CAREER: High-speed 3D Imaging of Colloidal Self-Assembly with Digital Holographic Microscopy

Harvard University, Cambridge MA

Investigators

Abstract

0747625 Manoharan The primary goal of the PI's proposed research is to investigate how colloidal particles self-assemble in confined and nonequilibrium systems, including particles trapped at liquid-liquid interfaces (e.g. emulsion droplets) and inside spherical containers. Although common in industrial formulations and fundamental condensed matter studies, these systems remain poorly understood, primarily because no existing experimental probes, including confocal microscopy, can yield real-space data with sufficiently fast acquisition times to resolve 3D dynamics. The PI proposes to use a powerful interferometric technique, Digital Holographic Microscopy (DHM), in concert with particle synthesis and algorithm development to overcome these limitations. Preliminary data show that the technique is capable of tracking several micrometer-sized colloidal particles with 30 nm spatial precision in all three dimensions on millisecond time scales. DHM may be able to yield the most complete physical picture to date of dynamics, interactions, and assembly in colloidal suspensions. Intellectual Merit The proposed research seeks to answer fundamental questions in colloid science by pursuing the following objectives: 1. Development and optimization of a Digital Holographic Microscope to investigate colloidal suspensions: A prototype of this instrument has been constructed and preliminary data are shown. The PI will develop new algorithms, data acquisition techniques, and instrumentation to make the technique as rapid and robust as possible. 2. Use of this instrument in the following experimental studies: ? Measuring the dynamics of particles trapped at planar liquid-liquid interfaces: determining the interactions governing the assembly of interfacially-bound particles. ? Measuring the dynamics and structure of particles trapped at spherical liquid-liquid interfaces: investigating the self-assembled structures of particles confined to an emulsion interface. ? Imaging self-assembly in dense colloids confined inside an interface: Determining the effect of a spherical droplet boundary on the structure and assembly of colloidal crystallites. Broader Impacts This work will benefit industrial product development by providing a rational framework for the formulation of multiphase colloidal systems. It will also yield insights into structure formation in complex fluids that may be useful in nanofabrication. In addition, an integrated education and outreach program will target 8th grade science students in the Cambridge school district, a diverse and urban school system with a majority of students from underrepresented minority groups and low-income households. Goals of the program are: 1. Developing a design module to engage at-risk 8th grade science students: The PI will work closely with a teacher from the Kennedy-Longfellow middle school to develop, implement, and assess an inquiry-based learning program that (a) meets Massachusetts standards for teaching physics and engineering in 8th grade and (b) targets all skill groups, including Special Education students. Harvard undergraduate volunteers from the new School of Engineering and Applied Sciences will be recruited as mentors and facilitators. The broader aim is to educate and engage more middle school students through mentorship, research, and open-ended design projects. 2. Undergraduate education through research and mentoring; graduate course development