A mathematical model for evaluating adhesion contact of an elastomeric seal-on-seal structure

For low impact docking systems (LIDS) developing for rendezvous and docking of spacecraft, the main interface docking seal (MID seal) is one of the key components, and its seal and adhesion performances are crucial for mating LIDS-adapted spacecrafts. An elastomeric seal-on-seal structure is one of the mainstream designs of the MID seal and is generally made of silicone rubbers that can adapt to complex space environments. For the MID seal of seal-on-seal structure, the adhesion performance has been confirmed to have significant effects on the separation reliability of mating spacecrafts. By analyzing the sealing and adhesive mechanisms of the MID seal that is an elastomeric seal-on-seal structure, an adhesive contact model of single rough peak is derived on the grounds of Johnson, Kendall and Roberts (JKR) theory. Utilizing the asperities model and the adhesive contact model of single rough peak, an adhesive contact model of the elastomeric seal-on-seal structure is further proposed. The experiments were performed to verify the adhesion model, and the satisfied consistencies were presented in the comparative studies of the experimental data and the calculated data. Based on the proposed mathematical model, the simulation analyses were performed to disclosure adhesive performances of the MID seal. The influence rules of some parameters on adhesive performances were presented, including material parameters, geometric parameters, and parameters of surface morphology. The research findings are proven to be favorable for the design, machining, assemblage and actual service of the MID seal, and can be also used for other elastomeric seals.

Adhesion of an elastic sphere on a tensioned membrane

Inspirited by the fact that classical models of adhesion contact (such as the Johnson–Kendall–Roberts model, Young’s equation or the Neumann equation) cannot be directly applied to adhesion of an elastic sphere on a membrane, the present work aims to develop an explicit general model for axisymmetric adhesion mechanics of an elastic sphere on a tensioned circular membrane. An explicit expression for the potential energy of the sphere–membrane system is derived, and explicit equations are given to determine the adhesion equilibrium state. The validity and accuracy of the proposed model are verified by good agreement between the predicted results and known results on both adhesion of a rigid sphere on a membrane and the critical condition for full wrapping of a rigid sphere by a membrane of non-zero bending rigidity.

Development of surface properties of ultra-high-molecular-weight polyethylene film using side-chain crystalline block copolymers

Ultra-high-molecular-weight polyethylene (UHMWPE) has been widely used in industry; however, the applications for UHMWPE are limited because of low hydrophilic and adhesive properties. Herein, we developed the surface properties of UHMWPE by using side-chain crystalline block copolymers (SCCBCs), which consist of a side-chain crystalline unit and a functional unit. This process only required immersing the UHMWPE film in the diluted SCCBC solution, which enabled the UHMWPE surface to be coated homogeneously. The results of the contact angle and tensile shear test showed that the surface of UHMWPE modified with SCCBC was improved in hydrophilicity and adhesive properties. In addition, high adhesion strength was measured on UHMWPE surfaces dipped in a SCCBC solution at high temperature with the UHMWPE film becoming elongated at all parts other than the adhesion contact area.

Adhesive contact of elastic solids with stohastic roughness

Model of normal adhesive contact between elastic bodies with stochastic surface roughness is under consideration. Roughness is simulated by Winkler-Fuss nonlinear layer, which can resist to compressive and tensile (in the case of adhesion) contact stresses. Mechanical properties of the layer are determined by statistical theories of adhesive contact between nominally flat rough surfaces. The contact of solids is described by nonlinear boundary integral equations with non-monotonic operators. Their solutions determine reduction of effective thickness of rough layer, contact stresses, contact region, adhesion force. Formulas for adhesion force calculation are presented for the most frequent nominal gap between solids in contact for DMT–theory of contact.

