Laser induced periodic surface structures on nano metal oxide filled polyvinylidene fluoride nanocomposites

Accepted Manuscript Title: Laser Induced Periodic Surface Structures on Nano Metal Oxide filled Polyvinylidene Fluoride Nanocomposites Authors: Deepalekshmi Ponnamma, Velautham Sivakumar, Anton Popelka, Yasser H.A. Hussein, Mariam Al Ali Al-Maadeed PII: DOI: Reference:

S0030-4026(18)31361-5 https://doi.org/10.1016/j.ijleo.2018.09.058 IJLEO 61497

To appear in: Received date: Accepted date:

9-7-2018 13-9-2018

Please cite this article as: Ponnamma D, Sivakumar V, Popelka A, Hussein YHA, Al Ali Al-Maadeed M, Laser Induced Periodic Surface Structures on Nano Metal Oxide filled Polyvinylidene Fluoride Nanocomposites, Optik (2018), https://doi.org/10.1016/j.ijleo.2018.09.058 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.

Laser Induced Periodic Surface Structures on Nano Metal Oxide filled Polyvinylidene Fluoride Nanocomposites

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Deepalekshmi Ponnamma1*, Velautham Sivakumar1, Anton Popelka1, Yasser H. A. Hussein2, Mariam Al Ali Al-Maadeed1,3

Center for Advanced Materials, Qatar University, P O Box 2713, Doha, Qatar.

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Chemistry and Earth Sciences Department, College of Arts and Sciences, Qatar University.

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Materials Science & Technology Program (MATS), College of Arts & Sciences, Qatar

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Author

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*Corresponding

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University, Doha 2713, Qatar

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Tel: (+974) 4403-5684; E-mail: [email protected] (D. Ponnamma)

Abstract

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The ability of polarized pulsed laser in surface modification of substrate surfaces without thermally destroying them is a well-established concept of scientific procedure. In this work, we

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report the laser induced surface structures that are created on the semi crystalline polyvinylidene

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fluoride (PVDF) polymer and its composites containing transition metal oxides-zinc oxide of 100 nm and iron oxide of 30 nm diameter. The PVDF nanocomposites are fabricated by solution casting method and films of 0.2 mm thickness are used for laser treatment. The periodic structures formed are demonstrated by atomic force microscopy and profilometry investigations. Influence of laser pulses on the material properties is also addressed by means of Fourier 1

transform infrared spectroscopy, contact angle measurements and thermogravimetric/differential scanning calorimetric studies.

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Keywords: LIPSS; Nanocomposites; PVDF; Surface morphology; Wettability.

1. Introduction

Different kinds of radiation techniques modify the surface features of metals, polymers and similar materials [1,2]. Our group developed various surface modification strategies by means of

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gamma irradiation [3], UV-irradiation [4] and laser treatment [5]. Nanofabrication of polymers

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and nanocomposites is essential in the modern society especially for industrial applications.

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Surface nanostructuring by imprinting nanoscale patterns by laser impulses has significance

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when compared to nanolithography which needs typical conditions such as vacuum and clean room atmosphere [6]. In the case of polymers and their composites, modification of surface has

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utmost significance as it can regulate the hydrophilicity/hydrophobicity desirable for their

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industrial use, in addition to determining the reagent flow behavior and the ease of adhesion.

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Different kinds of surface modification are practiced for the process among which the plasma treatment [7,8], corona discharge [9], electron beam and ion beam irradiation [10-14] and wet

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chemical etching [15] are well reported. Intense laser pulses of durations ranging from nanosecond to femtosecond provoke the

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appearance of spontaneous and superficial periodic nanostructures in many solid materials, like metals, dielectrics and semiconductors [1,2,16]. Such laser induced periodic surface structures (LIPSS) strongly depend on the wavelength of irradiating laser pulses, and the time of exposure. Work on the polarized laser irradiation on polymeric substrates at fluences below the ablation

