ABSTRACT
The confinement of materials at the nanoscale and the resulting alterations of their properties and
chemistry have been and continue to be a subject of considerable excitement and interest in numerous
science and technology sectors [1]. Recent results have shown dramatic effects in this regard including
profound changes in kinetics and reaction products of organic molecules in porous media [2], altered
structures and enhanced melting points of proteins and other macromolecules [3], new types of fluid
dynamics [4], modified fluorescence lifetimes [5], and the modification of the structure of liquid water
[6]. For many macromolecules, in particular polymers, three-dimensional confinement at a nanometer-
size scale is often comparable to a polymer’s radius of gyration and is of special interest in the context of
the so-called collapse transitions associated with semiconducting polymers and how the confinement
affects intra-and interchain organization. For a mixed polymer systems, there is the interesting question
of spinodal decomposition (sudden phase segregation) of such systems under three-dimensional
confinement, and the possibility of deeply quenched single-phase (homogeneous) polymer-blend
particles or polymer alloys [7] with specially tailored electronic [8,9], optical [10], or mechanical
properties [11-13]. However, commonly used techniques capable of producing these types of structures
such as thin-film or self-assembly processes can suffer from substrate interactions, which may dominate
or obscure the underlying polymer physics. In order to minimize these complexities we have recently
explored ink-jet printing methods for producing polymer particles with arbitrary size and composition.
This method is based on using droplet-on-demand generation to create a small drop consisting of a very
dilute polymer mixture in a solvent [14,15]. As the solvent evaporates, a polymer particle is produced
whose size is defined by the initial size of the droplet (typically between 5 and 30 mm), and the weight
fraction of polymer (or other nonvolatile species) in solution. Because the droplets are produced with
small excess charge during ejection from the nozzle, this approach lends itself naturally to spatial
manipulation of micro-and nanoparticles using electrodynamic focusing techniques [16]. Polymeric
particles in the micrometer-and nanometer-size range provide many unique properties due to size
reduction to the point where critical length scales of physical phenomena become comparable to or larger
than the size of the structure. Applications of these types of particles take advantage of high surface area
and confinement effects, leading to interesting nanostructures with different properties that cannot be
produced by using conventional methods. Clearly, there is an extraordinary potential for developing new
materials in the form of bulk, composites, and blends that can be used for coatings, optoelectronic
components, magnetic media, ceramics and special metals, micro-or nanomanufacturing, and
bioengineering. The key to beneficially exploiting these interesting materials is a detailed understanding
of the connection of nanoparticle technology to atomic and molecular origins of the process.
