On Neglecting the Polar Nature of Halogenated Hydrocarbons in the Surface Energy Determination of Polar Solids from Contact Angle Measurements

The generally accepted strategy of neglecting the polar nature of halogenated liquids in the surface energy determination using the Lifshitz-van der Waals/Lewis acid-base (LW/AB) approach may lead to erroneous and inconsistent results for polar solids. This was demonstrated in a simulation study carried out on monopolar basic surfaces using water, glycerol, and hypothetical liquids whose surface energy characteristics (gamma(L)(LW)=50 mJ/m(2), gamma(L)(-)=0, and gamma(L)(+)=0-1 mJ/m(2)) were chosen to approximate halogenated hydrocarbons. Neglect of the liquid polarity overestimates the LW component and underestimates the basic parameter of the solid surface energy. This effect increases rapidly with an increase in the actual (nonzero) gamma(L)(+) value of supposedly apolar liquid. Consequently, results with an appropriate level of precision can be obtained only with liquids having gamma(L)(+)<0.02 mJ/m(2). For liquids having gamma(L)(+) approximately 0.5 mJ/m(2) (diiodomethane, s-tetrabromoethane, and, probably, other halogenated hydrocarbons), neglect of the liquid polarity causes errors up to 15% in the LW component and up to 100% in the basic parameter of the solid surface energy. The quantitative trends established in the simulation study were indeed observed in an experimental study performed on the surfaces of poly(methyl methacrylate) and polystyrene using water, glycerol, and diiodomethane or s-tetrabromoethane as the test liquids. Copyright 2000 Academic Press.     

Surface characterization of poly(lactic acid) and polycaprolactone by inverse gas chromatography

Inverse gas chromatography (IGC) has been used to characterise the surface properties of polycaprolactone (PCL) and poly(lactic acid) (PLA). The dispersive component of the surface free energy (gamma(S)(D)) was found to be very small for both of them--values close to 30 mJ/m(2) in the case of the PLA and ca. 40 mJ/m(2) for the PCL. The retention times of the n-alkanes, necessary to calculate the dispersive component of the surface energy, were obtained from the maximum, the centre at half height and the centre of mass of the chromatographic peak. While the values obtained using the first two parameters appear not to be affected by the peak asymmetry, in spite of having been obtained above the glass transition temperature of the polymer, the values obtained using the latter have been found to be not reliable. The drawbacks of using n-alkanes with a very small retention time have also been discussed, estimating the error it can introduce in the final results. Finally, the acid-base properties of the two biopolymers were determined using the approaches suggested by Schultz et al. and by St. Flour and Papirer. Although both methods describe the surfaces of PLA and PCL as neutral ones, differences between the values of the parameters K(A), K(D) and S(C) were obtained.     

反相气相色谱法表征1-烯丙基-3-甲基氯代咪唑离子液体的表面性质

采用反相气相色谱(IGC)技术研究了不同温度下1-烯丙基-3-甲基氯代咪唑(［AMIM］Cl)的表面性质。以正己烷、正庚烷、正辛烷和正壬烷作为非极性探针分子测定［AMIM］Cl在343.15、353.15、363.15和373.15 K温度下的表面色散自由能;以二氯甲烷、三氯甲烷、丙酮、乙酸乙酯、四氢呋喃作为极性探针分子测定离子液体Lewis酸碱性质,并测定了吸附自由能和吸附自由焓变等热动力学参数。实验结果表明,［AMIM］Cl的酸解离平衡常数Ka为0.34,碱解离平衡常数Kb为1.68,其表面呈Lewis两性偏碱性特点。在343.15、353.15、363.15和373.15 K温度下,［AMIM］Cl的表面色散自由能分别为52.26、50.82、46.08和42.05 mJ/m2。这一结果对研究离子液体的表面性质及应用有指导作用。     

Surface energy of ethylene-co-1-butene copolymers determined by contact angle methods

