Supporting Information

1 Supporting Information Linear and Star Poly(ionic liquid) Assemblies: Surface Monolayers and Multilayers Andrew J. Erwin, Weinan Xu,, Hongkun He, Krzysztof Matyjaszewski, and Vladimir V. Tsukruk*, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245 USA. Center for Macromolecular Engineering, Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USA Keywords: poly(ionic liquid)s, layer by layer assembly, dewetting behavior, Langmuir- Blodgett monolayers, ultrathin films, porous morphologies *Vladimir@mse.gatech.edu Calculation of Macromolecular Dimensions End-to-end molecular dimensions R of linear PIL chains were calculated using Materials Studio Software according to the following procedure 1 : (1) a consistent-valence forcefield (CVFF) energy minimization, (2) NVT thermodynamic ensemble molecular dynamics employed to heat the PIL up to 473K (above T g ) and allow the chains to relax to the desired conformation, (3) a final CVFF energy minimization. Extended confirmation corresponds to a dihedral angle set to 0 while the dihedral angle was randomized for the random coil model. From the calculated R value of the random coil linear molecule, the statistical monomer length b (~1.15 nm) can be ascertained based on its degree of polymerization N. This in turn allows for the determination of the radius of gyration R g for linear chains assuming random walk configurations in three dimensions (i.e. at the θ temperature): 2 R g,linear = Nb2 6 (1) For star macromolecules with f arms, the linear and branched R g values can be related from the ratio: g = R 2 g,linear R2 = (3f 2) (2) g,star f 2 thereby allowing for a simple estimation of the radius of gyration of the star PILs in this report. 2 Note that this model assumes excluded volume effects for branched molecules are similar to those in their linear analogues. Furthermore, it is also assumed for these calculations that full initiation of the PILs from all 14 initiating arms occurred. This is justified by the well-defined star architectures and low polydispersity in arm lengths as

2 measured by GPC of star polymers and their cleaved arms formed via ATRP from BCD cores in similar studies. 3 Pressure-Area Isotherms An increase in surface pressure of the gaseous phase following the initial compression was observed for all samples, indicating a residual surface tension in the monolayer (Figure S1). This tension is likely a product of strong secondary intermolecular forces that lead to enhanced hydrophobic interactions and chain entanglement. 1 The residual pressure disappears only at very large expansions, suggesting that intermingled molecules are kinetically locked together upon expansion, and only after sufficiently long times can they recover their initial conformation. This is supported by AFM phase images of LB monolayers deposited from the gaseous phase before and after Figure S1. Compression/expansion hysteresis pressure-area isotherms of the linear (a) and a star (b) PIL sample. Solid and dashed lines indicate compressions and expansions, respectively. Black, red, and blue curves represent the first, second, and third cycles, respectively. Figure S2. High resolution AFM phase images of LB monolayers of SPIL-2 in the gaseous phase before (a) and after (b) the first compression/expansion at the same trough area. Scale bar is 100 nm; Z scale is 5.

3 compression (Figure S2). Figure S3. AFM phase images of LB monolayers LPIL (a), SPIL-1 (b), SPIL-2 (c), and SPIL- 3 (d) at a surface pressure of 5 mn/m. Scale bar is 100 nm; Z scale is 5. Figure S4. AFM phase images of LB monolayers LPIL (a), SPIL-1 (b), SPIL-2 (c), and SPIL- 3 (d) at a surface pressure of 20 mn/m. Scale bar is 100 nm; Z scale is 15.

4 Figure S5. ATR-FTIR spectra (a) measured from a bare Si substrate (black) and 20 bilayer PSS/SPIL-2 LbL films (red). Peak values corresponding to the VBBI + repeat unit (black) and the Tf 2 N - anion (blue) are displayed as a function of the bilayer number (b). Note that FTIR measurements were performed for both PSS-capped (half integer number of bilayers) and SPIL-capped (integer) films. The black and blue lines denote linear and exponential fits to the data, respectively.

