Dynamic behavior of polymer surface and the time dependence of contact angle

The increased attention has been focused on the re-searches of soft materials proposed by Pierre-Gilles de Gennes, a Nobel Prize Laureate in Physics. A special issue of “Science” on soft surfaces was published in 2002 to review specific surface properti…     

Effect of double bond on the surface properties of aqueous solutions of eicosapolyenoic acids

Surface tensions of aqueous solution of eicosapolyenoic acids (EA) with 25 double bonds were measured by use of a Du Nöuy tensiometer at pH 7.80 and 25°C, and the effects of double bond on the surface properties of EA were investigated. The value of critical micelle concentration of EA increased twofold with increasing number of double bonds. The free energy for the adsorption per double bond at the air-water interface was estimated as 2.47 kJ (double bond)^–1, and the negative value of free energy for the adsorption of EA molecule decreased with increasing number of double bonds.     

Dynamic surface tension behavior of aqueous solutions ofN-dodecyl-N,N dimethyl aminobetaine chlorohydrate

The adsorption behavior ofN-dodecyl-N,N dimethyl aminobetaine chlorohydrate (DDAB·HCl) at the air/aqueous interface was studied for solutions in pure water and phosphate buffer (pH=7.4). The equilibrium surface tension versus concentration curves were used to estimate the equilibrium adsorption parameters and CMCs. The buffer solution has a lower CMC and shows higher surface activity below the CMC than the pure water solution. Data and calculations of the dynamic tension behavior at constant-area conditions showed that the adsorption processes of DDAB·HCl solutions are about 10 to 300 times slower than those predicted by a diffusion-controlled model. A mixed kinetics adsorption model with a modified Langmuir-Hinshelwood kinetic equation, which considers an activation energy barrier for adsorption, was applied to find the kinetic adsorption parameters. The dynamic tension behavior at pulsating-area conditions with large amplitude was also examined for frequencies up to 90 cycles/min. The tension amplitude responses depended strongly on the concentration and frequency. Comparisons of diffusion-controlled model predictions and pulsating area tension data confirmed the need to use a mixed kinetics model. The latter model can improve the fit over the diffusion-controlled model, but it does not quantitatively match the observed tensions.     

Dynamic viscosity of polymer solutions

The dynamic viscosity of different long chain polymers in Aroclor permits an easy extrapolation to zero concentration only in the limiting cases of Newtonian, i. e., constant viscosity at low and high frequency, respectively. The first intrinsic viscosity []₀ is independent of any concept of the internal viscosity. In the case of polystyrene it is proportional toM ^0,65 which shows that Aroclor is a good solvent for this polymer. The second intrinsic viscosity [] turns out to be independent ofM. It is best reproduced by the model where the internal viscosity resists only the deformation rate of the single link. The displacement rate of more distant beads is affected by the internal viscosity only in the case that it involves the deformation rate of the links. The angles between successive links may be changed at any rate.In the intermediate range of frequencies the extrapolation of the observed dynamic viscosity to the intrinsic value was never made. The experimental data are so much affected by the concentration, i. e., by the interaction of adjacent molecules, that no conclusion may be derived from them about the properties of the isolated macromolecule. A master curve independent ofM andc is obtained by plotting of (G- )K/c over ₁. This means that the deformation mode in the whole molecular weight and concentration range investigated is the same. But this mode is different from that of the independent macromolecule in infinite dilution. The master curve may be described by the excess intrinsic viscosity of the Rouse model with the internal viscosity acting either between the beads on the same link only or between any distinct beads. As a consequence of the concentration effects, however, no conclusions about the properties of the single molecule can be derived from such an agreement.Dedicated to Prof. Dr. F. H. Müller.     

Elastic behavior of uniform star polymer chains

Elastic behaviors of uniform star polymer chains with two to seven branches (namely, functionality f = 2-7) are investigated using Monte Carlo simulation and the bond fluctuation model. Here chain dimensions and thermodynamic properties of uniform star polymer chains during the process of tensile elongation are studied, and comparisons with linear chain are also made. Static properties of chains such as chain sizes and asphericities of chains are calculated, and g-value of g = 〈S²〉_star/〈S²〉_linear decreases with elongation ratio increasing for different functionality f. Thermodynamic properties such as average energy 〈U〉, free energy per bond 〈A′〉 and elastic force F are also investigated during the process of tensile elongation. In the meantime, scatting functions P(q) are calculated for star polymer chains with different functionality f. Additionally, we also discuss the influence of elongation ratio on scattering form factor. The impenetrability of the star cores is known to cause a discontinuity in the osmotic pressure showed through a peak in the scattering functions, and some different behaviors in the tensile process for uniform star chain are obtained.     

