The significance of graphene oxide-polyacrylamide interactions on the stability and microstructure of oil-in-water emulsions Heidi Jahandideh, a Pejman Ganjeh-Anzabi, a Steven L. Bryant,* a and Milana Trifkovic* a a Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB Canada * steven.bryant@ucalgary.ca (SB) and mtrifkov@ucalgary.ca (MT) SUPPORTING INFORMATION Number of Pages: 17 Number of Figures: 18 Number of Tables: 1 S1
Figure S1. Characterization of synthesized GO by FT-IR (top) and Raman spectroscopy (bottom). Peaks are assigned to their proper bonds in FT-IR spectrum: 850, 1085 and 1116cm -1 (C O present in epoxy, carboxylate, and epoxy, respectively), 1627 and 1715cm -1 (C = O), 2097cm -1 (CO 2 ), 2849cm -1 (C H shouldering), and 3434cm -1 (O H). 1,2 S2
Figure S2. Viscosity match of paraffin oil and 2g/L PAM solution at constant shear rate of 10 s -1. Figure S3. Viscosity histories of GO-PAM dispersions at the constant shear rate of 10 s -1 with one additional concentration in between GO-PAM1 and GO-PAM2 (dashed orange line: 0.25g/L GO, 2g/L PAM), as well as one additional concentration between GO-PAM2 and GO-PAM3 (dashed green line: 0.75g/L GO, 2g/L PAM). At the GO concentration of 0.25g/L, the dispersion viscosity decays over time as well but not as much as GO- PAM1 and remains relatively constant after 2 minutes of applied shear. GO-PAM dispersion with 0.75g/L GO- 2g/L PAM appears to have a similar viscosity to the sample with 1g/L GO-2g/L PAM and is constant throughout the measurement. S3
Figure S4. (a) Viscosity and (b) shear stress profiles of GO-PAM dispersions as shear rate is ramped from 0.01 to 100 s -1. The viscosity curves shown in (a) show the shear thinning behavior of these dispersions under applied shear. While GO-PAM1 and GO-PAM3 have similar shear thinning behavior, viscosity of GO-PAM2 plateaus at higher shear rates. This observation suggests the re-dispersion of smaller GO-PAM2 flocs. S4
Figure S5. LSCM images of GO-PAM flocs show their large sizes. Increase in GO concentration has substantially increased the floc size in GO-PAM dispersions. While DLS results revealed the particle size of GO-PAM1 to be less than 10µm, LSCM images shown here display that (a) GO-PAM2 contains flocs that are generally smaller than 50 µm and (b) GO-PAM3 consists of flocs that are often larger than 100µm in size. S5
Figure S6. ZP of GO (left) and PAM (right) measured at different ph values. Note that the red circles denote the values corresponding to the individual components values as used in this study. The surface charges of GO and PAM are found to be -28±4 and -87±5 mv, while their ph values were 2-3.5 and 8-9, respectively. S6
Figure S7. Storage and loss moduli vs. angular frequency of PAM at different ph values. It is shown that PAM has a lower storage and loss moduli at ph value of 2.84, which is lower than its pka of ~5 (for acrylate functional groups), suggesting that the polymer has a coiled conformation and has shrunk in size. As ph increases, the conformation of PAM evolves and become extended and chains are entangled giving the solution a higher storage and loss moduli. 3 S7
Figure S8. Storage and loss moduli vs. angular frequency of GO-PAM 3 dispersion (1g/L GO, 2g/L PAM) in absence or presence of additional NaOH. Addition of 20µL 3M NaOH to 15 ml of GO-PAM 3 increased its ph value of 2.45 to 8.62. However, the change of ph did not show any change in the storage and loss moduli values. To examine the effect of PAM conformation on its adsorption strength onto GO sheets, the same amount of NaOH was added to the stock PAM solution prior to GO addition. The same concentrations of PAM, GO and NaOH were ultimately achieved and the mixture was homogenized in the same fashion the original GO-PAM3 was prepared. Interestingly, the resultant GO-PAM dispersion has the same storage and loss moduli values (and therefore, identical complex viscosity and loss factor) remain unchanged. S8
Figure S9. Cryo-TEM images revealed the crumpled structures of GO nanosheets when dispersed in water. Figure S10. Centrifuge tubes containing GO-PAM dispersions of different GO concentrations before (left), and after (right) ultracentrifugation at 12000 RPM for 5 hours. The first vial (GO-PAM1) was determined to have a stable suspension as it did not settle substantially. S9
