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Adhesive Forces (adhesive + force)
Selected AbstractsSuper-Hydrophobic PDMS Surface with Ultra-Low Adhesive Force,MACROMOLECULAR RAPID COMMUNICATIONS, Issue 22 2005Meihua Jin Abstract Summary: Rough polydimethylsiloxane (PDMS) surface containing micro-, submicro- and nano-composite structures was fabricated using a facile one-step laser etching method. Such surface shows a super-hydrophobic character with contact angle higher than 160° and sliding angle lower than 5°, i.e. self-cleaning effect like lotus leaf. The wettabilities of the rough PDMS surfaces can be tunable by simply controlling the size of etched microstructures. The adhesive force between etched PDMS surface and water droplet is evaluated, and the structure effect is deduced by comparing it with those own a single nano- or micro-scale structures. This super-hydrophobic PDMS surface can be widely applied to many areas such as liquid transportation without loss, and micro-pump (creating pushing-force) needless micro-fluidic devices. Etched PDMS surface containing micro-, submicro-, and nano-composite structures shows a self-cleaning effect with water CA as high as 162° and SA lower than 5°. [source] Fabrication and Characterization of Superhydrophobic Surfaces with Dynamic StabilityADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Xi Yao Abstract Superhydrophobic surfaces of dynamic stability are crucial for applications in water-repellent materials. In this work, a hierarchical structure composed of a dendritic microporous surface with nanostructured porosity is demonstrated that shows robust superhydrophobicity with dynamic stability. The hierarchical structures are obtained on both copper foils and wires by a dynamic gas-bubble template-assisted electrochemical deposition method. The substrates can then be modified with alkyl thiols to obtain the surface superhydrophobicity. A new kind of testing, mechanical monitor-assisted continuous water surface strokes, is developed to reveal the dynamic stability of the as-prepared superhydrophobic copper wires. The as-prepared superhydrophobic copper wires can exert a high propulsive force, and particularly, show little adhesive force in the process of continuous strokes on the water surface, exhibiting robust superhydrophobicity with dynamic stability. The approach allows a strategy for the fabrication of superhydrophobic surfaces with dynamic stability, and suggests a new method to evaluate the dynamic stability of superhydrophobic surfaces. [source] Self-Assembled Nanoparticles Based Fabrication of Gecko Foot-Hair-Inspired Polymer Nanofibers,ADVANCED FUNCTIONAL MATERIALS, Issue 13 2007S. Kustandi Abstract Wafer-scale polymer nanofabrillar structures have been fabricated using the combination of colloidal nanolithography, deep-silicon etching, and nanomolding to mimic the nanostructure of gecko foot-hairs. The artificial surface features densely packed polymeric nanofibrils with super-hydrophobic, water-repellent, and "easy-to-clean" characteristics. The lateral dimension of the nanofibrils is as small as 250,nm and an aspect-ratio as high as 10:1 has been achieved without lateral collapse between neighboring fibrils. The method allows both fabrication of synthetic structures over a large area and direct integration of a flexible membrane to assist the array of nanofibrils in making intimate contact with uneven surfaces. A single nanofibril exhibits a mean adhesive force ranging from (0.91,±,0.34),nN to (1.35,±,0.37),nN. In the macroscopic scale, the nanostructured surface can adhere firmly to a smooth glass substrate and inherits the in-use, self-cleaning property of the setal nanostructures found in gecko lamellae. [source] Improved lateral force calibration based on the angle conversion factor in atomic force microscopyJOURNAL OF MICROSCOPY, Issue 2 2007DUKHYUN CHOI Summary A novel calibration method is proposed for determining lateral forces in atomic force microscopy (AFM), by introducing an angle conversion factor, which is defined as the ratio of the twist angle of a cantilever to the corresponding lateral signal. This factor greatly simplifies the calibration procedures. Once the angle conversion factor is determined in AFM, the lateral force calibration factors of any rectangular cantilever can be obtained by simple computation without further experiments. To determine the angle conversion factor, this study focuses on the determination of the twist angle of a cantilever during lateral force calibration in AFM. Since the twist angle of a cantilever cannot be directly measured in AFM, the angles are obtained by means of the moment balance equations between a rectangular AFM cantilever and a simple commercially available step grating. To eliminate the effect of the adhesive force, the gradients of the lateral signals and the twist angles as a function of normal force are used in calculating the angle conversion factor. To verify reliability and reproducibility of the method, two step gratings with different heights and two different rectangular cantilevers were used in lateral force calibration in AFM. The results showed good agreement, to within 10%. This method was validated by comparing the coefficient of friction of mica so determined with values in the literature. [source] Leukocyte Adhesion in Capillary-Sized, P-Selectin-Coated MicropipettesMICROCIRCULATION, Issue 2 2008Prithu Sundd ABSTRACT Objective: Leukocyte retention in lung capillaries is observed in normal physiology and following a bacterial infection. It