Leslie S. Loo

Role of interface in dispersion and surface energetics of polymer nanocomposites containing hydrophilic POSS and layered silicates

Three different hydrophilic nanofillers--natural and synthetic layered silicate as well as octaammonium polyhedral oligomeric silsesquioxane (POSS)--were incorporated into polyamide-6 by a solution-mixing method. The surfaces of the resulting polymer nanocomposites were characterized by X-ray diffraction, polarized optical microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and contact angle measurements. All polymer nanocomposites displayed enhancement in surface hydrophilicity as well as increase in surface free energy due to surface enrichment of the nanofillers. The degree of enhancement was found to depend on both nanofiller type and dispersion state. Interfacial interactions in the form of hydrogen bonding played an important role in affecting the dispersion state of the layered silicates. Exfoliated layered silicates caused a larger increase in hydrophilicity than aggregated layered silicate. On the other hand, aggregated POSS molecules were able to induce a large increase in hydrophilicity. Significant spreading of water was also observed on surfaces containing POSS molecules. Surface models have been proposed to explain these phenomena.

Hot Filament Chemical Vapor Deposition of Polyoxymethylene as a Sacrificial Layer for Fabricating Air Gaps

In the rapid evolution towards electronic devices with smaller feature sizes and faster speed, the factor limiting overall performance is no longer gate delay, but the Resistance-Capacitance (RC) delays due to interconnects, which are the electrical connections between wires on different layers within the chip. In an attempt to alleviate this problem, novel materials of low dielectric constant (k) have been introduced to replace traditional silicon dioxide (k = 4.0). Air is a “material” with the lowest known dielectric constant (k = 1.0). Air gaps can be formed by the removal of a sacrificial layer deposited in an earlier processing step. The properties of the sacrificial layer material must satisfy the following criteria: ease of synthesis and integration, short time and low temperature of decomposition, removal in the absence of oxygen, negligible residue left behind after decomposition.

Deuterium nuclear magnetic resonance of deuterium oxide in nylon 6 under active uniaxial deformation

The large strain uniaxial tensile deformation behavior of nylon 6 plasticized by deuterium oxide is investigated by an in situ stretching device built in a deuterium nuclear magnetic resonance (NMR) probe. The D2O molecules probe the environment of the amorphous regions in nylon 6; they do not exist in a “free” state and remain associated with the amide groups by hydrogen bonding during deformation. Deuterium NMR spectra show that the quadrupolar splitting varies linearly with strain throughout the experiment, indicating that the orientation of the D2O molecules in the amorphous regions is simply a function of strain and not of stress. The line width increases rapidly with strain at low to moderate strains but more slowly at large strains (in the strain-hardening regime). From low to moderate strains, larger changes in line width arise from a decrease in the translational motion of the D 2O molecules between amide groups in the amorphous chains during elastic deformation and during the transformation of the lamellar structure of nylon 6 to a fibrillar one. At large strains, the existence and deformation of the fibrillar structure cause a slower decrease in the translational motion of the plasticizer. q 2000 Elsevier Science Ltd. All rights reserved.

A Novel Time Lag Method to Measure the Permeation of Vapor-Gas Mixtures

A novel time lag method was proposed to study the permeation of gas mixtures or vapor-gas mixtures. This technology, which is based on the difference in the boiling points of the components, can simultaneously measure the mass transport properties of each component. The permeation of a binary mixture of H 2 O(v)/CO 2 was measured on a composite polymer membrane to demonstrate the feasibility of the technology. The method is low-cost and convenient for the future study of the permeation/separation of such gas mixtures as natural gas, flue gas, etc.

Experimental Measurement and Modeling of Diffusion Anomalies in a CMS Membrane

The sorption isotherm, permeation time lag, and steady state permeability of a noble gas, argon, were measured on a CMS membrane at different temperatures and a range of permeation pressures. It is found that Ar permeation present strong diffusion anomalies (The deviation to the traditional Darken relation). The degree of the anomalies was found approximately same for the transient permeation time lag and the steady state permeability. Comparison studies with other permeation gases further reveals that the permeation behaviors are related to their molecular properties.

Synthesis of novel hybrid films of a layered silicate and alkylammonium cations on rough polymeric surfaces by Langmuir―Blodgett method

Hybrid films of a layered silicate and an amphiphilic alkylammonium (hexadecyltrimethylammonium) cation have been prepared by Langmuir-Blodgett (LB) method and transferred onto a polyamide surface by dip coating. This is the first time that stable LB hybrid monolayer and multilayer films have been formed on rough polymeric surfaces. The films were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and water contact angle measurements. XRD and FTIR showed that the hybrid multilayer was well-organized and the thickness of one layer was calculated to be 1.6nm. Furthermore, the layered silicate was determined to be on the substrate side and the amphiphilic molecule layer was exposed to the air side. This provides a novel methodology for the surface modification of polymers.