Chih-Wei Chiu

Facile Fabrication of Robust Superhydrophobic Epoxy Film with Polyamine Dispersed Carbon Nanotubes

Nanocomposite films of superhydrophobic surface are fabricated from the dispersion of unmodified carbon nanotubes (CNTs) and hydrophobic poly(isobutylene)-amine (PIB-amine). The PIB-amine prepared from the amidation of poly(isobutylene)-succinic anhydride and poly(oxypropylene)-amines is essential for dispersing the originally entangled CNTs into the debundled CNTs as observed by TEM. A robust CNTs/epoxy nanocomposite film with high dimensional stability is made by subsequent curing with epoxy resin. The self-standing film exhibits a superhydrophobic property, with water droplet contact angle > 152° due to the CNTs controlled alignment on the surface forming micrometer-size plateaus, as observed by SEM. The preparation of PIB-amine/CNTs dispersion and subsequently curing into a superhydrophobic CNTs/epoxy film is relatively simple and can potentially be applied to large surface coating.

First fabrication of electrowetting display by using pigment-in-oil driving pixels.

We report the first fabrication of pigment particle-based electrowetting display (EWD) by using the requisite poly(isobutylene)-imide (PIB-imide) for effectively dispersing insoluble colorant in decane/water system. The series of PIB-imide dispersants were prepared from the amidation/imidation of PIB-succinic anhydride with different hydrophobic lengths and a suitable amine. The structurally tailored dispersants by adopting the highly hydrophobic PIB tails allows the formation of homogeneous dispersion of nanosized pigment particles in decane and clearly separated from water. The pigment dispersion at particle size of ca. 100 nm and a low viscosity of 2-3 cps was obtained and fabricated into an EWD device which was operated at a driving voltage of 15-20 V in achieving a maximum aperture ratio of 80%. With the advantage of both fast response time and vivid color, the pigment-based EWD, as shown in the video, stands out as a promising new option for future transparent display and serves as a critical foundation for the next-generation advanced display applications.

A stepwise mechanism for intercalating hydrophobic organics into multilayered clay nanostructures

Intercalating organics into cationic clays generally occurs by ionic exchange. For a number of hydrophobic polyetheramines with a backbone of poly(oxypropylene) (POP), we observed that monoamines with a methyl terminus intercalated into montmorillonite (MMT) clay in two distinct steps. Remarkably, the monoamine with a molecular weight of 2000 g mol−1 widened the basal spacing of the layered clay up to 74 A; the space expanded further to 84 A, 96 A, and 100 A by a mechanism that was different from conventional ionic exchange. The organoclays that we examined were amphiphilic, dispersing in organic media and in water. Kinetic studies indicated that the first stage of intercalation occurred after a critical concentration of monoamine, while the second stage had no critical concentration. The methyl terminus of the POP-amine also appears to drive the aggregation of organics into the layered clay. Our findings show the potential for synthesizing new organoclay nanostructures that can encapsulate large molecules in natural clay.

Tailoring Pigment Dispersants with Polyisobutylene Twin-Tail Structures for Electrowetting Display Application

We have designed a class of highly hydrophobic dispersants for finely dispersing carbon black and organic pigment nanoparticles in apolar mediums. The synthesis involved the use of polyisobutylene-g-succinic anhydride (PIB-SA) and judiciously selected amines by amidation and imidation. The structures were characterized by infrared spectroscopy for anhydride functionalities in the starting materials and amide/imide linkages in the products. These polymeric forms of dispersants were structurally varied with respects to their PIB molecular weight, twin-tails, and linkages. Their relative performance for dispersing six different pigments in decane was evaluated against solution homogeneity, viscosity, stability, and particle size. The fine dispersion was achieved at particle sizes of ca. 100 nm, with the viscosity as low as 2-3 cP. The measurement of zeta potentials, which varied from -39.8 to -5.1 mV with pigment addition, revealed a strong surface-charge interaction between pigment and PIB dispersant molecules. Examination by TEM (transmission electronic microscope) showed the homogeneous dispersion of the primary structures of pigment particles at ca. 20 nm in diameter. The polymeric dispersants with different PIB tails and imide functionalities could be tailored for pigment stability in the oil phase, which is potentially suitable for the electrowetting devices.

Synthesis, characterization, and highly acid-resistant properties of crosslinking β-chitosan with polyamines for heavy metal ion adsorption

This study primarily used β-chitosan as the main reactant and benzaldehyde as the protecting group to convert the amine groups on location C2 of chitosan into Schiff bases. Grafting and crosslinking of epichlorohydrin and triethylenetetramine with chitosan was conducted and the structural changes were analyzed with Fourier transform infrared spectroscopy (FTIR), UV-visible spectroscopy (UV-Vis), thermogravimetric analysis (TGA), elemental analyses (EA), differential scanning calorimeter (DSC), X-ray powder diffraction (XRD), nuclear magnetic resonance (NMR), and scanning electron microscope (SEM) to prove the successful modification to form crosslinked β-chitosan. Lastly, this study compared the heavy metal ion (such as Cu2+ and Ag+) adsorption capacities of chitosan before and after the graft modification. The capacity of modified chitosan for adsorbing copper ions improved in acid environments with pH of 2 to 6. The capacity increased from 67.76 mg g−1 to 117.60 mg g−1 when the pH value was 6. In addition, the capacity of adsorbing silver ions was higher than that of adsorbing copper ions and it enhanced from 116.80 mg g−1 to 151.20 mg g−1 when the pH level was 6. Furthermore, the modified crosslinked β-chitosan had an excellent acid-resistant property.

