Browsing by Subject "Adhesion"
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Item Adhesion of particles on indoor flooring materials(2007-12) Lohaus, James Harold, 1968-; Siegel, Jeffrey A.This dissertation involved a theoretical and experimental investigation of the adhesive forces between spherical particles of four different diameters and two selected flooring materials under different air velocities. Previous theoretical work and experiments described in the literature tended to be conducted with idealized surfaces, and therefore have limited applicability to indoor environments. Controlled experiments were designed, constructed and executed to measure the air velocity required to overcome adhesion forces. The diameters of the particles investigated were 0.5, 3.0, 5.0 and 9.9 [mu]m, and the flooring materials were linoleum and wooden flooring. The critical velocity, the flow at which 50% of the particles detached, is presented as a function of particle diameter for each surface. The measured values were then compared to empirical and theoretical models as well as to a scaling analysis that considers component forces that act on a particle-surface system. The results suggest that critical velocity decreases with increasing particle diameter and that existing models have limited applicability to resuspension from flooring materials.Item Characterization of delamination in silicon/epoxy systems(2014-05) Gowrishankar, Shravan; Liechti, K. M.Microelectronic devices are multilayered structures with many different interfaces. Their mechanical reliability is of utmost importance when considering the implementation of new materials. Linear elastic fracture mechanics (LEFM) is a common approach that has been used for interfacial fracture analyses in the microelectronics industry where the energy release rate parameter is considered to be the driving force for delamination and the failure criterion is established by comparing this with the interface toughness. However this approach has been unable to model crack-nucleation, which plays an important part in analyzing the mechanical reliability of chip-package systems. The cohesive interface modeling approach, which is considered here, has the capability to model crack nucleation and growth, provided interfacial parameters such as strength and toughness of the system are available. These parameters are obtained through the extraction of traction-separation relations, which can be obtained through indirect hybrid numerical/experimental methods or direct experimental methods. All methods of extracting traction-separation relations require some local feature of the crack-tip region to be measured. The focus in this doctoral work has been on the comparison of the two methods for a mode-I DCB experiment and on the development of a universal loading device to extract mixed-mode traction-separation relations at different mode-mix values. The techniques that have been adopted for the local measurements are infrared crack opening interferometry (IR-COI) and digital image correlation (DIC). Apart from the global measurements of load-displacement (P-[delta]), local crack-tip parameters were measured using IR-COI or DIC. The combination of global and local measurements gave the relations between the fracture driving force (energy release rate or J-integral, J) and crack opening displacements, which were used to obtain the local tractions. IR-COI is an extremely useful technique to image and measure local crack-tip parameters. However, as IR-COI is restricted to normal measurements, the loading device was configured to accommodate a DIC system in order to make both normal and tangential measurements. In addition to measurements, fracture surface characterization techniques such as atomic force microscopy (AFM), profilometry and X-ray photoelectron spectroscopy were used to observe the fracture mechanisms.Item Electrowetting-based control of water adhesion to surfaces(2015-05) Galvin, Christopher D.; Bahadur, Vaibhav; Bogard, DavidThis thesis lays the foundations for the electrical control of adhesion of water drops and films to surfaces. Electrowetting (EW) is the increase in wettability of conducting liquids via the application of a concentrated interfacial electric field. EW can be exploited to keep a surface water-wet and displace non-conducting liquids away from the surface. This concept has various applications in the field of oil-gas flow assurance, such as hydrocarbon fouling mitigation, and heavy oil pumping via core annular flows. This dissertation presents experimental results that are the first step towards experimental validation of the concept of keeping surfaces water-wet under hydrocarbon flow conditions. The first experiments involve measurements of the electrically tunable water drop-surface adhesion. Adhesion is measured in terms of the tilt angle needed to roll off an electrowetted drop from the surface. Measurements show a 67 % increase in drop-surface adhesion at a 20 V/µm electric field. The second set of experiments show that electrowetting forces are strong enough to displace very viscous oil from a surface and wet the surface with water. The influence of the magnitude and frequency of the AC voltage on oil displacement with water is experimentally quantified. Along with the experimental efforts, first order modeling results to predict the retention of electrowetted water films under hydrocarbon shear conditions are presented. These efforts map the technical feasibility of the proposed concept for field conditions. It is