Supporting Information

Bio-Inspired Superhydrophilic Coatings with High Anti-Adhesion against

Mineral Scales

Tianzhan Zhang1,2, Yuefeng Wang1,5, Feilong Zhang3,5, Xiaodong Chen4,5, Guoqing

Hu4,5, Jingxin Meng1 and Shutao Wang1,5

1 CAS Key Laboratory of Bio-inspired Materials and Interfacial Science, CAS Center

for Excellence in Nanoscience, Technical Institute of Physics and Chemistry, Chinese

Academy of Sciences, Beijing, 100190, P. R. China2 College of Material Science and Engineering, Jilin Jianzhu University, Changchun,

130118, P. R. China3 Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key

Laboratory of Green Printing, Institute of Chemistry, Chinese Academy of Sciences,

Beijing, 100190, P. R. China4 The State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese

Academy of Sciences, Beijing, 100190, P. R. China5 University of Chinese Academy of Sciences, Beijing, 100049, P. R. China

Correspondence: Professor J Meng, Professor S Wang, CAS Key Laboratory of Bio-

Inspired Materials and Interfacial Science, Technical Institute of Physics and

Chemistry, Chinese Academy of Sciences, 29 Zhongguancun East Road, Haidian

District, Beijing, 100190, P. R. China.

E-mail: mengjx628@mail.ipc.ac.cn; stwang@mail.ipc.ac.cn

The anti-adhesive property of nano-hair from numerical simulation

We have carried out preliminary numerical simulations to understand the underlying

physics of anti-adhesive property of PHEMA nano-hair. Two-dimensional

simulations were based on the finite element method to consider fluid-structure

interactions between the flow and the nano-hairs using the COMSOL software. The

arbitrary Lagrangian-Eulerian technique was used to handle the deformation of the

nano-hair and the force transmission at the boundary between fluid and solid. Figure

S7a shows the setup of the numerical model. Twelve nano-hairs with length of 50 μm

and width of 0.4 μm were constructed with an interval of 0.4 μm. The bottoms of the

nano-hairs were fixed at the bottom boundary. The nano-hairs were modeled as linear

elastic solid materials considering to the physical properties of PHEMA hydrogel. The

fluid was modeled as Newtonian fluid considering to the physical properties of water.

The top part of the left domain boundary is set to be the inlet boundary. The normal

velocity at the inlet boundary was set according to the velocity profile in the pipe, as

well as a constant velocity at the top boundary. The bottom of the inlet boundary is 1

μm lower than the top of the nano-hair. The outlet condition was imposed at the top

part of the right domain boundary. No-slip boundary conditions were imposed at the

other boundaries. The simulation ran for several days on four CPUs to reach a quasi-

steady state with a physical time of about 16 s. Automatic remeshing of the

computational domain was used to reduce grid distortion. Figure S7b-c show the

initial and final meshes, respectively.

Note that the complicated interactions between the CaOx crystal with the fluid

and nanohair were excluded in the present study. The typical size of CaOx crystal is

about 2-3 μm, which is much larger than the diameter of the nanohairs. It is thus hard

for the CaOx crystals to embed in between the nano-hairs. Most likely, the interaction

between the crystals and nano-hairs happen on the top end of the nanohairs. There

may exist several mechanisms that induce the anti-adhesive property of the nanohairs.

First, the contact area between a crystal and the surface is reduced by the existing of

the structure surface of nanohairs. Second, if the relative velocity between the crystals

and nanohairs is large, the crystals could bounce back at the top of the deformed

nanoharis. Third, in practice, the nonuniform distribution of the nanohairs could likely

cause relative motions of the adjusted nanohairs, which could increase the unevenness

of the flow around the crystal moving above the surface. Lift force is likely to be

induced by the relative motion of the nanohairs. Four, if a crystal sticks to the top end

of the nanohairs, the nanohairs might bend further to throw off the crystal. All the

above mentioned factors could reduce the adhesive force of the nanohair. Our

ongoing research is dealing with more complicated situations to consider the

interactions between the crystals and nanohairs, as well as the interactions between

the nanohairs.

Figure S1. The morphology and corresponding energy dispersive X-Ray

spectroscopy (EDS) data of mineral crystals (i.e., CaOx) adhered on nanohair and flat

hydrogel coatings at room temperature.

Figure S2. The distribution of mineral crystals adhered on nanohair hydrogel from

SEM image and EDS analysis. The color lines in SEM image of a) correspond to the

EDS data of calcium elements in b-c).

Figure S3. SEM images of nanohair hydrogel coatings with different heights

including a) 0.4 ± 0.1 μm for short nanohair, b) 21.5 ± 3.0 μm for mediate nanohair,

and c) 51.0 ± 3.8 μm for long nanohair, respectively.

Figure S4. The contact angles (CAs) of two kinds of hydrogel coatings with short and

mediate nanohair. a) Short nanohair was hydrophilic with a CA of 50 ± 2°, b)

mediate nanohair was superhydrophilic with a CA of around 0°.

Figure S5. SEM images of nanohair and flat hydrogel coatings after different

incubation times in mineral solution. a) Under the dynamic state, the amounts of

crystal adhered on the nanohair hydrogel coatings are always less than that on the flat

ones, revealing that anti-adhesion against mineral crystals of nanohair coatings. b)

Under the static state, the adhesion amounts of crystals on both coatings keep similar

after different incubation times, suggesting that static state is not benefit for resisting

mineral adhesion.

Figure S6. The excellently structural stability of nanohair hydrogel coatings at harsh

conditions. SEM images show the morphology of nanohair hydrogel coatings after

incubating at different conditions including initial state (top), after incubating at a

high flow rate of 717 cm/min (middle) and a high temperature of 80 oC (bottom).

Nanohair coatings always keep their structural features, suggesting their excellently

structural stability.

Figure S7. a) Simulation setup. b) Initial mesh. c) Final mesh.

Figure S8. Distributions of velocity magnitude for a) nanohair and b) flat surfaces.

Figure S9. The morphology and corresponding EDS data of mineral crystals (i.e.,

CaCO3) adhered on nanohair and flat hydrogel coatings at a high temperature of 80

oC.