Journal of Alloys and Compounds 765 (2018) 677e684
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
Influence of particle size in fluorine free corrosion resistance
superhydrophobic coating - Optimization and stabilization of interface
by multiscale roughness
C. Anitha a, c, S. Syed Azim a, c, Sundar Mayavan b, c, *
a
b
c
Corrosion and Materials Protection Division, CSIR e Central Electrochemical Research Institute, Karaikudi 630 003, India
Lead Acid Battery Section, ElectroChemical Power Soruces Division, CSIR e Central Electrochemical Research Institute, Karaikudi 630 003, India
Academy of Scientific and Innovative Research, New Delhi, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 April 2018
Received in revised form
15 June 2018
Accepted 18 June 2018
Available online 22 June 2018
Fluorine free superhydrophobic coatings with stabilized air-water interface had been fabricated by utilising different particle sized silica. Coatings were formulated with various composition of different sized
nanosilica's along with nanotitania and aluminium stearate embedded in a matrix of silicone resin of Mn
~1,65,000. The as-prepared coating exhibited higher contact angle (CA) 152.5 along with high mechanical properties like abrasion, adhesion and impact resistance. As particles with different sizes were
incorporated in the coating, the interface was stabilized during immersion in water uptake study. In
addition most of these coatings also exhibited exceptional corrosion resistance withstanding upto 1000 h
of salt spray.
© 2018 Elsevier B.V. All rights reserved.
Keywords:
Nanosilica
Silicone resin
Superhydrophobic
Corrosion resistance
Water uptake
1. Introduction
Superhydrophobicity had sprouted in later 1970's and extended
its branches in both experimental as well as theoretical research. In
the recent decades superhydrophobic surfaces with surpassed CA
(contact angle) of 150 and lower tilting angle (TA) are being
explored in different arenas like self-cleaning [1] wind shields for
automobiles, stain resistant textiles [2], anti-soiling architectural
coatings [3] and so on. Mostly, these surfaces are fabricated by
using low surface energy fluoro materials with appropriate surface
roughness [4e6]. Besides their low surface energy, the shortcomings associated with fluoro compounds are their intoxication to
human beings [7] and environment along with high price. Superhydrophobic coatings that are free of fluorine [8e10] are an active
area of research whereas in this study we had fabricated fluorine
free superhydrophobic coatings with stabilized interface with the
* Corresponding author. Lead Acid Battery Section, ElectroChemical Power
Soruces Division, CSIR e Central Electrochemical Research Institute, Karaikudi 630
003, India.
E-mail addresses: anithachemi16@gmail.com (C. Anitha), azimcecri@gmail.com
(S. Syed Azim), sundarmayavan@cecri.res.in (S. Mayavan).
https://doi.org/10.1016/j.jallcom.2018.06.214
0925-8388/© 2018 Elsevier B.V. All rights reserved.
help of different particle sized nanosilica. In our previous work we
had produced superhydrophobic coating using silicone resin and
nanosilica and tuned the micro/nano roughness by changing the
concentration of nanosilica. As a continuation of our previous work,
where nanosilica of size 50 nm alone were used whereas here
combination of nanosilica with different sizes were used to increase
the hierarchical roughness which endow stability to CassieeBaxter
state (CB).
Customarily, superhydrophobic surfaces are elucidated by two
states, namely sticky Wenzel state and easy roll off CB state. Wenzel
state is a homogenous state where there is no entrapped air but in
CB state air is entrapped and exists in heterogeneous state. CB
composite state is preferred and desirable for many practical applications because the entrapped air acts as a cushion and induce
collateral self-cleaning property [11,12]. Downside being the CB
state is metastable and collapse into Wenzel on external perturbations [13], gravitational force, capillary force [14], critical hydrostatic pressure [15] and nucleation/condensation of water [16]
within the micro/nano roughness [17]. CB impalement take place
more readily because it is also energetically more favourable. Sustaining the stability of the CB state is a major challenge which can
be done by taking advantage of nature's resourcefulness.
