**2.1.3 Plasma treatment of woven PET samples**

All plasma treatments were carried out using an atmospheric plasma machine (see Fig. 12) called 'Coating Star' manufactured by Ahlbrandt System (Germany). The following machine parameters were kept constant: electrical power of 1 kW, frequency of 26 kHz, electrode length of 0.5 m and inter-electrode distance of 1.5 mm. The outer layer surfaces of both electrodes were of ceramic (a dielectric material), so that when these electrodes were subjected to a potential difference, a glow discharge called the 'Dielectric Barrier Discharge' (DBD) was created.

Fig. 12. (a) Optical microscopic view of the PET woven fabric, (b) chemical formula of PET

Atmospheric air was used during the atmospheric plasma treatments. The textile samples were subjected to varying plasma Treatment Power (TP) which is the plasma power applied per m² of textile sample, expressed in kJ/m². The TP is related to the velocity of the treatment (V) and the electrical power (P) of the machine, by the equation (Eq. 1):

$$TP = \left(\frac{P}{V \times L}\right) \times 0.06\tag{1}$$

P = Electrical Power (W) L = Electrode length (m) V =Velocity of the sample (m/min)

Plasma treatment was carried out at velocities (V) of 1 m/min, 2 m/min, 5 m/min and 10m/min. It was also performed at constant speed with varied electrical power (P) of 400 watts, 700 watts and 1000 watts. After plasma treatment, each plasma treated sample was separated from waste fabric and kept in aluminium foil away from light.

## **2.1.4 Ageing methods**

246 Atomic Force Microscopy – Imaging, Measuring and Manipulating Surfaces at the Atomic Scale

measuring the surface tension of final rinsing water (used to clean the PET samples), which remained constant and equal to 72.6 mN/m ,which is the surface tension of pure water.

The PET woven fabric was cut into square pieces of 50cm X 50cm on the basis of the electrode length of the plasma machine (50 cm). The speed of the fabric in the discharge

All plasma treatments were carried out using an atmospheric plasma machine (see Fig. 12) called 'Coating Star' manufactured by Ahlbrandt System (Germany). The following machine parameters were kept constant: electrical power of 1 kW, frequency of 26 kHz, electrode length of 0.5 m and inter-electrode distance of 1.5 mm. The outer layer surfaces of both electrodes were of ceramic (a dielectric material), so that when these electrodes were subjected to a potential difference, a glow discharge called the 'Dielectric Barrier Discharge'

(a)

(b) Fig. 12. (a) Optical microscopic view of the PET woven fabric, (b) chemical formula of PET

Atmospheric air was used during the atmospheric plasma treatments. The textile samples were subjected to varying plasma Treatment Power (TP) which is the plasma power applied

**2.1.2 Sample preparation for plasma treatment** 

**2.1.3 Plasma treatment of woven PET samples** 

zone could be varied through the control.

(DBD) was created.

Effect of ageing on air-plasma treated PET fabric samples was observed by monitoring changes in water contact angle as well as surface topography of the samples, 20 days after plasma treatment. Ageing of plasma treated sample was carried out in two different ways:


#### **2.1.5 Effect of PET fabric dyeing conditions (High temperature conditions)**

The plasma treated PET samples were immersed in aqueous conditions at 90°C for 30 minutes without the presence of any dye.

## **2.1.6 Effect of adhesion of PEG 1500 on PET fabric**

As ageing with time causes loss of hydrophilic species formed by plasma treatment (Krump, 2005), immobilizing a hydrophilic oligomer like PEG -poly(ethylene glycol) immediately after plasma treatment would perhaps yield a more durable hydrophilic treatment. PEGpoly(ethylene glycol) has been used for surface modification because of its unique properties such as hydrophilicity and flexibility (Harris, 1992).

PEG of molecular weight 1500 g/mol , i.e PEG 1500 from Fluka chemicals was immobilized on cleaned-untreated PET fabrics as well as plasma treated PET fabric samples using padding and curing method. For the padding process the open-width PET fabric was passed through an aqueous solution of PEG 1500 in water and through two squeezing rollers (see Fig. 13). At a squeezing pressure of 4 bars, the weight pick up remained almost constant around 56%.

