Two particle transition density and two particle bond order and their applications to electronic energy shifts caused by two particle interactions via geometric deformations

The concept of two particle transition density (TPTD ) and two particle bond order (TPBO ) is introduced and formally developed in order to extend the considerations of Callis, Scott, and Albrecht [1] to two particle interactions. These interactions may become important if the TPTD (TPBO ) for one particle effects is small or the perturbation considered is essentially a two particle perturbation. As an example the geometric deformation of annulene perimeters is studied in detail. This deformation can be interpreted as a two particle perturbation because one particle effects do not contribute considerably. As a result of the perturbation characteristic energy shifts of the four lowest electronic singlet excitations depending on the type of deformation can be observed.     

Characterization of plasma polymerized C, H, and O containing compounds by MALDI mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is used for the first time to characterize radio frequency plasma-deposited polymers and for investigation of the plasma polymerization process. The MALDI mass spectra of the plasma polymers of allyl alcohol, di(ethylene glycol) vinyl ether and ethylene glycol butyl vinyl ether are all reported using solvent-based MALDI sample preparation approaches. The MALDI mass spectra of each of the three plasma polymers contain distinctive polymer series ion signals having molecular weight distributions below 2000 Da. Unexpectedly, however, the ion signals from each of the three plasma polymers show a common polymer repeat unit of 44 Da, for which the chemical formula is most likely -(C(2)H(4)O)-, and no evidence of the expected radical chain polymerization polymer is detected. These results are discussed in terms of the likely involvement of gas-phase radical species having different stabilities in the radio frequency plasma environment.     

TEM-cross section investigations of plasma polymer silver composite films

Plasma polymer silver composite films were investigated by means of cross section transmission electron microscopy (XTEM). The silver is encapsulated in the form of small particles in a nearly homogeneous plasma polymer matrix. The shape and the size of the particles vary with the polymerization power density. At lower polymerization power density the silver particles appear almost spherical and a three-dimensional particle distribution can be found in the polymer matrix. However the shape of particles at higher power density is more elliptic and the particle distribution is two-dimensional. The different kinds of encapsulation can be interpreted as being due to the different densities and porosities of the plasma polymer matrix.     

The effect of clay on the morphology of multiphase latex particles

The effect of montmorrilonite clay (MMT) platelets on the morphology of polystyrene/poly(methyl methacrylate) (PMMA) composite latex particles prepared via PMMA-seeded (semi-) batch emulsion polymerization of styrene was studied. It was found that the particle morphology obtained greatly depended on the ability of the clay platelets to diffuse through the polymer particle. Indeed, when the reactions were strictly under kinetic control, i.e., where the clay platelets were unable to diffuse during polymerization, anisotropic core-shell-like morphologies with split core were observed. A better mobility of the clay platelets could more or less restrict the diffusion of the second-stage polymers within the host polymer, leading to original kinetically controlled morphologies. In the case of a full migration of the clay platelets to the particle surface, the penetration of the second-stage polymer species in the seed latex was found to be more limited, enhancing the formation of secondary particles.     

Optical properties of plasma polymer films with encapsulated silver particles

Plasma polymer thin films with encapsulated small metal particles were prepared by simultaneous plasma polymerization and metal evaporation. Based on transmission electron microscope (TEM) micrographs, particle size and shape were analysed on films with continuously varying filling factor. Thermal annealing causes dramatic changes of the particle size and shape. The optical (UV, VIS, NIR) properties of the films were determined by the UV-absorption of the plasma polymer and by the plasma resonance absorption of the metal particles. The changes in the transmission spectra during thermal annealing were simulated with different effective medium theories. The calculated transmission spectra were fitted to the experimental spectra.     

Probing the surface of polymer colloids by conductometric surfactant titration

This work revisits the use of surfactant titrations for the characterization of latex particle surfaces. Experiments were performed to study the effect of comonomer composition and the effect of acid comonomers, and the technique is applied to the characterization of particle morphology in composite latices for several different systems. It is confirmed that the packing density of surfactant on a polymer surface is a linear function of copolymer composition. Inclusion of acid comonomers has the expected effect of decreasing the amount of surfactant adsorbed on the polymer surfaces. The usefulness of the technique in the determination of particle morphology is demonstrated, in particular toward the detection of thin layers of either seed or second-stage polymer on the particle surface which are not easily detected by other techniques such as transmission electron microscopy (TEM). Finally, it is shown that the use of acid comonomers in composite particles greatly reduces the usefulness of the surfactant titration technique for morphology characterization. A possible explanation for this effect is proposed.     

