Effect of sonication and freezing-thawing on the aggregate size and dynamic surface tension of aqueous DPPC dispersions

The effect of sonication and freezing-thawing on the aggregate size and dynamic surface tension of aqueous dipalmitoylphosphatidylcholine (DPPC) dispersions was studied by cryogenic-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), UV-vis spectroturbidimetry, and surface tensiometry. When 1000 ppm (0.1 wt%) DPPC dispersions were prepared with a certain protocol, including extensive sonication, they contained mostly frozen vesicles and were quite clear, transparent, and stable for at least 30 days. The average dispersed vesicles diameter was 80 nm in water and 90 nm in standard phosphate saline buffer. After a freeze-thaw cycle, this dispersion became turbid, and precipitates of coagulated vesicles were observed with large particles of average size of 1.5x10(3) nm. The vesicle coagulation is due to the local salt concentration increase during the freezing of water. This dispersion has much higher equilibrium and dynamic surface tension than those before freezing. When this freeze-thawed dispersion was subjected to a resonication at 55 degrees C, smaller vesicles with sizes of ca. 70 nm were produced, and a lower surface tension behavior was restored as before freezing. Similar behavior was observed at 30 ppm DPPC. These results indicate that the freeze-thaw cycle causes substantial aggregation and precipitation of the vesicles. These results have implications for designing efficient protocols of lipid dispersion preparation and lung surfactant replacement formulations in treating respiratory disease and for effective administration.     

Competitive adsorption of fibrinogen and dipalmitoylphosphatidylcholine at the air/aqueous interface

The competitive adsorption of fibrinogen (FB) and DPPC at the air/aqueous interface, in phosphate buffer saline at 25 degrees C, was studied with tensiometry, infrared reflection absorption spectroscopy (IRRAS), and ellipsometry. For FB/DPPC mixtures with 750 ppm (0.075 wt%) FB and 1000 ppm (0.10 wt%) DPPC, the tension behavior was found to be similar to that of FB when alone, even with DPPC and FB being at the interface. Thus, FB interferes with adsorption of DPPC and inhibits its surface tension lowering ability. When FB protein is introduced in the solution after a DPPC monolayer has formed, the adsorption of FB is inhibited by the DPPC monolayer. When a DPPC monolayer is spread onto a solution with a preadsorbed FB layer, the DPPC monolayer excludes FB from the surface and controls the tension behavior with little inhibition by FB. When a DPPC dispersion is introduced with the Trurnit method, or sprayed dropwise, onto an aqueous FB/DPPC surfaces, the DPPC layer formed on the surface prevents the adsorption of FB and dominates the surface tension behavior. These results have implications in controlling the inhibition of lung surfactant tension behavior by serum proteins, when they leak at the alveolar lining layer, and in developing surfactant replacement therapies for alveolar respiratory diseases.     

New protocols for preparing dipalmitoylphosphatidylcholine dispersions and controlling surface tension and competitive adsorption with albumin at the air/aqueous interface

The adsorption behavior of dipalmitoylphosphatidylcholine (DPPC), which is the major component of lung surfactant, at the air/aqueous interface and the competitive adsorption with bovine serum albumin (BSA) were studied with tensiometry, infrared reflection absorption spectroscopy (IRRAS), and ellipsometry. Dynamic surface tensions lower than 1 mN/m were observed for DPPC dispersions, with mostly vesicles, prepared with new protocols, involving extensive sonication above 50 °C. The lipid adsorbs faster and more extensively for DPPC dispersions with vesicles than with liposomes. For DPPC dispersions by a certain preparation procedure at T > T_c, when lipid particles were observed on the surface, dynamic surface tensions as low as 1 mN/m were measured. Moreover, IRRAS intensities and ellipsometric δΔ values were found to be much higher than the values for other DPPC dispersions or spread DPPC monolayers, suggesting that a larger amount of liposomes or vesicles adsorb on the surface. For DPPC/BSA mixtures, the tension behavior is controlled primarily by BSA, which prevents the formation of a dense DPPC monolayer. When BSA is injected into the subphase with a spread DPPC monolayer or into a DPPC dispersion with preadsorbed layers, little or no BSA adsorbs and the DPPC layer remains on the surface. When a DPPC monolayer is spread on a BSA solution at 0.1 wt% at 25 °C, then DPPC lipid can displace the adsorbed BSA molecules. The lack of BSA adsorption, and the expulsion of BSA by DPPC monolayer is probably due to the strong hydrophilicity of the lipid polar headgroup. When a DPPC dispersion is introduced with Trurnit's method or when dispersion drops are sprayed onto the surface of a DPPC/BSA mixture, the surface tension becomes lower and is controlled by DPPC, which can prevent the adsorption of BSA. The results may be important in understanding inhibition of lung surfactants by serum proteins and in designing efficient protocols of surfactant preparation and administration.     

