Assembly of Cu nanoparticles in a polyacrylamide grafted poly(vinyl alcohol) copolymer matrix and vapor-induced response

A vapor-sensitive electroconductive film was designed and assembled by inserting Cu²⁺ particles into a polyacrylamide grafted poly(vinyl alcohol) (PAM-g-PVA) in virtue of a complexation between Cu²⁺ and PVA even PAM, as well as the establishment of inter- and intramolecular attractions between polymer matrices, which were in turn reduced into Cu nanoparticles by sodium hypophosphite as a reducing agent. The PAM-g-PVA graft copolymer was prepared via a simple free radical polymerization reaction initiated by a redox reaction. The resistance responsiveness of the film samples to various organic vapor surroundings was investigated. The responsive magnitude, response time and recovery properties depend on the molecular weight of the graft polymer or the PAM chain length and initial resistances of the film samples or Cu particle contents upon exposed to ether and petroleum ether vapor, etc. The structure and morphologies of the PAM-g-PVA/Cu were characterized by a Fourier transform infrared spectroscope and a transmission electron microscope. The response mechanism of the PAM-g-PVA/Cu films to solvent vapors was accounted for by a swelling theory and an interaction between solvent vapor molecules and nanocomposites as well as the type and strength of interaction that each solvent vapor exhibits on the material.     

Tribological characteristics of novel branched perfluoropolyether lubricant films in hard disk drives

In this study, the basic tribological characteristics of novel branched perfluoropolyether (PFPE) lubricant films such as TA-30 and QA-40 were examined. Their surface free energy characteristics and adhesive and friction forces were investigated using an atomic force microscope. The interactions between the lubricant molecules and the water molecules were also examined by monitoring the changes in the contact angle of distilled water on the test lubricant films. The interactive forces such as the adhesive and friction forces of a film that is approximately one monolayer thick were found to be strongly dependent on the conformation of the lubricant molecules on diamond-like carbon thin films. In addition, the TA-30 and QA-40 lubricant molecules appeared to interact with the water molecules more actively than conventional Ztetraol2000 molecules. These results afforded fundamental insight into the tribological performance of novel branched PFPE lubricants in the head-disk interface.     

Comparison of conductometric humidity-sensing polymers

Films of differently modified PVA (polyvinyl alcohol), TA (phthalocyaninosilicon) and Nafion in different ionic forms (H⁺, Li⁺, and Na⁺) have been prepared by using casting methods. Impedance changes of the films with relative humidity are examined. The results demonstrate that the content and hydrophilicity of the hydrophilic group in PVA, ionization of TA, and the cation in Nafion have significant effects on sensing properties of the films.     

Hydrophilicity modification of poly(methyl methacrylate) by excimer laser ablation and irradiation

Because of the micromachining characteristic of excimer laser ablation, the microchannels ablated with this technique on poly(methyl methacrylate) (PMMA) substrate have definite surface roughness. Utilizing this characteristic, the hydrophilicity of PMMA microchannels could be directly modified during fabrication process both by the mechanism of photochemical ablation and the effect of surface roughness. The contact angle is inversely proportional to the surface roughness under ablation with same fluence and could be reduced to 25° by choosing ablation parameters reasonably (7.38 J/cm², 20 Hz, 10 mm/min). Excimer laser irradiation of PMMA substrates for different irradiation times at fluence below the ablation threshold also results in the surfaces becoming more hydrophilic without any marked change in the surface topography. The contact angle decreases with the increase of irradiation times and finally reaches the saturated status after irradiation for 2,500 times. Under same irradiation times, higher fluence led to PMMA substrates more hydrophilic.     

