This paper presents the results of transmission electron microscopy (TEM) studies on the distribution of polystyrene/polyisoprene/polystyrene (SIS) triblock copolymer compatibilizer in polystyrene-polyethylene homopolymer blends. The principal independent variable studied is the major-phase rheological properties (PSmajor/PEminor and PEmajor/PSmimor blends). The polyisoprene block was preferentially stained by OSO4 and could be clearly identified in cryo-ultramicrotomed TEM sections. The microstructural data show that when the Theologically strong PS phase is the major constituent, the compatibilizer follows the classical model localizing itself at the PS/PE interface. In the PEmajor/PSminor blends, however, the SIS compatibilizer is not localized at the PE/PS interface. Instead microdispersions of PS in SIS form which in turn are dispersed in the PE matrix. While the various microstructures are affected by the mixing protocol and polymer rheology, quiescent annealing after mixing indicates that the compatibilizer distribution is in part driven by thermodynamic effects.

We have investigated the diffusive properties of model metal nanoparticle dispersions in polymeric matrices of several different molecular weights. Rutherford Backscattering Spectrometry was used to measure the depth distribution of gold nanoparticles within thin layers of poly(t-butyl acrylate) (PTBA). The gold nanoparticles were created by evaporation of a discontinuous gold layer onto a thin film of PTBA. A second PTBA film was placed onto these samples to create “sandwiches” in which the gold existed between two PTBA films. Gold particle diffusion coefficients were obtained from measured gold particle depth distributions in annealed samples for which the molecular weights of the two PTBA layers were identical. The experiments revealed that particle mobility was decreased by two to three orders of magnitude compared with the predictions of the Stokes-Einstein model of particle diffusion. These results are attributed to bridging interactions between particles arising from slow exchange kinetics of polymer segments at the polymer/metal interface. Experiments for which the molecular weights of the two polymer films are different are sensitive to the ability of polymer molecules to pass through the gold particle layer. Experiments done with thermally evaporated particles are consistent with a picture in which polymer molecules are able to freely pass through the gold particle layer. Results obtained with gold deposited by electron-beam evaporation are strikingly different. The gold in this case is not able to diffuse, and polymer molecules are not able to penetrate the gold layer. These results, in addition to preliminary results from optical absorption experiments, indicate that much smaller particles are obtained by electron-beam evaporation than by thermal evaporation.

Photographic applications rely greatly on the permeability and swelling behavior of multilayer thin films. This behavior is, at least, a function of (I) material properties such as particle size, percent solids and solubility, and (II) processing conditions that affect film formation, such as rate of drying, maximum web temperature and nature of underlying layers.

In order to test permeability of multilayer structures, an alkaline medium is allowed to permeate sample. In the structure under test, the bottom most layer is acidic in nature. This acid neutralizes the alkali as it permeates through the layers. Neutralization causes a change in ionic concentration in the sample and this is measured using a high frequency cavity sensor (commercially available as the conductivity Puntex technique) that changes its resonant frequency in response to change in conductivity of the sysytem. This frequency change can be monitored to to give a time transient for permeability. In the event that frequency changes even before neutralization has occured, it can be correlated to capacitance changes within the layers produced by swelling and water uptake.

For a porous layer within the sample, the permeation proceeds along two paths. One through the porosity and the other through the bulk. In this case the bulk signal is superimposed over the signal from porous component. For such a system, a transient of the time derivative of resonant frequency proved to be a useful tool to study interfacial interactions between the acid layer and the layer above it. Impact of drying was also inferred from similar measurements. Data indicate that the higher temperature of drying of constituent layers resulted in a microstructurally tighter film, that took longer time for the alkali to permeate.

Thermal behavior of a coextruded microlayer composite with 388 alternating layers of polycarbonate and polymethyl methacrylate (PMMA) was investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Two distinct glass transition temperatures were observed with DSC for the coextruded composite, however both were shifted very slightly towards each other, compared to the glass transition temperatures of the pure components, indicating limited miscibility. Adhesion between the alternating microlayers appeared to be very good; delamination did not occur after the microlayer composite was subjected to a high speed impact test. Adhesion is attributed to limited miscibility since little mixing resulted from the laminar flow which was required in the coextrusion process. DMA results revealed an additional damping peak, which was not observed with DSC, at a temperature between the glass transitions of the two components. This intermediate transition peak is more sensitive to change in frequency compared to the response for the individual pure components.