has been hypothesized that cells either become mechanically trapped or adhere to capillary endothelial cells via adhesion molecules. We propose that retention involves both mechanical and adhesive forces and that the biochemical adhesive force is modulated by mechanical forces that alter the area of contact between leukocytes and endothelium. Methods: To probe this hypothesis, an adhesion assay has been developed in which individual HL-60 cells were aspirated into micropipettes pre-coated with P-selectin. Following aspiration, cells were exposed to physiological pressure differences. Results: Little adhesion was seen in micropipettes coated with BSA, whereas significant adhesion was observed in micropipettes coated with P-selectin. The frequency of cell arrest on P-selectin in the micropipette was much greater than on P-selectin in a parallel plate flow chamber even though the disruptive force in the micropipette assay exceeds that in the parallel plate flow chamber. These results demonstrate that receptor,ligand interactions can enhance adhesion in a capillary geometry and that differences in capillary geometry vs. venule geometry can significantly influence the adhesive phenotype. Conclusions: Taken together, these observations support the hypothesis that an interplay between mechanical and biochemical adhesive forces can play a major role in retention. [source] The geometry and motion of nematode sperm cellsCYTOSKELETON, Issue 6 2009Evgeny Demekhin Abstract The nematode sperm cell crawls by recycling major sperm protein (MSP) from dimers into subfilaments, filaments, and filament complexes, as a result of thermal writhing in the presence of hydrophobic patches. Polymerization near leading edges of the cell intercolates MSP dimers onto the tips of growing filament complexes, forcing them against the cell boundary, and extending the cytoskeleton in the direction of motion. Strong adhesive forces attach the cell to the substrate in the forward part of the lamellipod, while depolymerization in the rearward part of the cell breaks down the cytoskeleton, contracting the lamellipod and pulling the cell body forward. The movement of these cells, then, is caused by coordinated protrusive, adhesive and contractile forces, spatially separated across the lamellipod. This paper considers a phenomenological model that tracks discrete elements of the cytoskeleton in curvilinear coordinates. The pseudo-two dimensional model primarily considers protrusion and rotation of the cell, along with the evolution of the cell boundary. General assumptions are that pH levels within the lamellipod regulate protrusion, contraction and adhesion, and that growth of the cytoskeleton, over time, is perpendicular to the evolving cell boundary. The model follows the growth and contraction of a discrete number of MSP fiber complexes, since they appear to be the principle contributors for force generation in cell boundary protrusion and contraction, and the backbone for the dynamic geometry and motion. Cell Motil. Cytoskeleton 2009. © 2009 Wiley-Liss, Inc. [source] Designing Superhydrophobic Porous Nanostructures with Tunable Water AdhesionADVANCED MATERIALS, Issue 37 2009Yuekun Lai Basic principles of capillary-induced adhesion and roughness-enhanced hydrophobicity are utilized to design three superhydrophobic porous-nanostructure models whose adhesion forces ranged from strong to weak. The design idea is well-supported by experimental results, which indicated that adhesive forces may be tailored by modifying structural morphologies to manipulate solid,liquid contact behavior and air-pocket composition in open or sealed systems. [source] Cohesive-driven particle circulation in the solids conveying zone of a single-screw extruderADVANCES IN POLYMER TECHNOLOGY, Issue 2 2008Michael R. Thompson Abstract Aspects of heat transfer within the solids conveying zone of a single-screw extruder were studied by using a specially constructed drum testing apparatus. Experiments were conducted with linear low-density polyethylene, polystyrene (PS), and polypropylene (PP) samples by examining their transient temperature profile while the heated drum was stationary or moving. In accordance with classic solids conveying theory, the granular beds of PP and PS remained as plugs while the drum rotated. In such cases, the dominant modes of heat transfer for these systems are conduction through the contact area of a particle and conduction through the interstitial gas. An exception to this behavior was found with PE, in which the bed temperature increased more rapidly while the drum rotated. Visual observations of the bed showed that the particles circulated in the presence of shear and that this complex flow pattern increased in velocity as the drum temperature approached the onset temperature for melting the PE material. With strong correlation between the rate of circulation and the temperature rise in the bed, the movement of particles was assumed to act in a convective heat transfer mode bringing about more uniform heating of the polymer. The circulation phenomenon was attributed to dominant adhesive forces at the particle,drum interface overcoming the cohesive strength of the bulk. