形状记忆聚合物表面水下油黏附性的可逆调控

采用模板法在形状记忆聚合物表面获得一种具有形状记忆特征的表面微结构, 在氧等离子作用下, 表面呈现低黏附的水下超疏油特性. 在外压作用下, 表面微结构发生坍塌, 失去水下超疏油性, 同时表面对油滴呈高黏附特征. 在120 ℃热处理后, 表面微结构恢复到了原始状态, 在等离子进一步作用下, 表面即可恢复到最初的低黏附水下超疏油状态. 因此通过外压、 热处理及等离子作用即可实现对表面微结构及其水下油黏附性能的可逆调控. 研究表明, 表面不同的微结构状态赋予表面不同的黏附性能, 在原始表面液滴处于低黏附的Cassie态, 而在坍塌结构表面水滴处于高黏附的Wenzel态.     

粘滞性粒子动力学中的二维非自相似初值问题

研究了二维粘滞性粒子动力学中的非自相似初值问题．该初值被一圆环分为内外两块常状态．利用广义特征分析的方法和广义Rankine-Hugoniot关系,该关系是常微分方程组,一个包含狄拉克激波和真空的整体解被构造性地得到．     

Morphological Responses of Vascular Endothelial Cells Induced by Local Stretch Transmitted Through Intercellular Junctions

It has been well established that mechanical stimuli including fluid shear stress and cyclic stretch play a key role in endothelial cell (EC) remodeling. However, in contrast to global remodeling to these mechanical stimuli, little is known of how local mechanical forces are transmitted through cells to induce cell remodeling leading to alteration in cell functions. In this study, we demonstrated that EC remodeling can be exerted by local tension generated in a neighboring EC. In this technique, a glass microneedle was used to apply local stretch in an EC in confluent monolayer and the resulting tension is transmitted to a neighboring EC across intercellular junctions. Local stretch induced reorientation and elongation of ECs parallel to the direction of stretch associated with reorganization of stress fibers. In addition, recruitment of Src homology 2-containing tyrosine phosphatase-2, binding to intercellular adhesion molecules platelet-endothelial cellular adhesion molecules-1, was selectively observed at the force-transmitted intercellular junctions after application of local stretch. These findings suggest that intercellular junctions can not only transmit but also sense local forces, and are potentially involved in EC mechanotransduction pathways.     

Dynamic Measurements of Impulses Generated by the Separation of Adhered Bodies under Near-Zero Gravity Conditions

The present paper is aimed at investigating the dynamics of release of objects in free-falling conditions, which constitutes a typical phase of some space applications. In the presence of surface interaction forces, a quick separation of the released body from the constraining one will result in a momentum transfer, provided that the inertial forces exceed the maximum attractive force. The release conditions as well as the related parameters affecting the momentum acquired by the released body through the adhesion rupture play a fundamental role. An experimental technique aimed at measuring the momentum transfer has been developed. The basic concept of the measuring apparatus is to suspend both bodies from two pendulums. A position sensor detects the weakly damped oscillation of one object due to the momentum transferred upon pulling the other one away. Particular attention has been placed on the capability to accurately reproduce the stress status on the adhesive contact patch between the two bodies, on the noise sources affecting the measurement, and on the performances of a noise optimal-filtering technique. This paper presents measurements of momentum transfer between adhered surfaces upon quick separation.     

Polymerization of Langmuir–Blodgett films of diacetylenes

Monolayer and multilayer assemblies of Langmuir–Blodgett films of 10–12 pentacosadyinoic acid (12–8 diacetylene) were deposited on flat gold substrates. Micrometre-size features were patterned by polymerization of the films by using standard electron beam lithography. Polymerized areas on a monolayer and bilayer, as well as multilayer films, were examined by scanning electron microscopy, atomic force microscopy and resonant Raman spectroscopy. It was established that polymerized areas on a monolayer and bilayer LB film adhere onto the gold substrate after development. The exposure curve, sensitivity, contrast and resolution of the polymer have been determined by using atomic force microscopy and correlated with the deposition conditions and molecular parameters. Stresses induced in the organic film during polymerization lead to an in-plane buckling of the micrometre-size polymer structure. A simple self-consistent theory was developed to predict critical strain and critical length of buckling. The observed effect of buckling of polymers might open an avenue for a wide range of important practical applications in the area of nanomechanical engineering.     