A combination of small angle neutron scattering (SANS) and contrast matching techniques is used to determine the size and quantity of voids incorporated during fabrication of polyethylene/carbon black composites. The analysis used to extract void morphology from SANS data is based on the three-phase model of microcrack determination via small angle x-ray scattering (SAXS) developed by W. Wu12 and applied to particulate reinforced composites.

The microphase separated morphology of diblock copolymers can be used to generate well-ordered nanometer scale patterns over a large area. To achieve this goal, it is important to understand and control the behavior of diblock copolymer thin films on substrates, which can differ from the bulk behavior. We have investigated the morphologies and ordering in thin polystyrene-polybutadiene (PS-PB) diblock copolymer films on bare silicon and silicon nitride substrates, and also on polymethylmethacrylate (PMMA) coated substrates. The PS-PB copolymers are synthesized to form, in bulk, PB cylinders or spheres in a PS matrix. In thin films (10–60 nm thick), prepared by spin-coating, we observe that the morphology and ordering of the microdomains are affected by strong wetting constraints and a reduced chain mobility on the substrate. The thinnest self-assembled layer of the copolymer films shows no in-plane microphase separation on both types of substrates. The PS blocks wet the PMMA substrates whereas the PB blocks wet the bare substrates as well as the air interface. Hence, different film thicknesses are necessary on the two types of substrates to obtain a uniform film of the first self-assembled cylindrical or spherical microdomain layer. The first layer of the cylindrical copolymer can vary from cylindrical to spherical morphology with a few nanometer decrease in film thickness. In the case of spherical PS-PB diblock copolymer films, we observe that the ordering of the microdomains is improved in the films on the PMMA substrates, compared to those on the bare substrates. We also demonstrate a successful transfer of the microdomain patterns to silicon nitride substrates by a reactive ion etching technique.

The effect of diblock copolymer on the phase-separation process of polymer blends has been investigated by using light scattering and optical microscopic observations. To quench the system into the two phase region, a shear-jump technique is employed instead of the conventional temperature-jump technique. The samples studied are blends of low-molecular-weight polystyrene and polybutadiene with and without added styrene-butadiene block copolymer as a compatibilizer. It was observed that the addition of diblock copolymers could accelerate the phase separation kinetics depending on the shear history. As the concentration of diblock copolymer increases, the distribution of domain sizes becomes narrower and the growth rate slows down. The extent of slowing-down depends on the molecular weight and concentration of the copolymer. The time dependence of domain growth is clearly observed with optical microscopy.

We present a new technique, laser induced decohesion spectroscopy (LIDS), which is capable of measuring the practical work of adhesion G between a transparent polymer film and an opaque substrate. In LIDS, a laser pulse directed onto the sample creates a blister at the film/substrate interface. The blister's internal pressure depends on the laser pulse energy, and at a critical pressure the sample fractures. We have derived a theoretical analysis of this experiment based on elasticity theory and fracture mechanics, and present the results. By measuring physical variables such as the thickness of the transparent polymer, the blister radius, and the blister curvature, it is possible to deduce G between the two coatings. Here we report G for a matrix of automotive finish systems consisting of four opaque basecoats of various colors (black, white, red, green) coated with a clearcoat of various thicknesses. We expect G to be a system parameter for each basecoat independent of clearcoat thickness. The values of G for the different basecoats yield the relative adhesion of the various pigmented paint formulations.

Image contrast for the examination of multiphase polymers in the transmission electron microscope (TEM) usually requires differential staining by a heavy element (Os, Ru, U). Staining methods have provided a wealth of microstructural information in polymers, but there are situations, particularly where high resolution is needed, where staining is undesirable or impossible. This research has collected microstructural information from multiphase polymers without heavy-element stains using spatially-resolved electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). The technique is known as spectrum imaging. The principal problems facing spectrum imaging in polymer applications are: (1) the identification of spectral fingerprints distinguishing different polymer phases; and (2) the extraction of meaningful microstructural data from large data sets where the signal is weak due to instrumentation and materials constraints. This paper describes applications of spectrum imaging to PE/PS and HDPE/Nylon 6 blends. The aim is to identify adequate spectral features and establish data acquisition and extraction procedures for applications to general, unstained, multiphase polymers.

