Evaluation of imbedded fiber retraction phenomenological models for determining interfacial tension between molten polymers

In this work, the interfacial tension for several polymer pairs, namely polypropylene/polystyrene (PP/PS), PP/polycarbonate (PC), PP/polyamide 6 (PA-6) and low density polyethylene (LDPE) and ethylene vinyl alcohol copolymer (EVOH) was evaluated as a function of temperature using the imbedded fiber retraction method (IFR). Two phenomenological models were used and compared to infer the interfacial tension from the evolution of the imbedded fiber back into a sphere: [Carriere CJ, Cohen A, Arends CB. J Rheol 1989;33:681-9. [1] and Tjahjadi M, Ottino JM, Stone HA. AIChE J 1994;40:385-94. [2]]. It was shown that Carriere et al.'s model overestimates the value of interfacial tension whereas Tjahjadi et al.'s model leads to results that corroborate the ones obtained using other experimental methods. A method to further increase the accuracy of Tjahjadi et al.'s model was proposed. Using this method the interfacial tension for the different polymer pairs studied was evaluated and shown to decrease linearly with increasing temperature.     

Studies on some factors influencing the interfacial tension measurement of polymers

To improve the accuracy of polymer interfacial tension measurement using deformed drop retraction method (DDRM), we examined some factors, such as the shape parameter, the retraction scale D₀, and the distortion criterion γ by means of dissipative particle dynamics (DPD) simulation with 6 different models and analysis with three observation data, and proposing a new shape parameter P. Results show that the shape parameter order of suitable to various retraction scales and larger distortion is P>(a²−b²)>D. This study found that choosing a suitable retraction scale is very important, and that D₀≅0.15 is the most suitable retraction scale in DDRM measurement. In the scale, the three shape parameters cannot make much difference on the measurement deviation from the standard. This study also found that the distortion criterion γ varies with different shape parameters. We also found here when D₀≅0.15 the distortion criterion becomes γ<0.15, and one has a reliable measurement with any shape parameter.     

Interfacial tension of polycaprolactone/polystyrene blends by the imbedded fiber retraction method

Polycaprolactone (PCL) is a biodegradable polyester that is widely used in blends with synthetic and natural polymers for various applications. PCL is blended with biopolymers such as starch to improve its wet mechanical properties without impairing the biodegradability and other useful properties of starch. In spite of its importance, little is known about the interfacial tension of PCL blends. Indirect estimates of the room‐temperature interfacial tension of PCL blends using wettability methods have been reported. However, direct measurements of the interfacial tension of PCL blends have not been achieved until now, mainly because of the unsuitability of existing equilibrium methods for measuring the interfacial tension of high viscosity blends. We have measured the interfacial tension of PCL/PS blends using the imbedded fiber retraction (IFR) method. The IFR is a dynamic method that allows for the measurement of interfacial tension of high viscosity polymer blends in a relatively short period of time. The interfacial tension of PCL/PS blends was measured from 160 to 200°C. In this temperature range, the interfacial tension of PCL/PS blends is independent of temperature and has a value of 7.6 ± 1.8 dyn/cm. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3145–3151, 2002; DOI 10.1002/app.10178     

Comparative measurement of interfacial tension by transient dynamic methods

An experimental comparison between different techniques for the interfacial tension measurement is presented for polyamide‐6 and polystyrene pair. The techniques are transient dynamic methods, which include the breaking thread (BT) method, the imbedded fiber retraction (IFR) method, the deformed drop retraction (DDR) method, and two modified DDR methods. The modified DDR methods combine the analytical power of the DDR method with experimental simplicity of the BT and IFR methods, respectively. Interfacial tension values obtained by the modified DDR method that combines the BT method is much lower than those by the other methods. Among all techniques, the modified DDR that combines the IFR method is found to be most convenient and accurate method. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99:1910–1918, 2006     

时间效应在悬滴法测定表面张力中的影响

表面张力是流体重要的物理性质,测定表面张力的方法通常包括毛细管上升法、最大气泡压力法、拉环法、旋滴法和悬滴法等。目前,最普遍的表面张力的测定方法为国家标准推荐的平板法或拉环法。然而,悬滴法作为一项成熟的表面张力测定方法且具备静态表面张力及动态表面张力测定功能,目前使用该法测定的较少。文章使用悬滴法测定较低含量的表面活性剂溶液静态表面张力时发现结果与拉环法差异较大,而测定单组分液体及含量较大的表面活性剂溶液,悬滴法与拉环法的测定数据差异较小,这种情况的相关报道较少。另外,使用动态表面张力测定探索了静态测定时出现差异的原因,并对应用悬滴法进行表面张力测定的适用范围进行了总结。使用悬滴法测定表面张力时,应注意时间效应的影响。     