等离子体改性聚合物表面动力学的动态接触角法研究

不同聚合物经CF~4/CH~4等离子体处理后,在浸水过程中表面动力学衰减常数对温度通过Arrhenius关系作图,对于所研究的聚合物都有一个明显的转折点。转折点处的温度称作表面构型转变温度(T~s),大约为15℃,与表面邻近水的Drost-Hansen温度一致。T~s以上及以下的活化能数值较小,说明表面构型变化的本质可看作是由于基团的翻转运动,而不需要整个大分子或链段的迁移运动。在浸水过程中,接触角滞后Δθ在表面构型转变温度T~s附近有转变,并有极小值,此后随着温度的升高出现极大值,继续升高温度接触角滞后Δθ又反而下降。     

Thermodynamics of interface elasticity

We generalize and extend a series of articles on the thermodynamics of interface elasticity. The whole formulation is based on taking into account a finite elastic deformation. This leads to generalized forms of the equations for the surface excess of the internal energy, the Gibbs adsorption equation and the Shuttleworth equation. In all cases correction terms occur containing the strain tensor. Although the deformation might be small, the corrections are critical in performing derivatives with respect to the strain which are needed to obtain equations connecting measurable quantities. These consequences are demonstrated in detail for the simple case of the spherical electrode. In the traditional electrochemical treatment, the densities of extensive quantities are related to the deformed surface, which is usually not mentioned. In analogy to the theory of volume elasticity, where the densities are related to the unstrained solid, one can also relate the densities of surface excess quantities to the unstrained surface. This formulation gives at first an additional proof for some of the generalized equations. Moreover, within this formulation one can express the surface excess of the energy density by the superficial work of the unstrained surface and three surface elastic constants, two of them being the surface Lamé constants. In the alternative formulation, the Shuttleworth equation appears simply as the relation between a generalized force and a generalized potential. Published in Elektrokhimiya in Russian, 2009, Vol. 45, No. 1, pp. 78–86. The text was submitted by the authors in English. This study was prepared for the special issue devoted to the 100th anniversary of B.V. Ershler.     

Studies on the viscosity behavior of polymer solutions at low concentrations

Viscosity measurements had been made on poly(vinyl alcohol) (PVA), poly(N-vinyl-2-pyrrolidone) (PVP) and poly(ethylene oxide) (PEO) solutions down to low concentrations. It was found that defined as the flow time of the pure solvent in ideal conditions and obtained practically by extrapolating the flow time of polymer solution t to zero concentration, was not equal to the flow time of the pure solvent t₀ measured. The reduced viscosity η_sp/C determined by (t/t₀-1)/C exhibited either a drastic increase or a significant decrease with dilution, depending upon the polymer solution investigated. On the other hand, η_sp/C determined by was proportional to C even at low concentrations. The anomalous viscosity behavior of neutral polymer solutions at low concentrations, therefore, was due to the incorrect method by which η_sp/C was determined. The detailed experiments indicated that the effective diameter of the viscometer capillary, the surface property of the capillary wall and the additional pressure corresponding to the measurement of t and t₀ for PVA, PVP and PEO solutions were not the same. Taking into account the contact anger and the surface tension of the liquid, together with the geometric parameter of the viscometer, the influence of the additional pressure upon the flow time measurement could be studied quantitatively. The calculation was in a good agreement with the experimental result. According to the method presented in this paper, the thickness of the adsorbed polymer layers on the capillary walls could be determined. It was noted that the thickness of the adsorbed polymer layers on the capillary walls was closely related to the solvent in which the polymer molecules were dissolved. The polymer molecular weight, however, had little or no effect on the thickness of the adsorbed polymer layers on the walls of the viscometer capillary.     