Adsorption of bovine serum albumin at the air/water interface and its effect on the formation of DPPC surface film

The adsorption of bovine serum albumin (BSA) at the air/water interface and its effect on the transport of dipalmitoylphosphatidylcholine (DPPC) to form a surface film were studied with tensiometry, infrared reflection absorption spectroscopy (IRRAS), and ellipsometry. For 1, 10, 100, and 1000 ppm BSA solutions, the steady-state tension ranges from 55 to 50 mN m⁻¹. At pulsating area (at 20 cycles min⁻¹), both the minimum and maximum tensions decrease with increasing bulk concentration. Even though the steady-state tension is similar for 100 and 1000 ppm BSA, IRRAS and ellipsometry results indicate that the adsorbed density is higher for 1000 ppm BSA. For 1000 ppm/1000 ppm BSA/DPPC mixture, the tension behavior was found to be similar to that of 1000 ppm BSA when alone. Results from IRRAS and ellipsometry also demonstrate that BSA is the dominant adsorbed component at the air/water interface. Thus, at 1000 ppm, by adsorbing fast and possibly irreversibly, BSA interferes with the transport and adsorption of DPPC and inhibits its ability to lower the surface tension. However, when DPPC is introduced via a spread monolayer mechanism, DPPC expels partly or completely the adsorbed BSA monolayer and then controls the tension behavior with little or no inhibition by BSA. Thus, the competitive adsorption of DPPC and BSA depends strongly on the path or mechanism of introducing DPPC to the surface and involves path-dependent nonequilibrium adsorption phenomena.     

Roles of gamma-Globulin in the Dynamic Interfacial Behavior of Mixed Dipalmitoyl Phosphatidylcholine/gamma-Globulin Monolayers at Air/Liquid Interfaces

This study investigated the roles of gamma-globulin in the dynamic interfacial behavior of dipalmitoyl phosphatidylcholine (DPPC)/gamma-globulin monolayers at air/liquid interfaces at 25 degrees C. The surface tension behavior demonstrated that gamma-globulin had a large adsorption time scale. Moreover, the surface pressure-area hysteresis behavior of adsorbed gamma-globulin monolayers suggested that no significant desorption occurred during the compression stage, and the respreading of gamma-globulin molecules at the interface during the expansion stage was slow. From the hysteresis behavior of adsorbed gamma-globulin monolayers with spread DPPC molecules, it was found that gamma-globulin molecules were expelled from the interface as DPPC molecules were in a condensed state. The squeeze-out of gamma-globulin molecules seemed to induce the loss of DPPC molecules at the interface with the extent depending on the initial gamma-globulin surface concentration. Furthermore, the expelled gamma-globulin molecules re-entered the monolayer and participated in the surface pressure increase during the following expansion stage. The exclusion of gamma-globulin associated with the removal of DPPC during monolayer compression and the re-entry of gamma-globulin during subsequent monolayer expansion represented a mechanism for DPPC depletion and gamma-globulin enrichment at the interface, which may explain the inhibitory effect of certain proteins on the surface activity of DPPC. Copyright 2000 Academic Press.     

