Fabrication of biomimetic superhydrophobic surface based on nanosecond laser-treated titanium alloy surface and organic polysilazane composite coating

Accepted Manuscript Title: Fabrication of Biomimetic Superhydrophobic Surface Based on Nanosecond Laser-Treated Titanium Alloy Surface and Organic Polysilazane Composite Coating Authors: Leyong Hu, Ling Zhang, Deren Wang, Xuechun Lin, Yiqing Chen PII: DOI: Reference:

S0927-7757(18)30632-0 https://doi.org/10.1016/j.colsurfa.2018.07.029 COLSUA 22684

To appear in:

Colloids and Surfaces A: Physicochem. Eng. Aspects

Received date: Revised date: Accepted date:

26-5-2018 17-7-2018 17-7-2018

Please cite this article as: Hu L, Zhang L, Wang D, Lin X, Chen Y, Fabrication of Biomimetic Superhydrophobic Surface Based on Nanosecond LaserTreated Titanium Alloy Surface and Organic Polysilazane Composite Coating, Colloids and Surfaces A: Physicochemical and Engineering Aspects (2018), https://doi.org/10.1016/j.colsurfa.2018.07.029 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Fabrication of Biomimetic Superhydrophobic Surface Based on Nanosecond Laser-Treated Titanium Alloy Surface and Organic Polysilazane Composite Coating

1

Institute for Advanced Materials and Technology, University of Science and

SC R

Technology Beijing, Beijing 100083, China. 2

IP T

Leyong Hu1，Ling Zhang2，Deren Wang1*，Xuechun Lin2*, Yiqing Chen3

Laboratory of All-solid-state Light Sources, Institute of Semiconductors, Chinese

State Key Laboratory of Metal Material for Marine Equipment and Application,

N

3

U

Academy of sciences, Beijing 100083, China.

A

Anshan 114002, China.

M

*Corresponding authors: Tel: +86 010-62333524; E-mail: [email protected]

ED

(Deren Wang);

CC E

PT

Tel: +86 010-82304165; E-mail: [email protected] (Xuechun Lin)

A

Graphical abstract

IP T SC R

N

U

Graphical Abstract

A

ABSTRACT

M

Superhydrophobic surfaces have shown great potential applications in many fields

ED

and attracted tremendous attention and research efforts in recent years. In this study, the nanosecond laser technology was applied on the surface of titanium alloy and then

superhydrophobic

surface.

The

lotus-leaf-like

micro-nanoscale

CC E

biomimetic

PT

functionalized the surface by the organic polysilazane (OPZ) coating to obtain a novel

hierarchical structure have been prepared on titanium alloy surface under the combined action of pulse laser’s ablation, melting and bombardment by the

A

nanosecond laser. By applying OPZ instead of the expensive fluorocarbon which is harmful to the environment to modify the substrate, we found that the as-synthesized surfaces exhibited outstanding water repellence (water contact angle (WCA) = 164.1°) and non-stickiness behavior (sliding angle (SA) = 1.5°), which indicates the low

surface free energy of OPZ coating. Furthermore, the addition of ZnO nanoparticles into the OPZ coating significantly improves the corrosion resistance and antibacterial property of the super hydrophobic surface after laser treatment, achieving inhibition rate of 93.89% in fighting against E. coli. It is believed that the facile and low-cost

SC R

adhesive on titanium alloy in biomedical and anti-fouling fields.

IP T

method can expand the new application of superhydrophobic surface with low

KEY WORDS nanosecond laser, superhydrophobic surface, organic polysilazane,

M

1.INTRODUCTION

A

N

U

corrosion resistance, antibacterial properties.

ED

Biomimetic superhydrophobic surfaces exhibit potential for multifarious applications due to their self-cleaning [1, 2], fluid-drag reduction [3, 4], anticorrosion

PT

[5-7], anti-icing [8-10], and antifouling properties [11, 12]. These properties have led

CC E

to widespread interest among researchers in various countries. The wettability of superhydrophobic surfaces is determined by 1) low surface energy and 2) surface topography [13, 14]. Based on the superhydrophobic mechanism, artificial

A

superhydrophobic surfaces can be fabricated using two steps: the creation of hierarchical organised structures and the reduction of the surface’s free energy [15]. Low-surface-energy materials reduce a surface’s free energy. Therefore, the key to preparing superhydrophobic surfaces is to construct a suitably sized hierarchical

microstructure on a solid surface [16]. With the continual progress in technology, numerous methods have been developed for constructing microstructures on solid surfaces, such as micromachining techniques, plasma-etching techniques, chemical and physical vapour-deposition techniques, chemical-etching techniques, and sol-gel

IP T

techniques as well as static electricity, spinning, and spraying technologies [17-23]. However, these methods involve respective limitations including high costs,

SC R

complicated processes, and time intensiveness, and they may produce environmental pollution. These limitations have severely restricted the development of industrial

U

preparation methods and applications for superhydrophobic surfaces.

N

With the introduction of laser technology, laser-based methods have been

A

developed to produce materials for suitable microstructures. Laser-based methods

M

involve advantages such as high processing speed, high processing precision, wide

ED

processing range, and environmental friendliness. Laser technology has been rapidly developed and is applied in various industrial fields. The use of laser technology to

PT

control the wettability of solid surfaces has become a widely investigated research

CC E

topic [24-31]. Most light sources used in this application are femtosecond lasers. Laser ablation can be used to prepare periodic micro/nanoscale hierarchical structures on the surfaces of most materials [32]. However, the high cost of femtosecond lasers

A

and the relatively slow production speed related to their use in the described process limit their large-scale application in industrial fields. Most artificial superhydrophobic surfaces cannot be widely used due to their insufficient mechanical and chemical stability in rigorous real-world applications [33].