The DLVO theory in microbial adhesion

Adhesion of microorganisms to various interfaces has been explained by the classical Derjaguin–Landau–Verwey–Overbeek (DLVO) theory of colloid stability. The theory has been used as a qualitative model, but also in a quantitative way to calculate adhesion free energy changes involved in microbial adhesion. In this paper some important investigations will be review that show how the DLVO theory is used in microbiology, mainly for bacteria. Other models have also been developed in order to predict adhesion, such as the thermodynamic approach and later the extended DLVO theory. These will be discussed in relation to the ‘classical’ DLVO theory. The theories assume that microbial cells behave as inert particles. The implications that follow from the fact that they are biologically active and have heterogeneous cell surfaces will also be exemplified and discussed.     

Blocking and ripening of colloids in porous media and their implications for bacterial transport

A model accounting for the dynamics of colloid deposition in porous media was developed and applied to systems containing similarly charged particles and collectors. Colloid breakthrough and intracolumn retention data confirmed that blocking reduced overall colloidal adhesion to soil. The surface coverage at which blocking occurred varied for the type of colloid, as shown by changes in the clean-bed collision efficiency, _0, and the excluded area parameter, β. Excluded area parameters were relatively high due to unfavorable interactions between particles and collectors, and ranged from 11.5 for one bacterium (Pseudomonas putida KT2442) to 13.7 and 24.1 for carboxylated latex microspheres with differing degrees of charged groups on their surfaces. Differences in β values for the three colloids were correlated with electrophoretic mobility, with the most negatively charged colloid (carboxylated latex; CL microspheres) having the highest β. No correlation between hydrophobicity and ₀ or β was found. Besides using colloidal particles capable of blocking, the addition of chemical additives to the soil has been suggested as a means for reducing attachment of colloids to porous media. Dextran addition caused an order-of-magnitude reduction in the overall (for carboxylated-modified latex; CMLs). This reduction was not attributed to blocking, but to the sorption of dextran to the soil which lowered ₀. The filtration-based numerical model used to fit the ₀ and β parameters was used to demonstrate that blocking could result in significantly enhanced bacterial transport in field situations.     

Effect of wetting and drying on soil physical properties

Agricultural soils are subject to seasonal wetting and drying cycles. Effect of drying stress, as influenced by one cycle of wetting and drying, on physical properties of a clay–loam soil was investigated in the laboratory. The physical properties studied were soil bulk density, cone penetration resistance, shear strength, adhesion and aggregate size and stability. Three drying stress treatments were made by wetting air-dried soil of initial moisture content of 12% (on dry weight basis) to three different higher moisture contents, namely 27, 33 and 40%, and then drying each of them back to their original moisture content of 12%. Thus, the soil was subjected to three different degrees of drying stress. The results showed that the soil strength indicated by cone penetration resistance and cohesion, and soil aggregate size, increased with the degree of drying stress. However, the soil bulk density did not change significantly with the drying stress.     

Design and mechanism of agglomeration of aspirin crystals in pure solvents

Agglomeration with improved flowability for platy crystals is desirable in pharmaceutical downstream processing. The formation of agglomerates in pure solvents without the aid of bridging liquids is a convenient and low-cost method compared with complex spherical crystallization. In this work, the adhesion free energies between aspirin crystals in six solvents were calculated using Lifshitz-van der Waals acid-base theory to screen suitable solvents for agglomeration. The maximum stirring rate for agglomeration was determined by adhesion forces and dispersion forces. Then the agglomerates of plate-shaped aspirin were successfully prepared in acetone, methanol, ethanol, 2-propanol, and ethylene glycol without additives by simple cooling crystallization. The interactions between solvent and crystal surfaces were also used to explain the outcomes. A feasible mechanism for the agglomeration process of platy crystals was elucidated, involving the adhesion of dominant crystal facets at the beginning. The effect of stirring rate, cooling rate, and initial supersaturation on agglomeration degree and particle size of aspirin agglomerates were studied. The obtained aspirin agglomerates under the optimal conditions exhibited a uniform particle size distribution, a high agglomeration degree, and superior flowability.