Figure S11. Quantification of PAM adsorption onto GO nanosheets displays that the amount of PAM adsorbed equals to ~ 1.76 times of unit mass of GO. S10
Figure S12. Camera images of vials with equal oil to water ratios containing varying amounts of PAM. Pictures are taken only minutes after mixing and it is clear that no emulsion was formed when PAM is used solely. Formation of foam in these samples is a side effect of using probe sonicator as the mixing tool. Upon destruction of the said foams, polymer molecules were attached to the internal surface of glass vials. S11
Figure S13. The interfacial tension (IFT) measurements for paraffin oil and different water phases at room temperature are shown here. Even though the addition of 2g/L PAM to the water phase was able to reduce the IFT by 33%, it did not form an emulsion at any concentration (Figure S8). On the other hand, addition of adequate amounts of graphene oxide resulted in a stable emulsion but lowered the IFT by only 23±1%. This suggests that in GO-PAM emulsions, part of the stability can be due to the fact that PAM lowers the IFT making it easier for the amphiphilic GO particles to remain at the O/W interface. S12
Figure S14. Camera images of emulsions in 2-dram vials. Pictures are taken 1 week after preparation. S13
Figure S15. Oil droplet size distributions recorded for GO emulsions: (a) G2 and (b) G3 recorded 1, 7, 14, 21, 28, and 210 days (7 months) after emulsification. As shown, the coalescence of GO emulsions takes place in the first 2 weeks. Moreover, higher GO content in G3 has resulted in a smaller droplet size and a narrower distribution. S14
Figure S16. Oil droplet size distributions recorded for GO-PAM emulsions: (a) GO-PAM1, (b) GO-PAM2, and (c) GO-PAM3 recorded 1, 7, 14, 21, 28, and 210 days (7 months) after emulsification. As shown, some of GO-PAM1 emulsion droplets coalesce significantly while the majority of droplets remain in the smaller side of S15
the droplet size spectrum. This is mainly due to the insufficient amount of GO to provide a uniform droplet surface coverage for all droplets of GO-PAM1 sample. GO-PAM2 exhibited the least change in its droplet sizes and distribution, which is in agreement with its slow creaming rate. Moreover, higher GO content in GO- PAM3 has resulted in larger flocs which are simply unable to emulsify small oil droplets and therefore, this sample displays the largest and widest droplet size distribution. Figure S17. Optical images of GO-PAM emulsions taken 7 months after emulsification. (a) GO-PAM1 large oil droplets covered with smaller oil droplets. (b) An up-close image of GO-PAM1 sample showing the distribution of small droplets residing on the surface of a large oil droplet. (c) Oil droplets in GO-PAM2 emulsion sample are more uniform in size and are less than 10 µm in diameter. (d) GO-PAM3 emulsion sample has droplets that are larger than GO-PAM2 droplets but smaller than the large oil droplets in GO- PAM1. S16
Figure S18. A summary of the LSCM images of paraffin oil in water emulsion stabilized by different GO concentrations in absence or presence of 2g/L PAM. S17
Table S1. Normalized average interfacial areas per unit emulsion volume calculated for each sample based on their acquired LSCM 3D images. As shown below, GO-PAM2 whose oil droplets were found to be smallest in size exhibit the largest normalized interfacial area. Moreover, oil volume fractions are listed here to support the emulsion creaming rate and droplet packing trends observed. As shown here, GO-PAM2 with the slowest creaming rate has the smallest oil volume fraction as it simply holds more water. Sample ID Normalized interfacial area (µm 2 /µm 3 ) Oil volume fraction G1 N/A N/A G2 0.0238 0.6323 G3 0.0466 0.6436 GO-PAM1 N/A N/A GO-PAM2 0.0734 0.4993 GO-PAM3 0.0152 0.6017 REFERENCES 1 H. J. Kim, S. M. Lee, Y. S. Oh, Y. H. Yang, Y. S. Lim, D. H. Yoon, C. Lee, J. Y. Kim and R. S. Ruoff, Unoxidized graphene/alumina nanocomposite: Fracture-and wear-resistance effects of graphene on alumina matrix, Sci. Rep.,, DOI:10.1038/srep05176. 2 A. Kumar, L. Rout, R. S. Dhaka, S. L. Samal and P. Dash, Design of a graphene oxide- SnO 2 nanocomposite with superior catalytic efficiency for the synthesis of β-enaminones and β-enaminoesters, RSC Adv.,, DOI:10.1039/C5RA03363B. 3 M. D. Bishop, S. Kim, A. M. Palomino and J. S. Lee, Deformation of tunable claypolymer composites, Appl. Clay Sci.,, DOI:10.1016/j.clay.2014.08.014. S18