Superhydrophobicity
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Superhydrophobicity

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explain what it is, how silanes are used in manufacturing, applications etc.

explain what it is, how silanes are used in manufacturing, applications etc.

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Superhydrophobicity Presentation Transcript

  • 1. SUPERHYDROPHOBICITY
  • 2. HYDROPHOBICITY • Hydrophobicity is the physical property of a molecule that is repelled from a mass of water. • Hydrophobic molecules tend to be non-polar and, thus, prefer other neutral molecules and non-polar solvents. • Water on hydrophobic surfaces will exhibit a high contact angle.
  • 3. DEFINITION
  • 4. Superhydrophobicity is a surface phenomenon that indicates a very low affinity to water, and, in turn, the surface is very difficult to be wetted. Therefore, water droplets on superhydrophobic surfaces typically form spherical beads and can be easily shaken away from the surface. A generally accepted definition of superhydrophobicity is to have a water contact angle above 150 degrees and a start-rolling angle to be lower than 10 degrees at room temperature and ambient pressure.
  • 5. KEY TERMS
  • 6. WETTABILITY • A surface is said to be wetted if a liquid spreads over the surface evenly without the formation of droplets. • Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together.
  • 7. CONTACT ANGLE • Angle where water drop makes contact with the surface. • The relative degree of interaction of a liquid with a solid surface is the contact angle of a liquid droplet on a solid substrate. • Hydrophilic: θ < 90 • Hydrophobic: θ > 90 • Superhydrophobic : θ > 150
  • 8. WATER DROP MAKES CONTACT WITH THE SURFACE
  • 9. CRITICAL SURFACE TENSION Liquids with a surface tension below the critical surface tension (c) of a substrate will wet the surface, i.E., Show a contact angle of 0 (cose = 1). The critical surface tension is unique for any solid and is determined by plotting the cosine of the contact angles of liquids of different surface tensions and extrapolating to 1. Hydrophobic behavior is generally observed by surfaces with critical surface tensions less than 35 dynes/cm. At first, the decrease in critical surface tension is associated with oleophilic behavior, i.E. The wetting of the surfaces by hydrocarbon oils. As the critical surface tensions decrease below 20 dynes/cm, the surfaces resist wetting by hydrocarbon oils and are considered oleophobic as well as hydrophobic.
  • 10. SILANES AND SURFACE MODIFICATION
  • 11. SILANES SILANES ARE SILICON CHEMICALS THAT POSSESS A HYDROLYTICALLY SENSITIVE CENTER THAT CAN REACT WITH INORGANIC SUBSTRATES SUCH AS GLASS TO FORM STABLE COVALENT BONDS AND POSSESS AN ORGANIC SUBSTITUTION THAT ALTERS THE PHYSICAL INTERACTIONS OF TREATED SUBSTRATES. PROPERTY MODIFICATIONS INCLUDE: • HYDROPHOBICITY • DIELECTRIC • ABSORPTION • ORIENTATION • HYDROPHILICITY • CHARGE CONDUCTION
  • 12. HOW DOES A SILANE MODIFY A SURFACE? • MOST OF THE WIDELY USED ORGANOSILANES HAVE ONE ORGANIC SUBSTITUENT AND THREE HYDROLYZABLE SUBSTITUENTS. IN THE VAST NMAJORITY OF SURFACE TREATMENT APPLICATIONS, THE ALKOXY GROUPS OF THE TRIALKOXYSILANES ARE HYDROLYZED TO FORM SILANOL-CONTAINING SPECIES. • SILANES CAN MODIFY SURFACES UNDER ANHYDROUS CONDITIONS CONSISTENT WITH MONOLAYER AND VAPOR PHASE DEPOSITION REQUIREMENTS. EXTENDED REACTION TIMES (4-12 HOURS) AT ELEVATED TEMPERATURES (50°-120°C) ARE TYPICAL. OF THE ALKOXYSILANES, ONLY METHOXYSILANES ARE EFFECTIVE WITHOUT CATALYSIS. THE MOST EFFECTIVE SILANES FOR VAPOR PHASE DEPOSITION ARE CYCLIC AZASILANES.