Mostly superhydrophobic structures observed in nature are
678
C. Anitha et al. / Journal of Alloys and Compounds 765 (2018) 677e684
found to have hierarchical micro/nano roughness. Lotus leaf, the
epitome of superhydrophobicity have microroughness with nano
level asperities [18]. Mostly the transition between CB state and
Wenzel are irreversible because of the energy barrier in between
where CB state rest at a higher energy state [19]. Many theoretical
and experimental studies were carried out with different structural
shapes and sizes to study the stability of SA (sliding angle) interface
of CB state. With increased pillar height and decreased distance
between adjacent pillars the SA interface was stabilized [20]. Thus,
to effectively resist the impalement of less stable CB interface and
to hamper the transition, multiscale hierarchical roughness is
needed [21]. Mostly, CB interface was studied on a microscopic
scale with few microliter of water droplet with the aid of external
stimuli. In this study in addition to FESEM analysis, the as-prepared
coatings were studied by water uptake and water vapour permeation studies in a macroscale. It is noteworthy that these coatings
also possessed markedly high corrosion resistance behaviour in salt
spray. This process of creating superhydrophobicity has a vital
significance in industrialization on account of the advantages
associated with them like low cost, easy to construct in the field and
can be applied over large area.
2. Experimental
2.1. Materials and methods
2.1.1. Materials
Nanosilica (50 nm), Nanosilica (250 nm), Nanosilica (500 nm),
nanotitania (20 nm) were procured from nanoshell. Silicone resin
of molecular weight Mn ~165000 was purchased from Wacker
silicones. Xylene, magnesium silicate and aluminium stearate of LR
grade were used. All chemicals were utilized as such without
further purification.
2.1.2. Preparation of coating
Coatings with varying composition of pigments were prepared
accordingly as given in Table 1. Silicone resin of molecular weight
Mn ~165000 was used as the binder. Pigment volume concentration (PVC) of the coating was fixed as 15% with 36% volume solids
(VS) and the concentration of nanosilica in the 15% PVC was fixed as
60%. Calculated amount of pigments were dispersed in the silicone
matrix with intended amount of solvent (Xylene) in a high speed
homogenizer for 20 min. After the fineness of coating was checked
in tapered Hegman gauge, the prepared coatings were coated over
precleaned mild steel panels using a spray gun with an air pressure
of 2.5 kg/cm2. The coatings were dried at room temperature and
evaluated after seven days of curing.
2.2. Characterizations
Static water contact angle measurements for the coatings were
made by OCA 35 Data Physics goniometer with Millipore water by
LaplaceeYoung fitting. CA were measured at five different places.
Morphology of the coatings were analysed by field emission
scanning electron microscope Carl Zeiss AG (Supra 55VP) with an
acceleration voltage of 5e30 kV. The physical properties of the
pigments like density and oil absorption were performed according
to ASTM standards, ASTM D153 and ASTM D1483 which were given
in supplementary information. Physical properties of the coatings
in wet as well as in dry state were studied as per ASTM standards.
The resistance of the coating to abrasion was examined by ASTM
D4060. The coated specimen was mounted on a rotating disc with
constant weight of 1 kg and an abrading wheel of CS 10. The test
panels were weighed before and after testing and wear index (WI)
was calculated.
WI ¼
Weight of specimen ðbefore afterÞ abrasion X 1000
Number of abrasion cycles
Adhesive tensile strength of the coating was determined by
ASTM 4541. A dolly was fixed normal to the substrate with coating
using an epoxy adhesive and allowed to cure for 7 days. The testing
apparatus was aligned with the dolly fixed on the substrate and
force normal to the coating was applied gradually. The force
necessary to detach the dolly from the surface gave the tensile
strength of the coating. Adhesion strength of the coating was also
assessed by tape test as per ASTM D3359, where a cross hatch cut
was made with 6 cuts at 2 mm apart on a substrate. Then, an adhesive tape was applied and peeled off at 180 angle and the area
was inspected after removal of tape. It was then indexed according
to the damage in the coating. The thickness of the coating was
measured by using magnetic pull-off gauges as per ASTM D7091.
The dry film thickness of nonmagnetic coatings over ferrous metal
base is based on the attraction forces and a static magnetic field.
The force required to pull a permanent magnet from a coated
ferrous metal surface was correlated with the thickness of
nonmagnetic coating.
Flexibility of coating was determined by mandrel bend test as
per ASTM D522. The coated sample was clamped in between
mandrel and the drawbar. The lever was then moved to 180 at a
uniform velocity, kept for one second and the coated sample was
visually examined for cracks along the bent. Impact resistance of
the coating was evaluated by ASTM D6905. A standard weight
(1.8 Kg) was indented from different height over coated sample and
visually observed for damage in the coating on the other side. Salt
spray, an accelerated test to evaluate the corrosion resistance of the
Table 1
Composition of pigment in the prepared coating.