Importance of erythrocyte deformability for the alignment of malaria parasite upon invasion

ABSTRACTInvasion of erythrocytes by merozoites is an essential step for the survival and progression of malaria parasites. In order to invade red blood cells (RBCs), parasites have to adhere with their apex to the RBC membrane. Since a random adhesion contact between the parasite and membrane would be too inefficient, it has been hypothesized that merozoites are able to actively re-orient toward apex-membrane alignment. This is supported by several experimental observations which show that merozoites frequently induce considerable membrane deformations before the invasion process. Even though a positive correlation between RBC membrane deformation and successful invasion is established, the role of RBC mechanics and its deformation in the alignment process remains elusive. Using a mechanically realistic model of a deformable RBC, we investigate numerically the importance of RBC deformability for merozoite alignment. Adhesion between the parasite and RBC membrane is modeled by an attractive potential which might be inhomogeneous, mimicking possible adhesion gradients at the surface of a parasite. Our results show that RBC membrane deformations are crucial for successful merozoite alignment, and require strengths comparable to adhesion forces measured experimentally. Adhesion gradients along the parasite body further improve its alignment. Finally, an increased membrane rigidity is found to result in poor merozoite alignment, which can be a possible reason for the reduction in the invasion of RBCs in several blood diseases associated with membrane stiffening.STATEMENT OF SIGNIFICANCEPlasmodium parasites invade erythrocytes during the progression of malaria. To start invasion, the parasites have to re-orient themselves such that their apex establishes a direct contact with erythrocyte membrane. The re-orientation (or alignment) process is often associated with strong membrane deformations, which are believed to be induced by the parasite and are positively correlated with its alignment. We employ a mechanically realistic erythrocyte model to investigate the interplay of membrane deformations and merozoite alignment during parasite adhesion to an erythrocyte. Our model clearly demonstrates that erythrocyte membrane deformations are a key component of successful parasite alignment, since the re-orientation of parasites at rigidified membranes is generally poor. Therefore, our results suggest a possible mechanism for the reduction in erythrocyte invasion in several blood diseases associated with membrane stiffening.

Physical and chemical bases of processes of formation of polymeric coverings on a solid surface

Лакокрасочные покрытия используются в различных отраслях народного хозяйства. Удачно сочетая комплекс положительных свойств, присущих полимерным материалам, с декоративными и физико-механическими свойствами древесины и древесных материалов, покрытия позволяют успешно реализовать многочисленные задачи по формированию защитно-декоративных покрытий на современном этапе научно-технического прогресса. В связи с широким использованием лакокрасочных покрытий в технике интенсивно разрабатываются новые лакокрасочные материалы, методы нанесения и приемы образования покрытий, совершенствуются аппаратура и методы исследования, расширяется область применения. В настоящей статье, основу которой составляют результаты многочисленных работ в области физико-химических процессов, проходящих на границе раздела жидкость – подложка при образовании лакокрасочных покрытий, сделана попытка обобщить накопленные материалы за годы исследований, при этом стремились к объективной оценке имеющихся данных, что позволяет указать на необходимость дальнейшего развития научных представлений, лежащих в основе процессов образования покрытий. Авторы стремились вскрыть физико- химическую сущность процессов образования покрытий и показать многофактурность процесса формирования лакокрасочного покрытия. При этом в меньшей степени обращалось внимание на конкретность того или иного режима, а рассматриваются кинетические закономерности и тенденции процесса. Формирование лакокрасочных покрытий включает в себя сложный комплекс стадий и технологических операций, каждая из которых требует специальных материалов и оборудования. Известные полимерные материалы могут быть модифицированы с учётом требований технологии и свойств твердой поверхности, которая играет определяющую роль во взаимодействии с лакокрасочными материалами, приводящими к образованию прочного адгезионного контакта и обеспечивающими требуемые физико-механические и защитно-декоративные свойства покрытия. Сложность физико-химических явлений на границе полимер – твердая поверхность требует использования имеющихся в смежных областях рекомендаций и теоретических представлений. Проведённые исследования позволяют утверждать, что для каждого конкретного сочетания лакокрасочного материала с подложкой устанавливаются параметры, присущие только данной конкретной системе взаимодействия, хотя общий экстремальный характер сохраняется. Проведенные исследования показывают, что подогрев поверхности подложки способствует улучшению смачивания её лакокрасочными материалами, что, в конечном итоге, повышает качество покрытий. Таким образом, если ставится задача рационального выбора технологического процесса отделки, необходимо учитывать влияние многочисленных факторов взаимного влияния межфазовых взаимодействий газовой среды, жидкости и твердого тела. Paint coatings are used various branches of the national economy. Successfully combining a complex of the positive properties inherent in polymeric materials, with decorative and physic-mechanical properties of wood and wood materials, coverings allow to realize successfully numerous tasks of formation of a protective decorative coating at the present stage of scientific and technical progress. Due to the wide use of paint coatings in technique new coating compositions, methods of drawing and methods of formation of coverings are intensively developed, the equipment and research techniques is improved, the range of application extends. In this article which principles results of numerous works in the field of the physical and chemical processes which are taking place liquid on a demarcation – a substrate are at formation of paint coatings the attempt to generalize the saved-up materials for years of researches is made, at the same time aspired to objective assessment, the available data that allows to indicate the need of further development of the scientific representations which are the cornerstone of processes of formation of coverings. Authors sought to open a physical and chemical substance of processes of formation of coverings and to show a process ambiguity of formation of a paint coating. At the same time the attention to concreteness of this or that mode was to a lesser extent paid, and kinetic regularities and tendencies of process are considered. Formation of paint coatings includes the composite complex of stages and technological operations, each of which demands express materials and an inventory. The known polymeric materials can be modified taking into account requirements of technology and properties of a solid surface which plays a defining role in interaction with the coating compositions leading to formation of strong adhesion contact and providing demanded physic-mechanical and protective and decorative with properties of a covering. Complexity of the physical and chemical phenomena on border polymer – the solid surface demands use of the recommendations which are available in interfacing areas and theoretical representations. The conducted researches allow to claim that for everyone concrete a combination of a coating composition to a substrate the parameters inherent only in this concrete system of interaction are set though the common extreme character remains. The conducted researches show that heating of a surface of a substrate promotes wetting improvement by its coating compositions that, finally, increases quality of coverings. Thus, if the task of the rational choice of technological process of finishing is set, it is necessary to consider influence of numerous factors of interference of the phase interactions of a gaseous fluid, liquid and a solid body.

