ME 597 final ppt_Force Distance curves on Polyurethane foam
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Transcript of ME 597 final ppt_Force Distance curves on Polyurethane foam
Young’s Modulus of Polyurethane foam from Force Spectroscopy using AFM
Tejasvi Parupudi
Department of ECET
Purdue University
Motivation
• Polyurethane foams - used in flexible implants.
• Polyurethane in conjunction with Polyethylene-glycol or PEG coatings used for neural electrodes
• Comparison of Young’s Modulus in macroscaleand nanoscale
(Tsukruk et al., 2000)
Project Goals
• To determine Young’s Modulus based on the indentation (strain) produced and force applied per area (stress) by an AFM tip on two different regions- 1)on the cell and 2)in between cells
• To understand the viscoelastic properties of polyurethane (a soft sample because it is a polymer) using contact mode force-distance curves
• To explore adhesion forces from retraction curves
Deflection sensitivity
• On pretreated glass (Ethanol + DI), thrice
Deflection Z curve on glass before (left) and after (right) force curve experiment on polyurethane foam
Spring constant• Thermal tune
• Lorentzian fit
• Average of five trials
K=0.0471 N/m and 0.12 N/m(Soft cantilever)
Tip properties
Bruker Inc.
VEDA Simulations- Approach curves
With Adhesion force 1.2 nNWith Adhesion force 6 nN
Experiment 1: K=0.04708 N/m; JKR model; Z start: 10nm; Z end: -5 nm; Sample YM: 2.323kPa
k=0.0471N/mFadh= 6nN
k=0.0471N/mFadh= 1.2nN
VEDA Simulations- Approach curves
With Adhesion force 1.2 nNWith Adhesion force 6 nN
Experiment 2: K=0.1197 N/m; JKR model; Z start: 10nm; Z end: -5 nm; Sample YM: 2.323kPa
k=0.1197N/mFadh= 6nN
k=0.1197N/mFadh= 1.2nN
Flattened height image and section profile 3D height image
Laser position on cantilever before (left) and after (right) force curve experiment. SUM: 7.24V
Tapping Mode height image of Polyurethane
Force-distance curves and Sneddon fitExperiment 1
Image Data Deflection Error X Data Type Ramp (Z position)Sens. DeflSens 44.62 nm/VPlot Units Force Spring Constant 0.04708 N/mDisplay Mode Deflection Error vs. Sep Plot Invert Normal / Invert
δ
InputsActive Curve Extend (Approach)Fit Method Linearized Model Include AdhesionForce Yes Max Force Boundary 70 %Min Force Boundary 10 %Fit Model Sneddon (Conical)
ResultsR² 0.8195 Young's Modulus 6.79MPa
Force-distance curves and Sneddon fitExperiment 2
Image Data Deflection Error X Data Type Ramp (Z position)Sens. DeflSens 27.69 nm/VPlot Units Force Spring Constant 0.1197 N/mDisplay Mode Defl Error vs. Sep Plot Invert Normal
InputsActive Curve Extend (Approach)Fit Method Linearized Model Include Adhesion Force Yes Max Force Boundary 70 %Min Force Boundary 10 %Fit Model Sneddon (Conical)
ResultsR² 0.9901 Young's Modulus 0.0279 MPa
Nanoindentation experiment using AFM on Polyurethane resulted in vales of Young’s Modulus between 10-20 MPa
(Chizhik et al., 1998)
Comparison of Young’s Modulus from literature
Conical punch
Experiment 1 Experiment 2Y= 6.79 MPa Y= 27.9 kPa
Sneddon model equation
Adhesion force
δ
Conclusions/Recommendations
• Young’s Modulus value is dependent on location of indentation, theoritical model used, tip geometry and shape.
• Value of Young’s Modulus closely relates to the value from other studies but is higher than the macroscalemodulus (=>higher mechanical strength)
• Viscoelastic nature of polyurethane foam (non linear region) is clearly seen
• Adhesion force is greater when a indentation was performed with softer cantilever
• Need for viscoelastic model on VEDA