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Many technological and societal challenges require novel materials with properties precisely fine-tuned for specific applications. For example, in the energy transition, much attention focuses on developing electronic components based on carbon instead of silicon for use in solar cells. These devices not only promise to be cheaper to produce, but also have properties not found in other materials, thereby enabling a broader range of applications. Another example lies in the (bio)medical field, where researchers are exploring novel materials for targeted medicine delivery, ensuring that the medicine are applied only where needed.

Soft materials

These examples illustrate typical applications of so-called soft materials, which are called soft because they are relatively easy to process. The properties of these materials depend not only on their composition, but also on their structure on the scale of millionths to thousandths of a millimeter, or in other words, on their microstructure.

These microstructures form spontaneously during the production process through a phenomenon known as self-assembly. The exact workings of self-assembly and how precisely the production settings influence self-assembly is generally poorly understood. This makes the rational design of such materials challenging and often more art than science.

Theoretical models

For his PhD thesis, developed theoretical models to investigate and understand various aspects of self-assembly in different types of soft materials. Although the materials studied were very different, De Bruijn could still make use of similar descriptions that were based on the strong agreements in the behavior of the large collections of particles that these materials consist of.

First, he examined how the production methods used for carbon-based materials affected their microscopic structure. These materials were fabricated from a solution wherein the active components were dissolved. The solution was then deposited on a stationary or moving surface, after which the solvent evaporated out of the solution. The active components crystallised or demixed during the evaporation of the solvent.  The microstructure that formed persisted in the dry, solid thin film and greatly affected the properties of the material.

Solvent evaporation

De Bruijn鈥檚 research focused on modelling and understanding how solvent evaporation influences the demixing and crystallisation processes, and how the deposition of the solution on a moving surface influences the demixed structure.

His findings demonstrated that the speed with which the surface moves and the rate at which the solvent evaporated have a large influence on the shape and size of the emergent structures, which can be repeating or non-repeating, dependent on the deposition conditions.

Conductive material

Second, De Bruijn studied how the addition of a small amount of (electrically) conductive material to a non-conductive material can make the whole material conductive. He focused on how just a small amount of conductive material is required to achieve this.

Such an approach is relevant for the fabrication of conductive plastics, that are not only light but also transparent. He focused on the case where the conductive material is not randomly dispersed throughout the non-conductive material but confined to a smaller part of it.  It turns out that the structure of the space in which the conductive material was confined has a large influence on the amount of material required to produce a conductive material.

Control

Lastly, De Bruijn investigated how one may exert control over the binding of specially designed proteins to DNA, with the goal to encapsulate the DNA in a protective coat for gene therapy.

Inspired by recent experiments, he developed a model that shows that the process can be made more efficient by using other specialized proteins that are pre-attached at specific positions on the DNA and assist in the encapsulation process.

Using his model, De Bruijn and his collaborators not only explain the experimental findings but also provide new predictions for optimizing the encapsulation process.

Title of PhD thesis: . Supervisors: Paul van der Schoot, Jasper Michels (External), and Anton Darhuber.