Amphoteric surface hydrogels derived from hydrogen-bonded multilayers: reversible loading of dyes and macromolecules

We used hydrogen-bonded multilayers of poly(N-vinylpyrrolidone) (PVPON) and poly(methacrylic acid) (PMAA) as precursors for producing surface-bound hydrogels and studied their pH-dependent swelling and protein uptake behavior using in situ attenuated total reflection Fourier transform infrared spectroscopy and in situ ellipsometry. The hydrogels were produced by selective chemical cross-linking between PMAA units using carbodiimide chemistry and ethylenediamine (EDA) as a cross-linking reagent, followed by complete removal of PVPON from the film obtained by exposing the film to pH 7.5. As shown by in situ ellipsometry, hydrogels exhibit distinctive polyampholytic swelling as a function of pH, with minimum swelling at pH 4.2-5.7, and increased film thickness at both lower and higher pH values. Film swelling at lower pH values occurs as a result of the presence of amino groups within the hydrogels, which originate from the one-end attachment of the EDA cross-linker to PMAA chains. The pH-switching of hydrogel swelling was fast and reversible. The degree of hydrogel swelling could be also controlled by varying the time allowed for cross-linking. The produced hydrogels were able to absorb large amounts of dyes and proteins of opposite charge reversibly, in response to pH variations. Finally, we demonstrate that proteins included within the hydrogel can easily be replaced with linear polycations. These surface hydrogels hold promise for bioseparation and controlled delivery applications.     

Ultrasonic synthesis of stable, functional lysozyme microbubbles

High-intensity ultrasound induces emulsification and cross-linking of protein molecules in aqueous medium. The stability and the functionality of the resultant protein-coated microbubbles are crucial in many of their applications. For example, the stability of drug-loaded microbubbles should be sufficiently long enough, in vivo, so that they can be ruptured only at specific sites for release of the drugs. In this study, we report the synthesis of stable and functional microbubbles, coated with chemically reduced lysozyme, using high-intensity ultrasound in aqueous solution. In the absence of chemical reduction, stable microbubbles were not produced with native lysozyme, indicating the importance of free -SH functional groups for protein cross-linking. The degree of cross-linking between lysozyme molecules was controlled by manipulating both the extent of chemical reduction of the intramolecular disulfide bonds and sonication time. The lysozyme-coated microbubbles are stable for several months and retain the enzymatic (antimicrobial) activity of lysozyme. The layer-by-layer (LbL) deposition of polyelectrolytes onto the protein-shell air-core template has been used as a versatile procedure to modify the surface properties of the microbubbles, indicating the possibility of adsorbing potential drugs and/or biolabels on the surface of these microbubbles for therapeutic and diagnostic applications.     

Effect of carbon foams as negative current collectors on partial-state-of-charge performance of lead acid batteries

Flooded lead acid batteries were assembled by using a pitch-based carbon foam and a punched lead sheet as the negative current collectors, respectively. Comparative galvanostatic charge–discharge experiments were performed on the batteries to evaluate the effect of the carbon foam as a negative current collector material on the performance of lead acid batteries under partial-state-of-charge operation. The results indicate that the carbon foam negative current collector can significantly improve the cyclability of lead acid batteries under partial-state-of-charge operation. This is mainly attributed to the high specific surface area and three-dimensional, interconnected carbon ligaments of the carbon foam negative current collector.     

Preparing of high-quality carbon film from polyimide films by gradient heat treatment process

A series of carbon-graphite films were prepared via the gradient heating based on polyimide films under nitrogen atmosphere. FTIR spectroscopy, X-ray diffraction, Raman spectrum were used to systemically investigate the evolutions of chemical structure, crystal structure, thermal stability, morphological microstructure and properties of the carbon-graphite films. The study shows that the segment fracture and thermal cross-linking reaction occur first during the low temperature pyrolysis process of PI films, and the thermal cross-linking reaction changes the structure of polyimide. Radicals start restructuring and the thermal condensation becomes sharp with the increase of heat treatment temperature, and the amorphous structure of film is transformed into the ordered graphite structure, at the same time the crystallinity and orientation of the films are improved. When it reaches a certain temperature, the crystal lattice is further improved, and the structure of film can be transformed into polycrystalline graphite structure. With the increase of the temperature, the carbon content of film is gradually increasing, and the surface resistivity is smaller and smaller. It is obvious that once the continuous conductive network of carbon formed, the conductivity of composite sheet films hardly changed.     