  • 13. HOW TO COAT LAYER OF SILANE OVER SUBSTRATE ? 1. HYDROLYSIS - Hydrolysis of the three labile groups occurs. 2. CONDENSATION - Condensation to oligomers 3. HYDROGEN BONDING - The oligomers then hydrogen bond with OH groups of the substrate. 4. BOND FORMATION - Finally, during drying or curing, a covalent linkage is formed with the substrate with concomitant loss of water.
  • 14. SELECTING A SILANE FOR SURFACE MODIFICATION
  • 15. FACTORS INFLUENCING SILANE SURFACE MODIFICATION SELECTION INCLUDE • CONCENTRATION OF SURFACE HYDROXYL GROUPS • TYPE OF SURFACE HYDROXYL GROUPS • HYDROLYTIC STABILITY OF THE BOND FORMED • PHYSICAL DIMENSIONS OF THE SUBSTRATE OR SUBSTRATE FEATURES
  • 16. • SURFACE MODIFICATION IS MAXIMIZED WHEN SILANES REACT WITH THE SUBSTRATE SURFACE AND PRESENT THE MAXIMUM NUMBER OF ACCESSIBLE SITES WITH APPROPRIATE SURFACE ENERGIES. • SILANES WITH THREE ALKOXY GROUPS ARE THE USUAL STARTING POINT FOR SUBSTRATE MODIFICATION. • THESE MATERIALS TEND TO DEPOSIT AS POLYMERIC FILMS, EFFECTING TOTAL COVERAGE AND MAXIMIZING THE INTRODUCTION OF ORGANIC FUNCTIONALITY. • MONOALKOXY-SILANES PROVIDE A FREQUENTLY USED ALTERNATIVE FOR NANO- FEATURED SUBSTRATES SINCE DEPOSITION IS LIMITED TO A MONOLAYER. • DIPODAL SILANES FORM TIGHTER NETWORKS AND MAY OFFER UP TO 105X GREATER HYDROLYSIS RESISTANCE MAKING THEM PARTICULARLY APPROPRIATE FOR PRIMER
  • 17. HYDROPHOBIC SILANE SURFACE TREATMENTS FACTORS WHICH CONTRIBUTE TO THE ABILITY OF AN ORGANOSILANE TO GENERATE A HYDROPHOBIC SURFACE ARE ITS ORGANIC SUBSTITUTION, THE EXTENT OF SURFACE COVERAGE, RESIDUAL UNREACTED GROUPS. ALIPHATIC HYDROCARBON SUBSTITUENTS OR FLUORINATED HYDROCARBON SUBSTITUENTS ARE THE HYDROPHOBIC ENTITIES WHICH ENABLE SILANES TO INDUCE SURFACE HYDROPHOBICITY. THE HYDROPHOBIC EFFECT OF THE ORGANIC SUBSTITUTION CAN BE RELATED TO THE FREE ENERGY OF TRANSFER OF HYDROCARBON MOLECULES FROM AN AQUEOUS PHASE TO A HOMOGENEOUS HYDROCARBON PHASE. FOR NON-POLAR ENTITIES, VAN DER WAALS INTERACTIONS ARE PREDOMINANT FACTORS IN INTERACTIONS WITH WATER AND SUCH INTERACTIONS COMPETE WITH HYDROGEN BONDING IN ORDERING OF WATER MOLECULES. ENTITIES WHICH PRESENT STERICALLY CLOSED STRUCTURES THAT MINIMIZE VAN DER WAALS CONTACT ARE MORE HYDROPHOBIC THAN OPEN STRUCTURES THAT ALLOW VAN DER WAALS CONTACT.
  • 18. LOTUS EFFECT
  • 19. LOTUS EFFECT • The lotus effect refers to the very high water repellence (superhydrophobicity) exhibited by the leaves of the lotus flower (nelumbo). • Dirt particles are picked up by water droplets due to a complex micro- and nanoscopic architecture of the surface, which minimizes adhesion. • Due to their high surface tension, water droplets tend to minimize their surface by trying to achieve a spherical shape. • The cause of self-cleaning properties is the hydrophobic water-repellent double structure of the surface. • This enables the contact area and the adhesion force between surface and droplet to be significantly reduced resulting in a self-cleaning process.
