Nanoindentation test techniques were combined with deposition of highly stressed overlayers to study the interfacial fracture susceptibility of spin coated Epon 828/T403 on aluminized glass substrates as a function of film thickness. The test techniques required to induce fracture differed between samples. Nevertheless, the resulting interfacial fracture energies decreased monotonically with film thickness to a value near 0.5 J/m2. This value is higher than the ‘true work of adhesion' for uncured epoxy oliogomers on a methyl-terminated aluminum surface. However, it may indicate that we have irreversible specific interactions such as hydrogen bonding. Then 0.5 J/m2 may be near the fundamental value for such an interaction, or the ‘practical work of adhesion’.

Ionically self-assembled monolayers (ISAMs) have recently been shown to spontaneously exhibit a polar ordering that gives rise to substantial second order nonlinear optical response. The deposition of ISAMs has been studied in situ via second harmonic generation. This is a particularly sensitive probe of the growth of nanometer-thick films since the centrosymmetry of the immersion solutions, the substrate, and the container yields no SHG contribution from these bulk components. Upon immersion in the NLO-active polyelectrolyte solution, the SHG rises sharply over the first minute. When a film is immersed into salt water, the SHG decreases significantly only to be restored when the salt solution is replaced with deionized water.

Adhesion at the fiber-matrix interface of composites is often related to a combination of factors such as mechanical interlocking, physico-chemical interactions, and chemical bonding of the fiber-matrix interphase region. We demonstrate the use of self-assembled monolayer (SAMs) approach for depositing silane coupling agent on glass fiber and studying the impact of the individual interactions on the adhesion process. Through some unique chemistry, functionalized and non-functionalized C11 chlorosilanes were deposited on to E-glass fiber and modified. The adhesion of diglycidyl ether of bisphenol-A (DGEBA) cured with meta-phenylene diamine (m-PDA) to SAM layer on E-glass fibers was measured by performing single fiber fragmentation tests (SFFT). The extent of adhesion between the fiber and matrix was found to be dependent on carbon chain length of coupling agents, and the functional group at the end of the SAMs layer. Furthermore, the contributions to adhesion by physico-chemical interaction and covalent bonding has been individually assessed.

SFM probe tips have been functionalized with polypropylene (PP) layers by immersion into dilute solution. The immersion process was carefully controlled and monitored using a programmable dynamic contact angle analyzer (DCA) equipped with a microbalance and a motor capable of speeds ranging from 2-24 μm/s. Probes were submitted to treatment with ozone prior to coating to eliminate surface contamination, particularly silicone oils, resulting from commercial packaging methods. The chemical composition of the tip surface after the cleaning, coating, and scanning processes was analyzed by Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). The three-dimensional tip shape and dimensions before and after coating were evaluated by blind reconstruction from images of a columnar titanium thin film using Digital Instruments' Tip Evaluation algorithm. Coating thicknesses of up to 20 nm were calculated, with the thicker coatings showing a larger degree of non-uniformity.

A key process in our approach to monolithic three-dimensional (3D) integration is the bonding of 200-mm wafers using dielectric polymer thin films as bonding glues. After discussing the desired properties of polymer thin films, we describe how bonding protocols are evaluated using silicon and glass wafers. After bonding, the fraction of bonded area was inspected optically and a razor blade method was used to indicate bonding strength. Thermal stability and bonding integrity were evaluated using thermal cycling and backside grinding and polishing. To date, we have studied benzocyclobutene (BCB), Flare™, and methylsilsesquioxane (MSSQ) and Parylene-N as bonding glues. Wafer pairs bonded using BCB showed a larger fraction of bonded area, and those using Flare indicated higher thermal stability. Both BCB and Flare glues provided good bonding integrity after backside grinding tests. Changes in the chemical structures of BCB and Flare glue during bonding were analyzed using FTIR in order to understand the bonding mechanism and to improve the bonding process.