Plane Contact and Adhesion of Two Elastic Solids With an Interface Groove

A systematic study is performed on the plane contact and adhesion of two elastic solids with an interface groove. The nonadhesion and Johnson–Kendall–Roberts (JKR) adhesion solutions for a typical groove shape are obtained in closed form by solving singular integral equations and using energy release rate approaches. It is found that the JKR adhesion solution depends solely on a dimensionless parameter α and the groove is predicted to be unstably flattened with no applied load when α≥0.535. Furthermore, the corresponding Maugis–Dugdale adhesion model has been revisited with three possible equilibrium states. By introducing the classical Tabor parameter μ, a complete transition between the nonadhesion and the JKR adhesion contact models is captured, which can be recovered as two limiting cases of the Maugis–Dugdale model. Depending on two nondimensional parameters α and μ, where α2 represents the ratio of the surface energy in the groove to the elastic strain energy when the grooved surface is flattened, different transition processes among three equilibrium states are characterized by one or more jumps between partial and full contact. Larger values of α and μ tend to induce more energy loss due to adhesion hysteresis. Combination values of α and μ are also suggested to design self-healing interface grooves due to adhesion.

Research on CFD numerical simulation and flow field characteristics of countercurrent–cocurrent dissolved air flotation

Countercurrent–cocurrent dissolved air flotation (CCDAF), the popular water purification device, which consists of collision and adhesion contact zones, showed favorable flotation conditions for micro-bubble adhesion and stability. In this study, computational fluid dynamics (CFD) numerical simulation was employed to confirm that the unique CCDAF configuration create reasonable and that the flow field characteristics were good no matter for single phase or gas–liquid two-phase conditions. In addition, the turbulence of the flow field was enhanced with the increasing influent load; the swirling was remarkably reduced with the increase of gas holdup. Meanwhile, a thick micro-bubble filter layer was formed in the separation zone, which favored bubble-flocs agglomerating and rising. The force analysis also showed that the cross section within the tank contribute to the uniformity of the bottom water collection as well as enlargement of the bottom outflow area, therefore improving the overall flotation performance. The simulation results revealed for the CCDAF process can provide technical guidance for engineering design and application.