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Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - Non-wetting surfaces: robustness and applications - Robin Ras, Aalto University Finland

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    Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - Non-wetting surfaces: robustness and applications - Robin Ras, Aalto University Finland Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - Non-wetting surfaces: robustness and applications - Robin Ras, Aalto University Finland Presentation Transcript

    • Dr.  Robin  Ras,  Aalto  University,  Finland   Non-­‐we9ng  surfaces:    Robustness  and  applica@ons   Dr.  Robin  Ras   Molecular  Materials    Dept.  Applied  Physics   Aalto  University  (formerly  Helsinki  Univ.  Technology)   Helsinki,  Finland     hJp://Ly.tkk.fi/molmat/   robin.ras@aalto.fi  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Milestones  of  superhydrophobicity   700   •  1940’s-­‐1950’s   600   “Superhydrophob*”   #  publica@ons   500   based  on  Web  of  Knowledge  -­‐  May  2011   –  Theory   400   •  Wenzel   300   200   •  Cassie-­‐Baxter   100   •  1977  (BarthloJ,  Univ.  Bonn)   0   –  plant  systema@cs   –  assessing  the  value  of  certain  surface  structures  for  taxonomic  differen@a@on   •  1997  (BarthloJ  &  Neinhuis)   –  first  comprehensive  experimental  study  on  self-­‐cleaning  of  plant  surfaces   –  results  pointed  to  a  structural  basis  of  effec@ve  self-­‐cleaning    
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Lotus  leaf:  archetype  of  a  self-­‐cleaning  surface   A droplet takes up the dirt Water droplets roll down the while rolling down leaf of the Lotus flower Glue rolls down the leaf hJp://www.youtube.com/watch?v=XXHSM8ePuZw   of the Lotus flower
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Loss  of  non-­‐we9ng:  caused  by  damage   Remember  the  two  requirements  for  the   Cassie  state  of  superhydrophobicity:   Low  fric@on   1.  Topography  at  nano/micronscale   2.  Hydrophobic  surface  chemistry   Cassie  state:     •  low  contact  angle  hysteresis  (Δθ)   Droplet  pinning   •  low  sliding  angle     Δθ  =  θadv  −  θrec   Damage  to  1.  or  2.  leads  to  significantly   The  maximum  lateral  force  Flat  that  a   reduced  θrec  and  thus  increased  hysteresis   distorted  pinned  droplet  can  build  up   depends  on  θadv  and  θrec     Flat  =  cos  θrec  −  cos  θadv  ≅  Δθ  sinθ  (for  small  θ)         Verho,  Ras  et  al.,  Adv.  Mater.  2011,  23,  673–678  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Loss  of  non-­‐we9ng:  caused  by  we9ng   transi@ons   Not  only  damage  to  the  surface,  but  also  we9ng  transi@ons  can  lead  to   pinning  of  droplets     •  The  Cassie  state  of  we9ng  is  in  general  most  desired.     •  Droplet  is  in  contact  mostly  with  air   •  However,  transi@ons  from  Cassie  to  Wenzel  state  of   we9ng  are  possible.   •  e.g.  hydrosta@c  pressure,  dissolu@on  of  the  trapped   air,  a  drop  falling  from  a  certain  height   Cassie   •  This  also  leads  to  loss  of  non-­‐we9ng,  even  though  the   contact  angle  can  s@ll  be  high   transi@on   •  The  reverse  Wenzel-­‐to-­‐Cassie  transi@on  is  difficult,   though  possible  in  some  cases.   Important  for  underwater  applica@ons  (long-­‐@me  contact  with  water)   e.g.  Ship  hull   •  prevent  bio-­‐fouling  (algae,  mussels,  …)   Wenzel   •  drag  reduc@on  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Damage  to  non-­‐we9ng  surfaces  (1)   Two  types  of  damage   •  loss  of  roughness  (increases  the  area  of  contact  between  water   and  the  surface)   –  Mechanical  abrasion   •  intrinsic  hydrophobicity  of  the  surface  is  reduced   –  Damage  to  a  hydrophobic  surface  layer   •  Mechanical  abrasion   •  Ultraviolet  radia@on   •  …   –  Contamina@on  (organic/bio)    As  a  consequence,  the  Cassie  state  may  become  unstable  or  contact    angle  hysteresis  may  increase  due  to  hydrophilic  defects.   