Higher Work Of Adhesion Research Articles

Atomic insight on the electronic structure and interfacial bonding characterization of the Cu/TiC interface

The interfacial bonding characteristics of ceramic reinforced phase and metal matrix in metal matrix composites have a significant impact on their strength. Herein, the interfacial bonding properties and alloy element doping of the Cu/TiC interface in TiC-reinforced Cu matrix composites with a stoichiometric ratio of TiC of 1:1 were investigated by atomistic DFT simulations. The analysis of twelve Cu/TiC interfacial models reveals that the TiC(111) in Cu/TiC interface with C-terminated is more stable than that of TiC(111) interface with Ti-terminated due to the stronger covalent bonds formed by Cu-C. The Cu(110)/TiC(111)-C interface with the highest work of adhesion (2.871 J/m2) is the most stable interface among these Cu/TiC interfaces. Moreover, the Cu-Co/TiC interface has the highest Wad (4.223 J/m2) compared to Cu/TiC, Cu-Ni/TiC, and Cu-Zn/TiC interfaces. And the Cu-Zn/TiC interface has the lowest Wad (2.092 J/m2), which is even lower than that of the Cu/TiC interface (2.306 J/m2). During interfacial tension, the Cu/TiC, Cu-Ni/TiC, and Cu-Zn/TiC interfaces start to fracture either at the interface layer or the sub-interface layer on the Cu side, while the Cu-Co/TiC interface begins to fracture within the Cu slab. The Cu-Co/TiC interface has the highest tensile strength of 20.12 GPa at14 % strain compared to Cu/TiC (14.76 GPa), Cu-Ni/TiC (16.35 GPa), and Cu-Zn/TiC (15.30 GPa) interfaces, which is attributed to the strengthening of both the interface and sub-interface by Co doping. Thus, Co doping in the Cu matrix significantly strengthens the Cu/Ti interfacial bonding, Ni doping has a weaker strengthening effect, and zinc doping weakens the interfacial bonding.

Enhanced mucoadhesive properties of ionically cross-linked thiolated gellan gum films

Localized oral drug delivery offers several advantages for treating various disease conditions. However, drug retention at the disease site within the oral cavity is indeed a significant challenge due to the dynamic oral environment. The present study aimed to develop a mucoadhesive inner layer for a three-layer mucoadhesive bandage suitable for localized oral drug delivery. using gellan gum (GG) biopolymer. Gellan gum (GG) was modified using L-cysteine moieties via carbodiimide chemistry. Subsequently, gellan gum solution at different extents of thiolation was ionically cross-linked using aluminum ammonium sulfate. Thiolated gellan gum films of uniform thickness were prepared using a solvent casting method. The thickness of bare gellan gum film was 0.035 ± 0.0043 mm, whereas the thiolated gellan gum films, GG 1S and GG 2S showed a thickness of 0.0191 ± 0.0011 mm and 0.0188 ± 0.0004 mm respectively. A high work of adhesion was noted for thiolated gellan gum (GG 2S) with a value of 10 N.mm while using porcine buccal mucosa. An average tensile strength of 48.2 ± 2.46 MPa was measured for thiolated gellan gum films irrespective of the extent of thiolation. The high work of adhesion, favorable cytocompatibility, desirable mechanical properties, and free swell capacity in saline confirmed the suitability of ionically cross-linked thiolated gellan gum films as an inner mucoadhesive layer for the mucoadhesive bandage.