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threshold have been reported [17-19,5]. In most cases the lasers induce formation of selforganized ripple structures, with the period (L) depending on the laser wavelength (λ) and angle of incidence (θ). The following relation relates these parameters to the refractive index of the

𝐿=

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material (n), 𝜆

(1)

𝑛−𝑠𝑖𝑛𝜃

Laser irradiation can be used as a technique to modify the surface of metals/alloys to make them efficient for receiving coating. Other than process automation, complex surface processing and specific area treatment, laser enables precise adjustment of materials without thermally affecting

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the nearby areas. When a specific material is irradiated by laser, the laser-material interaction

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mechanism is rather complex (can be thermal and non-thermal) and can affect the physical

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nature of the material. This interaction will depend strongly on various irradiation parameters

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such as pulse form, power of the laser pulse, intensity, irradiation frequency and duration

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[20,21].

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Many metals and alloys practice the laser treatment as a technique to improve their structural applications. The laser allows the formation of intermetallic phases and refines the material’s

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microstructure. Generally, the surface topography will be very much affected by the laser pulses.

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In addition to the surface preparation of metal/polymer interface for structural applications, laser treatment can be useful for other applications such as enhancing the coating performance on

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biological implants [22,23]. Laser treatment is clean, fast, selective, and it is a non-contact process. Further its ability in creating complex surface structures in nanometer scale with precise control, localized treatment and no thermal effect has triggered its application in investigating many LIPSS studies on polymers and its composites and nanocomposites [2,24-25].

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Polyvinylidene fluoride (PVDF) is a semicrystalline polymer with a typical morphology consisting of spherulites of ~25 μm sizes [26]. Among the fluoride polymers, it has the lowest cost [27]. Composites of PVDF containing graphene, clay and ceramic nanoparticles are

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excellent materials for industrial applications such as sensors, flexible capacitors and piezoelectric devices [28-31]. The good ferroelectric properties and biocompatibility of PVDF established its applications in medical and dental industries [32-36]. PVDF and other polymers that were irradiated with laser can be utilized in electronic industry [37]. It is reported that the laser irradiation on PVDF has increased its electrical conductivity from 10-13 to 10-4 Ω-1cm-1 [38].

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In addition, laser treatment improves the hydrophobicity and adhesion strength between the filler

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and the polymer. This can lead to application in microelectronics, microfluidics and optics

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[27,39].

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In this paper we report the effect of LIPSS on PVDF nanocomposites containing two types of metal oxide nanoparticles, Zinc Oxide (ZnO) of 100 nm and Iron Oxide (FeO) of 30 nm

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diameters. Nanocomposites were prepared by mixing the polymer with the transition metal oxide

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nanoparticles at 5 wt.%, a composition above the percolation threshold at which the surface

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properties are prominent [40]. This percentage of additives was in accordance with our previous reports on polymer nanocomposites [40,41]. The periodic structures are monitored by means of

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atomic force microscopy and its influence is further studied using profilometry, Fourier

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transform infrared studies, contact angle measurements and thermal studies.

2. Experimental Details 2.1. Materials

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FeO of 30 nm particle size and ZnO of 100 nm particle size were purchased from Sigma Aldrich. PVDF of molecular weight Mw, 1,40,000 obtained from Sigma Aldrich was used for the study. Solvents like dimethyl formamide and acetone (99.0% purity) were purchased from BDH

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chemicals and used as such without any further purification. 2.2. Synthesis of composites

The PVDF nanocomposites were made by the solution casting method. For this solid PVDF pellets were dissolved in a 1:1 mixture of acetone and DMF (2 g in 20 ml solvent) by magnetic stirring at 70°C until the solution became homogeneous and clear. The nanoparticles in specific

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quantity (5 wt.% each) were dispersed in the same solvent mixture by ultrasonication for 2 h.

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Later the fillers were mixed with the polymer solution by magnetic stirring at room temperature

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overnight. Finally three samples were studied for the tests, neat PVDF, PVDF containing 5 wt.%

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FeO (PVDF/FeO) and that containing 5 wt.% of ZnO (PVDF/ZnO). The sample solutions were

thickness.