镓取代皂石的合成与交联的研究

以XRD、MAS NMR、IR和化学分析等方法研究了镓取代皂石及其羟基铝低聚物交联物。结果表明,Ga占据骨架四面体位置,影响四面体层电荷及Al柱的交联密度。交联物经焙烧后,Al柱与层形成Ga—O—Al_p键,实现了层与柱的交联,而Al_(13)基本结构不变。     

Viscoelastic properties of cross-linked polyvinyl alcohol and surface-oxidized cellulose whisker hydrogels

Reinforcement of polyvinyl alcohol (PVA) hydrogels was achieved by direct chemical cross-linking of surface modified microcrystalline cellulose (MCC) whiskers with PVA. In order to produce hydrogels, the MCC whiskers were first obtained by TEMPO-mediated oxidation of the cellulose substrate and ultrasonication followed by direct cross-linking to PVA (Mw 98,000) via forming acetal bonds and freeze–thawing. The viscoelastic properties of the produced hydrogels were clearly improved following the chemical cross-linking, featuring values for viscous and elastic moduli G′ and G″ on the order of 10 kPa, which is particularly interesting for biomedical orthopedic applications.     

Change of Surface Structure upon Foam Film Formation

The charge distribution and coverage with surfactant molecules at foam film surfaces plays an important role in determining foam film structure and stability. This work uses the concentration depth profiling technique neutral impact collision ion scattering spectroscopy to experimentally observe the charge distribution in a foam film for the first time. The charge distribution at the surface of a foam film and the surface of the corresponding bulk liquid were measured for a cationic surfactant solution and the surface excess as well as the electric potential were determined. Describing the internal pressure of foam films by using the electrochemical potential is introduced as a new concept. The foam film can be seen to have a more negative surface charge compared to the bulk liquid surface due to re‐arranging of the surfactant molecules. It is discussed how the change in surface excess and electric potential change the electrochemical potential and the stability of the foam film.     

Ultra-lightweight paper foams: processing and properties

A methodology for producing a low density cellulose-based foam has been developed by combining a surfactant with pulp, mixing at high velocity to entrain air, and then drying in a non-restrained fashion. The structure of the foam, characterized through optical microscopy and X-ray computed tomographic microscopy, consists of pulp fibres in random orientations surrounding air bubbles along with large void spaces. Through careful design of experiments, the effect of fibre type, length distribution, surfactant, and air content on the mechanical behavior and permeability of the foam material was investigated. The results indicate that foamed cellulose materials can be produced at a strength of one-half the tensile strength of a standard handsheet, but having a relative density of only one percent. No chemical additives were used to enhance the strength of these samples as the properties of the foam material are enhanced simply through variation of the process parameters. Thus, a strong cellulose-based foam, with a density as low as 10 mg/cm³, can be fabricated using standard papermaking infrastructure and hence at low cost.     

Effect of organic acid chain length on foam performance in a porous medium

We have systematically studied the effect of organic acid chain length on surface dilatational properties and foam flow performance in a porous medium. Surface dilatational properties were studied by oscillating drop module (ODM). ODM results in deionized water show that sufficient long chain length of organic acid is an essential requirement for high surface dilatational modulus. While, to various salinities, surfactant to acid ratio of achieving high surface dilatational modulus varies. Foam flow tests show that surface dilatational modulus has decisive effect on produced foam size, which partially determines foam flow pressure drop. Both surface dilatational modulus and surface tension determine foam flow pressure drop. Besides, surface loss modulus also contributes to pressure drop. Bulk foam tests show that addition of organic acids with proper chain length can enhance foam tolerance to oil significantly. Compared with alkane chain length, acid with longer chain has good ability in stabilizing foam. At last, foam flooding tests show that surface dilatational modulus and foam tolerance to oil play important roles in foam enhanced oil recovery.     

