季铵盐三聚表面活性剂在空气-水界面上单分子膜的崩溃压和分子极限面积

利用Langmuir膜天平研究了季铵盐三聚表面活性剂12-2-12-2-12在空气-水界面单分子膜的表面压-分子面积(π-A)等温线, 得到它的崩溃压对应的表面张力g_collapse和分子极限面积A_limit. 与12-2-12-2-12溶液临界胶束浓度对应的表面张力g_cmc和由Gibbs吸附方程得到的分子平均面积A_cmc相比较, 发现A_limit＜A_cmc, 而且g_collapse＞g_cmc. 分析12-2-12-2-12单分子膜的表面压随时间的衰减, 表明这个现象是由于表面活性剂从铺展单分子膜向水中溶解造成的, 而且初始表面压越大, 表面压的衰减越快.     

藻胆蛋白的Langmuir-Blodgett膜——Ⅰ.R-藻红蛋白单分子膜及蛋白构象变化的研究

测定了R-藻红蛋白(R-PE)在气/液界面上的表面压-面积曲线(tt-A等温线),结果表明R-PE具有很好的成膜性能,且由n-A等温线求得的单分子占有面积与R-PE以盘状形态“平躺”于液面上时的分子占有面积相同。R-PELB膜的透射电子显微镜(TEM)图象和椭圆偏振关于R-PE单分子膜厚度的测定,说明R-PE分子在基片上的取向是其盘平面与基片表面平行。根据这些依据,提出了R-PE单分子膜的结构。将R-PE在气/液界面上形成的单分子膜在适当表面压下用LB技术转移到基片上,测得了蛋白累积单分子膜的吸收及荧光光谱,R-PE单分子膜的吸收和荧光光谱与其在水溶液中无显著差别。膜的CD光谱与R-PE水溶液的CD光谱比较说明,当R-PE成膜后其二级结构发生了变化,即蛋白的p-折叠片构象组分增加。     

PSS/PDDA自组装膜形成过程中的临界浓度效应

Decher等提出的阴阳聚电解质层层组装膜技术(LbL),方便快捷,结构有序,其纳米级可控,可用于生物传感器、杂多酸多层膜修饰电极及天然多糖类功能膜等领域．LbL膜的厚度直接影响其性能,而膜厚度与紫外吸光度(A)成正比．故A是通常用于评价膜厚度的一种简便方法．紫外吸光度与聚电解质溶液浓度(cp)往往呈递增关系,随着溶液中cp的增大,单位面积上吸附聚电解质的量也增加。     

黑皂膜的光谱学研究

由溴化十六烷基三甲铵(CTAB)和甲基橙(MO)的混合溶液制成了含染料分子甲基橙的黑皂膜(BSF)。用电子吸收和FT-IR光谱考察了成膜的动态过程。水核厚度随溶液中甲基橙浓度增加而交薄,由普通型BSF最终交为Newton型BSF。脂链CH_2伸缩振动及甲基橙π—π~*吸收特征表明,两类BSF中CTAB的聚集态均为取向的液晶态,而MO在两类膜中亦具有相同的聚集形态和取向特征。以单轴取向模型建立了分子取向角与偏振Raman强度间的关系。由偏振Raman实验结果计算出MO在两类BSF中以相同的倾角(约80°)嵌在单分子膜壁上。     

聚丙烯微孔膜表面的等离子体接枝

通过氢气氛等离子体处理，在聚丙烯微孔膜表面接枝了聚丙烯酸，改善了膜表面的亲水性。接枝率与等离子体放电功率、放电时间和溶液浓度有关，微孔膜内外表面及不同位置接枝效率有差别。接枝后微也膜的表面孔径减少了。     

Nafion膜表面亲水性研究

Ｎａｆｉｏｎ膜在电化学体系中的应用越来越广泛,而其表面亲水性往往直接影响着使用性能．本文介绍一种适宜于表征Ｎａｆｉｏｎ膜表面亲水性的接触角测量方法,即束缚气泡法,并讨论了该膜与水溶液接触角的滞后现象、溶液表面张力的影响,简介了用全氟表面活性剂改善Ｎａｆｉｏｎ膜表面亲水性的尝试．     

