Contact angle hysteresis and pinning at periodic defects in statics

International audienceThis article deals with the theoretical prediction of the wetting hysteresis on nonideal solid surfaces in terms of the surface heterogeneity parameters. The spatially periodical chemical heterogeneity is considered. We propose precise definitions for both the advancing and the receding contact angles for the Wilhelmy plate geometry. It is well known that in such a system, a multitude of metastable states of the liquid meniscus occurs for each different relative position of the defect pattern on the plate with respect to the liquid level. As usual, the static advancing and receding angles are assumed to be a consequence of the preceding contact line motion in the respective direction. It is shown how to select the appropriate states among all metastable states. Their selection is discussed. The proposed definitions are applicable to both the static and the dynamic contact angles on heterogeneous surfaces. The static advancing and receding angles are calculated for two examples of periodic heterogeneity patterns with sharp borders: the horizontal alternating stripes of a different wettability (studied analytically) and the doubly periodic pattern of circular defects on a homogeneous base (studied numerically). The wetting hysteresis is determined as a function of the defect density and the spatial period. A comparison with the existing results is carried out

Cortical laminar necrosis after subarachnoid hemorrhage

Кортикалната ламинарна некроза е рядко наблюдавана при пациент след емболизиране на мозъчна аневризма. Съобщаваме случай на 51-годишна пациентка, която след емболизация на мозъчната аневризма на дясната средна мозъчна артерия остава в коматозно състояние.От извършения ядрено-магнитен резонанс имаше висок интензитет на сигнала в темпоралния лоб на мозъка на T2- изображенията, и линеарен хиперинтензитет по протежение на мозъчните кората на T1-изображенията с дифузно усилване на мозъчната кора.Cortical laminar necrosis has rarely been observed in a patient after coil embolization. We report a 51-year-old female patient who became comatose after the embolization of an aneurysm in the right middle cerebral artery. There were high signal intensities in the temporal brain on T2-weighted MRI images and linear hyperintensities along the cerebral cortices on T1-weighted images with a diffuse gyriform enhancement

Паралелен алгоритъм за метода на локалните вариации

Димитър С. Илиев, Станимир Д. Илиев - Актуално е изследването на поведението на течен менискус в околността на хетерогенна стена. До сега няма получено числено решение за формата на менискуса около стена, която е с хаотична хетерогенност. В настоящата статия е разработен алгоритъм за метода на локалните вариации, който може да се използва на многопроцесорни системи. С този метод е получен за първи път профила на равновесен течен менискус около вертикална стена с хаотична хетерогенност.The behavior of the liquid meniscus near heterogeneous solid wall of a rectangular tank is of great interest now [5]. No numerical solution for the behavior of the liquid meniscus near randomly heterogeneous wall is obtained so far. We construct a parallel algorithm for the local variations method and we use it to obtain the equilibrium state of the liquid free surface for a liquid in a container with one randomly heterogeneous vertical wall. *2000 Mathematics Subject Classification: 65M55, 65K15, 76D45.S.I. has received financial support from the NSF-Bulgaria under grant number DO 02 115/08

Dependence of the contact line roughness exponent on the contact angle on substrates with dilute mesa defects: numerical study

We compute the roughness exponent of the averaged contact line width of a liquid on heterogeneous substrates with randomly distributed dilute defects in statics. We study the case of circular “mesa”-type defects placed on homogeneous base. The shape of the liquid meniscus and the contact line are obtained numerically, using the full capillary model when a vertical solid plate, partially dipped in a tank of liquid, is slowly withdrawing from the liquid. The obtained results imply that the contact line roughness exponent depends on the contact angle $$\theta$$, which the liquid meniscus forms with the solid homogeneous base. The roughness exponent grows when $$|\theta - 90^{\circ } |$$ decreases, and it changes from 0.5 at $$|\theta - 90^{\circ } |= 70^{\circ }$$ to 0.67 at $$|\theta - 90^{\circ } |= 0^{\circ }$$. A wide range of contact angles ($$60^{\circ }$$–$$107.5^{\circ }$$) is present, where the roughness exponent is practically constant, equal to previously obtained experimental results on the magnitude of the roughness exponent and its dependence on $$\theta$$