One-pot synthesis of highly folded microparticles by suspension polymerization

A facile method of preparing highly folded cross-linked polymeric microparticles has been developed via one-pot suspension polymerization under high-speed homogenization. The wrinkles result from the evaporation of solvent in the cross-linked microparticles. The effects of microparticle cross-linking density and solvent on the polymer have been studied in detail. It was found that a medium cross-linking density (DVB/St = 0.5 by weight) is optimal for producing the most folded surface and the higher the solvent content, the deeper the surface wrinkles. This method is very simple and in principle can be applied to produce wrinkled microparticles with other chemical compositions.     

Emulsion-templated fully reversible protein-in-oil gels

We have developed a new method allowing us to transform low-viscous apolar fluids into elastic solids with a shear elastic modulus of the order of 10(3)-10(5) Pa. The elasticity of the elastic solid is provided by a percolating 3D network of proteins, which are originally adsorbed at the interface of an oil-in-water emulsion template. By cross-linking the protein films at the interface and upon removal of water, the template is driven into a structure resembling a dry foam where the protein interfaces constitute the walls of the foam and the air is replaced by oil confined within polyhedral, closely packed droplets. Depending on the density of the protein network, the final material consists of chemically unmodified oil in a proportion of 95 to 99.9%. The physical properties of the elastic solid obtained can be tuned by changing either the average diameter size of the emulsion template or the cross-linking process of the protein film. However, the original low-viscosity emulsion can be restored by simply rehydrating the solidified fluid. Therefore, the present procedure offers an appealing strategy to build up solid properties for hydrophobic liquids while preserving the low viscosity and ease of manufacturing.     

Covalent immobilization of lysozyme on stainless steel. Interface spectroscopic characterization and measurement of enzymatic activity

A new strategy aiming at the protection of metallic surfaces against the growth of biofilms is presented here. This work reports the grafting of primary amines by aminosilanization of oxidized stainless steel followed by chemical coupling of the glycosidase lysozyme from hen egg white using glutaraldehyde as homobifunctional cross-linking agent. Controlled characterization of a stainless steel surface by X-ray photoelectron spectroscopy and Fourier transform infrared reflection-absorption spectroscopy at each step enabled the mode of binding, coverage, and orientation of the grafted molecules to be addressed. As a result, the stainless steel samples covered with a covalently immobilized layer of lysozyme showed some lytic activity on a suspension of bacteria Micrococcus lysodeikticus.     

Characterization of the mechanical properties of cross-linked serum albumin microcapsules: effect of size and protein concentration

A microfluidic technique is used to characterize the mechanical behavior of capsules that are produced in a two-step process: first, an emulsification step to form droplets, followed by a cross-linking step to encapsulate the droplets within a thin membrane composed of cross-linked proteins. The objective is to study the influence of the capsule size and protein concentration on the membrane mechanical properties. The microcapsules are fabricated by cross-linking of human serum albumin (HSA) with concentrations from 15 to 35 % (w/v). A wide range of capsule radii (～40–450 μm) is obtained by varying the stirring speed in the emulsification step. For each stirring speed, a low threshold value in protein concentration is found, below which no coherent capsules could be produced. The smaller the stirring speed, the lower the concentration can be. Increasing the concentration from the threshold value and considering capsules of a given size, we show that the surface shear modulus of the membrane increases with the concentration following a sigmoidal curve. The increase in mechanical resistance reveals a higher degree of cross-linking in the membrane. Varying the stirring speed, we find that the surface shear modulus strongly increases with the capsule radius: its increase is two orders of magnitude larger than the increase in size for the capsules under consideration. It demonstrates that the cross-linking reaction is a function of the emulsion size distribution and that capsules produced in batch through emulsification processes inherently have a distribution in mechanical resistance.     