System
1.
2.
3.
4.
5.
6.
7.
8
9.
10.
11.
12.
13.
14.
SiO2 50 nm (%)
60
40
35
30
25
20
e
40
35
30
25
20
e
SiO2 250 nm (%)
SiO2 500 nm (%)
TiO2 20 nm (%)
Magnesium silicate (%)
Aluminium stearate (%)
e
20
25
30
35
40
60
e
e
e
e
e
e
Pristine
e
e
e
e
e
e
e
20
25
30
35
40
60
resin
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
C. Anitha et al. / Journal of Alloys and Compounds 765 (2018) 677e684
coating was done in a controlled corrosive environment. The coated
samples were exposed to salt solution of 5% NaCl in the form of fog,
atomized through the nozzle at 27 C with humidity greater than
95%. Edges of the samples were coated with wax to avoid galvanic
corrosion. The samples were tilted from vertical to 30 and aligned
parallel to the direction of flow of fog in the chamber. After exposure the samples were inspected periodically after cleaning with
water to remove salt deposits followed by immediate drying. Water
resistance of the coatings were tested by complete immersion of
coatings in distilled water at ambient temperature according to
ASTM D870. Weight gain of coated glass plates were checked
periodically for every 24 h after the samples were dried using tissue
paper to remove the surface moisture. Water vapour transmission
(WVT) of the coatings were evaluated as per ASTM D1653. Payne
cup method was adopted and the free film of the coating was cut in
circular form and placed with distilled water in it. It was placed in a
desiccator with calcium chloride and weight loss was measured
periodically for every 24 h and the results were plotted as weight
loss against time. WVT rate was calculated knowing the area of
exposure and period of exposure. The detailed experimental procedure for testing the coatings in the wet state were given in
supplementary information. All the experiments were done in
triplicates.
679
showed superhydrophobicity till 30:30 (30% of SiO2 20e50 nm:
30% of SiO2 250 nm and 30% of SiO2 20e50 nm: 30% of SiO2500 nm)
combination of each nanosilica (system 5 and 11). TA decreased
with increased concentration of larger sized nanoparticles as a
consequence and occurrence of different wetting state as given in
Fig. 1. With incorporation of dual sized nanosilica particles in
addition to Cassie and Wenzel state of wetting, there occurred four
different states of wetting. Fig. 1a and b occurred where the micro
and nano grooves were completely filled either by air or water and
formed micro-nano Cassie and micro-nano Wenzel state. Fig. 1c
and d occurred when the micro grooves and the nano grooves in
which one was occupied by air and the other by water and gave rise
3. Results and discussions
Interaction between various sized nanosilica in the silicone resin
matrix in superhydrophobic coatings was reviewed in terms of
their CA, morphology, porosity, water uptake and corrosion studies.
3.1. CA, TA, work of adhesion and fractional surface of solid
CA angle for pristine resin was in hydrophobic domain
(CA ¼ 90º-150 ) whereas incorporation of nanoparticles and other
pigments increased surface roughness and reached superhydrophobic domain (150 ). Wetting characteristic of silicone
resin in all system other than system 1 was dominated by the
physical roughness offered by the pigments. Incorporation of
nanosilica's in the coating enhanced higher CA and lower TA via
entanglement of air within the micro/nano roughness which can be
seen from CA values in Table 2. Wetting state of pristine resin was in
Wenzel region of homogeneous wetting where other systems with
higher CA were in mixed Cassie wetting state. In single sized
nanosilica coatings (system 2 and 8) other than system 14 all system flaunted superhydrophobicity. In dual sized nanosilica combination there evinced superhydrophobicity when there were
higher concentration of smaller nanosilica particles. The coating
Fig. 1. Different wetting states involved in multiscale roughness (a) Micro-nano Cassie
state, (b) Micro-nano Wenzel state, (c) Micro Cassie-nano Wenzel state and (d) Micro
Wenzel-nano Cassie state.
Table 2
Concentration of nanosilica with their CA, TA, W and fractional surface of solid.
System
1.
2.
3.
4.
5.
6.
7.
8
9.
10.
11.
12.
13.
14.