Wilhelmy plate measurements of contact angles with a series of test liquids are used to calculate the surface energies of two poly(ethylene-co-1-butene) random copolymers. Results from five methods of calculation are reported: one-liquid (Good-Girifalco and Neumann), two-liquid (harmonic mean and geometric mean), and three-liquid (Lifshitz-van der Waals acid-base) methods. We find that all five methods are sensitive to the choice of test liquids used for contact angle measurements, as previously reported, but consistent results are obtained if recommended combinations of liquids are used. The mean results of the three-liquid acid-base method are judged to be the most reliable and informative, leading to surface energies of 30.8 mJ/m2 for poly(ethylene-co-1-butene) copolymer composed of 92 mol% ethylene and 30.2 mJ/m2 for copolymer composed of 88 mol% ethylene.     

Determination of dispersive and nondispersive components of the surface free energy of glass fibers

The dispersive component _s ^d of the surface free energy of glass fibers and its interaction energy with alkanes, benzene, 1-nitropropane, ethyleneglycol, glycerol, formamide, and water were quantitatively determined by the tensiometric method within two liquids. The values of nondispersive interaction energy I _SL ^p were found to be a linear function of the square root of the nondispersive component of the surface free energy of liquids. This suggests that the nondispersive interaction energy may be represented by the geometric mean of the nondispersive component of the surface free energy of a solid and a liquid. The slope gave the nondispersive component _s ^p of the surface free energy. The _s ^p values are 33 and 14 mJ/m² for the untreated and aminosilane-treated fibers, respectively, suggesting that organophilic character has developed on the surface after aminosilane treatment. The _s ^p value was almost similar after the treatment, probably because of the polar characteristics of amino groups.     

Thermoresponsive poly(N-isopropylacrylamide) copolymers: contact angles and surface energies of polymer films

Surface properties of poly(N-isopropylacrylamide) (PNIPAM) copolymer films were studied by contact angle measurements and optical and atomic force microscopy. We prepared a series of copolymers of N-isopropylacrylamide with N-tert-butylacrylamide (NtBA) in order of increasing hydrophobicity. The measurements of the advancing contact angle of water at 37 degrees C were hampered by the observation of a distinct stick/slip pattern on all polymers in the series with the exception of poly(NtBA) (PNtBA). We attributed this behavior to the film deformation by the vertical component of liquid surface tension leading to the pinning of the moving contact line. This was confirmed by the observation of a ridge formed at the pinned contact line by optical microscopy. However, meaningful contact (without the stick/slip pattern and with a time-independent advancing contact angle) angles for this thermoresponsive polymer series could be obtained with carefully selected organic liquids. We used the Li and Neumann equation of state to calculate the surface energy and contact angles of water for all polymers in the series of copolymers and van Oss, Chaudhury, and Good (vOCG) acid-base theory for PNtBA. The surface energies of the thermoresponsive polymers were in the range of 38.9 mJ/m2 (PNIPAM) to 31 mJ/m2 (PNtBA) from the equation of state approach. The surface energy of PNtBA calculated using vOCG theory was 29.0 mJ/m2. The calculated contact angle for PNIPAM (74.5 +/- 0.2 degrees ) is compared with previously reported contact angles obtained for PNIPAM-modified surfaces.     

Use of inverse gas chromatography to characterize cotton fabrics and their interactions with fragrance molecules at controlled relative humidity