Some aspects of plasma polymerization investigated by pulsed R.F. discharge

The polymerization of organic compounds in glow discharge (plasma polymerization) was investigated by using pulsed R.F. discharge (100 μsec on, 900 μsec off). The effects of pulsed discharge on polymer deposition rate, pressure change in plasma, ESR signals of free spins in both plasma polymer and substrate, and the contact angle of water on the plasma polymer surface were investigated for various organic compounds. The results are correlated to the mechanisms of polymer formation in plasma (plasma polymerization) which has been postulated as repeating processes of stepwise (propagation) reactions. The effect of the pulse is different from one group of organic compounds to another depending on whether or not they contain an olefinic double bond and/or a triple bond. The main difference seems to be the addition polymerization which can occur exclusively during the off-period of pulsed discharge. Ultraviolet emission from pulsed discharge is much less than from continuous discharge. Consequently, the fragmentation of the monomer and the free-radical formation in the substrate are less with the pulsed discharge. Properties of polymers from some organic compounds formed in continuous and in pulsed discharge were found to be significantly different, and the differences were postulated from the changes of polymerization mechanisms in the pulsed discharge.     

FTIR Analysis of Plasma Damage of Kapton

Recently, Kapton (polyimide) has been used in the reduction of dust particles in plasma etching chambers. However, it is found that there is a limit of lifetime for Kapton in trapping particles. Beyond this time limit, particle contamination becomes serious and even causes defect on wafers. In this study, two plasma etching recipes were used to test the particle/polymer trapping efficiency of Kapton. A Fourier Transform Infrared (FTIR) spectrometer was used to examine the functional groups change of the Kapton surface after plasma etching. The increase of IR absorption of CF_x (x = 2, 3) indicates the growth of fluorocarbon polymer on the Kapton surface. The Kapton surface was damaged as indicated by the change of C=O, -NH₂, and C - H IR intensities. IR Spectroscopic data show that Kapton has a very good particle/polymer reduction efficiency when using high-polymer recipe but not very efficient with oxygen-rich recipe. It has drawn our attention that when testing metal contamination of the processed wafers using chambers with Kapton coating, the concentration of aluminum was always high as compared to those without using Kapton. It can be ascribed to the plasma damage of Kapton, as supported by the surface chemical analysis with energy dispersion spectroscopy (EDS). Data collected from FTIR and EDS are correlated to interpret the mechanisms of plasma damage of Kapton.     

Surface structures of fluoropolymer,polyolefin and polyester films after modification by graft polymerization

Pristine and argon plasma pretreated polytetrafluoroethylene (PTFE), polystyrene (PS), high-density polyethylene (HDPE) and poly(ethylene terrephthalate) (PET) films have been subjected to near-UV light-induced graft polymerization with water-soluble acrylamide (AAm), the sodium salt of styrene sulfonic acid (NaSS), acrylic acid (AAc) and N,N-dimethylaminoethylmethylacrylate (DMAEMA) monomers. The structure and composition at the substrate surface with grafted polymer were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). In most cases, the density of surface grafting is enhanced by plasma pretreatment. For each polymer substrate with a substantial amount of grafting, the hydrophilic graft penetrates or becomes partially submerged beneath a thin surface layer of dense substrate chains. This stratified microstructure is consistent with the static secondary ion mass spectroscopy (SIMS) and Ar⁺ beam depth profiling results. The two latter techniques also suggest that when the grafted polymer has a bulky substituent, there is less efficient penetration of the grafted polymer below the surface.     

The effect of positive ion energy on plasma polymerization: a comparison between acrylic and propionic acids

Using a novel RF biasing technique, the energy of positive ions at a depositing substrate is controlled, independently of other parameters. Under bias conditions which gave the maximum and minimum ion energies, plasmas of propionic and acrylic acid were investigated using mass spectrometry, an ion flux probe, quartz crystal microbalance, and X-ray photoelectron spectroscopy (XPS). For both compounds investigated, the ion energy affects the deposition rate but leaves the neutral gas-phase chemistry and positive ion fluxes unchanged. The chemistry of the polymer deposit for acrylic acid is unaffected by the change in ion energy, but the chemistry of the propionic acid plasma polymer changes markedly. We argue that the results presented are consistent with the hypothesis that, under the plasma conditions explored, the carbon-carbon double bond present in acrylic acid plays a significant role in the formation of the polymer. Conversely, the absence of this bond in propionic acid leads us to conclude that positive ions contribute significantly to film formation for this compound.     