Turning waste into wealth: Li2CO3 impurity conversion into ionic conductive and lithiophlic interphase for garnet-based solid-state lithium batteries

Garnet-type solid-state electrolytes (SSEs) show great potential because of high ionic conductivity and steadiness against metallic Li. However, the unstable property of garnet in air and poor interface contact with Li metal dramatically influence the electrochemical performance. In this manuscript, TiO2 gel is coated on the surface of Li6.75La3Zr1.75Ta0.25O12 (LLZTO) pellets by a spin coating process, to remove the surface impurity and in-situ construct an air-stable and lithiophilic LixTiyOz (LTO) layer on the garnet electrolyte surface. The LTO interface layer can enhance interface contact, improve ionic transport and suppress Li dendrite growth. The low interfacial resistance (18.40 Ω cm2) in Li|LTO@LLZTO|Li symmetric cells manifests good wettability. Density functional theory (DFT) calculation results indicate that the modification layer owns higher work of adhesion and interfacial energy, suggesting excellent stability and inhibition in Li dendrite growth. Specifically, the Li symmetric cells with LTO-modified electrolyte show an enhanced critical current density of 0.9 mA cm−2 and outstanding capability to survive long cycling over 5000 h at 0.1 mA cm−2. The assembled LiFePO4-based full cell displays both high reversible capacity and cycling capability. This work provides a promising strategy to take advantage of interfacial Li2CO3 impurities on the garnet electrolytes.

Cell Adhesion, Elasticity, and Rupture Forces Guide Microbial Cell Death on Nanostructured Antimicrobial Titanium Surfaces.

Naturally occurring and synthetic nanostructured surfaces have been widely reported to resist microbial colonization. The majority of these studies have shown that both bacterial and fungal cells are killed upon contact and subsequent surface adhesion to such surfaces. This occurs because the presence of high-aspect-ratio structures can initiate a self-driven mechanical rupture of microbial cells during the surface adsorption process. While this technology has received a large amount of scientific and medical interest, one important question still remains: what factors drive microbial death on the surface? In this work, the interplay between microbial-surface adhesion, cell elasticity, cell membrane rupture forces, and cell lysis at the microbial-nanostructure biointerface during adsorptive processes was assessed using a combination of live confocal laser scanning microscopy, scanning electron microscopy, in situ amplitude atomic force microscopy, and single-cell force spectroscopy. Specifically, the adsorptive behavior and nanomechanical properties of live Gram-negative (Pseudomonas aeruginosa) and Gram-positive (methicillin-resistant Staphylococcus aureus) bacterial cells, as well as the fungal species Candida albicans and Cryptococcus neoformans, were assessed on unmodified and nanostructured titanium surfaces. Unmodified titanium and titanium surfaces with nanostructures were used as model substrates for investigation. For all microbial species, cell elasticity, rupture force, maximum cell-surface adhesion force, the work of adhesion, and the cell-surface tether behavior were compared to the relative cell death observed for each surface examined. For cells with a lower elastic modulus, lower force to rupture through the cell, and higher work of adhesion, the surfaces had a higher antimicrobial activity, supporting the proposed biocidal mode of action for nanostructured surfaces. This study provides direct quantification of the differences observed in the efficacy of nanostructured antimicrobial surface as a function of microbial species indicating that a universal, antimicrobial surface architecture may be hard to achieve.

Hard and Highly Adhesive AlMgB14 Coatings RF Sputtered on Tungsten Carbide and High-Speed Steel

We report a new industrial application of aluminum magnesium boride AlMgB14 (BAM) coatings to enhance the hardness of tungsten carbide ceramic (WC-Co) and high-speed steel tools. BAM films were deposited by RF magnetron sputtering of a single dense stoichiometric ceramic target onto commercial WC-Co turning inserts and R6M5 steel drill bits. High target sputtering power and sufficiently short target-to-substrate distance were found to be critical processing conditions. Very smooth (6.6 nm RMS surface roughness onto Si wafers) and hard AlMgB14 coatings enhance the hardness of WC-Co inserts and high-speed R6M5 steel by a factor of two and three, respectively. Complete coating spallation failure occurred at a scratch adhesion strength of 18 N. High work of adhesion and low friction coefficient, estimated for BAM onto drill bits, was as high as 64 J/m2 and as low as 0.07, respectively, more than twice the surpass characteristics of N-doped diamond-like carbon (DLC) films deposited onto nitride high-speed W6Mo5Cr4V2 steel.

