A New Equation between Surface Tensions and Solubility Parameters without Molar Volume Parameters Simultaneously Fitting Polymers and Solvents

Both surface tension and solubility parameter are decided by molecular interactions. There are several empirical equations describing their connection. However, at least two limitations exist for them: polymers cannot be treated and only apolar or weakly polar solvents can be fitted. We found when only the dispersive properties were considered, for 37 solvents and 22 polymers, a linear relationship exists between γ ^d and γ/δ^2/3 _d , fitted by a new equation. Compared with the previous equations, the value of the new equation is that most solvents and common polymers could be treated simultaneously. This equation will be of value for estimating the accuracy of reported surface tension data or solubility parameters of polymers.     

Relationship between Dispersive Surface Tension and Density and Molecular Weight of Solvents and Polymers

The surface and interfacial properties of polymers are important for their applications. Generally, the surface property is quantitatively characterized by the surface tension or surface tension component parameters, which are obtained with the contact angle technique. However, the contact angle technique has an inherent problem, contact angle hysteresis phenomenon, which will result in many incredible surface tension data. In order to find a simple and easy method to estimate the rationality of a surface tension result, the relationship between dispersive surface tension component and density and molecular weight is researched in this work. It is found that for 30 organic solvents, there is a good relationship between the dispersive surface tension r^d and the parameter . In addition, for 12 polymers, when the molecular weight is replaced with the molecular weight of the repeat unit, there is still the same relationship as for small liquids. However, because it is difficult to judge the accuracy of the published dispersive data of the polymers, the found experiential relationship needs further confirmation, requiring more reliable published data.     

Monte Carlo Simulations of Chain Dimensions and Conformational Properties of Various Poly(n-alkyl methacrylates) in Solution

Rotational Isomeric State (RIS) Metropolis Monte Carlo (RMMC) simulations of the conformational properties and chain dimensions of a series of chemically different poly(n-alkyl methacrylates) including poly(methyl methacrylate), poly(n-butyl methacrylate), poly(n-hexyl methacrylate), and poly(phenyl methacrylate), in the θ state were investigated, and (〈r²〉/M)^1/2, (〈s²〉/M)^1/2 and C _n were calculated and compared in order to obtain fundamental understanding of the influence of the chemical structure. Simulations were conducted for different molecular weights. Results obtained from the simulations are compared with experimentally obtained dimensions in the literature using the Mark-Houwink relationship as well as, in some cases, data available from direct determinations in θ solvents. Good agreement between simulation and experimental data was obtained. The backbone conformation is predominantly trans in these polymers. Increase in bulkiness and rigidity of the substituting acrylate side group results in an increase in trans and a decrease in gauche backbone conformer population. In the case of rotatable bonds in the side-group structure, increase in rigidity of the side group leads to a decrease in the trans population, although this effect is not uniformly observed.     

Relationship between Hansen Solubility Parameters and Lewis Acid–Base Parameters of Polymers

Hansen solubility parameters and Lewis acid–base parameters are two groups of parameters that are used to characterize solvents, polymers, and the interactions between polymer matrix and additives. Although their definitions are very different, they can well explain the interactions in polymer composites. Therefore, some relations should exist between them. In this paper, the Lewis acid–base parameters of three polymers (PET, PS, and PVA) were measured by IGC technique. Including five other polymers (PE, PMMA, PC, PVC, and PVDF), the relationship between total Lewis acid–base intensity (K _a+K _b) and total polar intensity (δ² _p+δ² _h) of the eight kinds of polymers are discussed, where δ_p and δ_h are the polar components of the Hansen parameters. It is found that these polymers are all Lewis base polymers according to the values of K _b/K _a. Generally, a polymer with a larger (K _a+K _b) value possesses a higher (δ² _p+δ² _h) value.     

Methods to determine surface energies of natural fibres: a review

To tailor the interaction across composite interfaces especially for the development of green composites, i.e. composites made completely from renewable materials, information about the fibre surfaces is required. We review the current state of the art of methods to determine the surface tension of natural fibres and discuss the advantages and disadvantages of techniques used. Although numerous techniques have been employed to characterise surface tension of natural fibres, it seems that commonly used wetting techniques are very much more affected by the non-ideal character of natural fibres. Inverse Gas Chromatography (IGC) is a much better suited technique to determine the surface energetic properties of natural fibres than wetting techniques. The surface tension of natural reinforcements, determined using IGC, was reported for nanosized bacterial cellulose as well as bamboo, cornhusk, flax, hemp and sisal, covering a wide range of cellulose content. The effect of methods to separate/extract fibres from the plants as well as of a few surface modification procedures on the fibre surface properties is also reviewed. The dispersive part of the natural fibre surface tension γ ^d _S varies from 32 to 61 mJ/m². The fibre surface tension increases with increasing cellulose content of natural fibres. We also found that a higher basicity (Donor Number, K _B to Acceptor Number, K _Aratio) was observed for fibres containing more cellulose. This may be reflective of higher crystalline cellulose content in the surfaces of the fibres, as only the ether linkage of the cellulose is labile for hydrogen bonding.     