The nanoscale patterns formed by poly(methyl methacrylate) (PMMA) stereocomplexes at the surface of silicon wafers, glass and mica, were investigated by tapping mode atomic force microscopy (TM-AFM). The effects of the solvent nature, PMMA concentration, i/s-ratio (stoechimetry) and surface nature on the morphology of the stereocomplex thin layer at a surface were addressed. The aggregation phenomena are well described by the diffusion limited cluster-cluster aggregation model (DLA) and the fractal exponent D calculated. The i/s-ratio strongly influences the fractal exponent D which is equal to 1.35 for the 1:2 ratio is lower than for the other i:s ratios which are 1.46, 1.61, 1.82 for 1:1, 2:1 and 4:1 ratios, respectively. The low values of the fractal dimension D are indicative of a fast aggregation process and higher values of D correspond to a slow aggregation process.

Significant changes in materials properties of siloxane based polymers can be obtained by the addition of inorganic fillers. In silica-filled polydimethylsiloxane (PDMS) based composites the mechanism of this reinforcing behavior is presumably hydrogen bonding between surface hydroxyls and backbone siloxane species. We have chosen to investigate in detail the effect of chemisorbed (hydroxyls) and physisorbed water on the interfacial structure and dynamics in silica-filled PDMS based composites. Toward this end, we have combined molecular dynamics simulations and experimental studies employing DMA and NMR analysis. Our results suggest that the polymer-silica contact distance and the mobility of interfacial polymer chains significantly decreased as the hydration (hydroxyl and/or physisorbed water) level at the interface was reduced. The reduced mobility of the PDMS chains in the interfacial domain reduced the overall motional properties of the polymer, thus causing an effective "stiffening" of the polymer matrix. The role of the long-ranged Coulombic interactions on the structural features and chain dynamics of the polymer were also examined. Both are found to be strongly influenced by the electrostatic interactions as identified by the bond orientation time correlation function and local density distribution functions. These results have important implications for the design of nanocomposite silica-siloxane materials.

The adhesion of a thin-film of PMMA to substrates consisting of Ti or Al was measured using a four-point bend technique. Initial results revealed that cracks propagated along the PMMA/metal interfaces at stable rates. Subsequent experiments showed intermittent (“stick-slip”) interfacial crack propagation consisting of cycles of crack initiation, unstable propagation, and arrest. To investigate the origin of stick-slip fracture behavior at PMMA/metal interfaces the effect of water uptake by PMMA on fracture behavior was studied. Four-point bend sandwich specimens were stored in vacuum or deionized water environments at either 25 °C or 65 °C for a period of 7 days prior to testing. The PMMA/Al system stored at 25 °C showed a transition from stable to stick-slip crack propagation when the exposure environment was changed from vacuum to water. Interface crack propagation was stable for both the PMMA/Ti and PMMA/Al systems on exposure to 65 °C water, but the critical strain energy release rate, GC was markedly reduced, indicating that water uptake promoted stick-slip fracture up to some critical degree of hydration. No change in stick-slip behavior was observed from a variation in imposed load-point displacement rate.

The stability and interfacial structure of ultra thin films of perfluoro-ion containing polymers (ionomers) have been studied using atomic force microscopy and neutron reflectometry. These complex polymers have significant technological applications from thin coatings, to fuel cells as polymer electrolyte membranes, to protective clothing. In particular we focused on the study of [(CF2CF2)n (CF2CFR)]m where R= [OCF2CF2SO3 (X)] and X=H, (800 equivalent weight), coated on silicon oxide. Neutron Reflectometry has shown that film consists of three distinct regions: a region of high density at the interface with the silicon oxide, an intermediate layer with constant density and an air-interface layer where the density decreases due to interfacial roughness. In contrast to noionic polymers, the films proven stable as a function of annealing time above the bulk glass transition, i.e the films do not dewet. This stability is attributed to electrostatic interactions.