  • 20. COMPUTER GRAPHIC OF A LOTUS LEAF SURFACE
  • 21. (a,b) Superhydrophobic and self-cleaning leaves of lotus (nelumbo nucifera) and (c,d) the superhydrophobic and air-retaining leaves of the water fern salvinia biloba.
  • 22. PROPERTIES • NON WETTABILITY • DURABILITY • RESTORABLE • SELF CLEANING • ANTI CORROSIVE • ANTI BIO FOULING
  • 23. APPLICATIONS
  • 24. • SEPARATING OIL AND WATER WITH SUPERHYDROPHOBIC VERTICALLY ALIGNED CNT MEMBRANES • ANTI-CORROSIVE TREATMENT FOR METALS SUCH AS RIMS • ANTI-ICING COATINGS ON POWER LINES, INSULATORS, INFRASTRUCTURE (E.G. TRANSFORMER CASINGS, BUILDINGS, SIDEWALKS, DRIVEWAYS, TRE
  • 25. •ACTS AS A THERMAL INSULATOR ON COATED FABRICS •EVAPORATIVE DESALINIZATION •WATER PROOF COATINGS FOR ELECTRICAL DEVICES AND POWER ELECTRONICS. •WATER FREE GOGGLES, WINDSHIELDS, AND
  • 26. • CONTAINERS THAT HAVE NO LIQUID RESIDUE WHEN EMPTIED • PREVENTS NEARLY ANY EXPOSED STRUCTURES, SUCH AS BRIDGES AND DECKS, FROM WATER DAMAGE • PROTECTION FOR METALS, GLASS, WOOD, PLASTICS, FIBERGLASS AND OTHER MATERIALS • DRAG REDUCTION
  • 27. •GLASS LENSES THAT REMAIN DRY IN THE RAIN •COATING FABRIC AND BANDAGES •COATING RADARS, RADOMES AND MILITARY •CARBON REDUCTION •ACT AS A GAS EXCHANGE MEMBRANE •VARIOUS FORMS OF ENERGY SAVINGS
  • 28. PRACTICAL & REAL LIFE EXAMPLES Lotus Flower Rose Water sports Car Windshields Skiing
  • 29. CONCLUSION IT’S A AMAZING CONCEPT WHICH CAN CHANGE OUR ROUTINE LIFE + INDUSTRIAL LIFE. AS A CHEMICAL ENGINEER WE SHOULD KNOW ABOUT ITS IMPORTANCE.
  • 30. REFERENCES • HTTP://WWW.NSEC.OHIO- STATE.EDU/TEACHER_WORKSHOP/SUPERHYDROPHOBICITY.PDF • HTTP://VOH.CHEM.UCLA.EDU/CLASSES/SUPERHYDROPHOBIC_SURFACES/PDF/SUP ERHYDRO%20%20PRESENTATION.PDF • HTTP://WWW.IOP.ORG/EJ/ARTICLE/1468-6996/6/3-4/A05/STAM_6_3- 4_A05.PDF?REQUEST-ID=0F3098BB-6D01-4FD6-898D-BDEDE519F8B8 • HTTP://EN.WIKIPEDIA.ORG/WIKI/SUPERHYDROPHOBIC • HTTP://WWW.WIRED.COM/SCIENCE/DISCOVERIES/MAGAZINE/16-11/ST_INFOPORN# • HTTP://INVENTORSPOT.COM/ARTICLES/FIORAVANTI_SEES_FUTURE_NO_WINDSH_1 1050
  • 31. G R O U P M E M B E R S AMIT KUMAR GOMEY (U12CH026) SEEMA MEENA (U12CH025) RISHABH SAMBRIYA (U12CH024) GAUTAM (U12CH023)
  • 32. THANKS