Usually you cannot control the spatial location of the components of a solution: When we pour a glass of orange juice, we cannot arrange for all the pulp to collect in in the bottom left of the glass. And it becomes even more hopeless to separate the pulp from a mixture of orange and grapefruit juice on opposite sides of the glass.
However, a team at DTU Energy will do the seemingly impossible. Their aim is to develop methods to identify, capture and sort different components of a solution using light and sound, and then lock the components in a 3D polymer structure using a 3D printer. The ultimate object is to create composite materials whose properties are defined while printing.
"If we are able to sort and direct materials in a solution, it opens up new possibilities within a lot of areas, including energy materials, integrated optics and more futuristic ideas like remote-controlled robots for surgery," says senior researcher at DTU Energy Roar R. Søndergaard, leader of the DTU-team.
3D printed electrical components
3D printing technology has come a long way since 3D printers were big, expensive and very complicated machines, but most 3D printing is still basically plastics in different forms. Now Roar and his colleague Thue Trofod wants to make the 3D componentss with completely novel properties.
"Our success criteria is to be able to build a 3D structure where we have two different components that we can place and lock in a 3D structure, exactly at the places we want"
Roar R. Søndergaard, senior researcher at DTU Energy
"Our goal is to add a variety of properties to the 3D components. One example could be making some parts of the component electrically conductive, and in this way make 3D printed electronic circuits.”
A common type of 3D printer works by filament extrusion, where a roll of plastic material in the form of a thin plastic wire is heated and in liquid form applied in thin layers, typically with a thickness of 0.1 mm. The new research project "In situ solution synthesis and 3D structuring of multi-property nanocomposites", funded by the Villum Foundation, uses stereolithography instead. Here the materials are mixed in a ‘soup’ that is then illuminated by UV light in particular patterns after which the material solidifies in the chosen pattern. This creates 3D prints that are both more detailed and half as thin.
"We want to make it possible to make much smaller details compared to the current technology. Normally the thickness of the extruded plastic wire defines and controls the degree of detail. We want to assemble all the components into one single fluid so that all the building blocks are mixed, and then use laser tweezers to control the structure of the composite in great detail," explains Roar R. Søndergaard.
However, this requires that you can identify, capture and sort different types of materials contained in the same fluid. This is as challenging as separating orange and grapefruit pulp. The DTU researchers will be using light and sound to capture, sort and concentrate various mixtures in the fluid.
"We will be able to create traps in the fluid by means of sound waves, hindering particles from escaping the trap. This allows us to collect one kind of particles in one corner and another type of particles in the other. You could think of it as picking up a particle of orange or grapefruit pulp individually. Our goal is to guide materials with certain types of functionality to wherever we want, giving the entire structure a function."
100% control of the soup is needed
The printing itself is done by means of stereolithography in a converted 3D printer, where the fluid containing the mixture of materials is contained in a special box with a glass surface at the bottom. UV light is then focused through the bottom at the liquid soup, creating the wanted patterns and causing the liquid soup to harden just above the glass, making layers of material with a thickness of 50 μm (1 μm = 1 millionth of a meter).
"And we have to be quick getting the materials back and forth in the fluid, as each layer takes less than a second to make," says researcher Thue Trofod.
This requires the DTU-researchers to have complete control of the individual types of materials and where they are in the ‘soup’, to be able to sort the materials and at the same time be sure that the individual materials do not mix when they are moved back and forth to be printed. Normal flow is totally suspended in the fluid.
"We need total control over everything in the soup, and this makes it a rather ambitious project. We’ll probably not be able to reach the final goal in a year and a half, but we will prove that one can move the materials around in the ‘soup’ and in this way be able to build with them," says Roar R. Søndergaard.
The ultimate goal is to enable 3D printing of materials with features defined in situ, making a functional device in a single print. As a first step, the DTU researchers expect to be able to print a simple structure with different types of functional material embedded in it.
"Our success criteria is to be able to build a 3D structure where we have two different components that we can place and lock in a 3D structure, exactly at the places we want," says Roar R. Søndergaard.