Manufacturing of Three-dimensionally Microstructured Nanocomposites through Microfluidic Infiltration

The overall goal of this procedure is to manufacture 3D micro structured composite beams through the directed and localized infiltration of nano composites into 3D porous microfluidic networks. The microfluidic networks are fabricated by depositing liquid ink layer by layer. Then the empty spaces between the filaments are filled using a low viscosity resin and the encapsulating epoxy is cured.

The fugitive ink is then removed from the structure by liquefying the ink, followed by a washing of the channels with hot water and heane. Next, the resulting tubular microfluidic networks are infiltrated with thermo setting nano composite suspensions containing nano fillers and subsequently cured. The final step is curing the manufactured beam and cutting the excess parts to the desired dimensions.

Ultimately, various morphological and mechanical characterization techniques are used to show the capability of the manufacturing technique for the design of functional nano composite macroscopic products. We have worked for several years now on the development of advanced materials, specifically thermoplastic and thermo cell based nano composites. We are now trying to push the boundaries of our method by looking into a new material system and also new ways to manufacture complex 3D parts.

The main advantage of this technique over existing methods like injection molding, is that the PRIs technique allows sufficient control of the three dimensional orientation and positioning of the nano tube reinforcement during the manufacturing of a product for optimal conditions. This flexible manufacturing technique extend toward the utilization of other thermo setting materials and nano fillers. Several applications include structural health monitoring, vibration absorption products and microelectronics To make the fugitive ink melt, microcrystalline wax and petroleum jelly over a hot plate magnetic mixer at 80 degrees Celsius when melted and mixed load the ink into a three cc syringe barrel.

Install a 150 micrometer disposition nozzle on the syringe and mount the syringe onto the syringe holder of the dispensing robot. Use an Excel program to design the moving path of the dispensing robot for the fabrication of the desired 3D scaffold structure. This information should include the structure's, dimensions, the filament spacing, the number of layers, and the on-off status of the dispensing at each location during the fabrication.

In this case, the dimensions are 60 millimeters in length, 7.5 millimeters in width, and 1.7 millimeters in thickness with 0.25 millimeter horizontal spacing between each filament for a filament diameter of about 150 micrometers. Set the deposition pressure to 1.9 megapascals on the pressure regulator and set the robot dispensing speed to 4.7 millimeters per second. Next, activate the deposition of the ink based filaments on an epoxy substrate.

This results in a 2D pattern, which is the first layer of the micro scaffold. Continue depositing additional layers of the micro scaffold by successively incrementing the Z position of the dispensing nozzle by an amount equal to the diameter of the filament. Each layer takes about four to five minutes to make self-supporting structures that are a few hundred layers can be built in this fashion.

The next step is to prepare the epoxy that will be used for encapsulation. Begin by mixing the resin and hardener, and then degas the epoxy mixture under vacuum for 30 minutes. After degassing, load the epoxy into a three cc syringe barrel by applying negative pressure using a fluid dispenser.

Then place a nozzle with an ID of 0.51 millimeters into the syringe barrel. Place the ink scaffold at an incline to help the flow of the resin. Then using the same fluid dispenser and mounted nozzle place drops of epoxy at the upper end of the incline scaffold structure.

The epoxy then flows into the empty spaces between the filaments driven by gravity and capillary forces. Continue placing drops of epoxy over the scaffold until the empty space between the scaffold filaments is completely filled. Let the encapsulating epoxy pre currere at room temperature for 24 hours and then put the structure in an oven to post cure at 60 degrees Celsius for two hours.

After curing, use a precision saw to cut the excess parts of the epoxy. Then drill a hole approximately one millimeter in diameter at each end of the structure. To reach the ink scaffold, insert a plastic tube into each of the holes.

The next step is to remove the fugitive ink from the structure. Begin by putting the samples in an oven at 90 degrees Celsius for 30 minutes to liquefy the ink. After removing the samples from the oven, wash the channel network by suctioning hot distilled water through the plastic tubes for five minutes.

