Supporting Information

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1 Supporting Information Hierarchical Polymer Brushes with Dominant Antibacterial Mechanisms Switching from Bactericidal to Bacteria repellent Shunjie Yan a,c, Shifang Luan a,*, Hengchong Shi a, Xiaodong Xu b, Jidong zhang a, Shuaishuai Yuan a, Yuming Yang a, and Jinghua Yin a,* a State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun , People s Republic of China b Polymer Materials Research Center and Key Laboratory of Superlight Materials & Surface Technology, Ministry of Education,College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin , People s Republic China c University of Chinese Academy of Sciences, Beijing , People s Republic of China * Corresponding authors. Tel.: ; fax: addresses: sfluan@ciac.ac.cn; yinjh@ciac.ac.cn 1

2 Scheme S1. Schematic of the immobilization of silane-terminated SBDC photoiniferter on the silicon substrate (A) and construction of hierarchical architecture via photograft polymerization (B). 2

3 Table S1. XPS data of the samples (dry state). Samples UV exposure time / [min] Composition (at.%) * [C] [O] [N] [S] Si-SBDC Si-g-QAC Si-g-QAC-b-SBMA Si-g-SBMA * The surface composition of the dried samples was determined via X-ray photoelectron spectroscopy (XPS; VG Scientific ESCA MK II Thermo Avantage V 3.20 analyzer) with an Al Kα(hν= ev) anode mono-x-ray source at a detection angle of 90. The spectra were collected over a range of ev, and high-resolution C 1s spectra were collected. The atomic concentrations of the elements were determined by the peak-area ratios. 3

4 Figure S1. Water contact angles and thicknesses of the samples. (a) pristine Si, (b) Si-g-QAC, (c) Si-g-QAC-b-SBMA, (d) Si-g-SBMA. *The water contact angle was measured on Drop Shape Analysis System (DSA; KRÜSS GMBH, Germany) by a sessile water drop method. **The thickness of the sample was measured using an Alpha-Step D-100 Stylus Profiler (KLA- Tencor, USA). Error bars: standard deviations, n = 3. The graft density of the polymer layer was calculated using the following equation:. Where σ b is the graft density, M nb is number average molecular weight of grafted chains, h b is the polymer layer thickness, ρ b is density of copolymer and N A is the Avogadro s number. 1 As the hierarchical layer was achieved by re-growing an outer layer from the first pqac background layer in a controlled manner, the graft density of the hierarchical sample can be estimated according to the one-layer Si-g-QAC sample. The Si-g-QAC exhibited an average height of 24 nm in the dry state, and the M n value for the grafted chains was estimated as 36,000-48,000 g mol -1. 2, 3 Thus the grafting density can be calculated as 0.03 chain nm -2, corresponding to the moderately dense regime ( chains/nm 2 ) in which graft chains overlap each other but the volume fraction of polymer in the layer is still low. 4 4

5 Figure S2. High-resolution N 1s and Br 3d spectra of the samples. According to the XPS N 1s core-level spectra, the ratios of quaternization on the pqac brush were estimated as 78% and 71% for the Si-g-QAC and Si-g-QAC-b-SBMA surfaces, respectively. 5

6 pristine Si Si-g-QAC Si-g-SBMA Si-g-QAC-b-SBMA Figure S3. AFM three-dimensional images and root mean square roughness (RMS) values of the samples. The surface morphology of the samples was examined by atomic force microscopy in contact mode (AFM; SPA300HV with a SPI 3800 controller, Seiko Instruments Industry). The surface morphology and root-mean-square roughness were provided by AFM analysis. 6

7 pristine Si Si-g-QAC Si-g-QAC-b-SBMA S. aureus (A) pristine Si Si-g-QAC Si-g-QAC-b-SBMA E. coli (B) Figure S4. Representative CLSM images of S. aureus (A) and E. coli (B) on the samples in dry conditions. Bacterial aqueous suspension (10 8 cells ml 1 ) was sprayed onto the samples, followed by incubating for 2 h. 7

8 Si-g-SBMA S. aureus E. coli SEM CLSM 8

9 pristine Si Si-g-QAC Si-g-QAC-b-SBMA S. aureus (A) pristine Si Si-g-QAC Si-g-QAC-b-SBMA E. coli (B) Figure S6. Representative CLSM images of S. aureus (A) and E. coli (B) on the samples after the releasing procedure. The samples contact with bacteria (10 8 cells ml 1 ) for 2 h in dry conditions, followed by releasing procedures in wet condition. 9

10 (A) (B) Figure S7. Percentages of S. aureus (A) and E. coli (B) releasing from the samples. (a) pristine Si, (b) Si-g-QAC, (c) Si-g-QAC-b-SBMA. The quantitative data are calculated from CLSM images before and after the releasing procedure (Figure S3 and Figure S5) by using Image J software. Error bars: standard deviations, n = 3. 10