SiO2 20e50 nm (%)
SiO2 250 nm (%)
SiO2 500 nm (%)
Contact angle (º)
Tilting angle (º)
Work of adhesion (mN/m)
Fractional surface of solid (f1)
60
40
35
30
25
20
e
40
35
30
25
20
e
Pristine
e
20
25
30
35
40
60
e
e
e
e
e
e
resin
e
e
e
e
e
e
e
20
25
30
35
40
60
93.5
152.5
151.6
150.1
152.3
145.4
148.6
151.5
154.5
154.7
151.4
144.6
141.9
132.3
60
20
23
28
30
32
38
45
35
29
24
42
48
52
68.4
8.2
8.74
9.66
8.32
12.85
10.64
8.79
7.06
6.96
8.86
13.43
15.48
23.78
1
0.1199
0.1277
0.1413
0.1216
0.1879
0.1555
0.1286
0.1033
0.1017
0.1295
0.1964
0.2264
0.3478
*Concentration of nanosilica's alone are mentioned here other pigments like aluminium stearate and nanotitania are given in Table 1.
680
C. Anitha et al. / Journal of Alloys and Compounds 765 (2018) 677e684
to kind of mixed states namely, micro Cassie-nano Wenzel and
micro Wenzel-nano Cassie state. These mixed state resulted with
increased TA due to pinning [22] of water droplets in the micro/
nano grooves. Work of adhesion, the work done to part the water
and solid surface was given by the Dupre' equation W ¼ g LA
(1 þ cos q) [23]. It was very much higher for pristine resin because
the fractional surface of solid (f1) i.e the area of solid in contact with
the water droplet was higher for system 1. f1 was calculated by the
following equation, cos q ¼ f 1 (cos qsþ1) - 1 (where q and qs is the
CA for rough surface and for pristine resin, respectively) and the
values were given in Table 2 [24]. W was lower for other systems
except system 1 which is typical for a superhydrophobic surface
since there was lower contact area between water and solid. Based
on these CA measurements system 1, 2, 5, 8, 11 and 14 were scrutinized for further evaluation and their CA were given in Fig. 2.
pristine resin was smooth, continuous and featureless which can be
perceived from Fig. S1. CA for pristine resin was in the hydrophobic
region (93.5 ) which further endorsed the necessity of roughness to
exist in superhydrophobic state. FESEM image of system 2, 5, 8, 11
and 14 in Fig. 3 shed light on the topography of coatings which
unveiled the micro/nano roughness in them. Micro/nano structures
were observed in low magnification image (left side) which
increased surface roughness compared to that of pristine resin
rendering the coating superhydrophobic. Higher magnification
images (right side) showed nano cavities over the micron globular
structures. The micro/nano roughness was contributed by the
different composition of the coating system with pigments of
different size and proportion assimilated in them. Spraying process
gave rise to globular micro structures with microgrooves by the
agglomeration of nanopigments. The required nanogrooves were
3.2. Morphology of the prepared coating
Surface roughness an important parameter to ascertain superhydrophobicity was investigated by FESEM analysis. System 1
Fig. 2. CA for a) System 1, (b) System 2, (c) System 5, (d) System 8, (e) System 11 and (f)
System 14.
Fig. 3. FESEM images of (aeb) System 2, (ced) System 5, (eef) System 8, (geh) System
11 & (iej) System 14.
C. Anitha et al. / Journal of Alloys and Compounds 765 (2018) 677e684
ensured by the nanoparticles in them. Since, nanoparticle get
agglomerated as a consequence of their high surface energy
different sized nanosilica particles were effectively utilized to
create hierarchical micro/nano roughness required for superhydrophobicity. Hierarchical roughness was further enhanced by
solvent evaporation which triggered the formation of nanoroughness over the micron sized globules. After complete evaporation of
solvent the roughness and porosity in the coatings were enhanced
and occurred nanocavities which were non continuous and
shallow. These cavities can entrap the chloride ions and prevent
them from reaching the steel substrate via longer path length. From
the CA values it became obvious that the globular structures along
with nanoroughness and cavities created by the pigments
decreased the surface wetting nature of the coating and increased
the CA from hydrophobic regime of pristine resin to superhydrophobic for other systems given in Fig. 2. Micro/nano roughness displayed by the single sized nanosilica contained coating
system 2, 8 and 14 where explicated in their low magnification
images whereas high magnification image exposed their rough
porous surface. Fig. 3ced resided by system 5 with dual sized
nanosilica particles were less porous compared to that of single
sized nanosilica particles contained coating systems. Fig. 3geh
belonged to system 11 was least porous compared to all other
system which was an outcome of tight and efficient packing of
pigments with different sizes.
