The pH and temperature dual-responsive micelle transition in the mixture of hydrotrope potassium phthalic acid and quaternary ammonium surfactants cetyltrimethylammonium bromide

A facile and effective route to prepare a pH and temperature dual-responsive surfactant micelle has been introduced based on hydrotrope potassium phthalic acid (PPA) and quaternary ammonium surfactants cetyltrimethylammonium bromide (CTAB). The system can be switched between viscoelastic solution and water-like fluid by adjusting pH values. In this paper, different binding abilities between the hydrotrope and surfactants have been demonstrated during the process of adjusting pH because the hydrotrope has different ionization degrees with the pH variation. And with the aid of rheological measurements and cryo-TEM observation, we discussed the different effects of the hydrotrope on surfactants at various pH values in detail and analyzed the possible aggregate transition mechanism of CTAB–PPA system induced by pH. Besides, this CTAB–PPA system has temperature-responsive property when pH?<?2.50. The temperature sensitivity and reversible control of rheological properties may greatly facilitate practical applications of such responsive viscoelastic solution.     

Formation and transformations of polyelectrolyte gel-ampholyte dendrimer-surfactant ternary complexes

The reactions of complex gels formed via the sorption of a poly(propylenimine) ampholyte dendrimer of the fourth generation by oppositely charged lightly cross-linked polyelectrolyte hydrogels with ionogenic micelle-forming surfactants have been studied. The sorption of surfactant ions likely charged relative to the complexed ampholyte dendrimer by complex gels is associated with two parallel chemical reactions controlled by the concentration of the surfactant and pH which give rise to the formation of network-dendrimer-surfactant tertiary complexes. The reactions of complex gels with surfactant ions likely charged relative to the network polyelectrolyte make it possible at different solution pHs to prepare both negatively and positively charged hydrogels reinforced by disperse particles of the dendrimer-surfactant complex.     

Preparation of zinc oxide nanorods using pulsed laser ablation in water media at high temperature

ZnO columnar single crystals were formed by pulsed laser ablation in deionized water and surfactant aqueous solutions of lauryl dimethylaminoacetic acid (LDA) and cetyltrimethylammonium bromide (CTAB) at 80 degrees C. ZnO particles produced by laser ablation were dissolved at a higher temperature than 60 degrees C, and then crystalline growth to columnar structure proceeded. While large ZnO columnar crystals were obtained in deionized water, the crystals prepared in surfactant solution were smaller than those in deionized water due to inhibition of crystalline growth by surfactant adsorption on ZnO surfaces. The size of ZnO nanorods depended on how surfactant molecules adsorb on ZnO surface.     

Temperature-dependent vesicle formation of aqueous solutions of mixed cationic and anionic surfactants

The phase behavior of aqueous solutions of mixed cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) was examined at different temperatures (20, 30, 40, and 50 degrees C). While stable vesicles were formed in a narrow composition range on the SOS-rich side at 20 degrees C, the range widened remarkably when the temperature was raised to 30 degrees C. Thus, the vesicle region extended to cover almost the entire composition range, CTAB:SOS = 0.5:9.5-5.0:5.0, at the total surfactant concentrations of 50-70 mM on the SOS-rich side. To analyze the temperature dependence of this phase behavior of the mixed surfactant system, DSC and fluorescence polarization measurements were performed on the system. The experimental findings obtained revealed that pseudo-double-tailed CTAB/SOS complex, the major component of the bimolecular membrane formed by the surfactant mixture, undergoes a gel (Lbeta)-liquid crystal (Lalpha) phase transition at about 26 degrees C. This phenomenon was interpreted as showing that the bimolecular membrane has no curvature and is rigid and easy to precipitate at temperatures below the phase transition point, whereas it has a curvature and is loose enough to disperse in the solution as vesicles at temperatures above the phase transition point. Vesicles formed by the anionic/cationic surfactant complex were then stable at temperatures above the phase transition temperature of the complex.     

Micellar aggregates and hydrogels from phosphonobile salts

The aggregation properties of novel bile acid analogs-phosphonobile salts (PBS)-have been studied. The critical micellar concentration of 23 and 24-phosphonobile salts were measured using fluorescence and 31P NMR methods. All the ten synthesized phosphonobile salts formed gels at different pH ranges in water. The pH range at which individual PBSs could gelate water was narrow and influenced by the number and conformation of hydroxyl groups. A reversible thermochromic system has been developed (with 23-phosphonodeoxycholate at pH 3.3), which changes color upon gelation. The investigation of the first hydrogels derived from trihydroxy bile acid analogs 1 and 6 was made using fluorescence, 31P NMR, X-ray crystallography, circular dichroism and SEM. The present studies reveal that the gel network consists of a chiral, fibrous structure possessing hydrophobic interiors.     

