表面活性剂吸附的电泳研究

实验测定了溴代烷基三甲胺的吸附对单分散聚苯乙烯胶乳电泳速度的影响.在Stern双电层模型的基础上,从电泳数据求得了吸附等温线,改进了计算吸附位数与吸附自由能的方法,并讨论了可能的吸附机构.     

烷基硫酸钠在二氧化钛上的吸附研究

表面活性剂在氧化物表面上的吸附,因其在浮选中的重要作用而被广泛研究。但迄今为上的工作多是关于表面活性离子在电性相反的氧化物表面上,例如阳离子表面活性剂在带负电的氧化物表面上的吸附,而对电性相同的表面活性离子的吸附则很少涉及,虽然许多实际问题中遇到的是后一种情形。本工作研究了烷基硫酸钠在带负电的TiO₂表面上的吸附,根据吸附与电泳的实验结果计算了吸附自由能,并提出了可能的吸附机理。     

电导滴定法研究阳离子乳胶粒的导电性能及其在棉织物上的吸附

阳离子乳胶粒与棉纤维存在静电作用而发生吸附,研究其导电能力与吸附作用具有重要理论和应用价值。 采用电导滴定法通过测定乳胶粒表面氯离子含量,研究了乳胶粒的导电能力,并探讨了乳胶粒在棉纤维表面的吸附模型。 结果表明,阳离子乳胶粒的浓度(cp)在0.05~0.3×10-8 mol/L 范围内与电导率(Λ)呈良好的线性关系(Λ=8.0913cp+1.8093,R2=0.9986);根据电解质理论计算得出阳离子乳胶粒中胶核的极限摩尔电导率在恒定温度（25 ℃）下随着乳胶粒浓度的增加呈降低趋势;此外,阳离子乳胶粒在棉纤维表面的吸附符合Langmuir型吸附模型。     

酰胺基团对Gemini表面活性剂表面活性和聚集行为的影响

本文合成了含酰胺基团和不含酰胺基团的两类Gemini阳离子表面活性剂,测定了其表面活性参数,研究了酰胺基团对表面活性剂的表面活性和聚集行为的影响。结果表明,酰胺基团提高了Gemini阳离子表面活性剂的临界胶团浓度,降低了胶团聚集数,增强了胶团微极性,增大了表面活性剂的饱和吸附量。     

SDS与PVP对碘化银溶胶稳定性的影响

研究了SDS、PVP及二者的混合物对AgI溶胶稳定性的影响。SDS主要通过表面活性负离子在AgI质点表面上的吸附使ζ电势升高,提高溶胶的稳定性。低浓度的PVP使AgI溶胶敏化,高浓度时又通过吸附层的空间稳定效应使其稳定。在PVP与SDS的混合溶液中,AgI溶胶的稳定性显著增加。根据PVP与SDS在固液界面上的相互作用讨论了这一增效作用。     

纳米SiO2与阳离子表面活性剂的相互作用及其诱导的正辛烷-水乳状液的双重相转变

研究了3种不同结构的水溶性阳离子表面活性剂对纳米二氧化硅颗粒的原位表面活性化作用, 它们分别是单头单尾的十六烷基三甲基溴化铵(CTAB)、单头双尾的双十二烷基二甲基溴化铵(di-C12DMAB)和双头双尾的Gemini型阳离子三亚甲基-二(十四酰氧乙基溴化铵)(II-14-3), 并通过测定Zeta电位、吸附等温线及接触角等参数对相关机理进行了阐述. 结果表明, 阳离子表面活性剂吸附到颗粒/水界面形成以疏水基朝向水的单分子层, 从而增强了颗粒表面的疏水性是原位表面活性化的基础. 通过吸附CTAB和II-14-3, 颗粒的疏水性适当增强, 能吸附到正辛烷/水界面稳定O/W(1)型乳状液; 而通过吸附di-C12DMAB所形成的单分子层更加致密, 颗粒的疏水性进一步增强, 进而使乳状液从O/W(1)型转变为W/O型; 当表面活性剂浓度较高时, 由于链-链相互作用, 表面活性剂分子将在颗粒/水界面形成双层吸附, 使颗粒表面变得亲水而失去活性, 但此时体系中游离表面活性剂的浓度已增加到足以单独稳定O/W(2)型乳状液的程度. 因此当采用纳米二氧化硅和di-C12DMAB的混合物作乳化剂时, 通过增加di-C12DMAB的浓度即可诱导乳状液发生O/W(1)→W/O→O/W(2)双重相转变.     

