Cheng Hao Lee

Formation of Nanostructured Materials Using Inexpensive Hollow Particles of Amphiphilic Graft Copolymers As Building Blocks: 1. Insight into the Mechanism of Nanotube Formation

The aim of this research is to elucidate the mechanism for the formation of nanotubes from hollow particles of amphiphilic graft copolymers, such as poly(ethyleneimine)-graft-poly(methyl methacrylate) (PEI-g-PMMA), under non-equilibrium conditions. The study was performed at either 15 or 17 °C with fluid shear in a mixture of dichloromethane (DCM)–water using the amphiphilic hollow particle as a building block. Effects of stirring rate and DCM to water ratio on the hollow particle assembly were systematically investigated. Surface properties and morphology of the hollow particles and the resulting assemblies in both DCM and water were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and atomic force microscopy. Results from these studies suggest four key features of this assembly process: (1) morphology of the amphiphilic hollow particle can be inverted in organic solvent and water. (2) The assembly process can only occur with appropriate fluid shear and DCM:water ratio. (3) The hollow particles can undergo deformation to ellipsoidal shapes with stirring rate at 350 rpm in an appropriate DCM:water (e.g. 3:7 v/v) mixture. (4) The elongated hollow particles then assemble to form linear aggregates via tip-to-tip connection, followed by coalescence and fusion to generate nanotubes with diameters less than 150 nm. The lengths of the nanotubes can be up to micron-scale, and they can be easily aligned via a simple dip-coating method. This simple and inexpensive assembly process using amphiphilic hollow particles as a building blocks is dramatically different from the well-known self-assembly of block copolymers into different nanostructures under equilibrium conditions.

Synthesis and characterization of solvent-invertible amphiphilic hollow particles

Previous researches on solvent-dependent polymer systems mainly focus on amphiphilic invertible polymers (AIPs), which are capable of forming solvent-dependent micellar or inverse micellar assemblies. However, polymer particles that are invertible in response to solvent polarity are almost unexplored. In this paper, we report a new type of invertible hollow polymer (IHP) particle that is comprised of polyethylenimine-g-poly(methyl methacrylate) (PEI-g-PMMA) copolymer. The amphiphilic PEI-g-PMMA hollow particles were first prepared through synthesis of well-defined PEI/PMMA core-shell particles, followed by removal of PMMA homopolymer from the core. The resulting IHP particles can be stably dispersed in both nonpolar solvent and water. We have investigated the morphology and surface property of the particles in both dichloromethane (DCM) and water using transmission electron microscopy, water contact angle measurement, and X-ray photoelectron spectroscopy analysis to gain insight into this unique particle dispersibility. Sustainability of the solvent-invertible property was carefully studied through repeated treatment of the IHP particles in DCM or water for up to six cycles. Solvent-dependent property of the dry films formed by IHP particles was also investigated through water contact angle measurement. Increasing water content on the DCM-treated IHP particle film could reduce the water contact angle from 94° to 51°. Our results demonstrate that the amphiphilic hollow particles are a new type of polymer design for smart materials that are invertible in response to nonpolar and aqueous media in both dispersed and solid states.

Effect of graphene oxide inclusion on the optical reflection of a silica photonic crystal film

In this study, the inclusion of graphene oxide in silica photonic crystals was found to affect optical reflectance intensity and reflectance peak broadening. The quantitative relationship between weight percentage and the reflected light intensity and corresponding wavelength shift of light GO-decorated photonic crystals was studied, providing a useful parameter in the rational design of antireflection coatings for GO-based photonic crystal films. Comparison of the experimental results with a pure SiO2 particle film shows that a SiO2 particle surface layer incorporated with a fixed graphene oxide weight percentage results in broadening of the peak and a decrease in reflectance intensity. The percentage of the reduction in reflectance intensity is a function of particle size, as indicated by the structured color film surface, demonstrating the possibility of estimating the effect of different graphene oxide inclusion percentages on the antireflection properties of photonic crystal films.

Influence of temperature on the formation and encapsulation of gold nanoparticles using a temperature-sensitive template.

This data article describes the synthesis of temperature-sensitive and amine-rich microgel particle as a dual reductant and template to generate smart gold/polymer nanocomposite particle. TEM images illustrate the influence of reaction temperature on the formation and in-site encapsulation of gold nanoparticles using the temperature-sensitive microgel template. Thermal stability of the resultant gold/polymer composite particles was also examined.

pH-induced formation of various hierarchical structures from amphiphilic core–shell nanotubes

Intriguing hierarchical structures, including nanotubular bundle, columnar, reticular plate-like and highly packed interwoven plate-like materials, have been created viaself-assembly of amphiphilic core–shell nanotubes in water through varying the solution pHs between 3 and 13.

Dyeing Properties of Cotton with Reactive Dye in Nonane Nonaqueous Reverse Micelle System

In this study, we explored the dyeing behavior of cotton with reactive dyes in poly(ethylene glycol)-based reverse micelle system in nonaqueous alkane medium of nonane (C9H20). Calibration of dyeing databases for both conventional aqueous-based dyeing method and nonaqueous nonane reverse micellar dyeing method was initially established, along with simulated dyeing of standard samples with known concentrations. Several color difference formulae were used to conduct computer color matching (CCM), by matching the color between batch samples and the standard samples, for both dyeing methods. Excellent color matching results were achieved as both dyeing methods showed that the CCM-predicted concentrations were nearly the same as the known concentrations. It indicates that utilizing nonane as a solvent to facilitate reverse micellar dyeing of cotton can achieve good color matching when compared with that of the conventional aqueous-based dyeing system. Relative unlevelness indices were used to evaluate the evenness of the dyed samples. Good to excellent levelness results were obtained, comparable to that of the conventional aqueous-based dyeing system. Color fastness to laundering of nonane reverse micellar dyed samples was found to be good for industrial applications. In addition, during the reverse micellar dyeing process, only very low level of volatile organic compound content was detected and 98% nonane could be recovered simply by fractional distillation. The results in this study explored the practical usage of nonane nonaqueous reverse micellar approach on the dyeing of cotton with the use of reactive dyes.