The present work focused on the surface characterization and fragrance interactions of a common cotton towel at different relative humidities (RHs) using inverse gas chromatography (IGC) and dynamic vapour sorption. The sigmoidal water sorption isotherms showed a maximum of 16% (w/w) water uptake with limited swelling at 100% RH. This means that water interacts strongly with cotton and might change its initial physico-chemical properties. The same cotton towel was then packed in a glass column and characterized by IGC at different relative humidities, calculating the dispersive and specific surface energy components. The dispersive component of the surface energy decreases slightly as a function of relative humidity (42 mJ/m2 at 0% RH to 36 mJ/m2 at 80% RH) which would be expected from swelling of the humidified cotton. The Gutmann's donor constant Kd increased from 0.28 kJ/mol at 0% RH to 0.42 kJ/mol at 80% RH, indicating that a greater hydrophilic surface exists at 80% RH, which is also as expected. Water, undecane and four fragrance molecules (dimetol, benzyl acetate, decanal and phenylethanol) were used to investigate cotton-fragrance interactions between 0 and 80% RH. The adsorption enthalpies and the Henry's constants were calculated and are discussed. The higher values for the adsorption enthalpies of polar molecules such as dimetol and phenylethanol suggest the presence of hydrogen bonds as the main adsorption mechanism. The Henry's constant of dimetol was also determined by headspace gas chromatography measurements at 20% RH, giving a similar value (230 nmol/Pa g by IGC and 130 nmol/Pa g by headspace GC), supporting the usefulness of IGC for such determinations. This work confirms the usefulness of chromatographic methods to investigate biopolymers such as textiles, starches and hairs.     

Surface properties and structures of diblock copolymer and homopolymer with perfluoroalkyl side chains

The surface free energy of diblock copolymer, composed of methyl methacrylate and 2-perfluorooctylethyl methacrylate (PMMA-b-PFEMA), was compared with that of PFEMA homopolymer (P-PFEMA) in correlation with their structures in the solid state and in the solution using dynamic contact angle, X-ray photoelectron spectroscopy, X-ray diffraction, and dynamic light scattering. The PMMA-b-PFEMA film cast from chloroform solution was found to possess very low surface free energy (7.8 mJ/m(2)) compared with the surface free energies of the P-PFEMA (8.5 mJ/m(2)) and the PMMA-b-PFEMA (9.8 mJ/m(2)) films cast from CF(3)CF(2)CHCl(2) solutions. These differences in the surface free energy were brought about by the variations in their surface structures. The very low surface free energy was considered to have originated from the surface segregation of the PFEMA segments highly self-assembled by the presence of chloroform.     

反相气相色谱法研究1,3,5-三氨基-2,4,6-三硝基苯的表面特性

采用反相气相色谱技术(IGC)研究了4种不同粒度的1,3,5-三氨基-2,4,6-三硝基苯(TATB)的表面性质。4种不同粒度的TATB表面自由能的色散分量（γds）随着温度的升高而增加;粒度越大的粒子,其色散自由能上升越快;在较高温度下,粗颗粒TATB显示了更强的色散作用(γds=193.2 mJ/m2,353 K),粒度最小的亚微米TATB显示了最弱的色散作用(γds=64.0 mJ/m2,353 K)。由于制备方法不同和粒子大小的差异,4种TATB的表面酸碱性质显示了明显的差别,细颗粒TATB表面有较强的亲电子特性;而其他3种TATB在极性探针分子的作用下的吸附均表现为吸热吸附,表现出在分子内和分子间具有强烈的相互作用,其Ka和Kb值均为负。     

聚苯并咪唑-锂盐-聚乙二醇单甲醚共混全固态聚合物电解质的制备及性能

使用共混后浇铸成膜的方法,制备了聚苯并咪唑-锂盐-聚乙二醇单甲醚组成的锂离子电池共混全固态聚合物电解质。通过傅里叶红外光谱(FT-IR)、X射线衍射(XRD)、差示扫描量热(DSC)、拉伸与交流阻抗测试表征了共混全固态电解质的结构与性能。研究了不同锂盐以及各组分含量对共混全固态电解质的力学性能与电导率的影响。结果表明:聚苯并咪唑与聚乙二醇单甲醚之间存在氢键;共混全固态电解质中聚乙二醇单甲醚处于无定形态;锂盐的加入使聚乙二醇单甲醚的玻璃化转变温度下降;聚乙二醇单甲醚含量越高,共混膜强度越低,电导率越高,并且使用三氟甲磺酸锂作为锂盐时其电导率最高,室温下可以达到3.58×10~(-5) S/cm,高温下可以达到3.3×10~(-3) S/cm,高温下满足对锂离子电池的使用需求。     

