试论汽车暖风电动机用电刷的研制

以经过高温处理的石墨粉为原料,按不同配比添加铜粉,制备了新型的、符合电机使用要求的汽车暖风电动机用电刷试样,同时研究了试样中铜含量对电刷的导电性、润滑性及耐磨性的影响。与以石墨粉为原料制备的电刷相比,由高温处理的石墨粉制得的电刷具有优良的导电性、润滑性及较低的运行噪音。     

Motion of nano-objects on polymer brushes

In this paper we review a new method to move nano-objects on a polymer surface that is made from diblock-copolymer and mixed brushes. Such brush systems consist of polymer chains covalently attached to a surface with high grafting density. If the two polymeric components the brush consists of are incompatible with each other, it shows microphase separation into nanopatterns of well defined size. Such a system possesses the unique property of changing the surface topography in response to different external conditions. Motion of nano objects adsorbed on the brush is induced by having the external conditions and thus the brush topography vary over time. This is shown by studying the distribution of silica nanoparticles adsorbed on several types of brushes while changing the external conditions. We identify parameters required for motion of nano objects, and discuss potential applications of the proposed technique for nano engineering.     

Dependence of thin polystyrene films stability on the thickness of grafted polystyrene brushes

We investigate the stability of thin polystyrene (PS) films on chemically identical grafted brushes of various thickness and grafting density. We observe an essential influence of the brush thickness on the stability of the PS films. For brushes with a thickness of 20-35 nm no de-wetting of the PS film occurs, while considerably thicker or thinner PS brushes lead to de-wetting of the PS top layer. We suggest that in the thin brush-like layers, the unfavorable interactions with underlying silica favor de-wetting. The tendency to de-wet is reduced once the brush is sufficiently thick to insulate the free PS layer from the surface. Beyond that point, the de-wetting process speeds up as the brush becomes thicker and has a higher grafting density with a substantial increase of the interfacial tension between the brush and the free polymer.     

Cross-linked polymer brushes. II. Formation and properties of poly(isobutyl vinyl ether)-b-poly[2-(vinyloxy)ethyl cinnamate] brushes

A diblock copolymer, i.e., poly(isobutyl vinyl ether)-b-poly[2-(vinyloxy)ethyl cinnamate] (PIBVE-b-PVEC), has been shown to form polymer brushes quickly on the surface of solid substrates by deposition from a solvent selectively poor for PVEC. The resultant brush could be cross-linked photochemically by initiating the dimerization between VEC groups of different polymer chains and the cross-linking was extremely efficient. Crosslinked polymer brushes, as expected, were resistant to organic solvent, such as chloroform, and nitric acid attacks. Important industrial applications are expected of cross-linked brushes. © 1994 John Wiley & Sons, Inc.     

Reactive patterning via post-functionalization of polymer brushes utilizing disuccinimidyl carbonate activation to couple primary amines

Polymer brushes provide an exceptional route to surface functionalization due to their chemical and mechanical robustness, lack of large-area defects, and high density of functional groups. In spite of these benefits, the synthetic difficulty and complex surface structure associated with polymer brushes have hindered their utilization for constructing multifunctional, patterned surfaces. In this contribution we describe the use of a rapid and highly efficient polymer brush post-functionalization technique as a facile method for controlling surface functionality of polymer brushes. Poly(2-hydroxyethyl methacrylate) (PHEMA) brushes are post-functionalized via activation with N,N′-disuccinimidyl carbonate (DSC) and subsequent coupling to molecules containing α-amine moieties. This post-functionalization effectively tailors surface energy resulting in water contact angles ranging from 40° to 100° using different conjugate molecules. Furthermore, the solvent tolerance, insensitivity to reactant concentration, and rapid reaction time of the aminolysis reaction enable surface energy patterning of the polymer brushes through the use of “reactive” soft lithography. Finally, these surface energy patterns could be “developed” by exposure to gold nanoparticle solutions to yield surfaces with patterned nanoparticle density.     

