In on[4]. Inspiration from natural superhydrophobic surfaces many

In recent years, naturally-occurring super hydrophobic surfaces include water-striderlegs and the leaves of many plants 1which have water contact angles (WCAs) ofmore than 150 and water sliding angles (WSAs) of less than 10 2 haveattracted extensive worldwide attention in research purpose as well asindustrial application. The key features of such smart surfaces are based ontwo parameters one is nano- and microscale surface roughness and other is lowfree surface energies 3. These two key features manifest water droplets toattain the spherical shape and roll off the surface carrying away the dirtparticles.

Such type of surfaces has potential applications in many fields including as self-cleaning paints,coatings for windows, textiles and solar panels, anti-icing, anti-fogging,protection of electronic devices and so on4. Inspiration from naturalsuperhydrophobic surfaces many approaches have been developed to design suchtype of smart surfaces by creating surface roughness combination with lowsurface energy materials such as organic silanes, fluorinated silanes, alkyl amines and silicates5. The popularapproaches are wet chemical reactions 6 sol–gel 7, layer-by-layerdeposition 8 chemical vapour deposition 9 plasma treatment 10 andelectrospinning 11 etc. All of the above processes have focused on the growthof inorganic materials or nanoparticles. Without using nanoparticle researchersare also able to impart surface roughness by applying polymerization reactionon substrate surfaces using organic compound. Between all of organic chemicals,the fluorocarbon-based products werefound to enhance oil and water repellence by lowering surface energy withincreasing surface roughness 12. Fluorine has a small radius and high electronegativity,thus the covalent bond between ?uorine and carbon is extremely stable. When?uorine is replaced by other elements such as H and C, in the order–CF3

Theincrease in the number of ?uorine-carbon bonds in the functional structuresurface energy decreases with increasing hydrophobicity 13. ASoft, fluffy cellulosic (90%) fiber cotton has low production cost, low density, good strength in bothwet and in dry condition and otherunique properties, make them even more attractive for future applications.Beside this, it is extremely hygroscopicin nature due to the presence of a largenumber of the hydroxyl group in the cellulosic backbone. So preperation of hydrophobiccotton surfaces is an emerging topic in todays research.Recently a new method of hydrophobic as well as oleophobicfinishing has been utilized as a guide for modifying the surface by forming onto it a water-insoluble continuous ultrathinpolymeric film by adsorption of surfactants which is links to solidsurface material by polar bonds.

This method has termed admicellarpolymerization. This film coating consists of four mainsteps: formation of surfactant bilayer i.e admicelle,monomer adsolubilization, polymeric filmformation, and surfactant removal 14 has shown in Figure 1.Admicellarpolymerization has been successfully used to coat thin films of polystyrene onsilica 15, poly (methylmethacrylate) onaluminum metal 16, polystyrene on cotton 17 styrene isoprene copolymer onglass fiber 18, and polypyrrole on mica 19, polypropylene on calcium carbonate 20 etc. Maity et.

al applieda fluoropolymer on to the cotton surface by admicellar polymerization to get excellent stain resistance and stainrecovery properties 21. Admicellar polymerizations have superior advantages over the aboveprocess for its simplicity with low energy consumption when used on textilefabrics. The objective of this paper is to design the rough cotton surfaceby the adsorption of fluorosurfactant and solubilization of fluoromethacrylateson a cotton surface through Admicellar polymerization technique to impart the water-repellent function. Fluorosurfactant is chosenin our study because they have sufficiently low critical micelle concentrationcompared to hydrocarbon surfactant 22.Beside this bothfluoromonomer and fluorosurfactant has stronger hydrogen bonding and alsolarger partition coefficients, higher surface activity compared to the hydrocarbon system. Beside the water repellency ofcotton fibre we have also checked the stability of the coating by applyingsimple technique. MaterialsPique cotton fabric was purchased fromthe local textile shop.