四乙铵离子对阴离子表面活性剂及其混合体系的表面活性和胶团形成的影响

研究了溴化四乙铵介质中十二烷基硫酸四乙铵、全氟辛基磺酸四乙铵及其混合体系的表面化学性质。四乙铵离子在浓度较小时主要起电解质反离子作用,在浓度较大时则明显参与表面吸附和胶团的形成,其作用相当于在表面活性离子的疏水链上“引入”碳氢链,从而导致表面活性提高和碳氢/碳氟表面活性剂混合体系中碳氢/碳氟链间的互疏作用减弱等。     

表面活性剂在低能固体表面上的吸附 Ⅲ: 聚苯乙烯胶乳粒子对阴离子表面活性剂的吸附

在无乳化剂的条件下合成了粒径均匀的聚苯乙烯胶乳, 发展了应用表面张力计测定吸附等温线的连续平衡法, 得到不同盐浓度下聚苯乙烯胶乳对十二烷基硫酸钠和十二烷基苯磺酸钠的吸附等温线, 它们属于Giles分类的L2 型或L1 型, 采有两阶段吸附模式讨论了吸附机理, 吸附层结构及等温线类型变化的规律。     

PS胶体粒子表面逐层自组装固定化SOD及其生物活性

通过逐层自组装技术成功地把超氧化物歧化酶(SOD)吸附在聚苯乙烯(PS)胶体粒子表面.zeta电位和TEM证明了聚阳离子或聚阴离子型SOD与相反电荷的聚电解质在PS胶体粒子表面的交替吸附.通过测定SOD被胶体粒子吸附后上清液的生物活性,得到聚阴离子型SOD(pH=8.0)和聚阳离子型SOD(pH=4.3)在PS胶体粒子表面的吸附量分别为12和51IU,相对活性分别为23.4%和2.9%.聚阴离子型SOD在PS胶体粒子表面能形成平滑规整的膜,导致较高的相对活性.研究结果表明,通过调节pH值,可以优化自组装固定化酶的聚集状态和生物活性     

表面活性剂在低能固体表面上的吸附 Ⅲ: 聚苯乙烯胶乳粒子对阴离子表面活性剂的吸附

在无乳化剂的条件下合成了粒径均匀的聚苯乙烯胶乳.发展了应用表面张力计测定吸附等温线的连续平衡法,得到不同盐浓度和温度下聚苯乙烯胶乳对十二烷基硫酸钠和十二烷基苯磺酸钠的吸附等温线.它们属于Giles分类的L_2型或L_4型,采用两阶段吸附模式讨论了吸附机理、吸附层结构及等温线类型变化的规律。     

The effect of metallic cations on the electrophoretic properties of a pretreatedHevea latex

High-ammonia latex concentrate prepared from doubly-centrifuged fieldHevea latex was exhaustively dialysed to remove any residual water-soluble non-rubber constituents. The electrophoretic mobilities of the dialysed latex in the presence of various metallic cations were investigated as a function of electrolyte concentration. The mobility decreased with increasing concentration of the cations Na⁺, Ba²⁺, Mg²⁺ and Ca²⁺ in a manner consistent with the effect of simple electrolyte on compression of the electric double layer. Anomalous behaviour was noted for the divalent ion copper, in that it reversed the charge of the latex particles at a concentration even lower than that of uranyl ions. Multivalent cations (lanthanum, cerium and thorium) had a profound influence on the latex particles where very low charge reversal concentrations were observed. It is believed that strong adsorption of hydrolysed species from the metallic ions was responsible for reversing the charge of the originally negative latex particles. These experiments indicated that the efficiency with which the cations reversed the charge of the latex particle surface was in the order: lanthanum > cerium > copper > thorium > uranyl > calcium > magnesium > barium > sodium. The number of cation binding sites on the latex particle surface and the chemical free energies of cation adsorption were calculated. It was found that the interaction of the latex particle with the hydrolysable metallic cations was much more stronger than that with the simple divalent cations and that this intercation was comparable to that of biological surfaces.     

十二烷基三甲基溴化铵在聚苯乙烯胶乳粒子上的吸附

实验测得C~1~2TAB在PS胶乳粒子表面的吸附等温线呈L型的二阶段吸附特征,这表明初始的C~1~2TA^+离子是将其季铵正电性头基吸引在PS链的负电性硫酸根端基上,并将碳氢链通过疏水相互作用吸附在PS链上。结合光子相关谱测得胶乳粒子流体力学半径R~H的变化,表明第I阶段围绕着这些初始吸附位的聚集吸附,产生平均聚集数为4.0的松散小聚集体,此时对应的浓度c/cmc=0.32是文献通常所指的临界表面胶团浓度csmc。其后的进一步聚集吸附最终生成了附着在PS链端基处且平均聚集数为19.5的球形吸附胶团。这一饱和吸附的结果增加了胶乳粒子在水溶液中的分散稳定性。     

SANS and SAXS analysis of charged nanoparticle adsorption at oil-water interfaces