Hierarchical micro/nanostructures are generally vulnerable to damage from finger contact,

water

impact,

abrasion,

and

scratching.

For

many applications,

superhydrophobic surfaces must be able to adapt to complex practical application environments. For example, superhydrophobic surfaces with both corrosion resistance

IP T

and antibacterial properties are critical to marine engineering materials and biomedical materials. Researchers have attempted to improve the comprehensive

SC R

performance of superhydrophobic surfaces, and various methods have been developed. Modification of the low-surface-energy coating may be an innovative and effective

U

means for solving the problem of unfavourable environmental adaptability. Privett et

N

al. prepared a superhydrophobic xerogel coating by combining nanostructured silica

A

colloids and fluorinated silane [34]. The study results revealed that the adhesion of

M

Staphylococcus aureus and Pseudomonas aeruginosa to the developed surface was

ED

approximately two orders of magnitude less than their adhesion to the control surface. Liu et al. prepared a superhydrophobic surface that was highly adhesive, and the

PT

substrate was substantially more corrosion resistant [35]. Peng et al. prepared

CC E

chemical modifications of superhydrophobic surfaces that substantially improved the mechanical stability of the surfaces [36]. A novel organic polysilazane (OPZ) that can be cured using atmospheric

A

moisture at low temperatures has generated considerable research interest. This material exhibits low surface energy and strong adhesion to most substrate surfaces (e.g., glass, metal, mineral, ceramic, and organic materials). Moreover, coatings prepared using OPZ demonstrate excellent corrosive resistance compared with other

polymer coatings. In the preparation of this coating in the present study, nano particles were added to liquid OPZ. After the OPZ was cured and formed, these particles were firmly fixed in the coating. This process presents new possibilities for the preparation of multifunctional superhydrophobic surfaces. A nanosecond laser

IP T

was used to form a micro/nanoscale hierarchical structure on a titanium alloy substrate. The scanning speed of the laser was adjusted, and the mechanism involved

SC R

in using a nanosecond laser to form a hierarchical structure was demonstrated. During these processes, OPZ was used on the surface of the substrate. In addition, particles

were

added

to

the

modified

layer,

resulting

in

U

antibacterial

N

superhydrophobic, corrosion-resistant, and antibacterial properties on the titanium

the titanium alloy.

2.1 Materials

ED

2.EXPERIMENTAL SECTION

M

A

alloy substrate. These properties considerably improved the overall performance of

PT

Organic polysilazane was obtained from Institute of Chemistry Chinese

CC E

Academy of Sciences. Titanium alloy plates (TC4, 1mm thick) were mechanically polished to mirror finish and cleaned ultrasonically with ethanol before laser treatment. The roughness of sample surface was 0.4μm. Nano-sized ZnO and silane

A

coupling agent KH570 were purchased from Sinopharm Chemical Reagent Co., Ltd. 2.2 Preparation of Titanium Surface Micro-nanostructures The laser used in this experiment is an optical fiber pulse laser with a center wavelength of λ=1064 nm, an average power of 20 W, a repetition frequency of 20

kHz, an output energy of 1 mJ/pulse, and a pulse width of 100 ns. The laser beam is controlled by the scanning galvanometer system and can be moved in a specified direction. The laser beam is focused by a lens with a focal length of f=80 mm on the sample surface to a spot of Φ=40 μm. Micro-nano structures were produced on the

IP T

surface of TC4 substrate by different scanning methods. All samples were prepared under standard atmospheric pressure in an open atmosphere at ambient temperature.

SC R

Preparation of Low Surface Energy Coating

In order to obtain stable superhydrophobic properties, it is necessary to coat the

U

laser-treated surface with a low surface energy coating. In this experiment, a novel

N

OPZ was selected as the coating material. At the same time, in order to further

A

improve the bactericidal properties of the substrate, nano-sized zinc oxide particles

M

were added into the coating. The coating preparation process is as follows: 1)

ED

Dispersion of nano-sized zinc oxide: Take 1g silane coupling agent KH570 into 200ml of isopropanol and stir for 20 minutes to make it evenly dispersed. After that

PT

3g of nano-zinc oxide powder were added to the mixture and stirred at high speed in a

CC E

water bath at 30° C for 2 hours to uniformly disperse the modified nanopowder in the mixture. The precipitate obtained after suction filtration is dried in an oven to obtain modified zinc oxide particles. 2) Configuration of the coating solution: The solution

A

consists of the diluent xylene and OPZ in a ratio of 20:1. After mixing, a certain amount (0~2%wt) of modified nano-sized ZnO is added. The low-temperature ultrasound was applied to disperse the mixture for 30 min so that the modified nanoparticles were uniformly dispersed in the solution. 3) Coating and curing: The

sample was hanged vertically in the solution, ultrasonically treated for 30 minutes, and allowed to dry for 20 minutes. The temperature was raised in the oven to 200°C, and the temperature was lowered to room temperature after heating for 4 hours. 2.4 Measurement and Characterisation

IP T

The surface morphologies were analyzed using a field emission scanning electron microscope (NOVA NANOSEM650, FEI, Germany). The topography

SC R

measurements were performed using laser scanning confocal microscope. (VK-X200, Keyence, Japan). The wettability of the samples with OPZ without ZnO coatings was

U

evaluated by measuring the apparent contact angles (CA), advancing CAs, and

N

receding CAs by using a video-based optical contact angle-measuring device (OCA20;

A

Data Physics Instruments, Germany) and the sessile drop technique. The water

M

volume on the surface area was increased and decreased to determine the advancing

ED

and receding CAs, respectively. The sliding behaviour of the sample was evaluated by measuring the sliding angles (SAs) using the tilting-plate method. When the sample

PT

was gradually tilted from a horizontal state, the droplets slid along the inclined surface

