: The U.S. Department of Defense is tasked to respond to a wide range of asymmetric threats with speed and efficiency. Historically, the time required for moving new materials and processing technologies from research to application is roughly 40 years. The Department of the Army is actively moving toward a culture of innovation where experimentation and prudent risk taking are not only encouraged but admired. Advanced materials are the foundation to the performance of complex armor and weapon systems that are often tailored to defeat specific threats. Adhesive failure is detrimental to both structural and ballistic performance. Understanding the adhesive response during a ballistic event is vital for rapid response armor design solutions. The goals of this research are as follows: (1) use materials informatics to efficiently capture, organize, and explore adhesives structure-property-performance relationships; (2) define adhesive performance specifications for composite integral armor applications; and (3) transform the Army's ability to carry out adhesive engineering, modeling, and simulation research, with a primary focus on high-rate loading. This vision will accelerate delivery of technical capabilities to win current and future fights via materials informatics.

An emulsion of a fluoroethylene vinyl ether polyol, Lumiflon FE-4400, was incorporated into clearcoats of two-part water-based military polyurethane topcoats. This additive was mixed with the aqueous dispersion polyol component. The polyol component was then mixed with the isocyanate component with a high speed disperser to properly mix the reactants. Films were prepared by drawing down the dispersion onto glass substrates using a 4-mil stainless steel Bird applicator. After drying at ambient conditions the films were removed from the glass for analysis. As measured using X-ray photoelectron spectroscopy, Lumiflon FE-4400 segregated to the surface providing significant fluorine enrichment at the air interface, as high as 90 times the bulk concentration. Although increasing the concentration of Lumiflon FE-4400 increased the surface concentration, the ratio of surface concentration to the bulk concentration decreased. As expected, water contact angle increased approximately in a linear fashion with the surface fluorine concentration. At 1–5wt% added Lumiflon FE-4400, the physical and mechanical properties were not significantly affected. However, addition of Lumiflon FE-4400 at or above 10% of polyol fraction significantly reduced the glass transition temperature, modulus, crosslink density, strength, toughness and weathering resistance. Phase contrast microscopy showed that the morphology of these films went from being uniform to having distinct aggregates that increased in size and number as fluorinated polyol fraction increased, likely explaining the reduction in film properties. Accelerated weathering of pigmented coatings was also performed. Although fluorinated resins typically improve weathering resistance of coatings, in this study, increasing the Lumiflon FE-4400 content decreased the weathering resistance as a result of the ethoxylation of the fluorinated additive necessary to produce an aqueous fluoropolymer emulsion.

: Quantitative determination of adhesive performance when bonding to ceramic substrates has traditionally been a challenge. The brittleness of ceramic materials limits the ability to easily machine these substrates into the specific geometries required for rigorous adhesive fracture energy measurements. In this research, a mixed-mode loading scheme was implemented using an asymmetric wedge test configuration to study the effects of adhesion, promoting surface treatments on fracture energy and bond line durability of titanium bonded to alumina using a structural epoxy film adhesive. This testing scheme limited bending to the more compliant titanium and minimized deformations in the thicker alumina. Additionally, machining the alumina was avoided due to the relative simplicity of the testing configuration. X-ray photoelectron spectroscopy showed that sandblasting the ceramic surface yielded improved reactivity toward the sol-gel adhesion promoter used in this study, which resulted in increased hot/wet bond durability. Weibull modulus calculations and field emission-scanning electron microscopy imaging of the ceramic fracture surfaces showed that surface flaws induced while sandblasting the ceramic did not decrease the flexural strength.

Hyperbranched polyethyleneimines were modified with methacrylated fluorosurfactants and aliphatic epoxides to provide a library of macromolecules with controlled chain ends and residual amine functionality. These materials were co-dissolved with a thermoplastic polyurethane-ether and the blends were subsequently deposited as films cast from solution. The surface chemistry of the cast films was determined using angle resolved X-ray photoelectron spectroscopy (AR-XPS) and Rutherford backscattering spectroscopy (RBS). Experimental results indicate that the modified hyperbranched polymers (HBPs) concentrate at the air–polymer interface. Furthermore, HBPs that were complexed to polyoxometalates (POMs) using electrostatic interactions also exhibited surface segregation in cast polymer films, resulting in ca. 10-fold increase of metal at the film surface relative to the known bulk concentration. Results from XPS and RBS examination of the films are consistent with surface segregation of the HBP–POM hybrids, exhibiting increased metal, fluorine, and nitrogen content near the surface of the film, as well as significant changes in wetting behavior. This study indicates that modified HBPs may be used to selectively transport inorganic species such as polyoxometalates to polymer film surfaces.

