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Scratches in polymer coatings and barrier layers negatively impact optical properties (haze, light transmission, etc.), initiate routes of degradation or corrosion (moisture permeability), and nucleate delamination of the coating. Detecting scratches in coatings on advanced materials systems is an important component of structural health monitoring but can be difficult if the defects are too small to be detected by the naked eye. The primary focus of the present work is to investigate scratch damage using fluorescence lifetime imaging microscopy (FLIM) and mechanical activation of a mechanophore (MP)-containing transparent epoxy coating. The approach utilizes a Berkovich tip to scratch MP-epoxy coatings under a linearly increasing normal load. The goal is to utilize the fluorescent behavior of activated MPs to enable the detection of microscale scratches and molecular scale changes in polymeric systems. Taking advantage of the amine functionality present in a polyetheramine/bisphenol A epoxy network, a modified rhodamine dye is covalently bonded into a transparent, thermoset polymer network. Following instrumented scratch application, subsequent fluorescence imaging of the scratched MP-epoxy reveals the extent of fluorescence activation induced by the mechanical deformation. In this work, the rhodamine-based mechanophore is used to identify both ductile and fracture-dominated processes during the scratch application. The fluorescence intensity increases linearly with the applied normal load and is sensitive to fracture dominated processes. Fluorescence lifetime and hyperspectral imaging of damage zones provide additional insight into the local (nanoscopic) environment and molecular structure of the MP around the fracture process zone, respectively. The mechanophore/scratch deformation approach allows a fluorescence microscope to probe local yielding and fracture events in a powerful way that enhances the optical characterization of damage zones formed by standard scratch test methods and leads to novel defect detection strategies.

The orthogonal superposition (OSP) technique is advantageous for measuring structural dynamics in complex fluids subjected to a primary shear flow. This technique superimposes a small-amplitude oscillation orthogonal to a primary shear flow to measure the real and imaginary components of the complex shear modulus. The commercial availability of OSP geometries and bi-axial transducers is expected to increase its adoption as a more routine rheological technique. It is important to understand calibration procedures and the influence of intrinsic inhomogeneous flow fields, residual pumping flow effects, and boundary forces at the leading edges of the geometry components on experimental error and measurement uncertainty. In this work, we perform calibration measurements of viscosity standards on a commercial shear rheometer using a double-wall concentric cylinder geometry. Newtonian calibration fluids with viscosities that range from 0.01 to 331 Pa s are used to obtain the end-effect factors in primary steady shear and orthogonal oscillatory shear directions. The corrections needed for the viscosity measured in steady shear range from 16 to 21%; whereas for the orthogonal complex viscosity, the errors range from 19 to 25%. Computational fluid dynamics simulations are used to understand the relationship between the end-effect corrections, OSP flow cell, and the imposed shear flow fields. We show that approximate linear shear deformation profiles are attained, in the double gap, for both primary rotational shear and orthogonal oscillatory shear deformation, with only a slight deviation for the fluid in the vicinity of the bob ends. We also present information on the velocity, pressure, and shear rate distributions for fluid within the entire flow cell. The overestimation of the orthogonal viscosity is attributed to the pressure forces exerted on the bob end surfaces (9%) and a higher shear rate in the double gap that leads to higher viscous stresses on the bob cylindrical surfaces (8%). The Newtonian fluid field information provides a benchmark for future simulations involving non-Newtonian fluids. Additionally, the operational knowledge (i.e., consistent sample filling) and measurement window (i.e., viscosity and frequency) described within are critical for proper use of the instrument and measurement accuracy.

In this work, different formulations of a room-temperature silicone composite backing material (SCBM) composed of polydimethylsiloxane (PDMS), fumed silica and corn starch were investigated using different characterization techniques, i.e., differential scanning calorimetry, thermogravimetry analysis, X-ray diffraction (XRD) and small-angle X-ray scattering, as a function of controlled relative humidity. At ambient relative humidities in the range of about 20–80%, the equilibrium water content in the SCBM ranges from approximately 4–10%, which is predominantly absorbed by the corn starch. This amount of water content has been shown to have minimal effect on thermal transition temperatures (melting and glass transition) of the SCBMs. The enthalpy of melting increases with increasing relative humidity, which reflects the heterogeneous semicrystalline structure of starch granules and the role of moisture in facilitating the formation of amylopectin double helices mainly in the imperfect crystalline regions. The thermal degradation of SCBM exhibits three major mass loss steps that correspond to dehydration, decomposition of corn starch and decomposition of PDMS. The XRD patterns reveal a characteristic diffuse peak for amorphous PDMS and an A-type crystallinity for the corn starch. The XRD results show no observable changes in the crystal type and crystallinity as a function of moisture content. Results from this work help clarify the fundamental structure–property relationships in SCBMs, which are important for future development of documentary standards, especially the handling and storage specifications of next-generation ballistic witness materials for body armor testing.

Orthogonal superposition (OSP) rheology is an advanced rheological technique that involves superimposing a small-amplitude oscillatory shear deformation orthogonal to a primary shear flow. This technique allows the measurement of structural dynamics of complex fluids under non-linear flow conditions, which is important for the understanding and prediction of the performance of a wide range of complex fluids. The OSP rheological technique has a long history of development since the 1960s, mainly through the custom-built devices that highlighted the power of this technique. The OSP technique is now commercially available to the rheology community. Given the complicated design of the OSP geometry and the non-ideal flow field, users should understand the magnitude and sources of measurement error. This study presents calibration procedures using Newtonian fluids that includes recommendations for best practices to reduce measurement errors. Specifically, detailed information on the end-effect factor determination method, sample filling procedure, and identification of the appropriate measurement range (e.g., shear rate, frequency, etc.) are provided.

