Moisture Force Research Articles

Low Fibrillation Lyocell Fiber: Analysis of Fiber and its Crosslinking Agent

AbstractIn this paper, the hydrolysis process of Dichlorohydroxytriazine (NHDT) under alkaline conditions are studied. A qualitative and quantitative method for the determination of HNDT and its hydrolysis products are established, which further clarified the hydrolysis mechanism of NHDT. Under alkaline conditions, the hydrolysis products are mainly compound 4, compound 6 and chloride (Cl−). The hydrolysis rate of NHDT at different NaOH concentration and temperature is studied. This research can be used to guide the high efficiency preparation of low fibrillation Lyocell fiber. According to the quantitative detection of wet abrasion numbers and the qualitative analysis of the fiber by SEM after slapping, it is concluded that the low fibrillation Lyocell fiber is less prone to fibrillation under the combined action of wet state and mechanical force. Due to hydrolysis of the unreacted second chlorine resulting in harmful products on the low fibrillation Lyocell fiber, the fibrillation propensity increased with the increase of storage time. The mechanical properties of low fibrillation Lyocell fiber prepared under different fiber states are studied. The tensile breaking strength of low fibrillation Lyocell fiber prepared in the form of sequentially arranged fiber bundles are better, which is closely related to the fiber surface.

Enhancing wet surface adhesion in walking robots: finite element-based analysis and morphology-changeable soft pads

In recent studies concerning walking robots, there has been a notable emphasis on investigating tribological phenomena and elucidating the role of capillary forces in tangential resistance. However, majority of these investigations have been restricted to specific geometric shapes, primarily spherical domes. In this research, we propose a novel approach based on the finite element method to address broader challenge of wet adhesion applicable to objects of various shapes. Additionally, we investigate the role of distributed domes on a soft foot in quantifying the tangential capillary force, which plays a crucial role in enhancing the performance of walking robots on wet surfaces. Through the optimization application, we identify that our designed foot (measuring 20 mm × 14 mm, comprising 78 domes with a radius of 0.5 mm and a distance of 1.5 mm between the two nearest domes) maximizes the value of the tangential capillary force. Moreover, we develop a finite element method using the Simulation Open Framework Architecture (SOFA) to model the interaction between wet liquid on a solid object's curved surface, enabling the calculation of wet adhesion force and capillary forces. Finally, to demonstrate the effectiveness of our proposed morphology-changeable soft pads foot, we conduct a presented a demonstration of a hexapod robot walking on different dry/wet condition of the surface. The obtained results are expected to pave a way to morphological design of soft pads for facilitating locomotion in various conditions. Supplementary video URL: https://youtu.be/yVteC95eqbo

Design of anti-mildew smart microcapsules with chitosan as encapsulant for advanced electronic packaging epoxy coating

Moisture protection, anti-mildew and anti-corrosion are essential to guarantee the normal service of electronic devices. Although the epoxy holds great potential for electronic packaging, its inferior anti-corrosive performance and anti-mildew capability significantly affect the lifespan of the coating and thus impede further technological advances in electronic devices. To address this concern, herein, we fabricate environmental-friendly anti-mildew smart microcapsules (MCs) by encapsulating benzotriazole (BTA) loaded halloysite clay nanotubes (HNTs) with chitosan (CTS). The coating presents superior anti-mildew property with 5 wt% MCs addition. Furthermore, the charge transfer resistance (Rct) of T2 copper beneath the coating is three orders of magnitude larger after 35 days' immersion, which confirms a significantly promoted anti-corrosive performance for the coating. Moreover, mechanism study shows that such enhanced corrosion protective performance of proposed coating benefits from an excellent self-healing property enabled by a sustainable release of BTA with water and dual-pH sensitivity as well as effective adsorption of BTA on metal surface. It is further uncovered that the release rate of BTA is simultaneously determined by solubility of BTA, acid pH sensitivity of CTS and interaction between BTA and CTS. In addition, mechanical properties of coatings are enhanced with the tensile strength and elongation significantly increased, while the wet adhesion force (72 h) is also enlarged from 4.03 MPa to 7.22 MPa. Such a delicate design of environmental-friendly anti-mildew smart MCs not only enhances the corrosion protective property and the anti-mildew performance of the electronic packaging coatings, but also can facilitate the fabrication of other multifunctional organic coatings by utilizing multifunctional inhibitor or polyelectrolytes.

