Creating Patterns With Complex Microstructures Spontaneously in Synthetic Materials

A polymerization front marked by heat gradients (red, higher temperature) allows spontaneous patterning of polymers with variable textures, colors and stiffness. Scale bar, 1 cm. Credit: Adapted from ACS Central Science 2021, DOI: 10.1021/acscentsci.1c00110

Nature produces a startling array of patterned materials, from the sensitive ridges on a person’s fingertip to a cheetah’s camouflaging spots. Although nature’s patterns arise spontaneously during development, creating patterns on synthetic materials is more laborious. Now, researchers reporting in ACS Central Science have found an easy way to make patterned materials having complex microstructures with variations in mechanical, thermal, and optical properties — without the need for masks, molds, or printers.

In animals, patterns form before birth in response to genetically controlled signals that often vary in concentration along a gradient. In contrast, traditional manufacturing approaches for creating patterns and structures involve multiple steps, such as layer-by-layer assembly, lithography, molding, or casting. Jeffrey Moore, Nancy Sottos, Philippe Geubelle and colleagues wanted to develop a spontaneous patterning method more akin to the biological process.

The team placed a solution of dicyclopentadiene monomer in a channel and then heated one end of the channel. The heat-activated a ruthenium catalyst, which caused the monomer to polymerize, generating more heat that traveled down the channel. This continued to happen until all available monomer in the region was consumed. Eventually, heat traveled farther down the channel to a location where fresh monomer was present, and the process began again. With this technique, the team produced resins with regular ridges, and they controlled the height and spacing of the ridges by adjusting the initial temperature of the solution. By using a different monomer or adding other compounds to the solution, the researchers created materials with patterns of color and stiffness. The new method could someday be used to create a variety of new “smart” materials, from tire or shoe treads to electronics and biomaterials, the researchers say.

Reference: “Spontaneous Patterning during Frontal Polymerization” by Evan M. Lloyd, Elizabeth C. Feinberg, Yuan Gao, Suzanne R. Peterson, Bhaskar Soman, Julie Hemmer, Leon M. Dean, Qiong Wu, Philippe H. Geubelle, Nancy R. Sottos and Jeffrey S. Moore, 24 March 2021, ACS Central Science.
DOI: 10.1021/acscentsci.1c00110

The authors acknowledge funding from the Air Force Office of Scientific Research, the Arnold & Mabel Beckman Foundation, the National Science Foundation and the Illinois Space Grant Consortium.

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