Revealing the pattern between anterior polymerization and normal pregnancy

A self-diffusing chemical reaction can convert a liquid monomer into a solid polymer, and the interaction between the diffusion front and the natural convection of the reaction leads to patterns in the resulting solid polymeric material. The new work at the University of Illinois at Urbana-Champaign shows how coupling between natural convection and forward polymerization leads to those observed patterns.

This research was led by a unique team of researchers: Materials Science and Engineering Professor Nancy Sotos, Aerospace Engineering Professor Philippe Gubel, and Leonardo Chamorro Professor of Mechanical Sciences and Engineering. A paper describing this research was recently published in Physical review letters.

Thermoplastic polymers and composites are used in a wide variety of industries, but producing such materials requires them to be processed at high temperatures in a slow, energy-intensive process. Forward polymerization of material processing is an attractive alternative method that is much faster and more energy efficient.

In forward polymerization, the self-diffusing chemical interface converts the liquid monomer into a solid polymer through a reaction that generates a large amount of heat. Monomers are a simple class of molecular “building blocks” that can react to form larger polymer molecules. All of the energy needed to form a polymer is contained within the monomer itself, and to harness that energy, only a small catalyst is required to start the reaction.

Because of the instability, the self-propagating front does not always move uniformly. Although it’s ideal for the front part to move smoothly at a constant speed for applications like composite manufacturing and 3D printing, Guebel says, “We’re actually very interested in these instabilities because they allow us to create patterns in the material. That’s very exciting, because for some materials This instability can lead to very different properties of matter.”

Gubel explains that the team’s goal was to “understand, experimentally and computationally, the interaction between the front that propagates into the monomer bath and the convection that occurs before it, and how the interaction between the two can lead to patterns in a material.”

To visualize and characterize the polymerization-recycling front-end interface, the team had to design a smart template that would allow them to make observations through both the top and the side. They built and used a glass block that allows the front to be observed from above and the laser beam to enter from the side.

They then used the particle image velocity (PIV) scale to describe the velocity field. To use PIV, they needed to seed the liquid with tiny “tracer” particles that follow flow and can be tracked by a camera and illuminated by a laser sheet to visualize patterns in the material. Choosing the particles has been one of the challenges of this work, says Chamorro. The team experimented with different types of particles before settling on silver-coated glass particles.

They were able to demonstrate that as the front diffuses and converts the liquid monomer into a solid polymer, the energy released generates convection. Convection is a process in which heat is transferred by the motion of a hot fluid. Like water in the ocean, when a liquid is heated, it expands, and due to buoyancy, the hotter liquid rises because it is less dense, and the cooler liquid replaces it by sinking to the bottom because it is denser. This process continues, creating a recycling flow.

The polymerization process produces a lot of heat, resulting in temperatures in excess of 350 degrees Fahrenheit, and this heat generated during transformation goes to the top of the surface. The researchers showed that this was a buoyancy-driven process, and that the recirculation associated with the heat of reaction, combined with the effect of gravity, leads to the formation of the patterning observed in the material and to influence the polymerization front. . Thanks to the re-spin, the front end is tilted rather than completely vertical. This inclined front can produce different speed or cooling effect and even different embossing effect.

Soto says the experiments revealed that not only does recirculation create patterns within the material that affect the material’s properties, but it “creates surface patterns on top of the material as well, because the monomer is pushed through the recycled flow.”

The revealed mechanisms of interaction between the polymerization front and the induced natural convection, and the resulting modeling, represent a deep understanding of the front polymerization that may prove useful in the future fabrication of polymeric materials.

Other authors on this work are Yuan Zhao (Postdoctoral researcher, Beckman Institute for Aeronautical Engineering and Engineering); Justine Paul (graduate student, Beckman Institute for Materials Science and Engineering); Manxin Chen (University Student, Beckman Institute for Aerospace Engineering); and Liu Hong (graduate student, mechanical science and engineering).