3.3. Water vapour transmission rate and water uptake studies
Porosity of the film was computed by investigating the water
vapour transmission rate as stated by ASTM D1653. WVT rate of
coating could also give information regarding corrosion protection.
Coating with low WVT rate would perform better because of low
water vapour in contact with the substrate. With constant coating
thickness of about 70 mm, the free film of different coating systems
were placed in the Payne cup and weight loss was measured
periodically. Weight loss was observed because water was lost in
the form of vapour from a low pressure region to high pressure
region [25,26]. WVT rate was calculated by plotting weight loss Vs
time. Incorporation of different sized nanosilica particles were very
well reflected in the WVT rate. As seen in Fig. 4. System 5 had the
lowest WVT rate with 3.7062 gm2h1 then comes system 11 with
Fig. 4. Plot of weight loss vs time for water vapour transmission studies of System 1,
System 2, System 5, System 8, System 11 and System 14.
681
5.2928 gm2h1 both had dual sized nanosilica particles in them
where system 1 (pristine resin) had the highest WVT rate of
9.1262 gm2h1. System 14, 8 and 2 had single sized nanosilica
particles where the WVT rates were 5.7099, 6.4328,
8.1583 gm2h1 was in between pristine resin and dual sized
nanosilica incorporated coatings. Dual sized nanosilica containing
coatings showed low WVT rate contributed by the tight and efficient packing of pigments as shown in Fig. 5.
Water droplet over a superhydrophobic surface touch the bottom of the groove as a consequence of sagging wherein the air
pockets were squeezed out by water. This wetting transition from
CB to Wenzel state are difficult to be studied because the amount of
micro and nano grooves filled with water is unknown and even
when they are filled there occur many wetting state as shown in
Fig. 1. Stability of CB state in the as-prepared coatings were
addressed through water immersion studies as per ASTM D870.
Water uptake by the coatings were checked periodically which was
reflected as weight gain. Water uptake was plotted against time and
presented in Fig. 6.
For pristine resin, system 1 the water uptake increased and then
reached a saturation state whereas all other system showed many
plateaus. Water uptake for pristine resin was lowest which indicated smooth and nonporous surface which was also substantiated
in FESEM image. For other systems presence of many plateaus
indicated many intermediate metastable states and their different
path length showed the different life span of those states. These
intermediate states can be well explained by the Gibbs energy diagram [19] with various metastable states and energy barriers as
given in Fig. 7 for various sized nanosilica. These energy barriers
were crossed by the energy provided by external vibrations, hydrostatic pressure and gravitational pull. The barriers in between
higher energy Cassie state and lower energy Wenzel states and
other metastable states can be increased by modifying the geometry of the surface with hierarchical roughness with nanostructures
overlaid on microstructures. For coating system 5 and 11 with dual
sized nanosilica particles there observed lower water uptake which
indicated less porous nature of the coating as identified in the
FESEM image. System 2, 8 and 14 with single sized nanosilica
particle where water uptake was comparatively higher than all
other system because of their porous nature as perceived in FESEM
images. Here, the plateaus were well defined with steep increase.
Water uptake data also supported the increased energy barriers by
hierarchical roughness for system 5 and 11 compared to system 2, 8
and 14. This correlation between superhydrophobic coating and
water uptake studies increase the understanding and the dynamics
of wetting transition to develope stable superhydrophobic surface
[27].
Fig. 5. (a). Optical image of Payne cup with different coating systems, (b) pictorial
representation showing tight and efficient packing of different sized nanosilica.
682
C. Anitha et al. / Journal of Alloys and Compounds 765 (2018) 677e684
Fig. 7. Qualitative correlation of Gibbs energy and various metastable states, stable
state and energy barrier in wetting transition for different sized nanosilica.
3.5. Corrosion resistance testing by salt spray
Fig. 6. (a). Plot of water uptake vs time of coatings for System 1, System 2, System 5,
System 8, System 11 and System 14, (b) Optical image of water immersion studies, (c)
Pictorial representation of CB to Wenzel transition in single sized nanosilica and dual
sized nanosilica containing coatings.
3.4. Physical properties of the coating
Coatings in the dried state consist of pigments embedded in the
polymer matrix whereas the degree of close packing of pigments
were determined by the sizes and shapes of the pigments used.
Physical properties of the coating in dry state were evaluated for
their mechanical properties and performance in salt spray test
were tabulated in Table 3. Physical parameters of the coating at wet
state are given in Table S2. Abrasion resistance of the as-prepared
coatings were less compared to that of system 1 (pristine resin).
