8 research outputs found
Effect of Concentration on the Dissolution of One-Dimensional Polymer Crystals:A TEM and NMR Study
We report a study of the dissolution
of core-crystalline polyferrocenylÂdimethylsilane-<i>block</i>-polyisoprene (PFS<sub>53</sub>-<i>b</i>-PI<sub>637</sub>, where the subscripts are the degrees of polymerization
of the two blocks) micelle fragments in decane for different concentrations
(ranging from 0.01 to 6 mg mL<sup>–1</sup>) by a combination
of transmission electron microscopy (TEM) and high-temperature <sup>1</sup>H NMR. We used self-seeding experiments at different temperatures
as an efficient, although indirect, way to evaluate the dissolution
of these micelles fragments. We annealed micelle fragment solutions
at five different temperatures (50, 60, 65, 70, and 75 °C) for
30 min and cooled them to room temperature to regrow the micelles.
The amount of micelle fragments that dissolved at the annealing temperature
was then evaluated by comparing the length of the regrown micelles
with that of the starting micelle fragments. We show that seed crystallites
are less prone to dissolution as their concentration increases. In
addition, by combining results of self-seeding experiments and <sup>1</sup>H NMR measurements at 75 °C, we evaluated the percentage
of unimer released upon the partial dissolution of seed fragments
at 75 °C and established that the mechanism of seed fragment
dissolution is also concentration dependent: at low concentrations,
they dissolve in a cooperative process, whereas at high concentrations,
they dissolve partially from both ends
Hierarchical Polymer–Carbon Nanotube Hybrid Mesostructures by Crystallization-Driven Self-Assembly
Multistep crystallization-driven self-assembly has great potential to enable the construction of sophisticated hybrid mesostructures. During the assembly procedure, each step modifies the properties of the overall structure. Here, we demonstrate the flexibility and efficiency of this approach by preparing polymer–carbon nanotube (CNT) hybrid mesostructures. We started by growing polyferrocenyldimethylsilane (PFS) homopolymer crystals onto multiwalled CNTs. This first step facilitated the redispersion of the coated CNTs in both polar (2-propanol) and nonpolar (decane) solvents. In the second step of hybrid construction, a unimer solution of a PFS block copolymer was added into the PFS-CNT solution. The PFS coating on the CNT initiated the growth of elongated micelles, resulting in structures that resembled hairy caterpillars. PFS-<i>b</i>-P2VP (P2VP = poly-2-vinylpyridine) micelles were grown from the surface of PFS-CNT hybrids in 2-propanol, and PFS-<i>b</i>-PI (PI = polyisoprene) micelles were grown from these hybrids in decane. These micelles, by transmission electron microscopy were seen to have an unusual wavy kinked structure, very different from the uniform smooth structures normally formed by both block copolymers. For hybrids with PFS-<i>b</i>-PI micelles, cross-linking of the micelle coronas locked the whole structure in place and allowed us to use the partial oxidation of PFS components to grow metal nanoparticles in the core of these micelles. We finally investigated the influence of the corona-forming block used to grow the micelles on the wettability of films made from these mesostructures. Films formed with CNT hybrids grafted with PFS-<i>b</i>-PI micelles were superhydrophobic (contact angle, 152°). In contrast, the surface of the films was much more hydrophilic (contact angle, 54°) when they were prepared from CNT hybrids grafted with PFS<i>-<i>b</i>-</i>P2VP micelles
Hierarchical Polymer–Carbon Nanotube Hybrid Mesostructures by Crystallization-Driven Self-Assembly
Lateral Growth of 1D Core-Crystalline Micelles upon Annealing in Solution
The emergence of one-dimensional
(1D) micelles obtained from the
crystallization driven self-assembly (CDSA) in solution of crystalline-coil
block copolymers has opened the door to the fabrication of a variety
of sophisticated structures. While the development of these fascinating
nanomaterials is blossoming, there is very little fundamental work
dedicated to understanding the morphological evolution of these 1D
micelles in solution. Here, using a combination of transmission electron
microscopy, electron tomography, and static and dynamic light scattering,
we studied the effect of annealing on a colloidal suspension of 1D
micelle fragments formed by the self-assembly of a crystalline-coil
polyÂ(ferrocenyldimethylsilane)-<i>block</i>-polyÂ(isoprene)
(PFS-<i>b</i>-PI) block copolymer in decane, a solvent selective
for PI. We are particularly interested in studying the evolution of
the rectangular cross-section of the crystalline core of these micelle
fragments. By electron tomography, we observed that the shorter dimension
of the cross-section became even thinner upon annealing at elevated
temperatures, while the longer dimension increased. In parallel, we
observed an increase in packing density of the crystalline block as
the fragments were annealed at temperatures above 60 °C. From
these results, we concluded that annealing the micelle fragments induces
a thinning of the crystalline core coupled with a lateral growth
Selective structural transformation of supramolecules to multinuclear heterosubstituted Pt complexes via ligand exchange
Organometallic–Polypeptide Diblock Copolymers: Synthesis by Diels–Alder Coupling and Crystallization-Driven Self-Assembly to Uniform Truncated Elliptical Lamellae
This
paper reports a new synthetic strategy for the preparation
of polyferrocenylsilane (PFS) block copolymers (BCPs), by conjugation
of two independently prepared homopolymers using Diels–Alder
cycloaddition. The PFS blocks were synthesized by photocontrolled
ring-opening polymerization, yielding polymers with a cyclopentadienyl
end group that serves as a diene in the conjugation reaction. In this
initial study we focused on the synthesis of organometallic–polypeptide
block copolymers PFS-<i>b</i>-PBLG (PBLG = polyÂ(Îł-benzyl-l-glutamate) using PBLG polymers with a terminal maleimide attached
by one-step postpolymerization modification. Five PFS-<i>b</i>-PBLG copolymers with different degrees of polymerization were synthesized
and purified by a series of selective precipitations. The self-assembly
of these samples was studied in <i><i>N,N</i></i>-dimethylformamide, a solvent selective for PBLG. The BCPs with a
PFS block longer than the PBLG block after annealing at 90 °C
formed highly uniform platelet micelles with a truncated elliptical
shape. Experiments at 75 °C showed that disordered elongated
structures formed initially, with fiber-like protrusions from the
ends. Over time, the structures became shorter and wider, evolving
into uniform truncated elliptical micelles. The process was monitored
by X-ray diffraction (XRD) measurements and by <sup>1</sup>H NMR spectroscopy.
AFM analysis showed that the micelles were flat and that their thickness
increased with the overall chain length of the BCP. Self-assembly
of these BCPs in the presence of PFS homopolymer led to formation
of flower-like mesostructures consisting of stacks of lamellar petals