Viscoelastic Behavior of Polymer Films During Scratch Test: a Quantitative Analysis

In this work, we study the indenter geometrical effects on the nanoindentation and scratch behaviors of polymers (epoxy resin and its based nanocomposites) through both experimental and numerical approaches. Two different types of indenter commonly used in nanoindentation tests, Berkovich (i.e., three-sided pyramid-shaped) and conical-shaped, are studied. An indenter (tip) geometry reconstruction procedure is presented and the results are input into finite element models to better understand the mechanisms of the geometrical effects on nanoindentation. The effect of indenter geometry on nanoscratch behavior is also investigated experimentally. Overall, our results show that the corrected Oliver and Pharr's method is applicable to nanoindentation of polymeric surfaces and the indenter geometry plays significant roles in both the nanoindentation and nanoscratch tests. The conical-shaped indenter provides slightly overestimated mechanical parameters for the polymers tested due to the material pile-up. Therefore, for nanoindentation and scratch tests, the type of indenter should always be mentioned and comparisons between tests using different types of indenter should be taken with caution.

An improved technique for characterizing the fracture toughness via scratch test experiments

The relationship between the scratch behavior and molecular aggregation states of polystyrene (PS), poly(2,6‐dimethyl‐1,4‐phenyleneoxide) (PPO), and their blends, is investigated based on differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), polarized optical microscopy (POM), and indentation and scratch tests. DSC reveals that all the PS/PPO blends show the single glass transition temperature (Tg) and the Tg monotonically increase and Tg breadth exhibits a maximum, with an increase in PPO content. Furthermore, density and intermolecular chain distance obtained by WAXD exhibits maximum and minimum values at near 50 wt% of PPO, respectively. It is evident that densification occurs by blending PS and PPO. The scratch coefficient of friction (SCOF) value of PS is the largest and PS exhibits a fish‐scale pattern after scratch testing, while the SCOF value of PPO is much smaller than PS and PPO exhibits smooth groove formation. The PS50/PPO50 and PS20/PPO80 blends exhibit superior scratch and indentation resistance than PS and PPO. Damage morphology observation by POM and indentation tests reveals that molecular orientation is more restricted, and resistance against indentation increases for blends. This is due mainly to densification of the blend system.

In this work delamination behavior <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1,6\ \mu\mathrm{m}$</tex> thin AF4 coatings on silicon (Si) and glass (SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ) substrates were tested by scratch testing. The coatings were deposited by vapor deposition polymerization (VDP) technique on untreated and polished 8-inch Si and SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> wafers, with root mean square (RMS) roughness of 4 and 2 nm, respectively. Scratch tests were performed in displacement and load controlled mode, where scratch depths were varied from 1 to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1,6\ \mu\mathrm{m}$</tex> . The indentation loads and subsequently depths, were varied to observe different delamination features over the penetration depth at the substrate-coating interface. Additionally, the scratches were observed in-situ with scanning electron microscopy (SEM) to better understand the changes in lateral force during the test. The results showed that cohesive failure in AF4 happens before adhesive failure at indentation depths down to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1,4\ \mu\mathrm{m}$</tex> , At <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1,4\ \mu\mathrm{m}$</tex> depth we can observe first adhesive failure features on the AF4 coating - SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> substrate interface. This shows that the AF4 coating on the SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> substrate has a slightly lower adhesion than on the Si substrate. The adhesion failures on both samples start to occur at scratches near the AF4-substrate interface, without chipping on the sides. The results also showed that if the scratch depth is not near the AF4-substrate, only the cohesive failure in AF4 can be seen, which indicates very good adhesion for both samples.

Instrumented indentation and scratch testing evaluation of tribological properties of tin-based bearing materials

Head and neck squamous cell carcinoma (HNSCC) and acute myeloid leukemia are the major causes of mortality and morbidity in Fanconi anemia (FA) patients. The objective of this study was to investigate the antineoplastic activity of PB, an antineoplastic nutrient mixture (containing quercetin, curcumin, green tea, cruciferex and resveratrol) on human FA HNSCC in vitro and in vivo. Human FA HNSCC cell line OHSU-974 (Fanconi Anemia Research Fund) was cultured in RPMI medium supplemented with 20% FBS and anti-biotics. At near confluence, cells were treated in triplicate with different concentrations of PB: 0, 10, 25, 50, 75 and 100 µg/ml. Cells were also treated with PMA to induce MMP-9 activity. Cell proliferation was detected by MTT assay, secretion of MMPs by gelatinase zymography, invasion through Matrigel, migration by scratch test and morphology by hematoxylin and eosin (H&E) staining. In vivo, athymic male nude mice (n=12) were inoculated with 3x106 OHSU-974 cells subcutaneously and randomly divided into two groups: group A was fed a regular diet and group B a regular diet supplemented with 1% PB. Four weeks later, the mice were sacrificed and their tumors were excised, weighed and processed for histology. NM inhibited the growth of OHSU-974 tumor by 67.6% (p<0.0001) and tumor burden by 63.6% (p<0.0001). PB demonstrated dose-dependent inhibition of cell proliferation, with 27% (p=0.0003) and 48% (p=0.0004) toxicity at 75 and 100 µg/ml, respectively. Zymography revealed MMP-2 and PMA-induced MMP-9 secretion. PB suppressed secretion of both MMPs in a dose-dependent manner, with total block of both at 50 µg/ml. PB inhibited cell migration (by scratch test) and OHSU-974 invasion through Matrigel in a dose-dependent fashion with total block at 50 µg/ml. H&E staining showed no morphological changes below 50 µg/ml. The results suggest that PB has potential therapeutic use in the treatment of human FA HNSCC.

