Surface modification using polymer Langmuir-Blodgett films

We describe a simple and effective approach to introduce a functional group into polymer film on a solid surface using reactive polymer LB films. N-dodecylacrylamide copolymers containing terminal amino groups in the side chains as the reactive moiety form a stable monolayer, and the monolayer was transferred onto a solid support to modify the solid surface using the Langmuir-Blodgett method. The transferred coatings were characterized with fluorescence, IR spectroscopies, and X-ray diffraction. The reactivity of the terminal amino group incorporated in the LB films was investigated in detail using fluorescein isothiocyanate (FITC) as a fluorescent probe. The chemical reaction between amino groups in the LB films and FITC in the bulk solution was completed within approximately 30 minutes and the chemical bond formation was confirmed by infrared spectroscopy. Furthermore, the fluorescent image of the multilayers reacted with FITC were observed with fluorescent microscopy. This method is effective for tailoring functional organic ultrathin films on solid substrates.     

聚氨酯表面接枝丙烯酸甲酯改性研究

对聚氨酯(PU)的表面进行除油、除污等预处理,然后表面经甲苯-2,4-二异氰酸酯(TDI)活化,在表层形成未反应的自由异氰酸酯基团(NCO).再通过2-溴乙醇与表面自由的异氰酸酯基团反应,在表层形成溴原子端基.该原子在催化剂氯化亚铜(CuCl)和配体2,2-联二吡啶(Bpy)的存在下,将丙烯酸甲酯通过原子转移自由基聚合(ATRP)接枝到PU表面.动力学研究揭示,丙烯酸甲酯的接枝率与反应时间成线性关系:表明表面链增长反应为可控活性聚合.使用衰减全反射傅立叶红外光谱(ATR-FTIR)和X-射线光电子能谱(XPS)表征分析每一步处理后的PU膜片.     

Surface modification of poly(dimethylsiloxane) microfluidic devices by ultraviolet polymer grafting

Poly(dimethylsiloxane) (PDMS)-based microfluidic devices are increasing in popularity due to their ease of fabrication and low costs. Despite this, there is a tremendous need for strategies to rapidly and easily tailor the surface properties of these devices. We demonstrate a one-step procedure to covalently link polymers to the surface of PDMS microchannels by ultraviolet graft polymerization. Acrylic acid, acrylamide, dimethylacrylamide, 2-hydroxylethyl acrylate, and poly(ethylene glycol)monomethoxyl acrylate were grafted onto PDMS to yield hydrophilic surfaces. Water droplets possessed contact angles as low as 45 degrees on the grafted surfaces. Microchannels constructed from the grafted PDMS were readily filled with aqueous solutions in contrast to devices composed of native PDMS. The grafted surfaces also displayed a substantially reduced adsorption of two test peptides compared to that of oxidized PDMS. Microchannels with grafted surfaces exhibited electroosmotic mobilities intermediate to those displayed by native and oxidized PDMS. Unlike the electroosmotic mobility of oxidized PDMS, the electroosmotic mobility of the grafted surfaces remained stable upon exposure to air. The electrophoretic resolution of two test peptides in the grafted microchannels was considerably improved compared to that in microchannels composed of oxidized PDMS. By using the appropriate monomer, it should be possible to use UV grafting to impart a variety of surface properties to PDMS microfluidics devices.     

Electroviscoelastic effect of polymeric composites consisting of polyelectrolyte particles and polymer gel

The dynamic viscoelasticity of polymeric composites consisting of silicone gel and polymethacrylic acid cobalt(II) salt (PMACo) particles was studied in d.c. electric fields. It was measured by applying sinusoidally varying shear strain or compressive strain to the composites. It was found that the electric fields enhanced the storage and loss moduli of the composites, and changed the loss tangent (electroviscoelastic effect). The amount of the electroviscoelastic effect was influenced by the content of absorbed water in the PMACo particle, the fraction of PMACo particles, and the intensity of the electric field. It also depended on the amplitude and frequency of the applied strain. The increments of the compressive moduli due to the electroviscoelastic effect were much larger than those of the shear moduli.     

