PubMed Health⌕ Search

Biomedical subjects

S D Hudson

Publications and source records attributed to S D Hudson.

5 recordsLinked to original sources

Self-organization of supramolecular helical dendrimers into complex electronic materials.

The discovery of electrically conducting organic crystals and polymers has widened the range of potential optoelectronic materials, provided these exhibit sufficiently high charge carrier mobilities and are easy to make and process. Organic single crystals have high charge carrier mobilities but are usually impractical, whereas polymers have good processability but low mobilities. Liquid crystals exhibit mobilities approaching those of single crystals and are suitable for applications, but demanding fabrication and processing methods limit their use. Here we show that the self-assembly of fluorinated tapered dendrons can drive the formation of supramolecular liquid crystals with promising optoelectronic properties from a wide range of organic materials. We find that attaching conducting organic donor or acceptor groups to the apex of the dendrons leads to supramolecular nanometre-scale columns that contain in their cores pi-stacks of donors, acceptors or donor-acceptor complexes exhibiting high charge carrier mobilities. When we use functionalized dendrons and amorphous polymers carrying compatible side groups, these co-assemble so that the polymer is incorporated in the centre of the columns through donor-acceptor interactions and exhibits enhanced charge carrier mobilities. We anticipate that this simple and versatile strategy for producing conductive pi-stacks of aromatic groups, surrounded by helical dendrons, will lead to a new class of supramolecular materials suitable for electronic and optoelectronic applications.

Journal Article↗

Definitive support by transmission electron microscopy, electron diffraction, and electron density maps for the formation of a BCC lattice from poly[N-[3,4,5-tris(n-dodecan-1-yloxy)benzoyl]ethyleneimine].

Transmission electron microscopy (TEM), electron diffraction (ED), and electron density maps (EDM) experiments were carried out on a poly[N-[3,4,5-tris(n-dodecan-1-yloxy)benzoyl]ethyleneimine] [poly[(3,4,5)12G1-Oxz]] with a degree of polymerization (DP) of 20. All experiments confirmed the thermotropic body-centered cubic (BCC) Im3m lattice suggested previously by X-ray diffraction (XRD) experiments. The unit cell parameter determined by ED at 23 degrees C is a = 42.4 A, in good agreement with XRD results which show a = 42.6 A after quenching from 70 degrees C. EDM of the XRD results confirm that the supramolecular minidendrimer obtained from poly[(3,4,5)12G1-Oxz] adopts a spherical "inverse micellar-like" structure, with the polyethyleneimine backbone and the aromatic groups microsegregated and concentrated in the corners and in the center of the cubic unit cell. A space-filling continuum is realized by the n-alkyl groups that radiate out of the aromatic core of the spherical dendrimer. This manuscript is only the second example of complete structural analysis of a lattice generated from supramolecular objects and complements the previous example reported from our laboratory on the Pm3n lattice.

Journal Article↗

Droplet growth by coalescence in binary fluid mixtures.

The evolution of the drop-size distribution in immiscible fluid mixtures following well-specified shear histories is investigated by in situ microscopy, allowing determination of the shear-induced coalescence efficiency epsilon. At small capillary number Ca, epsilon is constant, whereas at larger values of Ca, epsilon decreases, in agreement with theory accounting for slight deformation of the drops in close approach. Coalescence causes the drop-size distribution to broaden in general, but greater deformation of the larger drops at high shear rates causes the drop-size distribution to remain narrow.

Journal Article↗

Poly(oxazolines)s with tapered minidendritic side groups. The simplest cylindrical models to investigate the formation of two-dimensional and three-dimensional order by direct visualization.

The synthesis of 2-[3,4-bis(n-alkan-1-yloxy)phenyl]-2-oxazolines with alkan = octan, decan, dodecan, and tridecan is presented. Their living cationic ring opening polymerization produces cylindrical macromolecules that self-organize in a hexagonal columnar two-dimensional phase. The structural analysis of these polymers was carried out by a combination of techniques including differential scanning calorimetry, thermal optical polarized microscopy, X-ray diffraction, transmission electron microscopy, electron diffraction, scanning force microscopy, and atomic force microscopy (AFM). The diameter of these cylindrical macromolecules ranges from 33 to 44 A, and therefore they represent the simplest cylindrical macromolecules that can be directly visualized by AFM on a surface. Preliminary experiments have demonstrated the use of these cylindrical macromolecules as models to investigate the creation of two-dimensional and three-dimensional order via direct visualization and thus they represent the simplest nonbiological systems that mimic the role played by the complexes of nucleic acids with proteins in structural analysis by direct visualization.

Calorimetry, Differential Scanning↗