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2.3. Laser treatment

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dried and hot pressed at 170°C to obtain smooth and flat nanocomposite films of 0.2 mm

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The surfaces of PVDF composites filled with ZnO and FeO nanoparticles (5 wt.%) were irradiated with pulsed laser with a pulsed width of 5 ns. For this, the polymer nanocomposite

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films were exposed to 355 nm laser at right angle (the angle of incidence is zero) and with a spot size of 3 mm diameter. Energy of the laser pulse was varied from 0.5 to 4 mJ and the number of

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pulses per spot was varied between 500 and 1000 pulses. Figure 1 represents the laser irradiation arrangement.

2.4. Characterizations 5

2.4.1 Surface morphology investigation. The changes in the surface morphology were investigated by Atomic Force Microscopy (AFM). The MFP 3D- AFM device (Asylum Research, USA) was used in this study. Measurements were

OLTESPA, Olympus) in the tapping mode in air (AC mode).

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carried out under ambient conditions by a Silicon probe (Al reflex coated Veeco model –

The confocal profilometer Leica DCM8 provides non-destructive three-dimensional surface profiling for the tested samples as well. This equipment contains high resolution sensor for quick capturing of high contrast images. The images were captured by EPI 100X-L objective.

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2.4.2 Infrared spectroscopy analysis

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The Fourier transformed infrared spectroscopy (FTIR) with attenuated total reflectance was used

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to investigate the chemical composition of the samples. The spectra of the samples were

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recorded by the FTIR Spectrometer Frontier (PerkinElmer, USA) in the middle infrared region (400-1800 cm-1) with resolution of 2 cm-1. A pressure clamp ensuring a good contact between the

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2.4.3 Wettability measurement

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crystal and the investigated sample was used to achieve high spectral quality.

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The wettability changes of the samples after laser treatment were analyzed by the OCA35 optical system (Data Physics, Germany) using the sessile drop technique. The contact angle of water

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was tested to investigate wettability changes in the laser affected areas of the surface. A volume of 3 µL water was used to eliminate gravitational effects of the drops. A representative value of

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the contact angle was obtained from 3 separate readings. The contact angle was characterized by the angle between the solid/liquid and liquid/vapor interface. 2.4.4 Thermal properties

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The thermal degradation behavior of the samples was tested by thermogravimetric analyzer, TGA 4000 - Perkin Elmer, the samples were heated to 600 °C at a rate of 10 °C/min, starting from room temperature in N2 atmosphere. Thermal transition and phase change for the samples

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within the range of 20-200 °C temperature, at 10 °C/min were studied by differential scanning calorimetry, DSC 8500 - Perkin Elmer. The first cooling and second heating curves were recorded and analyzed.

3. Results and Discussion

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3.1. Atomic force microscopy

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The formation of ripples on PVDF samples by laser energy was less reported, and here we used

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different energies to investigate this effect. In order to obtain LIPSS in a typical material, by the

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irradiation of nanosecond laser pulses, high absorption coefficient at laser wavelength is highly preferred. This means the need of knowing the UV visible spectral information of the

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corresponding materials is essential [25]. The laser treatment at an appropriate wavelength and

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fluence is capable of forming ripples provided that the laser wavelength is below the ablation

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threshold. It also must be fired with enough number of pulses. Figure 2 represents the formation of ripples in the nanostructured area of the neat PVDF polymer with varying the laser pulse

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energy. For fluences < 25 mJ/cm2, no morphological changes were observed on the surface; however at fluence of 25.5 mJ/cm2, deformation started on the surface in the form of parallel and

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well defined ripples. Here the ripple axis is parallel to the laser beam polarization vector. For fluences ˃ 28.3 mJ/cm2, the LIPSSs became distorted and ablation of the polymer was observed at 3.1 mJ/cm2.