Fabrication of biomimetic superhydrophobic surfaces by a simple flame treatment method

A simple flame treatment method was explored to construct micro/nanostructures on a surface and then fabricate a biomimetic superhydrophobic surface at a relatively low cost. SiO₂‐containing polydimethylsiloxane (PDMS) was used as a substrate. The PDMS replicas with various micropatterned surfaces were fabricated using grass leaf, sand paper, and PET sheet with parallel groove geometry as templates via PDMS replica molding. The PDMS replica surfaces with micron structures and the surface of a flat PDMS sheet as a control sample were further treated by flame. The fabricated surfaces were characterized by scanning electron microscopy and water contact angle measurements. The effect of surface microstructures on the transparency of PDMS was also investigated. The studies indicate that the fine nanoscale structures can be produced on the surfaces of PDMS replicas and a flat PDMS sheet by a flame treatment method, and that the hierarchical surface roughness can be adjusted and controlled by varying the flame treatment time. The flame‐treated surfaces of PDMS replicas and a flat PDMS sheet possess superhydrophobicity and an ultra‐low sliding angle reaching a limiting value of 1°, and the anisotropic wettability of the PDMS replica surface with oriented microgroove structures can be greatly suppressed via flame treatment. The visible light transmittance of the flame‐treated flat PDMS surface decreases with prolonged flame treatment times. Copyright © 2016 John Wiley & Sons, Ltd.     

PP/PP-g-MAH与铝板粘接界面相的XPS研究

用X射线光电子能谱(XPS)研究铝板/聚丙烯层状复合材料的粘接界面相，提出了粘接界面的化学反应机制.研究发现,聚丙烯(PP)中加入马来酸酐接枝聚丙烯(PP-g-MAH)时，铝板面上Al 2p、O 1s谱线明显向高结合能端移动，表明PP-g-MAH与铝板表面发生了化学反应，形成Al－O－C配位键.配位键的形成使界面粘接强度明显提高. PP中不含PP-g-MAH时，铝板面上Al 2p、O 1s谱线处于低结合能端，聚丙烯未与铝板表面形成化学配位作用.     

Chemical template directed iodine patterns on the octadecyltrichlorosilane surface

A carboxylic-terminated nanometer-scale chemical pattern on an octadecyltrichlorosilane (OTS) surface can guide the deposition and crystallization of iodine, forming an iodine pattern on the chemical pattern. The iodine in the pattern is gel-like when fabricated by the solution-deposit method. In contrast, a dendritic, snowflake-shaped polycrystalline iodine sheet is formed by the vapor-phase condensation method. The data demonstrate that iodine is a good tracing and visualizing agent for studying liquid behavior at the nano scale. The topography of the iodine stain reveals that the "coffee ring" effect can be suppressed by reducing the pattern size and increasing the evaporation rate. The chemical template-bound iodine pattern has an unusually low vapor pressure and it can withstand prolonged baking at elevated temperature, which differs significantly from bulk iodine crystals.     

Stabilization of foams with inorganic colloidal particles

Wet foams are used in many important technologies either as end or intermediate products. However, the thermodynamic instability of wet foams leads to undesired bubble coarsening over time. Foam stability can be drastically improved by using particles instead of surfactants as foam stabilizers, since particles tend to adsorb irreversibly at the air-water interface. Recently, we presented a novel method for the preparation of high-volume particle-stabilized foams which show neither bubble growth nor drainage over more than 4 days. The method is based on the in-situ hydrophobization of initially hydrophilic particles to enable their adsorption on the surface of air bubbles. In-situ hydrophobization is accomplished through the adsorption of short-chain amphiphiles on the particle surface. In this work, we illustrate how this novel method can be applied to particles with various surface chemistries. For that purpose, the functional group of the amphiphilic molecule was tailored according to the surface chemistry of the particles to be used as foam stabilizers. Short-chain carboxylic acids, alkyl gallates, and alkylamines were shown to be appropriate amphiphiles to in-situ hydrophobize the surface of different inorganic particles. Ultrastable wet foams of various chemical compositions were prepared using these amphiphiles. The simplicity and versatility of this approach is expected to aid the formulation of stable wet foams for a variety of applications in materials manufacturing, food, cosmetics, and oil recovery, among others.     