聚合物刷子的合成进展

聚合物在材料表面物理吸附或化学接枝所形成的刷子状单分子层被称为聚合物刷子,本文介绍了聚合物刷子的概念、分类以及合成方法。     

Swelling of Planar Polymer Brushes in Solvent Vapors

The swelling of densely grafted planar homo- and copolymer brushes in solvent vapors was studied by the dissipative particle dynamics method. It is shown that the distribution of the solvent inside the polymer film is inhomogeneous with the explicit maximum at the polymer–vapor interface. The value of the maximum does not depend on the grafting density and is mainly defined by the concentration of solvent vapors. At the same time, the distribution function of the free ends in homopolymer brush swollen in vapors of a good solvent is closer to the respective function in dry (solvent-free) brush: it has a rather narrow maximum at the upper border of the brush. In case of copolymer brushes, the swelling in vapors of a selective solvent can be accompanied by separation, the character of which is defined by the sequence of polymer segments (random or gradient) and also by the mean fraction of the segments of different types. The distribution function of free ends in the copolymer brush is calculated.     

Surface functionalization of nanodiamond particles via atom transfer radical polymerization

Ultradispersed diamond (UDD)/polymer brushes having excellent solution dispersibilities are prepared by atom transfer radical polymerization (ATRP) using the “grafting-from” synthesis strategy. ATRP initiators, covalently attached to oxidized surface carbon atoms of UDD aggregates using esterification chemistry, initiate polymerization of methacrylate monomers to form hydrophobic UDD/poly(iso-butyl methacrylate) and UDD/poly(tert-butyl methacrylate) polymer brushes. Acid hydrolysis of a UDD/poly(tert-butyl methacrylate) polymer brush affords a hydrophilic UDD/poly(methacrylic acid) polymer brush. Based on surface area measurements and GPC data, the calculated surface density of a representative UDD/polymer brush material is ca. five polymer chains/100 nm². A wide variety of UDD/polymer brush materials having controlled dispersibility and functional group reactivity are now potentially available using this synthesis strategy.     

Structure of bimodal and polydisperse polymer brushes in a good solvent studied by numerical mean field theory

We apply a lattice-based self-consistent mean field theory in order to investigate poly-disperse polymer brushes dissolved in good solvent. The systems investigated consist of asymmetric poly(dimethylsiloxane)-polystyrene di-block copolymers near air-ethylbenzoate interface and of diblock copolymer polystyrene-poly(ethyl oxide) deposited on a air-water interface. Our results have been compared to experimental data from neutron reflectivity experiments and have shown very good agreement. We have also systematically studied the structure of the bi-disperse and tri-disperse brush for various values of the molar fraction of the chains and of the overall surface densities. In addition, we have investigated the behavior of the brushes in other type of solvents.     

Homo- and mixed polymer brushes prepared by surface-grafting of asymmetric non-sticky/sticky diblock copolymers and their stimuli–responsive behaviors

We synthesize a non-sticky/sticky diblock copolymer, poly[styrene-b-3-(trimethoxysilyl)propylmethacrylate], to produce polymer brushes using the grafting-to technique. Uniform coatings of the polymer brushes are efficiently produced because of the multiple reactive groups offered by the sticky block, and the surface coverage and nanoscopic morphology of the brush layer are adjusted by varying the concentrations of the immersion polymer solutions and the immersion time of the substrate. The nanoscopic pattern of the polymer brushes is subsequently utilized to produce mixed polymer brushes. The resulting homo- or mixed polymer brushes change their nanoscopic morphology in response to external stimuli of temperature and solvent. The results indicate that grafting of the asymmetric non-sticky/sticky block copolymer is an efficient method for producing a surface of polymer brushes with nanoscopic chemical heterogeneity.     