Dynamic tension and adsorption behavior of aqueous lung surfactants

The dynamic tension behavior, at constant or at pulsating area conditions, of two commercial lung surfactants in saline is reported. The bubble method, at constant or pulsating area, at 37°C and the pendant drop method at 23°C were used. For Exosurf, a commercial synthetic lung surfactant consisting of dissolved tyloxapol and dispersed dipalmitoylphosphatidylcholine (or DPPC) and hexadecanol (H), the equilibrium and dynamic tensions are high (over 30 mN m⁻¹) and similar to those of tyloxapol alone. Aqueous DPPC/H mixtures have lower tensions than Exosurf. Survanta, a commercial lung surfactant replacement drug consisting of DPPC, other lipids, and two hydrophobic lung surfactant proteins, produces dynamic surface tensions that are substantially lower than those of Exosurf. Diluted 10-fold, Survanta produces under pulsating area (at 20 cycles min⁻¹) lower minimum tensions than undiluted Survanta (6 vs. 12 mN m⁻¹), but higher maximum tensions. In addition, Survanta tension behavior is unusual, having three local maxima and three local minima per cycle, suggesting major variations of its surface composition in each cycle. Monolayer pressure-area isotherms and Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy results on deposited Langmuir–Blodgett films support this suggestion. They also provide direct evidence of the presence of phospholipids (DPPC or others) on the surface, but only indirect evidence of the presence of other components, on the surface of aqueous Exosurf or Survanta.     

Surface activity of lysozyme and dipalmitoyl phosphatidylcholine vesicles at compressed and supercritical fluid interfaces

The surface activities of lysozyme and dipalmitoyl phosphatidylcholine (DPPC) vesicles at aqueous/compressed fluid interfaces are examined via high-pressure interfacial tension measurements using the pendant drop technique. The density and interfacial tension in compressible fluid systems vary significantly with pressure, providing a versatile medium for elucidating interactions between biomolecules and fluid interfaces and a method to elicit pressure-dependent interfacial morphological responses. The effects of lysozyme concentration (0.0008, 0.01, and 1 mg/mL) and pressure (> or = 7 MPa) on the dynamic surface response in the presence of ethane, propane, N2, and CO2 at 298 K were examined. Interfacial lysozyme adsorption reduced the induction phase and quickly led to interfacial tensions consistent with protein conformational changes and monolayer saturation at the compressed fluid interfaces. Protein adsorption, as indicated by surface pressure, correlated with calculated Hamaker constants for the compressed gases, denoting the importance of dispersion interactions. For DPPC at aqueous/compressed or aqueous/supercritical CO2 interfaces (1.8-20.7 MPa, 308 K), 2-3-fold reductions in interfacial tension were observed relative to the pure binary fluid system. The resulting surface pressures infer pressure-dependent morphological changes within the DPPC monolayer.     

丙烯酸酯共聚物表面活性剂/多异氰酸酯乳液的制备及表面施胶性能

以低分子量甲氧基聚乙二醇甲基丙烯酸酯(MPEG350MA)和甲基丙烯酸丁酯(BMA)为单体,通过自由基聚合反应制得具有两亲结构的共聚物P(MPEGMA-co-BMA)。测得最佳单体比例下,P(MPEGMA-co-BMA-3)的表面张力为0.77 g/L。以P(MPEGMA-co-BMA)分散1,6-己二异氰酸酯三聚体(HDIT),制得HDI三聚体分散液(LHAHT分散液)。考察了共聚物P(MPEGMA-co-BMA)中亲疏水单体质量比[m(MPEGMA)/m(BMA)]对LHAHT分散液粒径、稳定性和施胶性能的影响。结果表明:[m(MPEGMA)/m(BMA)]为3/1时,LHAHT-3分散液的平均粒径为147.70nm、PDI指数为0.143、TSI为0.58,适用期为6.5 h。以100 g质量分数为10%的LHAHT-3分散液与350 g浓度为10%的聚乙烯醇(PVA1799)复配成1000 g施胶液对木浆原纸进行表面施胶,测得纸张耐折度为128次,抗张指数为55.32 Nm/g,纸张施胶度为26 s,纸张与水接触角为110.49°。     

