Crystalline structure at surfaces of uniaxially drawn polypropene films

A series of uniaxially drawn films of isotactic polypropene and ethene-propene random copolymer was prepared. The differences in the crystal orientation between the bulk and the surface layer were examined using wide-angle X-ray diffraction and grazing incidence X-ray diffraction techniques. It was found that the c-axis orientation of the surface layer is almost identical with that of the bulk. The magnitude in the b-axis of the polypropene films decreased with increasing draw ratio. The changes in the b-axis at the bulk were found to be greater than those at the surface layer.     

Effects of surface modification by Ar+ irradiation on wettability of surfaces of poly(ethylene terephthalate) films

Surfaces of poly(ethylene terephthalate); PET, films were irradiated with Ar⁺ at 1 keV using various ion doses (ID) from 10¹⁴ to 10¹⁷ ions/cm² (isc) with and without an O₂ environment. The wettability of the modified surfaces of PET was determined by measuring the contact angle between water droplets and the modified surfaces. The modified surfaces were also characterized by AFM (atomic force microscopy) and XPS (X-ray photoelectron spectroscopy) for changes in the surface morphology, and the chemical composition and molecular structure, respectively. The contact angle decreased from 70° for unmodified surfaces to 45° for modified surface with ID = 10¹⁴ isc without O₂ and remained relatively constant with higher ID. The contact angle, however, reached a minimum value of 8° for modified surfaces with ID = 10¹⁶ isc with O₂. The improved wettability may be due to a combination of the formation of hydrophilic groups, chemical and molecular structural changes, physical structural or morphological changes, and increased roughness of the surface. The wettability of the modified surfaces also depended on the time of exposure to air. The wettability worsened with exposure time to air, but was revived by immersing the films into water. Possible mechanisms for the change of the wettability of the modified surfaces are given.     

Light-induced wettability changes on polymer surfaces

Altering the surface wettability by external stimulation has received great attention recently. While different stimuli, such as temperature, pH, etc. can be applied for this purpose, light combines several advantages. It is a contact-free stimulation, which can be applied locally, thereby allowing a versatile patterning. This review article summarizes recent developments in the area of polymers that allow a light-induced change in surface wettability. For this purpose, different photochromic dyes have been incorporated into polymers, which enable a photo-isomerization upon light irradiation resulting in a change in polarity. Several examples based on azobenzene or spiropyran will be discussed, but also some more exotic examples, such as those based on salicylideneaniline, will be highlighted. The different approaches how to apply these photochromic dyes to various surfaces are presented and discussed. Additionally, the combination with other stimuli-responsive moieties will be explored and the paper will be concluded by mentioning the remaining challenges and by providing a future perspective.     

Factors affecting the wettability of polymer surfaces

The inconsistencies in contact angle data presented in the literature can be attributed to a number of factors. The awareness of these factors would allow novice researchers to make meaningful contact angle measurements and interpretations. In this survey the effects of surface roughness and heterogeneity, surface preparation and the presence of contaminants, the vapor environment, pressure and temperature, drop size, electrical charge, and heat transfer on the wettability of polymer surfaces were examined.     

Characterization of non-uniform wettability on flame-treated polypropylene-film surfaces

The flame treatment of polypropylene (PP) film involves the use of impinging, conical flames to oxidize the surface of the PP.Depending on treatment conditions, the PP film can be exposed to an inhomogeneous environment because of the conical shape of the flames. This environment can lead to cross-web variations, or 'lanes', in the wettability of the film. We have developed a simple method to quantify these non-uniformities using the information provided by the Wilhelmy plate technique of dynamic contact angle measurement. Both surface-averaged and spatially resolved surface-energy data can be obtained by this technique. In the case of our PP film, the spatial nonuniformities were found to be caused by variations in surface chemistry, not topography. These nonuniformities are not observed on untreated PP. Use of this method enables a quantitative evaluation of the effects of flame-treatment process variables on treatment uniformity.     