5 Table S1. Thickness, roughness, and contact angle measurements for LbL films. Assembly Condition Dip-LbL MeOH Wash SA-LbL MeOH Wash SA-LbL H2O Wash SA-LbL H2O Wash 0.01M NaCl Growth Rate Ellipsometry 1μm x 1μm 10μm x 10μm Contact Sample (nm/bilayer) Thickness (nm) Rq (nm) Rq (nm) Angle ( ) LPIL 0.14 ± 0.01 4.8 ± 0.6 1.3 ± 0.4 1.8 ± 0.3 67.6 ± 2.4 SPIL-2 0.10 ± 0.02 4.4 ± 0.4 2.0 ± 0.2 2.4 ± 0.3 65.1 ± 2.8 LPIL 0.89 ± 0.01 18.4 ± 0.7 3.3 ± 0.4 3.4 ± 0.4 70.9 ± 2.9 SPIL-1 0.97 ± 0.01 21. 4 ± 0.9 1.5 ± 0.3 1.7 ± 0.4 72.5 ± 3.0 SPIL-2 0.89 ± 0.01 16.9 ± 0.8 2.5 ± 0.4 3.2 ± 0.6 70.6 ± 0.8 SPIL-3 1.10 ± 0.01 24.0 ± 1.5 1.8 ± 0.4 2.5 ± 0.4 75.2 ± 1.3 LPIL 1.49 ± 0.03 30.7 ± 2.1 4.6 ± 1.4 3.6 ± 0.5 72.3 ± 1.8 SPIL-1 1.45 ± 0.21 28.8 ± 0.6 3.8 ± 1.6 3.4 ± 1.2 74.3 ± 1.5 SPIL-2 1.84 ± 0.02 27.8 ± 6.6 5.8 ± 1.9 5.7 ± 1.5 79.8 ± 1.3 SPIL-3 1.50 ± 0.06 29.0 ± 0.7 8.8 ± 1.9 7.8 ± 2.4 80.0 ± 0.7 LPIL 2.27 ± 0.06 43.3 ± 4.0 8.2 ± 2.1 10.9 ± 2.3 70.6 ± 2.2 SPIL-2 2.30 ± 0.08 42.9 ± 1.2 6.8 ± 2.3 10.4 ± 0.7 77.5 ± 2.1 Figure S6. (a,b,d,e) AFM topography and (c,f) phase images for dip-lbl PEI-[PSS/PIL] 20 films containing (a-c) LPIL and (d-f) SPIL-2. PSS layers were washed with water; PIL layers were washed with MeOH. Scale bar for (a,c,d,f) is 100 nm; scale bar for (b,e) is 1 μm. Z scale is 6 nm for topography images and 7 for phase images.

6 Figure S7. Thicknesses of SA-LbL films as a function molecular weight. Open and filled symbols denote LbL films constructed in water-washing and MeOH-washing conditions, respectively. Figure S8. Radially integrated PSD profiles corresponding to 1 x 1 μm 2 AFM scans of SA- LbL films washed by water.

7 Figure S9. Radially integrated PSD profiles corresponding to 10 x 10 μm 2 AFM scans of SA- LbL films washed by water (solid lines) and methanol (dashed lines). Figure S10. AFM topography images of SA-LbL PEI-[PSS/PIL] 20 film containing (a,e) LPIL, (b,f) SPIL-1, (c,g) SPIL-2, (d,h) SPIL-3. PSS layers were washed with water; PIL layers were washed with MeOH. Scale bar for (a-e) is 100 nm; scale bar for (e-h) is 1 μm. Z scale is 10 nm for top; 15nm for bottom.

8 Figure S11. SA-LbL PEI-[PSS/LPIL] 20 (a,b) and PEI-[PSS/SPIL-2] 20 (c,d), after 1 h immersion in water (a,c), and then after 1 h in MeOH (b,d). Scale bar is 100 nm; Z scale is Figure S12. Radially integrated PSD profiles corresponding to 1 x 1 μm 2 AFM scans of asassembled SA-LbL LPIL films washed by water (black line), followed by water submersion (red line), and then MeOH submersion (blue line).

9 Figure S13. AFM topographical images of SA-LbL PEI-[PSS/SPIL-2] with one complete bilayer (a), 5 bilayers (b), 10 bilayers (c), and 15 bilayers (d), and their corresponding PSD profiles (e). Inset of (e) shows R q as a function of the number of bilayers, collected from 5 independent 1 x 1 μm 2 scanning areas. Scale bar is 100 nm; Z scale is 6 nm. References 1 Xu, W.; Ledin, P. A.; Iatridi, Z.; Tsitsilianis, C.; Tsukruk, V. V. Multiresponsive Star-Graft Quarterpolymer Monolayers. Macromolecules 2015, 48, 3344-3353. 2 Mazur, J.; McCrackin, F. Configurational properties of star-branched polymers. Macromolecules 1977, 10, 326-332. 3 Chmielarz, P., Park, S., Sobkowiak, A., & Matyjaszewski, K. Synthesis of β-cyclodextrin-based star polymers via a simplified electrochemically mediated ATRP. Polymer 2016, 88, 36-42.