聚合物／聚合物分子复合材料的研究动态

综合讨论了聚合物／聚合物分子复合材料的定义、特征和优势,重点介绍了分子复合材料相容的有效途径及分子复合材料的常用制备方法。并简述了热固性分子复合材料的研究情况及分子复合材料研究前景。     

Enhancement of polymer film adhesion using acid-base interactions determined by contact angle measurements

Quantitative correlations among surface chemical composition, acid-base thermodynamics, adhesion strength, and locus-of-failure are demonstrated. Four types of functional Teflon surfaces were prepared: two acidic (containing hydroxyl and carboxyl groups), and two basic (containing acetyl and dinitrobenzoate groups). X-Ray photoelectron spectroscopy (XPS) and attenuated total reflection infrared (ATR-IR) spectroscopy were used to characterize the molecular structure of the surface region. Contact angle adsorption isotherms were determined using phenol as an acidic probe and tetrahydrofuran (THF) as a basic probe. The carboxylated surface had a higher molar ?H^ab with basic THF than the hydroxylated surface, and neither surface had any interaction with the acidic phenol probe. The acetylated surface behaved as a base, interacting with phenol but not with THF, while the dinitrobenzoyl surface had both acidic and basic character. Adhesion tests were carried out in the 180° peel mode using post-chlorinated poly(vinyl chloride) as a model acidic adhesive between pairs of each type of film. The two surfaces with basic character had significant peel strengths, while the two acidic surfaces had very low peel strengths. Scanning electron microscopy (SEM) of the basic failure surfaces showed significant plastic deformation of the Teflon polymer, while the acidic failure surfaces showed no deformation. XPS analysis of the failure surfaces confirmed interfacial failure for the acid-acid pairs, and bulk FEP failure for the acid-base pairs. These results demonstrate directly and quantitatively the enhancement of adhesive bond strength through acid-base interactions.     

液体成型用环氧树脂体系与碳纤维表面浸润性能研究

采用1,4-丁二醇二缩水甘油醚(BDDGE)、聚乙二醇二缩水甘油醚(PEGDGE)、双酚A聚氧乙烯醚06(BPE-06)3种活性环氧树脂稀释剂,分别制备了低黏度适合复合材料液体成型工艺(LCM)的环氧树脂体系,研究了体系与国产碳纤维(HF10)的表面浸润性。首先,研究了稀释剂结构、用量对环氧树脂体系与碳纤维湿润性的影响;其次,研究了稀释剂/树脂/固化剂体系的湿润温度、反应程度对树脂与碳纤维表面的浸润性影响。采用DCAT21表面/界面张力仪分析了树脂与碳纤维界面的前进接触角;采用Young-Dupre法,计算了树脂与碳纤维的热力学粘附功。结果表明,采用稀释剂降低黏度,可以有效改善树脂体系与碳纤维的浸润性;相同黏度时,不同结构稀释剂提高浸润性效果顺序为:PEGDGEBPE-06BDDGE;升高温度可以提高环氧树脂与碳纤维的浸润性;随着反应程度的提高,树脂体系与碳纤维的湿润性变好。     

Effect of surfactant compounding on the wettability of talcum powder

Talcum powder is one of the leading causes of pneumoconiosis, adding compound surfactants to the dust removal process can significantly increase the effectiveness of the dust removal. Therefore, it is of great significance to study the effect of compound surfactants on the wettability of talcum powder. This paper focuses on the ability of compound surfactants to increase the wettability of talcum powder surface by using Materials Studio 8.0. The simulation results were analyzed from the water adsorbed amount, interaction energy, and water molecule concentration profile. Combined with the experimental data of contact angle, the optimal surfactant compounding method was obtained. The simulation results revealed that stable adsorption structures can be formed by the compound of anionic and nonionic surfactants, which can reduce the electrostatic repulsion between anionic surfactants effectively and promote the directional arrangement of nonionic surfactants on the talcum powder surface. When the molar ratio of sodium dodecyl sulfate (SDS) and Polysorbate 80 was 0.4:0.6, the amount of absorbed water reached 113, which is better than monomers and other compound surfactants. The contact angle experiment results indicated a consistent variation law with the simulation results. The contact angle decreased from 68.48° to 19.84° using the compounding method mentioned above, which has the optimum wetting effect among the four compounding methods. The research results will provide a reference for the application of compound surfactants in talcum powder dustproof work.     

