Switchable surfaces were fabricated by grafting of two different polymers: polystyrene (PS) and poly-2-vinylpyridine (PVP) onto the surface of Si-wafers. The binary brushes of various composition, molecular weight and grafting density were synthesized via free radical polymerization initiated by the azo-initiator covalently attached to the surface of Si-wafers. Investigations showed that the binary brushes are very sensitive to the surrounding media. After exposition to a solvent selective for PVP (ethanol, water + HCl) the surface becomes hydrophilic and the top of the layer is covered by PVP. After exposition to a solvent selective for PS (toluene) the surface becomes hydrophobic and the top of the layer is enriched with PS segments. Switching kinetics depends on grafting density and layer composition and varies from several seconds to several minutes at room temperature. Surface morphology of the layers switches as well as the wetting behavior. Results show that the layer reconstruction is reversible and can be repeated many times.

Using scaling theory, we determine the equilibrium behavior of a melt of functionalized and non-functionalized polymers confined between two infinite, planar surfaces, which model clay sheets. The functionalized chains contain two end-groups (one at each chain-end) that are highly attracted to the surfaces. Through these calculations, we delineate the conditions for the formation of thermodynamically stable polymer/clay mixtures in terms of the end-group adsorption energy, volume fraction of the end-functionalized chains, and polymer chain lengths.

The changes in hydrogen bonding at the interface of silica-reinforced polysiloxane composites due to aging in gamma radiation environments were examined in this study. Solvent swelling was utilized to determine the individual contributions of the matrix polymer and polymer-filler interactions to the overall crosslink density. The results show how the polymer-filler hydrogen bonding dominates the overall crosslink density of the material. Air irradiated samples displayed decreased hydrogen bonding at the polymer-filler interface, while vacuum irradiation revealed the opposite effect.

Poly(acrylic acid) (PAA) was grafted onto RF plasma treated PET films and onto SiO2 covered glass surfaces. PET films with various amounts of grafted PAA (0.4, 5, 11 and 19 μm/cm2) were immersed into a solution of collagen to allow for polyionic complex formation as a method for protein immobilization. It was found that the amount of complexed collagen was close to proportional to the amount of PAA. A closer investigation of the optical density of the PAA brushes close to the glass surface wa was performed using Reflectometric Inteference Spectroscopy. The supression of possibilities of extension and collaps of the brushes upon variation in pH is suggested to be caused by polyionic crosslinking between protonated collagen and deprotonated PAA. Such PAA-collagen surfaces with PAA concentrations lower that 10 μm/cm2 were shown to be suitable substrates for growth of human bladder smooth muscle cells.

Symmetric diblock copolymers undergo a disorder to order transition below a microphase separation transition temperature. In this temperature range the structure is characterized by alternating lamellae of thickness L. In thin film geometries, the lamellae are oriented normal to the substrate if there is a preferential interaction between either of the block constituents and the substrate/copolymer or copolymer/vacuum interfaces. Depending on the relation between the film thickness and L, the topography of the film might comprise of holes, islands or spinodal-like structures. We show that in a polystyrene-b-poly(methyl methacrylate) diblock copolymer of molecular weight 20, 000 g/mol, above the microphase separation transition temperature, the topography of the film depends on the thickness. A heirarchy of bicontinuous patterns and holes is observed with increasing film thickness for films thinner than 35 nm.

Microcellular polymeric foams (MPFs) hold tremendous promise for engineering applications as substitutes to their solid analogs in light of reduced manufacturing/materials costs and improved properties. We present a two-part study addressing the generation of such materials in the presence of supercritical carbon dioxide (scCO2). The first part describes the production of polystyrene MPFs in a continuous extrusion process, as well as the effect of operating conditions such as temperature and CO2 concentration on foam morphology. The second part discusses microcellular foaming of poly (vinylidene fluoride) (PVDF), a semicrystalline polymer, via blending with the amorphous polymer poly (methyl methacrylate) PMMA. Foams of pure PVDF possess ill-defined morphologies, whereas those of PVDF-PMMA blends show an improvement with cell sizes on the order of 10 mm or less and cell densities in excess of 109 cells/cm3.

Neutron reflectometry is used to measure the rate of interdiffusion between bilayer samples of deuterated and hydrogenated poly(methyl methacrylate) (PMMA) films with the polymerpolymer interface near the native oxide surface of a silicon wafer. In this work, the effects of a favorable substrate interaction and the molecular weight of each polymer layer are determined. Both the film thickness and the molecular weight of the lower d-PMMA layer are kept constant with a thickness of approximately one radii of gyration (Rg) of the polymer and the molecular weight of the upper hydrogenated layer is varied. Earlier experiments show that the mobility of the polymer chains within Rg of the substrate is much lower than that of the bulk, suggesting that the mobility of surface-pinned polymers controls the interdiffusion rate. In this study, we find that the rate of interdiffusion is strongly dependent upon the molecular weight of the top layer.