反气相色谱法测定苯乙烯-氧乙烯-苯乙烯三嵌段聚合物的表面能

 采用反气相色谱法测定了苯乙烯 氧乙烯 苯乙烯三嵌段聚合物 (PS PEO PS)的色散成分的表面能 (γsd) ,研究探讨了温度及嵌段聚合物链段结构组成对γsd 的影响 ,并确定了γsd 与温度的数学关系式。研究结果表明 :在 70℃～ 12 0℃范围内 ,PS PEO PS的表面能较低 ;随着PS PEO PS表面组成中氧乙烯 (EO)成分的增加 ,色散成分的γsd 增大 ,且对温度的变化极其敏感 :随温度的升高 ,γsd 急剧地呈线性下降。     

Kb/Ka X-ray intensity ratios in calcium and potassium compounds

Summary Kb/Ka X-ray intensity ratios of some K and Ca compounds were studied. The samples were excited with 59.5 keV g-rays emitted from 75 mCi ²⁴¹Am radioisotope source and characteristic K X-ray from the samples were counted by means of an Si(Li) detector which has a resolution 155 eV at 5.9 keV. We found that Kb/Ka X-ray intensity ratios are changed by chemical effect for different K and Ca compounds. The experimental values were compared with the calculated theoretical values for elemental K and Ca.     

Effect of intermolecular hydrogen bonding on low-surface-energy material of poly(vinylphenol)

We discovered that poly(vinylphenol) (PVPh) possesses an extremely low surface energy (15.7 mJ/m2) after a simple thermal treatment procedure, even lower than that of poly(tetrafluoroethylene) (22.0 mJ/m2) calculated on the basis of the two-liquid geometric method. Infrared analyses indicate that the intermolecular hydrogen bonding of PVPh decreases by converting the hydroxyl group into a free hydroxyl and increasing intramolecular hydrogen bonding after thermal treatment. PVPh results in a lower surface energy because of the decrease of intermolecular hydrogen bonding between hydroxyl groups. In addition, we also compared surface energies of PVPh-co-PS (polystyrene) copolymers (random and block) and their corresponding blends. Again, these random copolymers possess a lower fraction of intermolecular hydrogen bonding and surface energy than the corresponding block copolymers or blends after similar thermal treatment. This finding provides a unique and easy method to prepare a low-surface-energy material through a simple thermal treatment procedure without using fluoro polymers or silicones.     

Analysis of different approaches for evaluation of surface energy of microbial cells by contact angle goniometry

Microbial adhesion on solid substrate is important in various fields of science. Mineral-microbe interactions alter the surface chemistry of the minerals and the adhesion of the bacterial cells to mineral surface is a prerequisite in several biobeneficiation processes. Apart from the surface charge and hydrophobic or hydrophilic character of the bacterial cells, the surface energy is a very important parameter influencing their adhesion on solid surfaces. There were many thermodynamic approaches in the literature to evaluate the cells surface energy. Although contact angle measurements with different liquids with known surface tension forms the basis in the calculation of the value of surface energy of solids, the results are different depending on the approach followed. In the present study, the surface energy of 140 bacterial and seven yeast cell surfaces has been studied following Fowkes, Equation of state, Geometric mean and Lifshitz-van der Waals acid-base (LW-AB) approaches. Two independent issues were addressed separately in our analysis. At first, the surface energy and the different components of the surface energy for microbial cells surface are examined. Secondly, the different approaches are evaluated for their internal consistency, similarities and dissimilarities. The Lifshitz-van der Waals component of surface energy for most of the microbial cells is realised to be approximately 40 mJ/m2 +/-10%. Equation of state and Geometric mean approaches do not possess any internal consistency and yield different results. The internal consistency of the LW-AB approach could be checked only by varying the apolar liquid and it evaluates coherent surface energy parameters by doing so. The electron-donor surface energy component remains exactly the same with the change of apolar liquid. This parameter could differentiate between the Gram-positive and Gram-negative bacterial cells. Gram-negative bacterial cells having higher electron-donor parameter had lower nitrogen, oxygen and phosphorous content on their cell surfaces. Among the four approaches, LW-AB was found to give the most consistent results. This approach provides more detailed information about the microbial cell surface and the electron-donor parameter differentiates different type of cell surfaces.     

