In-situ metrology and testing of nanotwinned copper pillars for potential air gap applications

We have performed in-situ nanocompression testing in a transmission electron microscope (TEM) of copper pillars having dimensions of the same order of typical via and line structures used in the semiconductor industry. We show direct evidence that twin boundaries can withstand extensive plastic deformation and still retain their structure when compared to regular grain boundaries. Through real-time TEM observations we have verified the deformation mechanisms of twin boundaries predicted by molecular dynamic (MD) simulations. Our quantitative in-situ stress measurements are also in close agreement with those reported by MD and energetics based calculations.     

Shear Adhesion Strength of Gecko-Inspired Tapes on Surfaces with Variable Roughness

With the aim to gain a wider understanding on the design rules of bioinspired adhesives for application in the medical field, the adhesion of fibrillar structures on soft and stiff polymers was determined in bench top studies on surfaces with variable roughness and in ex-vivo wet tissue tests. The adhesion strength of stiff fibrillar structures was found to be dependent on the roughness of the adherent surface. For a given fibril width and density, the optimal adhesion was seen when the length of the fibrils was of the same range as that of the roughness of the surface it was tested against. Over this limit, the adherence decreased. In the case of soft adhesive structures, the same trend was observed where an optimum adhesion was seen when the size of the pillars matched that of the adherent surface roughness. This observation was attributed to an increase in surface contact. The adhesion of fibrillar structures on tissue samples in ex-vivo tests showed a similar trend with enhanced fibrillar interpenetration favoring a larger number of contacts and a stronger capillary force expected to account for the adhesion enhancement.     

Non-isothermal curing kinetics of epoxy/mechanochemical devulcanized ground rubber tire (GRT) composites

The curing behavior of diglycidyl ether of bisphenol A (DGEBA) epoxy and specially ground mechanochemical devulcanized ground rubber tire system (GRT) in the presence of polyoxyalkyleneamine curing agent was investigated by non-isothermal differential scanning calorimetry technique at different heating rates. Scanning electron microscopic-energy dispersive X-ray spectroscopy, and attenuated total reflection infrared spectroscopy were used to characterize the GRT particles. The kinetic parameters of curing process were determined by isoconversional method given by Málek. The average activation energy E _a was found to be 52.3–60.7 and 45–59.2 kJ/mol for neat epoxy amine (Epo am 31) and epoxy/amine with GRT (5 Epo am 31) systems, respectively. It was observed that the presence of GRT in epoxy/amine promotes the curing. A two parameter (m, n) autocatalytic model (SB equation) was found to be the most adequate to describe the cure kinetics of the studied epoxy/GRT system. A dominant catalyzing effect of GRT on the curing reaction was observed which is attributed to the complexity of the reaction at later stages of curing, therefore, it was not possible to model the reaction over the whole range of degree of conversion.     

Activation energy for diffusion and welding of PLA films

The bonding of polylactic acid (PLA) films was investigated for a broad range of temperatures and contact times above the glass transition temperature in a lap shear joint geometry using an impulse welding system. It was observed that interfacial strength was linearly dependent to the fourth root of welding time until it approached the bulk material strength. Using models based on reptation theories, the interfacial strength of lap shear welds was estimated based on thermal histories. In more detail, the activation energy for interfacial healing and self‐diffusion coefficient was calculated based on shear strength measurements of samples welded with well‐defined thermal histories. The parameters were then used to predict interfacial strength with varying temperature histories. This is the first work to measure the activation of energy for the interfacial welding PLA. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Sliding wear behavior of nanocrystalline nickel coatings: Influence of grain size

In the present study the sliding wear behavior of pulse electrodeposited nanocrystalline Ni coatings as a function of grain size including bulk annealed Ni has been systematically studied using pin-on-disc configuration against the WC-Co counter body. The sliding wear has been analyzed with respect to wear rate, coefficient of friction, subsurface deformation and composition of wear debris. The result indicates that the sliding wear rate and coefficient of friction of Ni decreases with decreasing grain size. The subsurface beneath the worn pin surface is composed of a near surface shear region and beneath it a region of bulk plastic deformation. The ratio of the depth of the shear region to the depth of bulk deformed region decreases with decreasing grain size indicating a greater localization of near surface deformation with decreasing grain size.     

