Very flexible and rugged Ag-Ga nanowires of constant diameter (50-500 nm diameter, 7-70 microns l... more Very flexible and rugged Ag-Ga nanowires of constant diameter (50-500 nm diameter, 7-70 microns long) can be simply grown onto AFM tips at room temperature. These nanowires are electrically conductive and have stiffness that is well matched to visco-elastic properties ...
A high aspect ratio and constant diameter Ag 2 Ga nanoneedle grown on an AFM cantilever was used ... more A high aspect ratio and constant diameter Ag 2 Ga nanoneedle grown on an AFM cantilever was used to perform FD experiments on four different molecular weights of PDMS surfaces. The needle is partially inserted into and retracted from the liquid surface in various scan ...
Polymer fiber can be formed by pulling a thread of polymeric liquid if the fiber solidifies befor... more Polymer fiber can be formed by pulling a thread of polymeric liquid if the fiber solidifies before it breaks up by capillary thinning. Fiber diameter is well correlated with a processing parameter that is a simple function of viscosity, surface tension and evaporation rate. The ...
The micro-Wilhelmy method is a well-established method of determining surface tension by measurin... more The micro-Wilhelmy method is a well-established method of determining surface tension by measuring the force of withdrawing a tens of microns to millimeters in diameter cylindrical wire or fiber from a liquid. A comparison of insertion force to retraction force can also be used to determine the contact angle with the fiber. Given the limited availability of atomic force microscope (AFM) probes that have long constant diameter tips, force-distance (F-D) curves using probes with standard tapered tips have been difficult to relate to surface tension. In this report, constant diameter metal alloy nanowires (referred to as "nanoneedles") between 7.2 and 67 µm in length and 108 and 1006 nm in diameter were grown on AFM probes. F-D and Q damping AFM measurements of wetting and drag forces made with the probes were compared against standard macroscopic models of these forces on slender cylinders to estimate surface tension, contact angle, meniscus height, evaporation rate, and viscosity. The surface tensions for several low molecular weight liquids that were measured with these probes were between -4.2% and +8.3% of standard reported values. Also, the F-D curves show well-defined stair-step events on insertion and retraction from partial wetting liquids, compared to the continuously growing attractive force of standard tapered AFM probe tips. In the AFM used, the stair-step feature in F-D curves was repeatably monitored for at least 0.5 h (depending on the volatility of the liquid), and this feature was then used to evaluate evaporation rates (as low as 0.30 nm/s) through changes in the surface height of the liquid. A nanoneedle with a step change in diameter at a known distance from its end produced two steps in the F-D curve from which the meniscus height was determined. The step features enable meniscus height to be determined from distance between the steps, as an alternative to calculating the height corresponding to the AFM measured values of surface tension and contact angle. All but one of the eight measurements agreed to within 13%. The constant diameter of the nanoneedle also is used to relate viscous damping of the vibrating cantilever to a macroscopic model of Stokes drag on a long cylinder. Expected increases in drag force with insertion depth and viscosity are observed for several glycerol-water solutions. However, an additional damping term (associated with drag of the meniscus on the sidewalls of the nanoneedle) limits the sensitivity of the measurement of drag force for low-viscosity solutions, while low values of Q limit the sensitivity for high-viscosity solutions. Overall, reasonable correspondence is found between the macroscopic models and the measurements with the nanoneedle-tipped probes. Tighter environmental control of the AFM and treatments of needles to give them more ideal surfaces are expected to improve repeatability and make more evident subtle features that currently appear to be present on the F-D and Q damping curves.
2006 Sixth IEEE Conference on Nanotechnology, 2006
Polymer fibers have been directly self-assembled into suspended bridges by manually brushing poly... more Polymer fibers have been directly self-assembled into suspended bridges by manually brushing polymer dissolved in a volatile solvent across a microstructured surface. This process is extended by adding multiwall carbon nanotubes to the liquid polymer solution of poly-(methyl methacrylate) (PMMA) in chlorobenzene. Suspended nanotube/polymer fibers with diameters between 20 nm and 20 microns (with bulk conductivities as large as 9.91 S/m) are created by brushing. Immersing the suspended fibers in acetone dissolves most of the polymer, leaving behind suspended bridges of nanotubes. The filamentary structures remain suspended following removal from the solvent bath and air drying. The nanotubes appear to be encased in a thin layer of polymer that assists in holding the bridge together. It is speculated that the residual coating is related to the organic functionalization that is added to the nanotubes to make them well dispersed and suspended in chlorobenzene.
Very flexible and rugged Ag2Ga nanoneedles of constant diameter (sub 100 nm diameter, 7-70 micron... more Very flexible and rugged Ag2Ga nanoneedles of constant diameter (sub 100 nm diameter, 7-70 microns long) can be securely grown onto AFM tips at room temperature. These nanoneedles are electrically conductive and have stiffness well matched to viscoelastic properties of complex fluids and biological materials. This talk specifically presents the abilities of the needles to (1) make precise AFM measurements
Very flexible and rugged Ag-Ga nanowires of constant diameter (50-500 nm diameter, 7-70 microns l... more Very flexible and rugged Ag-Ga nanowires of constant diameter (50-500 nm diameter, 7-70 microns long) can be simply grown onto AFM tips at room temperature. These nanowires are electrically conductive and have stiffness that is well matched to visco-elastic properties ...
