十二烷基硫酸钠微乳色谱体系中pH值对其电渗流行为与微结构的影响

以十二烷基硫酸钠(SDS)/正己烷/正丁醇/硼砂微乳液为毛细管电色谱运行研究体系,以甲醇峰为微乳体系电渗流峰(EOF),考察不同pH值条件下微乳体系电渗流出峰时间(tEOF)和变化趋势.以微乳液滴粒径和ξ电位考察pH值对SDS缓冲溶液微乳体系微结构的影响,用微乳体系的电导值分析pH值条件下微乳液滴与氢氧根离子之间的相互...     

鼠李糖脂应用于微乳毛细管电动色谱快速测定化妆品中激素类物质

采用生物表面活性剂鼠李糖脂建立了无需助表面活性剂的微乳体系,并应用于微乳毛细管电动色谱快速分析化妆品中皮质类激素泼尼松、泼尼松龙和氢化可的松。考察了pH值、鼠李糖脂浓度、离子强度、油相种类和浓度、分离温度、分离电压及进样电压和时间的影响,得出微乳体系最佳组成为0.1%(w/w)鼠李糖脂+0.8%(w/w)正庚烷+99.1%(w/w)硼砂缓冲液(80 mmol/L,pH 9.2)。分离温度20℃,分离电压20kV,电动进样10 kV×3 s,泼尼松、氢化可的松和泼尼松龙在9.4 min内可基线分离。重复进样7次,迁移时间和峰面积的RSD分别小于0.2%和5.0%。3种分析物线性范围均为5～100 mg/L;检出限分别为1.0,1.1和1.3 mg/L(S/N=3)。仅需简单萃取即可用于化妆品样品测定,回收率为81.6%～108%;RSD均小于4.8%。     

四-(4-苯基磺酸基)卟啉在反相微乳内相中的聚集行为

本文系统研究了四-(4-苯基磺酸基)卟啉(TPPS)在由聚乙二醇辛基苯基醚（TX-100）构筑的反相微乳液内相中的聚集行为。通过改变反相微乳水相液滴的pH值、粒径及TPPS的浓度,发现在反相乳液内相中TPPS的表观pKa明显小于在水溶液中的pKa（4.9）,并且,TPPS的表观pKa随着水相液滴粒径的减小而降低;当水相液滴的pH > pKa时,TPPS以去质子化单体H2TPPS4-形式存在,而当pH < pKa时,TPPS以质子化单体H4TPPS2-和J-聚集两种形式存在,并且TPPS浓度的增大,促进了H4TPPS2-向J-聚集转变;在pH值不变的条件下,随着水相液滴粒径的增大,TPPS的存在状态由H2TPPS4-向H4TPPS2-转变,并形成J-聚集。     

羧甲基壳聚糖/海藻酸钠半互穿网络水凝胶的制备及性能研究

以羧甲基壳聚糖(CMC)和海藻酸钠(SA)为原料,京尼平(GP)为交联剂,制备具有pH敏感性的CMC/SA半互穿网络(semi-IPN)水凝胶.利用特性黏数、红外光谱对CMC/SA水凝胶的半互穿网络结构及形成机理进行了分析与表征;对水凝胶的力学性能进行了测试;探讨了pH值及交联剂含量对水凝胶溶胀性能的影响.结果表明,京尼平交联的CMC/SA水凝胶具有半互穿网络结构.当w(CMC)∶w(SA)=5∶5时,CMC/SA水凝胶的断裂强度达到最大值(59 MPa),分别比纯的CMC(40 MPa)和SA(36 MPa)提高了47.5%和63.9%;当SA含量为60%时,CMC/SA水凝胶的断裂伸长率达到最大值(13.0%).当pH3.0时,溶胀率随pH值的增大而减小,pH=3.0时,溶胀率最小(186%);当pH3.0时,溶胀率随pH值的增大而增大,pH=9.0时,溶胀率最大(886%).京尼平交联的CMC/SA半互穿网络水凝胶具有明显的pH敏感性、溶胀可逆性及对pH的快速响应性.     

