Silane Modification of Glass and Silica Surfaces to Obtain
Equally Oil-wet Surfaces in Glass-covered Silicon Micromodel
Applications
Jay W. Grate*, Marvin G. Warner, Jonathan W. Pittman, Karl J. Dehoff, Thomas W.
Wietsma, Changyong Zhang, and Mart Oostrom
Supplementary information:
Micromodels
Figure S1. A. Image of a silicon-silica/glass micromodel with a homogeneous pore network between single inlet
and single outlet ports, as seen through the glass cover plate. B. The schematic drawing shows a cross-sectional view,
not to scale, to illustrate the glass and silica surfaces around the fluid channel in the pore throat.
To treat the interior surfaces of a micromodel with boiling nitric acid, a Nanoport with a
PerlastTM O-ring was temporarily bonded to an inlet port using 5 minute epoxy. The micromodel
was filled with concentrated nitric acid by syringe and tubing connection. The Nanoport was
cleaved off the micromodel and the entire device was submerged in nitric acid in a beaker on a
hot plate. The acid was brought to boiling for at least 60 minutes. Then the model was taken out
of the beaker, the nitric acid was removed using a vacuum suction method, and the model was
rinsed with water by the same vacuum suction method. Once the interior had been thoroughly
rinsed, Nanoports could be applied by the conventional methods using the supplied solid epoxy
rings at elevated temperature, and all subsequent fluid injections used those ports. To silanize the
surface, neat HMDS was injected, and the model was held at 75-90oC overnight in a
crystallization dish topped with a watch glass.
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Contact Angles:
All contact angles on the silica and glass surfaces were determined on a Ramé-Hart
Model 500 Advanced Goniometer (Netcong, NJ) using the static sessile drop method with DROP
Image Advanced Software as described in detail previously[Grate et al., 2012]. Air−water
contact angles were obtained for water droplets in air and oil−water contact angles for
hexadecane droplets in water. The contact angles reported here are the contact angles through
the water phase as shown in Figure 2 and exactly as explained previously[Grate et al., 2012].
Figure 2. Contact angle images of glass surfaces silanized with HMDS. Glass surfaces precleaned with
(A). SC1, and (B) boiling concentrated nitric acid. Although the air-water contact angles are similar, the
oil-water contact angles are quite different depending on prior glass surface history. The reported contact
angles through the water phase are shown in (C).
2
Clean water-wet silica and glass
The combination of silicon-silica and glass is normally of little consequence for obtaining
micromodels of uniform wettability so long as both surfaces are thoroughly cleaned to provide
water-wet surfaces. Our own contact angle measurements on silica and borosilicate glass
surfaces confirm this as indicated in Table 1. Oil-water contact angles in the range of 10 to 15
degrees were observed on rigorously cleaned silica and glass surfaces.
Table 1. Contact angle measurements on clean silicaa and glass surfaces.
Contact Angles
Oil-water b
Air-water
Std
a
b
Std
Surface Treatment
Surface
Mean
Dev
n
Mean
Dev
n
SC1 cleaneda
Silica
3.7
0.8
9
11
3.3
9
SC1 cleaned
Glass
9.8
1.0
9
11
1.7
9
UV-Ozone cleaneda
Silica
3.3
0.6
9
13
3.1
9
UV-Ozone cleaned
Glass
11
1.6
9
14
2.9
9
Results on silica from our previously published work [Grate et al., 2012] .
Hexadecane is the oil
3
Intermediate wet surfaces:
Contact angle measurements for surfaces modified with silanes previously identified
[Grate et al., 2012] to yield intermediate-wet surfaces on silica are presented in Table 2. The
contact angles on glass are in the intermediate wet range. Hence, the selected silanes, 2-(3trimethoxysilylpropylthio)-thiophene , and triethoxy-2-thienylsilane, yield intermediate wet
surfaces on both silica and glass . Glass surfaces were cleaned with either SC1 or boiling
concentrated nitric acid prior to silanization. Even when the glass surfaces were baked at 400oC
for 25 minutes and then cooled prior to solution cleaning in boiling nitric acid, the surface
silanized with triethoxy-2-thienylsilane was similar in wettability to similarly silanized glass
surfaces that had not been prebaked at 400oC. Hence the silanization of glass surfaces to obtain
intermediate wet surfaces using triethoxy-2-thienylsilane is not critically dependent on the surface
thermal history or cleaning method.
Table 2. Contact angle measurements on intermediate-wet silanized silicaa and glass surfaces
Contact Angles
n
9
Oil-water b
Std
Mean Dev
100
5.2
n
9
Surface Modification
2-(3trimethoxysilylpropylthio)thiophene
“
“
Surface
Silica
Air-water
Std
Mean Dev
75
1.6
Glass
Glass
68
70
1.5
2.0
9
9
101
110
2.6
2.1
9
9
Triethoxy-2-thienylsilane
“
“
Silica
Glass
Glass
79
64
72
1.7
2.9
3.0
9
9
0
95
83
102
3.1
5.9
2.9
9
9
9
Silica
82
1.1
9
115
1.6
9
Triethoxy-2-thienylsilane on
surface pretreated at 400 oC d
“
Glass
76
1.6
9
105
1.2
9
Results on silica from our previously published work. [Grate et al., 2012]
b
Hexadecane is the oil
c
Concentrated nitric acid.
d
Surfaces baked at 400oC for 25 minutes and then cooled prior to solution cleaning.
Cleaning
method
UV-ozonea
SC1
Boiling nitric
acid c (30
min)
UV-ozonea
SC1
Boiling nitric
acid c (30
min)
Boiling nitric
acid c (30
min)
Boiling nitric
acid c (30
min)
a
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References for supplementary information
Grate, J. W., K. J. Dehoff, M. G. Warner, J. W. Pittman, T. W. Wietsma, C. Zhang, and M.
Oostrom (2012), Correlation of Oil–Water and Air–Water Contact Angles of Diverse Silanized
Surfaces and Relationship to Fluid Interfacial Tensions, Langmuir, 28(18), 7182-7188.
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