Plasma Deposition of Polymeric Thin Films on Organic Corrosion-Inhibiting Paint Pigments: A Novel Method to Achieve Slow Release

Slow release of corrosion-inhibitive paint pigments is a great challenge to the paint industry, because of the urgent need to replace chromate-containing pigments. Unfortunately, most effective corrosion inhibitors are too soluble for use in paints. In this paper, we present a novel method to modify selected water-soluble organic inhibitor particles to achieve the purpose of slow release. A plasma polymerization technique was used to deposit an ultrathin polymer film on the surface of the inhibitor particles. Infrared spectroscopy (FTIR), time-of-flight secondary ion mass spectroscopy (TOFSIMS), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), and contact angle data confirmed the successful deposition of the polymer thin film on the inhibitor particles. Using immersion tests and electrochemical techniques, we have demonstrated that the encapsulated water-soluble inhibitor can slowly release into the environment to protect a metal as needed. This technique is a feasible and promising method to promote the replacement of chromate pigments in paints.     

Conformation and diffusion behavior of ring polymers in solution: a comparison between molecular dynamics, multiparticle collision dynamics, and lattice Boltzmann simulations

We have studied the effect of chain topology on the structural properties and diffusion of polymers in a dilute solution in a good solvent. Specifically, we have used three different simulation techniques to compare the chain size and diffusion coefficient of linear and ring polymers in solution. The polymer chain is modeled using a bead-spring representation. The solvent is modeled using three different techniques: molecular dynamics (MD) simulations with a particulate solvent in which hydrodynamic interactions are accounted through the intermolecular interactions, multiparticle collision dynamics (MPCD) with a point particle solvent which has stochastic interactions with the polymer, and the lattice Boltzmann method in which the polymer chains are coupled to the lattice fluid through friction. Our results show that the three methods give quantitatively similar results for the effect of chain topology on the conformation and diffusion behavior of the polymer chain in a good solvent. The ratio of diffusivities of ring and linear polymers is observed to be close to that predicted by perturbation calculations based on the Kirkwood hydrodynamic theory.     

Effect of dense plasma on the spectral properties of hydrogenic ions

The effect of strongly coupled plasma on the energy levels, dynamic polarizabilities, oscillator strengths, and transition probabilities of a number of hydrogenic ions is estimated, using the ion‐sphere (IS) model. The transition properties are calculated using time‐dependent variation perturbation theory. The variation of the atomic properties under different plasma densities are analyzed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Particle stability in polymer-assisted reverse colorimetric DNA assays

“Reverse” colorimetric DNA detection by the formation of core-shell particles upon DNA hybridization is described. Specifically, the assay is based on a strategy to covalently link polymer reaction initiators to suspended nanoparticles upon DNA hybridization. These initiators then prompt polymer chain growth to form a thick polymer shell outside of particles, acting as the physical barrier to keep Au particles apart. Particles without DNA hybridization aggregate, accompanied by a pronounced solution color change from red to blue. The focus of this report is to address reaction kinetics of two co-occurring processes: polymer growth and particle aggregation during the reverse colorimetric DNA assay. The results show that Cu ions used as the polymerization catalyst bind strongly to the bases in DNA molecules, resulting in crosslinking of DNA-attached gold nanoparticles and their subsequent precipitation. Both Cu-ion-assisted particle aggregation and polymer growth are found to depend strongly on Cu ion concentration, salt concentration, and reaction temperature. Under the optimized conditions, faster polymer chain growth on the surface overcomes particle aggregation and preserves particle stability via steric stabilization.     

A light scattering study of the influence of poly(ethylene glycol) on the droplet size and the interdroplet interaction in a water-in-oil-microemulsion

Dynamic and static light scattering techniques were used to study the droplet size and the interdroplet interaction of w/o microemulsions consisting of cetyltrimethyl-ammonium bromide (CTAB), hexyl carbitol, toluene, water and poly(ethylene glycol). The results were analyzed in terms of a hard-sphere model with a perturbation. For the microemulsions without polymer, their droplet sizes increased only slightly (R=10.1 to 11.0 nm) and the perturbation became more attractive as the molar ratio of H₂O/CTAB was raised from 50 to 82. In contrast, an increase in polymer concentration or polymer molecular weight not only increased the droplet sizes but also changed the perturbation to become more repulsive. In addition, it is envisaged that the interactions between the cationic groups of CTAB and the ether linkages of the poly(ethylene glycol) may also enhance the rigidity of the interfaces, hence the stability of the microemulsions.     