CC E

at a critical slope angle. This angle was defined as the SA. The water droplet volume for CA and SA measurement was 4 μL. Following our previous work [37], the three-liquid method by Good and van Oss that is based on Young’s equation was used

A

to study and quantitatively calculate the sample surface’s free energy from the CAs. The high-power transfer target polycrystalline X-ray diffractometer (Rigaku Corporation, Japan) was used to analyze the surface phase of the sample with Cukα as the X-ray source. The continuous scanning was performed using a 2θ/θ coupled

scanning method with a step width of 0.02° and the tube voltage is 40KV. The scanning speed is 10°/min, and the scanning range is 10°~90°. The corrosion resistance properties of the fabricated coatings were studied using an electrochemical workstation (ParStat 2273, Princeton, USA) at room temperature

IP T

in a three-electrode cell, with the sample as the working electrode. Ag/AgCl electrode filled with saturated KCl solution served as a reference electrode and a Pt sheet as a

SC R

counter electrode. The corrosive medium was a 3.5% NaCl solution in contact with air maintained at room temperature. Prior to the electrochemical measurements, the

U

samples were immersed in the solution for 30min. The potentiodynamic polarization

N

curves were registered at a scan rate of 1 mV/s in an applied potential range from −0.5

A

to 0.5V (versus Ag/AgCl).

M

The E. coli (ATCC 8739) strains were obtained from the Institute of Metal

ED

Research, China Academy of Sciences. The E. coli strains were cultured in Lysogeny broth (LB) solid medium and incubated at 37 °C overnight in an incubator. The

PT

overnight solid bacterial culture was diluted by phosphate buffer saline (PBS) and

CC E

then inoculated into the LB broth. The concentration of the bacteria in broth was approximately 106 cells /mL. Subsequently, the samples were placed into 24-well plates with 1 mL of the diluted bacterial suspension, then the plates were incubated at

A

37 °C for 1 day, respectively. After incubation, the samples were taken out and washed with phosphate buffer saline (PBS) 3 times to remove the planktonic bacteria on the surfaces. After washing, samples were shaken vigorously for 1 min. Serial dilutions were

made with PBS, and the suspensions were plated on LB broth and incubated at 37 °C for 24 h. The reduction of bacterial growth (RA) on the different sample in comparison with the substrate was calculated as Equation (1). RA (%)= (C−A)/C×100% （1）

IP T

where C is the number of bacteria-forming units on the substrate after 24 h of incubation and A is the number of bacteria-forming units on the other surfaces under

SC R

the same conditions. 3.RESULTS AND DISCUSSION

U

3.1 Surface Structure and Phase Composition

N

Ultrafast lasers do not create a heat-affected zone during processing [38]. In this

A

study, ablation was used to fabricate micro/nanostructures on the surface of the

M

substrate. The pulse width of a nanosecond laser is much wider than that of an

ED

ultrafast laser. The heat-affected zone of the nanosecond laser played a critical role in the formation of micro/nanoscale hierarchical structures in the study samples.

PT

Because the laser used in the present experiment was a Gaussian beam, the energy at

CC E

the centre of the spot was relatively high and exceeded the ablation threshold of the substrate. After the base metal vaporised directly from the substrate surface, the area at the edge of the spot was heated only to the melting point. The substrate melted

A

from the impact of the pulsed laser and then sloshed around and accumulated on both sides of the scanning area. Due to the heat-affected zone, the substrate near the edge of the spot also melted. During scanning of the substrate in the x-direction, the substrate surface formed a groove along the direction of the laser scan, and the

deposition of splash droplets on both sides of the groove increased the groove’s depth. After the substrates were scanned one by one at 45° in the x-direction, tapered protrusions formed in the gaps between two adjacent scans, and pits formed at the crossing points of the two scans. Nanoscale wrinkles emerged on the surface of the

IP T

micron-sized structures. The microscopic morphologies of the substrate at various scan speeds are illustrated in Figure 1.

SC R

Changes in the scanning speed resulted in significant differences in the substrate’s morphology. Specifically, the overlapping area between the two pulse

U

spots and the number of laser pulses received at the same position of the substrate at

N

various scanning speeds differed. The laser energy received by the substrate varied

A

considerably. When the scanning speed was increased, a sharply arranged tapered

M

structure formed on the substrate’s surface. The tip of the tapered cone was spherical

ED

and filled with nanoscale folds. After the scanning speed was reduced, the overlapping area of the spot increased, and the increase in the laser energy resulted in additional

PT

slimming of the tapered structure of the base body. When the scanning speed was

CC E

further reduced, the pyramidal structure periodically arranged on the substrate’s surface was destroyed. Due to the increase of the heat-affected zone, the large area of the substrate at the bottom of the cone melted and gradually levelled, connecting the

A

bottom tips of the substrate, and the nanostructure on the surface of the cone gradually disappeared. The scanning speed was further reduced, and the ablated and melted area increased over the area scanned using the laser spot. More liquid substrates were blown by the laser pulses and piled on both sides of the scanned area. The area of the

melted tip was not heated repeatedly. It rapidly cooled and solidified. The liquid substrate could not flow, and it formed a spherical shape because of the effect of surface tension [39]. In summary, as the scanning speed decreased, the area swept by the laser spots overlapped and the area around the spot was heated several times.

IP T

Subsequently, the conical structures were gradually overwhelmed; only the spherical tip of the cone was retained. Additionally, the sputtered liquid substrate solidified in a

SC R

new connecting plane. The spherical shape increased the number of connected spherical projections, as illustrated in Figure 1(h), and the tip of the spherical structure

U

again exhibited a relatively dense and uniform nanostructure, which was similar to the

N

surface morphology of a lotus leaf. After the scanning speed was further reduced,

A

because of the large size of the heat-affected zone, the groove on the surface of the

M

substrate was filled in until it flattened out and disappeared, as depicted in Figure 1(i)

ED

and 1(k).