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The observed results are explained on the basis of Z-sensor profiles as represented in Figure 3. There is no clear dependence on the height of the ripples as determined from the AFM images on

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the laser fluence. But the height is comparatively larger for the fluence at which ripple formation is observed. This can be attributed to the increase in depth heated by laser irradiation with the increase in fluence. This is in accordance with the previously published data [2].

In addition, the less periodicity observed in the PVDF ripples can be attributed to its low absorption coefficient (~ 0.4 cm-1 for wavelengths of 266 nm) compared to the higher values

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noted for conjugated polymers and aromatic polyesters [42]. The laser induced periodicity for the

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non-absorbing polymers such as poly(vinylidene fluoride–trifluoroethylene) copolymer through

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bilayer formation was studied by Rebollar’s research group [43]. A bilayer system is fabricated

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from the polymer in which the bottom layer efficiently absorbs at the irradiation wavelength and induces LIPSS over the top layer. However, effort has been made here to see the ripple formation

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on the normally solution casted PVDF films containing two commonly used metal oxide

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nanoparticles-ZnO and FeO of different dimension. In order to generate LIPSS on a polymer

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surface, irradiating energy more than glass transition (Tg) is required, which ensure the chain dynamics and structuring of the different segments in the polymer. When the irradiating energy

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is more than Tm, crystallization happens and different segments arrange themselves to form

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ripples. Heating above Tg, creates more rough surface in the polymer.

In the case of composites, the surface deformation follows a different procedure when compared to the neat PVDF. When the surface is analyzed using AFM, some parallelly oriented ripples are found for PVDF/5ZnO samples with 5 wt.% ZnO irradiated at 18.8 mJ/cm2 fluence. Interestingly

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this periodic structure is not visible for low energy pulses (about 1 mJ) or high energy pulses (above 2.2 mJ), indicating that the ripples form only on a small range of fluence corresponding to the fluence below the ablation threshold. The ripple formation seen in ZnO composite is

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represented in Figure 4 in the form of amplitude traces and in Figure 5 in the form of height profiles. In addition, the concentration of metal oxide above the percolation threshold imparts

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specific good properties, and it is really important to tailor these new ripples on the surface.

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The results show periodic structural formation in PVDF/5ZnO polymer surface when irradiated

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with 355 nm pulsed laser having pulse energy of around 2 mJ per pulse and total of 500 pulses.

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The PVDF/5FeO composite thin film samples were also irradiated with UV (355 nm) pulsed laser. Irradiation was carried out at normal incidence on self-standing films with the fluence

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range of 14-50 mJ/cm2 and 1000 number of pulses. Similar to the previous observation of

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PVDF/5ZnO films, periodic structures were seen on the surface of the irradiated PVDF/5FeO films, but here the images were rather clearer. The AFM images of untreated and laser irradiated

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PVDF/5FeO are shown in Figure 6 and 7.

Untreated samples show no formation of ripples on the surface. The ripples formation starts at the fluence of 14 mJ/cm2 and exists for a range of fluence of 14-43 mJ/cm2 after which deformation starts to appear. At 14 mJ/cm2 fluence, clear periodic structure with ripples separated by a distance of about 700 nm was observed. At 48 mJ/cm2 the deformation becomes 9

severe due to the ablation taking place within the system. The mechanism of ripples formation on the laser irradiated surface can be further explained as follows: At 14 mJ/cm2, the order of magnitude of separation, L obeys the relation of equation (1) mentioned before. With normal

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incidence (θ=0o) and typical refractive index of 1.5 of polymers, the periodicity L is roughly 2/3 of the laser wavelength [2,24,25]. However the periodicity observed as per Figure 7b is almost 2.4 times the calculated value, which can be attributed to the presence of nanoparticles within the composite samples. The height of the ripples is observed to be about 20 nm. When the energy is doubled, we can notice the melting of surface with enhanced roughness. Still parallely oriented

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periodic surface with 600- 700 nm separation is noticeable. At higher fluence of 43 mJ/cm2,

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rougher ripples were observed (Figure 7c).

