Improved Adhesion Strength Research Articles

Improving adhesion strength of sol-gel coating on CoCrMo by electrochemical pretreatment

CoCrMo is commonly used as the femoral head material in the artificial hip joint. In order to increase the wear and corrosion resistance of the femoral head, the use of ceramic coating has been reported. Besides the tribological properties of the coating, coating adhesion is of paramount importance in prolonging the service life of the implant. The present study aims at improving the adhesion of ZrO2 sol-gel coating on CoCrMo substrate via pretreatment of the substrate. Two types of pretreatment, namely, electro-etching and electrodeposition of Co, were attempted to create different surface topography on the substrate. It is found that electrodeposition under appropriate conditions (current density of 100 mA/cm2 for 150 s) could effectively increase the adhesion strength, by about 37% and 83% for the load of first crack (Lc1) and the load of breakthrough (Lc2), respectively. The improvement could be attributed to the creation of a densely populated “prolate spheroids”, which provided an increased contact area for bonding and mechanical interlocking.

Influence of Adhesive Strength, Fatigue Strength and Contact Mechanics on the Drilling Performance of Diamond Coating.

Adhesive strength of the coating significantly affects the lifetime of the coating. However, it is still inevitable for the coating, even with strong adhesive strength, to peel off from the substrate after working for a while. In this work, fatigue and wear behaviors were employed to analyze the effect on the mechanics of coating and contribute to a fundamental understanding of peeling of the coating. A small-size Co-cemented tungsten carbide drill bit was selected as the examined substrate to fabricate the diamond coating. Roughening pretreatment with a diamond slurry combined with ultrasonic vibration was performed for the substrate surface to enhance adhesive strength. Meanwhile, a diamond coating without roughening pretreatment was also fabricated for comparison. The lifetime and quality of the coating were evaluated by the drilling test. Although the diamond coating could grow on the substrates with and without roughening pretreatment, the diamond coating with roughening pretreatment possessed a higher lifetime and stronger wear resistance than that without roughening pretreatment. We found that both substrates with and without roughening pretreatment exhibited a coarse surface, whereas the roughening pretreatment could remove the original machined surface of the substrate and thus make the near surface with numerous integrated crystalline grains become the new topmost surface. This increased the contact area and surface energy of the interface, leading to the improvement of adhesive strength. Finally, fatigue strength and contact mechanics were studied to trace the changes in the stress of the diamond coating in the whole process of drilling from a theoretical point of view. We suggest that fatigue strength and contact mechanics may play vital roles on the durability and peeling of the coating.

Enhancement of mineralization on porous titanium surface by filling with nano-hydroxyapatite particles fabricated with a vacuum spray method.

Nano-hydroxyapatite (nano-HA) coating has been proved to be effective to modify the titanium surface for better bone formation. A simple and economical nano-HA coating method that filling the nano-HA particles into the porous titanium substrate by using vacuum suction was introduced in this study. Two kinds of nano-HA modified titanium surfaces, nano-HA filled type (nHA-f) and nano-HA coated type (nHA-c), were prepared by a 2-step and 3-step protocol, respectively. Nano-HA modified titanium surfaces with and without thermal treatment were compared. The physicochemical properties including morphology, elemental composition, coating thickness, adhesion strength and in vitro mineralization ability were characterized. The SEM results showed that nano-HA particles were effectively filled into the porous titanium substrate under the function of vacuum suction in the nHA-f and nHA-f-heat groups. The thickness of the nano-HA layer was about 1μm and 7-8μm in the nano-HA filled type and nano-HA coating type, respectively. Localized separation between the nano-HA layer and the titanium substrate was observed in the thermal-treated groups, which may increase the risks of detachment. In the in vitro mineralization test, the unheated groups (nHA-f and nHA-c) showed promoted calcium phosphate compounds deposition than the heated groups (nHA-f-heated and nHA-c-heated) because of the active biological behavior of the amorphous nano-HA; the nHA-f group with a thin nano-HA layer showed no difference to the thick coating group (nHA-c) at the early stage, which was due to the effect of the porous structure as a cage to protect the nano-HA particles from fast dissolution. In conclusion, the vacuum spray method is effective to create a thin amorphous nano-HA layer with improved adhesion strength and sustained-release ability to induce mineralization by filling the nano-HA particles into the porous titanium substrate without thermal treatment.