11 Table S2. XPS data of Si-g-QAC-b-SBMA in dry and hydrated states. Composition (at.%) * [C] [O] [N] [S] dry state hydrated state *For the XPS measurements in pseudo-hydrated states, the samples were immersed in water overnight, dried under vacuum in an auxiliary deaeration chamber of the XPS machine and then immediately measured. 5 Quantitative analyses showed the C, N and S atom compositions increased after immersion in water, which suggested that the psbma polymer chains were enriched at the outmost layer. 11

12 Figure S8. High-resolution C 1s XPS spectra of Si-g-QAC-b-SBMA in the dry and hydrated states. Upon immersion in water, the characteristic O=C O peak (288.6 ev) of the QAC species decreased while the characteristic O=C N peak (287.3 ev) of the SBMA species increased, indicating a strong swelling of the outer block on the Si-g-QAC-b-SBMA surface. 12

13 Table S3. Static WCAs of the samples in dry and hydrated conditions. Si-g-QAC Si-g-QAC-b-SBMA WCAs in dry conditions WCAs in hydrated conditions* The difference of WCAs *For the water contact angles (WCAs) measurements of the hydrated surfaces, the samples were placed in distilled water overnight at ambient temperature. After the residual water on the samples was carefully removed under a nitrogen flow, the WCAs measurements were conducted immediately. Under the experimental conditions as applied with our samples, there is a water layer present on the surface. No obvious change of the WCAs in dry and hydrated conditions was found for Si-g-QAC due to the homogeneous pqac brushes on the surface. As expected, Si-g-QAC-b-SBMA were more sensitive to the aqueous environment, and the change of WCAs between the dry and hydrated conditions was as high as ~ 10. This could be attributed to that the psbma chains collapsed in a dry state, then the collapsed psbma brush would try to maximize the polymer-solvent contacts and swelled in wet conditions. 6 13

14 Table S4. OCAs of the samples in dry and hydrated conditions. Si-g-QAC Si-g-QAC-b-SBMA the difference of OCAs OCAs in dry conditions* 1 underwater OCAs** 14 * For the oil contact angles (OCAs) measurements under dry conditions, the samples were thoroughly dried in a vacuum oven at 40 C for 24 h. A oil droplet (2 µl, tetrachloromethane) was dropped onto the dry surface with a microsyringe and then the OCAs of the samples were recorded timely. The OCAs of Si-g-QAC-b-SBMA was similar to that of Si-g-QAC, suggesting that the SBMA block collapsed in order to minimize as much as possible its contact with the oil (tetrachloromethane) and the QAC block eventually dominated the surface properties in dry conditions. 7 While in the presence of water, which is a good solvent for the SBMA, the psmba groups on Si-g-QAC-b-SBMA would be highly hydrated to preferentially occupy the outer-most layer, thereby a much larger OCA (152 ) was obtained for the hierarchical Si-g- QAC-b-SBMA, compared with OCA (138 ) for Si-g-QAC. 14

15 E. coli Si-g-SBMA Si-g-QAC-b-SBMA Si-g--QAC pristine Si S. aureus Figure S9. Representative SEM images of S. aureus and E. coli on the samples. The samples were exposed to PBS suspension of bacteria (108 cells ml 1) for 2 h. 15

16 S. aureus Day 1 Day 2 Day 4 Si-g-QAC-B-SBMA Si-g-QAC E. coli Day 1 Day 2 Day 4 Si-g-QAC-B-SBMA Si-g-QAC Figure S10. Representative CLSM images of the Si-g-QAC and Si-g-QAC-b-SBMA samples. The samples were incubated in growth medium containing bacteria cells (initial concentration: 10 6 cells/ml) for 1, 2, and 4 days. The bacterial suspension was changed every 24 h. Scale bar is 50 µm. 16

17 Table S5. Static WCAs in hydrated conditions and underwater OCAs of the samples. Si-g-QAC-b-SBMA Si-g-SBMA WCAs in hydrated conditions* underwater OCAs** * Although a slightly higher level of WCA was achieved for the Si-g-QAC-b-SBMA compared to the Si-g-SBMA, the surface hydrophilicity (WCA: 20.8 ) of the hierarchical surface is sufficient to resist bacterial adhesion. 8 **The underwater OCAs test is additional evidence that the samples containing block SBMA brushes (Si-g-QAC-b-SBMA) share strikingly similar surface characteristics with the homo-sbma modified samples (Si-g-SBMA). When in contact with aqueous solutions, the SBMA moieties of hierarchical Si-g-QAC-b-SBMA surface are highly hydrated and migrated to the surface in order to maximize the contact with water, so the hydrophobic QAC moieties would be buried. 9 17

18 Si-g-SBMA Day 1 Day 2 Day 4 E. coli S. aureus Figure S11. Representative CLSM images of the Si-g-SBMA samples. The samples were incubated in growth medium containing bacteria cells (10 6 cells/ml) for 1, 2, and 4 d. The bacterial suspension was changed every 24 h. Scale bar is 50 µm. 18

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