Temperature-Dependent Sheet and Contact Resistivity Measurements on Ag and Ag-Ni Circuit Pastes

The metal circuits and brazes used in electronic, energy conversion, and/or energy storage devices often have difficulty wetting and adhering to ceramic and/or ceramic-passivated metal substrates. Here, a novel Particle Interlayer Directed Wetting and Spreading (PIDWAS) technique is demonstrated that utilizes screen printing, the low wetting angle of silver on nickel, and the high work of adhesion between nickel and various ceramics to produce well-adhered, self-assembled silver patterns on ceramic and/or stainless-steel substrates not normally wet by silver. The resulting Ag-Ni circuits have higher sapphire adhesion strengths (up to 30 MPa on sapphire), higher densities (>97% on sapphire), and similar high-temperature electronic resistivities to those made using commercially-available Heraeus C8710 or DAD-87 silver circuit pastes. Similarly, Ag-Ni brazes between a variety of ceramic and/or stainless-steel substrates have better microstructural stability with rapid thermal cycling, reduction-oxidation cycling, and dual atmosphere isothermal aging than conventional Ag-CuO brazes. In addition, the residual Ni in these Ag-Ni circuits and brazes can be used to chemically getter surface segregated Al, ensuring low contact resistances on a variety of chromia- and/or alumina-passivated stainless steels.Reference:[1] Hu G, Zhou Q, Bhatlawande A, Park J, Termuhlen R, Ma Y, Bieler TR, Yu HC, Qi Y, Hogan T & Nicholas JD. Patterned Nickel Interlayers for Enhanced Silver Wetting, Spreading and Adhesion on Ceramic Substrates. Scripta Materialia, 2021; 196, 113767. 10.1016/j.scriptamat.2021.113767[2] Park J, Phongpreecha T, Nicholas JD & Qi Y. Enhanced Liquid Metal Wetting on Oxide Surfaces via Patterned Particles. Acta Materialia, 2020; 199, 551-560. 10.1016/j.actamat.2020.08.037

Improvement of the bonding strength of A2/Cu interface by Co, Ni, P and B addition in planar flow casting process based on first-principle calculations

Introduction of alloying elements into interface is proven effective in improving bonding strength of the A2/Cu interface, which improves surface quality of silicon steel strip in the planar flow casting (PFC) process. In this research, we explored how the additions of Co, Ni, P and B influence interfacial bonding by the first-principles method. The method does not rely on other empirical parameters, and only needs five basic physical constants. Starting from the chemical composition and crystal structure of the material, various ground state properties of the material can be obtained by solving the Schrodinger equation. Five various interfaces were constructed due to different stacking sequences and interface IV has the highest work of adhesion (Wad), 3.24 J/m2. Co and Ni dopants can enhance Wad and improve interfacial bonding, but P and B dopants cannot. When doping amounts increase, Wad value of Co and Ni doped interfaces continuously rises from 0 J/m2 to 176.52 J/m2 and 351.05 J/m2, respectively. The larger Wad value represents a stronger interfacial bonding. 3.5 wt% doping amounts for Co (3.24 at%) and Ni (3.25 at%) were demonstrated appropriate to strengthen interfacial bonding when the influences of doped atoms on magnetic properties of A2 phase are considered. Electronic structure is also analyzed, and the results suggest bonds in interface models are the mix of covalent and metallic bonds, and Co and Ni addition can strengthen the interfacial bonding. Therefore, the dope of 3.5 wt% Co or 3.5 wt% Ni content into silicon steel was considered optimal to strengthen interfacial bonding, and further improve the surface quality of the strip and reduce strip adhesion phenomenon during preparation process. These results also can provide a theoretical guide for fabricating high-quality silicon steel strip in PFC process.