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The main mechanism of LIPSS formation on polymer nanocomposites upon the

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irradiation of nanosecond laser pulses is the interference between the laser incident and the surface waves scattered [2]. As a result, a modulated energy distribution also happens at the

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surface of the nanocomposite materials. Though the laser does not cause any thermal damage to

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the material, it can cause the thermal energy of the upper layer of the nanocomposite to enhance

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and this variation can be estimated at different depths with respect to time. There is a threshold value for the laser fluence since a minimum fluence is needed for the surface temperature to

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overcome the glass transition. At this stage, polymer surface devitrification takes place affecting the polymer chain movement. The significance of nanofillers and nanocomposites in regulating

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the LIPSS here becomes more pronounced. Since the nanoparticles are embedded in the polymer chain and many networks are formed at the percolation level, the laser irradiation can affect molecular motion and distribution of filler particles. Both metal nanoparticles are added to PVDF at 5 wt.% which is above its percolation level. There are reports on the extended induction period

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to generate LIPSS due to higher glass transition of the polymer [44]. The temperature increase also can cause the formation of material regions exhibiting low superficial viscosity [45]. For the rest of the discussion, we will focus on studying the samples with the most

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periodic surface structures (PVDF irradiated with 24.3 mJ/cm2, PVDF/ZnO with 18.8 mJ/cm2 and PVDF/FeO with 14 mJ/cm2 fluence). Both bulk and surface study will be presented in the subsequent sections. LIPSS formation on the analyzed PVDF/ZnO and PVDF/FeO composites are further observed from the profilometric images represented in Figure 8. The surface roughness calculated from the analysis suggested an increase in surface roughness by 0.9 times

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for the PVDF/ZnO (irradiated at 18.8 mJ/cm2 fluence) sample and 1.5 times increase for the

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PVDF/FeO (irradiated at 14 mJ/cm2 fluence) sample upon laser irradiation.

3.2. Fourier Transformation Infrared Spectroscopy (FTIR)

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The FTIR spectra of the samples were recorded to test their chemical structure and to investigate

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the effect of laser treatment on the chemical composition of the inner skeleton of the polymer

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nanocomposites. Figure 9 shows the typical FTIR spectra of the PVDF/ZnO and PVDF/FeO samples with and without the laser irradiation. The results reveal similar appearance for the

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chemical structure before and after the treatment. This indicates that the sample chemical structure was not affected by the laser treatment. There are no shift in band positions for both

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nanocomposites, illustrating the incapability of the laser pulses in changing the stretching and bending vibrations of the functional groups present within the systems. The energy of the laser is not strong enough to cleave the chemical bonding within the macromolecular system.

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Though a slight change in the intensity of the bands is observed which suggest the rearrangement of molecular conformation taking place within the polymer nanocomposite system. Rebollar et al. addressed this concept by means of Raman spectroscopy and proved the presence of higher

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amount of oxygen atoms in the irradiated samples due to surface oxidation [25].

3.3. Contact Angle measurements

The surface morphology and surface chemistry play major role in regulating the surface

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wettability of a particular material [19]. There are different theories to explain the influence of

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surface roughness on wettability. The theory by Wenzel [22] assumes the filling of liquid on the

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whole area of rough surface whereas the theory by Cassie and Baxter [23] assumes the partial

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wetting of liquid on the rough surface [20]. Mathematically, the two theories can be respectively expressed by Equation 2 and 3.

