聚乙烯醇硫酸钾水凝胶电机械化学行为研究

通过将交联聚乙烯醇硫酸酯化的方法制备了一种新型电刺激响应性聚乙烯醇硫酸钾(PVSK)智能水凝胶,并探讨了溶液离子强度和pH对PVSK水凝胶的溶胀吸水率、机械性能以及电机械化学行为的影响.结果表明,制备的PVSK水凝胶的平衡溶胀比随NaCl溶液离子强度的增大而减小,在pH2.39～10.83范围内基本不受溶液pH的影响;经不同离子强度和pH的NaCl溶液充分溶胀的PVSK水凝胶具有良好的机械性能,在非接触的直流电场作用下,该水凝胶向电场负极弯曲,凝胶的弯曲速度和弯曲偏转量随外加电场强度的增加而增大,随NaCl溶液离子强度的增大出现临界最大值,但不随溶液pH(2.08～10.53)的改变而改变;在循环电场作用下,PVSK水凝胶的电机械化学行为具有良好的可逆性.     

UV固化共聚制备含铕(Ⅲ)水凝胶及其荧光行为

以氧化铕(Eu2O3)、邻菲罗啉(phen)和丙烯酸(AA)为原料,制备了含铕(Ⅲ)三元活性配合物(Eu(AA)3phen),将其与丙烯酸-丙烯酰胺凝胶体系进行UV共聚,制备了含铕水凝胶。研究了凝胶中Eu(AA)3phen含量对其吸水性、温敏性及荧光性能的影响,同时探讨了温度及溶胀时间对其荧光性能的影响。结果表明:随Eu(AA)3phen含量的增加,凝胶吸水率先增加后减少,荧光强度逐渐增强;对于特定的凝胶体系,其12 h溶胀度随温度增加而增加,凝胶的荧光强度随溶胀时间和温度增加而减弱。当Eu(AA)3phen的添加量为3.5%时,凝胶综合性能最佳:平衡溶胀度为631 g·g-1,4 h内吸水率达90%以上,荧光强度为175a.u.。所研制的水凝胶在吸水及荧光性能方面对温度均具有良好的响应性。     

声-光-力-热耦合作用下光热敏感水凝胶的溶胀变形行为

超声波在两种介质间传播时，声动量的转移在界面处产生超声辐射应力引发水凝胶形变。为研究光热敏感水凝胶在超声波、光辐射、机械载荷以及温度耦合作用下的大变形行为，采用变分法建立了光热敏感水凝胶声-光-力-热耦合本构模型，研究了声匹配条件下水凝胶单轴预拉伸时超声波强度、光强和温度对其溶胀行为的影响。研究结果表明：单轴预拉伸数值越大，水凝胶的平衡溶胀率越大；超声波强度越强，水凝胶的平衡溶胀率越大，平衡溶胀率随超声波强度增大呈线性递增关系；而随着温度升高，水凝胶的平衡溶胀率先减小后增大，存在一极小值；平衡溶胀率达到极小值时的温度值随预拉伸和超声波强度的增加而升高，随光强增加而降低；当环境温度超过极小值出现时的温度值后，预拉伸和超声波强度变化对水凝胶溶胀行为几乎没有影响，但光强变化对水凝胶溶胀行为仍有一定影响。     

荧光光谱跟踪结冷胶水溶液的溶液-凝胶转变

将异硫氰酸荧光黄(FITC)标记在结冷胶分子链,用荧光光谱跟踪了结冷胶水溶液凝胶化过程中FITC荧光强度和各向异性比的变化.结果表明在结冷胶的凝胶化转变中,FITC的荧光相对强度和各向异性随温度降低而增大,在某一温度荧光相对强度和各向异性比对温度的曲线出现了明显的转折点,这个转折点的温度低于流变温度扫描曲线中G′=G″的温度.利用荧光的方法确定物理交联体系的关于重均聚合度和凝胶分数的相关临界指数γ和β.γ和β不符合Flory-Stockmayer和逾渗模型的预测.     

