Whitesides Research

Whitesides Group Research

Materials and Programmable Matter

Overview

This project integrates experiment and theory to develop strategies toward “programmable matter”. Programmable matter comprises systems of “components” that self-assemble into functional structures; these systems have the unique characteristic that their properties can be programmed to direct the same set of components toward different structures and functions, on demand. The objective of the work is to carry out parallel, cooperating programs in experiment and theory to survey seven strategies for programmable matter, and determine which is most appropriate for the subsequent objectives. We will demonstrate principles by designing and fabricating programmable matter that will form—on demand—all members of a set of regular geometrical shapes (cube, sphere, prism, cylinder), with strength for the ensemble equivalent to that of a structural polymer. These seven strategies are represented in the Figure 1.

Thermally reversible objects molded in thermally reversible molds

The concept of using a geometrical template to fix the form of an object is at the lowest level of sophistication in the project. It also has the greatest potential for immediate utility, if it can be used with new materials. Our work examines meso-Tm alloys (200º – 300ºC) with carbon fiber and/or SiC fillers, to determine if they have sufficient toughness to be used as simple tools e.g., a wrench).

The approach has the potential to minimize the weight carried by missions – a single set of tools can be replicated in the field, used as needed and then recycled. Both the material used in the molds and replicated objects themselves are thermally reversible: this method is good for materials with similar Tm (Figure 2). The novelty in the approach comes from the use of a low-melting metal matrix reinforced with ceramics or fibers.

Minimization of interfacial free energy in liquids

The use of templating and interfacial free energy is a versatile method of making 3D solid shapes of a complexity that would be extremely difficult to imagine making by any other procedure (Figure 3). Our demonstrations have been simple, but convincing as a demonstration of principle. They have, however, been carried out using polymers that have no particular utility (outside, perhaps, in optics for difficult-to-form optical elements). Understanding this kind of system from the vantage of mathematical topology will guide experimental work that will be carried out in practically useful materials.

Guided Self-Assembly.

There are a number of approaches to guided self-assembly. We propose initially to fabricate identically shaped slabs containing magnets that can be oriented independently, and to explore magnetically directed self-assembly. Depending on the orientation of the magnets inside these slabs, upon agitation, different structures are formed.

Self assembly of magnetically interacting cubes by a turbulent fluid flow

Previous work has demonstrated that combining mechanical vibration with magnetic interactions can result in the self assembly of complex structures, albeit at low yield. Our current work introduces a system where the yield of self assembled structures is quantitatively predicted by a theoretical analysis. Millimeter sized magnetic blocks (Figure 5) are designed to form chains as their minimal energy state are placed in a turbulent fluid flow. The distribution of chain lengths that form is quantitatively consistent with predictions, showing that the chain length distribution coincides with that of monomers/polymers in a thermal bath, with the turbulence strength parameterizing the effective temperature (Figure 6).

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