Surface Energy Adhesion Research Articles

Surface analysis of polymeric substrates used for inkjet printing technology

Purpose – This paper aims to find an optimal surface treatment of commonly used polymeric substrates for achieve the high adhesion of printed structures. For this reason, the investigation of substrates surfaces from different perspectives is presented in this paper. Design/methodology/approach – The contact angle measurements as well as the roughness measurements were realised for the analysis of surface properties of investigated substrates. The impact of applied chemical agents for surface treatment onto the wettability is analysed for polyimide, polyethylene terephthalate and polyethylene naphthalene substrates. Findings – The results prove the correlation among wettability, surface energy and work of adhesion with respect to the theoretical background. The surface treatment of polymeric substrates by chemical agents, such as acetone, toluene, ethanol, isopropyl and fluor silane polymer, has a significant impact onto the wettability of substrates which affects the final deposition process of nanoinks. Originality/value – The main benefit of the surfaces’ investigation presented in this paper lays in surface modification by readily available chemical agents for optimising the deposition process nanoinks used in inkjet printing technology.

Investigating Effects of Water Conditioning on the Adhesion Properties of Crack Sealant

This paper investigates the effect of water exposure on three different crack sealants commonly used in cold, moderate and hot climates. It is hypothesized that water penetrates into the interface between crack sealant and substrates causing progressive adhesion failure and that the rate of failure varies depending on the sealant’s surface chemistry as relates to its interaction with water molecules in different environmental conditions. Accordingly, this paper measures the change in sealant’s adhesion strength and surface energy before and after water conditioning. To study adhesion strength and its change due to water conditioning, three different types of sealant were tested using Direct Adhesion Tester (DAT). It was found that the adhesion strength of all three crack sealants reduces due to water exposure. In addition, to evaluate the surface properties and water phobicity of each sealant, the contact angle between a droplet of water and sealant surface was measured before and after conditioning at different temperature. The objective of the latter experiment was to determine whether sealants susceptibility to water would vary with pavement surface temperature. To do so, a sessile drop method utilizing FTA-1000 was used to determine the contact angle for each of the aforementioned water-sealant pairs at different temperatures. The results obtained were further used to calculate the work of adhesion at each scenario to be correlated to mechanical adhesion strength measured with DAT.

Fluorine-Enriched Melt-Blown Fibers from Polymer Blends of Poly(butylene terephthalate) and a Fluorinated Multiblock Copolyester.

Melt-blown fibers (dav ∼1 μm) were produced from blends of poly(butylene terephthalate) (PBT) and a partially fluorinated random multiblock copolyester (PFCE) leading to enhanced hydrophobicity and even superhydrophobicity (static water contact angle = 157 ± 3°) of the associated fiber mats. XPS measurements demonstrated quantitatively that the surface fluorine content increased systematically with the bulk loading of PFCE, rising to nearly 20 atom %, which corresponds to 41 wt % PFCE at a bulk loading of 10 wt %. The PBT/PFCE fibers exhibit greater fluorine surface segregation than either melt-blown PBT/poly(ethylene-co-chlorotrifluoroethylene) (PBT/PECTFE) fibers or electrospun fibers obtained from blends of poly(styrene) and fluoroalkyl end-capped polystyrene (PS/PSCF). Dynamic contact angle measurements further demonstrated decreased surface adhesion energy of the melt-blown PBT/PFCE fiber mats due to the blooming of PFCE to the surface.

Nanomechanical Switch Designs to Overcome the Surface Adhesion Energy Limit

An analytical model is developed to assess the switching energy of a nanomechanical switch. Alternative switch designs are proposed to leverage spring-restoring force to counterbalance surface adhesion force, reducing the depth of the potential energy well created by contact adhesion and thereby overcoming the surface adhesion energy limit.

Template-controlled mineralization: Determining film granularity and structure by surface functionality patterns.