(2)

cos 𝜃𝑚 = 𝜑 cos 𝜃𝑠 + 𝜑 − 1

(3)

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cos 𝜃𝑚 = 𝑟 cos 𝜃𝑠

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Where θm and θs represent the contact angle measured on a structured surface and the equilibrium contact angle on an ideally smooth surface, respectively, r the roughness factor (ratio

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of actual rough surface area to geometrically projected area) and φ the ratio of wetted surface

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area to its projected area. Table 1illustrates the water contact angle for the composite surface before and after the

laser treatment. The water contact angle slightly increased upon laser irradiation. This indicates that the hydrophilicity has decreased for both polymer/metal nanoparticle composites. This can be due to the ablation of various types of oxidized groups such as carbonyl or hydroxyl with 12

increasing the laser pulses and energy [21]. This phenomenon was probably also caused by changes in the surface roughness. It is also reported that the laser interaction with the materials surface can create irregular roughness and peroxide radicals at various rates depending on the

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properties of irradiated laser and composition of the material [20,2]. The increased surface roughness of the laser irradiated surfaces traps air underneath the liquid making the surface superhydrophobic [46]. The laser ablation confirmed from the AFM images is rather evidenced

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from the contact angle enhancement.

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Periodic surface modification is much easier with FeO composite than the ZnO as the former

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requires about 14 mJ/cm2 fluence, which is half of the fluence required for the latter. This is

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evidenced from the contact angle values as the FeO composite showed a significant increase in the value (during laser treatment) when compared to the ZnO filled composite (Table 1). The

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viability of metal oxide nanocomposites towards laser irradiation seems to be different from each

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other. When the semiconductor nanoparticles are irradiated with energies larger than their band gap, electron-hole pairs are created and the electrons reduce metal ions to metal atoms. Thus a

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metal shell layer will be formed on the surface of the material [47]. The band gap for FeO is 2.1

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eV whereas for the ZnO it is 3.2 eV. This is suggested as the reason for the lower energy required for the LIPSS formation in FeO filled PVDF nanocomposites.

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3.4. Thermal Properties The bulk properties due to LIPSS are also studied in terms of temperature influences. For this, the TGA and DSC curves obtained for all the samples are provided in Figure 10. Clear difference is observed between the laser treated and untreated samples. The high fluence of laser irradiation generally creates better surface activation [48]. On the polymer surface layers, the laser fluence 13

imparts heat and this induces the formation of low molecular weight degraded products from the polymers (e.g. CO2, O2, H2O) [48]. Here, the stability of laser treated samples was found to be higher when compared to the untreated samples (Table 2). This is clear from the change in

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degradation temperature from 483.16 °C to 488.67 °C for the PVDF-ZnO composite and from 469.87 °C to 475.91 °C for the PVDF-FeO sample upon laser irradiation. However the onset of degradation is lower for the irradiated samples (small shoulders at 402.06 °C and 396.4°C respectively for PVDF-ZnO and PVDF-FeO treated samples). This can be due to the increased surface activity of the sample because of laser ablation [48]. A slight change is observed in the

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behavior of PVDF-FeO untreated sample (small shoulder at 293.58 °C) is ascribed to the metal

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oxide impurities present in it. The results were against the investigation of Nouh et al. in which

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they established the lower thermal stability on laser irradiation because of the degradation

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mechanism and removal of stabilizer groups due to steric hindrance [49].

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The deviation in thermal behavior can be attributed to the presence of nanoparticles within the

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PVDF polymer and the lower laser fluence used in the present work. Similar observations were

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noticed for the DSC melting and crystallization curves as well (Figure 10c and 10d). From the curves it is noticed that the laser irradiated samples follow similar behavior, while the

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unirradiated samples show similarity with the neat PVDF. The melting/crystallization data along with the crystallinity index values of all samples are represented in Table 2. In the PVDF-ZnO

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and PVDF-FeO composites, the crystallization temperature increases and the crystallinity decreases compared to neat PVDF. This ensures the loss of regularity due to the addition of nanoparticles [50]. However, the crystallization temperature for the laser irradiated PVDF/ZnO and PVDF/FeO composite systems were slightly higher than the unirradiated samples. This can

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be attributed to the formation of various networks within the composites upon laser irradiation. This can also be due to the breaking and reformation of bonds within and sometimes, the removal of certain moieties. All these points substantiate the surface activation and

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morphological variation occurring in the PVDF composites upon laser irradiation.

