Analysis of stresses in adhesive joints applicable to IC chips using symbolic manipulation and the numerical method

In this study, a concentrated force is applied to both adherends bonded by an adhesive under pin–pin boundary conditions. First a mathematical model is derived with governing equations and boundary conditions. These complicated, and analytically problematic, coupled equations are solved numerically using symbolic manipulation and singular value decomposition (SVD). Also discussed are the effects of major factors, including the relative thickness of adherends, joint length and the action point of the concentrated force on the peel and shear stresses in the adhesive layer. This study identifies the conditions under which the upper adherend without breakage can be fully separated from the lower adherend. Particularly, it is found that the thickness of the lower adherend should be greater than ten times that of the adhesive layer but less than one-third that of the upper adherend, the adhesive layer should be relatively thin (h _a ≤ 0.01 mm), and the adhesive joint should be relatively short (thickness to length ratio γ ₁ ≥ 0.08).     

An analytical approach for the adhesion of a semi-infinite elastic body in contact with a sinusoidal rigid surface under zero external pressure

An analytical approach for the adhesion of a semi-infinite elastic body in contact with a sinusoidal rigid surface under zero external pressure is presented. Although Johnson (Int. J. Solids Struct. 32, 423 (1995)) has proposed an analytical solution for a slightly wavy surface, while Zilberman and Persson (Solid State Commun. 123, 173 (2002); J. Chem. Phys. 118, 6473 (2003)) have given a numerical solution for a highly wavy surface by considering the curvature of the contact area in the calculation of the interfacial term of the total energy, our solution is not only for small amplitude of roughness (i.e., the slightly wavy surface as Johnson's) but also for large amplitude of roughness (i.e., the highly wavy surface as of Zilberman and Persson). Our solution considers the curvature of the contact area as do Zilberman and Persson. Our results which are obtained for the total energy and equilibrium condition of the system agree with both Johnson's and Zilberman and Persson's results. The effects of the material constants and the surface roughness on the adhesion are clearly expressed and discussed.     

Fracture mechanics testing of the bond between composite overlays and a concrete substrate

This paper presents a methodology for assessing the bond strength of composite overlays to concrete utilizing a fracture toughness test. The principles and practices of existing ASTM standards for determining the fracture toughness of adhesive bonds between double cantilever beam (DCB) metallic and composite specimens (D 3433-93 and D 5528-94a) have been extended to cover the case of an elastic composite layer bonded to a rigid concrete/masonry substrate. In the theoretical section, the dominant loading conditions, relevant ASTM standards, and the development of energy release rate concepts for analyzing a disbonding composite layer modeled as an elastic cantilever beam are presented. The experimental section covers specimen fabrication and preparation, experimental setup, test procedures, post-test evaluation of the specimens, and data processing. The discussion of test results focuses on explaining the variability in measured strain energy release rate, and identifies trends between the measured strain energy release rate and the fraction of the fracture surface retaining cement paste after disbonding. It was found that good-quality composite-to-concrete bond is associated with high fracture toughness of the adhesive and location of the crack path in the concrete substrate. Strict enforcement of surface preparation and adhesive handling procedures was found to play an important role in promoting good bond strength and high fracture toughness. The fracture toughness test developed in this paper can be used for screening various composite-repair systems, to assess the effect of different environmental attacks, and as a quality control tool.     

On the work of adhesion and peel strength between pressure sensitive adhesives and the polymeric films used in LCD devices

Peel strength, a convenient measure of bond strength in adhesive/adherend systems, is known to be a function of various factors such as the thermodynamic work of adhesion, rate of measurement, thermal history, and temperature. Generally, it is believed that the work of adhesion is primarily involved in the first stage of adhesion through wetting phenomenon and beyond that its role diminishes in that the portion of thermodynamic contribution to actual bond strength is insignificant. In practice, however, we often observe that a suitable surface treatment increases the surface energy of the substrate, which further enhances the bond strength. One practical example is the surface treatment carried out in LCD industry to obtain sufficient bond strength between pressure sensitive adhesives and polymeric films. To further our understanding of the effect of surface treatment, we attempted to establish a possible correlation, if any, between the thermodynamic work of adhesion and peel strength. For this, we carefully measured the contact angles of water and diiodomethane against various polymeric films, and calculated the surface energy and the thermodynamic work of adhesion using the two widely used approaches: Young-Fowkes-Girifalco-Good, and Wu methods. Before establishing a correlation, some general aspects of the above two methods are discussed. The values of the work of adhesion obtained were compared with the measured peel strength. Indeed, we observed a clear correlation between the two quantities: the increase of the work of adhesion led to the increase of peel strength. As a reason for this correlation, we proposed that the increase of surface energy might be associated with the increase of various surface functional groups, which, in turn, contributed to the formation of chemical bonding with the PSA leading to the increase of peel strength.     