A systematic study of the adsorption of charged nanoparticles at dispersed oil-in-water emulsion interfaces is presented. The interaction potentials for negatively charged hexadecane droplets with anionic polystyrene latex particles or cationic gold particles are calculated using DLVO theory. Calculations demonstrate that increased ionic strength decreases the decay length of the electrostatic repulsion leading to enhanced particle adsorption. For the case of anionic PS latex particles, the energy barrier for particle adsorption is also reduced when the surface charge is neutralized through changes in pH. Complementary small-angle scattering experiments show that the highest particle adsorption for PS latex occurs at moderate ionic strength and low pH. For cationic gold particles, simple DLVO calculations also explain scattering results showing that the highest particle adsorption occurs at neutral pH due to the electrostatic attraction between oppositely charged surfaces. This work demonstrates that surface charges of particles and oil droplets are critical parameters to consider when engineering particle-stabilized emulsions.     

PS纳米球在羧甲基化壳聚糖自组装膜表面静电吸附行为研究

用AFM研究了PS纳米球在自组装有羧甲基化壳聚糖(CM-CHI)单层膜的云母基底上的吸附行为及CM-CHI自组装膜形貌对PS纳米球吸附行为的影响.重点考察了盐浓度,吸附时间和温度对PS自组装动力学的影响.在CM-CHI自组装膜制备条件一定的情况下,20℃时PS最大覆盖率对应的盐浓度为0.5mol/L,平衡吸附时间为20min,对应的覆盖率约为48.0%.CM-CHI自组装膜形貌对覆盖率的影响主要表现为PS纳米球在由不同方法制备的CM-CHI自组装膜上的覆盖率在最宜吸附盐浓度,平衡吸附时间内随吸附温度的升高而显著增大,当PS吸附温度为60℃时甚至有部分覆盖率达65.0%.此外,还讨论了有关CM-CHI自组装膜是否干燥及PS自组装循环中冲洗用水盐浓度对PS纳米球覆盖率的影响.     

THE ADSORPTION OF LINEAR POLY(N-ISOPROPYLACRYLAMIDE)CHAINS ON SURFACTANT-FREE POLYSTYRENE NANOPARTICLES

The adsorption of linear poly(N-isopropylacrylamide) (PNIPAM) chains on surfactant-freepolystyrene (PS) nanoparticles was used as a model system to study the hydrophobic adsorption of polymeron the surface, because the hydrophobility of PNIPAM can be continuously varied by a small temperaturechange. The adsorption was investigated by a combination of static and dynamic laser light scattering (LLS)measurements, In static LLS, the absolute excess scattered light intensity led to the amount of PNIPAMadsorbed on the surface. In dynamic LLS, the hydrodynamic thickness of the adsorbed PNIPAM layer wasaccurately measured. For a given particle concentration, the adsorption increases as thc PNIPAMconcentration and the incubation temperature increase. The average density of the adsorbed PNIPAM layer isreciprocally proportional to the number of the PNIPAM chains on the surface, revealing a simple scaling ofthe chain density distribution. The adsorption follows the Langmuir's isotherm. The enthalpy changeestimated from the adsorption at 25℃and 30℃is slightly positive, indicating that the adsorption involvesthe coil-to-globule transition of the chains on the surface.     

Agglutination study of poly(allyl-alpha-D-glucopyranose/styrene) latex particles in the presence of Concanavalin A

Latex agglutination of the glucose-modified latex, which were synthesized by emulsion copolymerization of allyl-modified glucose and styrene monomers by specific binding interactions between Concanavalin A (Con A) and allyl-alpha-d-glucopyranose, were investigated. The surface of the glucose-modified latex was characterized by dye-partition method and the number of glucose was 1517 per latex particle. The average particle size and the polydispersity index of the latex were 78.3 and 1.005, respectively. Time-evolution adsorption behavior of various concentrations of the Con A and the consequent latex agglutination were studied by UV spectrophotometer at 540 nm and zeta-potential analyzer at the fixed latex concentration of 0.02 wt%. Specific binding between Con A and allyl-alpha-D-glucopyranose leaded the latex particles to coagulate by decreasing the electrostatic repulsion between the particles and mobility.     