Previous small-angle neutron scattering (SANS) studies [1] of heterogeneous ethylene-hexene linear low-density polyethylene (LLDPE) copolymers have confirmed the existence of a dispersed minority phase (volume fraction φ ∼ 10−2) consisting of highly branched, amorphous material. However, these experiments were conducted via a pinhole SANS spectrometer with an upper resolution limit ∼ 103 Å, whereas microscopy indicates that the dimensions of the disperse phase extend to the μm-range. We have therefore complemented these investigations via a Bonse-Hart ultra-small angle neutron scattering (USANS) instrument which increases the instrumental resolution in reciprocal space by a factor - 100, and thus particle size up to 30 μm can be resolved. The sensitivity of the USANS camera has recently been increased by two orders of magnitude by using the modified channel cut crystals [2], and the performance is therefore comparable to the best x-ray Bonse-Hart cameras. Xylene extraction removes the highly branched molecules and hence the volume fraction of the disperse phase is higher (φ ∼ 0.3) in the extracted material.

A newly available scanning probe microscopy, phase imaging, has been used to image polyethylene (PE) blends and composites. By providing not only a topographical map of the surface but also information on material properties, this technique has allowed ready identification of individual components within the mixtures investigated.

Micro-computed tomography (μCT) is a new and emerging technique for the nondestructive assessment and analysis of the three-dimensional trabecular bone architecture. The applications of μCT with respect to the analysis of bone are manyfold. Nevertheless, it also holds high promise for the microstructural measurement and analysis of porous biomaterials. For the purpose of the study, a desk-top μCT providing a nominal isotropie resolution of 14 μm was used. Since the polymeric material has a very low X-ray absorption coefficient, the scaffolds were stained prior to measurement using a commercial X-ray contrast agent. This allowed not only to acquire important microstructural features of the diree-dimensional scaffold but also to compute standard structural indices such as BV/TV, BS/BV, Tb.N, Tb.Th, Tb.Sp and the degree of anisotropy (DA) using mean intercept length measurements. The preliminary results show that different types of scaffolds can be distinguished both qualitatively (visualization) and quantitatively (morphometry) provided an adequate X-ray staining technique is used. It can be concluded that, in the future, μCT may be of considerable help in basic as well as in applied research and development.

The microstructure and thermal properties of copolymers of polyethylene terephthalate (PET) containing a crosslinkable terephthalic acid, 1,2-dihydrocyc Iobutabenzene 3,6 dicarboxylic acid (XTA) are reported. Wide angle x-ray scattering (WAXS) show that the addition of XTA does not alter the PET crystal structure in copolymers at low XTA contents. However, the degree of crystallinity drops for higher XTA levels. WAXS profiles show that PET-co-XTA 50% is amorphous, and that PEXTA homopolymer has a different crystal structure. Thermal data from DSC and TGA show that crosslinking of the benzocyclobutene groups (∼350°C) occurs at temperatures between melting (∼250°C) and degradation (∼400°C), making it possible to melt process the copolymers into fibers before the onset of crosslinking. Limiting oxygen index (LOI) measurements show that increased oxygen concentrations are required to sustain a stable flame in PET-co-XTA copolymers; whereas unmodified PET had an LOI value of -18%, the copolymers had LOI values near 32%. Further, while unmodified PET melts and drips as it burns, XTA copolymers formed a stable char that inhibiting flame propagation. An increased char was observed in optical micrographs for XTA containing polymers, and crystalline domains were observed near the burn surface in transmission electron micrographs.

Random copolymers of poly(methyl methacrylate-d8) (PMMA) and poly(methacrylic acid) (PMAA) were synthesized and blended with polyethylene oxide (PEO), and SANS was used to estimate the strength of interaction between the various polymer pairs. The addition of PMAA greatly reduced the scattering of the blend, giving a large negative Flory-Huggins interaction parameter. Copolymers of the type PMAA-g-PS, PMAA-r-PS, PMMA-g-PS, and PMMA-r-PS (g = graft, r = random) were used as compatibilizers for the melt blending of mixtures containing 80% PS and 20% PEO. Random copolymers containing half PMMA and half PS or half PMAA and half PS were ineffective compatibilizers while graft copolymers of these polymers produced a much finer dispersion of PEO in PS when blended at 190°C. Graft copolymers made with 90% PS were different, however, with PMMA grafts having only a small effect, while PMAA grafts having a large effect. Random and graft copolymers of PS and PMMA were also used to compatibilize blends of PS and PMMA. The results were similar to the same compatibilizers with blends of PS and PEO, with the graft copolymer causing a finer dispersion.