Mechanical characterization of Ni–P-based ternary coatings by RF magnetron sputtering

Pre-plated leadframe (PPF) is usually plated with nickel-palladium plating, and the hardness of the plating is much higher than tin (Sn) plating. However, in some cases, it is observed that the PPF is more prone to damage that resulted in exposed copper (Cu). The damage is induced by mechanical contact of the test pin with external lead of integrated circuit (IC) package. Currently, at Sn and PPF plating processes, quality checks such as plating layer hardness, thickness, grain size, surface roughness, and etc. were carried out. There is no measurement method that characterizes the damage resistance of a particular plating layer. This work studies the application of scratch test as a damage test method to characterize the in leadframe plating surface of both Sn and PPF, in relation with various types of diamond indenter and scratch techniques which is progressive load scratch and constant load scratch test. Recommendation is given at the end of this paper.

Dermal tissue penetration of in-plane silicon microneedles evaluated in skin-simulating hydrogel, rat skin and porcine skin

The effect of the substrate on the mechanical properties of TiN coatings

The aim of this thesis has been to provide the ground work for the electrochemical sensing of analytes in polymer-functionalized microchannels via gold-coated microfabricated microchannel electrodes and for the in-situ study of the adsorption of particles in polymer brushes through molecular dynamics simulations. Both these objectives encompass polymer systems that are out of equilibrium and reveal how particles interact with these polymers. The aim was accomplished via the successful fabrication of in-channel gold-coated electrodes within a microfluidic device. To these gold-coated electrodes a redox-active polymer, poly(ferrocenylsilane) (PFS), was attached, via which sodium ascorbate could be sensed. To further understand the effect of particles in polymer systems, molecular dynamics (MD) simulations were performed on the insertion of particles of various size, shape and orientation, into a polymer brush. The force-distance curves were successfully modelled by two different models, one using scaling arguments and one aided through MD. Furthermore, the effect of shaking the wall, to which the polymer brushes are attached, on the penetration depth of particles into the brush was simulated, to approximate biological microsystems. From these could be concluded that if the brush is oscillated at its resonance frequency at a complementary resonance amplitude, the increase in penetration depth is at its maximum.

Estimating filtration coefficients for straining from percolation and random walk theories

In the present study, TiN coatings have been deposited on D2 tool steel substrates by using cathodic arc physical vapor deposition technique. The objective of this research work is to determine the usefulness of TiN coatings in order to improve the micro-Vickers hardness and friction coefficient of TiN coating deposited on D2 tool steel, which is widely used in tooling applications. A Pin-on-Disc test was carried out to study the coefficient of friction versus sliding distance of TiN coating deposited at various substrate biases. The standard deviation parameter during tribo-test result showed that the coating deposited at substrate bias of -75 V was the most stable coating. A significant increase in micro-Vickers hardness was recorded, when substrate bias was reduced from -150 V to zero. Scratch tester was used to compare the critical loads for coatings deposited at different bias voltages and the adhesion achievable was demonstrated with relevance to the various modes, scratch macroscopic analysis, critical load, acoustic emission and penetration depth. A considerable improvement in TiN coatings was observed as a function of various substrate bias voltages.

Microscratch experiments were performed to evaluate effects of uniaxial stretching by 200 % in low density polyethylene (LDPE) along parallel and perpendicular directions with respect to stretching. Penetration depth, healing depth and viscoelastic recovery have been determined. Clear orientation effects are seen. The direction parallel to the extension axis shows strong resistance to scratching and also the highest recovery (a memory effect). Unoriented material exhibits behavior intermediate between that of oriented samples in parallel and perpendicular directions. The sliding wear was determined by multiple scratching along the same groove and here also was found orientation dependence. Polarized micro-Raman experiments on the oriented LDPE samples were carried out. Since scratching and sliding wear results are strongly affected by polymer orientation, one can use both kinds of tests as a measure of orientation - and also to vary orientation to control tribological properties.

The properties of TiBN-based coatings are significantly affected by adding alloying elements and coating parameters. Therefore, in this study, TiTaBN coatings with graded interlayer (CWGIL) were deposited on D2 steel substrates by pulsed DC biased (PDCB) and continuously DC biased (CDCB) closed field unbalanced magnetron sputtering (CFUBMS). The structural, mechanical, adhesion and tribological properties of the coatings were analysed with EDS, SEM, XRD, microhardness, scratch testing and a pin-on-disc tribo-tester (under various atmospheric conditions). TiTaBN CWGIL deposited by PDCB magnetron sputtering (MS) had a very dense microstructure, high hardness and a high critical load value. TiTaBN CWGIL deposited by PDCB MS had a lower friction coefficient, the wear rate and the penetration depth in all atmospheric conditions. In conclusion, the application of a PDCB substrate instead of a CDCB one dramatically increases the performance of CFUBMS-deposited TiTaBN coatings.