Foam slip on surfaces of intermediate or low wettability

Wall slip of foams is important in several practical contexts. If the surface is not perfectly wetted by the interstitial liquid, the foam-wall interface may exhibit a yield stress. This paper represents the first quantitative study of this phenomenon. A simple model of the interface between disorganized foam and a solid surface is presented. This model treats the interface as a network of soap film contact lines. Experimental data are presented on the tension at soap film contact lines, and the stress at the foam-solid interface, at very slow translation speeds and for several surfaces. These agree broadly with theoretical predictions up to parity of the interface yield stress with the bulk yield stress of the foam. The experimental data include the yield tension for a soap film contact line pulled in an oblique direction with respect to the contact line normal. These data are also broadly consistent with theoretical predictions.     

Modification of the wettability of polymer surfaces using nanoparticles

The effects of nanoparticles, embedded into the matrices of polymer films, on the wettabilities of the surfaces of the composite films are investigated following a two-fold procedure. First, five particles such as silica (of two sizes), tin oxide, alumina and zinc oxide ranged from 7 to 100 nm are mixed with a poly(methyl siloxane). Second, silica nanoparticles (7 nm) are embedded in five different polymers such as poly(methyl methacrylate), polystyrene and three poly (alkyl siloxane) products. Nanocomposite films are produced by adding nanoparticles in the polymer solutions which are then sprayed on silicon substrates.     

含氟丙烯酸酯共聚物涂膜表面润湿性的研究

以甲基丙烯酸甲酯(MMA)、丙烯酸丁酯(BA)、甲基丙烯酸β–羟乙酯(HEMA)、(甲基)丙烯酸高级酯(AAs)、含氟(甲基)丙烯酸酯(Fs)等单体为原料,HDI三聚体为固化剂,通过改变共聚物组成、氟碳链长、(甲基)丙烯酸高级酯烷烃链长等因素,合成了一系列的含氟丙烯酸酯共聚物。采用水、煤油和液压油接触角以及水滴滚动距离,表征了共聚物涂膜的表面润湿性,并探讨了其影响因素。结果表明,共聚物组成和结构、烷烃链长对水的接触角影响不大,而对水的滚动性能具有较大影响;氟碳链长以及氟单体的添加方式对油水接触角和水的滚动性能有较大影响;烷烃侧链的柔顺性对油的接触角影响较大,而对水几乎没有影响。     

On the injection molding of nanostructured polymer surfaces

Well‐defined nano‐topographies were prepared by electron‐beam lithography and electroplated to form nickel‐shims. The surface pattern consisted of square pillars repeated equidistantly within the plane of the surface in a perpendicular arrangement. The width and distance between the squares both ranged from 310 to 3100 nm. All the pillars were 220 nm high. The nickel‐shim was used as a surface‐template during injection molding of polycarbonate. Secondly, a nickel shim, with a surface pattern consisted of a squared sine with a period of 700 nm and amplitude of 450 nm, was mounted on, and it was in good thermal contact with the upper plate in a hot‐press. Polycarbonate/polystyrene was melted on the lower plate while the temperature of the shim was kept below the glass transition temperature. The upper plate was lowered until the shim was in contact with the melt. Experiments were carried out with a clean shim and a shim coated with a monolayer of fluorocarbonsilane. As a result of the surface coating, the amplitude of the replicated grating decreased from about 350 nm in polycarbonate and 100 nm in polystyrene to less than 10 nm. The experiments strongly suggest that the possibility to injection mold sub‐micrometer surface structures in polymers mainly relates to adhesive energy between polymer and shim. POLYM. ENG. SCI. 46:160–171, 2006. © 2005 Society of Plastics Engineers     

Altering the wettability of bitumen-treated glass surfaces with ionic surfactants

The abilities of three ionic surfactants—sodium methylnaphthalene sulfonate (SMNS), sodium dodecyl sulfate (SDS), and cetyl trimethylammonium bromide (CTAB)—to alter the wettability of bitumen-treated glass surfaces was examined. Surface wettability was characterized by contact angles, and all measurements were carried out under alkaline conditions by having sodium carbonate (Na₂CO₃) dissolved in the aqueous phase. It was found that Na₂CO₃ alone could slightly increase the hydrophilcity of bitumen-treated glass surfaces. With surfactants added to the system, it was demonstrated that SMNS and SDS (both anionic surfactants) were much more effective in enhancing the water wettability of bitumen-treated glass in comparison to CTAB (a cationic surfactant). X-ray photoelectron spectroscopy (XPS) analyses were also conducted to determine the functional groups and relative mass concentrations of various elements on the glass substrates. Based on these results, we speculate that most or all of the adsorbed hydrocarbon material could be removed from a glass substrate through synergistic effects between sodium carbonate, which provides the alkaline condition, and anionic surfactants, which likely interacted with adsorbed cationic materials. This resulted in dramatic alteration in the wettability of bitumen-treated glass surfaces—from oil-wet to water-wet.     

