Supporting Information: Bio-inspired Hierarchical Macromolecule-nanoclay Hydrogels for Robust Underwater Superoleophobicity By Ling Lin, 1,3 Mingjie Li, 2,3 Li Chen, 1,3 Peipei Chen, 2,3 Jie Ma, 1 Dong Han, 2 * Lei Jiang 1 * 1. Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Organic Solids, Institute of Chemistry Chinese Academy of Sciences, Beijing 100190, P. R. China 2. National Center for Nanoscience and Technology, Beijing 100190, China 3. Graduate University of Chinese Academy of Sciences, Beijing, 100049, P. R. China To whom correspondence should be addressed: jianglei@iccas.ac.cn, dhan@nanoctr.cn 1
Figure S1 Figure S1. Oil static contact angles (CAs) on different hydrogel surfaces with increasing C clay. Red curve represents bio-inspired hierarchical surfaces, while black curve represents smooth surfaces. By constructing hierarchical surfaces, hydrogels achieve superoleophobicity. Figure S2 Figure S2. Oil static contact angles (CAs) on different C-hydrogel surfaces using n-decane as the detecting oil. Substrate (S) = hydrogel, Liquid (L) = n-decane, Medium = water (W). a) Smooth surface shows oleophobicity with an oil CA of 144.5±1.4. b) Hierarchically micro- /nanostructured surface exhibits superoleophobicity with an oil CA of 156.2±1.6. The results confirm that hydrogels with hierarchical surfaces show superoleophobicity to different oils. 2
Figure S3 Figure S3. Compressive properties of as-prepared traditional PNIPAAm hydrogels (Thydrogels) with different cross-linking density (chemically cross-linked by BIS). a) Stressstain curves of T-hydrogels. As the cross-linking density decreases, strain at fracture increases. b) The compressive modulus enhances with the increase of cross-linking density, calculated from the slope of initial liner area (10-20%). Compared with C-hydrogels, T- hydrogels possess low modulus and stress, which are limited for the applications. 3
Figure S4 Figure S4. Tensile properties of hybrid PNIPAAm-nanoclay hydrogels (C-hydrogels). a) Photographs of C- hydrgel during a tensile test. C-hydrogel can be elongated extremely, while T-hydrogel is too fragile to be applied in our experiments. b) Stress-stain curves of C- hydrogels with different clay content. The tensile strength enhances with increasing C clay, without sacrificing most of the extensibility. c) The tensile modulus of C- hydrogels increases monotonically with increasing C clay. The modulus was calculated from the slope of initial liner area (20-50%). 4
Figure S5 Figure S5. Dynamic underwater oil-adhesion measurements on hydrogel surfaces with different preloads (3 µl n-decane droplet as the detecting oil). a) Statistical histogram of the adhesion forces on smooth and hierarchical surfaces with increasing C clay. On hierarchical surfaces, oil adhesion is largely reduced when no preload appears. b) Statistical histogram of the adhesion forces on hierarchical surfaces with increasing C clay, when different preloads are performed. High clay content hydrogel shows robust ultra-low affinity to the oil. 5
Figure S6 Figure S6. The approach force curves of AFM on hydrogel surfaces with different clay content. a) The small value of force curve slope on T-hydrogel surface indicates the low surface mechanical strength. The sharp slope of force curve on C-hydrogel surface shows high surface mechanical strength. b) Statistical values of approach slopes on different clay content hydrogels. 6
Figure S7 Figure S7. Energy dispersive spectroscopy (EDS) images of the element distribution on the surface of different C-hydrogels, in which C belongs to PNIPAAm, Si and Mg belong to the clay. a) Surface element distribution of low clay content hydrogel (C-05). b) Surface element distribution of high clay content hydrogel (C-25). With the increase of clay content (from C- 05 to C-25), the amount of Si and Mg increases while the amount of C decreases, indicating the increased proportion of clay on the surface. 7
Figure S8 Figure S8 Transmission electron micrograph (TEM) images of ultrathin films of dried C- hydrogels at a magnification of 100 000. a) Low clay content hydrogel (C-05). b) High clay content hydrogel (C-25). It is found that the clay is substantially exfoliated and dispersed homogeneously throughout the polymer matrix. With the increase of clay content (from C-05 to C-25), the number of exfoliated clay sheets largely increases. The arrows point at the exfoliated clay sheets. 8