The influence of metallic surface wettability on bacterial adhesion

The wettability of AISI 304 stainless steel with 2B and 2RB surface finishes expressed in terms of the solid surface free energy was investigated with respect to the cleaning process. It was shown that cleaning affects the wettability of a solid surface. Depending on the cleaning method, ranged from 43.4 to 277.8 mJ m^-2 for the 2RB surface and from 34.4 to 122.8 mJ m ² for the 2B surface. There was no direct relationship between the number of adhering bacteria and or the wettability of solids. However, it was found that the adhesion of Streptococcus thermophilus was driven by a balance between and The experimental results are as expected based on thermodynamic predictions when the spreading pressure is accounted for in the surface free energy of bacteria, determination.     

Characteristics of surface wettability and hydrophobicity and recovery ability of EPDM rubber and silicone rubber for polymer insulators

As power lines are built in contaminated environments, the industrial usage of power‐line materials requires high reliability. Nonceramic insulators offer better anticontamination performance than that of the traditional ceramic insulators. Among the nonceramic materials, EPDM and silicone rubber provide much better long‐term pollution resistance performance than that of any other materials. This study investigated the long‐term pollution performance by a corona aging treatment on the surface of the test slabs, which were made of EPDM and silicone rubber. Experimental results showed good hydrophobicity of those materials and their transfer of the contaminant layer deposited on the shed surface of the insulator. The EPDM and silicone rubbers are synthetic polymers of low density and they maintain an outstanding resistance to attack by oxygen and ozone. This study measured the contact angle between water droplets and other materials to determine the hydrophobicity and recovery ability of these synthetic polymers. We also studied surface morphology for a visual confirmation of the migration phenomena. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2251–2257, 2001     

Largely improved toughness of PP/EPDM blends by adding nano-SiO2 particles

As a part of long-term project aimed at super polyolefin blends, in this work, we report the toughness and phase morphology of polypropylene (PP)/EPDM/SiO₂ ternary composites. Two processing methods were employed to prepare PP/elastomer/filler ternary composites. One was called one-step processing method, in which the elastomer and the filler directly melt blended with PP matrix. Another one was called two-step processing method, in which the elastomer and the filler were mixed first, and then melt blended with pure PP. Two kinds of PP (grafted without or with maleic anhydride (PP-g-MA)) and SiO₂ (treated with or without coupling agent) were used to control the interfacial interaction among the components. The dependence of the phase morphology on interfacial interaction and processing method was investigated. It was found that the formation of filler-network structure could be a key for a simultaneous enhancement of toughness and modulus of PP and its formation seemed to be dependent on the work of adhesion (W_AB) and processing method. As the W_AB of PP/EPDM interface was much lower than that of PP/SiO₂ and EPDM/SiO₂, and the two-step processing method was used, the formation of filler-network structure was favorable. In this case, a super toughened PP ternary composite with the Izod impact strength 2-3 times higher than PP/EPDM binary blend and 15-20 times higher than pure PP could be achieved.     

聚乙烯表面的火焰处理

研究了火焰处理法对聚乙烯表面的氧化改性。研究发现,聚乙烯的表面氧化要比聚丙烯容易得多。即使在中等火焰强度的处理下,聚乙烯的表面氧化深度超过Ｘ光电子能谱的检测深度（约１２０埃）,高分辨Ｘ光电子能借结果表明,火焰氧化在聚乙烯表面引进了以下化学官能团,即Ｃ－Ｏ、Ｃ＝Ｏ及Ｃ（＝Ｏ）－Ｏ－。衰减全反射红外光谱也证实了氧化后的聚乙烯表面上谈基的存在。氧化后聚乙烯表面上的液体接触角滞后是由于表而化学不均匀性所致。火焰处理后的聚乙烯的粘合性得到大幅度的增强。     

常压等离子体改善合成纤维吸湿性的研究

用氦气作为等离子体的气体源、对涤纶、锦纶6、高强度聚乙烯纤维,Twaron 1000芳纶4种合成纤维进行常压等离子体处理,改善纤维的吸湿性能。结果表明:常压等离子体处理,对涤纶和锦纶6的表面有一定的刻蚀作用,但对高强度聚乙烯纤维、Twaron 1000芳纶的表面没有明显影响;经常压等离子体处理后,合成纤维表面氧、氮有所增加,吸湿性能得到提高,强度没有显著变化。     

Roles of molecular interactions in adhesion,adsorption, contact angle and wettability

This study is aimed at understanding the controversy between the surface tension component (STC) theory and the equation of state (EQS) approach for interfacial tensions. We attempt to relate molecular interactions to various components of surface tension. Molecular interactions consist of electrostatic (ES), charge transfer (CT), polarization (PL), exchange-repulsion (EX), dispersion (DIS), and coupling (MIX) components. These interactions can be the basis for the STC theory involving Lifshitz-van der Waals (LW) and the short range acid-base (AB) or donor-acceptor interaction. Each of these components is shown to contain two major parameters. New equations for the interaction energy and surface tension for polar molecules are proposed to include the ES and EX parameters, which happen in some cases to balance each other or nearly cancel out without being detected. The roles of molecular interactions on adhesion, adsorption, contact angle, and wettability are illustrated through the spreading coefficient S, the Hamaker coefficient A, and Derjaguin's disjoining pressure . We have found that the STC theory is applicable to the systems involving either physisorption or chemisorption, whlie the EQS applies to those involving ony physisorption.     