Verho,  Ras  et  al.,  Adv.  Mater.  2011,  23,  673–678  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Damage  to  non-­‐we9ng  surfaces  (2)   •  Most  superhydrophobic  surfaces  work  well  in  controlled  laboratory  condi@ons   •  But  fail  in  real-­‐life  applica@ons.   The  requirements  for  durability  depend  on  the  area  of  applica@on.     Different  kinds  of  durability   •  Robustness  in  weather  condi@ons  (e.g.  windows  of  traffic  cameras,  coa@ng  of   weather  sta@ons)   –  Fouling-­‐resistant   –  UV-­‐resistant   •  Robustness  against  skin  contact  (e.g.  touch  screens)   –  Mechanically  durable   –  Resistant  against  finger  grease   •  Food  packaging  /  kitchen  utensils   –  Resistant  against  oil-­‐contamina@on   –  (Mechanically  durable)   •  …  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Hierarchical  roughness   =  topography  at  two  or  more  length  scales   One  length  scale   Two  length  scales   Only  microroughness  is  present.  Abrasion   Microbumps  with  a  nanoroughness  on   causes  the  bumps  to  wear  off,  making  the   them.  Most  of  the  nanoroughness  is   Cassie  state  no  longer  stable.   unaffected  by  wear  and  the  Cassie  state   remains  stable.  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Hierarchical  roughness:  example  1   •  PET  fabric  coated  with  nanofilaments  before  and  awer  a  wear  test  that  simulates  skin   contact.   •  majority  of  the  filaments  are  protected  by  the  3D  microstructure  of  the  fabric   •  Since  the  residual  layer  awer  abrasion  is  also  s@ll  hydrophobic,  the  overall   superhydrophobic  proper@es  of  the  tex@le  are  retained.   •  Contact  angle  hysteresis  has  increased  slightly   Adv.  Funct.  Mater.  2008,  18,  3662–3669  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Hierarchical  roughness:  example  2  Micropyramids  with  nanoscale  roughness   θ=168°   Abrasion  with  Technicloth  paper   Sand  abrasion  (6  min)   Δθ=2°   θ=167°   θ=161°   Δθ=13°   Δθ=70°   Hydrophilic   Despite  an  increase  in  contact  angle  hysteresis,  the  surface    pinning  site   remained  superhydrophobic,  showing  that  the  microscale  pyramids   θrec(Si02)=0°   protected  the  nanoscale  features  on  the  walls  of  the  pyramids   Nanotechnology  21  (2010)  155705  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Hierarchical  roughness:  example  2  Micropyramids  with  nanoscale  roughness   θ=168°   Abrasion  with  Technicloth  paper   Sand  abrasion  (6  min)   Δθ=2°   θ=167°   θ=161°   Δθ=13°   Δθ=70°   Hydrophilic    pinning  site   •  Hydrophilic  bulk  materials  lead  to  pinning  sites  when  worn  off   •  Solu@on:  hydrophobic  bulk  material   Verho,  Ras  et  al.,  Adv.  Mater.  2011,  23,  673–678   Nanotechnology  21  (2010)  155705  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Hydrophobic  bulk  material   An  organoclay-­‐polymer  nanocomposite  before  and  awer  abrading  with  sand  paper   polishing  with  sandpaper  increased  the  contact  angle  hysteresis  only  from  4°  to   10°  even  though  scanning  electron  microscopy  showed  that  the  surface  had   suffered  considerable  damage.  hJp://www.youtube.com/watch?v=HxVnFlKiFRw   Applied  Physics  Express  (2009)  125003  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Weather  durability  (1)   Conven@onal  (A–D)  and  Lotus-­‐Effect®  (E–F)   façade  paint  specimens  awer  six  years  of   exposure  under  deciduous  trees.   