Glass bead grafting with poly(carboxylic acid) polymers and maleic anhydride copolymers

Glass beads were etched with acids and bases to increase the surface porosity and the number of silanol groups that could be used for grafting materials to the surfaces. The pretreated glass beads were functionalized using 3‐aminopropyltriethoxysilane (APS) coupling agent and then further chemically modified by reacting the carboxyl groups of carboxylic acid polymers with the amino groups of the pregrafted APS. Several carboxylic acid polymers and poly(maleic anhydride) copolymers, such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), poly(styrene‐alt‐maleic anhydride) (PSMA), and poly(ethylene‐alt‐maleic anhydride) (PEMA) were grafted onto the bead surface. The chemical modifications were investigated and characterized by FT‐IR spectroscopy, particle size analysis, and tensiometry for contact angle and porosity changes. The amount of APS and the different polymer grafted on the surface was determined from thermal gravimetric analysis and elemental analysis data. Spectroscopic studies and elemental analysis data showed that carboxylic acid polymers and maleic anhydride copolymers were chemically attached to the glass bead surface. The improved surface properties of surface modified glass beads were determined by measuring water and hexane penetration rates and contact angle. Contact angles increased and porosity decreased as the molecular weights of the polymer increased. The contact angles increased with the hydrophobicity of the attached polymer. The surface morphology was examined by scanning electron microscopy (SEM) and showed an increase in roughness for etched glass beads. Copyright © 2007 John Wiley & Sons, Ltd.     

Surface free energy of polyurethane coatings with improved hydrophobicity

The polarity of polyurethane coats was studied on the basis of the goniometric method for determination of wetting angle values, on the basis of calculated surface free energy (SFE) values by the van Oss-Good and Owens-Wendt methods, and on the basis of polarity measurements with the use of the (1)H NMR spectra. Test polyurethanes were synthesised in the reaction of methylene diphenyl 4,4'-diisocyanate (MDI) or 3-izocyanatomethyl -3,5,5- trimethylcyclohexyl isocyanate (IPDI) and polyoxyethylene glycols or polyesters poly(ε-caprolactone) diols and poly(ethyleneadipate) diol with different molecular weights, and some diols as chain extenders, in dioxane. The type of raw material was found to significantly affect the phase structure of the obtained polyurethane elastomers and to control physical interactions within those structures, thus influencing the SFE values. Fundamental reduction in the SFE value of a coating below 28?mJ/m(2) was achieved by the use of 2,2,3,3-tetrafluoro-1,4-butanediol as the urethane prepolymer chain extender.     

氟硅协同改性丙烯酸树脂的合成与防污性能研究

以甲基丙烯酸十二氟庚酯(FMA)、甲基丙烯酸聚二甲基硅氧烷基酯(SMA)、甲基丙烯酸甲酯、丙烯酸正丁酯、甲基丙烯酸正丁酯和丙烯酸乙酯为共聚单体,通过溶液聚合反应合成出侧链含有机氟、有机硅的丙烯酸树脂.通过核磁共振氢谱(1H-NMR)、核磁共振氟谱(19F-NMR)、红外光谱(FTIR)对聚合物的结构进行了表征.通过扫描电镜(SEM)、接触角测试和生物评价等方法,探讨了FMA、SMA含量对树脂涂膜性能的影响.结果表明氟硅改性的丙烯酸树脂比单独含氟或含硅改性的丙烯酸树脂具有更低的表面能,而且氟硅改性的丙烯酸树脂涂膜比商业化的聚硅氧烷涂膜具有更好的防污性能.     

