Photomechnical Materials
The
mechanical properties (such as length, shape, and stiffness) of a
photomechanical material change when exposed to light. A key feature of
such materials that would make them suitable for futuresque
applications such as ultra-smart morphing materials is the fact that
various parts of the material can communicate with other parts of the
material using light. Additionally, each part of the material acts as a
sensor and can change shape. These proprieties taken together can be
used to make a highly-intelligent neural network that has the ability
to change its physical form based on sensory data.
Potential Technological Applications
Photomechanical
materials are far from being a technology. Present research seeks to
set the scientific foundations for making a novel new material that has
the ability to morph in response to stress or light. In
contrast to common materials that are made of atoms or molecules, and
interact through electric fields, Kuzyk[1] has envisioned a system made
of microscopic units that each communicate with all others using light,
imbuing the system with enormous processing power and
intelligence. Add to each unit the ability to respond to stress
and perform actuation, and the system gains the ability to
intelligently morph into complex structures.
Such a material would fill a new realm of
applications. Just as a series of pictures on a piece of film can
be projected onto a screen to show motion on a two-dimensional plane,
the highly interconnected smart material could be made to go through a
series of shapes leading to true 3-dimensional animations of a solid
material. One that could be touched.
For example,
automobile designers could use such materials to continually change the
shape of a model to test its aerodynamics or aesthetics; a chair could
be made to automatically change shape to accommodate any body type; and
an exact replica of an individual could be made from information sent
from a distance. Having your Uncle Joe's three-dimensional
solid-body facsimile sitting next to you in casual conversation would
be far more advanced than picture phones, which transmit only
two-dimensional images. Other applications would include noise
cancellation wallpaper, reconfigurable air craft wings, ultra-stable
platforms for precision manufacturing or characterization, and
reconfigurable optical filters.
[1] M. G. Kuzyk, Polymer Fiber Optics: Materials, Physics, and Applications, CRC Press, Taylor & Francis Group, Boca Raton (2007). |
Materials Challenges
Since
the end materials are far from reality, present work seeks to take the
initial steps by setting a series of milestones that would demonstrate
the feasibility of this totally new material concept. The
approach taken by researchers is hierarchical in nature, which begins
with a demonstration of the fundamental building blocks, followed by
studies of how a small number of the building blocks interact with each
other when interconnected with light. The goal of such studies studies
culminates with the development of fabrication methods that can be used
to make a bulk material from a collection of microscopic building
blocks.
The fundamental physics underlying these
materials and technologies is, for the most part, in place; that is,
photomechanical materials exist, interferometers with photomechanical
materials can be built into polymer fibers, and a series of gratings
can be written into a fiber to make a network of interacting
units. The challenge lies in understanding how to build a system
from optimized units that works together to provide the desired
function.
The fundamental building block is a polymer
fiber-optic interferometer containing a nonlinear-optical and
photomechanical material -- thus simultaneously having the ability to
manipulate light, sense stress, and apply anisotropic stress to its
surroundings. Such devices have been dubbed Photomechanical Optical Devices
(POD). A POD simultaneously responds optically and mechanically
to yield mechanical/optical multistability, logic, stress/temperature
sensing, optical/mechanical memory, positioning, and more – all of
which have been separately demonstrated.
Smart Threads
A
network of PODs, interconnected by light signals along a fiber, would
in principle form the thread of an ultra-smart material with
functionality that goes well beyond present materials paradigms.
In contrast to a neural network, in which each neuron is connected to a
small number of neighbors, a linear array of PODS along an optical
fiber would interact with all others, processing information, reacting
to stress and responding by selectively passing light and stressing the
surroundings.
The tutorial that follows traces the
hisotry of photomechnical effects, describes recent advances in
photomehcnical materials, and reviews technological demonstrations that
show the feasibility of this interesting new field. |