Polymer brush coatings for combating marine biofouling

A variety of functional polymer brushes and coatings have been developed for combating marine biofouling and biocorrosion with much less environmental impact than traditional biocides. This review summarizes recent developments in marine antifouling polymer brushes and coatings that are tethered to material surfaces and do not actively release biocides. Polymer brush coatings have been designed to inhibit molecular fouling, microfouling and macrofouling through incorporation or inclusion of multiple functionalities. Hydrophilic polymers, such as poly(ethylene glycol), hydrogels, zwitterionic polymers and polysaccharides, resist attachment of marine organisms effectively due to extensive hydration. Fouling release polymer coatings, based on fluoropolymers and poly(dimethylsiloxane) elastomers, minimize adhesion between marine organisms and material surfaces, leading to easy removal of biofoulants. Polycationic coatings are effective in reducing marine biofouling partly because of their good bactericidal properties. Recent advances in controlled radical polymerization and click chemistry have also allowed better molecular design and engineering of multifunctional brush coatings for improved antifouling efficacies.     

Polystyrene Nanospheres Modified with a Hydrophilic Polymer Brush through Subsurface‐Initiated Atom Transfer Radical Polymerization as Biolubricating Additive

Hydration lubrication plays an important role including the cartilage of an organism. Here, polystyrene nanospheres modified with a hydrophilic polymer through subsurface‐initiated grafting as a biolubricating additive is proposed. The material provides good tribological performance when subjected to high load. Compared with surfaced‐initiated grafting polymer brushes, subsurface initiation can form much thicker hydration layers to obtain a lower friction coefficient and better mechanical properties for withstanding prolonged shearing forces with less measurable damage. The polymer brushes penetrate through the covalent network of the polystyrene nanospheres providing a match in mechanical properties between them, so that the additives obtain more excellent lubricity in an aqueous environment under shear pressure, which is expected to become a promising artificial joint biolubricating additive.     

聚合物刷的合成与应用研究进展

聚合物刷由于在吸附、粘附、润滑以及润湿方面的显著特点,在许多方面都有重要的应用,显示了潜在而巨大的研究价值。本文综述了聚合物刷的基本理论、合成方法及应用的最新研究进展,并着重介绍了可控自由基聚合合成聚合物刷的方法。     

Nitroxide polymer brushes as efficient and recoverable catalysts for the selective oxidation of primary alcohols to aldehydes

2,2,6,6‐Tetramethylpiperidinyloxyl (TEMPO)‐containing polymer brushes were grafted onto crosslinked polystyrene microspheres via surface‐initiated activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) of 2,2,6,6‐tetramethyl‐4‐piperidyl methacrylate, followed by an oxidation process with 3‐chloroperoxybenzoic acid as oxidant. The synthesized nitroxide polymer brushes included homopolymer brushes, block copolymer brushes, and random copolymer brushes with various TEMPO contents and molecular weights. They were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, nuclear magnetic resonance spectroscopy, and gel permeation chromatography. These nitroxide brushes bearing high TEMPO contents were used as recoverable catalysts for the hypochlorite and aerobic oxidation of primary alcohols to aldehydes. The effects of polymer brush structure on the catalytic properties were studied and discussed. The results showed that these nitroxide polymer brushes had excellent catalytic properties and good recycling performances. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44365.     

Glycopolymer brushes with specific protein recognition property

Here, we report the synthesis of glycopolymer brushes on the silicon substrate by interface‐mediated reversible addition‐fragmentation chain transfer polymerization of pentafluorophenyl acrylate as well as subsequent attachment of d ‐glucosamine to determine specific and nonspecific protein interactions. The root‐mean‐square roughness of the glycopolymer brushes is only about 3.1 nm, indicating unstable distribution of the collapsed glycopolymer chains on the surface. The water contact angle of glycopolymer brush was determined as ～53° indicating a hydrophilic behavior. The results of fluorescence microscopy studies indicated that the glycopolymer brushes have specific interaction with fluorescence‐labeled Concanavalin A and nonspecific interaction with fluorescence‐labeled bovine serum albumin. The glycopolymer brushes tested here are hoped to enlarge to our knowledge of recognition phenomena at the surface of polymer brushes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45238.     