Tuning structural and wettability properties of glass using ellipsoidal TiO2 nanoparticles

Self-cleaning glasses became demanding for various advanced applications due to their manifold advantages. In this view, some tellurite glasses containing TiO2 nanoparticles with varying concentrations were synthesized using the standard melt-quenching. These glasses were transparent with a reddish appearance. The HRTEM images of the glasses showed the presence of ellipsoidal TiO2 NPs with sizes ranging from 9−22 nm and 5−9 nm along the major and minor axis, respectively. The lattice fringe pattern of the selected TiO2 NPs confirmed their anatase structure with a lattice spacing of 0.36 nm. The observed reduction in the water contact angle from 67.5° to 43.0° of the glasses indicated their hydrophilic nature. The high work of adhesion (0.101− 0.126 N.m-1 ) of the glasses revealed the strong interfacial attractive force between water and glass. It was demonstrated that by adjusting the TiO2 NPs contents the hydrophilic traits of the glassed can be tailored, indicating the suitability for self-cleaning applications.

Bonding Strength and Fracture Properties of Al (021)/Al2CuMg (001) Interface and Ag‐Doped Modification: A First‐Principles Study

The Al (021)/Al2CuMg (001) interface models based on experimental orientation relationship are constructed, the structure, work of adhesion, tensile strength, stacking fault energy (GSFE), doping modification, and electronic structure are investigated by first‐principles calculations. The CuMg‐terminated interface evolves into Al2‐terminated interface, which is consistent with experimental observations. Due to stronger bond strength, the M1‐type interface has higher work of adhesion (2.023 J m−2) and tensile strength (6.78 GPa) than these of M2‐type interface. Meanwhile, Ag doping can enhance the tensile strength of M2‐type interface to 6.63 GPa. By calculating the 2 d plot of GSFE, it is found that most slip directions for all interfaces are [110], [010], and [100] directions in Al2CuMg, respectively. Doping Ag atom improves the antislip ability of the M2‐type interface and further influences the tensile and slip properties of the Al/Al2CuMg interface. The charge density difference, electron localization function, and partial density of states demonstrate that the metallic and covalent bonds are mainly formed by Al‐2p orbitals at the interface, so the charge distribution of atoms in the vicinity of the interface is affected by the extranuclear electron of doping Ag atom.

Computing the Work of Solid-Liquid Adhesion in Systems with Damped Coulomb Interactions via Molecular Dynamics: Approaches and Insights.

Recently, the dry-surface method [Langmuir2016, 31, 8335−8345] has been developed to compute the work of adhesion of solid–liquid and other interfaces using molecular dynamics via thermodynamic integration. Unfortunately, when long-range Coulombic interactions are present in the interface, a special treatment is required, such as solving additional Poisson equations, which is usually not implemented in generic molecular dynamics software, or as fixing some groups of atoms in place, which is undesirable most of the time. In this work, we replace the long-range Coulombic interactions with damped Coulomb interactions, and explore several thermal integration paths. We demonstrate that regardless of the integration path, the same work of adhesion values are obtained as long as the path is reversible, but the numerical efficiency differs vastly. Simple scaling of the interactions is most efficient, requiring as little as 8 sampling points, followed by changing the Coulomb damping parameter, while modifying the Coulomb interaction cutoff length performs worst. We also demonstrate that switching long-range Coulombic interactions to damped ones results in a higher work of adhesion by about 10 mJ/m2 because of slightly different liquid molecule orientation at the solid–liquid interface, and this value is mostly unchanged for surfaces with substantially different Coulombic interactions at the solid–liquid interface. Finally, even though it is possible to split the work of adhesion into van der Waals and Coulomb components, it is known that the specific per-component values are highly dependent on the integration path. We obtain an extreme case, which demonstrates that caution should be taken even when restricting to qualitative comparison.

