Haiwon Lee

Size-dependent elastic modulus of single electroactive polymer nanofibers

The authors report for the first time the size dependency of the elastic modulus of well-aligned single polymeric nanofibers. The nanofibers were fabricated from electroactive polymers (EAPs) and had an ellipsoidal cross section because of impingement between a solid surface and a polymer jet during electrospinning. Although the EAPs had very weak mechanical properties in the bulk, the elastic modulus of single EAP nanofibers increased exponentially as the diameter of the EAP nanofibers decreased to diameters of a few tens of nanometers. The elastic modulus of single nanofibers was measured using three-point bending tests employing an atomic force microscope.

Effect of annealing of polythiophene derivative for polymer light-emitting diodes

The nature of the interface between the light-emitting layer and the metal electrode is of importance in determining device performance. The heat treatment of the electroluminescence device can enhance the adhesion of the polymer on the electrode by reducing free volume or pores in the interface. The current–voltage–luminance characteristic of the device with heat treatment at various temperatures was investigated. The annealed device above glass transition temperature (Tg) showed the most efficient characteristics. The current density was increased about 20 times over that of the unannealed device. The light intensity was also increased dramatically by 40 times.

Mechanism of atomic force microscopy anodization lithography on a mixed Langmuir–Blodgette resist of palmitic acid and hexadecylamine on silicon

A degradation process of a resist was observed by an atomic force microscope (AFM) during AFM anodization lithography on a mixed Langmuir–Blodgett resist of palmitic acid and hexadecylamine. Based on the observation, we proposed a two-step mechanism as follows: (i) a partial degradation of the resist was first achieved and (ii) silicon oxide started to be grown in the presence of a resist. Lateral force microscopy was accomplished on the patterned area before and after the resist was stripped in order to confirm when the silicon oxide started to be grown in the area. This result provides us with the actual information on the mechanism of the anodization lithography on an organic resist.

A label-free electrochemical immunosensor for the detection of cardiac marker using graphene quantum dots (GQDs)

A label-free immunosensor based on electrochemical impedance spectroscopy has been developed for the sensitive detection of a cardiac biomarker myoglobin (cMyo). Hydrothermally synthesized graphene quantum dots (GQDs) have been used as an immobilized template on screen printed electrodes for the construction of an impedimetric sensor platform. The GQDs-modified electrode was conjugated with highly specific anti-myoglobin antibodies to develop the desired immunosensor. The values of charge transfer resistance (Rct) were monitored as a function of varying antigen concentration. The Rct value of the immunosensor showed a linear increase (from 0.20 to 0.31kΩ) in the range of 0.01-100ng/mL cMyo. The specific detection of cMyo was also made in the presence of other competing proteins. The limit of detection for the proposed immunosensor was estimated as 0.01ng/mL which is comparable to the standard ELISA techniques.

Reinforcement of polymeric nanofibers by ferritin nanoparticles

Poly(vinyl alcohol) (PVA) nanofibers containing bimolecular ferritin nanoparticles exhibited the enhancement of elastic modulus as compared to pure PVA nanofibers due to chemical interactions between the ferritin and the PVA matrix. The elastic modulus of the nanofibers was measured using a three-point bending test employing an atomic force microscope (AFM). To improve the reliability of the AFM measurements, uniform nanofibers were oriented linearly on an AFM calibration grating by introducing parallel subelectrodes in an electrospinning system. The length to diameter ratio of the measured nanofibers was >16. The PVA nanofibers reinforced by ferritin are applicable as artificial muscles and actuators.

Enhanced charge-collection efficiency of In2S3∕In2O3 photoelectrochemical cells in the presence of single-walled carbon nanotubes

This letter reports on the efficiency of In2S3∕In2O3 photoelectrochemical cells by enhanced charge collection and reduced recombination reaction in the presence of single-walled carbon nanotubes (SWCNTs) on indium-doped tin oxide substrate. Nanocomposite system as In2S3∕In2O3/SWCNTs was assembled using spray-coating and wet chemical processes. Due to enhanced charge collection and reduced recombination in the presence of SWCNTs, 52.9% increment of power conversion efficiency is achieved compared to those without SWCNTs layers.

One step preparation of bromo-2-pyrones via bromo-decarboxylation of 2-pyrone-carboxylic acids

Abstract Synthetically valuable 3-bromo-2-pyrone, 3-bromocoumarin, 5-bromo-2-pyrone, and 3,5-dibromo-2-pyrone were prepared in one step from readily available 2-pyrone-carboxylic acids via bromo-decarboxylation in good to fair yields.

Direct fabrication of twisted nanofibers by electrospinning

The authors have fabricated artificial twisted nanofibers that resemble naturally twisted fiber structures, such as collagen fibril and double-strand DNA, using a modified conventional electrospinning system to directly develop the twisted nanofibers. The system modification allowed for the fabrication of twisted nanofibers by controlling the whipping jet using a modified electric field from an auxiliary electrode. Moreover, the authors calculated the magnitude of the electric field strength vectors using the Maxwell software program to identify the effect of the rotating electric field on the auxiliary electrode. Twisted nanofibers have a potential application in biomimetics, such as in artificial muscles, actuators, and nanoelectromechanical systems.

Multidimensional manipulation of carbon nanotube bundles with optical tweezers

Optical manipulation of carbon nanotubes (CNTs) in aqueous solution was performed using a linearly polarized infrared tweezers system. Vertical and horizontal manipulation of single-walled and multiwalled carbon nanotubes (SWNTs, MWNTs) was carried out by changing the size of the CNTs and the trapping position. Rotation of MWNT bundles was confirmed using a circular polarized infrared optical tweezers system. Patterning of dots and letters with CNTs was successfully carried out on glass substrates.

Hierarchical and Multifunctional Three‐Dimensional Network of Carbon Nanotubes for Microfluidic Applications

Three-Dimensional network of carbon nanotubes: The 3D network of CNTs have hierarchical structures comprised of interconnected SWNTs between Si pillars in microfluidic channels. The Al(2)O(3) coated 3D networks were used for size different nanoparticles filtration and streptavidin capturing in very diluted solution. The 3D network of SWNTs systems will provide a robust multifuncitonal platform for a variety of biomedical and environmental applications.