Effect of AC interference on failure mechanism of zinc-rich epoxy coatings in alkaline environment

In this paper, the failure mechanism of Zn-rich epoxy coating under the AC interference in alkaline environment was revealed based on EIS tests. Using X80 steel as matrix, the coated X80 sample was formed by hand-brushing coating with the thickness of 25 ± 5 μm determined by five-point test. The EIS curves of the coated X80 sample in 3 wt% NaOH solution with immersion time was studied under (no) AC interference, and the failure evolution mechanism of Zn-rich epoxy coating was established through the fitting parameters. The results showed that during the curing process of the Zn-rich epoxy coating, Zn reacted with O2 in the air to generate ZnO, which coated the surface of Zn particle to form the ZnO-Zn structure. In alkaline environment, ZnO dissolved to form Zn(OH)2, namely the activation process of Zn particles, which was inhibited by AC interference. Furthermore, the activated Zn particles reacted to form Zn(OH)2 in alkaline environment, that is, the electrochemical reaction process of activated Zn particles, which was significantly promoted by AC interference. In conclusion, the non-conductive Zn(OH)2 generated in alkaline environment under AC interference, together with un-activated ZnO, can not only isolate the electrical connection between activated Zn particles, but also cut off the cathodic protection between Zn and Fe. Meanwhile, the matrix Fe was passivated in alkaline environment, which weakened the wet binding force between Fe and epoxy coating, resulting in coating stripping.

Janus mucosal dressing with a tough and adhesive hydrogel based on synergistic effects of gelatin, polydopamine, and nano-clay

There are many problems and challenges related to the treatment of highly prevalent oral mucosal diseases and oral drug delivery because of a large amount of saliva present in the oral cavity, the accompanying oral movements, and unconscious swallowing in the mouth. Therefore, an ideal oral dressing should possess stable adhesion and superior tough strength in the oral cavity. However, this fundamental requirement greatly limits the use of synthetic adhesive dressings for oral dressings. Here, we developed a mussel-inspired Janus gelatin-polydopamine-nano-clay (GPC) hydrogel with controlled adhesion and toughness through the synergistic physical and chemical interaction of gelatin (Gel), nano-clay, and dopamine (DA). The hydrogel not only exhibits strong wet adhesion force (63 kPa) but also has high toughness (1026 ± 100 J m−3). Interfacial adhesion of hydrogels is achieved by modulating the interaction of catechol groups of the hydrogel with specific functional groups (e.g., NH2, SH, OH, and COOH) on the tissue surface. The matrix dissipation of the hydrogel is regulated by physical crosslinking of gelatin, chemical crosslinking of gelatin with polydopamine (Michael addition and Schiff base formation), and nano-clay-induced constraint of the molecular chain. In addition, the GPC hydrogel shows high cell affinity and favors cell adhesion and proliferation. The hydrogel's instant and strong mucoadhesive properties provide a long-lasting therapeutic effect of the drug, thereby enhancing the healing of oral ulcers. Therefore, mussel-inspired wet-adhesion Janus GPC hydrogels can be used as a platform for mucosal dressing and drug delivery systems. Statement of significanceIt is a great challenge to treat oral mucosal diseases due to the large amount of saliva present in the oral cavity, the accompanying oral movements, unconscious swallowing, and flushing of drugs in the mouth. To overcome the significant limitations of clinical bioadhesives, such as weakness, toxicity, and poor usage, in the present study, we developed a simple method through the synergistic effects of gelatin, polydopamine, and nano-clay to prepare an optimal mucosal dressing (Janus GPC) that integrates Janus, adhesion, toughness, and drug release property. It fits effectively in the mouth, resists saliva flushing and oral movements, provides oral drug delivery, and reduces patient discomfort. The Janus GPC adhesive hydrogels have great commercial potential to support further the development of innovative therapies for oral mucosal diseases.

The co‐effect of microstructures and mucus on the adhesion of abalone from a mechanical perspective

Reliable and reversible adhesion underwater is challenging due to the water molecules and weak layers of contaminants at the contact interface, which requires to deepen the understanding of wet adhesion of biological surfaces. Herein, the co-effect of microstructures and mucus of abalone foot on wet adhesion is investigated from both experimental and theoretical perspectives. The morphologies, adhesion force and coefficient of friction indicate that the mucus in adhesion zone is crucial for successful attachment of abalone based on capillary forces and viscous forces, and the mucus in non-adhesion zone with lower adhesion force and friction coefficient may behave as a lubricant for the locomotion. The theoretical calculation manifests that the microstructures may help abalone to form multiple liquid bridges with the secreted mucus, and significantly increase the wet adhesion force of abalone. These findings will bring profound views into the underlying mechanisms of biological surface adhesion.