澄清溶液体系二次生长法NaA型沸石膜的生长机制及膜厚的控制合成

用晶种涂层二次生长成膜法研究了在含水量不同的澄清溶液合成体系中NaA型沸石膜的生长及沸石膜厚度的控制合成.用SEM,TEM和XRD表征手段分析了沸石膜的形成过程和微结构.在载体表面不涂晶种而直接合成则不易形成连续沸石膜;用晶种涂层二次法可以很容易形成均匀的连续膜.合成液中水量的高低强烈影响沸石膜的生长速率、形成结构和膜的厚度.在高水量(水硅摩尔比为2000)的合成体系中沸石生长速率慢,膜主要通过晶种层中的晶粒长大,交织成膜,且膜只有一层结构;而在低水量(水硅摩尔比为750)的合成体系中沸石生长速率快,膜则通过晶种层表面晶粒向外生长、交织成膜,而膜具有两层结构.通过调变合成液的水量可有效地控制沸石膜层的厚度,并能制得非常均匀、连续的膜.     

1-1型单组分盐溶液中荷电膜膜电位的研究

根据固定电荷模型和非线性最小二乘法, 研究膜体积电荷密度为定值和其大小随电解质主体溶液浓度呈指数变化的两种初始条件下, 五种纳滤膜(NTR 7450, ESNA 1, ESNA 1-LF, LES 90和UTC 60)在不同浓度的氯化钠和氯化钾溶液中的膜电位, 获得膜体积电荷密度与电解质主体溶液浓度的关系. 结果表明, 当体积电荷密度随浓度呈指数变化时, 拟合的膜电位与实验结果更接近, 得到的固定电荷密度更精确. 膜电位的大小与膜两侧电解质溶液浓度的比值相关. 在较高浓度时, 膜电位的值还与扩散系数相关; 其中阴阳离子的扩散系数之比大于1.0是膜电位反号的标志. 在中间浓度时, 膜电位随电解质主体溶液浓度近似呈线性变化.     

季铵盐型双子表面活性剂与十八醇的混合单分子膜

研究了双子表面活性剂12-2-16和12-2-12分别与十八醇(C18H37OH)在空气-水界面上混合单分子膜的π-A等温线. 在相分离表面压以下, 比较了不同表面压下和不同混合比单分子膜的混合表面过剩自由能ΔGMexo, 分析了双子表面活性剂与脂肪醇在空气-水界面上混合膜中的相容性. 结果表明, 12-2-16与C18H37OH在所有混合摩尔比下随着表面压增高, 自由能增大. 12-2-12与C18H37OH混合膜体系的相容性取决于两者的混合比, ΔGMexo随所加入C18H37OH摩尔分数的增加逐渐增大, 从异种分子间净的吸引作用转变到相互排斥作用体系, 转变点为C18H37OH加入量的摩尔分数0.65. 当混合为热力学自发过程时, 增大表面压将有利于混合; 而对相互排斥体系, 增加表面压将使体系内异种分子之间的相互排斥作用更大.     

电容测量研究铬表面氧化膜的半导体性能

利用电容测量技术,基于Mott-Sckottky分析,研究了在0.5 mol•L－1 H2SO4溶液中铬表面氧化膜的半导体性质,以及膜形成条件的影响.结果表明,铬在钝化电位区内所形成的表面氧化膜具有p-型半导体特性,膜的厚度约(1.2±0.3) nm.膜的阻抗响应表现出低频弥散行为,可以用介电弛豫普适定律来描述.膜的掺杂浓度NA随成膜电位及极化时间的延长而增大,溶液pH值则通过改变膜的表面电荷而影响膜的平带电位EFB.     