The success of computational materials science models for cement and concrete, at the micrometer-to-millimeter scale, is based on careful characterization of the two main starting materials – cement and aggregates. Concrete is a complex material, and models based on over-simplified chemical, geometrical, and topological assumptions have limits on the behavior they can realistically simulate. In this paper, a sample of Ottawa sand was carefully characterized, since this material is used in laboratories all around North America as the specified sand for many standard tests, including what is possibly the most highly-used ASTM test of all in the field of cement-based materials, C-109, the mortar cube strength test. Particle shape and size distributions were acquired via a combination of X-ray tomography, spherical harmonic analysis, sieve analysis, microscopy and image analysis, and laser diffraction. Quantitative X-ray diffraction showed that the Ottawa sand used was very pure α−quartz with 1% amorphous content. Elastic moduli information at the particle level was obtained via instrumented nanoindentation. Polarized light microscopy showed that the particles that were indented were single crystals. Results for the Young's modulus, E, of Ottawa sand were E = 110 GPa ± 5 GPa (assumed Poisson's ratio of 0.08), in agreement with other nanoindentation results for Ottawa sand in the literature but more than one standard deviation larger than the results obtained from isotropic averages of the elastic moduli tensor of α−quartz, measured by ultrasonic and Brillouin scattering techniques and averaged in various ways. This kind of disagreement has been seen for other minerals as well as α−quartz, and indicates that nanoindentation measurement of elastic moduli for particulate minerals used in cement and concrete and other applications must be used with some care. This characterization procedure can now be confidently employed for any class of sand or gravel particle that is desired to be used in a three-dimensional mortar or concrete model.

For the determination of the shear strength, strain and modulus of reinforced composites, nearly a dozen measurement techniques exist, several of which are supported by ASTM or ISO standards. One reason for so many options is the difficulty in obtaining a reasonably pure and uniform shear stress state in the test specimen. Typically, linear strain gauges and rosette strain gauges have been used to measure deformations for the determination of the elastic modulus and the strain to failure in many of these methods. The advent of optical strain measurement techniques such as digital image correlation (DIC), provide new opportunities to generate high resolution maps of the shear strain field as a function of the globally applied strain. DIC allows for the full-field mapping of the deformations (in-plane and out-of-plane for stereo DIC) and strains (normal and shear), revealing the pattern of deformation and damage throughout the specimen. In this work, it is shown that non-contact measurements of the strain field are an important enhancement to measuring the shear properties of FRP composites. This contribution describes the use of DIC for the shear strain response while performing standardized bias extension tests on ± 45° layups and non-standardized 10° off-axis tensile tests on glass fiber reinforced (GFRP) coupon specimens. Shear moduli and shear strengths obtained will be compared to results using the V-notched method.

Carbon nanotube (CNT) polymer nanocomposites are attractive multifunctional materials with a growing range of commercial applications. With the increasing demand for these materials, it is imperative to develop and validate methods for on-line quality control and process monitoring during production. In this work, a novel combination of characterization techniques is utilized, that facilitates the non-invasive assessment of CNT dispersion in epoxy produced by the scalable process of calendering. First, the structural parameters of these nanocomposites are evaluated across multiple length scales (10 −10 m to 10− 3 m) using scanning gallium-ion microscopy, transmission electron microscopy and small-angle neutron scattering. Then, a non-contact resonant microwave cavity perturbation (RCP) technique is employed to accurately measure the AC electrical conductivity of the nanocomposites. Quantitative correlations between the conductivity and structural parameters find the RCP measurements to be sensitive to CNT mass fraction, spatial organization and, therefore, the processing parameters. These results, and the non-contact nature and speed of RCP measurements identify this technique as being ideally suited for quality control of CNT nanocomposites in a nanomanufacturing environment. When validated by the multiscale characterization suite, RCP may be broadly applicable in the production of hybrid functional materials, such as graphene, gold nanorod, and carbon black nanocomposites.

Coaxial cables for data transmission are ubiquitous in telecommunications, aerospace, automotive, and robotics industries. Yet, the metals used to make commercial cables are unsuitably heavy and stiff. These undesirable traits are particularly problematic in aerospace applications, where weight is at a premium and flexibility is necessary to conform with the distributed layout of electronic components in satellites and aircraft. The cable outer conductor (OC) is usually the heaviest component of modern data cables; therefore, exchanging the conventional metallic OC for lower weight materials with comparable transmission characteristics is highly desirable. Carbon nanotubes (CNTs) have recently been proposed to replace the metal components in coaxial cables; however, signal attenuation was too high in prototypes produced so far. Here, we fabricate the OC of coaxial data cables by directly coating a solution of CNTs in chlorosulfonic acid (CSA) onto the cable inner dielectric. This coating has an electrical conductivity that is approximately 2 orders of magnitude greater than the best CNT OC reported in the literature to date. This high conductivity makes CNT coaxial cables an attractive alternative to commercial cables with a metal (tin-coated copper) OC, providing comparable cable attenuation and mechanical durability with a 97% lower component mass.