Cocontinuity and phase inversion in HDPE/PS blends: Influence of interfacial modification and elasticity

In this work the level of continuity and cocontinuity for blends of HDPE/PS prepared on a twin-screw extruder have been studied by both morphology and dissolution studies. Addition of SEBS as an interfacial modifier results in a shift of the percolation threshold for dispersed PS to higher concentrations. The region of phase inversion, however, is maintained at 70% PS. The shift in the percolation threshold to higher values is related to reduced elongation of the PS dispersed phase after interfacial compatibilization. These results indicate that an interfacial modifier significantly influences percolation phenomena without shifting the region of phase inversion. Models based on viscosity ratio have failed to predict the region of phase inversion in this study. Elastic effects are shown to be able to describe the basic tendencies. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1889–1899, 1998     

气-液界面上十六烷基溴化吡啶水溶液动态表面张力的研究

滴体积法测定了十六烷基溴化吡啶溶液的动态表面张力。考察了浓度、温度对动态表面张力的影响。讨论了十六烷基溴化吡啶分子在气／液界面上的吸附动力学,发现吸附遵从扩散-动力学控制机理．从表观扩散系数计算了吸附能垒,分析了吸附能垒存在的原因。     

On the collision efficiency in polymer flocculation of colloidal particles

The applicability of the conventional collision efficiency approach for the case where the collision of colloidal particles is not necessary for the rate-determining step is examined. On the basis of a dynamical treatment, we show that the fundamental assumption made in the conventional analysis may lead to a significant error. Depending upon the ratio of the number of sites on the colloidal surfaces to the number of polymer molecules, and the relative magnitudes of the desorption rate constant and the adsorption rate constant, the collision efficiency calculated by the conventional analysis may be either underestimated or overestimated. The present approach yields the temporal variation of the distribution of the fractional surface coverage. It can be shown that if the number of colloidal particles is large, using the mean fractional surface coverage instead of the exact distribution of the fractional surface coverage is sufficient for the evaluation of the collision efficiency.     

Kinetic behavior in self-assembly process of associative polymer solutions

Using associative polymers with different micro-block length (N_H), their kinetic behaviors in the self-assembly process have been discussed with steady flow, step shear rate and dynamic light scattering (DLS) experiments. The results showed that the N_H is the most important parameter to affect rheology of associative polymers, and the equilibrium time and viscosity recovery are an obvious difference from seconds to hours after violent pre-shearing. With DLS data, the hydrophobic micro-zone size is always a polydispersion distribution, and gradually concentrated three scales of size, the associative polymers with higher N_H values have a longer time to reach equilibrium state. The kinetic behavior of associative polymers has a greater potential to apply in enhanced oil recovery (EOR) field, we conclude that the polymers with medium associative strength have a smaller shear thinning index and higher viscosity recovery, and may satisfy the polymer flooding requirements of displacement efficiency and injectivity.     

酸性有机磷类萃取剂单分子膜的气-液界面行为:亚相pH和铺展溶剂的影响

液-液两相萃取过程中,有机磷类萃取剂分子的界面行为决定了其以何种形式参与到界面萃取反应中.为了阐明萃取剂分子界面行为的变化特点,采用Langmuir单分子膜技术研究了单分子膜中P507分子在气-液界面的吸附和聚集行为随亚相pH、有机溶剂极性的变化.通过测定表面压-分子面积等温线,并采用界面红外反射吸收光谱（IRRAS）分析表征气-液界面P507分子间相互作用,结果发现,以正己烷作铺展溶剂时,随亚相pH的降低,P507单分子膜质子化程度提高,P507分子极性端水化能力削弱,分子间相互作用增强,单分子膜中形成含有分子间氢键的聚集体.但采用极性有机溶剂（二氯甲烷和氯仿）铺展P507单分子膜,膜内P507分子界面聚集状态发生变化.铺展溶剂极性增强,单分子膜内会含有更多极性端水化能力强的P507分子单体,并且亚相pH降低,单分子膜不会出现类似正己烷条件下的π-A曲线收缩和P-O-H基团峰位红移现象.这证实了有机铺展溶剂极性可以改变P507单分子膜中分子界面存在形式和聚集状态.本工作为深入理解溶剂萃取过程中水油两相界面处酸性有机磷类萃取剂分子的聚集行为变化及其对界面反应活性的影响机制奠定了基础.     