Optimizing the balance between viscosity/modulus and impact in particulate composites

The objective of this study was to develop some new concepts of importance when trying to optimize the viscosity/modulus and impact relative to the particle‐size distribution in suspensions and particulate composites. The results of this study appear to indicate that, conceptually, it is possible to significantly improve the viscosity versus the impact balance for material formulations by optimizing the particle‐size distribution. For binary particle‐size distributions, the influence of the preferred particle‐size distribution, as determined using a square‐root distribution, did not yield the most desirable particle‐size distribution if the particle‐to‐particle component of the interaction coefficient was high. However, if three or more particles were utilized in the distribution, then the optimum particle‐size distribution utilized can apparently be characterized using the square‐root distribution even when the particle–particle component, σ_pc, of the interaction coefficient, σ, was found to be quite high. In addition, this same square‐root particle‐size distribution can also satisfactorily predict a probability of impact that can remain consistently high as long as the particles utilized are well chosen and not too close in size. Thus, this preferred particle‐size distribution can be utilized to predict at least one of the preferred distributions to optimize the balance of properties between impact and the viscosity/modulus. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 291–304, 2002     

Continuity of kinetics between sub- and supercritical regimes in the oxidation of a high-volatile solid substrate

Peat samples were subjected to oven experiments spanning a considerable temperature range, some resulting in ignition and some in failure to ignite. Heat release rates for the two display a temperature dependence describable by a single pair of Arrhenius parameters in spite of significantly greater volatiles release in some experiments than in others. Applicability of the Frank-Kamenetskii treatment to such materials is discussed in the light of these findings.     

Comparison between the adherence of a rigid axisymmetrical cone and a truncated one,in adhesive contact on an elastic half-space

We compare the equilibrium contacts and the kinetics of adherence of an axisymmetrical rigid cone and a flat-ended one with the same angle, applied against the flat and smooth surface of a soft elastomer sample (unfilled vulcanized natural rubber, cured with dicumyl peroxide), with the help of fracture mechanics concepts which can easily be introduced in this class of problems by using Sneddon's solution (1965) of Boussinesq's problem extended to all axisymmetric adhesive punches with a convex profile. The kinetics of adherence are measured when an imposed tensile force is applied in order to disturb the size of the contact area. Variations of the strain energy release rate, G, and of the associated dissipation function | =(G m w)/w, where w is the Dupré energy of adhesion, are studied as a function of the parameter, a T ± V, in which V is the crack propagation speed at the interface between a cone and a truncated one made of glossy Plexiglass®, and the rubber sample (the limit of the contact is considered as a crack tip), and a T , is the shift factor of the Williams-Landel-Ferry transformation. As expected, a master curve | (V) is found, confirming the variation of | as the power function V 0.55 , at fixed temperature, as recently established by Barquins et al. in adherence of a flat ended sphere and cone in pull-off/push-on tests, adherence and rolling of cylinders experiments and rebound of balls tests, with the same elastomer. Present results lead to propose one to write | =k ± (a T ± V) 0.55 , k=2520 and V being valued using S.I. units, for the reference temperature θ=25°C, with a quite good accuracy in the order of 1%.     