Wet Adhesion of Soft Curved Interfaces With Micro Pattern

Previous research reveals that a flat micropatterned soft pad, which mimics the structure of tree-frog's toes, increases adhesion when gripping an object in a wet environment. However, soft interfaces may change shape to adapt to curved environments, therefore, it is necessary to clarify the mechanics of wet adhesion in such cases. In this letter, we propose a method for evaluation of the adhesive ability of a soft curved interface with a specific micropattern in a concave contact interface. We focused on wet adhesion force in the normal direction on the contact interface in different contact scenarios. The micropattern soft pad used in this analysis has 3600 cells, each has 85 $\mu$ m × 85 $\mu$ m separated by grooves 15 $\mu$ m in width ×44 $\mu$ m in depth. This micropattern soft pad may deform to fit a concave surface. We also compared this micropattern soft pad with a similar soft pad without a micropattern in term of adhesion ability at the interface between the pad and the substrate. Obtained results have good agreement with the estimations, demonstrating that the surface of the micro-patterned pad enhanced contact force at the interface approximately 1-2 times than the non-parttern surface. This approach can be utilized in evaluation of wet adhesion in grasping objects with curved surface using soft pads with patterned surfaces.

Effects of hindlimb suspension and reloading on gastrocnemius and soleus muscle mass and function in geriatric mice

Reloading of atrophied muscles after hindlimb suspension (HLS) can induce muscle injury and prolong recovery after disuse in old rats, especially in fast contracting muscles. Less is known about the responses in mice and whether fast and slow muscles from geriatric mice will respond in a similar fashion to HLS unloading and recovery (HLS + R). Furthermore, while slow muscles undergo atrophy with disuse, they typically are more resistant to sarcopenia than fast contracting muscles. Geriatric (28 mo. of age) male C57BL/6 mice were randomly placed into 3 groups. These included HLS for 14 days n = 9, and HLS followed by 14 days of reloading recovery (HLS + R; n = 9), or normal ambulatory cage controls (n = 9). Control mice were not exposed to unloading. Electrically evoked maximal muscle function was assessed in vivo in anesthetized mice at baseline, after 14 days of HLS or HLS + R. As expected, HLS significantly reduced body weight, wet weight of gastrocnemius and soleus muscles and in vivo maximal force. There were no differences in vivo fatigability of the plantar flexor muscles and overall fiber size. There were only minor fiber type distribution and frequency distribution of fiber sizes that differ between HLS + R and control gastrocnemius and soleus muscles. Soleus muscle wet weight had recovered to control levels after reloading, but type I/IIA fibers in the soleus muscles were significantly smaller after HLS + R than control muscles. In contrast, gastrocnemius muscle wet weight did not recover to control levels after reloading. Plantar flexion muscle force (primarily influenced by the gastrocnemius muscles) did not recover in HLS + R conditions as compared to HLS conditions and both were lower than control force production signaling for apoptosis, autophagy and anabolic markers were not different between control and HLS + R gastrocnemius and soleus muscles in geriatric mice. These results suggest that molecular signaling does not explain attenuated ability to regain muscle wet weight, fiber size or muscle force production after HLS in geriatric mice. It is possible that fluid shifts, reduced blood flow, or shortened muscle fibers which failed to regain control lengths contributed to the attenuation of muscle wet weight after HLS and reloading and this affected force production. Further work is needed to determine if altered/loss of neural activity contributed to the inability of geriatric mice to regain gastrocnemius muscle weight and function after HLS and reloading.

Key parameters of biomimetic patterned surface for wet adhesion

Inspired by the polygonal arrays on the toe pads of tree frogs and newts, micro hexagonal pillars were fabricated on a cast polyurethane elastomer (CPUE) surface so that a network of interconnected channels was formed. To investigate the effect of channel sizes, adhesion experiments were carried out with a flat polymethyl methacrylate (PMMA) probe and the patterned surface of CPUE samples under wet conditions. It was found that single factors alone, such as channel width (W), length (L), and height (H) have a slight effect on wet adhesion force. Comparatively, the values of width-to-length (W/L), height-to-length (H/L), and height-to-width (H/W) determine the wet adhesion force significantly. Actually, the wet adhesion force is reduced with increasing W/L values. Furthermore, optimal ranges of H/L and H/W values clearly enhance the wet adhesion force, even considering the reduction with the increasing W/L values.