We present a promising first example towards controlling the properties of a self-assembling mineral film by means of the functionality and polarity of a substrate template. In the presented case, a zinc oxide film is deposited by chemical bath deposition on a nearly topography-free template structure composed of a pattern of two self-assembled monolayers with different chemical functionality. We demonstrate the template-modulated morphological properties of the growing film, as the surface functionality dictates the granularity of the growing film. This, in turn, is a key property influencing other film properties such as conductivity, piezoelectric activity and the mechanical properties. A very pronounced contrast is observed between areas with an underlying fluorinated, low energy template surface, showing a much more (almost two orders of magnitude) coarse-grained film with a typical agglomerate size of around 75 nm. In contrast, amino-functionalized surface areas induce the growth of a very smooth, fine-grained surface with a roughness of around 1 nm. The observed influence of the template on the resulting clear contrast in morphology of the growing film could be explained by a contrast in surface adhesion energies and surface diffusion rates of the nanoparticles, which nucleate in solution and subsequently deposit on the functionalized substrate.

Electronic structures and mechanical properties of Al(111)/ZrB2(0001) heterojunctions from first-principles calculation

Employing first-principles density functional theory (DFT), the structures and electronic and mechanical properties of Al(111)/ZrB2(0001) heterojunctions are investigated. It is found that both B-terminated ZrB2(0001) and Zr-terminated ZrB2(0001) can form heterojunction interfaces with Al(111) surface. The heterojunction with B-terminated ZrB2(0001) is demonstrated to be most stable by comparing the surface adhesion energies of six different heterojunction models. In the stable configurations, the Al atom is found projecting to the hexagonal hollow site of neighbouring boron layer for the B-terminated ZrB2(001), and locating at the top site of the boron atoms for Zr-terminated ZrB2(001) interface. The mechanisms of interface interaction are investigated by density of states, charge density difference and band structure calculations. It is found that covalent bonds between surface Al atoms and B atoms are formed in the B-terminated heterojunction, whereas the Al atoms and Zr atoms are stabilised by interface metallic bonds for the Zr-terminated case. Mechanical properties of Al/ZrB2 heterojunctions are also predicted in the current work. The values of moduli of Al/ZrB2 heterojunctions are determined to be between those of single crystal Al and ZrB2, which exhibit the transition of mechanical strength between two bulk phases. DFT calculations with the current models provide the mechanical properties for each heterojunction and the corresponding contributions by each type of interface in the composite materials. This work paves the way for industrial applications of Al(111)/ZrB2(0001) heterojunctions.

Bonding energy of Sylgard on fused quartz: an experimental investigation

The bonding energy between the polymer Sylgard and fused quartz is determined experimentally using a miniature bulge test combined with three-dimensional digital image correlation (3D-DIC). Based on the experimental observation, Mindlin plate theory is used to compute the bonding energy (adhesive energy or surface energy) between the Sylgard and the fused quartz. The experimental results demonstrate that the combination of the miniature bulge test and the 3D-DIC provides a viable tool to directly measure interfacial and bonding properties.

Forces on micron-sized particles randomly distributed on the surface of larger particles and possibility of detachment

Numerical calculations based on the Lattice-Boltzmann method were performed for a particle cluster consisting of a large carrier particle covered with small spherical drug particles which were exposed to a constant velocity air flow. Prior to these studies, the simulations were validated based on a test case where a single particle is situated on a plane wall and exposed to a linear shear flow. The present simulations were compared with analytical results and other simulations. Moreover, the required small particle resolution and the domain size were properly selected based on an extensive numerical study. The diameter of the carrier particles was 100μm, while the fine particles had diameters of 3μm and 5μm, respectively. The range of Reynolds numbers considered was between 1 and 200. Moreover, the coverage degree of the carrier by the small particles was varied in the simulations between 10% and 50%, and this influence on the detachment was determined. From these simulations the fluid dynamic forces on the drug particles were extracted in dependence of the angular position in order to estimate the possibility of drug particle detachment. Detachment might occur through lift-off, sliding or rolling. Lift-off was found to be not possible due to the acting small normal forces even at Re=200. The probability of sliding and rolling detachment in dependence of the angular position was estimated based on measured adhesion properties, i.e. van der Waals force, adhesion surface energy and friction coefficient. With these studies it is aimed to understand drug particle detachment from carrier particles in an inhaler device as a basis of modelling and optimising dry powder inhalation.