Joints held by polymeric adhesives are commonplace in many engineered products, but normal service can require exposure to environmental conditions that present a significant challenge for maintaining the structural integrity of the interface. In particular, aqueous environments can wreak havoc on the joint strength. Here, a mechanistic approach is used to understand the difference in the debonding behavior of an epoxy/aluminum (oxide) interface when exposed to deionized (DI) water and aqueous sodium chloride by correlating macroscopic failure with the sorption of salt and water into the adhesive and its nanoscale distribution. For the epoxy-aluminum system examined here, the presence of sodium chloride increases the resistance to crack growth in comparison to DI water. The debonding appears to be controlled by water near the buried interface. Salt water decreases the solubility of water in the epoxy and decreases the concentration of water near the buried interface, but the concentration of salt that enters the epoxy is below the detection limit. Thus, even if ions cannot penetrate or sorb into the adhesive, the presence of salt can significantly alter the water distribution within the adhesive and ultimately the strength of the joint. POLYM. ENG. SCI., 2015. © 2015 Society of Plastics Engineers

Manufacturers of stab-resistant body armor continually strive to improve the comfort of the armor wearer and maximize protection. As female officers make up a larger portion of the law enforcement and corrections workplace, armor manufacturers have begun to offer designs that accommodate contoured body shapes, such as the female bust region, which results in non-planar armor. Conventional test methodologies for body armor were designed for armor to be tested flat and do not accommodate contoured armor. This work reviews the available literature concerning common bust sizes and discusses the research performed to specify bust surrogate size, shape, and materials for testing stab-resistant female body armor. Two standard cup sizes, B and D, modeled as a paraboloid with a modified base, are recommended to meet breast volume requirements. Recommendations for manufacture of these surrogates for incorporation into standardized test methods are provided. Instrumented stab testing of these surrogates shows that impact location on a structured armor and the type of backing material increase the maximum deceleration of a spike impact.

A combined computational/experimental technique was developed to analyze the compressive elastic properties of a rigid organic foam. This technique combines X-ray computed tomography, image analysis, and large-scale finite element computations utilizing a new numerical technique. Predictions of Young’s modulus were validated with uniaxial compression testing. Good agreement was obtained between imaging/finite element computations and experimental mechanical measurements within experimental error, and the limited knowledge existing on the solid material comprising the backbone of the foam. Using the new combined experimental/theoretical procedures, it was found that the predicted Young’s modulus of the solid backbone differed by more than a factor of 100 % between two different grades of the foam, in accordance with the findings of other researchers. A significant variability of the backbone modulus was also found within the same grade. Density measurements identified the variability between different grades of foam and different as-received sample thicknesses within the same grade of foam.

Carbon nanotube (CNT) hierarchical composites are increasingly identified as next-generation aerospace materials, so it is vital to evaluate their long-term structural performance under aging environments. In this work, the durability of hierarchical CNT grafted aluminoborosilicate microfiber-epoxy composites (CNT composites) are compared against aluminoborosilicate composites (baseline composites), before and after immersion in water at 25 °C (hydro) and 60 °C (hydrothermal), for extended durations (90 d and 180 d). The addition of CNTs is found to reduce water diffusivities by approximately 1.5 times. The mechanical properties (bending strength and modulus) and the damage sensing capabilities (DC conductivity) of the CNT composites remain intact regardless of exposure conditions. The baseline composites show significant loss of strength (44%) after only 15 d of hydrothermal aging. This loss of mechanical strength is attributed to fiber-polymer interfacial debonding caused by accumulation of water at elevated temperatures. In situ acoustic and DC electrical measurements of hydrothermally aged CNT composites identify extensive stress-relieving micro-cracking and crack deflections that are absent in the aged baseline composites. SEM images of the failed composite cross-sections highlight secondary matrix toughening mechanisms in the form of CNT pullouts and fractures that enhance the service life of composites., Airbus Group, Boeing Company, EMBRAER, Lockheed Martin, Saab (Firm), ANSYS, Inc., Toho Tenax

Roma Plastilina No. 1 (RP1), an artist modeling clay that has been used as a ballistic clay, is essential for evaluation and certification in standards-based ballistic resistance testing of body armor. It serves as a ballistic witness material (BWM) behind the armor, where the magnitude of the plastic deformation in the clay after a ballistic impact is the figure of merit (known as &ldquo, backface signature&rdquo, ). RP1 is known to exhibit complex thermomechanical behavior that requires temperature conditioning and frequent performance-based evaluations to verify that its deformation response satisfies requirements. A less complex BWM formulation that allows for room-temperature storage and use as well as a more consistent thermomechanical behavior than RP1 is desired, but a validation based only on ballistic performance would be extensive and expensive to accommodate the different ballistic threats. A framework of lab-scale metrologies for measuring the effects of strain, strain rate, and temperature dependence on mechanical properties are needed to guide BWM development. The current work deals with rheological characterization of a candidate BWM, i.e., silicone composite backing material (SCBM), to understand the fundamental structure&ndash, property relationships in comparison to those of RP1. Small-amplitude oscillatory shear frequency sweep experiments were performed at temperatures that ranged from 20 &deg, C to 50 &deg, C to map elastic and damping contributions in the linear elastic regime. Large amplitude oscillatory shear (LAOS) experiments were conducted in the non-linear region and the material response was analyzed in the form of Lissajous curve representations with the values of perfect plastic dissipation ratio reported to identify the degree of plasticity. The results show that the SCBM exhibits dynamic properties that are similar in magnitude to those of temperature-conditioned RP1, but with minimal temperature sensitivity and weaker frequency dependence than RP1. Both SCBM and RP1 are identified as elastoviscoplastic materials, which is particularly important for accurate determination of backface signature in body armor evaluation. The mechanical properties of SCBM show some degree of aging and work history effects. The results from this work demonstrate that the rheological properties of SCBM, at small and large strains, are similar to RP1 with substantial improvements in BWM performance requirements in terms of temperature sensitivity and thixotropy.