4. Conclusions

The effect of laser irradiation in deriving LIPSS in PVDF nanocomposites containing nano metal

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oxides of various dimensions is reported. PVDF/ZnO and PVDF/FeO nanocomposites were used

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for the study. The laser energy, number of pulses and fluence rate were observed to be significant

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parameters in regulating the periodicity in LIPSS. PVDF/FeO showed better LIPSS compared to

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the PVDF/ZnO composite and the hydrophilicity was lower in both cases. The thermal analysis and differential scanning calorimetry technique shows the difference in chemical environment of

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the laser irradiated composite samples, and the laser treatment affects the surface more than the

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bulk. Moreover, the structural and functional properties of a polymer composite vary according

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to the laser fluence, number of pulses, time of exposure and the nature of samples undergoing irradiation. Since polymers and nanocomposites are widely applied in engineering and

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technology, laser surface treatments has utmost significance in extending its applications.

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Conflicts of Interest There are no conflicts to declare

Acknowledgement

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This publication is made possible by NPRP grant 6-282-2-119 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility

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of the authors.

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Figure captions

A

CC

EP

TE

D

M

A

N

U

Figure 1: Schematic representation of laser irradiation.

20

SC RI PT U N A M D TE EP CC A Figure 2: Amplitude AFM images of untreated and laser treated PVDF with different pulse energies of laser at different scan sizes.

21

SC RI PT U N A M D TE EP CC A

Figure 3: AFM 3D height images and Z-sensor line profiles graphs of untreated and laser treated PVDF with different pulse energies of laser.

22

SC RI PT U N A M D TE EP CC A Figure 4: Amplitude AFM images of untreated and laser treated PVDF/5ZnO with different pulse energies of laser.

23

SC RI PT U N A M D TE EP CC

A

Figure 5: AFM 3D Height images and line profiles graphs of untreated and laser treated PVDF/5ZnO with different pulse energies of laser.

24

SC RI PT U N A M D TE EP CC A

Figure 6: Amplitude AFM images of untreated and laser treated PVDF/5FeO with different pulse energies of laser.

25

SC RI PT U N A M D TE EP CC A

Figure 7: AFM 3D Height images of untreated and laser treated PVDF/5FeO with different pulse energies of laser.

26

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U

Figure 8: Topography images from profilometer for PVDF/ZnO a) unirradiated b) irradiated and

CC

EP

TE

D

M

A

N

PVDF/FeO c) unirradiated d) irradiated.

A

Figure 9: FTIR spectra of: a) PVDF/ZnO and b) PVDF/FeO composites untreated and laser treated.

27

SC RI PT U N A M D

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Figure 10: a) TGA, b) DTG c) melting and d) crystallization curves for untreated and laser treated

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EP

composites.

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Table

Table 1. Contact angle measurements for the laser treated at 28.3 (PVDF), 18.8 (PVDF/ZnO) and 14

Contact Angle (°)

PVDF untreated

99.6 ± 1.02

PVDF treated

101.2± 1.51

PVDF/ZnO untreated

85.01±1.99

PVDF/ZnO treated

92.03±2.07

PVDF/FeO untreated

75.32±1.20

PVDF/FeO treated

87.87±3.74

A

N

U

Samples

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(PVDF/FeO) mJ/cm2 and untreated composites.

Tm onset

Tc

ΔHf

CI

Td

169.46

160.76

135.83

38.85

37.06

475.63

168.12

160.42

137.55

34.45

6.56

483.16

TE

M

Table 2. Melting and crystallization data for the nanocomposites and the degradation temperature. Tm

PVDF PVDF-ZnO untreated

D

Samples

167.68

164.42

140.21

21.84

4.16

488.67

PVDF-FeO untreated

166.04

162.59

140.21

33.69

6.42

469.87

PVDF-FeO treated

167.72

164.35

140.98

18.80

3.58

475.91

A

CC

EP

PVDF-ZnO treated

29