The fabric wasresized and treated in 10% NaOH solution for 1 hour and then the fabric waswashed repeatedly until it was free from any remaining surfactant. The monomerused are 2, 2, 3, 3, 4, 4, 5, 5-octafluoropentylmethacrylate(OFPM) purchased from Sigma Aldrich. The surfactants usednon-ionic fluorosurfactant FS61 was purchased from Sigma Aldrich India. Theinitiator potassium persulfate was purchased from Merck. All chemicals wereused without further purification.Preparation ofsamplesSamples were prepared using admicellarpolymerization process. In this process, a 20-ml solution containing 2000ppm FS61,4mM OFPM, corresponding concentration of potassium persulfate and DI water ofpH 4 was placed in a 30-ml glass vialreactor.

Cotton swatches (1.0 g) were placed in 30 mL vial; Vial was sealedwith aluminum foil. Admicellar polymerization was carried out in two steps.

First,1.0g of washed cotton fabric added to 20 ml of a solution containingsurfactants and the monomers. Adsorption was carried out for 2 h at 400Cin a shaker bath at 180 rpm. Potassium persulfate as an initiator was thenadded, the vial resealed into and the polymerization was allowed to proceed foran additional 2h at 600C. The excesssurfactant was rinsed away with several volumes of water and the samplewas dried in an oven at 700C.Characterization of treated cotton fabricThe aim of the current study was tostudy the chemical and physical surface changes of cotton fabrics usingadmicellar polymerization and to identifyappropriate conditions for evaluating the effects of polymerization on cottonfabrics. Scanning electron microscopy (SEM JEOL JSM 5800 scanningmicroscope, samples were gold-coated beforescanning.

), wetting time analysis (WaterRepellency Tests), contact angle analysis, FTIR-ATR (L1600300Spectrum two Lita S.N.96499) spectroscopy, are someof the tools that have enabled the observation of nano-scale features on thecotton surfaces.Water Repellency TestsTwo test methods were employed for assessingwater repellency. An initial characterization of the treated surface was by thedrop test. A 10 ?L droplet of distilled water was placed on cotton fabricsurface carefully with no force from a 20 ?L syringe. Time for absorption ofwater and oil (wetting time) on a fabric surface in the drop test wasdetermined up to a maximum of 90 min, atwhich point the sample passed.

Contact anglemeasurementContact angle measurement of the sampleswas tested by using an optical tensiometer (TL100 Theta) and software suppliedwith the instrument at 240Ctemperature. A 10 ?L drop of distilled,deionized water was deposited on fabric by syringe from a height of 2 cm.Observations occurred over a 10min period with replicates at five differentsites on the fabric and the average value was used. Result and discussionIt is very difficult to evaluate fabrichydrophobicity by only one method.

The drop testenables a rapid and simple determination of water-repellent propertiesof a fabric is achieved due to the formation of the continuous, polymeric thinfilm on the cotton surface. To ascertain thewater-repellency characteristics of the fabric, the resistance of the fabric tosurface penetration by a spray and resistance to surface wetting should bemeasured. Tests have to be carried out in combination with each other in orderto obtain a complete understanding of performance. Samples were assessed forperformance using drop test, spray test, andcontact angle measurement.            Dropsof water form spheres on both of the cotton surfacesin Figure 2 can highlight that hydrophobic film on the surface was created andit prevents water or moisture to penetrate through the fiber. Contact angle measurements with water droplets revealedthat modified sample effectively repelled water even after 90 minutes to allowreliable measurementsattainable, apparent static contact angle values were obtained an average 1240has shown in Figure 3.The aim of the current study was tostudy the chemical and physical surface changes of cotton fabrics usingadmicellar polymerization and to identifyappropriate conditions for evaluating the effects of polymerization on cottonfabrics. Scanning electron microscopy (SEM) is used to study the surface morphology of the coated cotton surface afteradmicellar polymerization.

In previous reports scanning electron microscopy(SEM) was used to observe the surface characteristics of cotton fibers. The SEMimages explain the difference between treated and non-treated samples at thefiber level. SEM imaging reveals the existence of a coating in addition tocontact angle and wetting time analysis by providing pictorial evidence of thecoating. Typical SEM images are shown in Figure 5 before and aftermodification.  Inspired by natural surfaces (e.g. lotusleaves, butter fly wings) different typesof artificial surfaces have been designed and fabricated.

