TOWARDS SELF-ASSEMBLYING ACTIVE MICRO-STRUCTURES

Columbia University, New York NY

Investigators

Abstract

NONTECHNICAL SUMMARY The Division of Materials Research and the Division of Chemistry contribute funds to this award. It supports theoretical research and education focused on self-assembly of active nanoparticles into functional structures. Active matter is an exciting field in soft condensed matter and materials science that has come into prominence over the last decade. The synthesis of colloidal particles that can self-propel in solution at speeds of tens of microns per second played an important role in the emergence of this field. The propulsion mechanism is obtained by conversion of chemical or, more generally, environmental energy, into directed motion of the particles. The interplay between active and thermal forces in these systems gives rise to a remarkable collective behavior that is reminiscent of phenomena observed in living systems such as in schooling of fish, flocking of birds, or swarming of bacteria. One of the most appealing features of these nanoparticles is that, unlike biological entities, they can be synthesized into arbitrarily complex shapes and with a wide range of inter-particle interactions. Furthermore, their active behavior can be triggered and tuned with an external light source. The goal of this project is to use a combination of theory and computer simulations to understand how these propelling forces can be used to enhance the spontaneous formation of particles into organized structures, a process known as self-assembly. The PI aims to find ways to greatly speed up this otherwise lengthy process, and to uncover new strategies to design materials that not only have targeted static properties, but that can also perform work at the micro-scale. This project is aimed to significantly advance the field of nanoparticle self-assembly and materials engineering by suggesting new pathways of structure formation, with applications in manufacturing of stimuli-responsive materials and nano-medicine. The project has also a strong educational component, which includes training of graduate and undergraduate students, collaboration with on-campus organizations dedicated to the advancement of women and underrepresented minorities in science, and development of educational software for mobile platforms. TECHNICAL SUMMARY The Division of Materials Research and the Division of Chemistry contribute funds to this award. It supports theoretical research and education with the aim of understanding and controlling self-assembly of active nanoparticles. What makes active systems very exciting is that they are intrinsically out of equilibrium at the single particle level, thus generating a much more complex collective behavior than is possible in equilibrium systems. The research team plans to use theory and numerical simulations to develop rational design strategies to engineer functional aggregates of active particles. This will be achieved by studying the key role played by particle anisotropy, hydrodynamic interactions, and fluctuating activating fields in the self-assembly dynamics of active nanoparticles. Understanding how the geometry of the particles, the directionality of their interactions, and how the strength of the active forces can be exploited to optimize and impart functionality to self-assembled structures is one of the most important challenges in the field. The team will also analyze how active nanoparticles and the materials they form respond to propelling forces that can fluctuate over space and time. This field in active matter holds promise for potential applications that range from switchable materials to the development of microscopic actuators. The ultimate goal of this research is to be able to understand how to manipulate all these parameters to directly intervene in and dynamically affect the pathway of structure formation. This research may have an important impact in materials science and engineering as it could lead to the development of better strategies for a bottom-up approach to active structure design. The fundamental questions addressed in this project will also have important implications for biological systems that rely on similar physical mechanisms, and in nano-medicine. This award contributes to the education of undergraduate and graduate students. The research group will participate in outreach activities sponsored by on-campus organizations dedicated to the advancement of women and underrepresented minorities in science, and will develop educational software for hand-held devices to highlight the results of the research.