Adhesive forces significantly affect elastic modulus determination of soft polymeric materials in nanoindentation

The present study investigated the effects of adhesion on the elastic modulus determined from nanoindentation curves for soft polydimethylsiloxane (PDMS) elastomers with five different crosslink concentrations. Indentation load-displacement curves were obtained for samples of all concentrations at four different peak loads. All load-displacement curves were nearly linear, resulting in load independent contact stiffnesses (p < 0.003) for the range of loads tested. As a result, elastic modulus calculated from nanoindentation curves with the Hertz contact model exhibited significant differences (p < 0.004) both at different peak loads for a single PDMS concentration and between different PDMS concentrations at a single peak load (p < 0.001). The differences for different peak loads were attributed to the presence of substantial adhesive forces at the tip-sample interface. By taking these adhesive interactions into account with the Johnson, Kendall, Roberts (JKR) contact model, the differences in elastic modulus at different peak loads could be reconciled. Significant differences (p < 0.001) in moduli between different PDMS concentrations were still present. The results highlight the importance of considering adhesive forces in nanoindentation analyses of low modulus polymeric materials.     

散落在云南的日子

阳光下,圣洁的雪峰屹立着古老的沧桑,现代的神秘,让我一如既往地憧憬那天边的金色殿堂。大假。约驴友共赴春城。除了路途颠簸的两整天,剩余的八个日子有如繁星,轻轻地散落在云南的各个角落,以至长时间里几度提笔,也不曾找到自己被     

The optimal level of fuzz: case studies in a methodology for psychological research

Cognitive science research is hard to conduct, because researchers must take phenomena from the world and turn them into laboratory tasks for which a reasonable level of experimental control can be achieved. Consequently, research necessarily makes tradeoffs between internal validity (experimental control) and external validity (the degree to which a task represents behaviour outside of the lab). Researchers are thus seeking the best possible trade-off between these constraints, which we refer to as the optimal level of fuzz. We present two principles for finding the optimal level of fuzz, in research, and then illustrate these principles using research from motivation, individual differences and cognitive neuroscience.     

Sorption of Aniline by Montmorillonite

Sorption of aniline by montmorillonite was studied by infra-red, X-ray diffraction and differential thermal analysis methods. The amount of aniline sorbed and the type of bonding depend upon the interlayer cations: anilinium, H⁺- and Al³⁺- give anilinium aniline ions, NH₄⁴-ammonium aniline ions, alkalis and alkaline earths except Cs are bonded to aniline through water bridges and transition metal cations are coordinated to aniline partly directly and partly through water bridges. Sorption does not occur in the complete absence of water.     

Strong buffering characteristics and swelling behavior of cationic copolymers

The swelling behavior of crosslinked cationic copolymers of 2-hydroxyethyl methacrylate with (3-methacryloylamino propyl) trimethylammonium chloride was investigated in various buffered solutions as a function of ionic strength and pH. The equilibrium degree of swelling increased as the pH decreased or as the cationic group-containing comonomer in the polymer increased. The water transport in such copolymers was controlled by a non-Fickian mechanism. These results can be used in the development of physiologically sensitive controlled drug delivery systems. © 1994 John Wiley & Sons, Inc.     

Kindling-induced emotional behavior in male and female rats.

Modeling fear in animals is a critical approach for identifying the neural mechanisms involved in human disorders such as generalized anxiety and panic. Amygdala kindling has proven useful in this regard because it produces dramatic increases in fearful behavior. The purpose of this experiment was to compare the behavioral effects of kindling in male and female rats. Compared with the sham-stimulated rats, the kindled male and female rats showed similar increases in fearful behavior, with some sex differences in fear-related open-field activity. They also showed decreased immobility in the forced-swim test and increased sucrose consumption. These results suggest that kindling-induced fear is generally similar in male and female rats and that kindling does not appear to induce depression-like behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Robust Non-Wetting PTFE Surfaces by Femtosecond Laser Machining

Nature shows many examples of surfaces with extraordinary wettability, which can often be associated with particular air-trapping surface patterns. Here, robust non-wetting surfaces have been created by femtosecond laser ablation of polytetrafluoroethylene (PTFE). The laser-created surface structure resembles a forest of entangled fibers, which support structural superhydrophobicity even when the surface chemistry is changed by gold coating. SEM analysis showed that the degree of entanglement of hairs and the depth of the forest pattern correlates positively with accumulated laser fluence and can thus be influenced by altering various laser process parameters. The resulting fibrous surfaces exhibit a tremendous decrease in wettability compared to smooth PTFE surfaces; droplets impacting the virgin or gold coated PTFE forest do not wet the surface but bounce off. Exploratory bioadhesion experiments showed that the surfaces are truly air-trapping and do not support cell adhesion. Therewith, the created surfaces successfully mimic biological surfaces such as insect wings with robust anti-wetting behavior and potential for antiadhesive applications. In addition, the fabrication can be carried out in one process step, and our results clearly show the insensitivity of the resulting non-wetting behavior to variations in the process parameters, both of which make it a strong candidate for industrial applications.