聚酰胺-胺树形分子荧光性能研究及其在指纹识别领域应用初探

研究了不同温度、浓度、pH值条件下,不同代数、不同端基类型(酯端基和胺端基)的PAMAM(聚酰胺-胺)树形分子的强荧光发射性能.PAMAM树形分子发射强荧光是沿树形结构方向的酰胺基团中的n→π^*跃迁和其密实的球状结构共同作用的结果.树形分子的荧光强度在低pH值或者低温条件下大幅度提高,并且在稀溶液中与浓度成线性关系,在高浓度或者高代数条件下逐渐偏离线性关系.本文还对上述规律的内在机理进行了研究:第一,低pH值条件下,PAMAM树形分子内的叔胺基被氢离子质子化,酰胺荧光发射中心和叔胺基团之间的光诱导电子转移作用被抑制,甚至中断,因此荧光强度急剧升高;第二,随着温度升高,PAMAM树形分子的去活作用增强,荧光强度降低;第三,浓度超过临界点浓度后,由于浓度消光作用,PAMAM树形分子的荧光强度不再随浓度增加而线性增强.最后,将PAMAM树形分子水溶液用于锡纸上油印潜指纹的识别,经处理后的指纹在365 nm紫外光的激发下发射出蓝色荧光,潜指纹被成功地清晰识别.     

聚乙烯醇磷酸酯水凝胶电刺激响应行为的研究

以脲为催化剂,将聚乙烯醇(PVA)磷酸酯化制成聚乙烯醇磷酸酯,再经戊二醛交联制备了一种新型的聚乙烯醇磷酸酯水凝胶.研究了水凝胶的溶胀性能,力学性能和电刺激响应行为.结果表明,该凝胶在NaCl水溶液中其平衡溶胀率随NaCl溶液的离子强度增大而减小.在离子强度为0~0.2的NaCl水溶液中,其弹性模量为0.300~0.356 MPa,抗张强度为91.5~137.8 kPa,断裂伸长率为32.0%~37.5%,且均随离子强度的增大而增大.在去离子水和NaCl水溶液中于非接触直流电场作用下,凝胶向电场负极弯曲,弯曲速度和应变随外加电压的增大而增大,并随NaCl离子强度的增大于0.005处出现极大值.在循环电场作用下,聚乙烯醇磷酸酯水凝胶的电刺激响应行为具有良好的可逆性.     

辐射交联制备改性CMC水凝胶的溶胀行为研究

利用丙烯酰胺 (AAm)接枝改性纤维素 ,然后进行羧甲基化反应得到高取代度的丙烯酰胺 羧甲基纤维素钠 (AAm CMC Na) .对该材料进行γ射线辐照制备出新型改性CMC水凝胶 .研究了这种水凝胶的溶胀动力学、交联动力学以及温度、pH值和无机盐浓度对水凝胶溶胀行为的影响 ,并与CMC Na水凝胶进行了比较 .结果表明 ,该水凝胶和CMC Na水凝胶相比 ,优点在于辐照交联所用的剂量下降 ,而且所需的CMC浓度减少 .AAm CMC Na水凝胶的溶胀度随温度升高而增大 ,在pH为 6～ 8范围内达到最大值 ,并随无机盐浓度与吸收剂量增加而下降 ,表现出较好的温度敏感性和pH敏感性 ,可望作为吸水材料和水保持剂     

聚乙烯醇调控水溶性共轭聚噻吩的光学性质

针对发光共轭聚合物稀溶液在干燥形成固体时的荧光淬灭问题, 通过高分子聚乙烯醇(PVA)的氢键网络调控水溶性共轭聚噻吩在溶液中的聚集行为和构象, 并采用不同的干燥方式实现了调控其固体光学性质的目的. 紫外-可见光吸收、荧光发射光谱测试表明, 在水溶液中PVA可以分散共轭聚合物链, 并增强其共平面性; 高温干燥后, 聚噻吩薄膜与无PVA添加的聚噻吩溶液的荧光性质相似; 而采用冷冻干燥法, 薄膜则保留了添加PVA后混合溶液的发光特性. 该结果表明, PVA对聚噻吩在溶液状态下的聚集/分子构象的调控行为随干燥方式的不同得到了不同程度的保留——高温加热干燥仅维持了PVA对聚噻吩的分散作用; 而冷冻干燥则完整保留了PVA与聚噻吩的分子间相互作用, 将溶液中分子的分散状态和构象同时固定. 本研究从干燥方式的角度为固态共轭聚合物聚集行为及发光性质的调控提供了新的策略.     