Effect of crosslinking on tribological behavior of tung oil-based polymers

In this study, the tribological properties of tung oil-based polymers synthesized by the cationic copolymerization of tung oil with divinylbenzene and styrene are evaluated as a function of crosslinking density. Tribological measurements were performed using a ball-on-flat reciprocating microtribometer on samples with three crosslinking densities of 20%, 30% and 40% by weight of the crosslinking agent. Friction and wear characteristics during dry sliding were evaluated using a spherical (1.2 mm radius) silicon nitride probe as well as a conical (100 μm radius, 90° cone angle) diamond probe. Microscale friction behavior was evaluated from single strokes at ramped normal loads, whereas wear experiments were evaluated from 100 to 500 reciprocating cycles at fixed normal loads. Elastic modulus and hardness information were evaluated using nanoindentation tests. Scanning electron microscopy of wear tracks was used to elucidate deformation mechanisms in the various samples. All samples showed friction coefficients ranging from 0.06 to 0.49. It was found that a higher crosslinking density resulted in lower abrasive wear due to increased hardness. These results provide some insight into the friction and wear behavior of tung oil-based polymers.     

Comparison of immunoaffinity chromatography enrichment and nuclease P1 procedures for 32P-postlabelling analysis of PAH-DNA adducts

32P-postlabelling analysis for detecting DNA adducts formed by polycyclic aromatic compounds is one of the most widely used techniques for assessing genotoxicity associated with these compounds. In cases where the formation of adducts is extremely low, a crucial step in the analysis is an enrichment procedure for adducts prior to the radiolabelling step. The nuclease P1 enhancement procedure is the most established and frequently used of these methods. An immunoaffinity procedure developed for class specific recognition for polycyclic aromatic hydrocarbon (PAH)-DNA adducts has therefore been compared with the nuclease P1 method for a range of DNA adducts formed by PAHs. The evaluation was carried out with skin DNA from mice treated topically with benzo[a]pyrene, 7,12-dimethylbenz[a]anthracene, 5-methylchrysene or chrysene. The immobilised antibody had the highest affinity for adducts structurally similar to the BPDE-I-deoxyguanosine adduct ([+/-]-N2-(7r,8t,9r-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-1 0t-yl)-2'-deoxyguanosine) against which the antibody had been raised. Of the PAH-modified DNAs evaluated, the maximum adduct recovery was obtained for DNA containing the BPDE I-deoxyguanosine adduct. With DMBA-modified DNA, the profiles of adducts recovered from the column were similar when the column material was treated either with a digest of DMBA-modified DNA or with 32P-labelled DMBA adducts. I-compounds (endogenous adducts in tissue DNA of unexposed animals), which had similar chromatographic properties to PAH-DNA adducts, were not enriched by the immunoaffinity procedure. Compared to the simple nuclease P1 enhancement procedure, the immunoaffinity methods were lengthier and more labour intensive. Advantages of the immunoaffinity procedure include: specificity, allowing the selective detection of a certain class of adducts: efficient adduct enrichment, providing a viable alternative to other enrichment procedures; adequate sensitivity for model studies and the potential to purify adducts for further characterisation. However, as a general screen for detecting the formation of DNA adducts, the nuclease P1 procedure was viewed as the initial method of choice since it was capable of detecting a wider range of PAH-DNA adducts.     

Large-Scale Production of Liposomes by A Microfluidizer

Liposomes can be produced by a variety of techniques such as sonication, high-pressure homogenization, detergent dialysis, reverse-phase evaporation and ether injection. The Microfluidizer is a high-pressure homogenizer which is capable of making small size multilamellar vesicles. The mean vesicle size of the liposome reduced drastically from 0.64 micron to 0.16 micron after three passes through the Microfluidizer. Additional three passes did not reduce the size further. The polydispersity reduced about 1.25% per pass. The ability to scale up the liposome production from 100 ml to 4000 ml (representing minimal batch sizes for the lab scale and the production scale Microfluidizer) was investigated and found to be satisfactory.