Bioinsp.  Biomim.  2  (2007)  S126–S134  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Weather  durability  (2)   Awer  12  months   exposure  to  weather   elements   Untreated  glass   Superhydrophobic  glass   12  months  exposure   Organic  contamina@on   Silicone  nanofilaments   Colloids  and  Surfaces  A:  Physicochem.  Eng.  Aspects  302  (2007)  234–240  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Laundering  Durability  of   Superhydrophobic  CoJon  Fabric   Grawing  =  polymeriza@on  onto  a  solid  surface   1H,1H,2H,2H-­‐nonafluorohexyl-­‐1-­‐acrylate   grawed  onto  a  coJon  fabric.   Adv.  Mater.  2010,  22,  5473–5477  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Laundering  Durability  of   Superhydrophobic  CoJon  Fabric   Fluorinated  groups  are  covalently  bonded  to  the  coJon  fabric      superhydrophobicity  s@ll  retained  its  superhydrophobicity  awer  50  accelerated      laundering  cycles  (=  equivalent  to  250  commercial  or  domes@c  launderings).      binding  between  the  coJon  fiber  and  the  fluorinated  graw  chains  is  strong  enough    to  withstand  the  shear  force  of  the  water  and  the  stainless  steel  balls.   Adv.  Mater.  2010,  22,  5473–5477  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Transparent,  Thermally  Stable  and  Mechanically  Robust   Superhydrophobic  Surfaces  Made  from  Porous  Silica   Capsules   The  coa@ng  retains  its  superhydrophobicity   under  adhesion  tape  peeling  and  sand  abrasion   Adv.  Mater.  (2011)  DOI:  10.1002/adma.201100410  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   SuperHYDROphobic         superOLEOphobic  or  superOMNIphobic  ?   Young  equa@on  γsg  –  γsl  =  γlg  cos  θ   •  The  interfacial  energy  for   water   •     γlg=72.8  mN/m  (high)   •  The  interfacial  energy  for  oils   and  organic  maJer  much  lower   •  hexadecane  γlg=27.5  mN/m   •  decane  γlg=23.8  mN/m   •  octane  γlg=21.6  mN/m   Superoleophobic  surfaces:   The  contact  angle  >  150°  for  oils   •  Difficult  to  increase  contact   Three  requirements:   • Low  surface  energy   angle,   •  Remember:  The  lowest  known  are  for  fluorinated   • Roughness   chemical  groups   • Re-­‐entrant  curvature   •   γsg  =  6.7  mN/m  for  -­‐CF3,  a  bit  higher  for  –CF2-­‐   e.g.  Science  2007,  318,  1618.  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Self-­‐healing  superhydrophobicity  (1):   a  property  from  nature   Chem.  Commun.,  2011,  47,  2324–2326  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Self-­‐healing  superhydrophobicity  (2)   Angew.  Chem.  Int.  Ed.  2010,  49,  6129-­‐6133  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Self-­‐healing  superhydrophobicity  and   superoleophobicity  (3)   Chem.  Commun.,  2011,  47,  2324–2326  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Superhydrophobicity  =    Water  repellency   Superhydrophobicity   Superhydrophobic  applica@ons    in  nature   • Plant  leaves   •  Self-­‐cleaning   • Insect  wings   •  No  water  absorp@on  (tex@le  remains  dry)   –  Energy  efficient   •  An@-­‐icing   • Insect  eyes   •  An@-­‐fogging   • Desert  beetle   •  Dew  collec@on   • Water  strider   •  Floata@on   –  Locomo@on   •  Drag  reduc@on   plastron     •  Thermal  insula@on   • Breathing  by  underwater  insects   •  Gas  extrac@on  from  water  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Staying  dry   Cicada  wings   Clothing   Silicone  nanofilaments  Ras  et  al.  JACS  (2008)  130,  11253   Adv.  Funct.  Mater.  