In this manuscript a series of cubic silsequioxane monomers with their eight vertices functionalized by different organic tethers and terminated with triethoxysilane groups were acid hydrolyzed, spin cast, and vitrified into hard organosilicate films. Both the length of the organic ligands and the number of triethoxysilane groups were varied to change the degree of cross-linking and cubic silsequioxane content of the vitrified films. This resulted in a series of high-quality optical-grade coatings with excellent properties. In general, higher concentrations of the cubic silsequioxane moiety in the network and higher cross-link densities led to enhanced mechanical properties, lower porosity, higher density, lower thermal expansion, and a very hydrophilic surface. The manner by which these properties can be tuned via the cubic silsesquioxane content is discussed in comparison to the structure–property relations for other spin on silsequioxane type films. Copyright © 2013 John Wiley & Sons, Ltd.

The incorporation of carbon nanofiber (CNF) into glass fiber (GF) composites is a potential route to extend polymer composite service-life and enhance mechanical properties. Under nonstatic conditions, only limited information concerning water uptake and contaminant release properties of nanocomposite materials is currently available. Polyester composites containing GF and oxidized CNF were immersed in water for 30 days under nominal pressure at 23 °C, below the polymer's glass-transition temperature. Water was analyzed and changed every three days to simulate water chemistry regeneration similar to exposures in flowing systems. Composites with oxidized CNF had greater water sorption capacity and leaching rates than CNF-free composites. The total mass of organic contaminant released correlated with the amount of water sorbed by each composite (r2 = 0.91), although CNF dispersion was found to vary greatly within composites. The greatest and least contaminant release rates were found for the polyester-CNF and the polyester-GF composites, respectively. While volatile aromatic resin solvents and stabilizer compounds were detected, their concentrations declined over the 30 day exposure period. We hypothesize that the hydrophilic nature of the oxidized CNF increased the water sorption capacity of the polyester composites. Additional studies are warranted that examine the impact of this phenomenon on composite mechanical and long-term durability properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43724.

Polyethylene (PE) has been widely used in a myriad of consumer products and critical infrastructure products such as underground gas and water pipes. These products are often made of blends of multiple types of PE with different molecular architectures. Although the long-term performance of these products is largely dictated by their local molecular structure, it has been studied mostly by indirect and bulk-averaging methods such as calorimetry and neutron scattering due to lack of chemical contrast for conventional imaging techniques. We demonstrate that broadband coherent anti-Stokes Raman scattering (CARS) microscopy can acquire images of the chemical composition and molecular orientation of a miscible semicrystalline PE blend with two different molecular architectures. We discuss the detailed crystal structure observed at different length scales and new insights it provides into polymer crystal morphology.

Powdered samples of montmorillonite were functionalized with alkylammonium ions of various chain lengths and subjected to two different constant volume washing procedures: water only or sequential ethanol–water. The alkylammonium montmorillonites were analyzed with X-ray diffraction and differential scanning calorimetry to obtain insights into the effect of washing procedure. The ethanol–water procedure greatly reduced the amount of surfactant present that was not bound by cation exchange, and in some instances affected the crystallinity of the surfactant. Additionally, contact angle measurements on the compacted alkylammonium montmorillonites were obtained to assess the effect of functionalization and washing on the wettability of two common epoxides used in clay–epoxy nanocomposites. Regardless of surfactant treatment, the alkylammonium montmorillonites with ethanol–water washing exhibited lower contact angles for the epoxides, which is consistent with lower final surfactant content.

Objective The objective of this study is to improve the performance of dental resins by adding a small amount of titanium dioxide nanoparticles (TiO 2 NPs), which have outstanding mechanical properties and unique photoactivities. Methods Acrylic acid modified TiO 2 NPs (AP25) were prepared and added to a mixture of bis-phenol-A-dimethacrylate and triethylene glycol dimethacrylate (mass ratio 1:1) at seven mass fractions. Disks made of these resins were subjected to FTIR microspectroscopy, nanoindentation, microindentation, and 3-point bending to determine the degree of vinyl conversion (DC) modulus and hardness. The shear bond strengths (SBS) of dentin adhesives containing various amount of AP25 were also examined. Results The DC increased as a function of mass fraction of AP25 and reached a plateau at 0.1%. The DC of the resin mixture was improved by ≈7% up to 91.7 ± 0.8%. The elastic modulus and hardness of the composites increased initially as more AP25 were added, and decreased after reached the maximum value at approximately 0.06% mass fraction of AP25. The maximum elastic modulus was ≈48% higher than that of the NP-free resin, and the maximum hardness was more than twice higher than that of the NP-free resin. Using these resin composites as dental adhesives, the mean SBS using resins with 0.1% mass fraction of AP25 was ≈30% higher than those using NP-free resin. Significance By adding a small amount of AP25 to the resin, the DC and the mechanical properties of resins were improved dramatically. These findings could lead to better performing dental adhesives.