The reaction of perdeuterated amino-terminal polystyrene (dPS-NH2) with anhydrideterminal poly(methyl methacrylate) (PMMA-anh) at a PS/PMMA interface has been observed with forward recoil spectrometry (FRES). Bilayer samples were constructed by placing thin films of PS containing ∼8.5 wt % dPS-NH2 on a PMMA-anh layer. Significant reaction was observed only after annealing the samples at 174°C for several hours, a time scale at least two orders of magnitude greater than the time required for the dPS-NH2 chains to diffuse through the bulk PS layer. The topography of the interfacial region as copolymer formed was measured using atomic force microscopy (AFM). Roughening of the PS/PMMA interface was observed to varying degrees in all annealed samples. Furthermore, the extent of this roughening was found to depend on the PS matrix molecular weight. Reaction in the samples with a high molecular weight PS matrix resulted in a root mean square roughness approximately equal to the radius of gyration Rg of the copolymer. However, approximately twice as much roughening was observed in the low molecular weight PS matrix. This study reveals how the molecular weight of one of the phases can affect the rate of reaction at a polymer/polymer interface.

We investigate the mechanism by which an aminosilane adhesion promoter strengthens the interface between benzocyclobutene (BCB) and an oxidized silicon wafer. The adhesion promoter film is characterized using AFM and angle-resolved XPS to identify surface bond density, morphology, and chemistry for a range of adhesion promoter spin-coat solution concentrations. The adhesion strength of the SiO2 / adhesion promoter / BCB interface was also evaluated. The 0.0083% solution produces what appears to be a single monolayer on the surface, while the 0.014% concentration yields two monolayers. In both cases, the directionality of the films is preserved. That is, the amine functional group is oriented toward the BCB, and the silane groups are oriented toward the silicon oxide substrate. Finally, this solution concentration is optimized with respect to the mechanical strength of the interface, and 0.01% concentration is found to perform best. When the adhesion data is plotted versus the calculated surface bond density, a nearly linear relationship is seen, supporting a direct correlation.

In this paper we present three novel routes for the preparation of surface-attached polymer networks. In one system the network is formed in situ at the surface by thermal polymerization in solution and from the surface. Another synthetic route starts with a surface that carries photoreactive groups. Onto this surface a polymer is deposited that also carries photoreactive groups and both the crosslinks of the network and the covalent bond to the surface are formed by UV illumination. The third approach start with the in situ formation of surface-attached copolymers that again carry photoreactive groups that are subsequently linked together by UV light. We present evidence for the successful synthesis of these networks and their superior adhesion on glass surfaces.

The glass transition temperature (Tg) of thin supported films of stereoregular poly(methyl methacrylate) on silicon has been investigated by ellipsometry in temperature. The Tg of the spin coated layers of isotactic PMMA increases for thickness lower than 100 nm whereas a depression of the Tg is observed for the syndiotactic PMMA. This opposite trend in the Tg variation in thin layer between the two isomers evidenced a fascinating effect of the chain organization at an interacting interface. Hydrofluric acid surface etching of the silicon wafer was shown to decrease the threshold thickness at which the change in Tg occurs for both PMMA isomers. The influence of the interfacial interactions along with the tacticity dependent characteristics of the polymer will be discussed.

Cryogenic mechanical alloying has been employed to blend poly(methyl methacrylate) (PMMA) with up to 25 wt% polyisoprene (PI) and poly(ethylene-alt-propylene) (PEP). Mechanical milling of the individual polymers reveals that their molecular and bulk properties depend sensitively on milling time, post-annealing and, for PMMA, temperature. Characterization of the as-milled blends by scanning transmission x-ray microscopy and transmission electron microscopy has demonstrated intimate (nanoscale) dispersions within the blends, with the degree of mixing increasing with increasing milling time. Phase domains as small as 10 nm are observed after alloying for 10 h. Post-annealing of the blends above the Tg of PMMA (which depends on milling time) induces morphological changes, which differ for blends containing PI and PEP. In blends composed of PEP, the fine dispersions gained as a result of milling are largely compromised. Conversely, PI crosslinking hinders molecular mobility so that the milling-induced nanoscale dispersions of PI in PMMA are, for the most part, retained even after long-term annealing at elevated temperatures.

Adhesion strength of polyimide/Cr interfaces was measured using T-peel test on polyimide/Cr/Cu structures fabricated on BPDA-PDA polyimide, and correlation between adhesion strength and peeling angle has been investigated. Adhesion strength of BPDA-PDA/Cr interface decreased with increasing the thickness of Cr/Cu metal films to a critical value, and then increased with further increasing metal film thickness. When the thickness of Cr/Cu metal films was below a critical value, plastic bending of metal films mainly occurred during T-peel test. With metal films thicker than a critical thickness, however, plastic bending of polyimide film has been observed. A critical thickness of metal film, where transition from metal bending to polyimide bending occured, became thinner with decreasing the yield strength of metal film and increasing thickness of polyimide substrate. Without depending on the plastic bending of metal film or polyimide substrate, adhesion strength increased with increasing the peeling angle during T-peel test.