Li2O-2B2O3熔体的物性研究

系统测量了四硼酸锂(Li₂Ｏ-２Ｂ_２Ｏ_３)熔体的密度ρ、表面张力γ随着温度的变化规律，实验结果表明在1100K到1500K范围内Li₂Ｏ-２Ｂ_２Ｏ_３高温熔体的密度和表面张力随着温度的升高均线性减小.通过实验数据拟合得出熔体密度与温度关系为ρ(T)=2.574—4.89×１０^－４T，熔点处Li₂Ｏ-２Ｂ_２Ｏ关键词： 功能晶体 四硼酸锂 密度 表面张力     

Intrinsic and Extrinsic Temperature-Dependency of Viscosity-Sensitive Fluorescent Molecular Rotors

Molecular rotors are a group of environment-sensitive fluorescent probes whose quantum yield depends on the ability to form twisted intramolecular charge-transfer (TICT) states. TICT formation is dominantly governed by the solvent’s microviscosity, but polarity and the ability of the solvent to form hydrogen bonds play an additional role. The relationship between quantum yield ϕ _F and viscosity η is widely accepted as a power-law, f_F = C ·h^x\phi_F = C \cdot \eta ^x. In this study, we isolated the direct influence of the temperature on the TICT formation rate by examining several molecular rotors in protic and aprotic solvents over a range of temperatures. Each solvent’s viscosity was determined as a function of temperature and used in the above power-law to determine how the proportionality constant C varies with temperature. We found that the power-law relationship fully explains the variations of the measured steady-state intensity by temperature-induced variations of the solvent viscosity, and C can be assumed to be temperature-independent. The exponent x, however, was found to be significantly higher in aprotic solvents than in protic solvents. We conclude that the ability of the solvent to form hydrogen bonds has a major influence on the relationship between viscosity and quantum yield. To use molecular rotors for the quantitative determination of viscosity or microviscosity, the exponent x needs to be determined for each dye-solvent combination.     

Chemical effects in C60 irradiation of polymers

The C₆₀ erosion behaviour of poly(methyl)methacrylate (PMMA), poly(α-methyl)styrene (PAMS) and polystyrene (PS) has been studied at various temperatures and compared with that under Ga⁺ irradiation. Strong variations of erosion yields are observed, indicating that chemical degradation mechanisms are operating. In particular, our results suggest that fast depolymerization mechanisms are important in leaving the surface of the sputter crater virtually undamaged. Since such mechanisms are connected with the chemical nature of the polymer, the possibility of performing molecular depth profiling of polymers with C₆₀ appears to depend strongly on the chemical nature of the system under study.     

Mössbauer studies of iron stabilised polymethacrylates

Polymethyl methacrylate (PMMA), polyethyl methacrylate (PEMA) and polybutyl methacrylate (PBuMA) containing ferric chloride and ferrous sulphate as stabilisers, were prepared by free radical polymerization. Mössbauer spactra of ferrous sulphate stabilised polymers don't show any change in the value of isomer shift (1.30 mm/s) while quadrupole splitting values are quite different from those for pure ferrous sulphate. This indicates that environment of Fe²⁺ moiety changes in polymers and thus stabilises the polymers. In case of ferric chloride stabilised polymers the isomer shift values don't differ significantly for different polymethacrylates but quadrupole splitting values increase from polymethyl methacrylate to polybutyl methacrylate. The TGA analysis shows that the inclusion of iron salts stabilises the polymers by 40°C (approx.) and at higher temperatures α-Fe₂O₃ is formed.     

Isochoric temperature coefficient of surface tension andS o-parameter of quasi-spherical molecular liquids

The Sharma parameterS _o which is characteristic of molten alkali halides and polymers has also been shown to be characteristic of a wide variety of liquids. Calculated data using the volume expansivity of the liquid establish the constancy of theS _o-parameter which retains, on an average, a constant value of 1·11 for quasi-spherical molecular liquids. It is shown thatS _o-parameter is also related to volume expansivity of the surface layer of the liquid, temperature coefficient of surface tension of liquids and describes the temperature and volume or pressure dependence of thermodynamic Grüneisen parameter and isochoric heat capacity with significant contribution for influencing the thermoacoustic and surface tension properties of liquids.     