Structural View of Hydrophobic Ionic Liquid on Graphene: Comparing Static and Ab Initio Computer Simulations

Significant roles of hydrophobic interactions in diverse areas including chemical, biological, and geological processes motivated us to investigate the adsorption of [BMIM][PF6] on a substrate. Optimal adsorption position and orientation of ion-pair on graphene surface was determined and adsorption energies were calculated. Molecular doping, i.e. charge transfer between ionic liquid and surface, was discussed based on density of states and molecular orbitals of adsorbate. Accordingly, carbon atoms of graphene adsorb cation for appropriate interactions. Interesting properties of adsorbed IL such as structure, orientation, charge distribution, surface adhesive energy, and charge transfer with distinctive properties such as frontier molecular orbitals, natural bond orbital, and density of states of IL/graphene system were also investigated. Ab initio molecular dynamics simulation clarifies that both imidazolium ring of the cation and anion interact remarkably with solid surface. This observation is in good agreement with experimental and computational results. Cohesive energy equal to −168 meV indicates strong interaction between IL and solid surface. Cohesive energy density is a considerable value for a surface with 13.49 Å diameter. Molecular dynamics explains the properties of condensed phase of ionic liquid over graphene and regenerates orientation of ring with respect to the surface as first principles computations.

Using energy parameters based on the surface free energy concept to evaluate the moisture susceptibility of hot mix asphalt

Although the conventional laboratory test procedure is helpful in comparative analysis of moisture susceptibility of hot mix asphalt (HMA), it does not focus on measuring the fundamental material properties related to the mechanisms of moisture damage. In this study, comparing results of tensile strength ratio test and surface free energy method resulted in the determination of important energy parameters that can be employed as a quantitative indicator to assess moisture susceptibility of HMA. Three of the four parameters used in this research have a convenient correlation with the laboratory results. The ratio of the difference between the surface adhesion of asphalt–aggregate and the water–aggregate to the surface adhesion of the asphalt–aggregate (EP1) had the best correlation with the tensile strength ratio of 32 types of asphalt mixtures. This parameter can be used as a tool for moisture sensitivity detection with more caution. Also, the ratio of the surface energy of adhesion of the asphalt–aggregate to the difference between the surface energy of adhesion in dry and wet conditions (EP2) had good correlation with laboratory results.

Equilibrium states and stability of pre-tensioned adhesive tapes.

In the present paper we propose a generalization of the model developed in Afferrante, L.; Carbone, G.; Demelio, G.; Pugno, N. Tribol. Lett. 2013, 52, 439–447 to take into account the effect of the pre-tension in the tape. A detailed analysis of the peeling process shows the existence of two possible detachment regimes: one being stable and the other being unstable, depending on the initial configuration of the tape. In the stability region, as the peeling process advances, the peeling angle reaches a limiting value, which only depends on the geometry, on the elastic modulus of the tape and on the surface energy of adhesion. Vice versa, in the unstable region, depending on the initial conditions of the system, the tape can evolve towards a state of complete detachment or fail before reaching a state of equilibrium with complete adhesion. We find that the presence of pre-tension in the tape does not modify the stability behavior of the system, but significantly affects the pull-off force which can be sustained by the tape before complete detachment. Moreover, above a critical value of the pre-tension, which depends on the surface energy of adhesion, the tape will tend to spontaneously detach from the substrate. In this case, an external force is necessary to avoid spontaneous detachment and make the tape adhering to the substrate.

Interfacial dynamics and adhesion behaviors of water and oil droplets in confined geometry.

To simulate the interfacial behaviors in real heterogeneous systems, the point contact condition is constructed to study the classical immiscible displacement problem in this work. Specifically, the interfacial dynamics during the water droplet passing through the oil capillary bridge formed under the point contact condition is investigated. Emphasis is put on the influences of the wettabilities and the relative separation motion of the solid surfaces on the dynamic behavior of the droplets. The observations suggested that the capillary pressure had negligible effect on the movement of the water droplet when it was passing though the oil capillary bridge. The wettability and the relative separation of the disk and ball would influence the final adhesion behaviors of the water droplet after the droplet passed through the oil capillary bridge. Surface tension and adhesion energy were used to interpret these observations.

Towards the optimisation and adaptation of dry powder inhalers.