具有智能荧光特性的含二甲氨基查尔酮端基的PNIPAM研究

以偶氮二异丁腈为引发剂,含二甲氨基查尔酮基团的三硫代碳酸酯为链转移剂,在四氢呋喃溶剂中将N-异丙基丙烯酰胺(NIPAM)通过可逆加成断裂链转移(RAFT)自由基聚合制备了具有智能荧光特性的含二甲氨基查尔酮端基的聚N-异丙基丙烯酰胺(PNIPAM-DMAC),并通过红外光谱、核磁共振氢谱和紫外-可见光谱对其结构进行表征.研究了PNIPAM-DMAC聚合物的温敏性以及溶剂极性、温度、分子识别三重敏感的荧光特性.结果表明,PNIPAM-DMAC聚合物的低临界溶解温度(LCST)比聚N-异丙基丙烯酰胺(PNIPAM)聚合物低,且随着PNIPAM-DMAC聚合物分子量的降低、聚合物水溶液浓度的减小和α-环糊精(α-CD)的加入,其LCST温度均升高.随着溶剂极性的增加,PNIPAM-DMAC聚合物的荧光峰值波长基本上随着溶剂极性的增大而红移,荧光强度出现极小值和极大值,在甲醇和水中几乎无荧光,具有溶剂极性敏感的荧光特性;随着温度升高,PNIPAM-DMAC聚合物水溶液荧光强度显著增强,同时伴随荧光发射光谱的蓝移现象,且荧光随温度交替改变而呈现出可逆变化,具有可逆的温度“开/关”特性;α-CD的添加使得PNIPAM-DMAC聚合物水溶液的荧光强度增强,荧光峰值波长轻微蓝移,具有分子识别敏感的荧光特性.     

双敏性微凝胶的絮凝及聚沉行为

用沉降聚合法制备了聚(N-异丙基丙烯酰胺-co-甲基丙烯酸)微凝胶, 并用NMR, DLS分析测定了微凝胶结构及凝胶颗粒在不同离子强度下粒径和表面电势的变化. 25 ℃时在pH＝7的溶液中Zeta电位为－18 mV, 随离子强度增加, 逐渐减小. 当NaCl浓度达0.2 mol/L时基本不变, 表明微凝胶表面电荷受到屏蔽, 浓度继续增加主要使凝胶颗粒收缩. 加热引起微凝胶收缩, 颗粒表面电荷密度增大, Zeta电位增大. 在0.2 mol/L NaCl溶液中, 41 ℃时微凝胶的Zeta电位可达－12.4 mV, 使微凝胶稳定. 较高离子强度时, Zeta电位随温度升高发生突变, 微凝胶表面几乎为中性, 其突变温度与临界絮凝温度(CFT)相当. CFT随离子强度增加向低温迁移, 微凝胶聚集速率在高温时比低温时快.     

Composition of sodium cholate micellar solutions

To study the composition of sodium cholate solutions, an investigation was carried out at 25 degrees C and in N(CH3)4Cl, as a constant ionic medium, at three different concentrations (W = 0.100; 0.500 and 0.800 mol dm(-3)). Electromotive force measurements of three different galvanic cells, the first involving a glass electrode for hydrogen ions, the second an electrode for sodium ions and the third a lead amalgam electrode, were performed. Independently, lead (II) cholate solubility measurements in the presence of sodium ions were performed, as well. The experimental results obtained from both approaches were explained by assuming the formation of aggregates in cholate and sodium of different composition depending on W and on the cholate concentration. The maximum aggregation found number for cholate was 24 and even aggregation numbers were markedly predominant. Only two species with odd aggregation number were found, but at a low percentage. The assumed species and the relative constants were compared with those found for the other sodium salt of cholanic acids.     