Core/shell Ag@silicate nanoplatelets and poly(vinyl alcohol) spherical nanohybrids fabricated by coaxial electrospraying as highly sensitive SERS substrates

A novel, flexible, freestanding, and large-scale substrate for surface-enhanced Raman spectroscopy (SERS) was successfully prepared by coaxial electrospraying. Nanohybrids of silver nanoparticles (AgNPs)/triblock copolymer surfactant (copolymer)/silicate nanoplatelets (Ag@silicate) were prepared by the in situ reduction of AgNO3 in the presence of silicate platelets and a polymeric surfactant. Nonwoven mats of the hybrids were prepared via coaxial electrospraying, assembling Ag@silicate hybrids outside a poly(vinyl alcohol) (PVA) surface to form core–shell microstructures. Characterization showed that the core–shell Ag@silicate/PVA nanosphere substrate significantly enhanced the SERS signal intensity, with enhancement values approaching 5.1 × 105 for adenine molecules from DNA. These core–shell nanosphere hybrids fabricated by electrospraying have great potential as SERS substrates in biosensor technology.

Hierarchical self-assembly of random mica nanosheet-stabilized silver nanoparticles into flower microstructures for highly sensitive SERS substrates

In this study, we observed the formation of flower-like microstructures by the hierarchical self-assembly of random mica nanosheet (RMN)-stabilized silver nanoparticles (AgNPs) without organic stabilizers. The SERS spectra of adenine molecules from DNA were measured as functions of the AgNP sizes and microstructures with substrates formed using various RMN/AgNP precursor ratios. The AgNP@RMN substrates significantly contributed to the high SERS sensitivity to adenine molecules with a SERS enhancement factor (EF) of 1.5 × 105. These novel AgNP@RMN hybrid microstructures can be utilized as SERS substrates for biological sensing applications.

Immobilization of silver nanoparticles on exfoliated mica nanosheets to form highly conductive nanohybrid films.

Highly electrically conductive films were prepared by coating organic/inorganic nanohybrid solutions with a polymeric dispersant and exfoliated mica nanosheets (Mica) on which silver nanoparticles (AgNPs) had been dispersed in various components. Transmission electronic microscopy showed that the synthesized AgNPs had a narrow size distribution and a diameter of approximately 20 nm. Furthermore, a 60 μm thick film with a sheet resistance as low as 4.5 × 10(-2) Ω/sq could be prepared by controlling the heating temperature and by using AgNPs/POE-imide/Mica in a weight ratio of 20:20:1. During the heating process, the surface color of the hybrid film changed from dark golden to white, suggesting the accumulation of the AgNPs through surface migration and their melting to form an interconnected network. These nanohybrid films have potential for use in various electrically conductive devices.

Controlled self-assemblies of clay silicate platelets by organic salt modifier

We observed unique cubic microstructures and hierarchical dendrite formation from clay silicate platelet self-piling. The fundamental units of silicate platelets with dimensions of ca. 80 × 80 × 1 nm were previously prepared from natural clay stacks. By ionic exchange with the hydrochloride salt of diethylene glycolamine, the platelets could be connected with polar organic moieties. The self-piling of these silicate platelets generated cubic arrays of 1–4 μm in size that differed from the rod-like microstructures of 10–60 μm in length and 0.5–1.5 μm in diameter for non-modified platelets. The cubic self-assemblages were characterized to be hollow in structure by energy dispersive X-ray spectrometry for elemental analysis, scanning electron microscopy, and transmission electron microscopy. Dendrite arrays were further observed over a large area of a millimeter square, indicating high regularity of the cube unit interconnection. Both charge attraction and organic interaction had shifted the platelet piling directions, favoring 3-D cubes and further facilitating the formation of hierarchical dendrites.

Facile preparation of highly electrically conductive films of silver nanoparticles finely dispersed in polyisobutylene-b-poly(oxyethylene)-b-polyisobutylene triblock copolymers and graphene oxide hybrid surfactants

We report the development of a facile method for the preparation of highly electrically conductive silver nanoparticle (AgNP) films finely dispersed in novel organic/inorganic nanohybrid surfactants consisting of an amphiphilic polymeric dispersant and graphene oxide. The production of AgNPs with a narrow size distribution and a 20 nm diameter was observed by transmission electron microscopy. Moreover, a hybrid film exhibiting a low sheet resistance of 5.2 × 10−2 Ω sq−1 was prepared by controlling the heat treatment of the AgNP samples. The resulting highly electrically conductive films have great potential for application in electrically conducting devices.