响应性凝胶及其在药物控释上的应用

综述近年来在响应性凝胶材料研究方面的进展，介绍了能感应ｐＨ、温度、光、电场以及生化物质等外界因素变化的响应性凝胶的结构特点与响应机理，同时介绍了此类凝胶应用于药物控制释放方面的研究近况。     

Novel Interpenetrating Networks (IPNs) Hydrogels Prepared In Situ by Liquid-Phase Photopolymerization

Novel interpenetrating networks (IPNs) hydrogels responsive to temperature were prepared in situ by liquid-phase photopolymerization. The first network of the IPNs (poly isopropyl acrylamide) were formed with a special kind of hectorite (Laponite XLS) modified by tetrasodium pyrophosphate as cross-linker and 2-oxogultaric acid as photoinitiator. The samples were subsequently immersed in an acrylamide (AAm) aqueous solution for at least one day for preparing IPNs hydrogels, in which acrylamide aqueous solution containing N,N′-Dimetyl acrylamide (MBAA) as cross-linker and 2-oxogultaric acid as photoinitiator. Then the second networks were in situ formed by introducing ultraviolet light irradiated PNIPAAm gels. The swelling/deswelling behaviors of IPNs hydrogels were measured. Compared with the corresponding nanocomposite PNIPAAm hydroges(NC hydrogels), chemically cross-linked PNIPAAm and PAAm IPNs hydrogels, the results indicate that the new IPN hydrogel has a faster deswelling rate above its LCST (≈32 °C). The effect was explained as being an additional contribution of the PAAm chains in IPN hydrogels, which may act as a water-releasing channel when the hydrophobic aggregation of PNIPA takes place.     

Chiral separation of bupivacaine enantiomers by capillary electrophoresis partial-filling technique with human serum albumin as chiral selector

Capillary electrophoresis (CE) is a powerful technique for enantiomer separations due to its intrinsic high separation efficiencies, speed of analysis, low reagent consumption and small sample requirements. However, some chiral selectors present strong background UV absorption providing high detection limits. The present paper deals with the application of the partial-filling technique to the separation of bupivacaine enantiomers by capillary electrophoresis using human serum albumin (HSA) as chiral selector. In this procedure the cationic surfactant cetyltrimethylammonium bromide (CTAB) was used as a dinamic capillary coating in order to reduce the electro-osmotic flow and detect both bupivacaine enantiomers out of the chiral selector plug. Several experimental conditions such as CTAB concentration, pH, HSA concentration and plug length, background electrolyte concentration, temperature and voltage were studied. Under the selected conditions it is possible to detect the separated enantiomers out of the HSA plug in less than 4 min using 50 mM Tris pH 8 as background electrolyte with 50 microM CTAB, at 30 degrees C and using a separation voltage of 25 kV. The proposed methodology was then validated for analytical purposes and applied to the analysis of pharmaceutical preparations commercially available. The results obtained with the proposed methodology were in good agreement with those declared by the manufacturers. The simplicity, sample throughput, accuracy, reproducibility and low cost of the proposed method make it suitable for the control of the enantiomeric composition of bupivacaine in pharmaceuticals.     

Phase behavior of aqueous mixtures of 2-phenylbenzimidazole-5-sulfonic acid and cetyltrimethylammonium bromide: hydrogels, vesicles, tubules, and ribbons

We studied the phase behavior and aggregation in mixed aqueous solutions of the anionic UV-absorber 2-phenylbenzimidazole-5-sulfonic acid sodium salt, PhBSA (Na salt), and the cationic surfactant cetyltrimethylammonium bromide, CTAB. The mixtures of the two components behave similarly to catanionic surfactant mixtures. The samples on the PhBSA-rich side have low viscosity and are turbid. The turbidity, due to uni- and multilamellar vesicles (SUVs and MLVs), increases with the mole ratio of CTAB. The interbilayer distance inside the MLV changes with the mole ratio of the two components from a few 10 nm for the 7:3 (molar ratio of PhBSA, Na salt, to CTAB) system to practically zero for the 5:5 mixture. The latter mixture forms a precipitate within less than 1 h. With the exception of the 5:5 mixture, all samples on the PhBSA-rich side are stable for many days. After that period, within one more day, the turbid vesicle phases are transformed into more or less clear hydrogels. We found that the gelation is due to the formation of very long stiff tubules about 14 nm in diameter, which is independent of the mixing ratio of the samples. The hydrogels and the tubules melt around 45 degrees C. On the CTAB-rich side, the 4:6 sample behaves like the 6:4 sample, whereas at 3:7 a precipitate was found to form shortly after mixing. At still smaller PhBSA (Na salt) to CTAB ratios, only clear, viscoelastic solutions are found that do not change with time. We determined the micellar structures in the samples by cryo-TEM and by SAXS. The rheological properties of the hydrogels and of the viscoelastic samples were characterized by oscillating rheological measurements. DSC measurements indicated that the tubules are in a semicrystalline state and melt at around 45 degrees C. The semicrystalline bilayer of the tubules seems to have a 1:1 composition of PhBSA to CTAB. The excess PhBSA seems to be adsorbed on the tubules. It is assumed that the stiffness of the bilayer of the vesicles and the stiffness of the tubules are due to the stiffness of the PhBSA molecule.     