Thermodynamic studies on thin liquid films. II. Foam film stabilized by decyl methyl sulfoxide

Thermodynamic equations in Part I of this series were extended so as to be applicable to electrolyte mixtures and the resultant equations were applied to the experimental results of a NaCl-decyl methyl sulfoxide (DeMS) mixture. Film thickness and contact angle of the black foam film stabilized by DeMS were measured as a function of the total molality of NaCl and DeMS at constant mole fraction of DeMS in the mixture under constant disjoining pressure. Newton black film was observed only above a certain DeMS concentration and the phase transition between common black and Newton black films took place twice as NaCl concentration increased at constant DeMS concentration. The surface densities of NaCl and DeMS at the film surface and the differences in the surface densities between the adsorbed films at the film surface and bulk one coexisting at equilibrium were numerically evaluated by applying the thermodynamic equations to the film tension obtained from the contact angle. The film states and phase transitions were clarified in terms of the film thickness and surface densities.     

Foam films stabilized by dodecyl maltoside. 1. Film thickness and free energy of film formation

Foam films stabilized by a sugar-based nonionic surfactant, beta-dodecyl maltoside, are investigated. The film thickness and the film contact angle (which is formed at the transition between the film and the bulk solution) are measured as a function of NaCl concentration, surfactant concentration, and temperature. The film thickness measurements provide information about the balance of the surface forces in the film whereas the contact angle measurements provide information about the specific film interaction free energy. The use of the glass ring cell and the thin film pressure balance methods enables studies under a large variety of conditions. Thick foam films are formed at low electrolyte concentration. The film thickness decreases (respectively the absolute value of the interaction film free energy increases) with the increase of the electrolyte concentration according to the classical DLVO theory. This indicates the existence of a repulsive double layer electrostatic component of the disjoining pressure. An electrostatic double layer potential of 16 mV was calculated from the data. A decrease of the film thickness on increase of the surfactant concentration in the solution is observed. The results are interpreted on the basis of the assumption that the surface double layer potential originates in the adsorption of hydroxyl ions at the film surfaces. These ions are expelled from the surface at higher surfactant concentration.     

Properties of foam films stabilized with tetraethylammonium perfluorooctane-sulfonate

Properties of single foam films prepared with tetraethylammonium perfluorooctane-sulfonate (TAPOS) were studied. Film thickness was measured as a function of NH₄Cl concentration in the film forming solution. The dependence of the film disjoining pressure versus the film thickness (disjoining pressure isotherms) and the mean lifetime of the films were studied. The dependence of the film thickness on the electrolyte concentration showed the presence of an electrostatic double layer at the film surfaces. The electrostatic double layer component of the disjoining pressure was screened at a NH₄Cl concentration higher than 0.2 M where Newton black films (NBFs) of 6 nm thickness were formed. These films are bilayers of amphiphile molecules and contain almost no free water. The disjoining pressure isotherms of the foam films formed with 0.001 M TAPOS were measured at two different NH₄Cl concentrations (0.005 and 0.0005 M). The Deryaguin-Landau-Verwey-Overbeek (DLVO) theory describes well the isotherms with an electrostatic double layer potential of ∼140 mV. The mean lifetime, a measure of the stability of the NBFs, was measured depending on surfactant concentrations. The observation of NBF was possible above a minimum TAPOS concentration of 9.4 × 10⁻⁵ M. Above this concentration, the lifetime increases exponentially. The dependence of the film lifetime on surfactant concentration is explained by the theory for NBF-rupture by nucleation mechanism of formation of microscopic holes.     