Thermo-viscoelastic properties of two commercial, ambient temperature-cure epoxy structural adhesives were analyzed and compared. The adhesives were formulated by the same manufacturer and appeared to have the same base chemistry; however, one system contained accelerators for shorter cure times. In the laboratory, dynamic mechanical temperature/frequency sweeps were performed on both systems to generate dynamic mechanical data and predict creep compliance master curves using frequency-temperature superposition principles. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and moisture sorption analysis were also used to assess the thermal and hygroscopic properties of the materials. Differences were observed in the thermal, hydrolytic, and dynamic mechanical properties of the two adhesive systems as well as in their estimated creep compliance behavior, which were attributed to differences in the curing agent(s) and accelerator(s) used in the adhesive systems. In most cases the dif...

Thermoviscoelastic properties and creep response of two commercial ambient temperature cure epoxy structural adhesives were analyzed and compared. The adhesives were formulated by the same manufacturer and appeared to be chemically similar; however, one system contained accelerators to shorten its cure time. In the laboratory, dynamic mechanical temperature/frequency sweeps were performed on both systems to generate dynamic mechanical and creep compliance master curves using time-temperature superposition principles. Differences were observed in the dynamic mechanical properties of the two adhesive systems as well as in their calculated creep compliance, which have been attributed to differences in their curing agent(s) and accelerator(s). Full-scale creep tests were carried out on anchors installed in concrete slabs and subjected to sustained loads for 82 days. These results were in good agreement with the creep compliance estimated using time-temperature superposition, suggesting that dynamic mechanical...

Incorporating metal-oxide nanoparticles such as nano-alumina and nano-silica into polymer coatings to enhance mechanical durability is widely utilized in the current antiscratch and mar technologies. In this article, a quantitative study of the effect of a nano-alumina additive on the surface mechanical properties and scratch behavior of a two-part polyurethane coating is reported. An instrumented indenter with a conical diamond tip is used to measure surface mechanical properties (modulus and hardness) and to perform scratch tests, over a wide range of scratch loads. The scratch behavior in terms of the onset of elastic–plastic transition and scratch morphology were characterized by laser scanning confocal microscopy. The scratch results were correlated to the surface mechanical properties and relevant bulk material properties to understand the overall scratch behavior of the coatings. The results show that the scratch behavior of the coatings depends strongly on the concentration of nano-alumina.

Polyethylene is an advantageous material for the construction of buried pipelines. It is corrosion resistant, seismic tolerant, and utilizes low cost installation methods. The exceptional long term performance of polyethylene pipe has been fostered by an understanding of the structure–property relationships for the polyethylene chains, particularly the impact of molecular weight and short chain branching on tie chain formation. An area that remains a challenge for predicting performance is the thermal fusion bond created when two pipe sections are joined. The strength of the joint is predicated on the ability of the polyethylene chains to inter-diffuse and form inter-crystalline tie-chains across the two polyethylene surfaces. Testing the strength of the fusion bond is difficult because failure occurs under a biaxial stress state. A number of different destructive and non-destructive tests have been developed, but these allow ranking of joints. Instrumented indentation has the capability to measure elastic, plastic, and visco-elastic/plastic properties under a multi-axial stress state. In this work, instrumented indentation is used to develop structure–property relationships as a function of the local microstructure. Five different polyethylene resins used for pipe manufacturing are investigated. The impact of thermal processing is investigated by imposing three different thermal cooling histories (0.4, 9, and 100 °C/min) on the polyethylenes. The goal is to determine the impact of chain architecture, molecular weight, and crystallinity on modulus, hardness, yield stress, and viscoelastic properties. The results show that instrumented indentation using is capable of measuring many aspects of polyethylene behavior related to performance.

The mechanical response of living tissue is important to understanding the injury-risk associated with impact events. Often, ballistic gelatin or synthetic materials are developed to serve as tissue surrogates in mechanical testing. Unfortunately, current materials are not optimal and present several experimental challenges. Bulk measurement techniques, such as compression and shear testing geometries, do not fully represent the stress states and rate of loading experienced in an actual impact event. Indentation testing induces deviatoric stress states as well as strain rates not typically available to bulk measurement equipment. In this work, a ballistic gelatin and two styrene-isoprene triblock copolymer gels are tested and compared using both macroscale and microscale measurements. A methodology is presented to conduct instrumented indentation experiments on materials with a modulus far below 1 MPa. The synthetic triblock copolymer gels were much easier to test than the ballistic gelatin. Compared to ballistic gelatin, both copolymer gels were found to have a greater degree of thermal stability. All of the materials exhibit strain-rate dependence, although the magnitude of dependence was a function of the loading rate and testing method.

Normal and shear forces between opposing polystyrene (PS) brushes made from preferentially assembled PS–polyvinylpyridine diblock copolymers were measured in toluene and in near-theta cyclohexane at 32, 40, and 50 °C, using a modified surface forces apparatus. In cyclohexane, over the temperature window probed, the normal forces of interaction are repulsive and the range of those force profiles changes only slightly; however, for both of the PS brushes studied, the onset of shear forces in near-theta cyclohexane is strongly influenced by changes in temperature: As the temperature is increased, the onset of the frictional interactions between the brushes in cyclohexane shifts to smaller distances, approaching the distances where frictional forces are observed for brushes in the good solvent toluene. The pattern of behavior seen in the frictional response between the limits of good and theta condition is attributed to composition fluctuations, which increase near the theta condition because of the decrease in excluded volume interactions. These fluctuations may give rise to increased drag during shearing motion because of interfacial roughness or interchain coupling across the brush–brush interface. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 649–655, 2006