Comparison of n-tetradecane/electrolyte emulsions properties stabilized by DPPC and DPPC vesicles in the electrolyte solution

The properties of n-tetradecane/electrolyte emulsions with DPPC or DPPC vesicles in the electrolyte solution were investigated. The DPPC molecules form different aggregates, which possess different surface affinity, size and structure, and therefore we assumed some differences in the adsorption at the oil droplet/water interface. The n-tetradecane emulsions in 1:1, 1:2 and 1:3 electrolytes were prepared by mechanical stirring in the presence of DPPC at natural pH. Electrokinetic properties of the systems were investigated taking into account the effective diameter and multimodal size distribution of the droplets as well as the zeta potentials using the dynamic light scattering technique. The zeta potential of the droplets was negative in all systems with NaCl. In the emulsions with CaCl(2) at a higher concentration of electrolyte and emulsions with LaCl(3) with all investigated concentrations, positive values were observed. Similar measurements were performed for DPPC vesicles in the electrolyte solution. The pH and ionic strength changes induce those in the electrical charge of DPPC layer or vesicle surface. This is due to the fact that the DPPC molecule contains -PO(-) and -N(CH(3))(3) groups, which are in equilibrium with H(+) and OH(-), as well as other ions present in the solution, i.e. Na(+), Ca(2+), La(3+) or Cl(-). In the n-tetradecane/electrolyte emulsion stabilized by DPPC or DPPC vesicles the zeta potential may be also related to acid-base interactions. The effect of the ions from the solution on the DPPC layer adsorbed on n-tetradecane droplets or DPPC vesicles is discussed.     

Physicochemical properties of structured phosphatidylcholine in drug carrier lipid emulsions for drug delivery systems

Drug carrier emulsions were prepared with structured phosphatidylcholine (PC-LM) which has both a long hydrocarbon chain and a medium hydrocarbon chain, and the characteristics of PC-LM as an emulsifier were investigated by measuring the creaming ratio, the surface tension of the emulsion system, and the mean particle size and zeta potential of the oil droplets in emulsions. The emulsion prepared with PC-LM as an emulsifier kept the condition and the ratio of separation was lower than those with purified egg yolk lecithin (PEL). The mean particle size of the emulsion prepared with PC-LM was smaller than that with PEL when using only sonication, approximately 250 nm. When using a high-pressure homogenizer after sonication, the mean emulsion size with PC-LM was also smaller than with PEL, approximately 150 nm. The surface tension of the various emulsions and the zeta potential of the emulsion droplets were measured to investigate the stability of the systems. In emulsions with PC-LM or PEL, the surface tension as an index of stability increased as the pressure of the homogenizer increased. Moreover, the zeta potential of the emulsion droplets prepared with PC-LM also increased with an increase in pressure of the homogenizer. As a result, it was found that the drug carrier emulsion prepared with PC-LM had significant advantages in terms of stability and mean diameter. We considered it could be used for the preparations of nanoparticle dispersion systems in drug delivery systems.     

Stability and state of aggregation of aqueous fibrinogen and dipalmitoylphosphatidylcholine lipid vesicles