Abstract : Novel additives for polymeric coatings have been developed based on modified hyperbranched polymers. The additives are polyfunctional and have been prepared to spontaneously segregate to the surface of the polymer in which they are dispersed. They ave been used to install active sites in polymeric films, with little or no change in the formulation, bulk properties, or application of the coating.

In this work, polyamide (Nylon 6) fibers and films were treated under atmospheric pressure glow discharges (APGD) and the effects on the morphology and chemistry of the material were studied. The fibers were plasma treated with N-2, C2H2 in He for (0.6-9.6) s at a frequency of 90 kHz, leading to the functionalization of the surface through the addition of new reactive chemical groups such as -COOH and -OH and changing the energy, chemical composition and wettability of the surface.Surface characteristics were examined via contact angle measurements, XPS, and SEM. Wettability tests revealed the improvement of the hydrophilic character of the surface as the water contact angle measured after the plasma treatments significantly decreased. The corresponding changes of the total surface energy were evaluated with a dynamic contact angle analysis system revealing a significant increase due to the exposure that can be mainly attributed to the increase of its polar component. Preliminary XPS results show a significant increase in oxygen content with the addition of carboxylic and hydroxylic groups and a decrease in the carbon content of the surface. Most importantly, the plasma modified nylon fibers and films exhibit a stable wetting behavior, even for weeks after being treated, suggesting that it is a promising technique to minimize aging phenomena. (c) 2006 Published by Elsevier B.V.

: Evaluation of bond strength between dissimilar materials such as those in ceramic-metallic systems has to date been qualitative, offering no quantitative comparative results. This was due primarily to the difficulties inherent in handling and machining brittle materials such as ceramics. In this study a testing scheme was developed to circumvent the mechanical property inconsistencies of a metallic-ceramic system and allow quantitative evaluation of bond strength in a titanium/alumina composite system. Using a carefully designed half-wedge configuration, results are compared to a standard full-wedge test and show comparable bond strength and strain energy release rate values. Additionally, the effects of surface treatments on the ceramic-metallic bond strength are also evaluated with the half-wedge configuration as well as the effects of surface treatment on the mechanical integrity of the alumina ceramic.

Abstract : A series of hyperbranched materials have been developed that allow for the transportation of desired functional groups to the surface of a polymer blend by simple solution casting techniques. These materials have been employed to transport polyoxometalates, or POMs, to the surface of a polyurethane- polyether copolymer film. providing for a 10x increase in POM concentration at the surface compared to the bulk. The films were evaluated using x-ray photoelectron spectroscopy (XPS) and contact angle analysis, and their surface chemistry was dominated by the hyperbranched polymer incorporated into the blend.

: Electro-spinning is a process by which sub-micron polymer fibers can be produced with an electrostatically driven jet of polymer solution (or polymer melt). Electro-spun textiles are of interest in a wide variety of applications including semi-permeable membranes, filters, composite applications, and as scaffolding for tissue engineering. The goal of the research presented here is to demonstrate that it is possible to produce sub-micron fibers with a specific surface chemistry through electro-spinning. This has been accomplished by electro-spinning a series of random copolymers of poly(methyl methacrylate (random) tetrahyrdroperflourooctyl acrylate (PMMA-r- TAN) from a mixed solvent of toluene and dimethyl formamlde. X-ray photoelectron spectroscopy (XFS) analysis shows that the atomic percentage of fluorine in the near surface region of the electro- spun fibers is about double the atomic percentage of fluorine found in a bulk sample of the random copolymer, as determined by elemental analysis. These results are in good agreement with XPS and water contact angle results obtained from thin films of the same copolymer materials.

: This work describes the development and application of specialized characterization techniques used to study the environmental degradation mechanisms of organic coating systems employed by the United States Department of Defense (DOD). Traditional methods for studying automotive and architectural coatings cannot easily probe the structural and chemical changes associated with the unique formulations used by DOD. Modified methods were developed to permit the use of Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS). Additionally a new method to expose coating materials through their thickness based on ultra-fast laser ablation is introduced. Four discrete coating systems subjected to established weathering protocols were studied to identify and quantify degradation mechanisms. Complementary degradation mechanisms that occur in these multi-component coating systems have been determined for the first time. The results will guide the development of more durable military coatings systems and significantly augment traditional performance assessments of coatings durability.