Estimating work of adhesion using spherical contact between a glass lens and a PDMS block

This study proposes a method of estimating the thermodynamic work of adhesion using the spherical contact between a glass lens and a polydimethylsiloxane (PDMS) block. An equivalent stiffness of the measurement system is determined prior to the experimental measurements. Parameters such as force, contact radius, and displacement are measured during the contact processes that consist of a loading process and an unloading process. The elastic modulus of the PDMS is determined from the measured parameters. Hysteresis is observed in the contact process, showing that the process is in a non-equilibrium state. However, an equilibrium instant exists when the contact area attained a maximum value. The work of adhesion can be determined from the strain energy release rate using the parameters of the instant. The estimated work of adhesion is in the range estimated by another method. The limitation of the conventional method is also presented. The proposed method is suggested to be applicable to interface characterization in a practical adhesive contact with soft materials.     

The Formation of Epoxy/Metal Interphases: Mechanisms and Their Role in Practical Adhesion

When epoxy/diamine systems are applied onto metallic substrates and cured, an interphase, having chemical, physical, and mechanical properties quite different from bulk polymer is created between the substrate and the polymer. The aim of this work is to understand the interphase formation mechanisms and their role in practical adhesion. Mechanisms were deduced from comparison of behaviors when either epoxy and diamine monomers or epoxydiamine monomer mixtures were applied onto aluminum, titanium, and gold-coated surfaces. Using various analytical techniques (DSC, FTIR, FTIR-RAS, ICP, and POM) we will show both a chemical sorption of the diamine monomers and a partial dissolution of the surface oxide and/or hydroxide metallic layer. Then, metallic ions diffuse through the liquid monomer layer and react with amine groups to form an organo-metallic complex by coordination bonding. When the complex concentration is higher than its solubility limit, these complexes may partially precipitate to form needle-sharp crystals. The liquid part of the organo-metallic complex forms, with the epoxy prepolymer, a new amorphous network having a lower glass transition temperature. This new biphase material can also contain complex crystals which act as short fibers, randomly dispersed in the polymer matrix or oriented in the vicinity of the polymer/metal interface, inducing an increase of the Young's modulus and a decrease of the elongation at break. By using a three-point flexure test, we have determined the effect of the interphase formation on the practical adhesion before and after hydrothermal aging. Results obtained point out that the epoxy/metal interphase significantly affects the initial practical adhesion. However, formation of organo-metallic complexes greatly improve practical adhesion after aging. The created complexes act as corrosion inhibitors.     

Influence of the fiber surface properties on the mechanical strength of unidirectional fiber composites

The influence of the thermodynamic adhesion between fibers and matrix on the mechanical properties of a continuous fiber reinforced composite is studied for two systems: carbon fiber reinforced poly(ether ether ketone) and glass fiber reinforced poly(ether imide). The fibers are modified chemically and characterized by measuring the contact angle formed by molten resin on the fibers. Various fiber treatments yield a wide range of contact angles, which are determined optically. Unidirectional fiber reinforced laminates are manufactured and transverse flexural strength is measured with the values reported as a function of the specific work of adhesion. It is shown that adhesion at the fiber-resin interface correlates with both the composite strength and the void morphology within the laminate after consolidation.     

Dry coating of talc particles with fumed silica: Influence of the silica concentration on the wettability and dispersibility of the composite particles

Even though dispersion operations have been the object of several investigations, the importance of the various parameters and especially the physicochemical and surface properties are rarely treated. Dry particle coating can be used to create new-generation materials by combining different powders exhibiting different physical and/or chemical properties. In such processes relatively large particles (host particles) are mechanically coated with fine particles (guest particles), without using solvents and subsequent drying, to create new functionalities or to improve initial characteristics. The purpose of this study is to modify the surface of Talc particles by dry coating with different concentrations of hydrophobic Silica (Aerosil R972®), to examine the effect of the coating on the wettability of the coated Talc particles and to study the effects on the dispersibility of these same composite particles. Dry coating is found to modify the surface of Talc particles and to control their wettability and dispersibility in aqueous solutions.     

