For a modification of natural and synthetic fibrous polymers low-pressure ICRF plasma and liquid repellent
sol-gel fluoroalkyl-functional siloxane precursor were used. Plasma induced surface chemical and
morphological changes on fluorinated poly(ethylene terephthalate) and cellulose were analysed using X-ray
photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Wettability properties of sol-gel
functionalized polymers were determined by the goniometric water contact angles and water sliding angle
measurements. After plasma treatment the oxygen content on the surface of both polymers increased (increase
of O/C ratio) and a nanostructured surface roughness appeared. Plasma ablation caused partially
defluorinated nanostructured surface of fluorinated poly(ethylene terephthalate) polymer and increased its
hydrophilicity. Plasma activation and etching of cellulose polymer contributed to the creation of highly adhesive
and wash resistant sol-gel coating with superhydrophobic, oleophobic and self-cleaning properties.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3539

Gorjanc, M.

Mozetič, M.

Simončič, B.

Vasiljević, J.

Vesel, Al.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 1 No 4, 04PITSE03(4pp) (2012)   2304-1862/2012/1(4)04PITSE03(4) 04PITSE03-1  2012 Sumy State University Plasma and Sol-Gel Technology for Creating Nanostructured Surfaces of Fibrous Polymers  M. Gorjanc1,*, J. Vasiljević1, Al. Vesel2, M. Mozetič2, B. Simončič1,†  1 University of Ljubljana, Faculty of Natural Sciences and Engineering, Aškerčeva 12, 1000 Ljubljana, Slovenia 2 Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia  (Received 06 July 2012; published online 21 August 2012)  For a modification of natural and synthetic fibrous polymers low-pressure ICRF plasma and liquid re-pellent sol-gel fluoroalkyl-functional siloxane precursor were used. Plasma induced surface chemical and morphological changes on fluorinated poly(ethylene terephthalate) and cellulose were analysed using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Wettability properties of sol-gel functionalized polymers were determined by the goniometric water contact angles and water sliding angle measurements. After plasma treatment the oxygen content on the surface of both polymers increased (in-crease of O/C ratio) and a nanostructured surface roughness appeared. Plasma ablation caused partially defluorinated nanostructured surface of fluorinated poly(ethylene terephthalate) polymer and increased its hydrophilicity. Plasma activation and etching of cellulose polymer contributed to the creation of highly ad-hesive and wash resistant sol-gel coating with superhydrophobic, oleophobic and self-cleaning properties.  Keywords: plasma, sol-gel, modification, ablation, surface activation, nanostructure, XPS, AFM, poly(ethylene terephthalate), cellulose.    PACS number: 52.25.Kn                                                             * marija.gorjanc@ntf.uni-lj.si † barbara.simoncic@ntf.uni-lj.si 1. INTRODUCTION  Non-equilibrium plasma represents an extremely powerful medium for a modification of the surface properties of solid materials. A medium of particular interest is weakly ionized highly dissociated oxidative plasma that can be sustained in high frequency dis-charges in oxygen, air, carbon dioxide, water vapour, and mixtures of these gases with a noble gas. Such plasma has been successfully utilized in an extremely wide range of applications from nanoscience to fusion reactors [1-6]. The advantages of using plasma are eco-logical and economical. Moreover, the fibrous polymers subjected to the treatment are modified without an alteration of the bulk properties [7]. Plasma treated fibrous polymers have a higher specific surface area, which leads to new or improved properties of the treat-ed surface, i.e. increased surface activity, hydrophilic or hydrophobic properties, and increased absorption ca-pacity towards different materials, i.e. nanoparticles and nanocomposites [8-12]. The nanocomposites have broken through in the production of advanced fibrous materials (i.e. textiles) as sol-gel coatings [13]. These substances comprise a class of composite organic-inorganic materials that, under the appropriate appli-cation conditions, form a dense three-dimensional pol-ymer