N,O-羧甲基壳聚糖的合成和性质研究

采用多段升温法将壳聚糖改性,合成了取代度为1.84、平均分子量为3.08×105、等电点为7.28的N,O-羧甲基壳聚糖(CMC),分别用紫外光谱、红外光谱、荧光光谱对其结构进行了表征,并对其水溶液的Zeta电位、电导率、表面张力以及水分散体系中羧甲基壳聚糖微粒的粒径分布进行了研究.结果表明, N,O-羧甲基壳聚糖具有表面活性;介质的pH值和浓度对羧甲基壳聚糖溶液的稳定性有很大的影响.     

软段含羧基的水性聚氨酯物性研究

合成了单官能团小分子物质封端的软硬段皆含羧基的脂环族水性聚氨酯(PU),研究了反离子种类、固含量、外加小分子盐/酸、pH值对水性PU的粘度、粒径、CMC和电导率的影响,同时,比较了不同软段分子量水性PU分散液pH临界值和CMC的差异.实验结果表明,随固含量升高,PU分散液体系粘度增大,当固含量为30wt%时,粘度比固含量20wt%的体系粘度增大约20倍;随小分子盐NaCl的加入,PU分散液电粘滞效应逐渐消失,电导率呈现先减小后增大的趋势,随NaCl的加入/软段分子量提高,PU分散体系的CMC值减小,钙离子对PU粒子扩散双电层的破坏作用更加明显.随pH值的增大,PU分散液体系粒径减小,电导率则升高,随软段分子量提高,pH临界值增大,PU分散体对外加小分子酸存在缓冲作用.     

大气中无机盐粒水解过程中的微液滴现象

采用改变相对湿度, 无机盐/金属组合, 测定微液滴体系的pH值和电位分布等方法研究了微液滴形成和生长的特征. 结果表明, 微液滴的形成与大气腐蚀密切相关. 微液滴只在特定的盐粒/金属体系中出现, 微液滴区域具有较高的pH值和较高的电位分布. 此外, 微液滴形成和生长需要两个前提条件：第一, 环境相对湿度应高于盐粒水解液滴液面的饱和蒸汽压；第二, 在水解液滴下的金属能被液滴腐蚀.     

体系pH值、乳化温度和电解质离子对异丙甲草胺水乳剂稳定性的影响

通过测定药物液滴的平均粒径和Zeta电位研究了体系pH值、 乳化温度和电解质离子对乳化剂三苯乙烯基苯酚聚氧乙烯醚磷酸酯三乙醇胺盐(SCP)稳定的异丙甲草胺水乳剂稳定性的影响. 结果发现, 体系的pH值影响SCP分子在水中的电离能力, 当pH=9时, SCP完全电离, 能为液滴提供较大的静电稳定作用, 水乳剂稳定性最好; 乳化温度低时, SCP分子向液滴界面扩散慢, 且舒展不完全, 液滴所带负电荷较少, 水乳剂稳定性差; 温度升高后, 水相黏度减小, 布朗运动加剧, 液滴碰撞合并几率增大, 且SCP分子热运动增强, 易从界面逃逸, 液滴间静电斥力减弱, 同时SCP亲水性下降, 水乳剂稳定性变差; 电解质离子会压缩界面双电层, 降低Zeta电位, 液滴带电量减少而聚结, 离子浓度越大, 电荷数越大, 水乳剂稳定性越差. 在相同的离子浓度下, 水合半径小的Ca²⁺压缩双电层能力强于Mg²⁺, 添加Ca²⁺后水乳剂稳定性更差.     

鼠李糖脂对镧的淋洗效果及影响因素研究

以La为目标污染物,通过鼠李糖脂淋洗土壤试验,考察鼠李糖脂对La的淋洗效果及溶液pH影响,以淋洗前后不同形态稀土元素含量变化为基础,分析淋洗剂对La的稳定性和流动性的影响。结果表明:鼠李糖脂对土壤中稀土元素吸附能力较弱,最佳淋洗pH为6.9,最大淋洗效率为10.24%,相同条件下Cu,Zn的最大淋洗效率分别为67.75%和18.33%。淋洗剂pH值对淋洗效果的影响较大,考察的3个pH值中淋洗剂pH为6.9时淋洗效果最佳。多次淋洗有助于提高La的淋洗效率,最大累积效率为17.76%。当淋洗剂pH=10时,多次淋洗累积效率为7.42%,由于淋洗剂为碱性,使得体系中氧化结合态稀土元素的含量不断升高,该条件下稀土元素稳定性指数MF相对其他条件最大提高了33.67%,有助于稀土元素在土壤中的固化。     