The stability and state of aggregation of aqueous fibrinogen (FB) and dipalmitoylphosphatidylcholine (DPPC) vesicles in water or buffer at 25 degrees C were studied with dynamic light scattering (DLS), UV-vis spectroturbidimetry (ST), and cryo-transmission electron microscopy (cryo-TEM). In water, when 1000 ppm (0.10 wt %) DPPC dispersions were prepared with a protocol including extensive sonication, they contained mostly vesicles and were quite clear, transparent, and stable for at least 30 days. FB mixtures with water (0.075 wt %) were quite unstable and biphasic. They formed large aggregates which eventually precipitated. The addition of DPPC vesicles into these unstable FB dispersions reversed FB aggregation and precipitation and produced stable translucent microdispersions. The inferred lipid/protein aggregates were limited in size, with average diameters ranging from 200 to 300 nm. In buffer, DPPC dispersions were also clear and quite stable, with average dispersed particles diameter of ca. 90 nm. FB dissolved in aqueous buffer and formed transparent and stable solutions. Adding salt to an aggregated FB dispersion in water reversed the aggregation. FB aggregated and redissolved in the presence of the citrate and after the citrate was removed. There was no effect of citrate (present in FB initially) in the FB aggregation or redissolution. FB molecules in buffer form dimers or higher aggregates. Their average aggregation number is 2, determined with Rayleigh scattering analysis of turbidity data. The average hydrodynamic diameter of FB solutions from DLS was 30 nm. Mixing a stable FB solution in buffer and a stable DPPC dispersion in buffer produced highly unstable mixtures, in which large aggregates precipitated. These results have implications in understanding the interactions of lipids and proteins in many biological applications and food processing applications.     

Behavior of pure and mixed DPPC liposomes spread or adsorbed at the air-water interface

Liposomes from pure dipalmitoylphosphatidylcholine (DPPC) and mixed DPPC: distearoylphosphatidylcholine (DSPC): soybean lecithin (SL) prepared by the Bangham method with sonication were dispersed into solution or spread at the interface and the kinetics of the surface film formation was studied by measuring and recording the evolution of superficial tension, surface potential, and superficial (¹⁴C labeled) DPPC density.A simple theoretical approach can describe these kinetics by two processes: irreversible diffusion of closed vesicles into or from the bulk phase, and irrevers ible transformation of closed spherical vesicles into destroyed ones which form the surface film. Diffusion controls the phenomenon for small initial amounts of liposomes.Transformation controls the phenomenon for important initial amounts of liposomes. The kinetic constant of the transformation,K, does not depend on the technique used to form the surface film (spreading or adsorption).The equilibrium and rheological properties of surface films formed after liposome spreading are compared to those of monolayers     

生物基表面活性剂七叶皂素的界面行为

以天然三萜皂苷七叶皂素为研究对象, 分别采用吊片法、 悬滴法和高速摄像机动态拍摄法探究了七叶皂素分子在气-液、 液-液、 固-液界面的界面行为. 考察了以七叶皂素为乳化剂制备乳液的性质, 以及七叶皂素对液滴在疏水固体表面润湿铺展行为的调控规律, 并从分子层次角度分析了作用机理. 结果表明, 七叶皂素能在气-液界面发生吸附, 将水的表面张力降低至42.1 mN/m, 临界胶束浓度为5×10^?4 mol/L. 七叶皂素还可以在油-水界面吸附, 将亲油端插入油相, 亲水端插入水相, 形成稳定的界面膜, 降低界面张力. 以七叶皂素为乳化剂所制备的乳液, 随着浓度增大可以达到较小的粒径和较大的Zeta电势, 短时间内表现出较好的稳定性. 高浓度的七叶皂素可以很好地抑制液滴在疏水固体表面的弹跳和回缩, 达到很好的铺展效果, 有利于拓展其在诸多领域的应用.     

Influence of pH on colloidal properties and surface activity of polyglycerol fatty acid ester vesicles