Polymer thin films having tetraphenyl diaminobiphenyl (TPD) side chain were prepared by evaporating its acrylate monomer by the ionization-assisted deposition (IAD) method. IR absorption and GPC analyses showed that the electron irradiation to the evaporated material works efficiently to initiate the polymerization reaction on the substrate surface, while the simple evaporation produced films mainly consisting of the monomers. The reaction was enhanced by increasing the substrate temperature. However, the surface roughness increased with increasing substrate temperature. Post annealing can be an alternative method to enhance the polymer yield. Light emitting diodes were prepared by stacking the TPD polymer layer, Alq3 emissive layer, and Al electrode on ITO-coated glass. The IAD polymerization can be a useful method for preparing polymer thin films for organic optoelectronic devices.

The effect of a curved solid wall on the conformations of long, flexible polymer chains is studied in a dense polymer system and in the athermal limit by means of lattice Monte Carlo simulations. It is found that the wall does not perturb the atom number density, which is constant throughout the volume of the polymer, however the chain end density is higher at the wall compared to the bulk. The segregation effect decreases with increasing wall curvature. The bonds are preferentially oriented in the direction tangential to the wall over a two-bond thick layer next to the wall. When probing the preferential orientation on the chain segment length scale, the perturbed region has a thickness on the order of the probing metric considered. The chain mobility is evaluated by computing the bead diffusion coefficient in the direction perpendicular and tangential to the curved wall, and as a function of the distance from the interface. The bead mobility is reduced in a two-bond-thick layer in the vicinity of the wall in both the normal and tangential directions, the reduction being more pronounced in the normal direction. The mobility is seen to decrease with increasing wall curvature. The reduction is most pronounced when the particle size becomes smaller than the chain radius of gyration in the bulk, situation in which the average chain surrounds the particle, which hence becomes an effective entanglement site for the chains. This explains in part the increased strength of polymer-based nanocomposites with small fillers.

In this work we report on the influence of interfaces (metal/film, ITO/film) on the optical properties of ultrathin layers of poly(p-phenylene vinylene), PPV, adsorbed by self-assembly. PPV films were prepared exploiting the self-assembly method (SA) in addition to a low temperature conversion process for PPV. Using atomic force microscopy we show that 0.5 nm thick PPV layers can be homogeneously deposited on different metals (50% transmission Au, Cu, Pt, Ag, Cr films), glass and ITO surfaces. Absorption measurements reveal that the transitions involving φ-φ* conjugated states are blue shifted to different extents depending on the interface and on the film thickness. This indicates different extensions of interfacial disorder in the PPV layers. The ITO/PPV interface has the highest extension for disorder (∼16 nm) and highest surface roughness (RMS∼2.5 nm) while the lowest values (∼5 nm and 0.6 nm, respectively) were found for the quartz/PPV interface. The metal interface induces significant luminescence quenching and spectral shifts, which depend on the type of metal used. The effect from incorporation of carbonyl and from chemical modifications of the ITO/organic interface during PPV thermal conversion is discussed.

Polymer thin films and surfaces play a major role in the functionality of many components in the microelectronic and automotive industries. The characterization of their mechanical properties at a nanometer scale remains a technological challenge. Instrumented indentation testing with frequency-specific dynamic analysis provides access to viscoelastic measurement of near surface properties of polymeric materials. Development of biomaterials for tissue replacement raises the interest for testing polymers with storage modulus of less than 1 MPa. The development of specific testing methodologies with improved accuracy and precision for evaluating very soft polymeric materials are presented in this work. Results at various frequencies for polyurethane and polydimethylsilane using both Berkovich and Flat punch geometries are compared.

We investigate the adsorption of copolymers from copolymer / homopolymer mixtures at planar chemically patterned surfaces. The Monte Carlo bond fluctuation model is used in conjunction with configurational biased Monte Carlo moves to study the effect of: i) the copolymer microstructure, ii) the size and spatial distribution of chemical heterogeneities on the substrate, and iii) the polymer/substrate interactions on the ability of the copolymer to recognize the substrate chemical pattern. Our results confirm that the surface pattern recognition occurs whenever the characteristic size of the copolymer distribution sequence matches that of the surface heterogeneity domain. Moreover, the copolymer sequence distribution plays a crucial role in determining the extent of the surface pattern transfer into the bulk material. Our results reveal that more pronounced surface pattern transfer into the bulk occurs for small attractions of the adsorbing species to particular surface domains relative to the large attractions.

