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Production of Micro-and Nanoporous, …...Foam2 300 None 155 149 6 Foam1 400 None Absorbed Absorbed...
Transcript of Production of Micro-and Nanoporous, …...Foam2 300 None 155 149 6 Foam1 400 None Absorbed Absorbed...
Production of Micro- and Nanoporous,
Superhydrophobic layers from Sol-Gels
Neil J. Shirtcliffe, Paul Roach, Glen McHale, Michael Newton, Carole C. Perry
Silicate Sol Gels
Partially & fully hydrolysed silicates can link together
Sol-Gel= preparation of oxide materials from solution
Solvent creates porous structure unless complete separation occurs
Usually organosilicon compounds hydrolysed to form intermediates
Hydroxide and organic groups usually present until thermally treated
Mechanism
O RSi
CH3
OO
R
R OH2O RSi
CH3
OOH
R+ HCl+
OHSi
CH3
OO
R
R NH4
+ OSi
CH3
OO
R
R
OH+ +
OH Si
CH3
OO
R
ROSi
CH3
OO
R
R
O Si
CH3
OO
R
RSi
CH3
OO
R
R
+
Acid Hydrolysis
Base Catalysed Gelation
O RSi
CH3
OOH
ROSi
CH3
OO
RSi
CH3
OO
R
R
R
H+
2
Sol-Gel Phase Separation
As the chains grow they become more hydrophobic and eventually phase separate to form a bicontinuous structure
OH Si
CH3
OO
R
ROSi
CH3
OO
R
R
+
Polar O Si
CH3
OO
R
RSi
CH3
OO
R
R
Less Polar
Bi-continuous Structure
M. Stockenhueber
Shrinkage
Shrinkage caused by surface tension of drying solvent, varies with pore size. Means that total pore volume decreases with pore size.
Can be overcome by supercritical drying, this is technically easy but takes time=money
P=2γlv/r
r
Size Of Domains
•Rate of phase separation
•Polarity of solvent
•Starting material
•Temperature
•Rate of hardening
•Starting material
•Time in acid
•Temperature
•Shrinkage
•Surface tension
•Contact angle of solvent “r”
•Pore Size “r”
•Strength
•(Temperature/pH=coarsening)
Super-hydrophobicity
Max. Angle 120°
Super-hydrophobicity
Lotus LeafBarthlott&Neinhuis
Flat Teflon
Sol-Gel Foams
Materials
Sample Temp./°°°° C Post treatment
Advancing Angle Θ/°
Receding Angle Θ/°
Hysteresis ∆Θ/°
Flat 300 None 107 87 20
Flat 400 None 90 69 21
Flat 500 None 81 67 14
Flat 550 None 54 31 12
Foam1 300 None 153 137 16
Foam1 300 Abraded 156 152 4
Foam2 300 None 155 149 6
Foam1 400 None Absorbed Absorbed -
Advancing and receding contact angles of drops of water on organo-silica flat surfaces and foams. Foam 1- MTEOS sol-gel produced using 1.1 M ammonia: Foam 2- sol-gel produced using MTEOS and 2.2 M ammonia.
Effect of Heating
3500 3000 2500 2000 1500 1000-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
300º C
110º C225º C
400º C
500º C
Abs
orba
nce
Wavenumber/cm-1
100 200 300 400 500 600 7000.86
0.88
0.90
0.92
0.94
0.96
0.98
1.00
No
rma
lise
d M
ass
Temperature/° C
Pore Size/Ammonia
10 µm
MTEOS with 1.1 M ammonia, heated to 300° C MTEOS with 2.2 M ammonia, heated to 300° C
Contact Angle/Ammonia
130
135
140
145
150
155
160
165
170
0 1 2 3 4
Ammonia Concentration / M
Pore Size/End Group
10 µmMTEOS with 1.1 M ammonia, heated to 300° C PTEOS with 22 M ammonia, heated to 300° C
O RSi
CH2
OO
R
R
CH2
CH3
O RSi
CH3
OO
R
RO RSi
OO
R
R
H
Sol-Gel Films
Properties
Thermally insulatingWaterproof or water absorbingGas permeableUseful thickness depends on pore size
Recipe
CH3CH
CH3
OHN CH3
CH3
CH
O
DMF IPA
Water Contact Angle/Hydrolysis Time
144
146
148
150
152
154
156
158
20 40 60 80 100 120 140
Hydrolysis Time / mins
1
2
3
Thin Films Look Like Trees
and have lower contact angles
Conclusion
•Can produce layers of sol-gel that are very hydrophobic and porous.•Can vary pore size using hydrolysis time, solvent polarity and monomer•Can vary hydrophobicity by thermal treatment•With supercritical drying, will be attempting to decouple pore size and pore fraction•With suitable coupling agents have coated glass and gold