UV curable, flame retardant, and pressure-sensitive adhesives with two-way shape memory effect

Novel UV curable acrylic pressure-sensitive adhesives (PSAs) with exceptional flame retardancy and promising two-way shape memory effect have been developed using a commercial diethyl phosphoramidate as multifunctional tackifier for the first time. The abundant hydrogen bonds and high viscosity of the resultant networks contribute to the low temperature and repeatable adhesions. The PSA with 5 wt % tackifier exhibited the best overall adhesion at both 25 °C and 0 °C, especially with the relatively high peak adhesive stress and the highest work of adhesion. Owing to the synergistic effect with nitrogen containing acylate monomer, the 15 wt% diethyl phosphoramidate endowed the PSA sample with self-extinguishing ability. Moreover, the higher viscoelasticity makes the tackified PSAs with better two-way shape memory property. In particular, the elongation upon cooling and contraction upon heating are 57.2% and 55.9%, respectively. • A multifunctional tackifier for acrylic pressure-sensitive adhesives is reported. • The PSAs integrate UV curability, flame retardancy, and two-way shape memory effect. • A condensed phase flame retardant mechanism of phosphoramidate is proposed. • The higher viscoelasticity suggests better two-way shape memory property. • Two-way shape memory effect in cyclic freezing and thawing scenario is demonstrated.

Adhesive Boundary Element Method Using Virtual Crack Closure Technique

In this study, a new adhesive contact model is built upon a boundary element method (BEM) model developed by Pohrt and Popov (2015). The strain energy release rate (SERR) on the edge of the bonding interface is evaluated using Virtual Crack Closure Technique (VCCT) which is shown to have better accuracy and weaker mesh-size dependency than the closed-form SERR formula derived by Pohrt and Popov. A composite delamination criterion is proposed for crack nucleation and propagation. Numerical results predicted by the present model are in good agreement with the analytical solutions of two classic problems, namely, the axisymmetric parabolic contact and the sinusoidal waviness contact in the plane strain condition. The model of Pohrt and Popov can achieve a similar accuracy for the axisymmetric parabolic contact where the mesh grid is non-conforming to the crack front. Once the conforming mesh grid is used, the accuracy of their model is significantly deteriorated, especially at high work of adhesion and high mesh density. In both BEM models, however, the crack nucleation is found to be mesh-dependent which may be solved by introducing an upper limit for the tensile normal traction.

The outstanding interfacial adhesion between acrylo-POSS/natural rubber composites and polyamide-based cords: ‘An environmentally friendly alternative to resorcinol-formaldehyde latex coating’

Resorcinol formaldehyde latex (RFL) dipping system, very effective to enhance adhesion between rubber and cords in the tire industry, has substantial health & environmental (i.e., toxicity) and commercial (i.e., being time-consuming and expensive) negative effects. The present work eliminates these disadvantages, and more importantly reports much better adhesions between natural rubber (NR) and textile cords than RFL itself by proposing Acrylo-polyhedral oligomeric silsesquioxane (A-POSS), a new generation reactive hybrid nanoparticle. The H-adhesion forces between A-POSS/NR and virgin Nylon 6.6 cord highly increased to 123.0 N whereas the same forces between NR and RFL coated Nylon 6.6 was only 95.8 N. A thin layer of NR/A-POSS on the surface of Nylon 6.6 cords in SEM images confirmed a good interfacial H-adhesion between the Nylon 6.6 cord and NR/A-POSS even at the low A-POSS loadings. In addition, higher work of adhesion between NR/A-POSS and virgin Aramid than that of between NR and virgin Aramid was obtained. The strong adhesion between NR and polyamide cords in the presence of A-POSS was revealed by FTIR and NMR analyses. A-POSS/NR provided enhanced thermal stability, crosslinking density, and mechanical properties. Moreover, the tan δ value was reduced by ~9% for NR/A-POSS composites compared to the NR skim composite indicating better dynamic performance for a moving tire. Overall, it was concluded that the use of A-POSS nanoparticles in NR composites can be alternative to RFL dipping method currently being used in the tire industry due to enhanced adhesion between rubber composites and the polyamide cords.