The three-dimensional (3D) structure of the substrate at various laser-scanning

PT

speeds was observed using a 3D confocal laser microscope (Figure 2).

CC E

When the scanning speed was high, the pyramidal structure on the substrate’s surface was periodically distributed. As the scanning speed decreased, more substrates vaporised and left the substrate’s surface. Simultaneously, more metal droplets were

A

blown off through laser bombardment, increasing the depth of the groove. When the scanning speed was less than 40 mm/s, the heat-affected zones expanded and overlapped. The substrate melted during the laser-induced multiple-heating process, and the depressions between the pyramids were filled. The height of the structure

protruding from the surface was reduced in conjunction with the decrease in scanning speed. The average height of the microstructure is indicated in Figure 3(a). To verify that the spherical protrusions in Figure 1(h) were formed by the accumulation of the splashed metal droplets, a cross section of the protruding portion

IP T

of the substrate was subjected to ion-beam polishing and observed using a scanning electron microscope (SEM; Figure 3[b]). Numerous gaps were observed in the top of

SC R

the bulbous protrusion; these gaps were due to the rapid solidification of the liquid

after it had accumulated in the top. Air was trapped by the protrusions, and in the

U

middle of the protrusions, trapped air bobbles concentrated and formed a large gap.

N

X-ray diffraction analysis of the sample’s surface was conducted, and the results

A

are displayed in Figure 4. Compared with the substrate, only little metastable TiO

M

appeared after laser treatment. Under the pulsed laser, the substrate rapidly warmed

ED

and cooled [40]. Excessive cooling promoted metastable TiO formation. The crystal orientation of the titanium substrate changed because of the remelting of the titanium,

PT

which improved the mechanical properties of the titanium surface.

CC E

3.2 Hydrophobicity and Adhesion The laser-treated surface appeared to be superhydrophilic, mainly due to the

heightened surface energy of the sample after the laser treatment. When the sample

A

was placed in a dry-air environment, it adsorbed long-chain organic substances in the air, leading to lower surface energy. Under these conditions, the sample spontaneously became superhydrophobic. However, this process required a long time, and the hydrophobicity was unstable [41]. To rapidly stabilise the superhydrophobic

properties of materials, samples are usually modified using expensive fluorocarbons, which greatly increases production costs. In this study, OPZ was used to replace fluorocarbons, and appropriate amounts of ZnO nanoparticles were added to OPZ. Under ultrasound, ZnO particles were mainly fixed at the bottom of the hierarchical

IP T

structure, and the tip of the ZnO was also at nanoscale. The nanofolds at the top of the protrusions were also largely retained, as illustrated in Figure 5(b),(c). The size of the

SC R

modified nanoparticles was only 150 nm (Figure 5[d]). These surfaces exhibited excellent superhydrophobic properties; adhesion between the sample and water

U

droplets was weak.

N

The effects of various morphologies on the superhydrophobic properties of the

A

sample surface were studied. The morphology described in Section 3.1 was

M

constructed on the surface of the Ti6Al4V substrate by using various laser-scanning

ED

speeds. Due to the deposition of ZnO mainly occurs at the bottom of the grooves, the addition of ZnO exhibited few effects on sample wettability. After modification using

PT

a certain OPZ coating concentration, the sample’s apparent CAs, advancing CAs, and

CC E

SAs were tested. As illustrated in Figure 6(a), the increase in surface roughness increased substrate hydrophobicity. When the scanning speed was 100 mm/s, the CA of the substrate was 143.5°. When the scanning speed was 80 mm/s, the CA increased

A

to 147.3° due to the formation of a higher cone-shaped protrusion on the substrate surface. The scanning speed was further reduced, and the micro/nanoscale hierarchical structure on the surface of the substrate correspondingly decreased in CA because of the influence of the heat-affected zone. When the scanning speed was 20

mm/s, numerous micrometre-sized spherical protrusions formed on the surface, nanoscale folds appeared on the ball-shaped spherical protrusion, and the CA suddenly increased to 164.1°. The SA of the substrate surface complied with the aforementioned rules, exhibiting superhydrophobicity and low adhesion. At a sweep

IP T

speed of 20 mm/s, the SA was a minimum of 1.5 ± 0.5°. To examine the adhesion of the sample surfaces, the CA hysteresis (CAH) of the

SC R

water droplets on the surfaces was investigated. The CAH value was closely related to

that of the apparent CA (Table 1). In general, two models are used to describe solid–

U

liquid interactions: 1) a liquid completely fills the valleys of a rough solid surface (i.e.,

N

the Wenzel state) or 2) a liquid leaves air inside the valleys of a rough solid surface

A

(i.e., the Cassie state) [36]. In our experiments, the surface exhibited

M

superhydrophobicity with a large CA, low CAH, and small SA. These characteristics

ED

were similar to those of a lotus leaf. Thus, the sample’s excellent superhydrophobicity fits the Cassie model. At a suitable scanning speed (20 mm/s), the surface developed a

PT

coarse roughness from deep microstructures combined with rich nanostructures, and a

CC E

layer of air was trapped between the surface and droplets. In this state, the sample comprised a nonhomogeneous or composite regime with a three-phase solid–water– air interface, and the air areas of the surface were perfectly nonwetting [37]. The

A

sample in this state exhibited low water adhesion. Water droplets were dropped onto the surface of the sample, and we subsequently measured the surface CA and SA for 60 minutes. The results are presented in Figure 6(b). The water droplets did not completely wet all nanostructures

immediately after they fell on the substrate’s surface, and the unwetted nanostructures were gradually wetted because of gravity, which caused the CA to stabilise after the CA was slightly reduced. When the wetting angle decreased slightly, the SA of the substrate increased. This was because of the increased adhesion of the substrate to the

IP T

water after the nanoscale protrusions were completely wet, which resulted in an increase in the slding angle. When the water CA had stabilised at 157.1°, the sliding

SC R

angle rose to 3.5 ± 0.5°, which still indicated favourable superhydrophobic properties.

