Static and impact fracture toughness of a Polybutylene terephthalate (PBT)/Polycarbonate (PC)/Impact modifier (IM) blend was studied at different temperatures. The experimental results were interpreted by the specific fracture work concept and J-integral analysis. It is found that the specific fracture work concept characterizes the impact behavior of the blend very well. In the static fracture tests the specific fracture work gives the crack initiation resistance of the blend which is consistent with the JIC value obtained. The effect of temperature was also examined and the fracture mechanisms were investigated via TEM and SEM. Extensive cavitation of the impact modifiers and plastic flow of matrix in the vicinity of the crack tip is believed to be the major toughening process of the enhanced fracture toughness.

A novel toughened epoxy resin was obtained by using an epoxy-terminated prepolymer prepared from epoxy resin and hydroxy-terminated butadiene-acryl-onitrile copolymer (HTBN), and an amine curing agent. The cured, toughened resin has excellent mechanical properties due to the two-phase structure which was observed using SEM and TEM. When the HTBN content is 15 phr, the rubber phase separates effectively and the specimen presents a fine two-phase structure. However, when the HTBN content reaches 25 phr, the morphology appears continuous.

Rubber-toughened poly(methyl methacrylate) materials have been prepared by blending poly(methyl methacrylate) with specially-synthesised, refractive index matched particles containing two, three and four radially-alternating rubbery and glassy layers. The paper describes the effects upon mechanical properties of (i) two-, three- and four-layer particle structure and (ii) particle diameter and glassy core size for three-layer particles.

This paper describes the blends of epoxy/polybutadiene and the application of the blends to the encapsulation of capacitors. Experiments showed that the hydroxy-carboxyl terminated polybutadiene (HCTPB) had a good toughening effect on epoxy resins, and the blends of epoxy/HTPB or epoxy/HCTPB had good craze resistance at low temperatures. The phase separation and dynamic mechanical analysis of these blends are discussed below.

We have developed an amino-functional silicone resin to toughen epoxies which, when prereacted with the epoxy function in resins, undergoes in-situ phase separation during final epoxy curing. SEM analyses of the morphology of fracture surfaces of MY720- DDS, Epon 828-DDS and other epoxy matrices modified with the silicone resin showed rough surfaces with the formation of very uniform <10 μm spheres. Silicon and sulfur elemental distribution mapping showed silicon rich spheres embedded in an epoxy matrix. We report cavitation, particle debonding and pull-out, and an increases in fracture surface area as possible modes of toughening. Silicone modified materials give improvements in slow strain rate G1c fracture toughness measurements of 250–400%, similar to carboxy terminated polybutadiene-acrylonitrile copolymer (CTBN) modifiers, but with a much smaller flexural modulus loss. The Tg of the modified epoxy matrices are maintained, moisture resistance is improved, and flammability is reduced.

A means of generating high temperature polymer foams which leads to pore sizes in the nanometer regime has been developed. Foams were prepared by casting block copolymers comprised of a thermally stable block and a thermally labile material, such that the morphology provides a matrix of the thermally stable material with the thermally labile material as the dispersed phase. Upon a thermal treatment, the thermally unstable block undergoes thermolysis leaving pores where the size and shape of the pores are dictated by the initial copolymer morphology. Nanopore foam formation is shown for triblock copolymers comprised of a poly(phenylquinoxaline) matrix with poly(propylene oxide) as the thermally labile block. Upon decomposition of this block, a 10–20% reduction in density was observed, consistent with the initial PO composition, and the resulting PPQ foam showed a dielectric constant of ∼ 2.4, substantially lower than PPQ (2.8). Small angle X-ray scattering and transmission electron microscopy show pore sizes of approximately 100Å.

Electrically conducting patterns can be generated in insulating polymers or composites either via UV-flood exposure through a mask or via laser irradiation. Various lithographic concepts starting either from conventional or custom tailored polymers or from special composites have been developed and tested. Thereby electrically conducting polymers are photogenerated either directly from a self-developing photosensitive precursor or via a twocomponent redox approach using one of the components as a vapor in an otherwise dry process. The electrically conducting patterns so obtained may be reinforced by plating them with metals electrogalvanically. These processes may also be combined with laser induced ablation, whereby the intensity of the laser beam may be gated to either induce electrical conductivity of the substrate or to ablate it without rendering it conductive. Analogously, thin films of electrically conducting polymers on top of insulating polymer layers can be patterned directly using excimer laser ablation.