Pd/Al2O3表面上活性位性质及其与加氢反应动力学参数间的关系

近年发展起来的新的动态技术能够用于分离测定非均相催化反应的吸附平衡,吸附和表面反应速率系数,而中毒实验使人们能够测定催化剂表面上活性位的容量和强度性质。如果把两者结合起来(可称作动态中毒法)就有可能研究催化剂表面上活性位性质与其动力学参数间的关系。本文的目的,是要在作者早先工作的基础上,在三相浆态床反应器中,应用动态中毒法探索研究Pd/Al_2O_3催化剂表面上活性位性质及其与α-甲基苯乙烯     

Hydrolysis versus ion correlation models in electrokinetic charge inversion: establishing application ranges

In this article, we investigate experimentally a wide range of situations where charge inversion (i.e., overcompensation of the surface charge of a colloidal particle by the countercharge) can occur. To that end, the electrophoretic mobility of sodium montmorillonite, silica, and polystyrene latex as functions of pH and concentration of different salts is presented, and conditions are established where charge inversion occurs. The reason for this study is to provide experimental evidence for distinguishing between two existing models for the explanation of charge inversion. One of these is the specific adsorption of ions located in the Stern layer in combination with a Gouy-Chapman diffuse part of the double layer. The other ion-correlation theories explain the phenomenon in terms of purely physical arguments based on Coulombic pair interactions between ions and surface charges and on excluded volume effects. In distinguishing between these two interpretations, the influence of the pH plays a central role because of its effect on the hydrolysis of multivalent cations. In our experiments, it is found that although 1-2 and 2-2 electrolytes provoke a decrease in the absolute values of the electrophoretic mobilities when their concentration in solution is increased, they never lead to charge inversion, whatever the surface charge or the pH. However, in the case of salts of trivalent cations, electrokinetic charge reversal is often observed above a certain critical electrolyte concentration. In addition, the extent of overcharging increases when the concentration is raised above the critical value. This trend occurs for any system in which the surface charge is pH-independent, as in polystyrene latex and montmorillonite. Most of the results presented here are compatible with the specific adsorption of hydrolyzed metal ions as the main driving force for charge inversion. At low pH, when the hydrolysis of trivalent cations is likely to be absent, overcharging can be attributed to ion correlation effects.     

Surface clusters of colloid particles produced by deposition on sites

The possibility of producing surface clusters of well-defined structure formed by colloid particles was analyzed theoretically and experimentally. Theoretical results were derived by performing Monte Carlo-type simulations according to the generalized random sequential adsorption (RSA) mechanism. In these simulations, the jamming coverage of particles adsorbing irreversibly on spherical sites was determined as a function of the particle-to-site size ratio lambda. It was revealed that, by properly choosing lambda, a targeted site coordination can be achieved; for example, there can be one, two, three, and so forth particles attached to one site. The structure of the heterogeneous clusters produced in this way was described in terms of the pair correlation function. It was predicted that the extent of ordering within surface clusters was diminished as the concentration of sites increased. These theoretical predictions were checked by performing deposition experiments of negatively charged polystyrene latex particles (average diameter 0.9 mum) under the diffusion-controlled transport regime. Mica sheets precovered by positively charged polystyrene latex (average diameters 0.45 and 0.95 microm) were used as the substrate surface in these experiments. Positive latex (site) deposition was also carried out under diffusion-controlled transport conditions. The concentration of the sites and the adsorbed particles was determined by direct particle counting using optical microscopy. It was found, in quantitative agreement with theoretical simulations, that the structure of surface clusters produced in this way exhibits a significant degree of short-range ordering. It also was proven experimentally that clusters containing a targeted number of colloid particles (e.g., 2 and 4) could be produced by the deposition procedure.     

Is latex surface charge an important parameter for foam stabilization?

We describe the facile production of highly stable foams stabilized solely by cationic polystyrene latex particles. Three model polystyrene latexes were synthesized using either a cationic 2,2'-azobis(2-diisobutyramidine) dihydrochloride (AIBA) or an anionic ammonium persulfate (APS) radical initiator: a 724 +/- 81 nm charge-stabilized cationic polystyrene latex [AIBA-PS], an 800 +/- 138 nm sterically stabilized cationic latex prepared using a poly(ethylene glycol) monomethacrylate macromonomer [PEGMA-AIBA-PS], and a 904 +/- 131 nm charge-stabilized anionic polystyrene latex [APS-PS], respectively. The effect of particle surface charge, latex concentration, and solution pH on foam stability was studied in detail. The PEGMA-AIBA-PS latex proved to be the best foam stabilizer even at relatively low latex concentrations (3.0 wt %), with long-term foam stabilities being obtained after drying. The AIBA-PS latex also produced stable foams, albeit only at higher latex concentrations. However, the APS-PS latex proved to be an ineffective foam stabilizer. This is believed to be primarily due to the anionic surface character of this latter latex, which prevents its adsorption at the anionic air-water interface. This hypothesis is supported by the observation that the AIBA-PS latex no longer acts as an effective foam stabilizer above its isoelectric point (pH 7.04). Scanning electron microscopy studies revealed the formation of well-defined latex bilayers within dried foams, which indicates that the wet air bubbles are stabilized by latex monolayers prior to drying. However, little or no long-range ordering of the latex particles was observed on the surface of the bubbles, which is presumably related to the latex polydispersity.