Current high-throughput methodologies for measuring interfacial adhesion typically rely on serial or sequential testing of discrete or continuous libraries. We have developed a measurement platform that employs an array of micro-lenses to simultaneously measure adhesion at multiple points on a planar specimen library. This technique relies on the accurate measurement of the overall lens array displacement, rather than load and individual lens contact areas to quantify the work of adhesion using the Johnson, Kendall and Roberts (JKR) model. We demonstrate the ability of this technique to measure the work of adhesion (loading) and energy release rate (unloading) for a polydimethylsiloxane lens array against glass, and we compare our work of adhesion measurements to the traditional single-lens geometry. We find the work of adhesion measured with the multilens array is 18.9 mJ m−2 ± 9.4 mJ m−2 compared to 20 mJ m−2 ± 5 mJ m−2 for a single-lens experiment. Also, the micro-lens array deviates from the JKR model when the lens array displacement is comparable to lens height.

Three complementary techniques that probe different characteristics of curing: FTIR microspectroscopy, confocal microscopy and axisymmetric adhesion testing ware used to study discrete epoxy samples cured at different temperatures and to follow curing across a continuous gradient combinatorial library. Together, these techniques provide a comprehensive picture of chemical and physical changes.

Accelerated and natural aging of safety films used in protective glazing systems was investigated by the use of Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy, and tensile tests. Accelerated conditions involved simultaneous exposure of specimens to ultraviolet (UV) radiation between 295 and 450 nm and each of four temperature/relative humidity (RH) environments, i.e., (a) 30 °C at

Polyethylene is an advantageous material for the construction of buried pipelines. It is corrosion resistant, seismic tolerant, and utilizes low cost installation methods. Pipe sections are often joined using thermal fusion processes. The strength of the joint is related to the ability of the polyethylene chains to inter-diffuse and form inter-crystalline tie-chains across the two polyethylene surfaces. Testing the strength of the fusion bond is difficult and a number of different destructive and non-destructive tests have been developed, but it is not possible to understand the impact of the fusion process on the local microstructure from these tests. In this work, instrumented indentation with a flat punch is used to measure the local viscoelastic behavior of five different polyethylene resins used for pipe manufacturing at short times. High strain behavior related to slow crack growth is measured using a strain hardening measurement under tension. The impact of thermal processing is investigated by imposing three different thermal cooling histories (0.4, 9, and 100 °C/min) on the polyethylenes. The goal is to determine if short-term creep under indentation is capable of accurately measuring; (a) bulk creep behavior, (b) impact of resin architecture, and (c) the impact of thermal processing. The results show that indentation using a flat punch is capable of measuring creep within the range of bulk creep behavior, but not sensitive to the slow crack growth resistance of the resin.

In this manuscript a series of cubic silsequioxane monomers with their eight vertices functionalized by different organic tethers and terminated with triethoxysilane groups were acid hydrolyzed, spin cast, and vitrified into hard organosilicate films. Both the length of the organic ligands and the number of triethoxysilane groups were varied to change the degree of cross-linking and cubic silsequioxane content of the vitrified films. This resulted in a series of high-quality optical-grade coatings with excellent properties. In general, higher concentrations of the cubic silsequioxane moiety in the network and higher cross-link densities led to enhanced mechanical properties, lower porosity, higher density, lower thermal expansion, and a very hydrophilic surface. The manner by which these properties can be tuned via the cubic silsesquioxane content is discussed in comparison to the structure–property relations for other spin on silsequioxane type films. Copyright © 2013 John Wiley & Sons, Ltd.

An instrument that allows the simultaneous measurement of the mechanical deformation and Raman spectra of materials under contact loading is described. The instrument consists of a custom nanoindenter that operates on a laser-scanning Raman microscope.

Indentation-induced phase transformation processes were studied by in situ Raman microspectroscopy of the deformed contact region of silicon on sapphire samples during contact loading and unloading. During loading, the formation of Si-II and another phase, indentified as the bct5 structure, was observed, thus providing experimental evidence for both the existence of the bct5 phase and the possibility of generating this phase under indentation conditions. The pressure dependence of the Raman phonon frequencies for the bct5 modes was determined. During unloading, the transformation of the bct5 phase into the metastable bc8 (Si-III) and r8 (Si-XII) structures was observed. The measurements indicated that bc8 can form simultaneously with the r8 structure in indentation tests rather than subsequently from r8 in a separate process as previously assumed.

Soft elastomeric materials that mimic real soft human tissues are sought to provide realistic experimental devices to simulate the human body's response to blast loading to aid the development of more effective protective equipment. The dynamic mechanical behavior of these materials is often measured using a Kolsky bar because it can achieve both the high strain rates (>100 s−1) and the large strains (>20%) that prevail in blast scenarios. Obtaining valid results is challenging, however, due to poor dynamic equilibrium, friction, and inertial effects. To avoid these difficulties, an inverse method was employed to determine the dynamic response of a soft, prospective biomimetic elastomer using Kolsky bar tests coupled with high-speed 3D digital image correlation. Individual tests were modeled using finite elements, and the dynamic stiffness of the elastomer was identified by matching the simulation results with test data using numerical optimization. Using this method, the average dynamic response was found to be nearly equivalent to the quasi-static response measured with stress–strain curves at compressive strains up to 60%, with an uncertainty of ±18%. Moreover, the behavior was consistent with the results in stress relaxation experiments and oscillatory tests although the latter were performed at lower strain levels.