温度及pH敏感聚(丙烯酸)-co-(丙烯腈)水凝胶的合成及性能研究

温度及ｐＨ敏感聚（丙烯酸） ｃｏ （丙烯腈）水凝胶的合成及性能研究卓仁禧张先正（武汉大学化学系国家教委生物医用高分子材料开放实验室武汉４３００７２）关键词丙烯酸，丙烯腈，水凝胶，溶胀率关于水凝胶的环境敏感性研究始于八十年代初［１］．随后大量研究表明...     

快速响应大孔聚(N-异丙基丙烯酰胺-co-丙烯酸)水凝胶的合成及表征

以聚乙二醇6000为成孔剂,由自由基引发N-异丙基丙烯酰胺(NIPA)和丙烯酸(AAc)共聚交联得到大孔凝胶,研究了凝胶对环境温度的响应性能.在凝胶制备过程中,PEG6000分子充当成孔剂,得到的凝胶具有大孔结构.这种大孔结构有利于水分子的进出,大孔凝胶对温度变化有较快的响应速率.增加亲水单体AAc的含量,凝胶的LCST有所升高,凝胶的亲水性增强,在较低温度下凝胶的溶胀率也随之升高.振荡实验表明,所得的大孔凝胶具有反复使用的能力.     

疏水改性智能水凝胶P(NIPA-co-DiAB)的合成及其温敏行为

以N-异丙基丙烯酰胺(NIPA)和N,N-双烯丙基苄胺(DiAB)为共聚单体、N,N-亚甲基双丙烯酰胺(BIS)为交联剂、十二烷基硫酸钠(SDS)为表面活性剂、过硫酸铵(APS)-四甲基乙二胺(TMEDA)为氧化还原引发体系,采用自由胶束交联共聚法合成了疏水基团为芳香基的疏水改性温敏性智能水凝胶P(NIPA-co-DiAB)。研究了DiAB摩尔分数(x(DiAB))对水凝胶溶胀性能的影响。 在初始溶胀阶段,随着x(DiAB)由0增大至3%,P(NIPA-co-DiAB)水凝胶的溶胀行为由Fickian扩散转变为non-Fickian扩散。x(DiAB)分别为0、1%、2%和3%时,P(NIPA-co-DiAB)水凝胶的平衡溶胀率SR0在蒸馏水中分别为63.6、93.5、141.6和167.4,在0.01 mol/L SDS溶液中分别为63.1、71.0、59.0和77.5,在CTAB溶液中分别为37.6、42.2、44.1和60.0,在Triton X-100溶液中分别为30.9、49.4、68.5和88.3。 结果表明,P(NIPA-co-DiAB)水凝胶的(SR0)大于PNIPA水凝胶,且在蒸馏中比在0.01 mol/L表面活性剂溶液中要大。 加入0.01 mol/L Triton X-100、CTAB或SDS后,PNIPA水凝胶的体积相变温度或较低临界溶解温度(LCST)由32.5 ℃分别增加至35.4、45.6和80 ℃。P(NIPA-co-DiAB)水凝胶的LCST由32.0～32.5 ℃分别增加至34.7～35.6 ℃、45.8~46.2 ℃和80 ℃。 加入表面活性剂能增加P(NIPA-co-DiAB)水凝胶的体积相变温度,高的体积相变温度与DiAB含量无关。     

In-situ heating study on the structural change of surfactant-templated germanium oxide mesostructure