2008,  18,  3662–3669  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Superhydrophobic  Tracks  for  Low-­‐Fric@on,  Guided   Transport  of  Water  Droplets   •  A  water  droplet  does  not  penetrate  through  a   hole/groove  in  a  superhydrophobic  surface   •  Track  edge  keeps  the  drop  inline  with  the  track   gravita@on   Electrosta@c  force   Superhydrophobic  knife   Mertaniemi,  Ras  et  al.  Advanced  Materials  (2011)  in  press.        DOI:10.1002/adma.201100461  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   An@-­‐Icing  Superhydrophobic  Coa@ngs   Note:  also  robustness  is  a  problem  here,  as   the  growing  ice  crystals  may  damage  the   nano/micronscale  topography   Langmuir  2009,  25(21),  12444–12448   Langmuir  2011,  27(1),  25–29   hJp://www.youtube.com/watch?v=mxQy73rL3a8  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Delayed  Freezing  on  Water  Repellent  Materials   Ini@al  water  temperature  25°C   Copper  plate  at  -­‐7°C   Roughened  fluorinated   copper   =superhydrophobic  Figure  1.  Comparison  between  two  water  drops  (Ω  =  1200  μL)  deposited  on  microtextured  superhydrophobic  (black)  copper  (lew)  and  flat  (orange)  copper  (right),  both  at  a  temperature  T  =  -­‐7  C.  First  row:  the  drops  were  just  deposited;   Smooth  fluorinated    their  colors  reflect  the  substrates.  Second  row:  the  drop  on  flat  copper  has   copper  frozen.  Third  row:  both  drops  are  frozen.  There  is  no  difference  in  contact  angle   Normal  copper  between  the  drops,  because  a  thin  ring  (of  radius  R  =  10  mm)  has  been  etched  in  both  plates,  providing  pinning  for  the  contact  line  and  allowing  us  to  compare  the  freezing  of  drops  of  same  volume  and  same  surface  area.   The  drop  on  a  superhydrophobic  surface  contacts  more  air  than  solid     Insula@ng  proper@es  Langmuir  2009,  25(13),  7214–7216  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   An@-­‐fogging   Prevents  moisture  from  nuclea@ng   Adv.  Mater.  2007,  19,  2213–2217  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Harvesting of water by a desert beetle Hydrophilic peaks 10 µm     Superhydrophobic  Applica@on:  Fog  harves@ng   Tent  fabrics  and  roof  @les  to  collect  moisture  in  arid  areas.   Nature  (2001)  414,  33  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Floata@on  on  water  using  surface   tension  forces   Advances  in  Insect  Physiology  (2008)  34,  117  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Floata@on  on  water  using  surface   tension  forces   Hydrophilic  claws  to  grab  the  water  surface   Dimple:  stretching  of  the  water  surface   Advances  in  Insect  Physiology  (2008)  34,  117  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Meniscus-­‐climbing   Nature  (2005)  437,  733  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Water  strider  look-­‐alikes:  water-­‐ walking  devices   Exp  Fluids  (2007)  43:769–778   IEEE  TRANSACTIONS  ON  ROBOTICS,  VOL.  23,  NO.  3,  JUNE  2007   hJp://www.youtube.com/watch?v=756Tk9y0aNg   hJp://nanolab.me.cmu.edu/projects/waterstrider/  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Superhydrophobic  and  Superoleophobic  Nanocellulose  Aerogel  Membranes   Content as  Bioinspired  Cargo  Carriers  on  Water  and  Oil   Nanocellulose  aerogel   Chemical  vapor  deposi@on  of   perfluorinated  trichlorosilane   •  Low-­‐surface-­‐energy  coa@ng   •  Roughness  from  nano-­‐  to  microscale   •  Overhangs   Jin,  KeJunen,  Laiho,  Pynnönen,  Paltakari,  Marmur,  Ikkala,  Ras,  Langmuir  (2011)  1930.  