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: [email protected]; [email protected]
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.