Spin coating of hydrophilic polymeric films for enhanced centrifugal flow control by serial siphoning

In this paper, we implement rotational flow control on a polymeric microfluidic “lab-on-a-disc” platform by combining serial siphoning and capillary valving for sequential release of a set of on-board stored liquid reagents into a common (assay) channel. The functionality of this integrated, multi-step, multi-reagent centrifugal assay platform critically depends on the capability to establish very reproducible, capillary-driven priming of the innately only weakly hydrophilic siphon microchannels made from common poly(methyl methacrylate) (PMMA) substrates. Due to the relatively high contact angle of the native PMMA substrate, it was practically impossible to ensure sequential release of on-board stored reagents using the capillary-driven serial siphon valves. In this work, we demonstrate that spin-coated hydrophilic films of poly(vinyl alcohol) (PVA) and (hydroxypropyl)methyl cellulose (HPMC) provide stable contact angles on PMMA substrates for more than 60 days. The deposited films were characterized using contact angle measurements, surface energy calculations and X-ray photoelectron spectroscopy spectra. The PVA and HPMC films reduced the water contact angle of the PMMA substrate from 68° to 22° and 27° while increasing their surface energies from 47 to 62 and 57 mN m^?1, respectively. On the centrifugal microfluidic platform, the films were validated to enable the effective and reproducible priming of the serial siphon microchannels at low rotational frequencies while ensuring that the in-line capillary valves are not opened until their respective burst frequencies are passed. Furthermore, the biocompatibility of the proposed surface modification method was examined, and the platform was used to run a sandwich immunoassay for the detection of human immunoglobulin G, and its performance was proven to be comparable to dynamic coating using surfactants.     

HZSM-5中水吸附行为的实验与分子模拟

利用智能重量分析仪(IGA—003,HIDEN)测定了298K条件下水蒸汽在HZSM-5型分子筛中的吸附等温线。并采用巨正则系综Monte Carlo模拟方法(GCMC)研究了水在HZSM—5型分子筛中的吸附等温线,计算结果与实验结果吻合较好。分子模拟计算得到的水分子的微观吸附性质表明水分子吸附在氢离子和铝原子的周围,这是因为水分子是极性分子,分子筛上的氢在库仑力的作用下会与水分子发生强的相互作用,并导致分子筛骨架上的硅铝比与水分子的吸附量之间存在线性关系。计算结果还表明水的吸附热与H_2O/Al之间存在线性关系。     

Zone electrophoresis of proteins in poly(dimethylsiloxane) (PDMS) microchip coated with physically adsorbed amphiphilic phospholipid polymer

The zone electrophoresis of protein in poly(dimethylsiloxane) (PDMS) microchip coated with the physically adsorbed amphiphilic phospholipid polymer (PMMSi) was investigated. PMMSi was composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) and 3-(methacryloyloxy) propyltris (trimethylsiloxy) silane (MPTSSi) units in a random fashion. The membrane of PMMSi can be formed on the PDMS surface by a simple and quick dip-coating method. The membrane showed high hydrophilicity and good stability in water, as determined by contact angle measurement, fourier-transformed infrared absorption by attenuated total reflection (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS) analysis. High suppression of protein adsorption to the PDMS surface and reduction in electroosmotic flow (EOF) were achieved by PMMSi coating due to an increase of hydrophilicity, and a decrease of the ζ-potential on the surface of PDMS. For zone electrophoresis, the PMMSi30 containing 30 % hydrophilic MPC was the most suitable molecular design in terms of the stability of the coated membrane on PDMS surface. The average value of EOF mobility of PDMS microchip coated with PMMSi30 was 1.4 × 10^?4 cm² V^?1 s^?1, and the RSD was 4.1 %. Zone electrophoresis of uranine was further demonstrated with high repeatability and reproducibility. Separation of two FITC-labeled proteins (BSA and insulin) was performed with high efficiency and resolution compared with non-treated PDMS microchip.     

A modified microfluidic chip for fabrication of paclitaxel-loaded poly(l-lactic acid) microspheres

In this article, we present a simple PDMS surface modification method based on poly(vinyl alcohol)/glycerol (PVA/Gly) solution immersion, self-assembled absorption, and heat treatment. The results of contact angle and ATR-FTIR demonstrate the superhydrophilic surface in modified PDMS. It can allow for the stable production of monodisperse droplet in a highly reproducible manner. In addition, we demonstrate the fabrication of monodisperse paclitaxel (PTX) loaded poly(l-lactic acid) (PLLA) microspheres on this kind of modification chip with solvent evaporation. The PLLA microspheres can be adjusted to a range of different sizes depending on the system flow rate. Determination of microsphere size is carried out by optical microscopy and image analysis to reveal less than 4% variation in microsphere size. Compared with the results of published papers, the presented data demonstrate that PTX-loaded PLLA microspheres show good physical properties (spherical and discrete), high-drug loading, encapsulation efficiency, a small initial burst, and sustained-release behavior due to outstanding monodispersity. With the characteristic to prepare high-quality, monodisperse, biodegradable microspheres, the versatile and simple microfluidic method facilitates the development of more reliable and reproducible drug delivery systems, which have great potential to benefit pharmaceutical and biological applications.     

