31 research outputs found
Adhesion of fluid infused silicone elastomer to glass
Elastomers swollen with non-polar fluids show potential as anti-adhesive
materials. We study the effect of oil fraction and contact time on the adhesion
between swollen spherical probes of PDMS (polydimethylsiloxane) and flat glass
surfaces. The PDMS probes are swollen with pre-determined amount of 10 cSt
silicone oil to span the range where the PDMS is fluid free (via solvent
extraction) up to the limit where it is oil saturated. Probe tack measurements
show that adhesion decreases rapidly with an increase in oil fraction. The
decrease in adhesion is attributed to excess oil present at the PDMS-air
interface. Contact angle measurements and optical microscopy images support
this observation. Adhesion also increases with contact time for a given oil
fraction. The increase in adhesion with contact time can be interpreted through
different competing mechanisms that depend on the oil fraction where the
dominant mechanism changes from extracted to fully swollen PDMS. For partially
swollen PDMS, we observe that adhesion initially increases because of
viscoelastic relaxation and at long times increases because of contact aging.
In contrast, adhesion between fully swollen PDMS and glass barely increases
over time and is mainly due to capillary forces. While the relaxation of PDMS
in contact is well-described by a visco-poroelastic model, we do not see
evidence that poroelastic relaxation of the PDMS contributes to an increase of
adhesion with glass whether it is partially or fully swollen
Micropatterned Charge Heterogeneities via Vapor Deposition of Aminosilanes
Aminosilanes are routinely employed for charge reversal or to create coupling
layers on oxide surfaces. We present a chemical vapor deposition method to
pattern mica surfaces with regions of high-quality aminosilane
(3-aminopropyltriethoxysilane, APTES) monolayers. The approach relies on the
vapor deposition of an aminosilane through a patterned array of through-holes
in a PDMS (poly(dimethylsiloxane)) membrane that acts as a mask. In aqueous
solutions the surfaces have regular patterns of charge heterogeneities with
minimal topographical variations over large areas. This versatile dry lift-off
deposition method alleviates issues with multilayer formation and can be used
to create charge patterns on curved surfaces. We identify the necessary steps
to achieve high quality monolayers and charge reversal of the underlying mica
surface: 1) hexane extraction to remove unreacted PDMS oligomers from the
membrane that would otherwise deposit on and contaminate the substrate, 2)
oxygen plasma treatment of the top of the membrane surfaces to generate a
barrier layer that blocks APTES transport through the PDMS, and 3) decrease of
the vapor pressure of APTES during deposition to minimize APTES condensation at
the mica-membrane-vapor contact lines and to prevent multilayer formation.
Under these conditions, AFM imaging shows that the monolayers have a height of
0.9nm with an increase in height up to 3nm at the mica-membrane-vapor contact
lines. Fluorescence imaging demonstrates pattern fidelity on both flat and
curved surfaces, for feature sizes that vary between 6.5-40 um. We verify
charge reversal by measuring the double layer forces between a homogeneous
APTES monolayers and a mica surface in aqueous solution and we characterize the
surface potential of APTES monolayers by measuring the double layer forces
between identical APTES surfaces. We obtain a surface potential of 110mV at pH
4.0
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Adhesion of fluid infused silicone elastomer to glass
Elastomers swollen with non-polar fluids show potential as anti-adhesive materials. We study the effect of oil fraction and contact time on the adhesion between swollen spherical probes of PDMS (polydimethylsiloxane) and flat glass surfaces. The PDMS probes are swollen with pre-determined amount of 10 cSt silicone oil to span the range where the PDMS is fluid free (via solvent extraction) up to the limit where it is oil saturated. Probe tack measurements show that adhesion decreases rapidly with an increase in oil fraction. The decrease in adhesion is attributed to excess oil present at the PDMS-air interface. Contact angle measurements and optical microscopy images support this observation. Adhesion also increases with contact time for a given oil fraction. The increase in adhesion with contact time can be interpreted through different competing mechanisms that depend on the oil fraction where the dominant mechanism changes from extracted to fully swollen PDMS. For partially swollen PDMS, we observe that adhesion initially increases because of viscoelastic relaxation and at long times increases because of contact aging. In contrast, adhesion between fully swollen PDMS and glass barely increases over time and is mainly due to capillary forces. While the relaxation of PDMS in contact is well-described by a visco-poroelastic model, we do not see evidence that poroelastic relaxation of the PDMS contributes to an increase of adhesion with glass whether it is partially or fully swollen