Wettability and adhesion studies of plasma-treated plastic substrates for gelatin holograms

The feasibility study of using polycarbonate and poly(methyl methacrylate) substrates treated with the oxygen plasma for dichromated gelatin holograms is reported. The contact angles of water on both treated and untreated substrates were measured to indicate the wettability of substrate surfaces. An appreciable increase in adhesion between the dichromated gelatin film and the polycarbonate substrate after the oxygen plasma treatment was demonstrated.     

Adhesion interaction in water/n-alcohol mixtures between silanized silica and polymer particles

The adhesion of polyethylene and nylon particles to silanized silica plates was investigated in water/n-alcohol (methanol, ethanol, 1-propanol, and 1-butanol) mixtures. Silica plates were treated with γ-aminopropyltriethoxysilane, methyltriethoxysilane, and perfluoroethyltrimethoxysilane. The number of particles adhering to the plate at 60 min as an apparent equilibrium adhesion value increased as a result of the silanization of silica and decreased with increasing volume ratio of n-alcohol in the water/n-alcohol mixtures. The acid-base components of the surface free energies of the substrates and liquids were decreased by the silanization of silica and by the addition of cthanol to water. The apparent equilibrium particle adhesion is discussed in terms of the total potential energies of interaction which were calculated as the sum of the electrical double layer, Lifshitz-van der Waals, and acid-base interactions, using the electrokinetic potentials and the surface free energy components. In addition, the relationship between the extent of particle adhesion and the work of adhesion was investigated. The particle adhesion in the present systems was found to be dominated by the acid-base interaction between the particle and the substrate.     

A Comparison of the Work of Adhesion Obtained from Wetting and Vapor Adsorption Measurements

Some of the limitations to determining experimental values of the work of adhesion are discussed. Wetting measurements appear to provide the most direct means of assessing the work of adhesion for a solid-liquid system, but they require the formation of a finite contact angle by the liquid against the solid of interest, and the need for independent knowledge of the equilibrium spreading pressure of the liquid's vapor on the solid further limits their applicability. Vapor adsorption measurement using the technique of inverse gas chromatoraphy (IGC) provides a promising alternative means of determining the work of adhesion not subject to these limitations. The measurements are, furthermore, amenable to solids which are difficult to use with wetting measurements, e.g., those which are porous or granular. An attempt is made here to compare values of the work of adhesion determined using both wetting and vapor adsorption measurements. Good agreement is attained between the two methods for diiodomethane in contact with poly (vinyl chloride), poly (methyl methacrylate), and chemi-thermo-mechanical wood pulp fibers, suggesting that the technique of IGC is particularly well-suited for rapid determination of the work of adhesion.     

A Comparison of the Work of Adhesion Obtained from Wetting and Vapor Adsorption Measurements

Some of the limitations to determining experimental values of the work of adhesion are discussed. Wetting measurements appear to provide the most direct means of assessing the work of adhesion for a solid-liquid system, but they require the formation of a finite contact angle by the liquid against the solid of interest, and the need for independent knowledge of the equilibrium spreading pressure of the liquid's vapor on the solid further limits their applicability. Vapor adsorption measurement using the technique of inverse gas chromatoraphy (IGC) provides a promising alternative means of determining the work of adhesion not subject to these limitations. The measurements are, furthermore, amenable to solids which are difficult to use with wetting measurements, e.g., those which are porous or granular. An attempt is made here to compare values of the work of adhesion determined using both wetting and vapor adsorption measurements. Good agreement is attained between the two methods for diiodomethane in contact with poly (vinyl chloride), poly (methyl methacrylate), and chemi-thermo-mechanical wood pulp fibers, suggesting that the technique of IGC is particularly well-suited for rapid determination of the work of adhesion.     

Molecular dynamic modeling of interfacial energy

Molecular dynamic modeling is used to calculate the changes in the energy between two surfaces when the surfaces are first allowed to approach one another and, subsequently, separated. The equations of motion of the atoms, which were assumed to interact via a Lennard-Jones potential, were integrated using Verlet's algorithm. They were implemented in an environment of periodic boundary conditions, feedback loop temperature and pressure controllers, with direct computation of the stress and strain tensors. This approach allows one to calculate the temperature dependence of the 'leap-to-contact' phenomenon, the thermodynamic work of adhesion, the work needed to separate the surfaces, and the forces of attraction and separation. Effects that occur during approach and separation, such as surface roughening and vacancy formation, were included in the energetics calculations. Sound waves and the resulting thermal transients were also modeled. The adhesion hysteresis and irreversible behaviors during approach and separation that arise from these calculations are discussed in detail.