Dynamic surface and interfacial tensions of surfactant and polymer solutions

Dynamic surface and interfacial tensions are the most frequently measured non-equilibrium properties of adsorption layers at liquid interfaces. The review presents the theoretical basis of adsorption kinetics, taking into consideration different adsorption mechanisms, and specific experimental conditions, such as liquid flow and interfacial area changes. Analytical solutions, if available, approximations as well as numerical procedures for direct solution of the physical models are presented.Several experimental techniques are discussed frequently used in studies of the dynamic adsorption behaviour of surfactants and polymers at liquid interfaces: drop volume, maximum bubble pressure, and pendent drop technique, drop pressure tensiometry, pulsating bubble and elastic ring method. Experimental results, most of all obtained with different technique on one and the same surfactant system, are then discussed on the basis of current theories.Finally, the role of dynamic interfacial properties in several practical applications is discussed: foam and emulsion film formation and stabilisation, rising of bubbles and drops in a surfactant solution.     

Interpretation of surface dilational elasticity data based on an intrinsic two-dimensional interfacial compressibility model

The present analysis shows that the introduction of intrinsic two-dimensional compressibility of a surfactant adsorption layer allows a much better interpretation of experimental data on the limiting (high-frequency) elasticity and characteristic frequency of diffusional relaxation than models using Frumkin's or other adsorption isotherms. The proposed model describes experimental data on surface dilational elasticity, as well as on surface pressure, sufficiently well at low and high surfactant concentrations, assuming the Lucassen and van den Tempel model of surface dilational elasticity is realized.     

Dynamics of adsorption and desorption of proteins at an air/water interface

Adsorption and desorption dynamics of lysozyme and β-casein at the air/water interface were investigated through stress relaxation experiments. The resulting surface tension changes due to a step-type surface area disturbance, as a function of time, were measured through a capillary wave probe. The adsorption data, obtained after a surface area expansion, can be well fitted to a diffusion-controlled adsorption model. However, desorption relaxation following a surface compression is much slower and cannot be modeled by the diffusion theory. Characteristic diffusion frequency and high-frequency dilational elasticity for protein layers were also obtained and found to be consistent with data reported in the literature.     

Influence of conformational asymmetry on the surface enrichment of polymer blends II

We reexamine the influence of statistical segment length asymmetry on the surface segregation of homopolymer blends in a mean field thread model of polymer melts. By developing numerical self-consistent field solutions of the Edwards-Helfand equations, we demonstrate that the component with the smaller value of the parameter β² = a²/(6ν) (a is the statistical segment length and ν is the segment volume) is enriched at a neutral, impenetrable surface. Qualitatively, this finding is in agreement with our earlier analytical work and with experiment. However, in contrast to our earlier work, we find that the absolute magnitude of the segregation is a sensitive function of the chain lengths of the two species and of the compressibility of the system. © 1995 John Wiley & Sons, Inc.     

含氟表面活性剂溶液的动态表面张力研究

本文研究了阳离子氟表面活性剂CF₃CF₂CF₂O(CF(CF₃)CF₂O)₂CF(CF₃)CONH(CH₂)₃N⁺(C₂H₅)₂CH₃I^-(简写FC-4 )的动态表面性质，利用Krüss K12和MBP动态表面张力仪分别测定了该体系的平衡表面张力和动态表面张力。由平衡表面张力测定结果得到了临界胶束浓度和表面吸附量。利用渐进的Ward and Tordai方程对动态数据进行了分析。结果表明：在吸附的最初阶段符合扩散控制模型，而在吸附的后期，证明了吸附势垒的存在，表明在吸附后期属于混合动力学模型。计算得出25 ℃时，该体系势垒约在25到35 kJ/mol. 由于氟表面活性剂分子间作用力小，表面压是导致吸附势垒的主要原因。     

Langmuir单分子膜在海洋飞沫气溶胶表面特性研究中的应用

被表面活性有机物包裹的液相气溶胶,如海洋飞沫气溶胶(SSA),通常具有反胶束的结构,它由有机分子形成的疏水表面和一个水相内核构成.SSA界面有机膜的组分和形态对其物理、化学和光学特性有重要的影响.Langmuir单分子膜是由脂肪酸、脂肪醇和磷脂等具有低挥发性的长链表面活性有机物在空气-水界面上扩散形成的单层分子薄膜.采...