The micro/nano hierarchical structure that formed directly on the substrate and

U

the hard low-surface-energy modifying layer contributed to the excellent mechanical

N

stability of the superhydrophobic surface. We used 240-grade sandpaper friction to

A

test the mechanical durability of the superhydrophobic micro/nanostructure. Figure

M

7(a) presents a schematic of this abrasion test, and Figure 7(b) presents the change in

ED

the water CAs of the as-prepared superhydrophobic surface as a function of abrasion cycles. Samples with weights of 50 , 100 , and 200 g were pressed on the sandpaper

PT

and dragged 10 cm forward. We measured the CAs of the friction surface of each

CC E

sample and determined the relationships between the CAs and the friction values. After 10 friction cycles, the CAs decreased but remained above 150° (Figure 7[b]). The sandpaper wore off a part of the micro/nanostructures, but an SEM image of the

A

200-g sample revealed that micro/nanostructures remained on the surface (Figure 7[b]). Additionally, the excellent mechanical properties of OPZ and the increased adhesion between the micro/nanostructures increased the resistance of the superhydrophobic surface to abrasion, significantly improving its mechanical

durability. 3.3 Corrosion Resistance in Corrosive Electrolytes Due to the special wettability of the superhydrophobic material’s surface, part of the area between the substrate and the liquid was blocked by air, and the actual

IP T

contact part diminished. This property was favourable for corrosion resistance. If the superhydrophobic properties of the sample surface had not been uniform, severe

SC R

localised corrosion would have occurred in the area with inadequate hydrophobicity,

and the overall corrosion resistance of the material would have deteriorated. The

U

superhydrophobic properties of the material depended on the micro/nanoscale

N

hierarchical structure and the low-surface-energy substance; thus, the uniformity and

A

stability of the surface modification layer were critical factors in the durability of the

M

superhydrophobic material. To determine the main factors of the corrosion resistance

ED

of the substrate under superhydrophobic conditions, we examined the corrosion resistance of superhydrophobic surfaces with various modified layers after laser

PT

treatments. Figure 8 illustrates the polarisation curves for substrate, laser treatment

CC E

(superhydrophilic), laser treatment modified using OPZ (superhydrophobic), and laser treatment modified using OPZ–ZnO (superhydrophobic) samples. The corrosion current density and the corrosion potential measured from the Tafel slopes are

A

presented in Table 2. Analysis of the polarisation curve revealed that the corrosion potential of the Ti6Al4V substrate was positively drifted and the current density decreased after laser treatment. The application of OPZ coating to the laser-treated samples corresponded

with a dramatic drop in the corrosion current density. The transition from a superhydrophilic surface to superhydrophobic surface is mainly determined by water-repellent properties that reduce the area of real contact between a solid surface and electrolytes [29]. Thus, the hydrophobic layer on the rough Ti6Al4V surface

IP T

rendered the metal surface less susceptible to corrosion. The addition of ZnO particles substantially influenced the corrosion resistance of

SC R

the coatings. After the optimum amount of ZnO particles was determined through experimentation, this amount was added to the modified layer, and the corrosion

U

resistance of the sample improved. The corrosion current density was only 1.016 ×

N

10−9 A/cm2. On one hand, the presence of ZnO nanoparticles reduced the volumetric

A

shrinkage of the OPZ coating during hydrolysis and increased the density of the

M

coating. On the other hand, the nanosized ZnO particles were deposited on the bottom

ED

of the grooves, enhancing the uniformity of the micro/nanoscale hierarchical structure

resistance.

PT

as well as the stability of the hydrophobic properties, ultimately enhancing corrosion

CC E

3.4 Antibacterial Properties The critical self-cleaning nature of superhydrophobic surfaces limits the

proliferation of bacteria and other microorganisms [42, 43]. Favourable bactericidal

A

properties of ZnO have been reported. Adding ZnO particles to the OPZ-modified layer considerably improved the antibacterial performance of the surface. Under the combined action of ZnO particles and the surface’s superhydrophobicity, the substrate exhibited enhanced antibacterial properties. To maintain the corrosion resistance of

the sample, the amount of ZnO particles was not modified during studies on the sample’s antibacterial properties. The untreated Ti6Al4V substrate, laser-treated unmodified Ti6Al4V substrate, laser-treated OPZ-modified substrate, and laser-treated OPZ–ZnO composite coating

IP T

were studied using E. coli as the test species. The modified substrates were tested for antibacterial properties, and the results are displayed in Figure 9. The Ti6Al4V

SC R

substrate without any treatment served as a benchmark. After the laser treatment, the

increase in the surface area of the substrate offered more space for growth of E. coli,

U

and the antibacterial rate was negative. The substrate was subsequently modified

N

using pure OPZ, after which the substrate demonstrated superhydrophobic properties.

A

This result confirmed the effect of the antibacterial treatment; the calculated

M

antibacterial rate was approximately 71.67%. The substrate modified with the OPZ–

ED

ZnO composite coating exhibited the highest antibacterial activity with an antibacterial rate of 93.89%. This indicated that the ZnO nanoparticles in the coating

PT

played an antibactericidal role; the small amount of E. coli that adhered to the

CC E

substrate was killed by the ZnO nanoparticles and thus could not grow into colonies [44, 45].