Surface modification of poly(ethylene terephthalate) polymeric films for flexible electronics applications

The production of Flexible Electronic Devices (FEDs) by roll-to-roll large-scale manufacturing processes is a rapidly growing sector and the development of functional (inorganic and/or organic) thin layers onto flexible polymeric substrates represents one of the key issues for the low cost production of FEDs. However, the flexible substrates should meet advanced demands, as high optical transparency, high barrier properties and increased adhesion of the subsequent functional layers, which will have a major affect on their performance, efficiency and lifetime. Plasma treatment can be successfully employed for the improvement of the bonding structure and surface properties of flexible polymeric substrates. In this work, we report on the effect of Pulsed DC N⁺ ion bombardment using different ion energies, on the bonding structure, electronic and optical properties and surface nanotopography of Poly(Ethylene Terephthalate) (PET) substrates. For the investigation of the optical properties, we have used in-situ and real-time Spectroscopic Ellipsometry from the IR to Vis-farUV spectral region, in combination to advanced modeling procedures, whereas Atomic Force Microscopy has been employed for surface nanotopography investigation. As it has been found, the N⁺ bombardment leads to the appearance of new chemical bonds (C-N or C-O bonds in Φ-NH₂, Φ-NHR, C(O)-NHR, Φ-OH, or (CO)-OH), as well as partial disappearing of the C-O bond of ester group, on a surface layer of PET.     

Electrosynthesis and characterisation of poly(safranine T) electroactive polymer films

The phenazine safranine T has been electropolymerised by potential cycling at carbon film electrodes in nitrate-containing solutions at different pH: 2.0, 5.5, and 7.0, as well as from chloride solution, pH 5.5. The electroactive polymer obtained, poly(safranine T), has been analysed by cyclic voltammetry in different electrolyte solutions and its morphology examined using scanning electron microscopy. The surface coverage was calculated and found to be the highest for the film formed in chloride solution, pH 5.5, with 8.7 nmol cm^− 2. The other films had lower coverages, from 5.3 to 7.8 nmol cm^− 2, and are similar to those obtained for other phenazine dye polymers. Although the fastest polymerisation occurred in solutions at pH 5.5, the best electrochemical properties resulted from electropolymerisation at pH 2.0. Analysis of the cyclic voltammograms showed that in most cases the electrochemical processes at the polymer coated electrodes are limited by surface reactions. Scanning electron microscopy data confirmed the results obtained by cyclic voltammetry and showed that the most compact film was obtained in chloride solution.     

Temporal and spatial profiling of the modification of an electroactive polymeric interface using neutron reflectivity

Electropolymerized films of the functionalized pyrrole, pentafluorophenyl-3-(pyrrol-1-yl)propionate (PFP), were reacted with a solution-phase nucleophile, ferrocene ethylamine. This reaction was chosen as a model representative of a postdeposition modification of the polymer membrane's properties. For the first time, a nondestructive method for direct chemical analysis of the reaction profile within the electrodeposited polymer membrane after nucleophilic substitution is presented. This was achieved through the application of in situ neutron reflectivity with supplementary analytical information concerning the film's chemical composition obtained from XPS, FT-IR, and electrochemical measurements. The results presented illustrate how, for a partially reacted film resulting from a short reaction time, the extent of reaction with ferrocene ethylamine is not homogeneous throughout the thickness of the film, but occurs predominantly at the polymer/solution interface. We show that the progress of the reaction within the polymer film is limited by the transport of reacting species in the dense regions of the membrane that are furthest from the solution interface. The data do not fit an alternative model in which there is spatially homogeneous progression of the reaction front throughout the bulk of the thin film polymer. Guided by the neutron reflectivity measurements, suitable modifications were made to the electrodeposition method to prepare films whose architecture resulted in faster rates of reaction.     

Surface modification of natural rubber latex films via grafting of poly(ethylene glycol) for reduction in protein adsorption and platelet adhesion

Natural rubber (NR) latex films with surface grafted poly(ethylene glycol) (PEG) chains were prepared by UV-induced graft copolymerization of methoxy poly(ethylene glycol) monomethacrylate (PEGMA) onto the plasma-pretreated NR latex films. PEGMA macromononers of different molecular weights were used. The UV-induced graft copolymerization of PEGMA onto the plasma-pretreated NR latex films was also explored with PEGMA of different macromonomer concentrations and with different UV graft copolymerization time. The surface microstructures and compositions of the PEG-modified NR latex films were characterized by contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) measurements. In general, higher macromonomer concentration and longer UV graft copolymerization time led to a higher graft yield. Water contact angle measurements revealed that the hydrophilicity of the NR latex film surface was greatly enhanced by the grafting of the PEG chains. The NR surface with a high density of grafted PEG was very effective in reducing protein adsorption and platelet adhesion. A lower graft concentration of the high-molecular-weight PEG was more effective than a high graft concentration of the low-molecular-weight PEG in reducing protein adsorption and platelet adhesion. © 2001 Kluwer Academic Publishers     