Positron annihilation lifetime spectroscopy (PALS) is used to investigate polymer-based molecular composites of two separate thermotropic liquid crystalline polymers (TLCPs) and the thermoplastic matrix polyetherimide. Trends in PALS spectral components obtained isothermally at 20°C and 120°C as a function of TLCP content are discussed as a function of free volume and molecular structure. Differential scanning calorimetry was employed as a complementary technique to investigate the differences in miscibility of the two systems and possible effects on positron lifetime values.

Interpenetrating polymer networks (IPNs) have been synthesized from polymers that form miscible polymer blends. Full, semi-I and semi-II IPNs made from polystyrene-d8 and poly(vinylmethylether) can be made to phase separate by incorporating low levels of crosslinking. However, blends of these polymers have a negative Flory-Huggins interaction parameter, making them highly miscible. This indicates that formation of IPNs favors phase separation relative to blends.

IPNs made from polystyrene-d8 and polystyrene-h8 show that increased crosslink density also destabilizes the mixture as shown by small angle neutron scattering.

IPNs have also been made by crosslinking end functionalized polydimethylsiloxanes in the presence of nonfunctionalized, deuterated siloxanes. These IPNs are also destabilized by increasing crosslink density, suggesting that the destabilization is due to the network, and not to the particular type of network forming reaction.

The application of the sol-gel process for the formation. of inorganic-organic composites has received a great deal of attention in recent years. We have focused our efforts in this area toward the development of simultaneous polymerization/sol-gel reactions for the developement of inorganic-organic composites with a wide range of polymers. Further research in this area has led to the design and synthesis of tetraalkoxysilanes, and more recently, poly(silicic acid esters) possessing polymerizable alkoxides for the synthesis of non-shrinking sol-gel composites.

Elastomeric networks prepared by tetrafunctionally end linking hydroxyl-terminated poly(dimethylsiloxane) chains (PDMS) were filled by the in-situ precipitation of silica. The resulting networks were investigated under uniaxial elongation, biaxial extension, shear, and torsion in order to characterize the resulting changes in mechanical properties. Compared with the unfilled networks, the silica-filled materials showed large reinforcing effects. Specifically, their values of the modulus, ultimate strength, and rupture energy increased significantly. The results thus indicate that the PDMS networks filled by the in-situ precipitation of silica have very good mechanical properties in several, rather different deformations. Examples of other deformations of interest are equilibrium swelling, and dynamic cycling for characterization of compression set.

A detailed investigation of the molecular weight dependence of silica growth in in situ filled polydimethylsiloxane/tetraethylorthosilicate (PDMS/TEOS) materials was conducted using small angle neutron scattering (SANS). Composite materials were produced by using TEOS to simultaneously produce the glassy filler phase and to crosslink linear, hydroxyl terminated PDMS of variable molecular weight, M. Correlated domains of glassy filler were produced. The morphology of the in situ filled material showed a definite dependence on the molecular weight of the precursor polymer. The scale, R, of the glassy domains follows de Gennes' description of phase separation in a crosslinked system (R ∝ M1/2).

Selected topics on the use of particulate solids to build modulus and strength in silicone elastomers are briefly reviewed. Included are recent views advanced to explain the reinforcement phenomena, some more current approaches to particulate reinforcement and recommended areas for future endeavor.

A cross-linked copolymer of vinylferrocene and dimethyl-acrylamide is generated inside the less dense microporous domains of a cross-linked polydimethylacrylamide matrix. I.S.E.C. and E.S.R. data reveal that the obtained composite is in fact an I.P.N.(Interpenetrating Polymer Network) material.

Composite liquids – liquids composed of polymers, particles, and small molecule solvents – constitute an important class of synthetic and naturally occurring materials. Examples include molecular composites, ceramic precursors, lubricants, adhesives, and the cytoplasm in biological cells. Due to the complexity of these liquids, experimental studies of precisely defined systems are essential in developing an understanding of the interactions between all components in the liquid. Unfortunately, such fundamental studies have been relatively rare due to both the difficulty of synthesizing precisely defined composite liquids and the lack of adequate experimental methods to monitor the motions of the various constituents.