Surface and thermodynamic characterization of conducting polymers by inverse gas chromatography. I. Polyaniline

The surface thermodynamic characteristics of both doped polyaniline (PANI-HEBSA) and the non-conducting form (PANI-EB) were investigated using inverse gas chromatography. Fourteen solutes were injected into two separate chromatographic columns containing PANI-EB and PANI-HEBSA. All solutes interacted strongly with the conducting form PANI-HEBSA; in particular, undecane and dodecane showed stronger interaction due to the increase of the dispersive forces. Methanol and ethanol showed stronger H-bonding with the conducting form than propanol and butanol. A curvature was observed for acetates and alcohols with a maximum of around 145 degrees C as an indication of a phase change from a semicrystalline to amorphous phase. DeltaH(l)s value increased considerably (-3.35 to -46.44 kJ/mol) while the deltaH(l)s for the undoped PANI (PANI-EB) averaged about -0.03 kJ/mol. PANI-EB-alkane interaction parameters were measured and ranged from +0.40 to +1.50 (endothermic). However, PANI-HEBSA showed an exothermic behavior due to the polar surface (-1.50 to +1.2). Interaction parameters decreased as the temperature increased and are characteristic of the strong interaction. The dispersive surface energy of the non conducting PANI-EB ranged from 29.13 mJ/m2 at 140 degrees C to 94.05 mJ/m2 at 170 degrees C, while the surface energy of the conducting PANI-HEBSA showed higher values (150.24 mJ/m2 at 80 degrees C to 74.27 mJ/m2 at 130 degrees C). Gamma(s)d values for PANI-EB were found to be higher than expected. The trend of the gamma(s)d change direction is also surprising and unexpected due to the thermal activation of the surface of the polymer and perhaps created some nano-pores resulting in an increase in surface energy of the non-conducting form.     

Surface modification of glass beads with poly(acrylic acid)

Non‐porous P₂ glass beads were etched with sodium hydroxide to increase the number of silanol groups that could be used to modify the surface. The etched glass beads were then functionalized with 3‐aminopropyltriethoxysilane (APS) and/or glycidoxypropyltrimethoxysilane (GPS). The surface of the glass beads were further modified with poly(acrylic acid) (PAA) by reacting the carboxyl groups on PAA with the amino groups of the pregrafted APS. The chemical modifications were characterized by FT‐IR spectroscopy, particle size analyzer and tensiometry for contact angle and porosity measurements. Five different molecular weight PAA polymers ranging from 2000 to 3,000,000 were grafted with less than expected increase of grafted PAA with molecular weight. The amount of APS and PAA on the surface was determined from thermogravimetric analysis and elemental analysis data. The surface properties of the surface modified glass beads were determined by measuring water and hexane penetration rate and contact angle. The surface morphology was examined by scanning electron microscopy. Copyright © 2006 John Wiley & Sons, Ltd.     

Study of a core-shell type impact modifier by inverse gas chromatography

Inverse gas chromatography (IGC) has been used to study the Lewis acid-base properties of a technologically and commercially important core-shell type elastomer (MBS rubber). The parameters determined were the dispersive component of the surface tension, the surface free energy, the enthalpy and the entropy of adsorption of polar and apolar probes, the surface Lewis acidity constant (Ka), and the surface Lewis basicity constant (Kb). The results show that the MBS rubber is amphoteric but strongly Lewis basic. It is weakly Lewis acidic. The results are in accord with the analysis of the molecular structure of PMMA, the shell component of this impact modifier (IM). The interactivity of this elastomer with the remaining materials in multicomponent polymeric systems is expected to be strongly influenced by the particular surface energetic properties of the MBS rubber. The results presented would contribute to the interpretation, forecast and optimization of the adhesion properties and phase preferences shown by this impact modifier when incorporated in such complex polymeric systems as polymer blends and composites.