Changmo Sung

Morphological study of electrospun polycarbonates as a function of the solvent and processing voltage

Unlike conventional spin methods, electrospinning is capable of yielding fibers with sub-micron range diameters and high specific surface areas. In this study a Bisphenol-A polycarbonate was electrospun using two solvents: Chloroform and a 1:1 mixture of Tetrahydrofuran (THF) and Dimethylformamide (DMF). The morphological features of the electrospun polycarbonate fibers have been studied as a function of the solvent used and also as a function of the processing voltage. The studies were conducted using the SEM, TEM and Scion image analysis program. The results indicate that the morphological features of the fiber such as fiber diameter, diameter-distribution, internal structure and the Bead density variation with voltage are dependent on the solvent used. Electrospun polycarbonate fibers also exhibit a “Raisin like” puckered structure. However, such a feature is independent of the solvent used, and could enhance the functional efficiency of an electrospun material when used in an area-based application. In addition, studies on crazing of bulk polycarbonate and the surface features of electrospun polycarbonate fibers have been conducted. Results indicate that crazing of bulk polycarbonate results in surface damage and features that are also seen on the surface of electrospun polycarbonates.

Microcharacterization and identification of tire debris in heterogeneous laboratory and environmental specimens

Abstract Tire debris is produced by the normal wear of tires. Two problems are addressed herewith: characterization of debris particles and their identification in heterogeneous specimens, which come from laboratory wear tests and from the environment. Both problems are solved by analytical electron microscopy (EM). The scanning electron microscope (SEM) shows that tire debris has a typical, warped surface and pores, and that its characteristic elements, detected by energy dispersive X-ray spectroscopy (EDXS), are S and Zn. As a consequence, the identification of tire debris particles in heterogeneous laboratory specimens is straightforward. In those environmental specimens (road dust), where Zn cannot be detected, identification is possible in some cases, provided morphology, microanalysis, and X-ray mapping are combined. The analytical transmission electron microscope characterizes tire debris on the sub-micrometer scale by imaging, EDXS, and electron diffraction patterns. The microstructure exhibits typical elastomer–filler clusters. The representative elementary volume is found to be approximately 8×10 −23 m 3 .

ENZYMATIC SYNTHESIS OF MOLECULAR COMPLEXES OF POLYANILINE WITH DNA AND SYNTHETIC OLIGONUCLEOTIDES: THERMAL AND MORPHOLOGICAL CHARACTERIZATION

The assembly of electronic and photonic materials on biomacromolecules is of tremendous interest for the development of biofunctional nanocomplexes as well as highly selective biosensors. In the context of the use of electrically conducting polymers for sensing, polyaniline (Pani) and polypyrrole have received considerable interest because of their well-known electrical properties. Recently, we have reported an enzyme catalyzed synthetic procedure involving horseradish peroxidase (HRP) for the polymerization of aniline on a calf thymus DNA matrix. The mild reaction conditions involved in the synthesis have provided opportunities for the use of more delicate biomacromolecules as templates. The complexation of Pani with DNA has been found to induce reversible changes in the secondary structure of DNA leading to the formation of an over-wound polymorph. The thermal characterization (melting behavior) of the DNA in the complex and the morphological properties of the complex have provided corroborative evidence for the wrapping of Pani around the DNA matrix. Scanning probe and electron microscopy studies have indicated that the formation of Pani causes the DNA-Pani strands to agglomerate, presumably due to the neutralization of charge on the phosphate groups by the partially charged Pani. We also report the synthesis of Pani on a synthetic oligonucleotide (Poly[dA-dC].poly[dG-dT]). Demonstration of the use of a new biomimetic catalyst, polyethylene glycol modified hematin (PEG-hematin), in these reactions will also be presented. These results indicate that this biocatalytic synthetic approach is generic, versatile and can be adopted for both genomic and synthetic nucleic acids. †Deceased.