film approximately 10-nm thick, with a high level of chemical functionality. Sol-gel technology has opened new possibilities for the creation of fibres with novel functional and protective properties, such as hydropho-bicity, oleophobicity, decreased flammability and anti-microbial activity [14-18]. For our research low-pressure plasma was used for a modification of synthet-ic fibrous polymer fluorinated poly(ethylene tereph-thalate) in order to achieve hydrophilicity of the poly-mer. The same plasma parameters were used for a modification of cellulose to achieve better adhesion of liquid repellent sol-gel fluoroalkyl-functional siloxane precursor and to achieve superhydrophobic and self-cleaning properties of cellulosic fibrous polymer.   2. EXPERIMENTAL  2.1 Materials  For a research natural and synthetic fibrous poly-mers, such as cellulose (CO) and fluorinated poly(ethylene terephthalate) (PET-F) were used.  2.2 Plasma treatment   Polymers were modified using low-pressure induc-tively coupled radiofrequency plasma. The discharge chamber was a cylindrical Pyrex tube with a diameter of 27 cm and a length of 30 cm. Polymeric substrates were put onto a glass holder mounted in the centre of the discharge chamber. After closing the chamber the desired pressure of 0.2 mbar was achieved by a two-stage rotary pump with a nominal pumping speed of 65 m3/h. Water vapour was used as a working gas and the source of water vapour was the polymer itself. By switching on the RF generator, the gas in the discharge chamber was partially ionized and dissociated, starting the plasma modification of the polymers. The plasma treatment time was 30 s.  2.3 Application of sol-gel  Sol-gel method was used for creating water and oil repellent properties of substrates. As a precursor fluoroalkyl-functional siloxane (FAS) was used. The sol was prepared with 10 % concentration of FAS in a wa-ter medium at pH 5 by stirring with a high-speed stir- M. GORJANC, J. VASILJEVIĆ, AL. VESEL, ET AL. PROC. NAP 1, 04PITSE03 (2012)   04PITSE03-2 rer for about 1 hour at the room temperature. The sols were applied onto untreated and plasma treated cellu-losic substrates by the pad-dry-cure method, including full immersion at room temperature, wet pick-up of 85 %, drying at 100 C and curing at 150 C for 5 min. The substrates were then left for 14 days under stand-ard atmospheric conditions to complete the polymeriza-tion process.  2.4 Analysis and measurements  Information on the chemical composition and chemi-cal bonds of surface atoms of untreated and plasma modi-fied substrates was obtained with XPS analysis. In the photoelectron spectrum, which represents the distribu-tion of emitted photoelectrons as a function of their bind-ing energy, peaks can be observed which are typical of elements from the sample surface up to about 6 nm in depth. The morphological surface properties of fibrous poly-mers and their changes after plasma modification were studied using AFM where the primary objective is the measurement of the topographic surface properties in nanometre scale, from which the roughness of the sample can be obtained.  Wettability properties of polymers were determined by the static water drop contact angle measurements using DSA 100 contact angle goniometer, the function of which is based on the principle of the goniometer-sessile drop technique. Ten water drops (volume of 5 μL) were placed on different points on the substrate samples and were used for the determination of the average contact angle values. All values reported here correspond to con-tact angles obtained under stationary conditions, i.e. 60 s after the water drops were applied to the substrate. Since sliding behaviour of water droplets on solid sur-faces are among the fundamental results of wettability, the sliding angles were measured on a tilting base where the slope of the sample was slowly increased from the horizontal state. At a critical slope angle, the sliding an-gle was reached, where the water droplet rolled of the substrate. The oil repellency of sol-gel coated substrates was de-termined by hydrocarbon resistance test (ISO 14419:2000) which is applicable to the evaluation of a substrate's resistance to absorption of a selected series of liquid hydrocarbons of different surface