Leakage, Drag Power, and Rotordynamic Force Coefficients of an Air in Oil (Wet) Annular Seal

Wet gas compression systems and multiphase pumps are enabling technologies for the deep sea oil and gas industry. This extreme environment determines both machine types have to handle mixtures with a gas in liquid volume fraction (GVF) varying over a wide range (0–1). The gas (or liquid) content affects the system pumping (or compression) efficiency and reliability, and places a penalty in leakage and rotordynamic performance in secondary flow components, namely seals. In 2015, tests were conducted with a short length smooth surface annular seal (L/D = 0.36, radial clearance = 0.127 mm) operating with an oil in air mixture whose liquid volume fraction (LVF) varied to 4%. The test results with a stationary journal show the dramatic effect of a few droplets of liquid on the production of large damping coefficients. This paper presents further measurements and predictions of leakage, drag power, and rotordynamic force coefficients conducted with the same test seal and a rotating journal. The seal is supplied with a mixture (air in ISO VG 10 oil), varying from a pure liquid to an inlet GVF = 0.9 (mostly gas), a typical range in multiphase pumps. For operation with a supply pressure (Ps) up to 3.5 bar(a), discharge pressure (Pa) = 1 bar(a), and various shaft speed (Ω) to 3.5 krpm (ΩR = 23.3 m/s), the flow is laminar with either a pure oil or a mixture. As the inlet GVF increases to 0.9 the mass flow rate and drag power decrease monotonically by 25% and 85% when compared to the pure liquid case, respectively. For operation with Ps = 2.5 bar(a) and Ω to 3.5 krpm, dynamic load tests with frequency 0 < ω < 110 Hz are conducted to procure rotordynamic force coefficients. A direct stiffness (K), an added mass (M), and a viscous damping coefficient (C) represent well the seal lubricated with a pure oil. For tests with a mixture (GVFmax = 0.9), the seal dynamic complex stiffness Re(H) increases with whirl frequency (ω); that is, Re(H) differs from (K−ω2M). Both the seal cross coupled stiffnesses (KXY and −KYX) and direct damping coefficients (CXX and CYY) decrease by approximately 75% as the inlet GVF increases to 0.9. The finding reveals that the frequency at which the effective damping coefficient (CXXeff = CXX − KXY/ω) changes from negative to positive (i.e., a crossover frequency) drops from 50% of the rotor speed (ω = 1/2 Ω) for a seal with pure oil to a lesser magnitude for operation with a mixture. Predictions for leakage and drag power based on a homogeneous bulk flow model match well the test data for operation with inlet GVF up to 0.9. Predicted force coefficients correlate well with the test data for mixtures with GVF up to 0.6. For a mixture with a larger GVF, the model under predicts the direct damping coefficients by as much as 40%. The tests also reveal the appearance of a self-excited seal motion with a low frequency; its amplitude and broad band frequency (centered at around ∼12 Hz) persist and increase as the gas content in the mixture increase. The test results show that an accurate quantification of wet seals dynamic force response is necessary for the design of robust subsea flow assurance systems.

Investigation on biomimetic wet adhesive pads with variable cross-section surface microstructures

Mechanism of biomimetic adhesive pad and animal's pad are generally alike in stability and be independent of environment, including wet adhesion and seta adhesion. Biomimetic wet adhesive pad has an advantage over creeping on wet surface because of perfect ability of copy surface shape. The processes of adsorbing wall and peeling wall rapidly carry through alternate, so the ability of getting over the wet adhesion force in peeling and the ability of producing the force are equal of importance. This study focus on the problem of peeling from the wall of biomimetic wet adhesive pads, and a new adhesive pad with variable cross-sections microstructures is proposed. The experiments of adhesion force and peeling force of the proposed pads have been investigated, the result shows the validity of the variable cross-section surface microstructures.

Wet Nanoindentation of the Solid Electrolyte Interphase on Thin Film Si Electrodes.

The solid electrolyte interphase (SEI) film formed at the surface of negative electrodes strongly affects the performance of a Li-ion battery. The mechanical properties of the SEI are of special importance for Si electrodes due to the large volumetric changes of Si upon (de)insertion of Li ions. This manuscript reports the careful determination of the Young's modulus of the SEI formed on a sputtered Si electrode using wet atomic force microscopy (AFM)-nanoindentation. Several key parameters in the determination of the Young's modulus are considered and discussed, e.g., wetness and roughness-thickness ratio of the film and the shape of a nanoindenter. The values of the Young's modulus were determined to be 0.5-10 MPa under the investigated conditions which are in the lower range of those previously reported, i.e., 1 MPa to 10 GPa, pointing out the importance of the conditions of its determination. After multiple electrochemical cycles, the polymeric deposits formed on the surface of the SEI are revealed, by force-volume mapping in liquid using colloidal probes, to extend up to 300 nm into bulk solution.