Interfacial tension of compatibilized blends of LDPE and PA6: the breaking thread method

The interfacial tension of the uncompatibilized and compatibilized blends of low density polyethylene (LDPE) and polyamide 6 (PA6) has been measured by the breaking thread method. Different types of compatibilizer precursors have been used: poly(ethylene-co-acrylic acid) (Escor 5001, by Exxon) having 6 wt% concentration of acrylic acid; an ethylene-acrylic acid zinc ionomer (Iotek 4200); a triblock copolymer with polystyrene end blocks and a rubbery poly(ethylene–butylene mid block (SEBS) (Kraton G 1652); and SEBS-g-MA (Kraton FG 1901X) with 2 wt% maleic anhydride. The compatibilizing efficiency of the different types of the compatibilizer precursors towards the blends has been evaluated quantitatively by the values of the interfacial tension obtained. It has been shown that Iotek and SEBS-g-MA posses the highest compatibilizing efficiency, demonstrated by the strongest decrease of the interfacial tension and the dimension of the droplets of the dispersed phase. Contrary, SEBS almost does not influence the interfacial tension and the size of the particles. Hence, it possesses the lowest compatibilizing activity towards the blends. The compatibilizer Escor displays an activity lower than that of Iotek and SEBS-g-MA, but it is higher than that of SEBS.     

Interfacial tension of marine lipids in contact with high pressure carbon dioxide

Interfacial tension (IFT) of fish oil triglycerides (TG) and fatty acid ethyl esters (FAEE) in contact with carbon dioxide (CO₂) was measured according to the pendant drop method at 40, 55 and 70 °C and pressures up to 25 MPa. The IFT of both TG and FAEE decreased substantially with CO₂ pressure. The IFT of FAEE vanished at elevated pressures, whereas that of TG decreased to a fairly constant level of about 2 mN/m. The IFT was correlated using a model taking into account the density, pressure and temperature of CO₂, thereby facilitating the calculation of the ideal pendant drop volume as well as the surface excess concentration of CO₂. In the pressure range studied, the pendant drop volume for FAEE decreased with pressure, whereas for TG it increased at elevated presssures due to the predominant effect of buoyancy. Furthermore, the change in IFT over time was determined at 55 °C for TG in contact with CO₂ at pressures up to 11.4 MPa showing a decrease of IFT over time at low pressures, whereas at higher pressures it remained nearly constant. IFT influences drop formation as well as the disintegration of falling films thereby affecting the performance of separation processes.     

The effect of viscosity on surface tension measurements by the drop weight method

Viscosity is one of the parameters affecting the measured surface tension, as fluid mechanics affects the measurement process using conventional methods. Several methods including the selected planes (SPM) and WDSM which combines the weight drop method (WDM) and SPM, are applied to surface tension measurement of high viscous liquids. Yet, none of them treats the viscosity effect separately. The current publication presents a simple, easy to apply empirical approach of satisfactory accuracy, for evaluation of surface tension of liquids having wide range of viscosities up to 10 Pa s. The proposed method is based on Tate's law and the “drop weight” method using calibration curves of known liquids having similar surface tensions but different viscosities. Drop weight of liquids having viscosity ≥0.05 Pa s, was found to be significantly affected by the liquid viscosity. The shape factor, f, of high viscosity liquids was found to correlate linearly with the logarithm of viscosity, pointing the importance of viscosity correction. The experimental correlation presented in the current work can be used as a tool for the evaluation of surface tension for high viscosity liquids such as prepolymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Interfacial tension between demixed symmetrical polymer solutions: Polystyrene-poly(dimethylsiloxane)-propylbenzene system

Interfacial tension between demixed symmetrical polymer solutions of polystyrene-poly(dimethylsiloxane)-propylbenzene was measured as a function of temperature near the critical point at a fixed critical temperature (60.0°C) for molecular weights from 9000 to 1.0 × 10⁵. The interfacial tension increased as the molecular weight was lowered. The order of magnitudes of the interfacial tension was in good agreement with the theoretical prediction proposed previously by Nose. The critical exponents β and μ were estimated as near the values found for ordinary binary mixtures or liquids. Cloud point curves and coexistence curves were also obtained and properties related to incompatibility were also briefly discussed.     