Evaluation of DLVO theory with disjoining-pressure and film-conductance measurements of common-black films stabilized with sodium dodecyl sulfate

We develop a unique film holder combining a thin-film balance with AC impedance spectroscopy to measure disjoining pressure, film conductance, and film thickness simultaneously. Foam films stabilized by sodium dodecyl sulfate (SDS) are investigated with and without added sodium chloride (NaCl) electrolyte. Classical colloidal theory, Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory, is tested rigorously over a wide range of solution conditions by comparing the surface charge densities fit to disjoining-pressure isotherms with those estimated independently from film-conductance and surface-tension data. Film-conductance measurements strongly suggest that the adsorbed anionic surfactant is partially complexed with counterions. Therefore, to reconcile the different values of charge densities calculated from surface tension and film conductance with those from disjoining pressure, we propose a simple ion-binding electrostatic model. The ion-complexation framework predicts increased ion complexing with increasing solution ionic strength, in agreement with surface-tension and film-conductance data. Unfortunately, it is not possible to describe similarly the trends of the measured disjoining-pressure isotherms because the diffuse-layer charge density increases, or equivalently, the ion complexation decreases with increasing ionic strength. Accordingly, the ion-binding extension of classical DLVO theory does not permit agreement between theory and independent experimental data from surface tension, disjoining pressure, and film conductance.     

Interaction forces in thin liquid films stabilized by hydrophobically modified inulin polymeric surfactant. 2. Emulsion films

The interaction forces in emulsion films stabilized using hydrophobically modified inulin (INUTEC SP1) were investigated by measuring the disjoining pressure of a microscopic horizontal film between two macroscopic emulsion drops of isoparaffinic oil (Isopar M). A special measuring cell was used for this purpose whereby the disjoining pressure Pi was measured as a function of the equivalent film thickness hw. The latter was determined using an interferometric method. In this way Pi-hw curves were established at a constant INUTEC SP1 concentration of 2x10(-5) mol.dm-3 and at various NaCl concentrations. At a constant disjoining pressure of 36 Pa, a constant temperature of 22 degrees C, and a film radius of 100 microm, hw decreased with an increase in the NaCl concentration, Cel, and reached a constant value of 11 nm at Cel=5x10(-2) mol.dm-3. This reduction in film thickness is due to the compression of the electrical double layer, and at the above critical NaCl concentration any electrostatic repulsion is removed and only steric interaction remains. This critical electrolyte concentration represents the transition from electrostatic to steric interaction. At a NaCl concentration of 2x10(-4) mol.dm-3 the Pi-hw isotherms showed a gradual decrease in hw with an increase in capillary pressure, after which there was a jump in hw from approximately 30 to approximately 7.2 nm when Pi reached a high value of 2-5.5 kPa. This jump is due to the formation of a Newton black film (NBF), giving a layer thickness of the polyfructose loops of approximately 3.6 nm. The film thickness did not change further when the pressure reached 45 kPa, indicating the high stability of the film. Pi-hw isotherms were obtained at various NaCl concentrations, namely, 5x10(-2), 5x10(-1), 1.0, and 2.0 mol.dm-3. The initial thicknesses are within the range 9-11 nm, after which a transition zone starts, corresponding to a pressure of about 0.5 kPa. In this zone all films transform to an NBF with a jump, after which the thickness remains constant with a further increase in the disjoining pressure up to 45 kPa, with no film rupture. This indicates the very high stability of the NBF in the presence of high electrolyte concentrations. The high emulsion film stability (due to strong steric repulsions between the strongly hydrated loops of polyfructose) is correlated with the bulk emulsion stability.     

Nonflat equilibrium liquid shapes on flat surfaces

The hydrostatic pressure in thin liquid layers differs from the pressure in the ambient air. This difference is caused by the actions of surface forces and capillary pressure. The manifestation of the surface force action is the disjoining pressure, which has a very special S-shaped form in the case of partial wetting (aqueous thin films and thin films of aqueous electrolyte and surfactant solutions, both free films and films on solid substrates). In thin flat liquid films the disjoining pressure acts alone and determines their thickness. However, if the film surface is curved then both the disjoining and the capillary pressures act simultaneously. In the case of partial wetting their simultaneous action results in the existence of nonflat equilibrium liquid shapes. It is shown that in the case of S-shaped disjoining pressure isotherm microdrops, microdepressions, and equilibrium periodic films exist on flat solid substrates. Criteria are found for both the existence and the stability of these nonflat equilibrium liquid shapes. It is shown that a transition from thick films to thinner films can go via intermediate nonflat states, microdepressions and periodic films, which both can be more stable than flat films within some range of hydrostatic pressure. Experimental investigations of shapes of the predicted nonflat layers can open new possibilities of determination of disjoining pressure in the range of thickness in which flat films are unstable.     