Certain polyglycerol esters of fatty acids (PGE) form dispersions of uni- or multilamellar vesicles in dilute aqueous solution. These self-assembled aggregates reduce the surface-activity of PGE monomers such that interfacial films may take several hours to form. This is undesirable for processes, which rely on rapid surfactant adsorption, for example foaming. In the present work, we study the effect of pH on the colloidal (size distribution, morphology, surface charge) and interfacial (adsorption kinetics) properties of a commercial, non-purified PGE. Using dynamic light scattering, zeta-potential measurements and cryo-SEM, we show that changing the pH of the dispersion media can cause agglomeration and eventually osmotic rupture of PGE vesicles. The change in dispersion state also impacts the adsorption behavior at the water surface. Direct evidence that destabilized vesicle dispersion are more surface-active is provided by comparing the dynamic surface tension of solutions of different pH. The faster adsorption kinetics at low pH correlate with a remarkably increased foaming power. We suggest that an osmotic shock induced by changes in pH causes vesicles to deform and partially open, so that their hydrocarbon core is exposed to the dispersion media. This energetically unfavorable condition promotes the hydrophobically driven adsorption of surfactant monomers at surfaces and hence stimulates the foaming ability.     

Adsorption and direct probing of fibrinogen and sodium myristate at the air/water interface

Fibrinogen (FB), a serum protein, is considered a major inhibitor of lung surfactant function at the lining layer of the alveoli. In this study, the adsorption of aqueous bovine FB at the air/water interface was investigated with tensiometry and directly probed for the first time with ellipsometry and infrared reflection adsorption spectroscopy (IRRAS). The tension results show that FB has moderate surface activity. The surface densities of FB were calculated by using two different ellipsometry models to range from 3±0.2 to 17±2 mg/m², for 7.5 to 750 ppm of FB in water at 25°C. Although FB at concentrations from 75 to 750 ppm reached about the same steady surface tension value, the surface densities at 750 ppm FB were substantially larger. The same techniques were used for studying aqueous mixtures of 7.5 to 750 ppm FB with 2 mM of sodium myristate (SM) to investigate a possible interaction of the SM with the protein. The behavior of the FB/SM mixtures was found to be close to that of SM alone. The surface tension of the FB/SM mixtures reached values less than 10 mN/m under surface area oscillation at 20 or 80 rpm. These results and the ellipsometry and the IRRAS results indicate that at a concentration of 2 mM SM, FB, up to 750 ppm, does not inhibit the surfactant surface-tension-lowering function. In certain cases the results demonstrate that FB and SM may act cooperatively in lowering the surface tension.     

Induced removal of dipalmitoyl phosphatidylcholine by the exclusion of fibrinogen from compressed monolayers at air/liquid interfaces

The induced removal of dipalmitoyl phosphatidylcholine (DPPC) by the exclusion of fibrinogen from mixed DPPC/fibrinogen monolayers at compressed air/liquid interfaces was analyzed. The surface pressure-area hysteresis curves of the monolayers at interfaces were obtained by a Langmuir trough. The hysteresis curves of equilibrium fibrinogen adsorption layers suggest that fibrinogen desorption during the area compression stage became significant at a higher bulk concentration of 1000 ppm. For mixed monolayers of DPPC with fibrinogen, the fibrinogen molecules were expelled from the interface upon compression due to the presence of insoluble DPPC molecules. The squeeze-out of fibrinogen molecules evidently removed a significant number of DPPC molecules from the interface, with the extent depending on fibrinogen surface concentration. During the subsequent area expansion stage, fibrinogen molecules entered the interface and participated in the rise of surface pressure. The induced loss of free DPPC molecules at the interface by the expelled fibrinogen molecules during the area compression stage was then evaluated from the hysteresis curves.     

Lung surfactant dysfunction in tuberculosis: effect of mycobacterial tubercular lipids on dipalmitoylphosphatidylcholine surface activity