New procedure to increase the accuracy of interfacial tension measurements obtained by breaking thread method

The breaking thread method has been widely used to measure interfacial tension between molten polymers. However, various factors can introduce errors in the breaking thread measurements and is very difficult to obtain accurate values of interfacial tension. In this work a new procedure to enhance the accuracy of the breaking thread method is proposed. It consists of using Tomotika's original theory and Tjahjadi's et al. numerical simulation of the evaluation of a breaking thread simultaneously to identify fibers with residual stresses. These fibers should not be considered for breaking thread experiment. Also, a new experimental procedure for polymer pairs that cannot normally be tested using breaking thread method is presented. Using these two new procedures the interfacial tension between polypropylene and polystyrene and between polypropylene and polycarbonate was evaluated for temperatures ranging from 200 to 240 °C. It was shown that the accuracy of the method was increased by 28% when compared to the result obtained using one of the both theories, Tomotika or Tjahjadi et al, independently. The results of interfacial tension between polypropylene and polystyrene and between polypropylene and polycarbonate corroborated the results obtained using other methods.     

测定压敏胶乳液表面张力的简易珠滴重量法

介绍了一种利用常用的酸式滴定管、移液管和电子天平测定乳液表面张力的简易方法。首先通过测定已知表面张力液体的珠滴质量 ,由σ =D×M计算出D值 ,然后测定压敏胶乳液的珠滴质量 ,并利用同样的公式计算出乳液的表面张力。我们利用此方法测定了 5种压敏胶乳液的表面张力。结果表明 ,这种测定乳液表面张力方法操作简便 ,实用性强 ,结果准确可靠。     

Interfacial tension between coexisting polymer solutions in mixed solvents and its correlation with bulk thermodynamics: phase equilibria (liquid/gas and liquid/liquid) for the system toluene/ethanol/PDMS

Vapor pressures, phase equilibria and interfacial tensions σ were measured for solutions of poly(dimethylsiloxane) (PDMS, M_w[equals]75 kg/mol and M_n[equals]50 kg/mol) in mixed solvents of toluene (TL) and ethanol (EtOH) at 30, 40, 50 and 60 °C. The experimental ternary phase diagrams can be modeled quantitatively from the determined concentration and temperature dependent binary interaction parameters χ_ij if the experimentally inaccessible composition dependence of χ_EtOH/PDMS is adjusted. The relations between σ and the equation of state of the system differ from that applying to single solvents. The exponents as well as the amplitude prefactors of the corresponding scaling laws (e.g. the dependencies of σ on the length of the tie lines or on the hump energy, i.e. on the intrusion into the two phase regime quantified in terms of Gibbs energies) change considerably with temperature. However, this variation can be reduced significantly by normalizing the independent variables. Dividing the length of the tie lines by the length for the corresponding binary subsystem proves more efficient than the distance of these tie lines from the critical point of the ternary system relative to the maximum distance of the binary subsystem. A combined normalization does not improve the situation.     

Interfacial tension of demixed polymer solutions near the critical temperature: polystyrene + methylcyclohexane

Interfacial tension between demixed solutions of polystyrene + methylcyclohexane has been measured near the critical temperature as a function of temperature using polystyrenes with molecular weights 9000 ～ 1.26 × 10⁶. The critical exponent for the interfacial tension was determined to be about 1.30 for the lower molecular weight systems. However, for higher molecular weights the exponent could not be obtained because the system departed from critical behaviour. Magnitudes of the interfacial tension were proportional to about N^?0.44, where N is the polymerization index. Experimental results were compared with the recently-proposed theories and found to be in qualitative agreement. The tricritical theory of polymer solutions was also compared with the experimental results.     

Influence of temperature,molecular weight,and polydispersity of polystyrene on interfacial tension between low‐density polyethylene and polystyrene

In this work, the influence of temperature, molecular weight, and polydispersity of polystyrene on interfacial tension between low‐density polyethylene (LDPE) and polystyrene (PS) was evaluated using the pendant drop method. It was shown that interfacial tension between LDPE and PS decreases with increasing temperature for all LDPE–PS pairs studied. The temperature coefficient (∂γ/∂T) (where λ is interfacial tension and T is temperature) was higher for lower molecular weight and larger polydispersity of PS. The interfacial tension between LDPE and PS at a temperature of 202°C increased when the molecular weight of polystyrene was varied from 13,000 to 30,000. When the molecular weight of PS was further increased, the interfacial tension was shown to level off. The effect of polydispersity on interfacial tension between PS and LDPE, at a temperature of 202°C, was studied using PS with a constant‐number average molecular weight and varying polydispersity. The interfacial tension was shown to decrease with increasing polydispersity. However, the influence of polydispersity was lower for PS of higher molecular weight. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2423–2431, 1999     

用差分最大气泡压力法测定对二甲苯+乙酸体系的表面张力

本文采用经改进了的差分最大气泡压力法建立了一套表面张力测定装置,并对装置进行了测试。用该装置测定了对二甲苯和醋酸体系在常压下,30℃～70℃范围内,不同浓度下的表面张力,并用两种方法对数据进行了关联,为PTA的工程设计提供既方便又可靠的基础数据。