Nanoconfinement induced anomalous water diffusion inside carbon nanotubes

The diffusion mechanism and coefficient of water confined in carbon nanotubes (CNTs) of diameter ranging from 8 to 54 ? are studied by molecular dynamics simulations. It is found that the motions of water molecules inside the CNTs of diameter smaller than 12.2 ? follow a two-stage diffusion mechanism. Initially, the water diffusion exhibits a long-time super- or sub-diffusion mechanism, and thereafter it transits to the single-file type inside the (6, 6) CNT and shifts to the Fickian type inside the larger CNTs. As for the CNTs of diameter larger than 12.2 ?, the diffusion of the confined water occurs through the Fickian mechanism, which is identical to that of the bulk water. The simulation results further reveal that the diffusion coefficient of the confined water is non-monotonically dependent on the diameter, which can be ascribed to the double-edged effect of CNTs, i.e., the surface effect and the size effect.     

Preparation of chemical vapor sensing materials from composites of esterified poly(vinyl alcohol) and carbon black

Poly(vinyl alcohol) was modified by esterification to prepare poly(vinyl alcohol) copolymers. The degree of esterification on poly(vinyl alcohol) was elucidated by FTIR, ¹H NMR, and elemental analysis. The obtained products were poly(vinyl benzoate)-co-poly(vinyl alcohol) (B-PVA) and poly(vinyl p-toluoate)-co-poly(vinyl alcohol) (P-PVA). The chemical vapor sensors were fabricated by the mixtures of polymer and carbon black in dimethyl sulfoxide and their subsequent preparation as thin films onto the interdigited electrodes by the application of the spin-coating technique. The chemical vapor sensing properties of the sensors were examined with various solvents, such as hexane, toluene, methanol, ethanol, isopropanol, tetrahydrofuran, ethyl acetate, acetonitrile, dimethyl sulfoxide, and water. The experimental results indicated that modifying the chemical structure of PVA results in the decreased polarity of the obtained products. The composites of modified PVA consequently responded well to low polarity solvents, such as THF or ethyl acetate.     

Water diffusion in polymer nano-films measured with microcantilevers

We present a method to measure the absorption of water molecules from the liquid and the vapour phase into polymer nano-films and the diffusion inside these films. Film thickness can be down to 45 nm. To demonstrate the possibilities of this method we use polymer films that are deposited on the upper side of a silicon cantilever by plasma polymerization of norbornene. When a microdrop of water is deposited onto the initially straight cantilever, the drop causes the cantilever to bend while it evaporates. Evaporation of such small water drops usually takes less than a second. An upwards bending is due to capillary forces and a downwards bending is due to the diffusion of water into the polymer film – and the consequent volume expansion (swelling) of the film. The magnitude of the capillary forces and the extent of swelling continuously change during drop evaporation. When drop evaporation is over the cantilever returns to its initial straight position. We simulate the time dependent bending with a numerical model that qualitatively agrees with the experiment. From the time dependence of cantilever bending we are able to determine the diffusion coefficient of water in the thin polymer film.     

Gas sensing properties of the composite Langmuir–Blodgett films: effects of the film thickness and the Cd addition into the subphase

It was discovered in the previous studies that the kinetic response of NO sensors based on copper tetra-tert-butyl phthalocyanine (CuTTBPc) Langmuir–Blodgett films (LB films) could be greatly improved if CuTTBPc mixed with arachidic acid (AA) in optimized molar ratios was used instead of the phthalocyanine derivative alone. In this paper we investigate the effects of the film thickness and the ionic content of the subphase on gas-sensitive properties of CuTTBPc:AA (1:1 molar ratio) LB films with respect to NO. It was shown that both the sensitivity and the kinetic response of the LB films were influenced by the Cd²⁺ addition into the subphase. These distinctions, being rather small for the thinnest films, became much more pronounced for thicker ones. If “pure” water was used as a subphase, experimental data could be explained mainly by the gas diffusion into the film bulk whereas the surface adsorption was a predominant process in the case of the Cd²⁺-containing subphase. Obtained results are discussed as regards the sensor performance optimization.     

