 nm coatings fail to provide wetting transparency. The wetting transparency effect becomes apparent only when one goes down to 0.34 nm (i.e. the thickness of graphene). This highlights the importance of graphene in its ability to provide ultra-thin conformal coatings on a variety of substrates. NATURE MATERIALS | www.nature.com/naturematerials 5 DOI: 10.1038/NMAT3228 SUPPLEMENTARY INFORMATION © 2012 Macmillan Publishers Limited. All rights reserved
SUPPLEMENTARY INFORMATION D0:10.1038/NMAT3228 92 Near complete loss of wetting transparency Graphite even with 1-layer 91 8一8 90 ▣▣layer thickness of 10.0A layer thickness of 7.0 A 88 layer thickness of 3.4 A 86 g←—Copper 85 0 2 of Layers Figure S3:Effect of coating layer thickness on the water contact angle transition response. 6 NATURE MATERIALS www.nature.com/naturematerials 2012 Macmillan Publishers Limited.All rights reserved
Figure S3: Effect of coating layer thickness on the water contact angle transition response. Copper Near complete loss of wetting transparency Graphite even with 1-layer 6 NATURE MATERIALS | www.nature.com/naturematerials SUPPLEMENTARY INFORMATION DOI: 10.1038/NMAT3228 © 2012 Macmillan Publishers Limited. All rights reserved