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 27:74,88, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20121 [source] Leukocyte Adhesion in Capillary-Sized, P-Selectin-Coated MicropipettesMICROCIRCULATION, Issue 2 2008Prithu Sundd ABSTRACT Objective: Leukocyte retention in lung capillaries is observed in normal physiology and following a bacterial infection. It has been hypothesized that cells either become mechanically trapped or adhere to capillary endothelial cells via adhesion molecules. We propose that retention involves both mechanical and adhesive forces and that the biochemical adhesive force is modulated by mechanical forces that alter the area of contact between leukocytes and endothelium. Methods: To probe this hypothesis, an adhesion assay has been developed in which individual HL-60 cells were aspirated into micropipettes pre-coated with P-selectin. Following aspiration, cells were exposed to physiological pressure differences. Results: Little adhesion was seen in micropipettes coated with BSA, whereas significant adhesion was observed in micropipettes coated with P-selectin. The frequency of cell arrest on P-selectin in the micropipette was much greater than on P-selectin in a parallel plate flow chamber even though the disruptive force in the micropipette assay exceeds that in the parallel plate flow chamber. These results demonstrate that receptor,ligand interactions can enhance adhesion in a capillary geometry and that differences in capillary geometry vs. venule geometry can significantly influence the adhesive phenotype. Conclusions: Taken together, these observations support the hypothesis that an interplay between mechanical and biochemical adhesive forces can play a major role in retention. [source] A physical-mathematical model for the dispersion process in continuous mixersPOLYMER ENGINEERING & SCIENCE, Issue 1 2002H. Potente To modify the properties of polymers, mineral fillers are frequently added during the compounding process. Because of adhesive forces, these pulverized fillers tend to agglomerate. Therefore, in order to achieve good homogenization, it is essential not only to distribute them but also to break down the solid agglomerates. A number of relating models have been published, describing observations (agglomerate rupture, erosion, clustering) made during the dispersion process in a mostly isolated manner. New models for each observed effect have been developed and later superimposed in order to get a comprehensive model of the dispersion process. To verify the model, it was implemented into a program for the process simulation of co-rotating twin-screw extruders. It was then compared to experimental data. The results showed that the model is able to describe the experimentally determined data. [source] Re-entrainment of wall deposits from a laboratory-scale spray dryerASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2007M. J. Hanus Abstract This work has determined the magnitude of re-entrainment and established the operational parameters that may be manipulated to influence re-entrainment of salt particles for a small-scale spray dryer (Buchi B-290). The wetness of the spray dryer wall deposits was found to significantly influence the magnitude of re-entrainment. It was shown both experimentally and numerically that wet deposits form at low nozzle air-to-liquid ratios (<2000), which form large droplets that dry slowly, while the initial droplet velocity did not have a large influence on wet deposition. Wet deposits form strong liquid and solid bridges, and thus deposits formed from wet particles were difficult to re-entrain. Less than 2% of deposits formed at nozzle air-to-liquid ratios less than 2000 were re-entrained, while 15.4 to 21.2% of dry deposited particles (formed at nozzle air-to-liquid ratios ranging from 2308 to 3409) were re-entrained. The threshold re-entrainment velocity of sodium chloride particles in the Buchi B-290 spray dryer was found to be between 4 and 7.7 ms,1, which is consistent with the lower-end threshold velocities presented in the literature. No significant trend relating relative humidity to the magnitude of re-entrainment was found in the 0.2,7.4% average relative humidity range, suggesting that the adhesive forces in spray dryer wall deposits are fairly constant across this relative humidity range. Decreasing wall deposit wetness through use of high (>2000) nozzle air-to-liquid ratios and use of high main gas velocities increased the re-entrainment of wall deposits in this spray dryer. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Cell Detachment Model for an Antibody-Based Microfluidic Cancer Screening SystemBIOTECHNOLOGY PROGRESS, Issue 5 2006Swapnil P. Wankhede We consider cells bound to the floor of a microfluidic channel and present a model of their flow-induced detachment. We approximate hydrodynamic force and cell elastic response using static finite-element simulation of a single cell. Detachment is assumed to occur when hydrodynamic and adhesive forces are roughly equal. The result is extended to multiple cells at the device level using a sigmoidal curve fit. The model is applied to a microfluidic cancer-screening device that discriminates between normal epithelial cells and cells infected with human papillomavirus (HPV), on the basis of increased expression of the transmembrane protein ,6 integrin in the latter. Here, the cells to be tested are bound to a microchannel floor coated with anti ,6 integrin antibodies. In an appropriate flow rate range, normal cells are washed away while HPV-infected cells remain bound. The model allows interpolation between data points to choose the optimal flow rate and provides insight into interaction of cell mechanical properties and the flow-induced detachment mechanism. Notably, the results suggest a significant influence of cell elastic response on detachment. [source] | |||||||||||||||||||||||||||||||