Diffusion of water molecules in crystalline beta-cyclodextrin hydrates

To understand the rapid diffusion mechanism of water molecules in the crystal lattice of hydrated beta-cyclodextrin (beta-CD), molecular dynamics (MD) simulations of crystalline beta-CD were performed at five different relative humidities corresponding to hydration states ranging from beta-CD-9.4H2O to beta-CD-12.3H2O, and in aqueous solution. The trajectories for the crystalline beta-CD hydrates had lengths of 4 ns each, whereas the simulation in aqueous solution extended to 2 ns. Transport of water molecules in the crystal was characterized in terms of a spatially varying diffusion constant and the main direction of diffusion, which were evaluated using newly developed algorithms. The main diffusion pathway winds through the cavities of adjacent doughnut shaped beta-CD molecules and is slightly slanted with respect to the crystallographic b-axis. Water molecules outside the beta-CD cavities have access to the main diffusion pathway. The diffusion constant for transport of water molecules along the main pathway calculated from the MD simulation data adopts 1/30 of the value in bulk water at room temperature. This is in agreement with estimates that can be made from experimental data on the adjustment of a beta-CD crystal to changes in relative humidity.     

低温等离子体辅助聚乳酸表面接枝乳酸链球菌素 及抗菌性

该文主要通过低温等离子体处理聚乳酸薄膜,并研究了不同处理时间(0、15 s、30 s、45 s 和 60 s)后薄膜的表面形貌及亲水性。在此基础上,将低温等离子体处理后的聚乳酸薄膜浸泡到乳酸链球 菌素溶液中,对其抗菌性能进行测定。通过调节等离子体处理时间,可以明显改善聚乳酸薄膜的表面 亲水性及粗糙度。结果表明,随着处理时间的增加,聚乳酸薄膜表面粗糙度先增加后减小,接触角先 降低后增加。经过 60 s 低温等离子体处理的聚乳酸薄膜,浸泡乳酸链球菌素溶液进行接枝,可有效降 低单核增生李斯特菌的菌落总数。因此,低温等离子体处理聚乳酸薄膜,为其在食品抗菌包装领域提 供了一个非常好的思路。     

Functionalized poly (vinyl alcohol) polymer as chemodosimeter material for the colorimetric sensing of cyanide in pure water

New poly (vinyl alcohol) (PVA) derivative containing pendant chemoselective functionality is prepared for the cyanide detection in pure water. Particularly, incorporation of the chemodosimeter 4 on PVA is performed by direct coupling of the hydroxyl group of the dye 4 and PVA hydroxyl groups via ethereal linkage using di-bromoalkane as a cross-linking agent. The chemosensory capacity of the polymeric material for the colorimetric sensing of cyanide in water is based on the reactivity of this anion toward the chemodosimeter, and its water solubility is given by PVA moiety. The chemodosimeter is developed on the basis of the trifluoroacetyl group as electrophile receptor of the cyanide anions. The final water soluble functionalized polymer presents a sensible selectivity toward cyanide anions in pure water.     

Molecular dynamics simulations of diffusion of submonolayer polar liquid lubricant films on solid surfaces

A fundamental understanding of the diffusion phenomena of submonolayer polar liquid films is important for achieving reliable lubrication between moving mechanical parts separated by a nanometer-sized gap. To acquire this understanding, we conducted molecular dynamics (MD) simulations of diffusion phenomena of submonolayer polar perfluoropolyether (PFPE) Zdol films on solid surfaces. To improve the accuracy of these simulations, we developed an all-atom model that includes hydrogen-bond potential and refined atomic charges for Zdol molecules and tested it through MD simulations of spreading of step-shaped submonolayer PFPE films. Our MD simulations reproduced the experimentally observed effects of polar end groups on the diffusion speed and molecular conformation of Zdol. We then conducted MD simulations of self-diffusion of submonolayer Zdol films; these simulations demonstrated that as the thickness of the submonolayer Zdol films decreases, molecular conformation becomes flatter and the self-diffusion coefficient decreases. These changes in molecular conformation partially explain our experimental finding that the spreading of step-shaped submonolayer polar PFPE films slows down with decreasing initial thickness.     