We have recently reported the synthesis, characterization and some studies of the dynamics of a rod/sphere composite liquid system [1]. In our case the “polymer” constituent is a rigid rod polymer, poly(γ-benzyl-α,L-glutamate) (PBLG). Rigid rod polymers are frequently used in composite liquids as viscosity enhancers. PBLG is commercially available in a wide range of molecular weights and its static and dynamic behavior in dilute and nondilute solutions has been studied. It, in addition, forms mesophases in the concentrated regime. The ceramic “particles” in our composite liquid are coated silica spheres. These spheres are synthesized by the method of Stober et. al. [2] and coated with an organic coating (3-(trimethoxysilyl)propyl methacrylate (TPM)) following a procedure based on that of Philipse et. al. [3] to render them dispersible in organic solvents. The spheres with sizes in the range from 10 nm up to almost 1μm can be synthesized with a relatively narrow size distribution. The solvent in our studies is dimethylformamide (DMF). Both polymer and particle are dispersible as singlets (nonaggregating) in these solvents and the PBLG retains its rigid (or nearly rigid) rod conformation. The diffusion of both the polymer and the sphere in the composite liquid is measured by dynamic light scattering (DLS) [4]. In this paper, we focus on the spheres and examine the effects of rod concentration and rod length on the diffusion of different size spheres. This study suggests that the solution microstructure has an important influence on sphere diffusion.

Thin films of silsesquioxane, (HSiO3/2)n, were applied to aluminum panels and to CMOS microelectronic circuit surfaces by spin or dip coating organic solutions of the silsesquioxane. Nanoporous silica was obtained by oxidation of the silsesquioxane. These nanoporous silica films were then vacuum infiltrated with various viscosities of polydimethylsiloxanes (PDMS) to form hydrophobic nanocomposites. The nanocomposite films were shown to provide superior hermetic protection against salt fog exposure when compared to PDMS and silica films alone.

The composite films were characterized by FTIR and optical microscopy. FTIR spectra showed that the silica served as a skeletal framework holding the hydrophobic PDMS in place and preventing loss of adhesion. This is in contrast to PDMS films alone in which blistering of the film from the substrate can occur, thus, allowing ions and moisture to reach the surface and corrosion to take place.

Sol-gel synthesis can be used for generating nano particles from a variety of compositions. In order to avoid aggregation and undesired gelation, it is necessary to react the particle surfaces with ligands reducing their interaction but allowing the incorporation into desired matrices. Three examples (semiconducting and metal quantum dots, ZrO2 and Al2O3 containing composites) are described, their properties and some applications for optics and protective coatings are discussed.

The frequency dependent electrical properties of the intercalated polypyrrole/V2O5 system have been measured. This study continues the investigation into the charge transport mechanisms that have been identified in these layered polymer/inorganic composites. The polypyrrole/V2O5 material is prepared by in-situ oxidative polymerization of pyrrole in the intralamellar space of the V2O5 xerogel. This process produces a layered, two-dimensional structure in which the charge transport properties result from two parallel conduction paths: the polypyrrole chains and the V2O5 layers. Impedance spectroscopy data have been collected from free-standing film samples of the layered polypyrrole/V2O5. The experiments were conducted over the frequency range of 10 Hz to 0.5 GHz and a temperature range of 77 to 310 K. The polypyrrole/V2O5 impedance results are presented in various equivalent forms and compared to data collected from pristine V2O5·nH2O, and reduced Cs0.14V2O5·nH2O.

Simultaneous additions of lanthanum aluminate(LAL) and Al2O3 to Ce-TZP (12mol% CeO2-ZrO2) lead to the in-situ formation of lanthanum- β-alumina(LBA) platelets (∼1.0.μ m in width and 5 ∼10 μ m in length) in the Ce-TZP matrix during sintering. The composites showed a fracture toughness(SEPB method) of 9.5 MPa · m0.5 and fracture strength of 960 MPa. which are remarkably improved from Ce-TZP sintered body (8.5 MPa · m0.5 and 560 MPa).

The composites also exhibit the no degradation by hydrothermal treatment.

Submicron and nanocrystalline grain sizes were achieved in the Al2O3-ZrO2 eutectic composition through conventional, microwave and plasma sintering of rapidly solidified starting powders and through shock compaction of commercial powders. Post sintering studies revealed nanocrystalline intragranular ZrO2 in the 1–2 μm Al2O3 grains, which is thought to be a result of the solidification synthesis. Additions of B2O3 greatly increased the final density through liquid phase sintering. Shock compression of commercial powders produced dense, crack-free, fine grained ceramics with loading pressures up to 9.1 GPa and a metastable ZrO2 phase under higher pressures.