Pulmonary drug delivery by dry powder inhalers is becoming more and more popular. Such an inhalation device must insure that during the inhalation process the drug powder is detached from the carrier due to fluid flow stresses. The goal of the project is the development of a drug powder detachment model to be used in numerical computations (CFD, computational fluid dynamics) of fluid flow and carrier particle motion through the inhaler and the resulting efficiency of drug delivery. This programme will be the basis for the optimisation of inhaler geometry and dry powder inhaler formulation. For this purpose a multi-scale approach is adopted. First the flow field through the inhaler is numerically calculated with OpenFOAM(®) and the flow stresses experienced by the carrier particles are recorded. This information is used for micro-scale simulations using the Lattice-Boltzmann method where only one carrier particle covered with drug powder is placed in cubic flow domain and exposed to the relevant flow situations, e.g. plug and shear flow with different Reynolds numbers. Therefrom the fluid forces on the drug particles are obtained. In order to allow the determination of the drug particle detachment possibility by lift-off, sliding or rolling, also measurements by AFM (atomic force microscope) were conducted for different carrier particle surface structures. The contact properties, such as van der Waals force, friction coefficient and adhesion surface energy were used to determine, from a force or moment balance (fluid forces versus contact forces), the detachment probability by the three mechanisms as a function of carrier particle Reynolds number. These results will be used for deriving the drug powder detachment model.

Influence of metal surface preparation on its surface profile, contact angle, surface energy and adhesion with glass fibre prepreg

Surface preparation of metal plays a vital role to enhance the adhesion of polymer coatings in ensuring the desired performance of metal infrastructure for the oil and gas industry. In this study, a range of techniques for the surface preparation of mild steel were evaluated which included garnet grit blasting, disk sanding, needle gun, flap wheel, strip wheel and wire brush. The surface profile and apparent surface energy parameters such as apparent surface energy, work of adhesion, Lifshitz-van der Waals acid–base components were measured from these trials correlation made with these properties to the metal to polymer coating bond strength and bond failure mode.The dolly pull-off strength was used to quantify the bond strength while the laminate failure area (%) was used to assess the bond failure mode. Based on the testing results, it was found that irrespective of the surface preparation technique used, the dolly pull-off strength and laminate failure area increased with increasing surface profile up to a value of approximately 21µm and both of these properties followed a plateau up to 24μm and then decreased above this surface profile value. The dolly pull-off strength was also seen to increase with the increase of surface energy and work of adhesion and decrease of contact angle. It was found that the maximum adhesion could be attained with three of the four grit sizes of the garnet grit blasting technique which appeared to have achieved the most favourable properties amongst all the surface properties studied here. Wenzel model was found to be in agreement with the values of the surface profile of different surface preparation techniques.

The Influence of Laser-Induced 3-D Titania Nanofibrous Platforms on Cell Behavior

The current challenge in tissue engineering is to design a platform that can provide appropriate topography and suitable surface chemistry to encourage desired cellular activities and to guide 3-D tissue regeneration. Compared with traditional cell culture materials, 3-D nanofibrous platforms offer a superior environment for promoting cell functions by mimicking the architecture of extracellular matrix (ECM). In this study, we present a technique to engineer freestanding 3-D titania nanofibrous structures on titanium substrates using femtosecond laser processing. The crystallinity, surface adhesion, and surface energy of the synthesized nanostructures are discussed. The effects of synthesized nanoarchitectures on the proliferation, morphology, and viability of MC3T3-E1 mouse osteoblast-like cells and NIH 3T3 mouse embryonic fibroblasts are investigated. The nanofibrous structures show high surface energy and hydrophilicity. The results from in vitro studies reveal that the titania nanofibrous architectures possess excellent biocompatibility and significantly enhances proliferation of both cell lines compared to untreated titanium specimens. Study of the cell morphology shows dynamic cell migration and attachment on the titania nanofibrous architecture. The bioactivity and biocompatibility of the engineered 3-D nanostructures suggest noticeable perspective for developing bio-functionalized scaffolds and implantable materials in regenerative medicine and clinical tissue engineering.