Mesostructured germanium oxide has been well-synthesized by using a surfactant-templated approach under basic hydrothermal conditions. The cationic surfactant cetyltrimethylammonium bromide (CTAB) has formed nanotubes with uniform diameter of about 3.2 nm. Blanket-like morphology of the as-prepared sample has been observed with transmission electron microscopy (TEM). High-resolution TEM image reveals that the nanotubes are connected with inorganic germanium oxide and have self-assembled into periodic mesostructure. In-situ heating X-ray diffraction (XRD) patterns confirm that the germanium oxide is in amorphous phase in the temperature range from room temperature (RT) to 700 degrees C. In-situ heating small-angle X-ray scattering (SAXS) presents the mesostructural change with temperature. The local atomic structures around germanium atom have been obtained with in-situ heating X-ray adsorption fine structure (XAFS) techniques. The stability of this mesostructure has been determined to be correlated with the cationic surfactant CTAB. The structural evolution from the GeO 2/NaOH aqueous solution, the as-prepared sample to the sample heated at 700 degrees C, has been described, and the formation mechanism of mesostructured germanium oxide has been discussed.     

Surfactant head group and concentration influence on structure and dynamics of gellan gum hydrogels: Crossover from stretched to compressed exponential

In the present study, we have investigated the effects of surfactant addition on the structure and dynamics of gellan gum hydrogels. A strong interaction is seen between gellan gum and oppositely charged cationic surfactant, hexadecyltrimethylammonium bromide (CTAB) whereas rather weak or minimal interactions are observed when either anionic surfactant, sodium dodecylsulfate (SDS), or nonionic surfactant, Triton X-100 is added to the system. The dynamics of the hydrogels was studied, using dynamic light scattering measurements and the heterodyne method was used for data evaluation. The correlation function of parent hydrogel was fitted with a stretched exponential function, while a single plus stretched exponential function was employed to study the dynamics of hydrogel with surfactants and the corresponding relaxation times were appropriately analyzed. An interesting crossover from stretched to compressed exponential was seen when CTAB was added beyond critical micellar concentration to the system, which was not evidenced for the other two surfactants. Ensemble averaged intensity was also analyzed and the general picture that emerges is that the oppositely charged surfactant has the strongest ability to form large associations as oppose to nonionic and like-charged surfactants. The rheological measurements were carried out to determine the elastic response of the gels over a wide range of frequencies. It was seen that the elastic modulus was dependent on both the surfactant concentration and type. Cationic surfactant increased the elastic modulus markedly as opposed to the nonionic and anionic surfactants. These results may have implications for the use of polymer surfactant systems as potential products.     

离子键交联的聚两性电解质凝胶在不同pH和不同电解质溶液中溶胀行为研究

以丙烯酸(AA)和甲基丙烯酸二乙氨基乙酯(DEAM)形成的离子复合物与丙烯酰胺(AAm)共聚,合成了一种新型的离子键交联的聚两性电解质凝胶(PADA).由于分子之间的氢键作用,PADA凝胶并不是在A/C(负正离子单体摩尔比)为1,而是在A/C为1.55处有最大消溶胀.与共价键交联的聚两性电解质凝胶相比,PADA凝胶的溶胀行为具有更强的pH敏感性.PADA凝胶在不同pH缓冲溶液中的溶胀行为表明,在pH 3~4之间消溶胀程度最大.在偏离该pH区域时凝胶均发生溶胀.但凝胶的溶胀程度在pH<3的酸性溶液中随A/C的增加而降低;而在pH>4的偏碱性溶液中随其增加而增加.在不同价数的离子溶液中,离子浓度对于PADA凝胶的平衡溶胀有着不同的影响.对于一价的NaCl溶液,PADA凝胶有典型的反聚电解质效应.但对于高价的CaCl2和柠檬酸三钠溶液,只在较低的浓度下,才表现出反聚电解质效应.而在较高盐浓度时,随盐浓度的增加其溶胀比反而降低.这可能与高价离子形成的离子键交联有关.与pH对PADA凝胶溶胀程度的影响相似,在CaCl2溶液中,PADA凝胶的溶胀程度随A/C的增加而降低;而在柠檬酸三钠溶液中则刚好相反.这种独特的溶胀行为似乎与高价离子电荷的正负性有关.     

快速响应的温敏性聚(N-异丙基丙烯酰胺)水凝胶 Ⅰ.以CaCO_3为成孔剂制备方法、表征及动力学研究

以不同粒径的CaCO3粒子为成孔剂 ,合成了快速响应的温敏性聚 (N 异丙基丙烯酰胺 ) (PNIPA)水凝胶 .利用扫描电镜观察到水凝胶具有特殊的孔状结构 ,得到水凝胶的孔径大小为几十微米左右 .动力学研究表明 ,该水凝胶在温敏膨胀或收缩时 ,具有快速的响应速率 ,在 10min内的失水率可达 90 % .比较了干凝胶和4 0℃下失水后的凝胶两种不同状态下水凝胶的膨胀曲线 ,发现两者的溶胀动力学曲线明显不同 ,前者的曲线有拐点 .同时发现与失水收缩速率相比 ,水凝胶具有较慢的吸水膨胀速率 .     

