Project lead
Alex McGhee
Publications
Full-Field Deformation Measurements in Liquid-like-Solid Granular Microgel Using Digital Image Correlation
McGhee, A., Bennett, A., Ifju, P. et al. Exp Mech (2017). https://doi.org/10.1007/s11340-01
McGhee, A., Bennett, A., Ifju, P. et al. Exp Mech (2017). https://doi.org/10.1007/s11340-01
Project overview
An experimental method to measure the deformation within a yield stress material (YSM) due to the motion of a cylindrical object has been explored. A literature review of this subject showed that all previous measurements on this subject used a incremental digital image correlation (DIC) to do particle image velocimetry (PIV). The reason incremental correlation has been extensively used is that the speckles used have the same shape, so large deformations were not possible to track. By introducing a unique shape for each speckle, larger deformation measurements can be made, and allow for all deformation measurements to be made from a single reference. The novelty in this technique comes from the ability to print a speckle pattern at any depth within a volume of the YSM. Hard particles do not print well since they are prone to jamming, and hydrophobic particles will clump together and clog a printing tip. By cross-linking poly(ethylene glycol) with black water based paint and blending them into small fragments, soft hydrophylic speckles can be extracted.
Creation of polymeric speckles
Begin by creating a stock solution of polymer (this step ensures that the polymer is fully dissolved into solution)
|
PEG-A
Poly(ethylene glycol) methyl ether acrylate <Mn>=480 (Aldrich 454990) PED-DA Poly(ethylene glycol) diacrylate <Mn> 700 (Aldrich 455008) Irgacure 2-Hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone <Mw> 224.5 g/mol (Aldrich 410896) |
• measure 6.15g PEG-A into a cup
• add enough water to bring to 10mL total solution • measure 4 g PEG-DA into a cup • allow the polymer to melt at room temperature • add enough water to bring to 10 mL total solution • measure 0.125 g irgacure into a vial • add 1 mL ethanol • vortex for ~ 1 min, if there is still polymer at the bottom continue mixing. • wrap the vial in tin foil to block out UV radiation |
Mix these stock polymer solutions in the following concentration to make 10 mL
|
PEG-A
PEG-DA DI water |
1.83 (mL)
0.66 (mL) 7.47 (mL) |
Add water soluble paint, along with water in the following concentration
|
paint
|
0.310 (mL)
|
Wrap solution in tin foil to block out UV radiation before adding Irgacure
|
Irgacure
|
2.85 (mL)
|
Apply the final solution to a plate of glass, and use ultra-violet radiation (UV) to begin the curing process. The higher the concentration of paint, and the darker the color the more time is needed to complete the reaction.
PEG + Black paint takes approximately 5 minutes
A thin film of polymer should now be attached to the glass, and should look wrinkled, allow the polymer to complete the polymerization by letting it sit alone for ~15 min.
Since the black paint does not get trapped fully within the cross-links of the polymer, the thin film should be rinsed carefully until the runoff is no longer tinted. The remaining thin film should be placed into a blender along with enough water to allow the blender to function properly. After the speckles are thoroughly blended, the contents should be placed into a separate container with a flat bottom. Use a flash light to illuminate the container, and remove the large speckles (which should sink quickly) by sucking them out individually with a pipet (if the water is too dark then allow all the speckles to sink, and carefully remove the top layer of water and replace with fresh water). Keep disturbing the container and watching the particles sink until there is no longer any large particles in the container **if you are careless here, the quality of the speckle pattern when printing may suffer greatly. Now the water should be separated from the speckles. To do this, first let the speckles sink to the bottom of the container should be approx 15-30 minutes. Next suck out the speckles from the bottom using a 10 mL pipet, and place the speckle water mixture into a 10 mL vial. Place the 10 mL vials into a centrifuge and spin for 30 to 60 seconds. The speckles should form a black puck at the bottom of the vials, so the water can be easily separated by slowly pouring it into the container the speckles came from. Place the black speckle slurry into a larger container (max 10 cup) and label the container. Reuse the same vials until all of the speckles are taken from the bottom of the large container (there will be a point where not much speckles will be produced stop at any time).
PEG + Black paint takes approximately 5 minutes
A thin film of polymer should now be attached to the glass, and should look wrinkled, allow the polymer to complete the polymerization by letting it sit alone for ~15 min.
Since the black paint does not get trapped fully within the cross-links of the polymer, the thin film should be rinsed carefully until the runoff is no longer tinted. The remaining thin film should be placed into a blender along with enough water to allow the blender to function properly. After the speckles are thoroughly blended, the contents should be placed into a separate container with a flat bottom. Use a flash light to illuminate the container, and remove the large speckles (which should sink quickly) by sucking them out individually with a pipet (if the water is too dark then allow all the speckles to sink, and carefully remove the top layer of water and replace with fresh water). Keep disturbing the container and watching the particles sink until there is no longer any large particles in the container **if you are careless here, the quality of the speckle pattern when printing may suffer greatly. Now the water should be separated from the speckles. To do this, first let the speckles sink to the bottom of the container should be approx 15-30 minutes. Next suck out the speckles from the bottom using a 10 mL pipet, and place the speckle water mixture into a 10 mL vial. Place the 10 mL vials into a centrifuge and spin for 30 to 60 seconds. The speckles should form a black puck at the bottom of the vials, so the water can be easily separated by slowly pouring it into the container the speckles came from. Place the black speckle slurry into a larger container (max 10 cup) and label the container. Reuse the same vials until all of the speckles are taken from the bottom of the large container (there will be a point where not much speckles will be produced stop at any time).
Printing the black speckles
Many factors must be considered when printing the speckle pattern
After the speckle-YSM mixture is created, speed mix the container to remove any trapped air bubbles and randomize the speckles. Add the mixture to a syringe by plunging the syringe to the bottom of the speckle mixture, and pulling the mixture into the syringe. Add the printing needle to the end of the syringe, and remove any trapped air within the needle by dispensing some of the speckle mixture back into its container. Setup the syringe onto a 4 axis 3D printer and make contact with the syringe plunger. Wipe off any excess speckle mixure from the end of the printing needle, and move to the starting position of the plane. Using a raster pattern with a step over length of ~1/4 the needle diameter, move the syringe while the printer depresses the syringe plunger. The thickness and speckle pattern density of the plane can be controlled by the flowrate of the speckle mixture, and the translation speed of the printing needle. Keep the thickness of the plane at a minimum by increasing the density
- density of the desired speckle pattern
- thickness of the plane
- size of the cameras viewing window
- resolution of the camera
After the speckle-YSM mixture is created, speed mix the container to remove any trapped air bubbles and randomize the speckles. Add the mixture to a syringe by plunging the syringe to the bottom of the speckle mixture, and pulling the mixture into the syringe. Add the printing needle to the end of the syringe, and remove any trapped air within the needle by dispensing some of the speckle mixture back into its container. Setup the syringe onto a 4 axis 3D printer and make contact with the syringe plunger. Wipe off any excess speckle mixure from the end of the printing needle, and move to the starting position of the plane. Using a raster pattern with a step over length of ~1/4 the needle diameter, move the syringe while the printer depresses the syringe plunger. The thickness and speckle pattern density of the plane can be controlled by the flowrate of the speckle mixture, and the translation speed of the printing needle. Keep the thickness of the plane at a minimum by increasing the density