Debondable adhesives using shape memory fibers

We suggested new debondable adhesives which consisted of structural adhesives and shape memory fibers. According to the suggested debondable adhesives, we can accomplish both degradations of adhesion strength at the desired condition and improvement of adhesion strength at the operating condition. Reinforcing shape memory fibers in adhesives can improve the mechanical properties of adhesives. Also, peel stresses generated by the shape recovery of reinforced shape memory fibers can decrease adhesion strength.We investigated the feasibility of the suggested debondable adhesives by finite element analyses concerning the volume fraction of shape memory fibers and initial transformation strain. We found that shape recovery behaviors were changed concerning the volume fraction as well as initial transformation strain. Also, relatively large peel stresses could be generated during the shape recovery of shape memory fibers, which could decrease adhesion strength. We conducted the peel tests of adhesive joints with and without shape memory fibers and the proved analysis results were in good agreement with experiments.Therefore, we concluded that suggested debondable adhesives can be a better candidate for debondable adhesives to overcome the low strength of the developed debondable adhesives than usual structural adhesives.

Improvement of adhesion strength for wood-based material coating process using design of experiment methodology

The coating performance of wood-based materials is affected by different sanding conditions and coating application parameters. In particular, in the furniture industry, these processes are significant indicators for increasing the process efficiency and determining the optimum paint quantity. The purpose of this study was to improve the coating performance of medium density fiberboard using design of experiment methodology. In this study, independent variables were selected as coating amount, feed rate, belt speed and grit type, whereas the dependent variable was determined as adhesion strength. Face-centered composite design and analysis of variance were applied to determine the significant factors. Adhesion strength values of the specimens were determined by using pull-off adhesion test equipment. Sanding and coating application parameters for maximizing the adhesion strength were optimized by using response surface methodology and desirability function. Optimal processing parameters for maximizing the adhesion strength were achieved with a feed rate of 5 m/min, belt speed of 15.13 m/s, paint amount of 352.10 g/m2 and sandpaper type of SiC.

Influence of surface treatment with infrared nanosecond laser on adhesion performance of adhesion-bonded carbon fiber/epoxy composite

The surface treatment of carbon fiber/epoxy composites with a pulsed infrared (1064 nm wavelength) nanosecond (7 ns pulse duration) laser has been investigated. It is found that single 1064 nm laser pulse can remove the polymer matrix from composite surface to expose the carbon fibers by expansion of the pyrolysis gas resulting from laser-induced polymer degradation. The influences of laser power density and scan strategy on matrix removal process have been studied. The bonding strength of laser processed, adhesion-bonded CFRP (carbon fiber reinforced plastic) increase with lower matrix residues on the fibers and a linear relation is found. The adhesion-bonding strength of CFRP surfaces, tested by lap-joint shear test, exceeds the strength measured for untreated and abrasion treated (SiC paper) samples. The main origin of fiber damage of the laser-treated surface is mechanical fracture rather than thermal damage as found by laser scanning confocal microscope and scanning electron microscope. The characteristic morphologies and failure modes of shear-tested surfaces are analyzed. The obvious improvement of adhesive strength is achieved by the laser-treated surfaces attributed to matrix removal and carbon fibers protruding. A 1 D model is established to describe temperature and internal gas pressure of the irradiated surface. The new laser treatment method needs less laser energy and low pulse numbers and prove the way to an efficient, low-cost surface treatment for preparation of high quality adhesion bonded CFRP components.

Preparation of robust antistatic waterborne polyurethane coating

In this study, a novle robust antistatic waterborne polyurethane (WBPU)-ZrO2 nanoparticle (NP) coating is specially designed using sol-gel process. For this purpose the effective parameters on resin performance and surface resistivity of the synthesized coating investigated and optimized. The WBPU composite containing 6 wt% ZrO2 NPs, dissipates electrostaic charges with surface resistivity of 9.1 × 109 Ω sq−1 and also improves adhesion strength about 30 % compared with neat resin. Moreover, the homogenous distribution of modified ZrO2 NPs provides a surface roughness of 27.0 nm which can avoid the absorption of dust on the surface. Facile fabrication of robust WBPU–ZrO2 coating with considerable antistatic properity provides a pathway to the development of environmental friendly antistatic surfaces. The improved properties of synthesized WBPU–ZrO2 coating are mainly due to (i) stable adhesion of ZrO2 NPs into WBPU resin after cross-linking with resin matrix, (ii) formation of a rough structure on the coating surface, and (iii) modification of resin performance that provides film hemogenity.