Then suction hexane through the tubes for another five minutes to remove the residual traces of the ink from the channel walls after ink removal. What remains is an interconnected 3D microfluidic network, which can be stored at room temperature until it is needed. To prepare the nano composites, add 150 milligrams of carbon nano tubes to a 0.1 millimolar solution of zinc Proto porphyrin nine surfactant in either acetone or di chloro methane for a final nano tube concentration of 0.5 weight percent.

Next, sonicate the suspension in an ultrasonic bath for 30 minutes. To DB bundle the nano tube aggregates. Mix the epoxy or urethane resin with the nano tube suspension over a magnetic stirring hot plate at a temperature slightly below the solvent.

Boiling temperature for four hours is then place the nano composite mixture into the ultras, sunation, bath and sonicate while heating at 40 to 50 degrees Celsius for one hour. Next, heat the nano composite at 30 degrees Celsius for 12 hours and then heat it under vacuum at 50 degrees Celsius for 24 hours to evaporate the residual solvent. The next day.

Set aside a portion of the nano composite at room temperature for use as a baseline comparison to break any large nano tube aggregates. Set the speed of the apron roll of a three roll mixer to 250 RPMs, beginning with a gap of 25 micrometers between the rolls past the remaining nano composite mixture through the rolls five times. Then adjust the gap between the rolls to 10 micrometers and perform five more passes After a final reduction of the gap to five micrometers, do an additional 10 passes the nano composites before and after passing through the rollers are shown here.

Next, Degas the final mixture on your vacuum for 24 hours using a desiccate to remove the air bubbles trapped during the mixing. The next step is to inject the nano composite into the microfluidic device. After placing the nano composites into the fluid dispenser, apply a negative pressure to the fluid dispenser, which causes the nano composites to be loaded into a three cc syringe barrel.

Attach a fine nozzle into the syringe barrel and insert the nozzle into the tubes in the microfluidic to device. Then set the pressure on the fluid dispenser to 400 kilo pascals if needed, to assist the network filling. Apply a negative pressure to the outlet side of the microfluidic network using another fluid dispenser.

Once the pressure is applied, the microfluidic network is filled by the nano composite suspension, which enters the network through the plastic tube. Shortly after the injection exposed the nano composite filled composite beams to UV illumination for 30 minutes for pre curing. Then post cure the manufactured beams in the oven at 80 degrees Celsius or one hour followed by 130 degrees Celsius for another hour.

After cutting the excess epoxy parts using a saw polish, the beams to the desired dimensions, an isometric image of a manufactured 3D reinforced beam is shown here. This cross section shows nine layers of the nano composite filaments. This figure shows an SEM image of a manufactured beam's fracture surface and a higher magnification image of one of the channels embedded with nano composite microfibers.

Since no de bonding is seen at the channel wall, the surrounding epoxy and the infiltrated materials appear to be well adhered, presumably as a result of proper cleaning of the channels with hexane after the ink removal. In contrast shown here are beams broken during the mechanical testing in which hexane was not used during the ink removal. Fiber de bonding as a result of a poor mechanical interface is observed, which might be due to fugitive ink traces remaining after network cleaning.

The storage modulus of molded bulk epoxy samples used as benchmarks, and the 3D reinforced beams are shown here. The manufactured beams, which are the combination of the embedded and surrounding epoxy materials, show superior temperature dependent properties with the presence of only about 0.18 weight percent carbon nanotubes. A three point bending test shows that as a result of the positioning of the carbon nanotubes, the flexeral modulus of the 3D reinforced beams showed an increase of 34%compared to the pure epoxy infiltrated beams.

The molded bulk epoxy samples are shown for reference. This patterning approach could be used for a wide variety of applications ranging from flexible microelectronics to 3D non composite macro structures. For mems.

We are working toward pushing the boundaries of this technique by looking into new and material system, and also investigating new ways to build in 3D such as 3D freeform printing using thermoset and thermoplastic based nano composites. Thank you.