tensions. The repellency rating was expressed by the surface tension of the test liquid which did not wet and penetrate the sub-strate in 30 seconds. Wash durability of sol-gel coating was determined af-ter repetitive washing in an AATCC Atlas Launder-O-Meter Standard Instrument, which is widely used for evaluating laundry results on a laboratory scale. The duration of the washing cycles was 30 min, at a tempera-ture of 40 C. The washing cycles were carried out in a solution of standard detergent at a concentration of 5 g/l. After washing, the samples were rinsed in cold distilled water and then held under cold tap water for 10 min, squeezed and dried at a room temperature. The quality of sol-gel coatings was assessed after the first and fifth washing cycle by measuring static water drop contact angles.  3. RESULTS AND DISCUSSION  The plasma effects on fibrous polymers are depend-ent on the chemical and morphological properties of polymers [19] and since fluorinated poly(ethylene ter-ephthalate) has properties opposite of those of natural cellulose with respect to chemical composition, mor-phology and wetting behaviour the results are present-ed for each polymer separately.  In Table 1 the results of AFM and XPS analysis with measurements of static water drop contact angles on PET-F before and after plasma modification are pre-sented. The results show that water vapour plasma induced the nanostructuring of PET-F polymer surface due to plasma ablation. The surface roughness in-creased from 2.70 nm to 7.23 nm. After plasma modifi-cation the activation of the polymer was noticeable al-so; the surface of PET-F contained a higher O/C ratio, which means that it contained more of the oxygen and less of the carbon atoms. The atomic concentration of fluorine was decreased after plasma modification, and as a result of that lower static water drop contact angle was measured. The results show that plasma activated and functionalized the surface of PET-F polymer with oxygen rich functional groups and induced the surface nanostructuring and cleaning of the polymer.  Table 1 – Results of AFM and XPS analysis with measurements of static water drop contact angles on PET-F before and after plasma modification  Sample AFM Surface roughness (nm) XPS ( ) O/C ratio F (at.%) Untreated 2.70 0.16 34.2 140 Plasma 7.23 0.39 13.5 129  The increased hydrophilic properties of PET-F after plasma modification were especially noticeable after ten repetitive washings (Fig. 1). The static water drop contact angle of untreated PET-F was 140  and after washing 137 , while for plasma modified PET-F, the static water drop contact angle was 129  and after washing 80 .    Fig. 1 – Static water drop contact angles on untreated and plasma modified PET-F before and after repetitive washing  In Fig. 2 and Fig. 3 a practical demonstration of in-creased hydrophilic properties of PET-F after plasma modification are shown. The droplets of different  PLASMA AND SOL-GEL TECHNOLOGY FOR CREATING NANOSTRUCTURED… PROC. NAP 1, 04PITSE03 (2012)    04PITSE03-3  liquids, such as water (w), paraffin oil (o) and n-hexadecane (C16) were put on the PET-F substrate. The untreated PET-F is hydrophobic and oleophobic. After plasma modification the substrate immediately becomes oleophilic but stays hydrophobic. After ten repetitive washings the plasma modified substrate be-comes both oleophilic and hydrophilic, while the sub-strate that was not modified by plasma retains its hy-drophobic and oleophobic properties even after ten washings.    Fig. 2 – Picture of different liquid droplets on (a) untreated and (b) plasma modified PET-F substrate    Fig. 3 – Picture of different liquid droplets on (a) untreated and (b) plasma modified PET-F substrate after 10 washings  Plasma modification for achieving surface activation and nanostructuring was applied to a hydrophilic pol-ymer (CO). The purpose was to combine plasma and sol-gel technologies in order to achieve a surface with the »lotus effect«. In Table 2 the results of AFM and XPS analysis before and after plasma modification of CO are presented. The measurements of static water drop contact angles and water sliding angles on sol-gel coated CO polymers before and after plasma modifica-tion are presented also.  