Advanced Colloids Experiment-Heated-2 (ACE-H-2)

Small particles suspended in a mixture, known as colloids, can combine to form complex structures and be used in new advanced materials. Colloids are found in a wide range of foods and consumer products, but they can also include particles with unique surface chemistry or electrostatic properties that allow them bind to each other in various ways. The Advanced Colloids Experiment-H-2 (ACE-H-2) investigation studies a technique called nanoparticle haloing, which stabilizes colloidal mixtures and may be important for designing advanced materials for use in medicine, imaging and other fields.

The experiment has concluded, and science is being evaluated.

New functional materials can, in principle, be created using microscopic particles (called colloids) that self-assemble into a desired structure by means of a recognition and binding scheme. The Advanced Colloids Experiment-Heated-2 (ACE-H-2) experiments utilize optical microscopy for time- and space-resolved imaging of spherical colloids of various sizes and concentrations. Colloidal assembly and the structure’s stability can be controlled by mediating the particles’ electrostatic charge and surface chemistry. The introduction of smaller particles allows the tuning of the interactions between the larger colloids, and in this way control the structure of the colloidal dispersion. The particle surface interactions are reversible and sensitive to temperature.

Ultimately, the ability to design colloidal particles with a variety of well-controlled three-dimensional bonding symmetries opens a wide spectrum of new structures for colloidal self-assembly - beyond particle assemblies whose structures are defined primarily by repulsive interactions and shape. Such materials might include photonic crystals with programmed distributions of defects. Optical technology utilizing such materials may offer intriguing solutions to unavoidable heat generation and bandwidth limitations facing the computer industry.

To remain stable, colloids require a balance between attraction and repulsion. One method for stabilizing these mixtures is known as nanoparticle haloing, in which charged nanoparticles are mixed with larger colloidal particles. The nanoparticles self-organize and form a halo-like structure around the colloids. ACE-H-2 uses the microgravity environment of the International Space Station to study how changing the concentration of colloidal particles affects the haloing interaction. On Earth, gravity would cause the particles to sink and clump together, interfering with the observations. Results benefit research using colloids to build self-assembling structures.

Results from the ACE-H-2 investigation provide new insight that would be difficult or impossible to obtain on Earth, where gravity interferes with particle interactions. Understanding the fundamental physics of colloid interactions benefits materials science research on Earth, including research on self-assembling technologies.

Space Station Research Explorer