Recent advances and an industrial perspective of cellulose nanocrystal functionalization through polymer grafting

Cellulose nanocrystals (CNCs) are an emerging nanomaterial for applications ranging from coatings and construction to adhesives and biomedical devices. Owing to their high aspect ratio, stiffness, and reinforcing potential, CNCs have shown great promise to be used in polymer nanocomposites. However, due to their inherent hydrophilicity and compatibility with polar environments, the use of CNCs in hydrophobic polymer matrices or in organic solvent-based formulations has been limited. To overcome this incompatibility, many reports on grafting polymers onto the surface of CNCs have been published over the past ten years. This review describes the recent advances in CNC surface functionalization through polymer grafting, and comprehensively covers the existing work to date. Methods including polymer “grafting to” and “grafting from” are described in detail, using polymerization techniques such as free radical, ring opening, and controlled radical polymerization. Purification and characterization of polymer-grafted CNCs, the potential for upscaling these functionalization methods, and current perspectives from academic and industrial viewpoints are presented.     

聚偏氟乙烯基聚合物电解质接枝改性研究进展

聚偏氟乙烯基聚合物是锂离子电池用聚合物电解质较理想的基质材料,但也存在结晶度高、亲液性差等问题。主要综述了采用γ射线、电子束、紫外等辐射,原子转移自由基聚合及溶液接枝聚合等方法接枝苯乙烯、甲基丙烯酸缩水甘油酯、新戊二醇二丙烯酸酯、聚甲基丙烯酸甲酯、三丙烯乙二醇醚醋酸酯、聚乙二醇甲基丙烯酸酯、2-丙烯酰胺基-2-甲基丙磺酸、聚乙二醇等对聚偏氟乙烯基聚合物电解质的改性研究进展。接枝改性后的聚偏氟乙烯聚合物电解质对电解液的亲和性、离子电导率、电化学稳定性和循环性能都有一定程度的提高。     

Surface modification of titanium substrates with silver nanoparticles embedded sulfhydrylated chitosan/gelatin polyelectrolyte multilayer films for antibacterial application

To develop Ti implants with potent antibacterial activity, a novel “sandwich-type” structure of sulfhydrylated chitosan (Chi-SH)/gelatin (Gel) polyelectrolyte multilayer films embedding silver (Ag) nanoparticles was coated onto titanium substrate using a spin-assisted layer-by-layer assembly technique. Ag ions would be enriched in the polyelectrolyte multilayer films via the specific interactions between Ag ions and –HS groups in Chi-HS, thus leading to the formation of Ag nanoparticles in situ by photo-catalytic reaction (ultraviolet irradiation). Contact angle measurement and field emission scanning electron microscopy equipped with energy dispersive X-ray spectroscopy were employed to monitor the construction of Ag-containing multilayer on titanium surface, respectively. The functional multilayered films on titanium substrate [Ti/PEI/(Gel/Chi-SH/Ag) _n /Gel] could efficiently inhibit the growth and activity of Bacillus subtitles and Escherichia coli onto titanium surface. Moreover, studies in vitro confirmed that Ti substrates coating with functional multilayer films remained the biological functions of osteoblasts, which was reflected by cell morphology, cell viability and ALP activity measurements. This study provides a simple, versatile and generalized methodology to design functional titanium implants with good cyto-compatibility and antibacterial activity for potential clinical applications.     

Surface functionalization of Ag-nanoclusters–silica composite films for biosensing

Ag nanocluster–silica composite films have been obtained by Radio-Frequency (RF) co-sputtering on soda-lime substrates: their characteristic Localized Surface Plasmon Resonance (LSPR) can be employed for sensing applications after grafting of a specific molecule (folic acid) for the recognition of cancer cells. Preliminary results on the surface functionalization of Ag nanocluster–silica composite films by folic acid and the ability of functionalized layers to selectively recognize the proper antibody will be discussed.     

Strain dependence electrical resistance and cohesive strength of ITO thin films deposited on electroactive polymer

Transparent, conducting, indium tin oxide (ITO) films have been deposited, by pulsed dc magnetron sputtering, on glass and electroactive polymer (poly(vinylidene fluoride)—PVDF) substrates. Samples have been prepared at room temperature by varying the oxygen partial pressure. Electrical resistivity around 8.4 × 10^− 4 Ω cm has been obtained for films deposited on glass, while a resistivity of 1.7 × 10^− 3 Ω cm has been attained in similar coatings on PVDF. Fragmentation tests were performed on PVDF substrates with thicknesses of 28 μm and 110 μm coated with 40 nm ITO layer. The coating's fragmentation process was analyzed and the crack onset strain and cohesive strength of ITO layers were evaluated.     