Wetting films on a hydrophilic silica surface obtained from aqueous solutions of hydrophobically modified inulin polymeric surfactant

The thickness of wetting films on a hydrophilic silica surface was investigated using a microinterferometric technique. Aqueous solutions of hydrophobically modified inulin (INUTEC^®SP1) at various concentrations, in the presence or absence of NaCl or Na₂SO₄, were studied. The equilibrium film thickness (h _eq) showed a complex dependence on INUTEC^®SP1 concentration. At low electrolyte concentrations, h _eq decreased with an increase in INUTEC^®SP1 concentration, reaching a minimum at 10^?6 mol dm^?3. However, at high electrolyte concentrations, this dependence became less pronounced. At any given INUTEC^®SP1 concentration, the equilibrium film thickness decreased with an increase in electrolyte concentration as a result of the compression of the electrical double layer reaching a minimum value. After that, the film thickness showed a small decrease with further increase in electrolyte concentration. This indicates that the electrostatic component of disjoining pressure can be neglected, and the steric repulsion of the loops and tails of INUTEC^®SP1 determined the film thickness.     

Interaction forces in thin liquid films stabilized by hydrophobically modified inulin polymeric surfactant. 3. Influence of electrolyte type on emulsion films

The interaction forces in emulsion films stabilized using hydrophobically modified inulin (INUTEC SP1) were investigated as a function of concentrations of electrolytes of different types (NaCl, Na2SO4, and MgSO4). At a constant disjoining pressure of 36 kPa, a constant temperature of 22 degrees C, and a film radius of 100 microm, the film thickness, hw, decreased with an increase in electrolyte concentration until a critical value, Cel,cr, was reached above which hw remained constant. Cel,cr decreased with an increase in electrolyte valency (Cel,cr = 5 x 10(-2) mol.dm(-3) for NaCl and 1 x 10(-2) mol.dm(-3) for Na2SO4 and MgSO4). The reduction in film thickness below Cel,cr could be accounted for by the compression of the electrical double layer. The Pi-hw isotherms below Cel,cr could be fitted using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory (constant charge and constant potential cases were considered). At a certain pressure, the film jumped to a Newton black film. The pressure at the jump decreased with an increase in electrolyte valency as a result of the reduction of the electrostatic barrier. At electrolyte (NaCl, Na2SO4, or MgSO4) concentrations higher than Cel,cr, the jump occurred at a low pressure that was independent of the electrolyte type. The thickness of the Newton black film was independent of both the concentration and nature of the electrolytes studied. The results show clearly that the polyfructose loops and tails remain strongly hydrated both in water and in high concentrations of electrolytes of different types, and these results explain the high INUTEC SP1 emulsion stability against coalescence of emulsions prepared under such conditions.     

Direct measurement of molecular interaction forces in foam films from lung surfactant fraction

Molecular interaction forces, operative in microscopic foam films obtained from the isolated hydrophobic fractions of porcine lung surfactant (AS-B) are investigated by monitoring film thickness h as a function of electrolyte concentration (C _el) and direct measurements of disjoining pressure/thickness (Π(h)) isotherms. The steep decrease of the common film thickness with the increase of C _el evidences the action of long-range electrostatic surface forces. The experimental h(C _el) curve indicates that non-Derjaguin-Landau-Verwey-Overbeek (DLVO) repulsive forces are operative at C _el where common black (CBF) and Newton black films (NBF) are obtained including the physiologically relevant C _el=0.14 mol dm⁻³ NaCl. The action of additional non-DLVO forces is corroborated by the comparison of the experimentally measured Π(h) isotherm with the DLVO theory. Considering the presence of proteins in AS-B and the formation of lipid-protein complexes it is inferred that steric type forces are operative in CBF and NBF.