Fabrication of superamphiphobic-textured surfaces with reversibly switchable wettability

To realize switchable wettability for water and oils, we firstly design a facile approach to achieve superamphiphobic-textured surfaces that display the apparent contact angles greater than 150° and the sliding angles smaller than 10° for various liquids, such as water and hexadecane. Then, plasma treatment and surface fluorination were performed on the superamphiphobic surface. The tunability of the chemical composition, along with hierarchical rough surface structure, gave rise to reversibly switchable wettability between superamphiphobicity and superamphiphilicity. The wettability of the textured surface was demonstrated by visible experimental results and measurements. The reason of switchable wettability can be confirmed by X-ray photoelectron spectroscopy analysis. These results give a useful attempt in simultaneously and reversibly switching wettability for water and oils, which may have potential application in functional superamphiphobic materials.     

磁场作用下不同润湿性表面结霜实验研究

研究了在冷面温度Tw=-10℃和-30℃,环境相对湿度RH=60%和80%,3种润湿性表面在不同磁场强度下的结霜规律。通过可视化观测和图像二值化处理计算,分析了磁场强度和表面接触角对霜晶形态、水珠粒径、结晶时间、液滴和霜晶覆盖率、霜层厚度和密度的影响。结果表明:磁场作用下,疏水性表面水珠粒径减小40%左右,结晶时间延长500 s以上,凝结水珠分布更加稀疏;结霜厚度和密度随着磁场强度和接触角的增大而减小;随着冷面温度的降低和相对湿度的增大,表面特性和外加磁场对结霜过程的影响降低。     

Experimental study of frosting on different wettability surfaces under magnetic field

The frosting laws of three kinds of wettable surfaces under different magnetic field strengths were studied under cold surface temperature T_w=-10℃ and -30℃, environmental relative humidity RH=60% and 80%. Through visual observation method,image binarization is processed and calculated,the effect of frost morphology,water droplets diameter,water droplets crystallization time,water droplets coverage,frost crystal coverage,frost layer thickness and frost density under the different magnetic field intensity and surface contact angle are well explained. The results showed that adding magnetic field in combination with hydrophobic surface,the diameter of water droplets decreases by about 40%, and the crystallization time is prolonged by more than 500 s,the distribution of condensate droplets is more sparse. Frost thickness and frost density decrease as the increase of magnetic field strength and surface contact angle,providing possibility of restrain the frosting effectively. As the temperature of the cold surface decreases and the relative humidity increases, the influence of the surface properties and the external magnetic field on the frosting process decreases.     

Effects of surface flaws on the wettability of solids

Wetting hysteresis, or the variability of contact angle, is recognized to be caused by several phenomena. In particular, we consider it to be due to heterogeneity of the solid surface in contact with the liquid. Results describing the deformation of an initially straight triple line in the proximity of an isolated, small, energetic inhomogeneity are summarized. The theory is extended to describe the behaviour of a wetting front near a circular, high-energy (i.e. corresponding to zero intrinsic contact angle) flaw of dimensions comparable to those of the triple line distortion. A simple model is proposed to explain the breakaway of the isthmus of liquid connecting the flaw to the bulk liquid. Separation time is found to be proportional to ^-5, where 0 is the intrinsic contact angle of the solid/ liquid system. The behaviour of a triple line on a solid possessing a randomly distributed population of identical, small, circular flaws is considered. Contact angle hysteresis can thus be explained, as can the noise often observed in a (dynamic) Wilhelmy plate experiment. A simple statistical model is proposed in which random force fluctuations related to a moving triple line are shown to correspond to the Poisson process of probability theory.     