The surfacemicrostructure and composition of lotus leaves has been investigated byNeinhuis and coworkers 1. Neinhuis andco-workers investigated the micromorphological characteristics and showed thatthe water-repellency is based on surface roughness caused by differentmicrostructures (trichomes, cuticular folds and wax crystals) shown in Figure 4. They reported that water on thesolid surfaces is primarily in contact with air pockets trapped in the roughsurfaces. It is previouslyreported that SEM images of the untreated cotton surface Figure 5a have exposed characteristic parallel ridges andvery smooth surface. As shown in Figure 5b the surface morphology of thetreated cotton fabric was completely different from those of untreated one.

Theparallel ridges had almost vanished by admicellar polymerization and bumpyappearance was observed on the cotton surface makes the surface rougher. This new character on the cotton surface can be attributed to theformation of a thin fluorinated layer in the primary wall after treatment andsome rearrangement occurs on the surface of cotton fabric after fluorination.The wetting behavior of a water droplet on a hydrophobic cotton textile surfacecan be described by the equation of Cassie and Baxter as follows:cos ?CB = rf f cos ?0+ f – 1Where?CB is the observed water contact angle on a rough, poroussurface, ?0 is the intrinsic water contact angle on thecorresponding smooth surface, f is thefraction of the projected area of the solid surface wetted by water and rfis the surface roughness of the wetted area. For the fluoropolymermodified cotton fiber, the curvature of the cotton fiber renders rf> 1, which in comparison with a smooth wetted area, can enhancesurface hydrophobicity.

So,SEM images demonstrate thatthere are some polymeric layers exist between the fibers stays, which indicatedsome adhesion of fluoropolymer occursduring the polymerization. As a result, the dropletrests on the top of solid asperities and the gas is left in the voids below thedroplet indicating a shiny, transparent surface underneath the water has also shown in Figure 2. The chemical structure of fluoropolymer has also shown in Figure5c along with SEM images.Successful deposition of fluoropolymerichydrophobic coatings on the cotton sample was evaluated by comparing the FTIRspectra of coated cotton samples with the unmodified sample has shown in  Figure 6. In the FTIR spectra of modifiedcotton, the minor changes are observed,indicating in the admicellar process theinternal bonds of in cotton fabric are not destroyed.FT-IR ATR spectra of untreated fabric and fluoromonomerstreated fabric in Figure 6 showed characteristic cellulose peaks around1100-1200 cm-1.

Other characteristic bands related to the chemicalstructure of cellulose were the hydrogen-bonded OH stretching at 3350-3200 cm-1,the C-H stretching at 2900 cm-1, and the C-H wagging at1314 cm-1.The OH bending of absorbed water was also observed in 1642cm-1.Figure 6 shows an absorbance at around1751 cm-1 in the FT-IR ATR spectrum of fluorinated cotton, which wasattributed to the stretching vibration of the carbonyl group of methacrylatesmonomers attached to the fabric.

The frequency at 1010 cm-1 is acharacteristic frequency of the C-F bond 23. The C-F stretching frequency isabsent in case of untreated fabric but appears in the treated fabric indicatingpolar C-F bond between the cotton fabric and fluoromonomers.This data indicates that the hydrophobic cotton surface was achieved throughcopolymerization of the two monomers and fluorine is attached to the cottonsurface which affects the water repellence behavior of the modified cottonfabric although the two monomers are different in chemical structure. Thissurface polymerization clearly implies that hydrophobicity is strictly relatedto the quantities of the attached copolymer to the cotton surface rather than theirchemical composition.The stabilty of coatings on modified cotton fabric was alsoevaluated by the repeated tear test with an adhesive tape . In this test, thecotton surface was pasted onto an adhesive tape, and then it was peeled off inFigure 6. Even after repetition of the adhesive testfor 20 cycles the developed material remained hydrophobic, with an almostconstant water contact angle (WCA) of 10.

Thus, the results of thestudy indicate the stable and long term hydrophobicity of the preparedfluoropolymer modified cotton fabric  ConclusionWehave successfully created an artificial lotus leaf-likecotton surface by using a little quantity of fluoromonomer which showshydrophobic character with water contact angle1240  after admicellar polymerization. SEM imagesdemonstrate the surface roughness occurs after fluoropolymerizationon the cotton surface. FT IR alsoconfirms the attachment of fluorine moieties on the cotton surface by polymerization.

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