4.CONCLUSION

A

Superhydrophobic surfaces of Ti6Al4V were successfully synthesised using a nanosecond pulsed laser and an OPZ coating. A micro/nanoscale hierarchical structure was formed by adjusting laser irradiation conditions. OPZ was employed to modify the Ti6Al4V surface, and low surface energy and superhydrophobic stability were

achieved. The CA of the as-synthesised superhydrophobic surface was approximately 164.1°, and the SA was approximately 1.5°. The addition of ZnO nanoparticles in the OPZ coating enhanced the corrosion resistance of the sample, which exhibited a corrosion current density of 1.016 × 10−9 A/cm2. The surface antibacterial rate of the

IP T

Ti6Al4V modified through laser treatment and OPZ–ZnO composite coating against E. coli was 93.89%. The sample benefitted from superhydrophobic micronanostructures

SC R

and nanosized ZnO. The present study demonstrated the favourable corrosion resistance, antibacterial properties, and haemocompatibility of the OPZ–ZnO

N

U

composite coating, indicating the coating’s potential for clinical applications.

A

References

M

[1] J. Lee, R.S. Fearing, Wet self-cleaning of superhydrophobic microfiber adhesives formed

ED

from high density polyethylene, Langmuir 28(43) (2012) 15372-7. [2] S. Sethi, L. Ge, L. Ci, P.M. Ajayan, A. Dhinojwala, Gecko-inspired carbon nanotube-based

PT

self-cleaning adhesives, Nano letters 8(3) (2008) 822-825.

CC E

[3] B. Dean, B. Bhushan, Shark-skin surfaces for fluid-drag reduction in turbulent flow: a review, Philos Trans A Math Phys Eng Sci 368(1929) (2010) 4775-806. [4] Z. Ming, L. Jian, W. Chunxia, Z. Xiaokang, C. Lan, Fluid drag reduction on

A

superhydrophobic surfaces coated with carbon nanotube forests (CNTs), Soft Matter 7(9) (2011) 4391. [5] B. Yin, L. Fang, A.-q. Tang, Q.-l. Huang, J. Hu, J.-h. Mao, G. Bai, H. Bai, Novel strategy in increasing stability and corrosion resistance for super-hydrophobic coating on aluminum alloy

surfaces, Applied Surface Science 258(1) (2011) 580-585. [6] C.-J. Weng, C.-H. Chang, C.-W. Peng, S.-W. Chen, J.-M. Yeh, C.-L. Hsu, Y. Wei, Advanced

Anticorrosive

Coatings

Prepared

from

the

Mimicked

Xanthosoma

Sagittifolium-leaf-like Electroactive Epoxy with Synergistic Effects of Superhydrophobicity and

IP T

Redox Catalytic Capability, Chemistry of Materials 23(8) (2011) 2075-2083. [7] N. Wang, D. Xiong, Superhydrophobic membranes on metal substrate and their corrosion

SC R

protection in different corrosive media, Applied Surface Science 305 (2014) 603-608.

[8] Y. Wang, J. Xue, Q. Wang, Q. Chen, J. Ding, Verification of icephobic/anti-icing properties

U

of a superhydrophobic surface, ACS Appl Mater Interfaces 5(8) (2013) 3370-81.

N

[9] P. Guo, Y. Zheng, M. Wen, C. Song, Y. Lin, L. Jiang, Icephobic/anti-icing properties of

A

micro/nanostructured surfaces, Adv Mater 24(19) (2012) 2642-8.

M

[10] S. Rezaei, I. Manoucheri, R. Moradian, B. Pourabbas, One-step chemical vapor

ED

deposition and modification of silica nanoparticles at the lowest possible temperature and superhydrophobic surface fabrication, Chemical Engineering Journal 252 (2014) 11-16. J.A.

Howarter,

J.P.

PT

[11]

Youngblood,

Self-Cleaning

and

Anti-Fog

Surfaces

via

CC E

Stimuli-Responsive Polymer Brushes, Advanced Materials 19(22) (2007) 3838-3843. [12] X. Gao, X. Yan, X. Yao, L. Xu, K. Zhang, J. Zhang, B. Yang, L. Jiang, The Dry-Style Antifogging Properties of Mosquito Compound Eyes and Artificial Analogues Prepared by Soft

A

Lithography, Advanced Materials 19(17) (2007) 2213-2217. [13] Y. Shen, J. Tao, H. Tao, S. Chen, L. Pan, T. Wang, Nanostructures in superhydrophobic Ti6Al4V hierarchical surfaces control wetting state transitions, Soft Matter 11(19) (2015) 3806-3811.

[14] T. Ishizaki, N. Saito, O. Takai, Correlation of cell adhesive behaviors on superhydrophobic, superhydrophilic, and micropatterned superhydrophobic/superhydrophilic surfaces to their surface chemistry, Langmuir 26(11) (2010) 8147-8154. [15] L. Feng, S. Li, Y. Li, H. Li, L. Zhang, J. Zhai, Y. Song, B. Liu, L. Jiang, D. Zhu, Super‐

IP T

hydrophobic surfaces: from natural to artificial, Advanced materials 14(24) (2002) 1857-1860. [16] J. Song, W. Xu, X. Liu, Y. Lu, Z. Wei, L. Wu, Ultrafast fabrication of rough structures

SC R

required by superhydrophobic surfaces on Al substrates using an immersion method, Chemical Engineering Journal 211 (2012) 143-152.

U

[17] H. Liu, S. Szunerits, W. Xu, R. Boukherroub, Preparation of superhydrophobic coatings on

N

zinc as effective corrosion barriers, ACS Appl Mater Interfaces 1(6) (2009) 1150-3.