We have used the surface forces apparatus to measure the structural and frictional force profiles between opposing, solvated brush layers as a function of temperature. Two different polyvinylpyridine-polystyrene [PVP-PS] diblock copolymers were used to make PS brushes. The molecular weights (in thousands) of these PVP-PS materials were [114/103]k, [30/70]k, respectively. Structural and frictional force profiles in toluene and cyclohexane were measured, and the cyclohexane experiments were conducted at temperatures ranging from the theta-point to 50°C. In toluene the PS brushes needed to be compressed to ∼1/5th of their equilibrium height before frictional forces were measured, but this onset of frictional forces was detected at a much lower level of compression in near-theta cyclohexane. In cyclohexane the structural force profiles were basically insensitive to the temperature change, but the frictional forces depended strongly on the solvent temperature. When the cyclohexane temperature was raised, the onset of frictional forces decreased toward the good-solvent onset. We also discuss the dependence of frictional force on shearing parameters.

We have examined the structural evolution of a thin gold layer sandwiched between two polymer films using specular X-ray reflectivity. We used a depth-profiling model consisting of three independent layers, upper and bottom PS layers and an intermediate gold layer. The results show that a well-defined as-deposited Au layer of about 62 ± 3 Å breaks within 10 min of annealing at 120 °C. During the breakage of the Au film, the bottom low-Mw PS flows to fill into the void between the Au particles, causing the reduction of the bottom PS film, while the top polymer layer remains relatively constant.

The phase diagram of A/B block copolymers is determined when the A block is a flexible, linear homopolymer, and the B block has a regularly branched tree structure with G generations. The predictions of a classical-path analysis and a lattice self-consistent mean field calculation are in general agreement. The phase diagram is considerably skewed toward keeping the A blocks inside cylindrical or spherical cores with the branched block forming a corona. There is little, if any, tendency for the branched arms to fold back to facilitate packing.

The thermal-induced phase separation method is used to fabricate polymer membranes and polymer-dispersed liquid crystal films from polymer solutions. The resultant morphology consists of solvent droplets dispersed uniformly in a solid polymer matrix. Up till now, the modeling and computer simulation of the thermal-induced phase separation phenomenon in polymer solutions have considered the mobility to be a constant. The objective of this presentation is to compare the following three mobility modes: (1) mobility as a constant, (2) mobility following fast mode theory, and (3) mobility following slow mode theory. We present computer simulation results from models composed of the Cahn-Hilliard theory for phase separation, Flory-Huggins free energy density for polymer solutions, and the three aforementioned mobility modes. The numerical results indicate that there is no significant difference in the morphology formed; the only difference occurs in the phase separation time. Furthermore, the numerical results show that the only difference between the slow and fast mode theories is a factor of two; the mobility of the fast mode theory is twice that of the slow mode theory.

We synthesized copolymers of N-isopropylacrylamide (NIPAM) and azobenzene-containing acrylates or acrylamides by free radical polymerization, and investigated the water solubility of these polymers upon irradiation with ultra-violet and visible light. The solubility depended on concentration and structure of photoreactive azobenzene unit in the polymers. The soluble polymers showed the lower critical solution temperature, which was varied along with light irradiation. Photo-induced large wettability alteration was observed in the film.

The adhesion and interfaces involving polymers were studied by electrical resistance measurement. Adhesive bonding and bond degradation were monitored by measuring the resistance in real time during temperature or stress variation. The resistance measured was either the contact resistance of the joint interface or the apparent volume resistance of one of the two adjoining components in a direction in the plane of the joint interface. The polymers were in the form continuous carbon fiber thermoplastic-matrix composites, due to the importance of these composites for lightweight structures and due to the conductivity of carbon fibers and the necessity of conductivity for electrical resistance measurement. The technique was used for the case of both of the adjoining components being such composites, and for the case of one component being such a composite and the other component being concrete. The concrete case is relevant to the use of the composite to retrofit concrete structures.