含不同氨基酸反相微乳体系中胆红素钙的形成与稳定性

在聚乙二醇辛基苯基醚(OP)/正己醇/环己烷/水反相微乳液和甘氨酸、精氨酸、组氨酸3种含不同氨基酸的反相微乳液体系中成功地制备了胆红素钙,考察了氨基酸对胆红素钙的组成、形貌、配位方式及稳定性的影响。采用透射电子显微镜、表面Zeta电位、红外光谱和紫外光谱等测试技术对样品进行了表征。结果表明,此反相微乳体系中所得球形颗粒为中性胆红素钙,平均粒径80nm,在水分散体系中颗粒的稳定性随分散体系pH值的升高而先降低后增加,当pH=4.9时,颗粒表面Zeta电位值为0。3种亲水性氨基酸的加入促进胆红素钙颗粒的成核,最终影响胆红素钙的微结构、颗粒形貌和稳定性。当加入的氨基酸为组氨酸、甘氨酸时,所得胆红素钙球形颗粒形貌无明显变化,但平均粒径依次减小至60和40nm,其水分散体系中的稳定性明显增加;当加入的氨基酸为精氨酸时,所得胆红素钙颗粒形貌不规则,粒径非常小,不稳定,易形成聚集体。     

Microstructure of microemulsion modified with ionic liquids in microemulsion electrokinetic chromatography and analysis of seven corticosteroids

In this work, the influences of ionic liquid (IL) as a modifier on microemulsion microstructure and separation performance in MEEKC were investigated. Experimental results showed that synergetic effect between IL 1‐butyl‐3‐methylimidazolium tetrafluoro‐borate (BmimBF₄) and surfactant SDS gave a decreased CMC. With increment of IL in microemulsion, negative ζ potential of the microdroplets reduced gradually. The influence of IL on the dimensions of microdroplet was complicated. At BmimBF₄ less than 8 mM, IL made microemulsion droplet smaller in size. While at BmimBF₄ more than 10 mM, the size increased and reached to a maximum value at 12 mM, where the microdroplets were larger than that without IL. After that, the micreodroplet size decreased again. Relative fluorescence intensity of the first vibration band of pyrene to the third one (I₁/I₃) enhanced as IL was added to microemulsion, which indicated that this addition increased environmental polarity in the inner core of microdroplets. Prednisone, hydrocortisone, prednisolone, hydrocortisone acetate, cortisone acetate, prednisolone acetate, and triamcinolone acetonide were analyzed with MEEKC modified with IL to evaluate the separation performance. Cortisone acetate and prednisolone acetate could not be separated at all in typical microemulsion. The seven analytes could be separated by the addition of 10 mM BmimBF₄ into the microemulsion system. The method has been used for analysis of corticosteroids in cosmetic samples with simple extraction; the recoveries for seven analytes were between 86 and 114%. This method provides accuracy, reproducibility, pretreatment simplicity, and could be applied to the quality control of cosmetics.     

Colloid stability of lipid/polyelectrolyte decorated latex

The colloid stability of supramolecular assemblies composed of the synthetic cationic lipid dioctadecyldimethylammonium bromide (DODAB) on carboxymethyl cellulose (CMC) supported on polystyrene amidine (PSA) microspheres was evaluated via turbidimetry kinetics, dynamic light scattering for particle sizing, zeta-potential analysis, and determination of DODAB adsorption on CMC-covered particles. At 0.1 g L(-1) CMC and 2 x 10(11) PSA particles/mL, CMC did not induce significant particle flocculation, and a vast majority of CMC-covered single particles were present in the dispersion so that this was the condition chosen for determining DODAB concentration (C) effects on particle size and zeta potentials. At 0.35 mM DODAB, charge neutralization, maximal size, and visible precipitation indicated extensive flocculation and minimal colloid stability for the DODAB/CMC/PSA assembly. At 0.1 g L(-1) CMC, isotherms of high affinity for DODAB adsorption on CMC-covered particles presented a plateau at a limiting adsorption of 700 x 10(17) DODAB molecules adsorbed per square meter PSA which was well above bilayer deposition on a smooth particle surface. The polyelectrolyte layer on hydrophobic particles was swelled and fluffy (ca. 11-nm hydrodynamic thickness), and maximal adsorption of DODAB lipid onto this layer produced a compressed composite cationic film with 20 mV of zeta potential and about 10-nm mean thickness. The assembly of cationic lipid/CMC layer/polymeric particle was stable only well above charge neutralization of the polyelectrolyte by the cationic lipid, at relatively large lipid concentrations (at and above 1 mM DODAB) with charge neutralization leading to extensive particle aggregation.     