Application of surface modifiers in ceramic tile to improve adhesion strength with mortars

Nowadays, ceramic floor or wall tiles have been composed mainly of large ceramic tiles with low water absorption, which requires a greater need for bond strength between the tile and the adhesive mortar. Some researchers argue that adhesion is obtained mainly by mechanical interlocking, while othersclaim that adhesion is obtained mainly by increasing the contact surface. To provide this increase in the contact surface, some studies indicate the use of surface modifiers on the back of the ceramic plate. Thus, this research aimed to evaluate the influence of surface treatment on tensile strength. The research showed that factors such as the polymer content of the adhesive mortar, the absorption and the roughness of the ceramic back were more influential in the tensile strength than the use of the mentioned surface treatments.

Mutual intercropping-inspired co-silanization to graft well-oriented organosilane as adhesion promotion nanolayer for flexible conductors

Surface metallization of polymer substrate and film adhesion are crucial to the development of flexible electronics. This study demonstrates the co-silanization engineering on the polyimide (PI) film by mutual intercropping of two organosilane molecules to improve their grafting orientability and enhance the adsorbability toward the PI substrate and loaded metal atoms. The mutual intercropping-inspired co-silanization engineering is implemented by using 3-[(trimethylsilyl)ethynyl]pyridine (TEP) as a supporting organosilane to spatially confine the grafting orientation of the supported aminosilane, 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (ETAS), leading to the formation of a well-oriented organosilane composite nanolayer as adhesion promotion layer for flexible conductors. The flexible Cu conductor electrolessly deposited on the PI film by co-silanization shows improved adhesion strength (0.9kgf/cm) compared to those based on mono-silanization (0.51kgf/cm) and sputtered Ta/Cu (0.4kgf/cm). Superior deformability (bendability) was also achieved for the co-silanized Cu/PI sample by retaining good electrical property after bending cycle up to 1000.

Fe2Ti interlayer for improved adhesion strength and corrosion resistance of TiN coating on stainless steel 316L

Hard TiN coating (with a Vickers hardness higher than 1300 HV) on soft steel (smaller than 200 HV) has a great tendency to mechanical failure due to the significant mismatch in hardness. To tackle this issue, a Fe2Ti metallurgically bonding interlayer was designed and fabricated in between TiN coating and stainless steel 316L substrate. Results reveal that thickness of the Fe2Ti interlayer is tunable and plays an important role in adhesion strength and corrosion resistance of the resulting coating system. Fe2Ti interlayer with 5.0 μm in thickness significantly enhanced adhesion strength (50 N) and decreased corrosion rate (8.128 × 10−4 mm/yr), and the corrosion rate is one-tenth of the monolayer TiN coating fabricated by conventional CVD or PVD methods.

Synthesis of borosiloxane oligomers containing vinyl and epoxy groups for improving adhesion of addition-curable silicone rubber with epoxy resin

In this research, a kind of borosiloxane oligomer (BSiOVi) containing vinyl and epoxy groups, was synthesized as surface treatment agent to improve the interfacial adhesion property between addition-curable liquid silicone rubber (AL-SR) and epoxy resin (EP). The chemical structure of the BSiOVi was studied by Fourier Transform Infrared Spectra (FT-IR), Gel Permeation Chromatography (GPC), Nuclear Magnetic Resonance Spectroscopy (1H-, 13C-, 29Si- and 11B-NMR) and Thermo Gravimetric Analysis (TGA). The adhesion strength between EP and AL-SR was tested using Morphological analysis and Tensile Lap Shear test. The test results showed that the BSiOVi with vinyl and epoxy groups could significantly improve the strength of adhesion between EP and AL-SR The highest adhesion strength value (3.2 MPa) was collected from silicone rubber breakage for BSiOVi/EP/AL-SR system. Furthermore, the adhesive mechanism between EP and AL-SR was analyzed. The improvement of adhesion strength was a result of chemical bonding, because the vinyl and epoxy groups of BSiOVi could react with the active hydrogen of AL-SR and amino groups of EP surface respectively. In conclusion, the BSiOVi can solve the interfacial adhesion problems effectively and the feature of BSiOVi have great application potential to solve the adhesion problem for AL-SR with other materials possessing amino groups.

