Current research areas

Ron Alexander

Graduate Student

Ron is a graduate student working on holographic microscopy.

McKay 530, 9 Oxford St
Cambridge, MA 02138
p: (617) 495-9894

Braided nanowires

Getting spherical colloidal particles to self-assemble is hard enough, but we decided to try something even more difficult: getting nanowires to self-assemble. The goal of this project is to get long, thin nanowires to spontaneously braid themselves.

Virus physics

Viruses are ubiquitous: for every organism, there are multiple viruses that can infect it. Although we know much about the beautiful structures of viruses, and we understand how certain viruses (the ones that are bad for us) infect a cell, we know little about the dynamics of these organisms. We want to understand the life cycle of viruses from a physical point of view. We are particularly interested in understanding how they self-assemble.   Read more about Virus physics

Structural color

To make a material that is colored, one normally uses a dye or pigment. But another way to make color is to make a nanostructure that reflects or scatters light so that waves of certain frequencies can constructively interfere. These nanostructured materials are said to have structural color. Unlike traditional color, which comes from dyes or pigments that absorb light, structural color can be made resistant to fading. We use colloidal self-assembly to make nanostructures that have a variety of different colors. At the same time, we aim to understand the physics of the scattering process so that we can optimize these nanostructures for applications.  Read more about Structural color

Optical metamaterials

We are interested in making materials that have a negative index of refraction. No naturally occurring material that we know of has this property, but it could be achieved in an metamaterial . An optical metamaterial is composed of elements that are smaller than the wavelength of light, but that can interact with light in interesting ways. We are developing ways to make optical metamaterials through self-assembly. Read more about Optical metamaterials

Colloids and interfaces

Using digital holographic microscopy, we study how colloidal particles bind to oil-water interfaces. Small particles have a natural affinity for interfaces, and this affinity can be used to control their self-assembly and make some interesting materials. However, the dynamics of the particles before and after they breach the interface are not well-understood. We do experiments to observe these dynamics and find some surprising results. Read more about Colloids and interfaces

Holographic microscopy

We use a fast imaging method called holographic microscopy to watch self-assembling systems. In a holographic microscope, the sample is illuminated by laser light, and the resulting image (or hologram) can be used to determine the 3D structure, position, and orientation of a microscopic sample. We build new holographic microscopes and develop software to analyze the holograms. Read more about Holographic microscopy

Colloidal clusters

We do experiments on some of the simplest self-assembling systems, called "colloidal clusters," to understand  the basic physics of self-assembly. The clusters consists of a small number (say, fewer than 10 or so) spherical colloidal particles that attract one another. What shapes do they form and why?  By answering these questions, we gain insights into how to design particles that can self-assemble into exactly the structures we want.

Read more about Colloidal clusters

DNA and colloids

Short, custom-designed DNA molecules can be used to create "programmable" interactions between colloidal particles, meaning that we can control how the particles self-assemble through the DNA sequences. Currently we are trying to create colloids with programmable dynamic behavior. Using DNA, we make colloidal "motors" that move in a directed (non-random) way and colloidal suspensions that organize into patterns that change with time. Read more about DNA and colloids