Dichlorodimethylsilane as an anti-stiction monolayer for MEMS: acomparison to the octadecyltrichlorosilane self-assembled monolayer

This paper presents a quantitative comparison of the dichlorodimethylsilane (DDMS) monolayer to the octade-cyltrichlorosilane (OTS) self-assembled monolayer (SAM) with respect to the film properties and their effectiveness as anti-stiction coatings for micromechanical structures. Both coatings have been evaluated in several ways, including atomic force microscopy (AFM), contact angle analysis (CAA), work of adhesion by cantilever beam array (CBA) technique and coefficient of static friction using a sidewall testing device. While water and hexadecane contact angles are comparable, the DDMS coated microstructures exhibit higher adhesion than OTS coated ones. Furthermore, coefficient of static friction data indicate that the DDMS films are not as effective at lubrication as the OTS SAMs are, although both exhibit much improvement over chemical oxide. However, AFM data show that the samples which receive DDMS treatment accumulate fewer particles during processing than those which receive the OTS SAM treatment. The thermal stability of the DDMS film in air far exceeds the OTS SAM, as the DDMS remains very hydrophobic to temperatures upwards of 400°C     

Pressure-driven water flow through hydrophilic alumina nanomembranes

We present an experimental study that focuses on pressure-driven flow of distilled water through γ alumina membranes with 5, 10 and 20 nm pore radii. The nanopore geometry, pore size and porosity are characterized using scanning electron microscopy images taken pre- and post-flow experiments. Comparisons of these images have shown reduction in the pore size, which is attributed to precipitation of hydroxyl groups on alumina surfaces. Measured flowrates compared with the Hagen–Poiseuille flow relations consistently predict 2.2 nm reductions in the pore size for three different membranes. This behavior can be explained by the formation of a thick stick layer of water molecules over hydroxylated alumina surfaces, evidenced by water droplet contact angle measurements that exhibit increased hydrophilicity of alumina surfaces. Other possible effects of the mismatch between theory and experiments such as unaccounted pressure losses in the system or the streaming potential effects were also considered, but shown to be negligible for current experimental conditions.     

碳黑/聚乙烯醇电纺复合纤维的制备与气敏特性研究

通过碳黑(CB)/聚乙烯醇(PVA)混合溶液的电纺,制备了掺纳米CB的PVA复合纤维,用扫描电镜(SEM)观察了它的形貌。CB/PVA复合纳米纤维的形貌取决于混合物中CB的含量。随CB含量的增加,CB颗粒在纤维中的分布逐渐变得均匀;最佳CB/PVA的质量比为3∶10;继续增加CB含量,CB颗粒聚合成团析出,杂乱分布于PVA纤维中。乙醇蒸气测试表明:质量比为3∶10的CB/PVA纤维具有灵敏度高、响应恢复快等特点。     

Molecular dynamics prediction of nanofluidic contact angle offset by an AFM

This paper investigates the nano-fluidic contact angle measurement by performing molecular dynamics simulations. The contact angle between a nano-water droplet and a platinum surface is important for the design of the porous catalyst layer in low-temperature fuel cells. The measurement can generally be conducted by an atomic force microscope (AFM). However, the interaction force between the water droplet and the probe tip of the microscope may influence the measurement results. This paper employs the molecular dynamics technique to investigate the offset of the contact angle measurement. Calculations are in two sets, one simulated the water molecules clustering on the platinum surface, and the other involved the AFM measurement of the contact angle. The former case presents the original contact angle between the nano-scale water droplet and the platinum surface; the offset of the contact angle measurement due to intrusion of the AFM probe is predictable from the latter case. For engineering purposes, we present a correlation between the offset angle and the AFM measurement locations.