In pulmonary tuberculosis, Mycobacterium tuberculosis bacteria reside in the alveoli and are in close proximity with the alveolar surfactant. Mycolic acid in its free form and as cord factor, constitute the major lipids of the mycobacterial cell wall. They can detach from the bacteria easily and are known to be moderately surface active. We hypothesize that these surface-active mycobacterial cell wall lipids could interact with the pulmonary surfactant and result in lung surfactant dysfunction. In this study, the major phospholipid of the lung surfactant, dipalmitoylphosphatidylcholine (DPPC) and binary mixtures of DPPC:phosphatidylglycerol (PG) in 9:1 and 7:3 ratios were modelled as lung surfactant monolayers and the inhibitory potential of mycolic acid and cord factor on the surface activity of DPPC and DPPC:PG mixtures was evaluated using Langmuir monolayers. The mycobacterial lipids caused common profile changes in all the isotherms: increase in minimum surface tension, compressibility and percentage area change required for change in surface tension from 30 to 10 mN/m. Higher minimum surface tension values were achieved in the presence of mycolic acid (18.2 ± 0.7 mN/m) and cord factor (13.28 ± 1.2 mN/m) as compared to 0 mN/m, achieved by pure DPPC film. Similarly higher values of compressibility (0.375 ± 0.005 m/mN for mycolic acid:DPPC and 0.197 ± 0.003 m/mN for cord factor:DPPC monolayers) were obtained in presence of mycolic acid and cord factor. Thus, mycolic acid and cord factor were said to be inhibitory towards lung surfactant phospholipids. Higher surface tension and compressibility values in presence of tubercular lipids are suggestive of an unstable and fluid surfactant film, which will fail to achieve low surface tensions and can contribute to alveolar collapse in patients suffering from pulmonary tuberculosis. In conclusion a biophysical inhibition of lung surfactant may play a role in the pathogenesis of tuberculosis and may serve as a target for the development of new drug loaded surfactants for this condition.     

用超声波技术制备的Raney Ni催化剂及其催化加氢活性

 将超声波技术与碱抽滤方法相结合制备出一种Raney Ni催化剂. 以苯饱和加氢为探针反应,测定了超声处理时间对Raney Ni催化剂催化活性(包括吸氢速率和苯转化率)的影响. 结果表明,超声处理对催化剂的活性有明显的促进作用. 随着超声处理时间的延长,催化剂的活性先逐渐升高,后慢慢降低,超声处理15 min时可获得最高的催化活性. 通过ICP,XRD,XPS,BET和SEM等手段对Raney Ni催化剂的表面电子态、比表面积、孔体积、孔径、粒径及表面形貌等进行了表征,并对超声波的作用进行了初步讨论.     

Preparation of raspberry-like nanocapsules by the combination of Pickering emulsification and solvent displacement technique

Well-defined raspberry-like nanocapsules were prepared by the combination of Pickering emulsification and solvent displacement technique by using silica particles as stabilizer and hexadecane (HD) as soft template. The formation of the capsule morphology is caused by the phase separation of poly(styrene-co-4-vinyl pyridine) (poly(St-co-4-VP)) in the droplets due to the diffusion of good solvent for the (co)polymer to the aqueous continuous phase. The size of capsules was successfully reduced from tens of micrometers in the dispersion by simply stirring to the nanorange by the employment of sonication and Ostwald ripening. The formation of silica-particles-armored nanocapsules was confirmed by transmission electron microscopy (TEM), high-resolution scanning electron microscopy (HRSEM), dynamic light scattering (DLS), and zeta potential measurement. The colloidal stability and particle properties, including size and morphology, depend on the amount of HD, and copolymers, the sonication time, the dispersion pH value, the type of solvent, and the copolymer composition.     

Dynamic Surface Tension and Adsorption Mechanism of Surfactant Benzyltrimethylammonium Bromide at the Air/Water Interface

The air‐solution equilibrium tension, γ_c and dynamic surface tension, γ_t, of aqueous solutions of a novel ionic surfactant benzyltrimethylammonium bromide (BTAB) were measured by Wilhelmy method and Maximum bubble pressure method (MBPM), respectively. Adsorption equilibrium and mechanism of BTAB at the air‐solution interface were studied. The CMC was determined to be 0.11 mol/L. The results show that at the start, the adsorption process is controlled by a diffusion step. Toward the end, it changes to a mixed kinetic‐diffusion controlled mechanism with the adsorption activation energy of about 11.0 KJ/mol. Effects of temperature, inorganic salts, and alcohols on adsorption kinetics also are discussed.