2 research outputs found
Hollow Block Copolymer Nanoparticles through a Spontaneous One-step Structural Reorganization
The spontaneous one-step synthesis of hollow nanocages and nanotubes from spherical and cylindrical micelles based on poly(acrylic acid)-<i>b</i>-polylactide (P(AA)-<i>b</i>-P(LA)) block copolymers (BCPs) has been achieved. This structural reorganization, which occurs simply upon drying of the samples, was elucidated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). We show that it was necessary to use stain-free imaging to examine these nanoscale assemblies, as the hollow nature of the particles was obscured by application of a heavy metal stain. Additionally, the internal topology of the P(AA)-<i>b</i>-P(LA) particles could be tuned by manipulating the drying conditions to give solid or compartmentalized structures. Upon resuspension, these reorganized nanoparticles retain their hollow structure and display significantly enhanced loading of a hydrophobic dye compared to the original solid cylinders
Structural Characterization of Amphiphilic Homopolymer Micelles Using Light Scattering, SANS, and Cryo-TEM
We
report the aqueous solution self-assembly of a series of polyÂ(<i>N</i>-isopropylacrylamide) (PNIPAM) polymers end-functionalized
with a hydrophobic sulfur–carbon–sulfur (SCS) pincer
ligand. Although the hydrophobic ligand accounted for <5 wt % of
the overall homopolymer mass, the polymers self-assembled into well-defined
spherical micelles in aqueous solution, and these micelles are potential
precursors to solution-assembled nanoreactors for small molecule catalysis
applications. The micelle structural details were investigated using
light scattering, cryogenic transmission electron microscopy (cryo-TEM),
and small angle neutron scattering (SANS). Radial density profiles
extracted from the cryo-TEM micrographs suggested that the PNIPAM
chains formed a diffuse corona with a radially decreasing corona density
profile and provided valuable <i>a priori</i> information
about the micelle structure for SANS data modeling. SANS analysis
indicated a similar profile in which the corona surrounded a small
hydrophobic core containing the pincer ligand. The similarity between
the SANS and cryo-TEM results demonstrated that detailed information
about the micelle density profile can be obtained directly from cryo-TEM
and highlighted the complementary use of scattering and cryo-TEM in
the structural characterization of solution assemblies, such as the
SCS pincer-functionalized homopolymers described here