A

[18] D. Kontziampasis, G. Boulousis, A. Smyrnakis, K. Ellinas, A. Tserepi, E. Gogolides,

M

Biomimetic, antireflective, superhydrophobic and oleophobic PMMA and PMMA-coated glass

ED

surfaces fabricated by plasma processing, Microelectronic Engineering 121 (2014) 33-38. [19] J. Wang, X. Song, R. li, J. Shen, G. Yang, H. Huang, Fluorocarbon thin film with

PT

superhydrophobic property prepared by pyrolysis of hexafluoropropylene oxide, Applied

CC E

Surface Science 258(24) (2012) 9782-9785. [20] A. Hozumi, B. Kim, T.J. McCarthy, Hydrophobicity of perfluoroalkyl isocyanate monolayers on oxidized aluminum surfaces, Langmuir 25(12) (2009) 6834-40.

A

[21] M. Zhu, H. Gao, H. Li, J. Xu, Y. Chen, A facile processing way of silica needle arrays with tunable orientation by tube arrays fabrication and etching method, Journal of Solid State Chemistry 183(3) (2010) 595-599. [22] A. Milionis, K. Dang, M. Prato, E. Loth, I.S. Bayer, Liquid repellent nanocomposites

obtained from one-step water-based spray, Journal of Materials Chemistry A 3(24) (2015) 12880-12889. [23] T.M. Schutzius, I.S. Bayer, J. Qin, D. Waldroup, C.M. Megaridis, Water-based, nonfluorinated dispersions for environmentally benign, large-area, superhydrophobic coatings,

IP T

Acs Appl Mater Interfaces 5(24) (2013) 13419-13425. [24] D. Jiang, P. Fan, D. Gong, J. Long, H. Zhang, M. Zhong, High-temperature imprinting and

SC R

superhydrophobicity of micro/nano surface structures on metals using molds fabricated by ultrafast laser ablation, Journal of Materials Processing Technology 236 (2016) 56-63.

N

Light: Science & Applications 3(4) (2014) e149-e149.

U

[25] K. Sugioka, Y. Cheng, Ultrafast lasers—reliable tools for advanced materials processing,

A

[26] Z. Lian, J. Xu, Z. Wang, Z. Yu, Z. Weng, H. Yu, Nanosecond Laser-Induced Underwater

ED

34(9) (2018) 2981-2988.

M

Superoleophobic and Underoil Superhydrophobic Mesh for Oil/Water Separation, Langmuir

[27] B. Wu, M. Zhou, J. Li, X. Ye, G. Li, L. Cai, Superhydrophobic surfaces fabricated by

CC E

(2009) 61-66.

PT

microstructuring of stainless steel using a femtosecond laser, Applied Surface Science 256(1)

[28] F.A. Muller, C. Kunz, S. Graf, Bio-Inspired Functional Surfaces Based on Laser-Induced Periodic Surface Structures, Materials (Basel) 9(6) (2016).

A

[29] L.B. Boinovich, E.B. Modin, A.R. Sayfutdinova, K.A. Emelyanenko, A.L. Vasiliev, A.M. Emelyanenko, Combination of Functional Nanoengineering and Nanosecond Laser Texturing for Design of Superhydrophobic Aluminum Alloy with Exceptional Mechanical and Chemical Properties, ACS Nano 11(10) (2017) 10113-10123.

[30] M.M. Quazi, M.A. Fazal, A.S.M.A. Haseeb, F. Yusof, H.H. Masjuki, A. Arslan, Laser-based Surface Modifications of Aluminum and its Alloys, Critical Reviews in Solid State and Materials Sciences 41(2) (2015) 106-131. [31] D. Kray, A. Fell, S. Hopman, K. Mayer, G.P. Willeke, S.W. Glunz, Laser Chemical

IP T

Processing (LCP)—A versatile tool for microstructuring applications, Applied Physics A 93(1) (2008) 99-103.

SC R

[32] J. Long, P. Fan, D. Gong, D. Jiang, H. Zhang, L. Li, M. Zhong, Superhydrophobic surfaces fabricated by femtosecond laser with tunable water adhesion: from lotus leaf to rose petal,

U

ACS Appl Mater Interfaces 7(18) (2015) 9858-65.

N

[33] M. Qu, S. Liu, J. He, C. Yu, X. Liu, Y. Yao, J. Feng, Bioinspired fabrication of mechanically

A

durable superhydrophobic materials with abrasion-enhanced properties, RSC Advances 6(96)

M

(2016) 93403-93409.

ED

[34] B.J. Privett, J. Youn, S.A. Hong, J. Lee, J. Han, J.H. Shin, M.H. Schoenfisch, Antibacterial fluorinated silica colloid superhydrophobic surfaces, Langmuir 27(15) (2011) 9597-9601.

PT

[35] F. Peng, D. Wang, X. Ma, H. Zhu, Y. Qiao, X. Liu, “Petal effect”-inspired superhydrophobic

CC E

and highly adhesive coating on magnesium with enhanced corrosion resistance and biocompatibility, Science China Materials

(2017) 1-14.

[36] C. Peng, Z. Chen, M.K. Tiwari, All-organic superhydrophobic coatings with

A

mechanochemical robustness and liquid impalement resistance, Nature materials 17(4) (2018) 355. [37] J. Song, D. Wang, L. Hu, X. Huang, Y. Chen, Superhydrophobic surface fabricated by nanosecond laser and perhydropolysilazane, Applied Surface Science

(2018).

[38] R. Le Harzic, N. Huot, E. Audouard, C. Jonin, P. Laporte, S. Valette, A. Fraczkiewicz, R. Fortunier, Comparison of heat-affected zones due to nanosecond and femtosecond laser pulses using transmission electronic microscopy, Applied Physics Letters 80(21) (2002) 3886-3888.

IP T

[39] C. Liu, Q. Zhao, L. Wang, J. Zhang, Y. Tian, Y. Meng, One-step preparation of TiO2 particles with controllable phase and morphology by plasma electrolysis, RSC Advances 7(63)

SC R

(2017) 39824-39832.

[40] J. Kusinski, S. Kac, A. Kopia, A. Radziszewska, M. Rozmus-Górnikowska, B. Major, L.