Thorium colloid analysis by single particle inductively coupled plasma-mass spectrometry

Thorium colloid analysis in water has been carried out by a single particle mode using inductively coupled plasma mass spectrometry (ICP-MS). The flash of ions due to the ionisation of a thorium colloidal particle in the plasma torch can be detected and measured in a time scan for ²³²Th⁺ or ²⁴⁸[ThO]⁺ according to the sensitivity required by the mass spectrometer. The peaks of the recorded intensity of the MS signal can be analysed as a function of the particle size or fraction of the studied element in the colloid phase. The frequency of the flashes is directly proportional to the concentration of particles in the colloidal suspension. After discussing Th colloid detection, on the basis of the intensity of the ion flashes generated in the plasma torch, tests were performed on thorium dioxide colloidal particles. This feasibility study also describes the experimental conditions and the limitation of the plasma design to detect thorium colloids in a single particle analysis mode down to about 10 fg.     

Surface analysis of polymer materials by secondary ion mass spectrometry

Atomic as well as molecular secondary ions are emitted from the uppermost monolayer of a solid during ion bombardment. Mass analysis of these positive and negative secondary ions supplies detailed information on the chemical composition of the bombarded surface. High mass range (> 10,000 u), high mass resolution (m/Δm > 10,000), accurate mass determination (ppm range) and high sensitivity (ppm of a monolayer) are achieved by applying time-of-flight (TOF) mass analyzers. TOF-SIMS has been successfully applied to a wide variety of polymer materials, including polymer blends, chemically or plasma modified surfaces, and plasma polymerization layers. Detailed information on the composition of repeat units, endgroups, oligomer distributions, additives, as well as surface contaminants can be obtained. Basic concepts of TOF-SIMS will be described and typical analytical examples for the characterization of polymer materials will be presented.     

1,3-Butadiene as an Adhesion Promoter Between Composite Resin and Dental Ceramic in a Dielectric Barrier Discharge Jet

A pencil-type floating electrode dielectric barrier discharge (FE-DBD) jet was designed to improve adhesion of composite resin to dental ceramic by plasma deposition. Among various monomers used for plasma deposition, 1,3-butadiene (BD) merged as a promising monomer. Shear bond strength (SBS) and fracture modes were evaluated with specimens prepared at various flow rates of BD. The SBS values of the experimental groups were significantly higher than that of the negative control group and approached that of the positive control group when flow rate was higher than or equal to 2 sccm. Surface characterizations of plasma polymer-deposited ceramic surfaces were performed with FTIR-ATR and XPS. The deposited polymer on the ceramic surface contained methyl and methylene groups, ether and ester groups, and carbon–carbon double bonds. Formation of plasma deposited layer from BD was verified with TEM and EDS from specimens prepared using a focused ion beam technique. Adhesion between ceramic and composite resin was enhanced with BD plasma deposition using the FE-DBD jet. The adhesion effect was stemmed from chemical reactions between C=C double bonds remaining in the plasma deposited polymer and those in the adhesive monomers as well as increased wettability due to the ester and ether groups involved in deposited polymer.     

Phase-transfer reactions catalyzed by phosphonium salts bound to macroporous polystyrene supports

The rate of reaction of alkyl halides with aqueous sodium acetate or cyanide catalyzed by phosphonium salts supported on insoluble polystyrene resins, and rates of ion-exchange of the chloride ion in the catalysts against the acetate ion, were studied as a function of catalyst particle size, the percentage of ring substitution, the morphology of polymer support, and distance between active site and polymer backbone. Rates of 1-bromooctane or benzyl chloride with macroporous, 7–25% ring-substituted catalysts increased with increasing ring substitution. Rates with macroporous catalysts increased as a heptamethylene spacer was introduced between the active site and the polymer backbone. Rates of ion-exchange with macroporous catalysts were facilitated with increasing ring substitution or by the introduction of the spacer chain. A relation between the catalytic activity of macroporous or microporous catalysts and ion-exchange rates under triphase conditions was discussed.     

Origin of de-swelling and dynamics of dense ionic microgel suspensions

A direct consequence of the finite compressibility of a swollen microgel is that it can shrink and deform in response to an external perturbation. As a result, concentrated suspensions of these particles exhibit relaxation dynamics and rheological properties which can be very different with respect to those of a hard sphere suspension or an emulsion. We study the reduction in size of ionic microgels in response to increasing number of particles to show that particle shrinkage originates primarily from steric compression, and that the effect of ion-induced de-swelling of the polymer network is negligible. With increasing particle concentration, the single particle dynamics switch from those typical of a liquid to those of a super-cooled liquid and finally to those of a glass. However, the transitions occur at volume fractions much higher than those characterizing a hard sphere system. In the super-cooled state, the distribution of displacements is non-gaussian and the dependence of the structural relaxation time on volume fraction is describable by a Volger-Fulcher-Tammann function.