First-principles calculations on interfacial properties and fracture behavior of the [formula omitted] interfaces

To provide theoretical basis of the qualitative design for TiC particulate reinforced Mg matrix composite, the interfacial properties and fracture behavior of the Mg(11¯01)||TiC(11¯1) interfaces are systematically investigated by density functional theory. Five stable existing interfaces with different stacking sequences (FB, SA, SB, TC and TD interfaces) are identified after optimization. Results show that the stability order is TC> SA> SB> TD> FB interface in that TC interface with the highest work of adhesion (2.27 J/m2) and the lowest interface energy (−0.10 J/m2) after full relaxation is the steadiest. It also exhibits the greatest fracture energy of 1.76 J/m2 and the largest theoretical tensile strength of 6.690 GPa in the first-principles computational tensile tests (FPCTTs). When the separation distance is 0.05nm, the comparison of the separation energies on the five FPs (fracture plane) shows that the fracture commonly occurs on the FP-1 for FB, SB and TD interface, while FP-3 for SA and TC interface. The analyzation of charge density and density of states indicates that interfacial bonds largely come from Mg-Ti metallic/covalent mixed bonds, while the fractures mainly disrupt the Mg-Mg metallic bonds normally. The stacking sequence of TC interface can optimize the interface structure and even up the charge density, which can be the critical factors contributing to interfacial stabilization and strengthening.

Patterned nickel interlayers for enhanced silver wetting, spreading and adhesion on ceramic substrates

The metal current collectors used in electronic, energy conversion, and energy storage devices often have difficulty wetting and adhering to ceramic substrates. Here, a novel Particle Interlayer Directed Wetting and Spreading (PIDWAS) technique is demonstrated that utilizes 1) the low wetting angle of silver on nickel and 2) the high work of adhesion between nickel and various ceramics to produce well-adhered, self-assembled silver patterns on ceramics not normally wet by silver. This is achieved by partially sintering nickel patterns and melt infiltrating either 1) locally-applied silver or 2) silver that simultaneously dewets the bare ceramic and laterally spreads through the porous nickel network. The resulting Ag-Ni patterns have higher ceramic adhesion strengths, higher densities, and similar electronic resistivities to those made using commercially-available silver circuit pastes. Further, these dense Ag-Ni patterns can be produced without externally-applied pressure, making them desirable for circuit, sealing, die-attach, joining and other applications.

Interface properties of Ti3SiC2/Al2O3 ceramics: Combined experiments and first-principles calculations

The synthesis, characterization, and first-principles calculations of Ti3SiC2/Al2O3 ceramics were reported. X-ray diffraction measurements showed that the composite ceramics were highly pure. Scanning electron microscopy and transmission electron microscopy were used to characterize the interface information for Ti3SiC2 and Al2O3 crystals. Surface energies and interface properties were calculated using the first-principles method. The results suggested that Ti3SiC2 with Ti terminations and Al2O3 with O terminations are more stable than other terminations crystals. Thus powerful attraction between the coordinatively unsaturated Ti and O atoms on the Ti3SiC2∥Al2O3 interface would result in higher work of adhesion (Wad) and shorter boundary distance, demonstrating the intercrystalline strengthening of Ti3SiC2/Al2O3 composite ceramics.

Patterned Nickel Interlayers for Enhanced Silver Wetting, Spreading and Adhesion on Ceramic Substrates

The metal current collectors used in electronic, energy conversion, and energy storage devices often have difficulty wetting and adhering to ceramic substrates. Here, a novel Particle Interlayer Directed Wetting and Spreading (PIDWAS) technique is demonstrated that utilizes 1) the low wetting angle of silver on nickel and 2) the high work of adhesion between nickel and various ceramics to produce well-adhered, self-assembled silver patterns on ceramics not normally wet by silver. This is achieved by partially sintering nickel patterns and melt infiltrating either 1) locally-applied silver or 2) silver that simultaneously dewets the ceramic and laterally spreads through the porous nickel network. The resulting Ag-Ni patterns have higher sapphire adhesion strengths, higher densities, and similar electronic resistivities to those made using commercially-available silver circuit pastes. Further, these dense Ag-Ni patterns can be produced without the need for externally-applied pressure, making them desirable for circuit, sealing, die-attach, joining and other applications.