The effects of TiO2 sol concentration on single- and multiple-scratch damage in electroplated Ni–B-TiO2 sol composite coating

The electrodeposited sol-enhanced Ni–B–TiO2 composite coatings were elaborated using a novel electroplating process. This coating was assessed in terms of tribological behavior and corrosion resistance. However, the adhesion strength of this coating has not been discussed so far. The aim of this study is to evaluate the adhesion behavior of this coating, considering different TiO2 sol concentration in the plating solution in order to predict its effectiveness and its sustainability when used in mineral crushing process. A progressive load scratch test and multi-pass scratch test were performed on coatings. The morphology of scratched surfaces was analyzed to identify the scratch failure mechanism. The results indicate that the addition of TiO2 sol significantly enhanced the deposit adhesion to the substrate compared to pure Ni–B coating. No spallation failure was observed on the sol-enhanced coatings after progressive load scratch test, contrary to Ni–B coating. Moreover, the multi-pass scratch test demonstrated that the improvement in adhesion strength depends strongly on the quantity of the TiO2 sol added to the plating solution. For the optimal concentration of TiO2 sol (25 ml/L), the sol-enhanced Ni–B–TiO2sol composite coating boasts the best adhesion strength. However, further increase in TiO2 sol concentration results in a deterioration of coating adhesion.

Mechanical, antibacterial, and biocompatibility mechanism of PVD grown silver-tantalum-oxide-based nanostructured thin film on stainless steel 316L for surgical applications.

Surgical site infection associated with surgical instruments has always been a factor in delaying post-operative recovery of patients. The evolution in surface modification of surgical instruments can be a potential choice to overcome the nosocomial infection mainly caused by bacterial populations such as Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. A study was, therefore, conducted characterising the morphology, hydrophobicity, adhesion strength, phase, Nano-hardness, surface chemistry, antimicrobial and biocompatibility of SS 316L steel deposited with a Nano-composite layer of Silver (Ag) and Tantalum oxide (Ta2O5) using physical vapour deposition magnetron sputtering. The adhesion strength of Ag/AgTa2O5 coating on SS 316L and treated at 250-850 °C of thermal treatment was evaluated using micro-scratch. The Ag/Ag-Ta2O5-400 °C was shown a 154% improvement in adhesion strength on SS 316L when compared with as-sputtered layer or Ag/Ag-Ta2O5-250, 550, 700 and 850 °C. The FESEM, XPS, and XRD indicated the segregation of Ag on the surface of SS 316L after the crystallization. Wettability and Nano-indentation tests demonstrated an increase in hydrophobicity (77.3 ± 0.3°) and Nano-hardness (1.12 ± 0.43 GPa) when compared with as-sputtered layer, after the 400 °C of thermal treatment. The antibacterial performance on Ag/Ag-Ta2O5-400 °C indicated a significant zone of inhibition to Staphylococcus aureus (A-axis: 16.33 ± 0.58 mm; B-axis: 25.67 ± 0.58 mm, p < 0.01) and Escherichia coli (A-axis: 16.33 ± 1.15 mm; B-axis: 26.00 ± 0.00 mm, p < 0.01) when compared with SS 316L or Ag/Ag-Ta2O5-700 °C, which showed no inhibition. The biocompatibility tests on Ag/Ag-Ta2O5-400 °C demonstrated an excellent in cell attachment, F-actin protein expression and proliferation/viability of bone marrow derived mesenchymal stromal on day 14 when compared with uncoated or Ag/Ag-Ta2O5-700 °C. This study shows that the Ag segregation process, hydrophobicity, adhesion strength, crystallization, and hardness progressively improved after the annealing up to 400 °C.

Effect of CrAl interlayer on adhesion strength of CrAlN coating

ABSTRACTCrAlN coating is widely used to prevent Ti alloy from wear nowadays, however, the poor adhesion between the coating and substrate is an urgent problem to resolve. In this paper, CrAlN coating with CrAl intermediate layer is prepared on Ti alloy by RF magnetron sputtering technique. The adhesion strength of the coating is measured by automatic scratch tester. The results show that the adhesion strength of CrAl/CrAlN coating is much higher than that of mono-layer CrAlN coating. The CrAl layer with thickness of 5.07 μm displays an excellent adhesion strength, which is 84.2 N. The nano-hardness and elastic modulus are 26.45 and 215.33 GPa, respectively. The improvement of adhesion strength can be attributed to the two reasons: (1) the elastic modulus of the CrAl layer is between the Ti alloy and the CrAlN coating, playing a role of stress transition. (2) The intermediate layer inhibits the columnar growth of CrAlN.