Phased Evaluation Theory and Study on Adhesion between Asphalt and Stone Based on Surface Energy Theory

As for the existing surface energy adhesion theories which are used to evaluate asphalt and stone's adhesive performance quantitatively, they are either dealing with the interface between solid asphalt and solid stone which can not adhere according to the formulas and definitions in process of adhesion or else roughly characterizing the solid asphalt and stone's adhesion properties with the adhesion index of heated asphalt and solid stone. So according to the forming process of asphalt mixture , this paper puts forward the method and principle to evaluate asphalt and stone's adhesion based on the surface energy theory. It evaluates the adhesion properties of asphalt and stone under hydrous and anhydrous conditions respectively. In the anhydrous condition, we choose contact angle and the Gibbs free energy of failure stage as the indexes of evaluating asphalt - stone interface's adhesion properties, while the materials under the hydrous condition, we select cohesional work, contact angle, Gibbs free energy as the indexes of evaluating asphalt-stone system's resistance of moisture.

Probing microelectromechanical systems in an environmentally controlled chamber using long working distance interferometry

It is well known that the environment in which micromechanical systems operate significantly affects their performance. It is, therefore, important to characterize micromachine behavior in environments where the humidity, pressure, and chemical composition of the ambient can be precisely controlled. Achieving such a level of environmental control presents significant challenges in view of the required instrumentation. To that end, a custom micromachine characterization system is built that allows for full environmental control (pressure, humidity, and gas composition) while retaining full micromachine characterization techniques (long working distance interferometry, electrical probe connectivity, actuation scripting capability). The system also includes an effective in situ surface cleaning mechanism. As an example of the system's utility, a microcantilever crack healing experiment is conducted and surface adhesion energy measurements are tracked over time after a step change in humidity is applied.

Preparation of a Functionally Graded Fluoropolymer Thin Film and Its Application to Antireflective Coating

Fluoropolymer thin films were prepared by the ion-assisted vapor deposition polymerization (IAD) of 2-(perfluorohexyl) ethylacrylate (Rf-6) under Ar ion irradiation. The ion acceleration voltage Va largely affected the film characteristics. With increasing Va, the adhesion strength between the film and the substrate improved, while the surface energy and the refractive index increased. To attain a high adhesion strength, a low surface energy, and a low optical reflectivity simultaneously, a functionally graded film was prepared by varying Va from 300 to 0 V continually in the course of film growth. As a consequence, an antireflective coating with good adhesion and low surface energy was obtained. The optical reflectivity of a glass substrate was reduced from 4.9 to 0.55% at a wavelength of 400 nm by depositing a 100-nm-thick single-layer functionally graded fluoropolymer film. The surface energy of this film was 8.5 mJ/m2.

Molybdenum disulfide dc contact MEMS shunt switch

Atomic force microscopy pulsed force mode verifies that molybdenum disulfide (MoS2) has a smaller surface adhesion energy than graphene. MEMS switches based on MoS2 may have less stiction problems. Suspended MoS2 two-end fixed beams were fabricated, and their mechanical properties including Young's modulus were characterized by atomic force microscope (AFM) indentation. MoS2 dc contact MEMS (micro-electro-mechanical systems) switches were demonstrated with a pull-in voltage of less than 10 V.

Challenges in Nanoparticle Delivery: Cellular Uptake and Intracellular Escape

Control of cellular uptake of nanoparticles is crucial step in drug delivery and nanomedicine. However, the conditions under which passive endocytosis, i.e. not ATP driven, occurs are not well understood. using Molecular Dynamics simulations with coarse grained model we investigated the conditions of the passive uptake and consequential cytosol escape of the ligand-coated nanoparticles with varying size, shape, coverage, and receptor-binding strength. In qualitative agreement with Helfrich theory we have found that larger spherical particles undergo endocytosis easier than smaller ones due to a more favorable compromise between bending rigidity and surface adhesive energy. Moreover, our simulations and elastic analysis suggest that the prolate shape of spherocylinders can lead to more efficient delivery than spheres of the same diameter as both shapes seems to have the same kinetic barrier for uptake across a lipid membrane but the spherocylinders have a larger volume. In addition, we observed that the sharp edges on nanoparticles can hinder the uptake process. The cytosol escape of the uptaken nanoparticles can occur upon a decrease of ligand-receptor interaction and a sufficient deformation of the membrane vesicle from its equilibrium state. The deformation can be administered by a non-spherical shape or a pressure exerted by the nanoparticle. Large rigid spheres were not observed to be able of the escape during the time of simulations. The insight should be helpful in rational design of drug delivery nanocarriers.