Underwater Adhesion of Multiresponsive Complex Coacervates

AbstractMany marine organisms have developed adhesives that are able to bond under water, overcoming the challenges associated with wet adhesion. A key element in the processing of several natural underwater glues is complex coacervation, a liquid–liquid phase separation driven by complexation of oppositely charged macromolecules. Inspired by these examples, the development of a fully synthetic complex coacervate‐based adhesive is reported with an in situ setting mechanism, which can be triggered by a change in temperature and/or a change in ionic strength. The adhesive consists of a matrix of oppositely charged polyelectrolytes that are modified with thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM) grafts. The adhesive, which initially starts out as a fluid complex coacervate with limited adhesion at room temperature and high ionic strength, transitions into a viscoelastic solid upon an increase in temperature and/or a decrease in the salt concentration of the environment. Consequently, the thermoresponsive chains self‐associate into hydrophobic domains and/or the polyelectrolyte matrix contracts, without inducing any macroscopic shrinking. The presence of PNIPAM favors energy dissipation by softening the material and by allowing crack blunting. The high work of adhesion, the gelation kinetics, and the easy tunability of the system make it a potential candidate for soft tissue adhesion in physiological environments.

Microbially Synthesized Repeats of Mussel Foot Protein Display Enhanced Underwater Adhesion.

Mussels strongly adhere to a variety of surfaces by secreting byssal threads that contain mussel foot proteins (Mfps). Recombinant production of Mfps presents an attractive route for preparing advanced adhesive materials. Using synthetic biology strategies, we synthesized Mfp5 together with Mfp5 oligomers containing two or three consecutive, covalently-linked Mfp5 sequences named Mfp5(2) and Mfp5(3). The force and work of adhesion of these proteins were measured underwater with a colloidal probe mounted on an atomic force microscope and the adsorption was measured with a quartz crystal microbalance. We found positive correlations between Mfp5 molecular weight and underwater adhesive properties, including force of adhesion, work of adhesion, protein layer thickness, and recovery distance. DOPA-modified Mfp5(3) displayed a high force of adhesion (201 ± 36 nN μm-1) and a high work of adhesion (68 ± 21 fJ μm-1) for a cure time of 200 s, which are higher than those of previously reported Mfp-mimetic adhesives. Results presented in this study highlight the power of synthetic biology in producing biocompatible and highly adhesive Mfp-based materials.

A finite element study of adhesion of soft thin elastic films cast on rough surfaces

Contact instability of thin elastic films rigidly bonded to patterned substrates, in comparison to those bonded to smooth substrates, were found to form highly miniaturized patterns at their free surfaces. Through finite element simulations, we have found that irrespective of the widely varying substrate patterns used (step, sinusoidal, sawtooth and noisy sinusoidal, with different substrate parameters), the salient miniaturized surface features engendered in these films are found to be same for identical RMS substrate-roughnesses. Columns formed at the film-contactor interfaces of these patterned-substrate films are found to be very slender with larger contact area and are comparatively able to bear very high stresses (responsible for higher peak debonding forces). These columns simultaneously display higher stress release during debonding that leads to almost identical snap-off distances and consequentially, higher work of adhesion is observed. Additionally, work of adhesion also increases for higher debonding velocities. The RMS substrate roughnesses promote these films to perform as potentially better adhesives and, their influence on pattern miniaturization can be harnessed to enhance other surface properties.