Contact line motion for partially wetting fluids

We study the flow close to an advancing contact line in the limit of small capillary number. To take into account wetting effects, both long and short-ranged contributions to the disjoining pressure are taken into account. In front of the contact line, there is a microscopic film corresponding to a minimum of the interaction potential. We compute the parameters of the contact line solution relevant to the matching to a macroscopic problem, for example a spreading droplet. The result closely resembles previous results obtained with a slip model

The idea of «Questions» conscious in the aspect of teaching in comprehensive schools

In article is considered didactic importance and practical particularities of the using to idea «Questions» in realization of the principle to consciousness’s in education (on example of the study physicists). It highlights the main advantages and disclosed didactic importance of the issues in the study of material. The article shows the methodological feasibility of their use in the educational process, highlighted the basic techniques of student learning and the formation of posing questions. Awareness of the material being studied depends on the completeness of its perception, a holistic view of the problem. The ability to formulate a question displays a person's ability to perceive, synthesize and analyze incoming information. The emergence of the issue indicates that the student's conscious approach to the consideration of the problem in question, which is crucial in the study of natural sciences.Key words: consciousness, education, teacher, question, activity.В статье на основе архивных материалов и анализа педагогического опыта рассмотрено дидактическое значение и особенности практического применения идеи «Почемучки» в реализации принципа сознательности в обучении (на примере изучения физики), выделены основные преимущества и раскрыта дидактическая значимость вопросов при изучении материала, показана методическая целесообразность их использования в учебном процессе, выделены основные приемы обучения учащихся формированию и постановке вопросов. Осознание изучаемого материала напрямую зависит от полноты его восприятия, целостного представления о проблеме. Умение формулировать вопрос отображает способность личности воспринимать, синтезировать и анализировать входящую информацию. Появление вопроса свидетельствует о сознательном подходе учащегося к рассмотрению изучаемой проблемы, что принципиально важно в изучении естественных наук.Ключевые слова: сознательность, обучение, педагог, вопрос, активность

Universality in dynamic wetting dominated by contact line friction

We report experiments on the rapid contact line motion present in the early stages of capillary driven spreading of drops on dry solid substrates. The spreading data fails to follow a conventional viscous or inertial scaling. By integrating experiments and simulations, we quantify a contact line friction ($\mu_f$), which is seen to limit the speed of the rapid dynamic wetting. A scaling based on this contact line friction is shown to yield a universal curve for the evolution of the contact line radius as a function of time, for a range of fluid viscosities, drop sizes and surface wettabilities

Demand-side solutions for climate mitigation: Bottom-up drivers of household energy behavior change in the Netherlands and Spain

© 2019 The Authors Households are responsible for 70% of CO2 emissions (directly and indirectly). While households as agents of change increasingly become a crucial element in energy transitions, bottom-up mechanisms facilitating behavioral change are not fully understood. A scientific understanding of individual energy use, requires eliciting factors that trigger or inhibit changes in energy behavior. This paper explores individual energy consumption practices and behavioral aspects that affect them. We quantitatively study the determinants of three energy actions: (1) investments in house insulation, solar panels and/or energy-efficient appliances, (2) conservation of energy by changing energy-use habits like switching off unused devices or adjusting house temperature, and (3) switching to green(er) electricity sources. To address this goal, we conduct a comprehensive survey among households (N = 1790) in two EU regions: Overijssel, the Netherlands and Navarre, Spain. We use probit regression to estimate how behavioral factors, households’ socioeconomic characteristics and structural attributes of dwellings influence energy related actions. Our analysis demonstrates that awareness and personal and social norms are as important as monetary factors. Moreover, education and structural dwelling factors significantly affect households’ actions. These results have implications for governmental policies aimed at reducing residential CO2 footprints and facilitating demand-side solutions in a transition to low-carbon economy

Roughness of moving elastic lines - crack and wetting fronts

We investigate propagating fronts in disordered media that belong to the universality class of wetting contact lines and planar tensile crack fronts. We derive from first principles their nonlinear equations of motion, using the generalized Griffith criterion for crack fronts and three standard mobility laws for contact lines. Then we study their roughness using the self-consistent expansion. When neglecting the irreversibility of fracture and wetting processes, we find a possible dynamic rough phase with a roughness exponent of $\zeta=1/2$ and a dynamic exponent of z=2. When including the irreversibility, we conclude that the front propagation can become history dependent, and thus we consider the value $\zeta=1/2$ as a lower bound for the roughness exponent. Interestingly, for propagating contact line in wetting, where irreversibility is weaker than in fracture, the experimental results are close to 0.5, while for fracture the reported values of 0.55--0.65 are higher.Comment: 15 pages, 6 figure

Asymptotic theory for a moving droplet driven by a wettability gradient

An asymptotic theory is developed for a moving drop driven by a wettability gradient. We distinguish the mesoscale where an exact solution is known for the properly simplified problem. This solution is matched at both -- the advancing and the receding side -- to respective solutions of the problem on the microscale. On the microscale the velocity of movement is used as the small parameter of an asymptotic expansion. Matching gives the droplet shape, velocity of movement as a function of the imposed wettability gradient and droplet volume.Comment: 8 fig

Hydrodynamic theory of de-wetting

A prototypical problem in the study of wetting phenomena is that of a solid plunging into or being withdrawn from a liquid bath. In the latter, de-wetting case, a critical speed exists above which a stationary contact line is no longer sustainable and a liquid film is being deposited on the solid. Demonstrating this behavior to be a hydrodynamic instability close to the contact line, we provide the first theoretical explanation of a classical prediction due to Derjaguin and Levi: instability occurs when the outer, static meniscus approaches the shape corresponding to a perfectly wetting fluid

Front pinning in capillary filling of chemically coated channels

The dynamics of capillary filling in the presence of chemically coated heterogeneous boundaries is investigated, both theoretically and numerically. In particular, by mapping the equations of front motion onto the dynamics of a dissipative driven oscillator, an analytical criterion for front pinning is derived, under the condition of diluteness of the coating spots. The criterion is tested against two dimensional Lattice Boltzmann simulations, and found to provide satisfactory agreement as long as the width of the front interface remains much thinner than the typical heterogeneity scale of the chemical coating.Comment: 7 pages, 4 figures, submitted to Physical Review