(Sodium Alginate/Acrylamide) Semi‐Interpenetrating Polymer Networks and their Usability on Removal of Lead,Cadmium, Nickel Ions

In this study, (sodium alginate (NaAlg)/acrylamide (AAm)) interpenetrating polymer networks (IPN) have been prepared at three different compositions, where the sodium alginate composition varies 1, 2, and 3% (w/v) in 50% (w/v) acrylamide solutions. These solutions have been irradiated with a ⁶⁰Co‐γ source at different doses. The percent conversion was determined gravimetrically and 100% gelation was achieved at the 10.0 kGy dose. The swelling results at pH 7.0 and 9.0 indicated that (NaAlg/AAm)3IPN hydrogel, containing 3% NaAlg showed maximum % swelling in water, with swelling increasing in the order of Ni²⁺>Cd²⁺>Pb²⁺. Diffusion in aqueous solutions of metal ions within (NaAlg/AAm)IPN hydrogels was found to be Fickian character. Diffusion coefficients of (NaAlg/AAm)IPN hydrogels in water and aqueous solutions of metal ions were calculated. The maximum weight loss temperature and half life temperature for NaAlg, PAAm, (NaAlg/AAm)IPN and (NaAlg/AAm)IPN‐metal ion systems were found from thermal analysis studies. In the adsorption experiments, the efficiency of (NaAlg/AAm)IPN hydrogels to adsorb nickel, cadmium and lead ions from water was studied. (NaAlg/AAm)IPN hydrogels showed different adsorption for different aqueous solution of metal ion at pH 7.0. Adsorption isotherms were constructed for the (NaAlg/AAm)IPN‐metal ion systems. S type adsorption in the Giles classification system was found.     

Lanthanide-containing photoluminescent materials: from hybrid hydrogel to inorganic nanotubes

Functional photoluminescent materials are emerging as a fascinating subject with versatile applicability. In this work, luminescent organic-inorganic hybrid hydrogels are facilely designed through supramolecular self-assembly of sodium cholate, and lanthanide ions such as Eu(3+), Tb(3+), and Eu(3+)/Tb(3+). Fluorescence microscopy and TEM visualization demonstrates the existence of spontaneously self-assembled nanofibers and 3D networks in hybrid hydrogel. Photoluminescence enhancement of lanthanide ions is realized through coordination with cholate and co-assembly into 1D nanofibers, which can successfully shield the Eu(3+) from being quenched by water. The photoluminescence emission intensity of a hybrid hydrogel exhibits strong dependence on europium/cholate molar ratio, with maximum emission appearing at a stoichiometry of 1:3. Furthermore, the emission color of a lanthanide-cholate hydrogel can be tuned by utilizing different lanthanide ions or co-doping ions. Moreover, photoluminescent lanthanide oxysulfide inorganic nanotubes are synthesized by means of a self-templating approach based on lanthanide-cholate supramolecular hydrogels. To the best of our knowledge, this is the first time that the lanthanide oxysulfide inorganic nanotubes are prepared in solution under mild conditions.     

Temperature effect on formation of sodium cholate micelles

The micellization of sodium cholate (NaC) at 293.2, 298.2, 303.2, 308.2, and 313.2 K by cholate anion concentration was studied over the pH range from 6.0 to 7.2. Using a stepwise association model of cholate anions without bound sodium counterions, the aggregation number (nmacr;) of the cholate micelles was evaluated and found to increase with the total concentration, indicating that the stepwise association model is applicable. The nmacr; values go up and down with increasing temperature; 17 at 298.2 and 12 at 313.2 K and at 60 mM of the sodium cholate. The fluorescence of pyrene was measured in sodium cholate solution to determine the critical micelle concentration (CMC), indicating a narrow concentration range for CMC. A sodium-ion-specific electrode was used to determine a relatively low degree of counterion binding to micelles, supporting the validity of the present association model of cholate anions. The aggregation numbers evaluated at a constant ionic strength of 0.15 and at lower but variable ionic strengths were similar except for higher cholate concentrations.     