#### **2.2 AFM tapping mode images**

In a previous paper Leroux and al. ( Leroux, 2006) showed using AFM in the LFM mode, that friction forces measured at the surface of PET fabric is doubled after a plasma

Atomic Force Microscopy – For Investigating Surface Treatment of Textile Fibers 249

surface of water placed in a container. On immediate contact with the water surface, a sudden increase in weight (Wm) is measured due to meniscus formation on the fabric surface. The weight increases further as the liquid flows inside the fabric structure by capillarity (wicking). The capillary weight (Wc) after 6 minutes, is measured. From the meniscus weight (Wm) the water contact angle can be calculated. More detailed description

**3.1 Effect of varying speed and electrical power on plasma-treatment of PET woven** 

Irrespective of treatment power and speed setting, the water contact angle after plasma treatment was always around 45°, while the untreated PET fabric water contact angle was 80°. Any decrease in speed or increase in Treatment Power did not have a significant impact on this minimum contact angle value. However, tapping mode AFM images of samples (Fig. 14) subjected to an air–plasma treatment at varying Treatment powers "TP" of 0, 12, 24, 60

Fig. 14. Topographic images obtained by AFM in the tapping mode of a) an untreated PET fabric fiber surface, a plasma-treated PET fabric fiber surface at treatment power ''TP'' of (b)

Fig. 14 shows that as the treatment power is increased from 0 to 120 kJ/m² there is significant surface restructuring. At very low Treatment Power of 12 kJ/m² at a speed of 10

12 kJ/m², (c) 24 kJ/m² , (d) 60 kJ/m² and (e) 120 kJ/m² (Takke, 2009).

of this experiment can be found in our previous work (Leroux, 2006).

and 120 kJ/m² show considerable changes in fiber surface morphology.

**3. Results and discussions** 

**fabrics** 

treatment, and these forces remain homogeneous throughout the plasma treated PET fiber surface.

Fig. 13. Application procedure of PEG-1500 on PET fabric by padding, squeezing followed by curing and a final rinsing before drying.

In this chapter, surface investigation by imaging in the Tapping mode using AFM "Nanoscope III" from Digital Instrument, is presented. This mode was preferred to the AFM /LFM (contact mode AFM), since the Tapping mode overcomes problems associated with friction, adhesion, electrostatic forces which may arise after a plasma treatment, and which would distort image data (Kailash, 2008).

Tapping mode imaging was carried in ambient air using 'Budget sensor' tips from 'Nanoandmore', of length 125 µm, made of Si3 N4 with aluminium coating, and a resonance frequency of 300 kHz. The cantilever which scans the surface is oscillated at or near its resonant frequency using a piezoelectric crystal. The oscillating tip is moved toward the surface until it begins to lightly touch, or tap the surface, significantly reducing the contact time. During scanning, the vertically oscillating tip alternately contacts the surface and lifts off, generally at a frequency of 5000 to 500,000 cycles per second. As the oscillating cantilever begins to intermittently contact the surface, the cantilever oscillation is necessarily reduced due to energy loss caused by the tip contacting the surface. The reduction in oscillation amplitude is used to identify and measure surface features. When the tip passes over a bump in the surface, the cantilever has less room to oscillate and the amplitude of oscillation decreases. Conversely, when the tip passes over a depression, the cantilever has more room to oscillate and the amplitude increases (approaching the maximum free air amplitude). This feed back signal also allows construction of the topographic image. The fiber surface roughness Ra was calculated directly from AFM signals (Feninat, 2001) using the software supplied with the Nanoscope III.

#### **2.3 Water contact angle and capillary measurements**

The sessile drop method is useful for measuring water contact angles greater than 90° however for lower contact angles the porous woven fabric immediately absorbs the liquid drop. That is why wettability of textile surfaces was monitored indirectly through a wicking test using a tensiometer. This method allows the measurement of contact angle as well capillarity measurements. The tensiometer used is the 3S from GBX, France. During measurements, a vertically hanging fabric sample of defined dimension is connected to the tensiometer at the weighing position and progressively brought into contact with the surface of water placed in a container. On immediate contact with the water surface, a sudden increase in weight (Wm) is measured due to meniscus formation on the fabric surface. The weight increases further as the liquid flows inside the fabric structure by capillarity (wicking). The capillary weight (Wc) after 6 minutes, is measured. From the meniscus weight (Wm) the water contact angle can be calculated. More detailed description of this experiment can be found in our previous work (Leroux, 2006).