Removal of GPI-anchored membrane proteins causes clustering of lipid microdomains in the apical head area of porcine sperm

The release of extracellular proteins is a part of the sperm capacitation process; this allows the sperm surface reorganization that enables the sperm to fertilize an oocyte. Some of the components released are ‘decapacitation factors’, an uncoordinated or early release of which may cause inappropriate surface destabilization and premature capacitation. We studied the involvement of glycosylphosphatidylinositol-anchored proteins (GPI-APs) in sperm capacitation, and reported that CD52 and CD55 exhibit bicarbonate-dependent release during in vitro sperm capacitation. Treating sperm with phosphatidylinositol-specific phospholipase C (PIPLC) resulted in the enzymatic cleavage of CD55, in both capacitating and noncapacitating conditions. Moreover, PIPLC treatment in noncapacitating conditions caused surface reorganization events that included exposure of the ganglioside GM1, aggregation of flotillin-1, and the swelling of the apical acrosome region; all of which have been reported to be associated with sperm capacitation. The acrosomal swelling was monitored using wet mount atomic force microscopy, a new imaging technique that allows nanometer-level sperm surface measurements in samples hydrated with physiological buffer rather than dried. Despite these surface changes, PIPLC treatment in identical incubation conditions did not stimulate hyperactive sperm motility or protein tyrosine phosphorylation (other hallmarks of sperm capacitation in vitro). In full capacitating conditions (i.e., the presence of bicarbonate and albumin), PIPLC treatment caused sperm deterioration. The possible role of GPI-APs removal from the sperm surface during sperm capacitation is discussed.

Influence of surface roughness on wet adhesion of biomimetic adhesive pads with planar microstructures

Biological adhesive pads of some reptiles and insects, such as tree frogs and grasshoppers, are covered with planar microstructures and have strong and stable adhesive ability on both wet and dry substrates. These adhesion forces do not mainly come from van-der-Waals force but wet adhesion. In this study, the influence of substrates' surface roughness on the wet adhesion of man-made adhesive pads inspired by tree frog toe pads is investigated experimentally. Biomimetic polydimethylsiloxane adhesive pads with planar hexagon microstructures with a microchannels width of 10 μm are fabricated by combining electroforming with soft lithography. Experiments of wet adhesive force between the pads and sandpaper slices with different average surface roughness are carried out at various preloads. Results show that the rougher surface leads to the decrement of wet adhesion force. It is also observed that if the microcosmic profile height of the substrates is near or less than the width of microchannels in the biomimetic adhesive pads, the microstructures and preloads can increase significantly the wet adhesive force, otherwise the microstructures and preloads do not contribute indistinctively. The experimental results can be explained by analysing the relation between the solid contact area and the area with a liquid bridge.

Microgel Adhesives for Wet Cellulose: Measurements and Modeling

Nanostructured adhesive layers were prepared by adsorbing and/or grafting polyvinylamine (PVAm) onto carboxylated poly(N-isopropylacrylamide) (PNIPAM) microgels that were then assembled between layers of wet oxidized cellulose. The wet delamination force was measured as functions of PVAm content, PVAm molecular weight, coverage (mass adhesive/joint area), and the distribution of carboxyl groups in the PNIPAM microgels. The use of microgels is attractive because simple physical adsorption onto the cellulose surfaces before lamination gives much higher adhesive content and strength compared to the corresponding adsorbed linear PVAm. Wet adhesion increased with PVAm content in the microgels and the quantity of microgels in the joint whereas adhesion was independent of PVAm molecular weight. Physical adsorption of the PVAm onto/into the microgels gave the same adhesion as covalently coupled PVAm. Finally, the roles of microgel diameter, elasticity, and coverage were simulated by a simple peel adhesion model in which the microgels were treated as ideal springs.