Molecular Assembly by Sequential Ionic Adsorption of Nanocrystalline TiO2 and a Conjugated Polymer

Abstract Cationic nanocrystalline TiO2 particles have been synthesized for which the size and composition of the nanoparticles were analyzed by a transmission emission microscopy and energy dispersive x‐ray spectrometer (EDXS). Multilayered films have been fabricated by sequential adsorption of TiO2 nanoparticles and poly(3‐thiophene acetic acid) (PTAA). Each layer of the nanoparticles and PTAA in the thin film has also been characterized by x‐ray photoelectron spectroscopy, atomic force microscopy, and UV‐visible spectroscopy. These types of multilayered nanocomposite films may find applications in the fabrication of efficient light harvesting photovoltaic cells. #Dedicated to the memory of Professor Sukant K. Tripathy (deceased).

Optical scattering (TAOS) by tire debris particles: preliminary results.

Tire debris particles from low severity laboratory wear tests have been investigated by the TAOS optical scattering facility at Yale University. The incident wavelength is 532 nm. After the TAOS event some particle samples have been imaged by a scanning electron microscope and microanalyzed. The TAOS intensity patterns recorded within a solid angle in the backward sector have been processed by cluster analysis and compared with the patterns computed by a T-matrix code. Preliminary agreement has been found between TAOS data and the particle models (size, shape, refractive index). The purpose of the investigation is to obtain signatures of the material, based on its TAOS pattern.

Electrospinning of Polycarbonates and their Surface Characterization using the SEM and TEM

Unlike conventional spin methods, electrospinning is capable of yielding fibers with sub-micron range diameters and high specific surface areas. The use of such electrospun materials in applications, whose functionality depends on the area available, such as separation processes, will be useful. In this study a Bisphenol-A polycarbonate was dissolved in two solvents: Chloroform and a 1:1 mixture of Tetrahydrofuran (THF) and Dimethylformamide (DMF) and resulting polycarbonate solutions were then electrospun to produce polycarbonate fiber-mats. The morphological features of the electrospun polycarbonate fibers have been studied as a function of the solvent used and also as a function of the processing voltage. The studies were conducted using the SEM, TEM and Scion image analysis program. The results indicate bold differences in the fiber morphology and bead density trends with the solvent used. Electrospun polycarbonate fibers exhibit a “Raisin like” puckered structure. Such a structure will enhance the functional efficiency of an electrospun material when used in an area-based application. In addition, studies on crazing of bulk polycarbonate and the surface features of electrospun polycarbonate fibers have been conducted. Results indicate a relation between crazing and the topological features of electrospun polycarbonates.

Langmuir films of amino acid-modified diacetylenes as organic templates for biomimetic mineralization

Amino-acid modified diacetylenes were used as organic templates for controlled biomineralization. Macromolecular changes in the monolayers have been observed upon application of pressure or polymerization. The degree of film compression and film polymerization influenced calcium carbonate polymorph selectivity. The desired optimization of the physical properties of the biomineral product is approached via structural control of the organic monolayer.

Morphological classification of nanoceramic aggregates

Aluminum silicate nanoaggregates grown at near-room temperature on an organic template under a variety of experimental conditions have been imaged by transmission electron microscopy. Images have been automatically classified by an algorithm based on “spectrum enhancement”, multivariate statistics and supervised optimization. Spectrum enhancement consists of subtracting, in the log scale, a known function of wavenumber from the angle averaged power spectral density of the image. Enhanced spectra of each image, after polynomial interpolation, have been regarded as morphological descriptors and as such submitted to principal components analysis nested with a multiobjective parameter optimization algorithm. The latter has maximized pairwise discrimination between classes of materials. The role of the organic template and of a reaction parameter on aggregate morphology has been assessed at two magnification scales. Classification results have also been related to crystal structure data derived from selected area electron diffraction patterns.

The Chromic Phase Transition in Hydrogen Bonded Polydiacetylenes

Abstract Thermochromism in the polydiacetylenes(PDA) from the alkylurethanes of 5, 7-dodecadiyn-1, 12-diol is associated with a first order phase transition involving the expansion of the crystallographic unit cell, the preservation of the urethane hydrogen bonding, and possibly some relief of mechanical strain upon heating. Insights into thermochromism obtained from recent studies of nonthermochromic forms of PDA-ETCD are presented. Initial observations of the surfaces of single crystals of several PDA in this class by atomic force microscopy are consistent with known crystallographic data.