Synthesis,swelling properties,and network structure of new stimuli‐responsive poly(N‐acryloyl‐N′‐ethyl piperazine‐co‐N‐isopropylacrylamide) hydrogels

Poly(N‐acryloyl‐N′‐ethyl piperazine‐co‐N‐isopropylacrylamide) hydrogels were prepared by thermal free‐radical copolymerization of N‐acryloyl‐N′‐ethyl piperazine (AcrNEP) and N‐isopropylacrylamide (NIPAM) in solution using N, N′‐methylene bisacrylamide as the crosslinking agent. The gels were responsive to changes in external stimuli such as pH and temperature. The pH and temperature responsive character of the gels was greatly dependent on the monomer content, namely AcrNEP and NIPAM, respectively. The gels swelled in acidic (pH 2) and de‐swelled in basic (pH 10) solutions with a response time of 60 min. With increase in temperature from 23 to 80 °C the swelling of the gels decreased continuously and this effect was different in acidic and basic solutions. The temperature dependence of equilibrium water content of the gels was evaluated by the Gibbs–Helmholtz equation. Detailed analysis of the swelling properties of these new gels in relation to molecular heterogeneity in acidic (pH 2) and basic (pH 10) solutions were performed. Water transport property of the gels was studied gravimetrically. In acidic solution, the diffusion process was non‐Fickian (anomalous) while in basic solution, the diffusion was quasi‐Fickian. The effect was more evident in solution of pH 2 than in pH 10. Various structural parameters of the gels such as number‐average molar mass between crosslink (M_c), the crosslink density (ρ_c), and the mesh size (ξ) were evaluated. The mesh sizes of the hydrogels were between 64 and 783 Å in the swollen state in acidic solution and 20 and 195 Å in the collapsed state in basic solution. The mesh size increased between three to four times during the pH‐dependent swelling process. The amount of unbound water (free water) and bound water of the gels was also evaluated using differential scanning calorimetry. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

两亲性阴离子HBPN与阳离子表面活性剂CTAB络合机理的研究

用动态光散射研究了两亲性阴离子HBPN(高度枝化的聚酯纳米微粒)和阳离子表面活性剂CTAB(十六烷基三甲基溴化铵)在缓冲液中的相互作用及HBPN/CTAB络合物的形成.结果表明:在静电作用下,于碱性溶剂中,HBPN与由CTAB分子所构成的胶束形成了核壳结构络合物HBPN/CTAB.络合物粒径的大小和稳定性可以通过溶液的pH值和CTAB浓度来控制.     

DNA-based gels for oral delivery of probiotic bacteria

A single-stranded DNA, readily extracted from industrial discarded salmon milt, was used to prepare hydrogels and complex gels by cross-linking with gelatin and kappa-carrageenan, for the oral delivery of probiotic bacteria. The complex gels showed a higher protective capability over the hydrogels for approximately one log scale. However, the hydrogels were more stable during storage at 4 degrees C. The Lactobacillus and Lactococcus due to protection of the hydrogels could better tolerate to acid than the Bifidobacterium. Furthermore, food-graded hydrogels were prepared and optimized to a similar protective capability for future applications.     

Fibrous assemblies and water gelation in mixtures of lysine with sodium alkyl sulfates

Thermoresponsive, pH-sensitive fibrous structures and gels are formed in aqueous mixtures of the amino acid lysine with oppositely charged sodium alkyl sulfate surfactants. The formation of these assemblies depends on the chain length of the surfactant, which is varied between 8 and 16, the chirality and degree of protonation of the amino acid, and the molar ratio of these species. Self-assembly of the fibers occurs when specific lysine enantiomers are in solution and for pH conditions in which the majority of the amine groups are protonated (i.e., at near-equimolar amounts of HCl and lysine). Racemic mixtures of lysine do not form fibers with sodium dodecyl sulfate. Micelles are the fiber precursors, and the fibers, which can be hundreds of micrometers long, entangle to form gels. With increasing temperature, the gels melt, the fibers dissolve, and a single micellar phase forms. The micelles elongate with decreasing pH when the acid concentration is greater than equimolar with respect to lysine, and they shrink with increasing temperature.