Solid-liquid phase transition in small water clusters: a molecular dynamics simulation study

Water clusters, (H₂O) _n , of varying sizes (n = 8, 12, 16, 20, 24, 28, 32, 36, and 40) have been studied at different temperatures from 0 to 200 K using molecular dynamics simulations. Transitions between solid and liquid phases were investigated to estimate the melting temperature of the clusters. Although the melting temperatures showed non-monotonic behaviour as a function of cluster size, their general tendency follows the classical relationship T _m ∝ n ^?1/3 to the cluster size n. Moreover, it was observed that the liquid-solid surface tension decreased with the cluster size in a similar way to the liquid-vapour surface tension in bulk water. Upon cooling, ice-like crystals were formed from the smaller clusters with n up to 20, while the larger clusters were transformed to glassy structures. The decrease in the glass transition temperature with the cluster size was observed to be much less than the corresponding melting temperature. The mutual order of the melting and glass-transition temperatures were found to be reversed compared with that observed for bulk water.     

Chemical hardness-based prediction of the surface tension and enthalpy changes of sublimation for alkali halides

A new theoretical route employing the concept of chemical hardness has been developed to predict the surface tension γ and the changes of the standard enthalpies (CSEs) of sublimation Δ_sH⁰ of alkali halides. The values of these quantities have been calculated by means of the ratios η_M/V^1/3_m where η_M and V_m are the molecular hardness and molecular volume, respectively. The obtained results have been compared with those of previous theoretical models as well as with experimental data.     

Laser-induced optical recording in thin films

A model is presented to describe the hole opening in ablative optical recording. The model accounts for changes in geometry of the sensitive film, for adhesion of the film to the substrate, for surface tension gradients in the sensitive film and for evaporation or sublimation at the film-substrate interface. The changes in geometry during hole opening are shown to be responsible for an energy barrierF _act=10^?16 to 10^?15 J, corresponding to 1.5–6J/cm³ which is much too large to make thermal activation of hole opening possible.F _act is reduced by surface tension gradients in the liquid film and/or evaporation at the filmsubstrate interface. The predictions of the model are compared with laser recording experiments performed with Te-alloy films on various polymer sublayers. Experiments and model show that the threshold energyE _th for hole opening (andF _act) can be reduced by (i) lowering the surface tension and/or polarity of the polymer sublayer, (ii) reducing the dynamic work of adhesion, e.g. by decreasing the crosslink density or the mean molecular weight of the sublayer, and (iii) increasing the concentration of low molecular weight material in the sublayer, which reduces the adhesion of the film and stimulates evaporation at the interface.     

Model properties relevant to laser ablation of moderately absorbing polymers

A set of polymers including biopolymers and polymers from renewable resources are studied, with attention paid to their capability to form a foamy surface layer by laser irradiation. A model of laser-induced pressure wave is discussed, with its tensile tail giving rise to a fast and dense nucleation of cavities that can expand to microbubbles when filled with ablation gas. The intensity of the pressure wave has a maximum for an absorption coefficient of ∼1000 cm⁻¹. Polyvinyl acetate, studied as a prototype polymer experimentally and by modeling, allows discussing the role of the viscosity drop in the dynamics of the laser-induced cavitations. In the Zeldovich frequency factor, a T (temperature) and P (pressure) dependent model of viscosity, and a T-dependent model of surface tension are introduced. It is further suggested that the well-known free-volume nanoholes existing in the material before the irradiation can constitute the nuclei of importance and that their concentration is one of the factors controlling the pre-exponential factor in the nucleation rate law.     

Determination of the Solubility Parameter of Epoxidized Soybean Oil by Inverse Gas Chromatography

The thermodynamic parameters of epoxidized soybean oil (ESO) were determined by means of inverse gas chromatography (IGC) in the temperature range of 303.15 K-343.15 K. Two groups of probe solvents with different chemical natures and polarities were used to obtain information about ESO. The thermodynamic parameters—such as molar heat of sorption, weight fraction activity coefficient, Flory–Huggins interaction parameter, and partial molar heat of mixing—were obtained to judge the interactions between ESO and solvents at the studied temperatures. Also, the solubility parameters of ESO were found by plotting the graph of δ₁ ²/(RT) – χ^∞ ₁₂/V₁ vs. solubility parameters, δ₁, of the probes. The results showed that the selected solvent ethyl acetate was a moderate solvent for ESO; n-hexane was a moderate (but close to a better) solvent; while the probes n-heptane, n-octane, n-nonane, and chloroform were excellent solvents. From the extrapolation to 298 K, the solubility parameter value of ESO was 16.70 (J/cm³)^0.5.     