A high aspect ratio and constant diameter Ag 2 Ga nanoneedle grown on an AFM cantilever was used ... more A high aspect ratio and constant diameter Ag 2 Ga nanoneedle grown on an AFM cantilever was used to perform FD experiments on four different molecular weights of PDMS surfaces. The needle is partially inserted into and retracted from the liquid surface in various scan ...
Polymer fiber can be formed by pulling a thread of polymeric liquid if the fiber solidifies befor... more Polymer fiber can be formed by pulling a thread of polymeric liquid if the fiber solidifies before it breaks up by capillary thinning. Fiber diameter is well correlated with a processing parameter that is a simple function of viscosity, surface tension and evaporation rate. The ...
The micro-Wilhelmy method is a well-established method of determining surface tension by measurin... more The micro-Wilhelmy method is a well-established method of determining surface tension by measuring the force of withdrawing a tens of microns to millimeters in diameter cylindrical wire or fiber from a liquid. A comparison of insertion force to retraction force can also be used to determine the contact angle with the fiber. Given the limited availability of atomic force microscope (AFM) probes that have long constant diameter tips, force-distance (F-D) curves using probes with standard tapered tips have been difficult to relate to surface tension. In this report, constant diameter metal alloy nanowires (referred to as "nanoneedles") between 7.2 and 67 µm in length and 108 and 1006 nm in diameter were grown on AFM probes. F-D and Q damping AFM measurements of wetting and drag forces made with the probes were compared against standard macroscopic models of these forces on slender cylinders to estimate surface tension, contact angle, meniscus height, evaporation rate, and viscosity. The surface tensions for several low molecular weight liquids that were measured with these probes were between -4.2% and +8.3% of standard reported values. Also, the F-D curves show well-defined stair-step events on insertion and retraction from partial wetting liquids, compared to the continuously growing attractive force of standard tapered AFM probe tips. In the AFM used, the stair-step feature in F-D curves was repeatably monitored for at least 0.5 h (depending on the volatility of the liquid), and this feature was then used to evaluate evaporation rates (as low as 0.30 nm/s) through changes in the surface height of the liquid. A nanoneedle with a step change in diameter at a known distance from its end produced two steps in the F-D curve from which the meniscus height was determined. The step features enable meniscus height to be determined from distance between the steps, as an alternative to calculating the height corresponding to the AFM measured values of surface tension and contact angle. All but one of the eight measurements agreed to within 13%. The constant diameter of the nanoneedle also is used to relate viscous damping of the vibrating cantilever to a macroscopic model of Stokes drag on a long cylinder. Expected increases in drag force with insertion depth and viscosity are observed for several glycerol-water solutions. However, an additional damping term (associated with drag of the meniscus on the sidewalls of the nanoneedle) limits the sensitivity of the measurement of drag force for low-viscosity solutions, while low values of Q limit the sensitivity for high-viscosity solutions. Overall, reasonable correspondence is found between the macroscopic models and the measurements with the nanoneedle-tipped probes. Tighter environmental control of the AFM and treatments of needles to give them more ideal surfaces are expected to improve repeatability and make more evident subtle features that currently appear to be present on the F-D and Q damping curves.
2006 Sixth IEEE Conference on Nanotechnology, 2006
Polymer fibers have been directly self-assembled into suspended bridges by manually brushing poly... more Polymer fibers have been directly self-assembled into suspended bridges by manually brushing polymer dissolved in a volatile solvent across a microstructured surface. This process is extended by adding multiwall carbon nanotubes to the liquid polymer solution of poly-(methyl methacrylate) (PMMA) in chlorobenzene. Suspended nanotube/polymer fibers with diameters between 20 nm and 20 microns (with bulk conductivities as large as 9.91 S/m) are created by brushing. Immersing the suspended fibers in acetone dissolves most of the polymer, leaving behind suspended bridges of nanotubes. The filamentary structures remain suspended following removal from the solvent bath and air drying. The nanotubes appear to be encased in a thin layer of polymer that assists in holding the bridge together. It is speculated that the residual coating is related to the organic functionalization that is added to the nanotubes to make them well dispersed and suspended in chlorobenzene.
Very flexible and rugged Ag2Ga nanoneedles of constant diameter (sub 100 nm diameter, 7-70 micron... more Very flexible and rugged Ag2Ga nanoneedles of constant diameter (sub 100 nm diameter, 7-70 microns long) can be securely grown onto AFM tips at room temperature. These nanoneedles are electrically conductive and have stiffness well matched to viscoelastic properties of complex fluids and biological materials. This talk specifically presents the abilities of the needles to (1) make precise AFM measurements
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