Yern Seung Kim

Easy Preparation of Self-Assembled High-Density Buckypaper with Enhanced Mechanical Properties

A controlled assembly and alignment of carbon nanotubes (CNTs) in a high-packing density with a scalable way remains challenging. This paper focuses on the preparation of self-assembled and well-aligned CNTs with a densely packed nanostructure in the form of buckypaper via a simple filtration method. The CNT suspension concentration is strongly reflected in the alignment and assembly behavior of CNT buckypaper. We further demonstrated that the horizontally aligned CNT domain gradually increases in size when increasing the deposited CNT quantity. The resultant aligned buckypaper exhibited notably enhanced packing density, strength, modulus, and hardness compared to previously reported buckypapers.

Determination of solubility parameters of single-walled and double-walled carbon nanotubes using a finite-length model

Carbon nanotube (CNT) dispersions have been prepared using a variety of surface modification methods; however, these methods frequently have a negative effect on the intrinsic properties of CNTs or need to remove the surface modifiers. The Flory-Huggins theory suggests that such problems can be alleviated or eliminated, if ideally, when the solubility parameters of CNTs and a given medium are very similar or equal to each other. Since the earlier reported solubility parameters of CNTs were determined by indirect methods and varied in wide ranges, we suggested herein a possible way of directly determining the solubility parameter of various types of CNTs by using a finite-length model, and reported the determined solubility parameters of pristine single-walled carbon nanotubes (SWCNTs) and pristine double-walled carbon nanotubes (DWCNTs). Through the validity test of the suggested model it was found that a 2 nm finite-length of CNTs can represent the longer CNTs for the study of the solubility parameters. In addition, the pristine DWCNTs were found to have higher solubility parameters than the pristine SWCNTs, and within the given type of CNTs, the solubility parameters varied inversely with the diameter of the CNTs. Based on the obtained results, it was expected that the solubility parameters for pristine multi-walled carbon nanotubes (MWCNTs) should be similar to or slightly higher than the values for DWCNTs.

Highly reproducible thermocontrolled electrospun fiber based organic photovoltaic devices.

In this work, we examined the reasons underlying the humidity-induced morphological changes of electrospun fibers and suggest a method of controlling the electrospun fiber morphology under high humidity conditions. We fabricated OPV devices composed of electrospun fibers, and the performance of the OPV devices depends significantly on the fiber morphology. The evaporation rate of a solvent at various relative humidity was measured to investigate the effects of the relative humidity during electrospinning process. The beaded nanofiber morphology of electrospun fibers was originated due to slow solvent evaporation rate under high humidity conditions. To increase the evaporation rate under high humidity conditions, warm air was applied to the electrospinning system. The beads that would have formed on the electrospun fibers were completely avoided, and the power conversion efficiencies of OPV devices fabricated under high humidity conditions could be restored. These results highlight the simplicity and effectiveness of the proposed method for improving the reproducibility of electrospun nanofibers and performances of devices consisting of the electrospun nanofibers, regardless of the relative humidity.

Titration Method for the Identification of Surface Functional Groups

Titration method has been applied for both qualification and quantification of the surface functional groups of carbon materials. In this method, the number of the specific functional groups such as carboxylic, lactonic, and phenolic groups is established using the selective neutralization principles. In this chapter, the basic concept for easy understanding of the titration method is introduced and then the experiment and analysis techniques of the titration for determination of the degree of functionalization of carbon materials are provided.