Proliferation rate of fibroblast cells on polyethylene surfaces with wettability gradient

Surface wettability on anchorage‐dependent cells has an important role in cell growth rate. In our previous studies, we prepared a wettability gradient on polyethylene (PE) surfaces using corona discharge treatment from a knife‐type electrode whose power increased gradually along the sample length. The PE surfaces were oxidized gradually with increasing power and characterized by Fourier transform infrared spectroscopy, contact angle goniometry, and electron spectroscopy for chemical analysis. The purpose of this study is to determine the rate of proliferation on polymer surfaces with different wettability. The behavior of cell growth for NIH/3T3 fibroblast cells attached on the polymer surfaces with different hydrophilicity was investigated using wettability gradient PE surfaces prepared by corona discharge treatment. They were investigated for the number of grown cells from 24 to 60 h in terms of surface wettability. From the slope of cell number on PE gradient surface versus culture time, the proliferation rates (number of cell/cm² · h) were calculated. It was observed that the proliferation rate was increased more on positions with moderate hydrophilicity of the wettability gradient surface than on the more hydrophobic or hydrophilic positions, i.e., 1111 (number of cell/cm² · h) of 57° of water contact angle at the 2.5‐cm position (P < 0.05). This result seems closely related to the serum protein adsorption on the surface: the serum proteins were also adsorbed more on the moderately hydrophilic surface. In conclusion, surface wettability plays an important role in cell adhesion, spreading, and proliferation on the polymer surfaces. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 599–606, 2004     

微小通道内不同润湿性表面流动冷凝传热

利用丝网烧结和聚四氟乙烯溶液（Teflon）浸渍法,在铜表面上制备了亲疏水匹配的结构,即在疏水四氟涂层上有阵列排布的椭圆亲水点,仅有四氟涂层的全疏水表面和不作修饰的全亲水铜表面作为对照,考察了以这三种表面为底部换热区域的矩形微小通道（水力直径1.5 mm）的换热特性和流动特性。实验的通道内蒸汽质量流速为10～60 kg·m^-2·s^-1,干度为0.3～1,亲疏水匹配表面与亲水表面相比,蒸汽冷凝传热系数（HTC）最高增加了454.6%,与全疏水表面相比,传热系数最高增加了107.3%,利用高速相机拍摄可视化照片,观察了通道内气液两相,尤其是表面液滴成核、聚并、冲刷的周期运动过程,解释了亲疏水匹配表面强化传热的机理。     

Control over wettability of textured surfaces by electrospray deposition

Microtextured surfaces were prepared by electrospray deposition (ESD) from hydrophilic and hydrophobic acrylic resin solutions. The surface morphologies and topologies were characterized using scanning electron microscopy and laser profile microscopy, respectively. Wetting behaviors on the surfaces were characterized by contact angle and sliding angle measurements. The contact angle of the water droplet on the hydrophilic resin‐coated surfaces decreased with an increase in the surface roughness. On the other hand, the contact angle on the hydrophobic resin‐coated surfaces increased with an increase in the surface roughness. In addition, a patterned surface composed of aligned fibers by ESD showed anisotropy of both wetting and sliding behaviors. These results indicate that ESD is a useful method for designing a textured surfaces and controlling the surface wettability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3811–3817, 2007     

Studies on the controlled morphology and wettability of polystyrene surfaces by electrospinning or electrospraying

Polystyrene (PS) surfaces with various morphologies have been produced by electrospinning or electrospraying, such as beads with different sizes and shapes, bead-on-string structures with different aspect ratios of the beads and fibers with different diameters and shapes. Both the solution properties and the electrospinning conditions affected the PS surface morphology obtained. The results of water contact angle (CA) measurement indicated that the surface morphology could affect the wettability distinctively. It was found that CA values of PS surfaces comprised merely fibers were in the range of 140°-150°. The CA values of PS surfaces comprised bead-on-string structures were usually about 150°. However, the CA values of PS surfaces consisted of particles could reach up to 160°, which shows a superhydrophobic property. A bilayer fibers-on-beads surface was verified to be stable and superhydrophobic.