Surface‐tethered conjugated polymers created via the grafting‐from approach

Polyacrylate brushes with pendent terthiophenes [poly(terthiophene methyl methacrylate) (PTTMM)] were successfully grown from indium tin oxide and gold with surface‐initiated atom transfer radical polymerization. The films formed on both substrates were characterized by ellipsometry and Fourier transform infrared spectroscopy. Using cyclic voltammetry, we electrochemically crosslinked the PTTMM brush to form a conjugated polymer network. The conjugation lengths in the film were increased as evidenced by ultraviolet–visible spectroscopy. Additionally, an atomic force microscopy study on the surface‐modified solid substrate revealed the formation of a smooth and uniform polymer brush with a low surface roughness, even after electrochemical crosslinking. These uniformly grafted conducting polymer brushes may find use in photovoltaic devices. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41363.     

Excess free energy of nanoparticles in a polymer brush

We present an efficient method for direct determination of the excess free energy ΔF of a nanoparticle inserted into a polymer brush. In contrast to Widom's insertion method, the present approach can be efficiently implemented by Monte Carlo or Molecular Dynamics methods also in a dense environment. In the present investigation the method is used to determine the free energy penalty ΔF(R, D) for placing a spherical particle with an arbitrary radius R at different positions D between the grafting plane and the brush surface. Deep inside the brush, or for dense brushes, one finds ΔF ∝ R³ whereas for shallow nanoclusions ΔF ∝ R², regardless of the particle interaction (attractive/repulsive) with the polymer.The pressure and density fields around spherical nanoinclusions in a polymer brush are also investigated. Extensive Monte Carlo simulations show that the force, exerted on the particle by the surrounding brush, depends essentially on the proximity of the nanocolloid particle to the brush surface not only in strength but also with respect to its angular distribution. For shallow nanoinclusions close to the brush surface this angular distribution is shown to result in a growing buoyant force while deep inside the brush this effect is negligible.     

Stimuli response of cationic polymer brush prepared by ATRP: Application in peptide fractionation

Random cationic copolymer brushes composed of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and N-isopropylacrylamide (NIPAAm) were synthesized using the atom transfer radical polymerization (ATRP) method. The effects of varying the monomer feed ratios (30:70 and 70:30 DMAEMA:NIPAAm) and polymerization times on the film height, morphology and stimuli response to pH of the brush were evaluated. While the polymerization time was found to have little influence on the properties of the brushes, the monomer feed ratios had a great impact. The 70% DMAEMA polymer brush had similar height as the 30% DMAEMA brush after 45 min; however, it had a greater response to pH and morphological change compared to the 30% DMAEMA. The 70% DMAEMA brush was used to demonstrate an efficient approach to alleviate the ion suppression effect in MALDI analysis of complex mixtures by effectively fractionating a binary mixture of peptides prior to MALDI-MS analysis.     

Growth of silver nanoparticles on poly(acrylic acid) brushes and their properties

A simple procedure is employed for the growth of silver nanoparticles (Ag NPs) onto the silicon substrate modified by poly(acrylic acid) (PAA) brushes, via: (1) surface-initiated ATRP of tert-butyl acrylate on Si surface to the preparation of poly(tert-butyl acrylate) brushes, (2) acid hydrolysis of PBA to the formation of PAA, and (3) in situ synthesis of Ag NPs via chemical reduction of AgNO₃ in the presence of PAA brushes. The polymer brushes are thoroughly characterized. Moreover, Ag nanoparticles are homogeneously immobilized into the brush layer and have been used to fabricate a sensor platform of surface-enhance Raman scattering for the detection of organic molecules and effectively catalyze the reduction of methylene blue by NaBH₄.