Stereoscopic digital image correlation (DIC) is used to measure the shape evolution of a soft, transparent thermoplastic elastomer subject to a high strain rate compression test performed using a Kolsky bar. Rather than using the usual Kolsky bar wave analysis methods to determine the specimen response, however, the response is instead determined by an inverse method. The test is modeled using finite elements, and the elastomer stiffness giving the best match with the shape and force history data is identified by performing iterative simulations. The advantage of this approach is that force equilibrium in the specimen is not required, and friction effects, which are difficult to eliminate experimentally, can be accounted for. The thermoplastic is modeled as a hyperelastic material, and the identified dynamic compressive (non-linear) stiffness is compared to its quasi-static compressive (non-linear) stiffness to determine rate sensitivity.

Optical lithography deep in the UV spectrum is the predominate route for high-resolution, high-volume nanoscale pattering. However, state-of-the-art optical lithography tools are exceedingly expensive and this places serious limitations on the applications, technical sectors, and markets where highresolution patterning can be implemented. To date the only substantial market for high-end optical lithography tools has been semiconductor fabrication. Nanoimprint lithography (NIL) has recently emerged as an alternative to optical lithography and combines the potential of sub-fi ve-nanometer patterning resolution with the low cost and simplicity of a stamping process. [ 1–4 ] This has led to signifi cant efforts to implement NIL methods, not only for semiconductor logic devices, but also in fi elds as diverse as the direct patterning of interlayer dielectrics (ILDs) for back-end-of-line (BEOL) interconnect structures, [ 5–7 ] bitpatterned magnetic media for data storage, [ 8 , 9 ] and high-brightness light-emitting diodes (LEDs). [ 10 ] Some of these are new areas where nanoscale patterning has previously not been considered, and are made possible here by the low cost and simplicity of the NIL stamping processes.

Thermoplastic olefins (TPOs) are polymeric materials utilized for interior and exterior automotive parts. These materials are often painted to protect and enhance their appearance. TPO materials possess a low surface energy because of the aliphatic backbone, and adhesion promoters (APs), such as chlorinated polyolefins, are used to increase paint adhesion and improve paint performance. The impact of the AP structure and processing conditions on the mechanical properties and degree of interpenetration was investigated on cross sectioned coatings. The AP structure was varied by the chlorine content and molecular weight for the same TPO and polyester acrylic, melamine-cured paint system. Two different processing conditions were investigated. Mechanical properties were measured using depth-sensing indentation. Long-range diffusion of coating components across each interface was verified with confocal Raman microscopy. The AP interfaces, AP/base coat and AP/TPO, were chemically and mechanically sharp at the 1 mum lateral resolution of both techniques. Depth-sensing indentation measured a modulus gradient across the top coating cross section. The free air surface of the top coat had a higher modulus than the interior. Processing conditions and polishing to prepare the cross section for measurements were found to affect only the control AP.

Surface scratches in a series of controlled epoxy networks (CEN) were measured using a combination of instrumented indentation protocols and laser scanning confocal microscopy. Identical epoxy chemistry with increasing molecular weight between crosslinks provided different viscoelastic relaxation behaviors with the same modulus at ambient conditions. The glass transition temperatures (Tg)ranged between 70°C and 117°C. The high Tg CEN exhibited the lowest penetration depth and the highest elastic recovery. The results are analyzed with respect to the macroscale bulk properties and underlying molecular architecture of the CEN materials.

The objective of this study is to characterize the nanoparticle dispersion and to investigate its effect on the surface mechanical properties of nanoparticle-polymer systems. Two types of TiO2 nanoparticles were chosen to mix in two polymeric matrices: solvent-borne acrylic urethane (AU) and water-borne butyl-acrylic styrene latex (latex) coatings. Nanoparticle dispersion was characterized using laser scanning confocal microscopy. Overall, Particle A (PA, without surface treatment) dispersed better than Particle B (PB, organic treatment) in both systems. The AU-PA system exhibited the best dispersion of the four systems, however PB forms big clusters in both of the matrices. Surface mechanical properties, such as surface modulus at micron and sub-micron length scales were determined from depth sensing indentation equipped with a pyramidal tip or a conical tip. The surface mechanical properties were strongly affected by the dispersion of nanoparticle clusters, and a good correlation was found between dispersion of nanoparticle clusters near surface and the modulus-depth mapping using a pyramid tip.

The effect of pigment dispersion on durability of a TiO 2 pigmented epoxy coating during outdoor exposure has been investigated. Well-dispersed and poorly dispersed coating samples were prepared through the addition or absence of a dispersant in the coating formulation. Ultra small angle neutron scattering (USANS) and scanning electron microscopy (SEM) showed that pigment aggregation occurs in the absence of dispersant. A thin, clear layer of epoxy was observed at the air/exposed surface interface in both the dispersed and non-dispersed samples. Chemical degradation and physical changes during UV exposure were measured by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), atomic force microscopy (AFM), and laser scanning confocal microscopy (LSCM). Results showed that the degree of pigment dispersion and the thickness of the clear layer contributed to weathering. Changes in surface topography and gloss loss during UV degradation were correlated with degree of pigment dispersion. Ripples and bumps on the top surface of the poorly dispersed coating greatly affected gloss. Bulk and surface mechanical properties were investigated using dynamic mechanical thermal analysis (DMTA) and instrumented indentation, respectively. Relative to the neat epoxy coatings, the addition of TiO 2 particles into the epoxy coatings increased elastic modulus but decreased the glass transition temperatures (T g ) of both of the pigmented coatings. Relationships between surface and bulk mechanical property changes and chemical degradation are discussed.