Researchers have shown that thin, nonwetting, liquid homopolymer films dewet substrates, forming patterns that reflect fluctuations in the local film thickness. These patterns have been shown to be either discrete cylindrical holes or bicontinuous “spinodal-like” patterns. In this paper we show the existence of a new morphology. During the early stage of dewetting, discrete highly asymmetric holes appear spontaneously throughout the film. The nucleation rate of these holes is faster than their growth rate. The morphology of the late stage of evolution, after 18 days, is characterized by a bicontinuous pattern, distinct form conventional spinodal dewetting patterns. This morphology has been observed for a range of film thicknesses between 7.5 and 21nm. The structural evolution of this intermediate morphology is discussed.

The fracture of highly-crosslinked networks is investigated by molecular dynamics simulations. The network is modeled as a bead-spring polymer network between two solid surfaces. The network is dynamically formed by crosslinking an equilibrated liquid mixture. Tensile pull fracture is simulated as a function of the number of interfacial bonds. The sequence of molecular structural deformations that lead to failure are determined, and the connectivity is found to strongly control the stress-strain response and failure modes. The failure strain is related to the minimal paths in the network that connect the two solid surfaces. The failure stress is a fraction of the ideal stress required to fracture all the interfacial bonds, and is linearly proportional to the number of interfacial bonds. By allowing only a single bond between a crosslinker and the surface, interfacial failure always occurs. Allowing up to half of the crosslinker's bonds to occur with the surface, cohesive failure can occur.

Poly (methylphenylphosphazene) (PMPP) is an example of a unique class of inorganic polymers with alternating – (P=N)– backbones. Chemical modification of bulk PMPP can result in changes of physical properties such as chemical resistance, onset temperature of thermal degradation, elasticity, and flexibility. Surface modification of PMPP allows tailoring of the chemical properties at the polymer interface while maintaining the integrity of the bulk polymer. In this research, PMPP thin films were treated to form carboxylate or carboxylic acid groups at the surface. Surface modification was monitored by following changes in contact angle. The hydrophobic/hydrophilic interactions of carboxylated PMPP surfaces allow for mesoscale interactions of thin polymer films.

A number of researchers have reported an anomalous lowering of viscosity in immiscible polymer blends. Slip at the interfaces between the polymers has been proposed to explain these observations. Because of the complex morphology developed in melt blends it is difficult to test the slip hypothesis. However, using layer multiplication dies in coextrusion, two or more polymers can be alternatively combined into hundreds or even thousands of continuous layers generating a large amount of well-defined interfacial area. Polypropylene (PP) and polystyrene (PS) with closely matched viscosity were blended in a twin screw extruder and also coextruded into 2, 32, 128 alternating layers. The steady shear and dynamic shear viscosity of the blends was measured in a capillary rheometer and a rotational shear rheometer using parallel plates geometry. While the steady shear viscosity of the blends was lower than that of both homopolymers, the dynamic shear viscosity of the blends was the same as that of the homopolymers. The pressure drop of the coextruded multilayer melts through a slit die was lower than that of both homopolymers and decreased with an increase in the number of layers. From these results interfacial slip viscosity and velocity were estimated. Addition of diblock copolymer was able to suppress interfacial slip.

A new diamine monomer was synthesized by condensing 4,4'-methylene dianiline with 1,4-benzoquinone. The monomer was condensed with 3,3',4,4'-benzophenone tetracarboxylic dianhydride to give a polyamic acid that was soluble in N-methyl-2-pyrrolidinone. The polyamic acid was cast onto iron and thermally imidized to give the amine-quinone polyimide (AQPI-2). AQPI-2 had a thermal decomposition temperature (10% weight loss) of 540°C and a glass transition near 290°C, values typical of polyimides. The degradation of the coating on iron after exposure to NaCl electrolyte was followed by electrochemical impedance spectroscopy. Under these conditions a conventional polyimide failed after 3 days exposure, while AQPI-2 showed no change after 34 days exposure. The adhesive bond between the amine-quinone polyimide and the iron surface was so strong that it could not be broken by the electrolyte.

In this study we combined nanoindentation techniques with mechanics-based models to determine interfacial fracture energies in a 16 μm thick styrene-acrylate film on T-6061 aluminum sheet and a 1.6 μm thick Epon 828/T403 epoxy film on sputtered aluminum. For the styrene-acrylate film, interfacial fracture occurred at a fracture energy of 8.9 J/m2. The epoxy film failed much more readily with a fracture energy of 0.2 J/m2. However, the addition of an adhesion-promoting interlayer improved the epoxy film performance to the point where the films did not fail even when the indentations exceeded the film thickness.

The paper investigates the structure formation in thin polymer blend films. Such a control of the structure formation is of great importance in many industrial applications. In this paper we follow two different routes in order to control the surface structures. One is the creation of surface structured through a dewetting of the thin films. The dewetting is archived through a plastification of the film either annealing or by swelling in a solvent atmosphere. As a result the control of this process allows to form very small and regular structures. The second route utilizes the demixing of an strongly immiscible polymer blend during preparation and yields much less defined structures. To allow a quantitative comparison if the evolving surface structures are statistically analyzed in terms of their rms-roughness and Fourier spectrum and compared with predictions from existing growth models.