Hybrid particles of polystyrene and carboxymethyl cellulose as substrates for copper ions

The synthesis of hybrid particles was carried out by emulsion polymerization of styrene in complexes formed by carboxymethyl cellulose (CMC), a polyanion, and a cationic surfactant, cetyltrimethylammonium bromide (CTAB). CMC chains with variable molecular weights and degrees of substitution were tested. The polymerization condition chosen was that corresponding to CMC chains fully saturated with CTAB and to the onset of pure surfactant micelle formation, namely, at the critical aggregation concentration. The hybrid particles were characterized by zeta potential and light scattering measurements. The period of colloidal stability in the ionic strength of 2.0 mol L(-)(1) NaCl was observed visually. Upon increasing the CMC chain length, the particle characteristics remained practically unchanged, but the colloid stability was increased. The increase in the CMC degree of substitution led to particles with more negative zeta potential values. The adsorption of copper ions (Cu(2+)) on the surface of hybrid particles could be described by the Langmuir model, as determined by potentiometric measurements. The increase in the mean zeta potential values and X-ray absorption near-edge spectra evidenced the immobilization of Cu(2+) ions on the hybrid particles.     

Microstructure of microemulsion in MEEKC

The influences of the composition of microemulsion on the microstructure including dimensions and ζ potentials of microdroplets were measured in details. The average dynamic dimension of microdroplets was measured by dynamic laser light scattering, and ζ potential was determined to characterize average surface charge density of microdroplets. The experiment results showed that increase of the amount of surfactant resulted in decrease of microdroplet size but almost invariant ζ potential, which would enlarge migration time of the microdroplet in MEEKC. With increment of cosurfactant concentration, the microdroplet size had an increasing trend, whereas the ζ potential decreased. Thus, observed migration velocity of microdroplets increased, which made the separation window in MEEKC shortened. Neither dimension nor ζ potential of microdroplets changed by varying both the type and the amount of the oil phase. Adding organic solvent as modifier to microemulsion did not change the microdroplet size, but lowered ζ potential. The migration time of microdroplet still became larger, since EOF slowed down owing to organic solvent in capillary. So, besides increment of surfactant concentration, organic additive could also enlarge the separation window. Increase of cosurfactant concentration was beneficial for separation efficiency thanks to the looser structure of swollen microdroplet, and the peak sharpening might compensate for the resolution and peak capacity owing to a narrow separation window. Except the oil phase, tuning the composition of microemulsion would change the microstructure, eventually could be exploited to optimize the resolution and save analysis time in MEEKC.     

Electrophoretic properties of dodecyltrimethylammonium bromide micelles in KBr solution

Charge in ionic micelles determines the trends of their stability and their practical applications. Charge can be calculated from zeta potential (zeta) measurements, which, in turn, can be obtained by Doppler microelectrophoresis. In this study, the electrophoretic properties of dodecyltrimethylammonium bromide (DTAB) in KBr aqueous solution (0-6 mM) were determined by Doppler microelectrophoresis. At very low surfactant concentrations (up to 6 mM), zeta potential was quite constant and due to the ionized monomers (DTA+). Above 6 mM, zeta potential increased to a maximum at surfactant concentrations still below the critical micellar concentration (CMC). This increase could be explained by a formation of nonmicellar aggregates of DTAB. Then, above the CMC, zeta potential underwent an abrupt reduction, which was dependent qualitatively and quantitatively on KBr concentration, and which could be due to an increase of the number of counterions adsorbed on the micelle surface. Calculation of effective micellar charge from zeta potential gave the surface charge density. Comparing this value with the theoretical, obtained from geometrical considerations, a fraction of 0.29 of charged micellar headgroups was obtained when DTAB was in aqueous solution, which is consistent with the value obtained by conductivity measurements.     