Ni-15%Mo合金熔体热物理性质的Monte Carlo模拟

采用EAM势对6×6×6的Ni-15%Mo合金熔体进行Monte Carlo模拟,通过对不同温度下获得的NVT系统的平衡态统计分析得出Ni-15%Mo合金熔体在过冷态和过热态时的热物理性质.通过构造系统生成新表面,表面张力做功使系统能量发生改变,从而得到液态表面张力的模拟结果.Ni-15%Mo合金熔体的表面张力在1500—2000 K的温度范围内,随温度的变化规律为σ=1.918-1.130×10^-3（T-T_m） N/m 关键词： Monte Carlo模拟 表面张力 比热 Ni-15%Mo合金     

Preparation of Polypropylene/Glycidyl Methacrylate Modified n-TiO2-PMMA Composites via the RAFT Process: Grafting “Through” Surface-Modified Nanoparticles

Glycidyl methacrylate (GMA), a functionalized agent that can chemically link to TiO₂ nanomaterial (n-TiO₂), was used to modify the surface of n-TiO₂ via a Ti-ethereal bond, yielding a GMA-modified n-TiO₂ (mn-TiO₂). Then the GMA bonded to the TiO₂ surface was copolymerized with methyl methacrylate (MMA) via a reversible addition-fragmentation chain transfer (RAFT) polymerization in the presence of the RAFT agent S-1-dodecyl-S′-(α, α′- dimethyl -α″-acetic acid)trithiocarbonate (DDACT) to form mn-TiO₂-PMMA nanoparticles. The resulting mn-TiO₂ nanoparticles and mn-TiO₂-PMMA nanoparticle materials were characterized by using infrared spectroscopy (IR), thermal analysis, and electron microscopy. The mn-TiO₂ nanoparticles demonstrated good dispersive capacity in organic solvents. The results of TGA indicated that the amount of PMMA grafted onto the surface of TiO₂ increased with the polymerization time. Additonally, the effects of mn-TiO₂/PMMA on the thermal and mechanical properties of polypropylene were studied.     

RAFT “grafting-through” approach to surface-anchored polymers: Electrodeposition of an electroactive methacrylate monomer

The synthesis of homopolymer and diblock copolymers on surfaces was demonstrated using electrodeposition of a methacrylate-functionalized carbazole dendron and subsequent reversible addition-fragmentation chain transfer (RAFT) “grafting-through” polymerization. First, the anodically electroactive carbazole dendron with methacrylate moiety (G1CzMA) was electrodeposited over a conducting surface (i.e. gold or indium tin oxide (ITO)) using cyclic voltammetry (CV). The electrodeposition process formed a crosslinked layer of carbazole units bearing exposed methacrylate moieties. This film was then used as the surface for RAFT polymerization process of methyl methacrylate (MMA), styrene (S), and tert-butyl acrylate (TBA) in the presence of a free RAFT agent and a free radical initiator, resulting in grafted polymer chains. The molecular weights and the polydispersity indices (PDI) of the sacrificial polymers were determined by gel permeation chromatography (GPC). The stages of surface modification were investigated using X-ray photoelectron spectroscopy (XPS), ellipsometry, and atomic force microscopy (AFM) to confirm the surface composition, thickness, and film morphology, respectively. UV-Vis spectroscopy also confirmed the formation of an electro-optically active crosslinked carbazole film with a p \pi - p^* \pi^{{\ast}}_{} absorption band from 450-650nm. Static water contact angle measurements confirmed the changes in surface energy of the ultrathin films with each modification step. The controlled polymer growth from the conducting polymer-modified surface suggests the viability of combining electrodeposition and grafting-through approach to form functional polymer ultrathin films.     

The permittivities of PVDF/PMMA blends at hydrostatic pressure

The complex permittivities of poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends have been measured under variation of temperature T(20°-60°C), frequency v(5 Hz-300 kHz), and hydrostatic pressure p (0-260 MPa). The values can be represented by a master curve with the shift factors △p/△ log (v/Hz) = ?140 MPa at room temperature and △ (1 /T) /△ log (v/Hz) = ?2. 10^?4 K^?1 at atmospheric pressure. The dependence of the activation energy △E _A on pressure p is then given by △E _A=(100 + 0.02 MPa^?1 p) kJ/mol. Furthermore, the results indicate that the β-relaxation of PVDF is due to motions in the crystal-amorphous interphase. The interactions between the two polymers, which are miscible at all compositions, disturb the correlations between the PVDF monomer units at that location as well as the mobility of the PMMA side group.