seen that EW is a powerful tool to enforce water wetting under relevant field conditions; furthermore the benefits of using this concept will be transformative.Item Measurement of adhesion between soft elastomers with different mixing ratios(2014-05) Yu, Yalin; Lu, Nanshu; Landis, ChadThe JKR method is widely used to measure the work of adhesion between soft materials. In this report, the JKR theory is summarized and three dimensionless parameters are proposed as prerequisites to determine sample dimensions in designing experiments. Also, the work of adhesion between two commonly used soft elastomers PDMS (Sylgard 184) and Ecoflex 0300 are obtained with the measured pull-in and pull-off forces from a dynamical mechanical analyzer. The Young’s moduli of pristine PDMS are also calculated with a two point formula and the results are compared with that from tensile tests. Our results for the work of adhesion of pristine PDMS 10:1 agree well with those reported in the literature. The pull-off work of adhesion of pristine PDMS increases significantly as the mixing ratio increases from 10:1 to 20:1. With further increasing mixing ratios, the pull-off work of adhesion does not change much. However, for PDMS samples extracted with chloroform, the pull-off work of adhesion increases monotonically as the mixing ratio varies from 10:1 to 50:1. A similar trend is also observed for the case of contacts between pristine PDMS lenses and Ecoflex substrates. For the pull-in work of adhesion, the results are almost independent of the mixing ratios. An adhesion mechanism is proposed to explain these complex adhesion behaviors. It is concluded that the entanglement with each other and penetration into networks of tethered chains during the contact could enhance the pull-off work of adhesion. With both ends uncross-linked, free chains do not enhance the pull-off work of adhesion as significant as tethered chains. Therefore, for pristine PDMS with higher mixing ratios, the existence of more free chains reduces the chance of the entanglement and penetration of tethered chains, which compensates for the enhancement by more tethered chains.Item Size and shape effects for the nano/micro particle dynamics in the microcirculation(2010-08) Lee, Sei Young; Moser, Robert deLancey; Ferrari, Mauro, 1959-; Decuzzi, Paolo; Chen, Shaochen; Hidrovo, CarlosThe nano/micro particles have been widely used as a carrier of therapeutic and contrast imaging agents. The nano/micro particles have many advantages, such as, specificity, controlled release, multifunctionality and engineerability. By tuning the chemical, physical and geometrical properties, the efficacy of delivery of nano/micro particle can be improved. In this study, by analyzing the effect of physical and geometrical properties of particle, such as, size, shape, material property and flow condition, the optimal condition for particle delivery will be explored. The objectives of this study are (1) to develop predictive mathematical models and (2) experimental models for particle margination and adhesion, and (3) to find optimal particle geometry in terms of size and shape to enhance the efficiency of its delivery. The effect of particle size expressed in terms of Stokes number and shape, namely, spherical, ellipsoidal, hemispherical, discoidal and cylindrical particle on the particle trajectory is investigated. For discoidal and cylindrical particles, the effect of aspect ratio is also considered. To calculate particle trajectory in the linear shear flow near the substrate, Newton's law of motion is decomposed into hydrodynamic drag and resistance induced by particle motion. The drag and resistance is estimated through finite volume formulation using Fluent v6.3. Particle behavior in the linear shear flow does strongly depend on Stokes number. Spherical particle is transported following the streamline in the absence of external body force. However, non-spherical particles could across the streamline and marginate to the substrate. For non-spherical particles, the optimal [Stokes number] in terms of particle margination is observed; [Stokes number almost equal to] 20 for ellipsoidal, hemispherical and discoidal particle; [Stokes number almost equal to] 10 for cylindrical particle. For discoidal particle with [gamma subscript d]=0.2 shows fastest margination to the substrate. The effect of gravitational force is also considered with respect to the fluid direction. When the gravitational force is applied, mostly, gravitational force plays a dominant role for particle margination. However, using small particle aspect ratio ([gamma subscript d]=0.2 and 0.33), spontaneous drift induced by particle-fluid-substrate interaction could overcome gravitational effect in some cases ([Stokes number]=10, G=0.1). In addition the adhesion characteristic of spherical particle has been studied using in vitro micro fluidic chamber system with different particle size and flow condition. The experimental results are compared to the mathematical model developed by Decuzzi and Ferrari (Decuzzi and Ferrari, 2006) and in vivo test (Decuzzi et al., 2010). The optimal particle size for S=75 and 90 is found to be 4-5 [micrometer] through the in vitro non-specific interaction of spherical particle on the biological substrate. The suggested mathematical model has proven to be valid for current experimental condition. At the end, the mathematical model, in vitro flow chamber results and in vivo test have been compared and the scaling law for particle adhesion on the vessel wall has been confirmed.