Swelling Behavior and Metal-Ion Uptake Capacity of pH-Responsive Hydrogels of Poly(N-acryloyl-N′-ethylpiperazine)

New hydrogels based on N-acryloyl-N′-ethylpiperazine (AcrNEP) and N,N-methylene bisacrylamide (MBA) were prepared by thermal initiated solution polymerization. The hydrogels swelled extensively in buffer solutions of low pH due to protonation of the amine functions of the monomers, while the swelling was less significant in buffer solutions of high pH. The increased swelling of the gel in low pH is due to the development and interaction of fixed charges within the gel network. As a result of the electrostatic repulsion between the charges the elastic constraint of the gel is modified which leads to pronounced swelling and hence to high water uptake. Water transport in the hydrogel both in buffer solutions of pH 2.6 and pH 8.4 was non-Fickian due to polymer relaxation (anomalous process). The gels demonstrated good uptake of divalent metal ions such as Ni²⁺, Co²⁺, and Zn²⁺, with high selectivity for Ni²⁺ ions due to the formation of a more stable ligand-metal complex. The metal uptake capacity increased with increase in pH of the solution, while an increase in the crosslinker amount of the hydrogel reduced its metal uptake capacity. In the presence of metal ions the swelling of the hydrogel reduced considerably due to the formation of additional physical crosslinks within the hydrogel network. The metal ion loaded hydrogels could be stripped and regenerated with 1 M sulfuric acid without any loss in swelling or metal uptake capacities.     

Copper and Nickel Removal from Aqueous Solutions Using New Chelating Poly[Acrylamide/N‐vinyl pyrrolidone/3‐(2‐hydroxyethyl carbamoyl)acrylic acid] Hydrogels

New poly[Acrylamide/N‐vinyl pyrrolidone/3‐(2‐hydroxyethyl carbamoyl)acrylic acid], poly [AAm/NVP/HECA], chelating hydrogels with different composition of HECA monomer have been prepared via free radical solution polymerization using N,N‐methylene bisacrylamide as a crosslinker. The hydrogels obtained were loaded with metal ions and characterized by FT‐IR spectroscopy, Scanning Electron Microscope (SEM) and Thermogravimatric analysis (TGA). The removal of Cu²⁺ and Ni²⁺ from aqueous solutions by the hydrogel was examined by a batch equilibrium method. The influence of treatment time, pH, initial concentration of the metal ions and HECA content in the feed compositions on the amount of adsorbed metal ions was studied. Swelling of the hydrogel was also carried out in distilled water and metal ion solutions. The removal of the metal ions followed the following order: Ni²⁺>Cu²⁺. The amount of metal ions removed increased with increasing HECA content in the feed composition, treatment time, pH of the medium and initial concentration of metal ions. The desorption of metal ions were carried out using 1 N HCl and 0.5 N H₂SO₄. The poly[AAm/NVP/HECA] hydrogels could be used many times without significantly decreasing their adsorption capacity.     

Poly(ethylene glycol)–poly(L‐lactide) star block copolymer hydrogels crosslinked by metal–ligand coordination

The aqueous solution behavior and thermoreversible gelation properties of pyridine‐end‐functionalized poly(ethylene glycol)–poly(L ‐lactide) (PEG–(PLLA)₈–py) star block copolymers in the presence of coordinating transition metal ions were studied. In aqueous solutions, the macromonomers self‐assembled into micelles and micellar aggregates at low concentrations and formed physically crosslinked, thermoreversible hydrogels above a critical gel concentration (CGC) of 8% w/v. In the presence of transition metal ions like Cu(II), Co(II), or Mn(II), the aggregate dimensions increased. Above the CGC, the gel–sol transition shifted to higher temperatures due to the formation of additional crosslinks from intermolecular coordination complexes between metal ions and pyridine ligands. Furthermore, as an example, PEG–(PLLA)₈–py hydrogels stabilized by Mn(II)–pyridine coordination complexes were more resistant against degradation/dissolution when placed in phosphate buffered saline at 37 °C when compared with hydrogels prepared in water. Importantly, the stabilizing effect of metal–ligand coordination was noticeable at very low Cu(II) concentrations, which have been reported to be noncytotoxic for fibroblasts in vitro. These novel PEG–(PLLA)₈–py metallo‐hydrogels, which are the first systems to combine metal–ligand coordination with the advantageous properties of PEG–PLLA copolymer hydrogels, are appealing materials that may find use in biomedical as well as environmental applications like the removal of heavy metal ions from waste streams. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Novel mucoadhesive carriers based on alginate-acrylamide hydrogels for drug delivery