The interaction mechanism between microorganisms and substrate in the biodegradation of polycaprolactone

The present work concerns the interplay of the degradation mechanism and the nature of the interaction between microorganisms and substrate. The biodegradation of polycaprolactone films by a pure strain of microorganisms isolated from an industrial composting unit for household refuse was studied in minimal medium with the polymer as sole carbon source. In conditions where the polymer surface is colonized and a biofilm is formed (under a low stirring rate), polymer weight loss is limited, whereas total degradation is observed when stirring conditions prevent biofilm formation. In the first case, holes are observed in the degraded film and a polysaccharide responsible for microorganism adhesion was identified by FTIR. SEM observation of the polymer surface as a function of the degradation time suggests that the crystalline and amorphous phase are degraded at about the same rate in the first case, whereas the amorphous phase is preferentially degraded in the latter. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1334–1340, 2002     

Optimizing the balance between impact strength and stiffness in polypropylene/elastomer blends by incorporation of a nucleating agent

Isotactic polypropylene (iPP) blends were prepared with two different thermoplastic elastomers, a triblock copolymer styrene–ethylene butylene–styrene (SEBS) and a metallocenic ethylene‐octene copolymer (EO). The mechanical properties and morphology of blends with 0–50 wt% elastomer were studied to determine the influence of the presence of the elastomer on the improvement of toughness. The addition of a nucleating agent as a third component exerted a significant effect on the overall properties. Dynamic mechanical properties, flexural modulus, and impact strength as well as morphology were studied for nucleated and nonnucleated iPP/SEBS and iPP/EO blends. The improvement of impact properties found in binary blends was accompanied by a decrease in stiffness. However, the addition of the nucleating agent provided a good balance between impact strength and stiffness. From the results, SEBS was determined to be a better impact modifier for iPP than EO. The nucleated iPP/SEBS blends demonstrated improved mechanical properties compared with both the nucleated iPP/EO blends and the nonnucleated blends. POLYM. ENG. SCI., 48:80–87, 2008. © 2007 Society of Plastics Engineers     

Revisit the adhesive contact between a nanoscale rigid sphere and an elastic half-space: considering the effect of sphere size

The current paper revisits the adhesive contact between a rigid nanoscale sphere and an elastic half-space. Using analytical solution for traction and a modified numerical scheme, a new simulation is proposed. The adhesive contact is simulated faster and more easily than previous researches. The effect of sphere size is investigated. A modified spherical JKR model and spherical DMT model are proposed. The results are compared with spherical JKR, spherical DMT, and rigid sphere model. The load–approach and contact radius–load relations can be predicted by the modified spherical JKR model for sphere radius larger than 50?. Finally, approximation equations for pull-off force vs. Tabor parameter and jump-in distance vs. Tabor parameter are proposed.     

Modelling and analysis of the electrostatic adhesion performance considering a rotary disturbance between the electrode panel and the attachment substrate

In real-world applications of electrostatic adhesion technology, the electrostatic adhesion force decreases when the electrode panel slides or rotates relative to the attachment substrate due to an external disturbance. However, little work has been done to study this phenomenon. This paper presents a model and analysis method to evaluate the electrostatic adhesion performance considering a rotary disturbance between the electrode panel and the attachment substrate. First, dynamic variations of the electric fields for any point on the attachment substrate are analysed. Then the decrease in the electrostatic adhesion force is explained based on the analysis results and our previous work. The analysis results and explanations are experimentally validated on three different attachment substrates. The fundamental cause of the decrease in adhesion force is the loss of the lined layer polarization due to the rotary disturbance. The results provide a good explanation to the phenomenon and make the existing electrostatic adhesion theory more self-consistent.     

Combined enzyme and substrate design: grafting of a cooperative two-histidine catalytic motif into a protein targeted at the scissile bond in a designed ester substrate

A histidine-based, two-residue reactive site for the catalysis of hydrolysis of designed sulfonamide-containing para-nitrophenyl esters has been engineered into a scaffold protein. A matching substrate was designed to exploit the natural active site of human carbonic anhydrase II (HCAII) for well-defined binding. In this we took advantage of the high affinity between the active site zinc atom and sulfonamides. The ester substrate was designed to position the scissile bond in close proximity to the His64 residue in the scaffold protein. Three potential sites for grafting the catalytic His-His pair were identified, and the corresponding N62H/H64, F131H/V135H and L198H/P202H mutants were constructed. The most efficient variant, F131H/V135H, has a maximum k(cat)/K(M) value of approximately 14 000 M(-1) s(-1), with a k(cat) value that is increased by a factor of 3 relative to that of the wild-type HCAII, and by a factor of over 13 relative to the H64A mutant. The results show that an esterase can be designed in a stepwise way by a combination of substrate design and grafting of a designed catalytic motif into a well-defined substrate binding site.     