Genetic Structure of Pastoral and Farmer Populations in the African Sahel

Traditional pastoralists survive in few places in the world. They can still be encountered in the African Sahel, where annual alternations of dry and wet seasons force them to continual mobility. Little is known about the genetic structure of these populations. We present here the population distribution of 312 hypervariable segment I mitochondrial DNA (mtDNA) and 364 Y-short tandem repeat haplotypes in both farmer and pastoralist groups from the Lake Chad Basin and the West African Sahel. We show that the majority of pastoral populations (represented in the African Sahel by the Fulani nomads) fail to show significant departure from neutrality for mtDNA as evidenced by Fu's Fs statistics and exhibit lower levels of intrapopulation diversity measures for mtDNA when contrasted with farmers. These differences were not observed for the Y chromosome. Furthermore, analyses of molecular variance and population distributions of the mtDNA haplotypes show more heterogeneity in the sedentary groups than in the pastoralists. On the other hand, pastoralists retain a signature of a wide phylogenetic distance contributing to their male gene pool, whereas in at least some of the farmer populations, a founder effect and/or drift might have led to the presence of a single major lineage. Interestingly, these observations are in contrast with those recorded in Central Asia, where similar comparisons of farmer and pastoral groups have recently been carried out. We can conclude that in Africa, there have been no substantial mating exchanges between the Fulani pastoralists coming to the Lake Chad Basin from the West African Sahel and their farmer neighbors. At the same time, we suggest that the emergence of pastoralism might be an earlier and/or a demographically more important event than the introduction of sedentary agriculture, at least in this part of Africa.

Surface characterization of nanoparticles carrying pH-responsive polymer hair

The surface of near-monodisperse colloidal polystyrene (PS) latex particles carrying pH-responsive poly[2-(diethylamino)ethyl methacrylate] (PDEA) polymer chains as a steric stabilizer has been extensively characterized in dry and wet states. X-ray photoelectron spectroscopy and contact angle measurement studies confirm that PDEA chains are located on the PS latex particle surface. Transmission electron microscopy (TEM) studies reveal that the sterically stabilized PS particles have a core-shell morphology and wet atomic force microscopy data confirm that the pH-responsive PDEA component covers the PS latex core and the thickness of the protonated steric polymer is estimated to be approximately 15 nm. The PS latex particles can be easily dispersed in acidic aqueous media (pH 3.0) whilst they flocculate in basic aqueous media (pH 10.0) due to the pH-responsive PDEA hair. This dispersion–flocculation cycle of the PS latex is fully reversible.

Bovine Serum Albumin (BSA) as an adhesive for wet cellulose

Regenerated cellulose films were laminated using very thin layers of the protein Bovine Serum Albumin (BSA) as an adhesive. The wet delamination strength was measured as functions of pH, lamination time, temperature and pressure, as well as cellulose oxidation. Drying at elevated temperature (120 °C) was required for strong adhesion. Oxidation of the cellulose membranes to introduce surface carboxyl/aldehyde groups increased the wet delamination strength by 60%, implying that the peel failures happened at the protein/cellulose interface. The wet delamination force was independent of the pH and ionic strength of solutions used to apply the BSA; whereas adhesion decreased with increasing pH of the rewetting solution. Furthermore, the swelling of the BSA interplay region was also increased at high pH. It is proposed that covalent grafting of BSA onto the oxidized cellulose, and disulfide crosslinking within the protein layer contributed to wet adhesion.

Strain-mediated lateral SiGe island motion in single and stacked layers

We investigate the lateral motion of SiGe islands on Si(001) substrates in single and twofold stacked layers by using a combination of wet chemical etching and atomic force microscopy. A careful analysis of the footprints left over by the etched islands reveals that islands tend to repel each other, providing evidence that the lateral motion is triggered by the elastic strain repulsion between neighboring islands. This interpretation is further supported by finite element calculations. In closely stacked layers, the lateral island motion can be reduced and even suppressed. The SiGe islands in the upper layer are found to be Si richer compared with the islands in the first layer. Nevertheless, our results strongly suggest that the elastic interaction between vertically aligned islands is mainly responsible for the reduced island motion in the upper layer.

‘Density/solidity’ of recombinant battery separator material—its influence on both separator and battery performance in valve-regulated lead−acid systems

The relationship between the porosity of recombinant battery separator material (RBSM) and separator/battery performance is examined. The porosity is inversely related to the sheet solidity and bulk density of the separator. The connection between high porosity and high acid absorption in the separator is well understood. The ability of RBSM to provide a very high porosity is a major reason why this material functions well in valve-regulated lead–acid (VRLA) batteries. Investigations have shown that the separator, besides providing space for the acid, must also provide a force on the plate active-material to eliminate the effects of premature capacity loss. This study examines the effect of changes in separator porosity/density on the ability to retain the wet force between the plates. It is found that retention of the force in the plate group is enhanced by an increase in the bulk density of the separator.