Wetting of doubly periodic rough surfaces in Wenzel’s regime

In this work we present preliminary results from our numerical study of the shapes of a liquid meniscus in contact with doubly sinusoidal rough surfaces in Wenzel’s wetting regime. Using the full capillary model we obtain the advancing and the receding equilibrium meniscus shapes for a broad interval of surface roughness factors. The contact angle hysteresis is obtained when the three-phase contact line is located on one row (block case) or several rows (kink case) of physical defects. We find that depending on the mutual disposition of the contact line and the lattice of periodic defects, different stick-slip behaviors of the contact line depinning mechanism appear, leading to different values of the contact angle hysteresis

Wetting of doubly periodic rough surfaces in Wenzel’s regime

In this work we present preliminary results from our numerical study of the shapes of a liquid meniscus in contact with doubly sinusoidal rough surfaces in Wenzel’s wetting regime. Using the full capillary model we obtain the advancing and the receding equilibrium meniscus shapes for a broad interval of surface roughness factors. The contact angle hysteresis is obtained when the three-phase contact line is located on one row (block case) or several rows (kink case) of physical defects. We find that depending on the mutual disposition of the contact line and the lattice of periodic defects, different stick-slip behaviors of the contact line depinning mechanism appear, leading to different values of the contact angle hysteresis

Определяне на динамичния контактен ъгъл чрез профила на менискуса

Станимир Д. Илиев, Нина Хр. Пешева - Представен е хибриден експериментално-числен метод, работещ в реално време, за определяне на макроскопичния динамичен контактен ъгъл, който менискусът на течност в съд формира с вертикална пластина, която се потапя или издърпва с постоянна скорост от съда с течността. Този метод е приложим, когато системата е в стационарно състояние. Методът се базира на пълния хидродинамичен модел на Войнов. Той позволява да се получи числено с висока точност стационарната форма на профила на динамичния менискус (и от там ъгълът на наклон на менискуса) като се използва като гранично условие експериментално определената височина на менискуса на пластината.We present here a real time hybrid experimental/numerical method for determination of the macroscopic dynamic contact angle which the liquid meniscus forms with a withdrawing/immersing at constant speed vertical solid plate partially immersed in a thank of liquid when the system is in a stationary state. This method is based on the full hydrodynamic model of Voinov. It allows one to obtain numerically with high precision the stationary shape of the dynamic meniscus profile (and from there the angle of the meniscus slope) using as boundary condition the experimentally determined meniscus height. *2000 Mathematics Subject Classification: 76A05, 76B45.S. I. has received financial support from the NSF-Bulgaria under grant number DO 02 75/08

Wetting of doubly periodic rough surfaces in Wenzel's regime

In this work we present preliminary results from our numerical study of the shapes of a liquid meniscus in contact with doubly sinusoidal rough surfaces in Wenzel’s wetting regime. Using the full capillary model we obtain the advancing and the receding equilibrium meniscus shapes for a broad interval of surface roughness factors. The contact angle hysteresis is obtained when the three-phase contact line is located on one row (block case) or several rows (kink case) of physical defects. We find that depending on the mutual disposition of the contact line and the lattice of periodic defects, different stick-slip behaviors of the contact line depinning mechanism appear, leading to different values of the contact angle hysteresis.ISSN:2261-236

Characterization of enterococci isolated from homemade Bulgarian cheeses and katuk

International audienceA collection of 107 lactic acid bacteria (LAB) isolates was obtained from traditional Bulgarian dairy products--homemade cheeses and katuk samples, produced from heat-treated cow, goat, ewe and buffalo milk without the addition of any bacterial starter culture. The samples were collected from mountain region of Rhodope (south part of Bulgaria), Tracian valley and mountain region of Stara Planina (west part of Bulgaria). These LAB produced bacteriocin-like inhibitory substances (BLIS) and proteinases. Preliminary strain determination was performed according to their fermentation ability using API 50CHL and API 20 Strep. Most of the characterized strains (58) belong to genus Enterococcus; 21, 20 and 11 strains were identified as Lactobacillus sp., Streptococcus sp. and Lactococcus sp., respectively. Isolated enterococcal strains were characterized using phenotypic features as well as by DNA typing. The strains were identified as Enterococcus faecium (34), Enterococcus durans (22) and Enterococcus faecalis (2). The proteolytic activity varied from 0.094 to 0.455 mM/L Gly into the group of E. faecium and from 0.109 to 0.487 mM/L Gly into the group of E. durans strains, while both E. faecalis strains showed relatively high proteolytic activity. The samples obtained after 3 h of hydrolysis of b-casein by E. faecalis B1 strain were further used for mass spectrometry analysis, and 31 peptides were identified