完全混合活性污泥法处理含海水污水时基质降解与生物增长量之间的关系

介绍了采用完全混合活性污泥系统处理含海水污水,研究了基质降解与生物增长量之间的关系。结果表明,微生物产率系数随着污水中海水比例的增大而增长。     

Improvement in the adhesion between copper metal and polyimide substrate by plasma polymer deposition of cyano compounds onto polyimide

The surface modification of Kapton film by means of plasma polymer deposition is discussed from the viewpoint of improving the adhesion between copper metal and Kapton film substrate. Plasma polymers of AN (acrylonitrile) and FN (fumaronitrile) were used for the surface modification, and the adhesion between the copper metal and the plasma polymer-coated Kapton film was evaluated by the T-peel strength measurement. The surfaces of peeled layers were analyzed by X-ray photoelectron spectroscopy (XPS) and the failure mode is discussed. The plasma polymer deposition of AN and FN shows an effective improvement in the adhesion between the copper metal and Kapton film; in particular, the AN plasma polymer deposition increased the peel strength 4.3 times. Failure occurred mainly in the Kapton film, and the adhesion between the AN plasma polymer and the Kapton film and that between the copper metal and the AN plasma polymer were found to be quite strong.     

Modelling of the substrate heterogeneities experienced by a limited microbial population in scale-down and in large-scale bioreactors

A methodology based on stochastic modelling is presented to describe the influence of the bioreactor heterogeneity on the microorganisms growth and physiology. The stochastic model is composed of two sub-models: a microorganism circulation sub-model and a fluid mixing sub-model used for the characterization of the concentration gradient. The first one is expressed by a classical stochastic model (with random number generation), whereas the second one is expressed by a stochastic Markov chain. Their superimposition permits to obtain the concentration profiles experienced by the microorganisms in the bioreactor. The simulation results are expressed in the form of frequency distributions. At first, the study has been focused on the design of scale-down reactors (SDR). This kind of reactor has been reported to be an efficient tool to study at a small-scale the hydrodynamic behaviour encountered in large-scale reactor [P. Neubauer, L. Horvat, S.O. Enfors, Influence of substrate oscillations on acetate formation and growth yield in Escherichia coli glucose limited fed-batch cultivations, Biotechnol. Bioeng. 47 (1995) 139–146]. Several parameters affecting the shape of the frequency distributions have been tested. Among these, it appears that the perturbation frequency, the exposure time and the design of the non-mixed part of the SDR have a significant influence on the shape of the distributions. The respective influence of all these parameters must be taken into account in order to obtain representative results. As a general trend, the increase of the recirculation flow rate between the mixed and the non-mixed part of the SDR induce a shift of the frequency distribution for the lower relative concentrations, which suggests an attenuation of the scale-down effect. This has been validated by using the SDR in the case of the cultivation of Saccharomyces cerevisiae. However, the influence of the non-mixed part of the SDR is not quite well understood if only taking account of the frequency distribution analysis, and supplementary experiments are required to elucidate the underlying mechanism.

The aspect of the frequency distributions suggests that both the design and the operating conditions of a scale-down reactor need to be adjusted in order to match the behaviour of a given large-scale reactor. Examples of frequency distributions obtained in the case of large-scale reactors are given.     