Nitric acid oxidation on carbon dispersion and suspension stability

In this study, we have investigated the effect of nitric acid oxidation on the dispersion and suspension stability of activated carbon powder. We treated activated carbon powder with nitric acid at different concentrations. We measured the content of functional groups, the zeta potential and the powder particle size of the activated carbon powder with the Boehm titration, Fourier transform infrared spectroscopy, a zeta potential analyzer, and scanning electron microscopy. The results show that with the increase of nitric acid molar concentration, the content of acid functional groups increased, whereas the content of alkali functional groups decreased. At a nitric acid concentration of 10 mol/l, the surface‐modified activated carbon powder displays features such as the highest functional group content and zeta potential value, the smallest particle size, and the best dispersion and suspension stability in the solution. Copyright © 2008 John Wiley & Sons, Ltd.     

Polymethylmethacrylate derivatives Eudragit E100 and L100: Interactions and complexation with surfactants

Precipitation or coprecipitation of polyelectrolytes has been largely investigated. However, the precipitation of polyelectrolytes via addition of charged and non‐charged surfactants has not been systematically studied and reported. Consequently, the aim of this work is to investigate the effect of different surfactants (anionic, cationic, non‐charged and zwitterionic) on the precipitation of cationic and anionic polymethylmethacrylate polymers (Eudragit). The surfactants effect has been investigated as a function of their concentration. Special attention has been dedicated to the CMC range and to the colloidal characterization of the formed dispersions. Moreover, the effect of salt (NaCl) and pH was also addressed. It is pointed out that non‐ionic and zwitterionic surfactants do not interact with charged Eudragit E100 and L100. For oppositely charged Eudragit E100/SDS and Eudragit L100/CTAB, precipitation occurs, and the obtained dispersions have been characterized in terms of particle size distribution and zeta potential. It was established that the binding of SDS molecules to Eudragit E100 polymer chains is made through the negative charges of the surfactant heads under the CMC value whereas binding of CTAB to Eudragit L100 chains is made at a CTAB concentration 5 times above its CMC. For Eudragit E100/SDS system, a more acidic medium induces aggregation. A same result was observed for the Eudragit L100/CTAB at a more basic pH. Moreover, it was observed that increasing salt concentration (higher than 100 mM) led to aggregation as generally observed for polycations/anionic surfactant systems.     

The colloidal stability of raw bentonite deformed mechanically by ultrasound

The present study examined the effect of sonication time on the particle–size and the colloidal stability (i.e. point of zero charge, PZC and zeta potential, ζ) of raw bentonite (RB) from Saudi Arabia. In this study, bentonite suspensions were sonicated for various time intervals (30, 60 and 120 min). The effect of sonication time on specific surface area and the colloidal stability behavior of bentonite at various pH and in presence of different NaCl concentration were investigated. The increased in lightness and brightness of bentonite suspension was observed during sonication experiment which could be attributed to the reduction in the particles size.With increasing sonication time the specific surface area increased and consequently the zeta potential of bentonite suspension increased. Also a shifting in the PZC from pH 3 for raw bentonite to pH 2 after 120 min of sonication.The zeta potential of sonicated bentonite suspension in presence of different concentration of NaCl shows unusual trend compared to the unsonicated bentonite. In conclusion, the stability of raw bentonite suspension was significantly modified due the application of ultrasound with rending the particle-size of the bentonite.     

Evaluation of surface charge density and surface potential by electrophoretic mobility for solid lipid nanoparticles and human brain-microvascular endothelial cells

Electrophoretic mobility, zeta potential, surface charge density, and surface potential of cacao butter-based solid lipid nanoparticles (SLN) and human brain-microvascular endothelial cells (HBMEC) were analyzed in this study. Electrophoretic mobility and zeta potential were determined experimentally. Surface charge density and surface potential were evaluated theoretically via incorporation of ion condensation theory with the relationship between surface charge density and surface potential. The results revealed that the lower the pH value, the weaker the electrostatic properties of the negatively charged SLN and HBMEC. A higher content of cacao butter or a slower stirring rate yielded a larger SLN and stronger surface electricity. On the contrary, storage led to instability of SLN suspension and weaker electrical behavior because of hydrolysis of ionogenic groups on the particle surfaces. Also, high H+ concentration resulted in excess adsorption of H+ onto HBMEC, rendering charge reversal and cell death. The largest normalized discrepancy between surface potential and zeta potential occurred at pH = 7. For a fixed biocolloidal species, the discrepancy was nearly invariant at high pH value. However, the discrepancy followed the order of electrical intensity for HBMEC system at low pH value because mammalian cells were sensitive to H+. The present study provided a practical method to obtain surface charge properties by capillary electrophoresis.