Enhancement of charge-transport characteristics in polymeric films using polymer brushes

We show that charge-transporting polymer chains in the brush conformation can be synthesized from a variety of substrates of interest, displaying a high degree of stretching and showing up to a 3 orders of magnitude increase in current density normal to the substrate as compared with a spin-coated film. These nanostructured polymeric films may prove to be suitable for electronic devices based on molecular semiconductors as current fabrication techniques often provide little control over film structure.     

Surface characteristics of water-repellent polyelectrolyte multilayer films containing various silica contents

Water-repellent films were dip-coated onto glass substrate by mimicking a unique surface feature of the lotus leaf by a layer-by-layer deposition of polyelectrolyte, followed by SiO₂ particle to modify surface roughness, and finally a semifluorinated silane to lower the surface energy. Two types of the SiO₂, a fine-sized Aerosil^® 200 and a coarse-sized Aeroperl^® 300/30, were employed at various contents to modify the films' surface roughness. SEM and AFM analysis revealed that the Aerosil^® 200 had more uniform deposition onto the etched polyelectrolyte layer due to its very fined size while the Aeroperl^® 300/30 had less uniform deposition due to its coarser size. In both cases, higher SiO₂ content in the films led to more surface roughness and more hydrophobicity, although the effect was not dramatic in the case of Aerosil^® 200. The films containing the Aerosil^® 200 had very high contact angles of 167-175°and very low surface energy of 0.03-0.51 mJ m^− 2, while the films containing the Aeroperl^® 300/30 had lower contact angles of 132-154°and higher surface energy of 3.07-11.29 mJ m^− 2.     

Surface modification of natural and synthetic hydroxyapatites powders by grafting polypyrrole

The modification of hydroxyapatite surface by grafting polypyrrole has been investigated with two hydroxyapatites (HA) powders. One is natural derived from bovine bone, it was prepared by calcination at 750 °C. The other is synthetic synthesized by the sol–gel method using Ca(NO₃)₂·4H₂O and P₂O₅. The presence of (C₄H₃N) _n polymeric fragment bound to HA surface was evidenced by infrared analysis. X-ray powder analysis has shown that the apatite structure remains unchanged during the surface modification. The thermogravimetric analysis has shown that the weight loss exhibited by HA increased from 8.7 to 47.8 and from 18.3 to 42.8 wt% for natural hydroxyapatite (NHA)/polypyrrole and synthetic hydroxyapatite (SHA)/polypyrrole, respectively, as the pyrrole solution concentration increased from 5 to 15 wt%. Grafting of polypyrrole on HA surface caused an increase in specific surface area up to 113 m²/g for SHA and up to 107 m²/g for NHA aged in 15 wt% pyrrole solution (HA/15Pyrrole). According to the results found for these two apatites, a mechanism of surface modification was proposed for the formation of N–H hydrogen bonds as the result of a reaction between the C₄H₅N organic reagent and OH^? ions of the HA.     

甲基丙烯酸甲酯对纳米SiO2的表面接枝聚合改性研究

将经过硅烷化处理的偶联剂γ-MPS接枝到纳米SiO2表面,然后在引发剂AIBN的作用下引发单体MMA发生自由基聚合包覆.利用FTIR、TG、CA(接触角)以及TEM等手段分别表征了改性工艺条件对粒子改性前后化学组成结构、接枝率、表面亲水性以及形貌等的影响.系统研究了单体用量、引发剂用量以及反应时间对SiO2/γ-MPS/PM-MA纳米复合粒子接枝改性效果的影响.结果表明,经过PMMA接枝包覆制得了高接枝率的复合粒子,并大大改善了纳米粒子的分散性.     

聚偏氟乙烯膜表面丙烯酸接枝改性研究

采用自由基接枝聚合反应制备了丙烯酸改性的聚偏氟乙烯膜,研究了单体浓度对接枝率的影响,测定了改性后样品的红外光谱、表面接触角、水通量、蛋白吸附等.结果表明,通过自由基接枝聚合,丙烯酸接枝到膜的表面,明显提高膜的亲水性.接枝后膜的水通量也非常明显下降,特别是在高丙烯酸浓度下.改性的膜的通量对溶液的pH值有明确的响应关系,表明接枝链在水中的溶胀对膜的性能有显著的影响.蛋白吸附实验表明,改性后的膜相比未改性膜有较高的吸附量,而且在酸性情况下,膜的吸附量较大,这主要与丙烯酸和蛋白质之间的相互作用有关.