This lower values of abrasion index for the coatings were resulted
due to the incorporation of nanoparticles, where there was less
mass loss during abrasion. Adhesion was tested by two different
method viz. pull off adhesion (ASTM D4541) and tape test (ASTM
D3359). These coatings had very good adhesion compared to that of
system 1. The tape test images were given in Fig. 8.
These coatings were exposed to salt spray with a solution of 5%
sodium chloride to test its ability for corrosion resistance. System 1
withstood only 24 h of salts spray where other coatings which
include system 2, 8 and 11 had withstood upto 1000 h of salt spray
whereas in system 5 and 14 rust spots appeared after 850 and
800 h, respectively. The images of samples before and after exposure to salt spray were given in Fig. 9. The mechanism that was
intertwined with the corrosion resistance property and the coating
can be revealed based on their wettability nature. System 1 and 14
were hydrophobic whereas system 2, 5, 8 and 11 were superhydrophobic. When water droplet come in contact with the coatings system that were hydrophobic had a greater contact time since
the water droplets move slowly which were also substantiated by
their TA values in Table 2. With increased contact time there was a
greater possibility of water and chloride ions to penetrate the
coatings and to reach the mild steel substrate. Even though both
system 1 and 14 were hydrophobic, system 14 was more hydrophobic with greater CA had better corrosion resistance than system
1. In the case of superhydrophobic coatings the contact time of
water droplets were minimum and so was their TA values which
faded the possibility of water and chloride ions contact to the
substrate which could be seen from Fig. 10. This higher duration in
salt spray was resulted as a consequence of superhydrophobicity,
thereby repelling the salt solution that was sprayed upon. Since for
the electrochemical corrosion process to occur the electrolyte
should pass through the coating and reach the mild steel substrate
which was effectively prevented in the coated systems. Blistering,
delamination or corrosion spots were not observed in the coating
until 1000 h for system 2, 8 and 11. These coatings exhibited this
unusual corrosion resistance property without any inhibitive and
sacrificial pigment in them [8]. These coatings owed this behaviour
because of its associated barrier property along with superhydrophobicity. Superhydrophobic coating with hierarchical
structures provide lowest possible contact area (f1) available for
contact with water. This reduced total surface area in contact with
water was due to entrapment of air in hierarchical structures.
In a concluding remark we had studied the transition of composite CB interface to homogeneous Wenzel state by water absorption phenomena. Morphological influence of the coating with
C. Anitha et al. / Journal of Alloys and Compounds 765 (2018) 677e684
683
Table 3
Physical properties of the coating in dry state.
Physical Property
ASTM
System 1
System 2
System 5
System 8
System 11
System 14
Abrasion index
Adhesion (MPa)
Adhesion
Dry film thickness (mm)
Flexibility
Impact test (J)
Salt spray (hours)
D4060
D4541
D3359
D7091
D522
D2794
B117
0.4243
1
4B
70e80
Passed*
Passed upto 10.58
24
0.3374
1
4B
70e80
Passed*
Passed upto 10.58
1000
0.1302
1
4B
70e80
Passed*
Passed upto 10.58
850
0.3326
1.5
4B
70e80
Passed*
Passed upto 10.58
1000
0.2220
1.5
4B
70e80
Passed*
Passed upto 10.58
1000
0.3577
1.5
4B
70e80
Passed*
Passed upto 10.58
800
*No cracks were observed upto 5 mm.
Fig. 8. Optical images for tape test adhesion for coating (a) System 1, (b) System 2, (c) System 5, (d) System 8, (e) System 11 and (f) System 14.
Fig. 9. Optical images for coating before and after exposure to salt spray test (a, g) System 1, (b, h) System 2, (c, i) System 5, (d, j) System 8, (e, k) System 11 and (f, l) System 14.
two different sized nanoparticles with varying concentration in
coating with constant PVC and VS were studied by FESEM. As
particles with different sizes were included in the coating they
stabilized and maintained the interface during immersion condition. This indicated that particles with different sizes should be
used to increase the coalescing time of composite interface thereby
the surface retains its composite interface. In addition these coatings also exhibited unusual corrosion resistance behaviour.