Al 파우치-타입 리튬이차전지용 Ni 리드-탭과 리드-필름 간 결착력 향상을 위한 리드-필름 표면처리 연구

본 논문에서는 파우치 타입 리튬이차전지에 사용되는 Ni 금속 리드-탭과 리드-필름 간의 결착력 향상을 위한 화학적 표면처리 연구를 수행하였다. 과산화벤조일(BPO)을 리드-필름에 적용할 경우 다량의 산소 관능기가 필름 표면에 형성되는 것을 확인하였다. BPO 표면처리를 통해 표면에 형성된 산소관능기가 금속 Ni 리드-탭과의 결착력 향상에 미치는 영향을 관찰하기 위해 점착력 실험(peel test)을 수행하였다. 초기 점착력의 경우 표면처리 되지 않은 리드-필름 대비 Ni 금속 리드-탭과의 결착력이 38% 향상되었으며 상용 리튬이차전지에 적용되는 전해액에 80 ℃ 온도에서 24시간 함침시킨 후 점착력을 측정한 결과 20% 향상됨을 확인하였다.

Polydopamine functionalized graphene oxide nanocomposites reinforced the corrosion protection and adhesion properties of waterborne polyurethane coatings

In this work, a polydopamine (PDA)-functionalized graphene oxide (GO) nanocomposite was prepared by a simple and eco-friendly approach. The results recorded via FTIR, UV–vis absorbance spectroscopy, Raman, XPS spectral, as well as atomic force microscope (AFM) demonstrated the effective modification and overlay of PDA on the surface of GO. GO-PDA can be stably dispersed in aqueous solution, and GO-PDA was incorporated into waterborne polyurethane (WPU) by solution blending. The examinations of particle size analysis and zeta potential showed that the incorporation of GO-PDA can effectively improve the uniformity and stability of polyurethane aqueous dispersion. The observation results of SEM verified that PDA promoted the uniform dispersion of GO nanosheets in polymer coatings. The electrochemical impedance spectroscopy and salt spray test of the steel substrates coated with composite coatings confirmed that the incorporation of 0.5 wt% GO-PDA significantly enhanced the anti-corrosion performance of WPU. Compared with previous reports, the incorporation amount of GO-PDA was drastically reduced, and the corrosion protection of coating was effectively improved. In addition, the pull-off and contact angle tests also demonstrated improved adhesion strength and hydrophobicity of the coating. Only water was used as solvent in the whole preparation process of coating and its excellent corrosion protection make it promising in engineering.

Advanced Low-K Polymer Dielectric Materials and Interfaces for Fine-Pitch Re-Distribution-Layer (RDL) to Enable 2.5D and Fan-out Packages

The rapid increase of devices with artificial intelligence (AI) and machine learning capabilities is driving the demand for growth in compute performance. With transistor scaling reaching physical limitations, the semiconductor industry is looking to system-scaling to deliver the performance improvements. Advanced packaging architectures capable of supporting these applications are 2.5D interposers, 3D IC stacking, chiplets and fan-out based packaging. All of these architectures require high-density interconnects capable of routing >200 IOs/mm/layer. This talk demonstrates advanced ultra-thin ( <10 µm), low-Dk (< 3.0) polymer dielectric material candidates capable of achieving I/O densities of 500 IOs/mm/layer. Current commercially available solutions based on silicon interposers suffer from conductor and dielectric losses because of restrictions on the dielectric material (SiO2). Polymer based dielectrics offer a compelling alternative because of the potential to reduce the capacitance of the traces and improve power efficiency alongside compatibility with low-cost panel-scalable processes. This idea is explored will be explored in this talk and we will demonstrate through modelling and characterization that low-Dk polymer dielectrics are a superior candidate to current dielectric material candidates The choice of polymer dielectric is driven by technology trends towards a)high-density fine-pitch routing b)system level thermo-mechanical reliability c)panel-scalable processing. This work examines four dielectric material candidates comprising of 3 material classes, namely photo-sensitive epoxy, non-photo-sensitive epoxy and BCB for next-generation interconnect technology. High-speed electrical simulations indicate that low-Dk materials can support data rates of >10Gbps which overcomes the limitations faced by conventional high Dk epoxy dielectrics and SiO2 alternatives. The biggest challenge in moving towards low-Dk materials is that these polymers are typically non-polar and do not adhere well which poses challenges in package integration. This work proposes a unique approach to improve polymer/metal interfacial adhesion by creating a hybrid layer with tailorable material properties using vapor-phase-infiltration (VPI). VPI exposes the polymeric material to a metal-organic reactant such as trimethyl aluminium (TMA) in a heated environment. Diffusional kinetics of the reactant are highly dependent on each step of the sequential process such as temperature, time of hold, exposure time, and co-reactants used. This process is superior compared to Atomic Layer deposition (ALD) in promoting the diffusion of organometallic precursors into the polymer subsurface because of a hold-period after exposure. VPI thereby provides a highly adaptable process to create tunable hybrid interfaces with target properties. VPI-treated polymers showed a 3X improvement in adhesion strength at the polymer/metal interface. This work dives into the kinetic factors required to achieve this adhesion improvement and characterizes the corresponding material structure changes. In summary, advanced low-Dk polymer dielectrics capable of meeting next-generation high-performance computing requirements are discussed. This work evaluates the key performance benefits from moving to low-Dk dielectric materials and tackles a critical challenge of integrating these materials as re-distribution layer (RDL) dielectrics by demonstrating 3X improvement in adhesion using VPI.