Exploring macro- and microlevel connectivity of the urea phase in slabstock flexible polyurethane foam formulations using lithium chloride as a probe

Urea phase connectivity has been probed by systematically varying the hard segment content, and lithium chloride content, in a series of plaques based on slabstock flexible polyurethane foams. The plaque formulations are identical to those of slabstock polyurethane foams with the exception that a surfactant is not utilized. Small angle X-ray scattering (SAXS) is used to demonstrate that all materials investigated are microphase separated with similar interdomain spacings, irrespective of hard segment content (21-37 wt%) or LiCl content. Several complimentary characterization techniques are employed to reveal that urea phase connectivity is present at different length scales. Macrolevel connectivity, or connectivity of the large-scale urea rich aggregates typically observed in flexible slabstock polyurethane foams, is probed using SAXS, TEM, and atomic force microscopy. These techniques collectively show that the urea aggregation increases as the hard segment content is increased. Incorporation of LiCl is shown to systematically reduce the urea aggregation behavior, thus leading to a loss in the macroconnectivity of the urea phase. Wide angle X-ray scattering is used to probe the regularity in segmental packing, or the microlevel connectivity between the hard segments, which is observed to decrease systematically on addition of LiCl. The loss in microlevel connectivity is suggested to increase chain slippage, and leads to increased rates of stress-relaxation for the samples containing LiCl. Materials containing LiCl also display relatively short rubbery plateaus as compared to their counterparts which do not contain the additive. Modulus values, as obtained at ambient conditions by stress-strain analyses, are found to be a stronger function of LiCl content when the hard segment content is higher.     

Glass transition and free volume in the mobile (MAF) and rigid (RAF) amorphous fractions of semicrystalline PTFE: a positron lifetime and PVT study

The structure of the free volume and its temperature dependence in poly(tetrafluoroethylene) (PTFE) and of its copolymer with perfluoro(propyl vinyl ether) (PFA) was studied by pressure-volume-temperature (PVT) experiments (T=27-380 °C, P=0.1-200 MPa) and positron annihilation lifetime spectroscopy (PALS, T=−173-250 °C, P=10⁻⁵ Pa). From the analysis of these experiments we conclude on the volumetric properties of the mobile (MAF) and rigid amorphous fractions (RAF) in these semicrystalline polymers. The specific volumes of the MAF and RAF, V_MAF and V_RAF, were estimated assuming that V_MAF agrees with the specific volume of the melt extrapolated down to lower temperatures using the Simha-Somcynsky equation of state (S-S eos). V_RAF was then estimated from the specific volume of the entire amorphous phase, V_a, and the known V_MAF. The specific free volume V_f=V_a−V_occ was also estimated from V_a using the S-S eos hole fraction h, V_occ=(1−h)V_a. From the analysis of PALS data with the routine LT9.0 the mean volume, 〈v_h〉, and the width, σ_h, of the local free volume size distribution (holes of subnanometre size) were obtained. A comparison of 〈v_h〉 with V_f delivered the hole density N^′h. The volume parameters show that the RAF which is formed during crystallisation from the melt has a distinctly smaller specific free and total volume than the MAF. During cooling the contraction of the RAF slows down and finally, below room temperature, the RAF possesses a larger free volume than the MAF shows. Obviously, the restriction of the segmental mobility in the RAF by the crystals limits at high temperatures the free volume expansion and at low temperatures dense packing of the polymer chains. These conclusions from the analysis of the specific volume are confirmed by PALS experiments.     

Direct Measurement of the Affinity between tBid and Bax in a Mitochondria-Like Membrane

The execution step in apoptosis is the permeabilization of the outer mitochondrial membrane, controlled by Bcl-2 family proteins. The physical interactions between the different proteins in this family and their relative abundance literally determine the fate of the cells. These interactions, however, are difficult to quantify, as they occur in a lipid membrane and involve proteins with multiple conformations and stoichiometries which can exist both in soluble and membrane. Here we focus on the interaction between two core Bcl-2 family members, the executor pore-forming protein Bax and the truncated form of the activator protein Bid (tBid), which we imaged at the single particle level in a mitochondria-like planar supported lipid bilayer. We inferred the conformation of the proteins from their mobility, and detected their transient interactions using a novel single particle cross-correlation analysis. We show that both tBid and Bax have at least two different conformations at the membrane, and that their affinity for one another increases by one order of magnitude (with a 2D-KD decreasing from ≃1.6μm−2 to ≃0.1μm−2) when they pass from their loosely membrane-associated to their transmembrane form. We conclude by proposing an updated molecular model for the activation of Bax by tBid.