Multicomponent formulations coupled with complex processing conditions govern the final properties of photopolymerizable dental composites. In this study, a single test substrate was fabricated to support multiple formulations with a gradient in degree of conversion (DC), allowing the evaluation of multiple processing conditions and formulations on one specimen. Mechanical properties and damage response were evaluated as a function of filler type/content and irradiation. DC, surface roughness, modulus, hardness, scratch deformation and cytotoxicity were quantified using techniques including near-infrared spectroscopy, laser confocal scanning microscopy, depth-sensing indentation, scratch testing and cell viability. Scratch parameters (depth, width, percent recovery) were correlated to composite modulus and hardness. Total filler content, nanofiller and irradiation time/intensity all affected the final properties, with the dominant factor for improved properties being a higher DC. This combinatorial platform accelerates the screening of dental composites through the direct comparison of properties and processing conditions across the same sample.

Thermoplastic olefins (TPO) have made significant inroads as polymeric materials for interior and exterior automotive parts. Spray applied chlorinated polyolefins (CPO) are often used to improve paint adhesion to the low surface energy TPO substrates. The penetration of the CPO into the substrate is difficult to quantify, but is critical to achieving a good paint/TPO bond. The interphase between each layer in a coated TPO coupon was investigated using a combination of instrumented indentation and confocal Raman microscopy. The degree of CPO interpenetration was Thermoplastic olefins (TPO) have made significant inroads as polymeric materials for interior and exterior automotive parts. Spray applied chlorinated polyolefins (CPO) are often used to improve paint adhesion to the low surface energy TPO substrates. The penetration of the CPO into the substrate is difficult to quantify, but is critical to achieving a good paint/TPO bond. The interphase between each layer in a coated TPO coupon was investigated using a combination of instrumented indentation and confocal Raman microscopy. The degree of CPO interpenetration was altered by using three different CPOs exposed to two different manufacturing methods for the same TPO and base/clear coat system. It was found that the interfaces, CPO/base coat or CPO/TPO, were chemically and mechanically sharp at the 1 μm lateral resolution of both techniques. A gradient in the modulus through the thickness of the clear coat was observed using instrumented indentation.

Scratch and mar resistance is an attribute of great practical importance to polymeric materials. Physical measurements of scratch and mar resistance have been conducted, but the ability to link these resistance to other properties of a polymer and to the customer-perceived appearance of a surface has remained elusive. Thus, optimization of material properties enhancing scratch and mar resistance is not possible. Over the years, a multitude of scratch test devices and protocols has been developed, but the large amount of data generated has made it very difficult to compare and pool data, and ultimately to standardize any test protocol. Also, the relevancy of physical measures of scratch and mar are continually being raised, since a link between physical measurements of scratch and mar and consumer perceived failure caused by scratch and mar has not been established. Establishing a connection between physical and appearance characterizations of scratch and mar are difficult, since appearance measures of scratch and mar are almost always based on qualitative, as opposed to quantitative, assessments of damage. These appearance measurements are made through visual inspection, gloss changes, and changes in gray scale level or lightness. These qualitative assessments are seldom either repeatable or reproducible, and thus a reliable standardized test method for assessing scratch and mar from a consumer’s perspective is also not currently available to the polymeric materials community. In this chapter, progress is reported toward the development of a scientifically based standardized test method for quantifying scratch resistance based on optical scattering metrologies. A scratch protocol to impart a standard scratch deformation is described. Optical scattering measurements are conducted to identify the onset of plastic deformation by analyzing specular and off-specular intensities. The angular-resolved optical scattering reflectance profiles at various incident angles are measured using a custom-designed optical scattering instrument at the National Institute of Standards and Technology (NIST). Angular-resolved optical scattering from surfaces having a single or multiple scratches are compared to gloss measurements taken at 20° and 60° with a commercial glossmeter. By analyzing the specular and off-specular scattered intensities, scratch damage can be quantitatively assessed, even when the results from gloss measurements are indistinguishable. Additionally, the correlation between surface roughness and gloss measurements is presented. Finally, there is commentary herein on future research directions that includes implementing metrologies for linking appearance-based scratch resistance measurements to nanomechanical material properties measured through instrumented indentation.

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.

Instrumented indentation is a widely used technique to study the mechanical behavior of materials at small length scales. Mechanical tests of bulk materials, microscopic, and spectroscopic studies may be conducted to complement indentation and enable the determination of the kinetics and physics involved in the mechanical deformation of materials at the crystallographic and molecular level, e.g., strain build-up in crystal lattices, phase transformations, and changes in crystallinity or orientation. However, many of these phenomena occurring during indentation can only be observed in their entirety and analyzed in depth under in situ conditions. This paper describes the design, calibration, and operation of an indentation device that is coupled with a Raman microscope to conduct in situ spectroscopic and optical analysis of mechanically deformed regions of Raman-active, transparent bulk material, thin films or fibers under contact loading. The capabilities of the presented device are demonstrated by in situ studies of the indentation-induced phase transformations of Si thin films and modifications of molecular conformations in high density polyethylene films.