Table 2 – Surface roughness and O/C ratio of CO before and after plasma modification, static and sliding water contact angles and oleophobicity measurements of sol-gel coated CO polymers before and after plasma modification  Sample AFM Surface roughness (nm) O/C ratio Static water drop contact angle ( ) Sliding water angle ( ) Oleophobicity (mN/m) Untreated 4.01 0.44 148 13 23.5 Plasma 13.08 0.63 152 7 23.5  The results summarised in Table 2 show that in-creased surface roughness of CO (from 4.01 nm to 13.08 nm) resulted in increased static water drop con-tact angle from 148° for sol-gel coated CO to 152  for plasma modified sol-gel coated CO. The static water drop contact angle higher than 150  denotes the super-hydrophobic properties of a substrate. As mentioned previously, the measurements of sliding angle are among the fundamental results of wettability. From our results it can be observed when static contact angle is increased (from 148  to 152 ), the sliding angle is decreased (from 13  to 7 ). The sliding angle on plasma modified and sol-gel coated CO is below 10 , which de-notes the surface of a substrate with »lotus effect« properties. The CO samples also exhibit oleophobic properties regardless of the treatment. Increased O/C ratio on the surface of plasma modified polymer result-ed in increased bonding of sol-gel coating on the CO surface, which resulted in better wash durability of the coating. In Fig. 4 the results of measurements of static water drop contact angles before and after repetitive washing are presented. The static water drop contact angle starts to decrease after one washing for untreat-ed and sol-gel coated sample (from 148  to 146 ) and reaches 141  after five washings. Plasma modified and sol-gel coated sample exhibits better wash durability. After one wash the static water drop contact angle on the sample does not change and after five washings the contact angle reaches 146 .    Fig. 4 – Static water drop contact angles on untreated sol-gel coated and plasma modified sol-gel coated CO before and after repetitive washing.  4. CONCLUSIONS   Low-pressure ICRF plasma was used for a modifica-tion of hydrophobic synthetic fibrous polymer and hy-drophilic natural fibrous polymer. Plasma modification of oleophobic and hydrophobic fluorinated poly(ethylene terephthalate) fibrous polymer caused ablation of perfluorinated film on the surface of the polymer resulting in partially defluorinated nanostruc-tured surface, increased oleophilic properties and after washing the increased hydrophilic properties of the  M. GORJANC, J. VASILJEVIĆ, AL. VESEL, ET AL. PROC. NAP 1, 04PITSE03 (2012)   04PITSE03-4 polymer. The effects of plasma ablation, nanostructuring and functionalization with oxygen rich atoms were ex-ploited for the purpose of increasing the static water drop contact angle and decreasing the sliding angle of sol-gel functionalized cellulose polymer. By using plasma modification and sol-gel fluoroalkyl-functional siloxane precursor the surface of the cellulosic polymer exhibited oleophobic, superhydrophobic and self-cleaning (lotus effect) properties with a good wash durability. AKNOWLEDGEMENTS  This research was financially supported by Sloveni-an Research Agency (Programme P2-0213). Authors are grateful to the Editor-in-Chief of the Journal of Nano- and Electronic Physics Protsenko Ivan Yuhymovych for a critical reading of the manu-script and his valuable comments.   REFERENCES  1. M. Mozetic, U. Cvelbar, M.K Sunkara, S. Vaddiraju, Adv. Mater. 17, 2138 (2005).  2. R. Zaplotnik, A. Vesel, M. Mozetic, Sensors 12, 3857 (2012). 3. M. Mozetic, Vacuum. 86, 867 (2012).  4. A. Drenik, A. Vesel, M. Mozetič, J. Nucl. Mater. 386-388, 893 (2009).  5. A. Vesel, M. Mozetic, Vacuum. 86, 773 (2012). 6. J.A. Ferreira, F.L. Tabares, D. Tafalla, J. Vac. Sci. Tech-nol. A. 25, 746 (2007). 7. M. Gorjanc, P. Recelj, M. Gorenšek, Tekstilec. 50, 10-12 (2007).  8. M. Gorjanc, V. Bukosek, M. Gorensek, A. Vesel, Text. Res. J. 80, 557 (2010). 9. M. Gorensek, M. Gorjanc, V. Bukosek, J. Kovac, P. Jovancic, D. Mihailovic, Text. Res. J. 80, 253 (2010). 10. M. Gorenšek, M. Gorjanc, V. 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Plasma and Sol-Gel Technology for Creating Nanostructured Surfaces of Fibrous Polymers

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