Macroporous gels prepared at subzero temperatures as novel materials for chromatography of particulate-containing fluids and cell culture applications

Macroporous gels (MGs) with a broad variety of morphologies are prepared using the cryotropic gelation technique, i. e. gelation at subzero temperatures. These highly elastic hydrophilic materials can be produced from practically any gel-forming system with a broad range of porosity extending from elastic and porous gels with pore sizes up to 1.0 microm to elastic and sponge-like gels with pore sizes up to 100 microm. The versatility of the cryogelation technique is demonstrated by use of different chemical reactions (hydrogen bond formation, chemical cross-linking of polymers, free radical polymerization) mainly in an aqueous medium. Appropriate control over solvent crystallization (formation of solvent crystals) and rate of chemical reaction during the cryogelation allows the reproducible preparation of cryogels with tailored properties. Different approaches, such as chemical modification of reactive groups, grafting of the pore surface with an appropriate polymer, or direct copolymerization with functional monomers are used for control of the surface chemistry of MGs. Typically, MGs with pore sizes up to 1.0 microm are produced in the shape of beads and MGs with pore size up to 100 microm are prepared as monoliths, discs, and sheets. The difference in porous structure of MGs defines the main applications of these porous materials. Elastic beaded MGs are mostly used as carriers for cell and enzyme immobilization or for capture of low-molecular weight targets from particulate-containing fluids in expanded-bed mode. However, the elastic and sponge-like MG monoliths with interconnected pores measuring hundreds of mum have been successfully used as monolithic columns for chromatography of particulate-containing fluids (crude cell homogenates, viruses, whole cells, wastewater effluents) and as three-dimensional scaffolds for mammalian cell culture applications.     

丙烯酸共聚物囊壁的正十八烷微胶囊的制备和性能表征

以二丙烯酸1,4-丁二醇酯为交联剂, 成功制备了甲基丙烯酸甲酯-甲基丙烯酸共聚物为壁材, 正十八烷为囊芯的相变材料微胶囊. 采用扫描电子显微镜(SEM)、差示扫描量热仪(DSC)和热重分析仪(TG)分别考察了单体与芯材投料比、单体浓度和交联剂的含量对微胶囊形貌、相变热性能、热稳定性能的影响. 实验结果表明: 随着单体与芯材投料比或单体浓度的增加, 微胶囊表面均变得致密, 壁厚增加; 随着交联剂含量的增加, 微胶囊的表面变得更加致密光滑, 热稳定性显著增强; 随着单体与芯材投料比的增大, 微胶囊热焓值减小, 被包裹的囊芯含量减少.     

芳基油酸酰胺羟丙基磺基甜菜碱的合成及性能

合成了3种具有不同疏水基团的新型磺基甜菜碱两性表面活性剂,通过红外光谱对它们的结构进行了表征。 用滴体积法测定表面活性剂水溶液在25 ℃下的表面张力,从而确定其临界胶束浓度(cmc)及临界胶束浓度下的表面张力(γcmc);采用罗氏泡沫仪考察了浓度、温度对其泡沫性能的影响;采用分水时间法考察了其乳化性能。 结果表明,随着芳环在烷基链中的体积增大,cmc以及γcmc增大,饱和吸附面积Amin增大,而饱和吸附量Γmax减小。 3种表面活性剂的起泡性随浓度增大而增加,到一定值后趋于稳定;泡沫稳定性随浓度增大逐渐增强;起泡性随着温度的升高而显著增加,泡沫稳定性随温度升高而显著降低。 3种表面活性剂的乳化能力随浓度增大而逐渐增强然后趋于稳定。