New mucoadhesive two-component carriers for drug delivery based on synthetic acrylamide/diethylacrylamide and natural alginate hydrogels have been synthesized. The introduction of sodium alginate into polyacrylamide/ poly(diethylacrylamide) gels, followed by their crosslinking with metal ions, significantly changed structure and properties of hydrogels, such as swelling degree, drug capacity and drug release rate in physiological solution. The structure of the gels was characterized by FTIR spectroscopy and scanning electron microscopy.     

Effect of metal ion hydration on the interaction between sodium carboxylates and aluminum(III) or chromium(III) ions in aqueous solution

The interaction between sodium octanoate, decanoate, and dodecanoate and aluminum(III) and chromium(III) has been studied in water at natural pH values, starting well below the surfactant critical micelle concentration, using electrical conductivity, turbidity, and potentiometric measurements. With decanoate or dodecanoate, maximum interaction occurs at 3:1 stoichiometry, corresponding to charge neutralization. Although the solutions become turbid with both metal ions, indicating phase separation, differences are observed and attributed to the fact that aluminum(III) is relatively labile to substitution and rapidly replaces its water ligands, whereas chromium(III) is substitution inert. This shows up in well-defined floc formation with Al(3+), whereas Cr(3+) suspensions do not precipitate, probably because that replacement of coordinated water by carboxylate ligands is impeded. This can be overcome by increasing temperature, and differences in the thermal behavior with Al(3+) and Cr(3+) are suggested to be due to increased involvement of substitution reactions in the latter case. The effect of octanoate on the trivalent metal ions is less clear, and with Cr(3+) interaction only occurs when the carboxylate is in excess. Hydrophobic interactions between alkyl chains play a major role in driving phase separation. At high surfactant concentrations, the solid phases do not dissolve, in contrast to what is observed with the corresponding alkylsulfates. This has implications for use of these systems in metal separation through froth flotation. The concentration of metal ions in supernatant solution has been determined for sodium dodecanoate and sodium dodecylsulfate with Al(3+) and Cr(3+) over the whole surfactant concentration range by inductively coupled plasma-mass spectrometry (ICP-MS). From this, association constants have been determined and are found to be larger for the carboxylate than the alkylsulfate, in agreement with the greater Lewis basicity of the -CO(2)(-) group.     

Thermoresponsive behavior of poly(n-isopropylacrylamide) hydrogels containing gold nanostructures

We report the changes in the structure and thermoresponsive behavior of poly(N-isopropylacrylamide) (PNIPAm) hydrogels when gold nanostructures are synthesized in situ within the hydrogel matrix. Cross-linked PNIPAm hydrogels were synthesized using NIPAm and 0.00-3.50% (w/w versus NIPAm) of N,N'-methylenebisacrylamide (MBAm) and/or N,N'-cystaminebisacrylamide (CBAm) as cross-linking agents. The hydrogels were soaked in potassium tetrachloroaurate to introduce gold ions. The hydrogels containing Au3+ were then immersed in a sodium borohydride solution to reduce the gold ions. Infrared spectroscopy, UV-visible spectroscopy, and equilibrium swelling were used to examine the structural/physical differences between gels of different compositions; UV-visible spectroscopy and mass measurements were used to observe the kinetics and thermodynamics of the hydrogel volume phase transition. These studies revealed several differences in the physical characteristics and thermoresponsive behavior of hydrogels based on cross-linker identity and the presence or absence of gold nanostructures. Hydrogels with gold nanostructures and high CBAm and low MBAm content have equilibrium swelling masses 3-20 times their native analogues. In comparison, gold-containing hydrogels with high MBAm and low CBAm content have swelling masses that are equal to their native analogues. Additionally, the gold-containing PNIPAm hydrogels cross-linked with only CBAm have a deswelling temperature of approximately 40 degrees C, approximately 8 degrees C above the samples cross-linked with only MBAm. Varying the CBAm content and introducing gold enables tuning of the deswelling temperature.