Improvement of Adhesion Strength of the Sprayed Material

The effective way of enhancing resistance to deterioration of the parts is the change of surface properties due to coating with the required properties. Since the deposition process takes place at an elevated temperature, it is necessary to ensure the absence of phase and structural transformations in the metal, mixing of materials, changes in the chemical composition of the coating. The use of plasma spraying at the transport management facility showed a sufficiently high quality of the coating. However, the metallographic analysis showed the presence of discontinuities at the interface in the form of pores, oxide film and sections of decarburized steel. In the case of the process of melting–spraying, the overheating areas of the base metal are formed, which leads to disadvantages similar to the deposition process. To ensure the minimal thermal impact on the part, the thermal field calculations are required. For this purpose, the time of local melting of the part by a single-phase plasma jet was calculated. The temperature field of a part in which heat is transferred by thermal conductivity, the solution of the differential equation of thermal conductivity is described. The boundary conditions of three genera are formulated. The first kind is the distribution of temperature on the enclosing surfaces. The second kind – the task on the surface of the part of the heat flux density. The third kind – setting the temperature of the medium, which acts as a plasma jet, washing the surface of the part, and the intensity of heat exchange. The mathematical model of melting of the product is constructed. The formula for calculating the reflow time is derived. The temperature distribution expressions for the molten and solid zones are obtained by the solution of the problem with moving boundaries by the Fourier’s method. On the basis of theoretical calculations it is proposed to increase the strength of the sprayed layer with the base to apply the process of plasma spraying with preliminary local melting by periodic exposure to a single-phase plasma jet.

Mucoadhesive electrospun nanofibers for drug delivery systems: applications of polymers and the parameters' roles.

Electrospun nanofibers have been widely studied for many medical applications. They can be designed with specific features, including mucoadhesive properties. This review summarizes the polymeric scaffolds obtained by the electrospinning process that has been applied for drug release in different mucosal sites such as oral, ocular, gastroenteric, vaginal, and nasal. We analyzed the electrospinning parameters that have to be optimized to create reproducible and efficient mucoadhesive nanofibers, among them are: electrical field, polymer concentration, viscosity, flow rate, needle-collector distance, solution conductivity, solvent, environmental parameters, and electrospinning setup. We also revised the mucoadhesive theories as well as the mucoadhesive properties of the polymers used. This review shows that the most studied mucosal site is the oral cavity, because it is accessible and easy to evaluate, while the rest are uncomfortable for the patient and difficult to assess in vivo. We found problems that need to be solved for mucoadhesive electrospun nanofibers, such as improving adhesion strength and mucosal permanence time, and the design of unidirectional release, multilayer systems for the treatment of several pathologies, to ensure the drug concentration in the tissue or target organ.

Influence of Ground Temperature on Shotcrete-to-Rock Adhesion in Tunnels

Long and deep tunnels are increasingly designed and built worldwide, often in severe geothermal environments characterized by high temperature in the rocks. This issue cannot be ignored because high temperature definitely affects the strength of the adhesion between the concrete and the surrounding rocks, whatever the lining cast in place, segmental or sprayed using shotcrete. The causes of geothermal heat and the effect of the temperature on tunnel linings during and after their construction are recalled and discussed in this paper. Both temperature and humidity are shown to be the most relevant factors affecting adhesion strength, whose loss is related to the microdamage in the shotcrete layers closest to the rock. Possible ways to improve adhesion strength and to minimize the high-temperature detrimental effect are also presented and discussed.