4. Conclusions
In this work, we have incorporated different sized nanosilica
pigments which were fabricated by simultaneous evaporation of
solvent during spray coating combined with agglomeration of
nanoparticles which tend to create micro/nano roughness. Life time
of the trapped air in the coating was correlated by water immersion
studies. Incorporation of various sized pigments stabilized the CB
684
C. Anitha et al. / Journal of Alloys and Compounds 765 (2018) 677e684
Fig. 10. Schematic illustration showing the mechanism of corrosion resistance over
superhydrophobic coating.
interface during intrusion of water. The micro/nano roughness in
the coating improves various physical properties of the coating like
abrasion, adhesion and flexibility. Most of the as-prepared coatings
possesses excellent corrosion resistance that withstand 1000 h of
salt spray. This study might help us to understand the two-scale
roughness and to fabricate various artificial surfaces with optimal
design and stable Cassie-Baxter interface.
Acknowledgements
C. A, thank Department of Science and Technology (DST), India
for availing INSPIRE fellowship (IF130877). The authors thank CMP
division, LAB section and CIF-CECRI, for their support.
Appendix A. Supplementary data
Supplementary data related to this article can be found at
https://doi.org/10.1016/j.jallcom.2018.06.214.
References
[1] J. Li, S. Lu, W. Xu, G. He, T. Yu, Y. Cheng, B. Wu, Fabrication of stable
NieAl4Ni3eAl2O3 superhydrophobic surface on aluminum substrate for selfcleaning, anti-corrosive and catalytic performance, J. Mater. Sci. 53 (2018)
1097e1109, https://doi.org/10.1007/s10853-017-1569-5.
[2] H. Zhang, C. Hou, L. Song, Y. Ma, Z. Ali, J. Gu, B. Zhang, H. Zhang, Q. Zhang,
A stable 3D sol-gel network with dangling fluoroalkyl chains and rapid selfhealing ability as a long-lived superhydrophobic fabric coating, Chem. Eng.
J. 334 (2018) 598e610, https://doi.org/10.1016/J.CEJ.2017.10.036.
[3] M.J. Mosquera, L.A.M. Carrascosa, N. Badreldin, Producing superhydrophobic/
oleophobic coatings on Cultural Heritage building materials, Pure Appl. Chem.
90 (2018) 551e561, https://doi.org/10.1515/pac-2017-0404.
[4] I.O. Arukalam, M. Meng, H. Xiao, Y. Ma, E.E. Oguzie, Y. Li, Effect of perfluorodecyltrichlorosilane on the surface properties and anti-corrosion
behavior of poly(dimethylsiloxane)-ZnO coatings, Appl. Surf. Sci. 433 (2018)
1113e1127, https://doi.org/10.1016/J.APSUSC.2017.10.096.
[5] S.M.R. Razavi, R.E. Neisiany, A. Marjani, A chemically durable superhydrophobic aluminum surface coated with silicon carbide nanoparticles and
perfluoro acrylic copolymer, Theor. Appl. Fract. Mech. 94 (2018) 181e185,
https://doi.org/10.1016/J.TAFMEC.2018.02.001.
[6] T. Bharathidasan, A. Mandalam, M. Balasubramanian, P. Dhandapani,
S. Sathiyanarayanan, S. Mayavan, Zinc oxide-containing porous boron-carbonnitrogen sheets from Glycine-Nitrate combustion: synthesis, self-cleaning,
and sunlight-driven photocatalytic activity, ACS Appl. Mater. Interfaces 7
(2015) 18450e18459, https://doi.org/10.1021/acsami.5b04609.
[7] H. Zuo, L. Chen, M. Kong, L. Qiu, P. Lü, P. Wu, Y. Yang, K. Chen, Toxic effects of
fluoride on organisms, Life Sci. 198 (2018) 18e24, https://doi.org/10.1016/
J.LFS.2018.02.001.
[8] C. Anitha, S.S. Azim, S. Mayavan, Salvinia inspired fluorine free superhydrophobic coatings, Appl. Surf. Sci. (2017), https://doi.org/10.1016/
J.APSUSC.2017.11.120.
[9] C. Anitha, S.S. Azim, S. Mayavan, Fluorine free superhydrophobic surface
textured silica particles and its dynamicseTransition from impalement to
impingement, J. Alloys Compd. 711 (2017) 197e204, https://doi.org/10.1016/
J.JALLCOM.2017.03.338.
[10] S. Gao, X. Dong, J. Huang, S. Li, Y. Li, Z. Chen, Y. Lai, Rational construction of
highly transparent superhydrophobic coatings based on a non-particle, fluorine-free and water-rich system for versatile oil-water separation, Chem. Eng.