U

Major, J. Marczak, A. Lisiecki, Laser modification of the materials surface layer – a review

N

paper, Bulletin of the Polish Academy of Sciences: Technical Sciences 60(4) (2012).

A

[41] J. Long, M. Zhong, H. Zhang, P. Fan, Superhydrophilicity to superhydrophobicity transition

M

of picosecond laser microstructured aluminum in ambient air, J Colloid Interface Sci 441 (2015)

ED

1-9.

[42] P. Tang, W. Zhang, Y. Wang, B. Zhang, H. Wang, C. Lin, L. Zhang, Effect of

PT

Superhydrophobic Surface of Titanium onStaphylococcus aureusAdhesion, Journal of

CC E

Nanomaterials 2011 (2011) 1-8. [43] B.J. Privett, J. Youn, S.A. Hong, J. Lee, J. Han, J.H. Shin, M.H. Schoenfisch, Antibacterial fluorinated silica colloid superhydrophobic surfaces, Langmuir 27(15) (2011) 9597-601.

A

[44] H. Meruvu, M. Vangalapati, S.C. Chippada, S.R. Bammidi, Synthesis and characterization of zinc oxide nanoparticles and its antimicrobial activity against Bacillus subtilis and Escherichia coli, J. Rasayan Chem 4(1) (2011) 217-222. [45] K.R. Raghupathi, R.T. Koodali, A.C. Manna, Size-dependent bacterial growth inhibition

and mechanism of antibacterial activity of zinc oxide nanoparticles, Langmuir 27(7) (2011) 4020-4028.

IP T

Figure 1. SEM images of the surface structured by a nanosecond laser with different scanning speeds: (a, b) 100, (c, d) 80, (e, f) 60, (g, h) 40, (i, j)29, and(k, l)10 mm/s.

SC R

Figure 2. 2D topography map and the corresponding cross-section profiles measured

with three-dimensional confocal laser scanning microscope. Ti6Al4V in the area

U

scanned and structured by a nanosecond laser at various scanning speeds: (a, b)

N

100mm/s, (c, d) 60mm/s, and (e, f) 20 mm/s

A

Figure 3. (a) The measured average height of the surface microstructures; and the

M

schematic diagram of different microstructure formation. (b) The SEM cross-sectional

ED

morphology of the spherical protrusion.

Figure 4. Phase analysis of substrate surface before and after laser treatment

PT

Figure 5. Surface morphologies after the modification of OPZ-ZnO composite coating:

CC E

(a)1000 ×, (b) 30000 ×, (c) the ZnO nanoparticles fixed at the bottom of the hierarchical structure, (d) the size of ZnO nanoparticles. Figure 6(a) Water contact angle and sliding angle of the sample at different sweep

A

speeds. (b) Change in sliding angle and contact angle varies with time. Figure 7 (a) Schematic of the abrasion test employed to evaluate mechanical durability on a superhydrophobic surface. Inset: SEM image of the surface morphology of 200 g after 10 cycles friction; (b) the change of water CAs of the

as-prepared micro/nanostructures and coating as a function of abrasion cycle. Figure 8. Corrosion resistance of substrates under different processing conditions (1) TC4 substrate; (2) superhydrophilic laser treat sample; (3) superhydrophobic laser treat modified by OPZ sample; (4) superhydrophobic laser treat modified by

IP T

OPZ-ZnO sample. Figure 9. Colonies of living E. coli cells on different substrates after 1 day; (a)

SC R

Substrate, (b)Substrate modified by OPZ coating (OPZ); (c) Laser irradiation (La), (d) laser Irradiation OPZ coating (LO), and (e) laser Irradiation OPZ-ZnO coating (LOZ),

A

CC E

PT

ED

M

A

N

U

(f) number of living E. coli colonies on different substrates after 1 day.

A ED

PT

CC E

IP T

SC R

U

N

A

M

Figure 1:

A ED

PT

CC E

IP T

SC R

U

N

A

M

Figure 2:

A ED

PT

CC E

IP T

SC R

U

N

A

M

Figure 3:

20μm

A ED

PT

CC E

IP T

SC R

U

N

A

M

Figure 4:

IP T

Figure 5:

2μm

M

A

N

U

SC R

300μm

A

CC E

PT

ED

2μm

A ED

PT

CC E

IP T

SC R

U

N

A

M

Figure 6:

A ED

PT

CC E

IP T

SC R

U

N

A

M

Figure 7:

A ED

PT

CC E

IP T

SC R

U

N

A

M

Figure 8:

A ED

PT

CC E

IP T

SC R

U

N

A

M

Figure 9:

Table 1.advancing contact angles (θa), receding contact angles (θr), and the contact angle hysteresis (Δθ = θa − θr) for the laser irradiated surfaces with diff erent scanning speed.

IP T

Table 2. Corrosion resistance of samples with different processing

SC R

Table 3. The data of different surface antibacterial properties

U

Table 1:

80

60

θa

144±1

148±1

142±2

θr

136±2

142±1

Δθ

8

20

10

140±1

164±1

152±1

128±2

127±2

162±1

147±1

17

13

2

5

M

ED

CC E

PT

6

40

A

100

N

Scanning speed(mm/s)

A

Table 2：

Samples

Ecorr (mV)

Icorr (A/cm2)

Substrate

-475

5.243×10-5

Laser

-257

5.34×10-7

Laser+OPZ

-366

2.93×10-8

Laser+OPZ-ZnO

-50.807

1.016×10-9

Table 3：

Substrate

180

Laser

405

Laser + OPZ

51

Laser+OPZ+ZnO

11

RA (%)

IP T

Average number

-

SC R

-125

71.67 93.89

A

CC E

PT

ED

M

A

N

U

2μm

Samples