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   TiO2-­‐coated  nanocellulose  aerogel   Nanocellulose aerogel TiO2-coated nanocellulose aerogel (highly porous solvent-free (coated by chemical vapor deposition network) CVD or atomic layer deposition ALD) Precursor: TiO2 thickness ca. 7 nm on nanocellulose fibril ALD  or  CVD   Korhonen,  Hiekkataipale,  Malm,  Karppinen,  Ikkala,  Ras,  ACS  Nano  (2011)  1967.  KeJunen  (née  Pääkkö),  Silvennoinen,  Houbenov,  Nykänen,  Ruokolainen,  Sainio,  Pore,  Kemell,  Ankerfors,  Lindström,  Ritala,  Ras,  Ikkala,                                Adv.  Funct.  Mater.    (2011)  510.  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Op@cally  controlled  water  absorp@on  within  TiO2-­‐coated  cellulose  aerogel   No illumination Ultraviolet illumination After ultraviolet λ = 350 nm illumination Rejects water Absorbent Rejects water High Zero contact High contact angle on contact angle on surface angle on surface surface Recovering slowly Water Water Water expelled absorbed in expelled from the the pores: from the pores 16 x water pores vs the aerogel weightKeJunen  (née  Pääkkö),  Silvennoinen,  Houbenov,  Nykänen,  Ruokolainen,  Sainio,  Pore,  Kemell,  Ankerfors,  Lindström,  Ritala,  Ras,  Ikkala,                                Adv.  Funct.  Mater.    (2011)  510.  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Humidity  sensing  using  TiO2  nanotube  aerogels   Nanotube  films  act  as  fast  resis@ve  humidity   sensors.     Korhonen,  Hiekkataipale,  Malm,  Karppinen,  Ikkala,  Ras,  ACS  Nano  (2011)  1967.  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Plastron:  a  thin  layer  of  trapped  air  at  the  surface  of  an   immersed  superhydrophobic  surface   Mirror-­‐like  silvery  appearance   Bioinsp.  Biomim.  2  (2007)  S126–S134   Reflec@vity  96%   SoL  MaMer,  2010,  6,  714       Angew.  Chem.  Int.  Ed.  2007,  46,  1710  –1712  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Slip  and  drag  reduc@on:   lower  fric@on  of  flowing  water   To  analyze  con@nuum  liquid  flows,  a  so-­‐called   “no-­‐slip”  boundary  condiUon  is  typically  made.   This  condiUon  implies  that  the  flow  velocity  of   a  given  fluid  at  a  solid  wall  is  zero.   True  for  most  surfaces,  not  for  superhydrophobic  surfaces  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Superhydrophobic  Copper  Tubes  with  Possible  Flow   Enhancement  and  Drag  Reduc@on  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Underwater  breathing:  plastron  func@ons  as   external  lung   J.  Fluid  Mech.  (2008),  vol.  608,  pp.  275–296.   CO2   O2  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Gas  extrac@on  from  water   A  sphere  of  3m  diameter  would  provide  enough  oxygen  for  a  human  to  survive     APPLIED  PHYSICS  LETTERS  89,  104106  (2006)  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Conclusion   •  Robustness  of  superhydrophobic  surfaces  was  long  @me  ignored   •  Last  two  years  progress  made  towards  robust  superhydrophobic  surfaces   •  Some  promising  routes,  but  more  work  needed   •  We  can  learn  a  lot  from  nature  (=biomime@cs)   •  Wide  range  of  applica@ons  beyond  self-­‐cleaning  for  non-­‐we9ng  surfaces  
    • Dr.  Robin  Ras,  Aalto  University,  Finland   Acknowledgements   Aalto  Univ.  (Finland)   •  O.  Ikkala,  H.  Mertaniemi,  T.  Verho,  H.  Jin,  M.  KeJunen  (née   Pääkkö),  J.  Korhonen,  P.  Hiekkataipale,  A.  Laiho.,  M.   Karppinen,  J.  Malm,  S.  Franssila,  V.  Jokinen,  L.  Sainiemi.   Technion  (Israel)   •  A.  Marmur   Nokia  Research  Center  -­‐  Cambridge  (UK)   •  P.  Andrew  and  C.  Bower     Funding   •  Nokia  Research  Center,  UPM  Kymmene,  TEKES,  Acad.  Finland.   Dr.  Robin  Ras   Aalto  University,  Helsinki,  Finland   robin.ras@aalto.fi   hJp://Ly.tkk.fi/molmat/