J. 333 (2018) 621e629, https://doi.org/10.1016/J.CEJ.2017.10.006.
[11] C. Angles, Thermodynamic derivation of Wenzel's modification of Young's
equation for contact Angles; together with a theory 159 (1951) 139e140.
[12] A.B.D. Cassie, S. Baxter, Wettability of porous surfaces, Trans. Faraday Soc. 40
(1944) 546e551, https://doi.org/10.1039/TF9444000546.
[13] B. Bhushan, Modeling of Contact Angle for a Liquid in Contact with a Rough
Surface for Various Wetting Regimes, Springer, Cham, 2016, pp. 35e62,
https://doi.org/10.1007/978-3-319-28284-8_3.
[14] A. Grosman, C. Ortega, Capillary Condensation in Porous Materials . Hysteresis
and Interaction Mechanism without Pore Blocking/Percolation Process, 2008,
pp. 3977e3986.
[15] T. Maitra, C. Antonini, M.K. Tiwari, A. Mularczyk, Z. Imeri, P. Schoch,
D. Poulikakos, Supercooled water drops impacting superhydrophobic textures, Langmuir 30 (2014) 10855e10861, https://doi.org/10.1021/la502675a.
[16] Y.C. Jung, B. Bhushan, Wetting behaviour during evaporation and condensation of water microdroplets on superhydrophobic patterned surfaces,
J.
Microsc.
229
(2008)
127e140,
https://doi.org/10.1111/j.13652818.2007.01875.x.
[17] L. Piao, H. Park, Two-dimensional analysis of airewater interface on superhydrophobic grooves under fluctuating water pressure, Langmuir 31 (2015)
8022e8032, https://doi.org/10.1021/acs.langmuir.5b01847.
[18] W. Barthlott, C. Neinhuis, Purity of the sacred lotus, or escape from contamination in biological surfaces, Planta 202 (1997) 1e8, https://doi.org/10.1007/
s004250050096.
[19] A. Marmur, Soft contact: measurement and interpretation of contact angles,
Soft Matter 2 (2006) 12e17, https://doi.org/10.1039/B514811C.
[20] Y.C. Jung, B. Bhushan, Wetting transition of water droplets on superhydrophobic patterned surfaces, Scripta Mater. 57 (2007) 1057e1060, https://
doi.org/10.1016/j.scriptamat.2007.09.004.
[21] B. Bhushan, Y. Chae Jung, Wetting study of patterned surfaces for superhydrophobicity, Ultramicroscopy 107 (2007) 1033e1041, https://doi.org/
10.1016/j.ultramic.2007.05.002.
[22] N. Gao, Y.Y. Yan, X.Y. Chen, D.J. Mee, Superhydrophobic surfaces with hierarchical structure, Mater. Lett. 65 (2011) 2902e2905, https://doi.org/10.1016/
j.matlet.2011.06.088.
[23] M. Nosonovsky, B. Bhushan, Multiscale friction mechanisms and hierarchical
surfaces in nano- and bio-tribology, Mater. Sci. Eng. R Rep. 58 (2007)
162e193, https://doi.org/10.1016/j.mser.2007.09.001.
[24] M. Nosonovsky, B. Bhushan, Hierarchical roughness optimization for biomimetic superhydrophobic surfaces, Ultramicroscopy 107 (2007) 969e979,
https://doi.org/10.1016/j.ultramic.2007.04.011.
[25] S. Shreepathi, S.M. Naik, M.R. Vattipalli, Water transportation through organic
coatings: correlation between electrochemical impedance measurements,
gravimetry, and water vapor permeability, J. Coating Technol. Res. 9 (2012)
411e422, https://doi.org/10.1007/s11998-011-9376-4.
[26] P. de Lima-Neto, A.P. de Araújo, W.S. Araújo, A.N. Correia, Study of the anticorrosive behaviour of epoxy binders containing non-toxic inorganic corrosion inhibitor pigments, Prog. Org. Coating 62 (2008) 344e350, https://
doi.org/10.1016/j.porgcoat.2008.01.012.
[27] P.R. Jones, X. Hao, E.R. Cruz-Chu, K. Rykaczewski, K. Nandy, T.M. Schutzius,
K.K. Varanasi, C.M. Megaridis, J.H. Walther, P. Koumoutsakos, H.D. Espinosa,
N.A. Patankar, Sustaining dry surfaces under water, Sci. Rep. 5 (2015) 12311,
https://doi.org/10.1038/srep12311.