共查询到18条相似文献,搜索用时 625 毫秒
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荧光光谱跟踪结冷胶水溶液的溶液-凝胶转变 总被引:2,自引:0,他引:2
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. 相似文献
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以溶质、溶剂间的协同作用作为高分子电解质体系的凝胶化条件,以松软粒子结构(Bolb)间的三维逾渗的凝胶化模型,将高分子电解质体系的凝胶化分为松软粒子的形成和逾渗过程。结合海藻酸溶液的Cu^2+、Ca^2+、Mn^2+和Co^2+离子添加体系的凝胶化,分析了高分子电解质溶胶-凝胶相转移的实质,得到了体系相对粘度的临界指数k=-0.90 ̄1.14,与逾渗模型的预测值相吻合,探讨了松粒子的形成对相转移介 相似文献
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本文以St/DVB凝胶、St/DVB超髙交联凝胶为参比网络结构,用荧光光谱方法跟踪研究了St/DVB交联凝胶氯甲基化反应过程中网络结构形态的衍变.发现随着凝胶中氯百分含量的增加,其苯基激基缔合物320nm荧光谱带趋于消失;在最初反应阶段.苯基多环聚集体420nm荧光谱带强度迅速上升.而后急剧下降,同时在488nm左右出现一新的荧光谱带,与超高交链凝胶荧光谱带相近似:红外光谱证实了氯甲基化凝胶中亚甲基交联桥的增加.结果表明,伴随氯甲基化反应发生的后交联反应可使交联凝胶疏松网络区结构趋向紧密,使溶剂难以逾渗的微凝胶核松弛解体,从而使St/DVB交联凝胶网络涨落趋向均匀. 相似文献
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以溶质、溶剂间的协同作用作为高分子电解质体系的凝胶化条件,以松软粒子结构(Blob)间的三维逾渗的凝胶化模型,将高分子电解质体系的凝胶化分为松软粒子的形成和逾渗过程。结合海藻酸溶液的Cu2+、Ca2+、Mn2+和Co2+离子添加体系的凝胶化,分析了高分子电解质溶胶-凝胶相转移的实质,得到了体系相对粘度的临界指数k=0.90~1.14,与逾渗模型的预测值相吻合,探讨了松软粒子的形成对相转移临界点fc的影响,明确了临界点附近相对粘度的幂次公式ηrel∝(fc—f)-k)的适用范围。 相似文献
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《高分子学报》2015,(7)
以羧甲基纤维素钠(Na CMC)-烷基三甲基溴化铵(CnTAB)复合体系为研究对象,在Na CMC亚浓缠结溶液中考察了CnTAB烷基尾链长度对CnTAB临界缔合浓度(cac)及溶液流变行为的影响.采用荧光探针法测得cac值,根据吉布斯自由能定量分析了烷基尾链对胶束缔合行为的影响.稳态流变测试结果表明,较高浓度CnTAB对Na CMC亚浓缠结溶液有强烈的增黏作用.显微观察表明,低浓度CnTAB形成孤立胶束(约5nm),而较高浓度CnTAB则形成胶束复合聚集体(约30 nm).扣除胶束电荷中和所致降黏作用后,孤立胶束表现为等效刚性球,Na CMC亚浓缠结溶液的黏度变化符合Einstein方程;相反,胶束在临界浓度以上发生逾渗,形成胶束复合聚集体,进一步形成贯穿于Na CMC分子缠结网路的胶束逾渗网络.首次揭示了复合体系增黏的实质是胶束网络逾渗,而不是由胶束吸附聚电解质链形成物理网络.增黏阶段Na CMC亚浓缠结溶液的黏度变化符合逾渗模型和平均场理论.长程静电相互作用控制胶束缔合与逾渗行为,逾渗临界胶束体积分数随CnTAB尾链长度增加而降低,临界胶束表面间距随CnTAB尾链长度增加而增大. 相似文献
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以丙烯酰胺(AM)为亲水单体,脂肪醇聚氧乙烯醚丙烯酸酯(AEO-AC-n-m,n为疏水端烷基链碳的数目,m为亲水端PEG链的长度,n,m=13,5;10,5;13,10)为疏水单体,十二烷基硫酸钠(SDS)为表面活性剂,过硫酸钾(KPS)为引发剂,通过胶束聚合制备了3种聚丙烯酰胺-co-脂肪醇聚氧乙烯醚丙烯酸酯(AM-co-AEO-AC)疏水缔合水凝胶.以疏水烷基链为直链的疏水单体AEO-AC-13-5合成的直链型水凝胶的网络结构均匀且强度高,其形态在水中可维持180 d.而以疏水烷基链为支链的疏水单体AEO-AC-10-5与AEO-AC-13-10合成的支链型水凝胶的机械性能较弱,60 d内即溶解于水中.在相同条件下,直链型水凝胶断裂时的最大应力是支链型水凝胶的4~5倍.利用弹性橡胶理论中的新胡克方程计算了直链型和支链型水凝胶的有效交联密度ν0和有效交联点间的分子量Mc. 相似文献
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The sol-gel transition in aqueous alginate systems induced by in situ released calcium cations was monitored with rheology methods. Four alginate samples with different molecular weights and M/G ratios were used over the concentration C(Alg) of 2 approximately 6 wt % with different mole ratios f of Ca2+ to the alginate repeat unit. The scaling for the zero shear viscosity eta(0) before the gel point and the equilibrium modulus Ge after the gel point was described as eta(0) approximately epsilon(-k) and Ge approximately epsilon(z), respectively, where the relative distance to the gel point f(gel) was epsilon = (/f-f(gel)/)/f(gel). The relaxation critical exponent n was determined with Winter's criterion, and the critical exponents k and z estimated respectively from independent measurements of eta(0) and Ge gave n from z/(k + z). Before the gel point, the storage and loss moduli G' and G' obtained at various epsilon can be superposed fairly well to form the master curve. The critical exponents n, k, and z were also evaluated from the shift factors and the structure self-similarity was found in the critical gel. The critical exponents evaluated with different methods agreed well with each other, suggesting two categories of the gelation as growth and cross-link. For the alginate with lower molecular weight, the critical exponents were almost independent of alginate concentration and close to the percolation prediction. For the alginate with higher molecular weight, the critical exponents, however, changed with alginate sample and concentration. The relative alginate concentration C(Alg)/C(Alg)* was found to serve as a criterion to divide these two transitions. 相似文献
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Romain Valentin Raluca Horga Barbara Bonelli Edoardo Garrone Francesco Di Renzo Françoise Quignard 《Macromolecular Symposia》2005,230(1):71-77
Supercritical drying of alginate gels is an efficient way to prepare aerogels with high surface area (>300 m2 · g−1). FTIR spectroscopy allows to monitor the adsorption of NH3 from the gas phase onto the acid sites of the alginate. Free carboxylic groups are effective Brønsted sites, whereas the divalent cations used in the ionotropic gelation present the properties of Lewis sites. The ratio between Brønsted and Lewis sites provides infomation on the role of pH in alginate gelation and suggests that non-buffered gelation by transition-metal cations is a mixed ionotropic-acid process. 相似文献
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测定了 4个分子量和分子量分布不同、M G不同的海藻酸钠试样在不同浓度下的恒温 (2 5℃ )动态粘弹谱 ,发现 4个试样随溶液浓度升高都会发生溶胶 凝胶 (Sol gel)转变 .实验结果表明 ,该转变符合Winter和Chambon的凝胶化点临界状态的松弛模量G(t)方程 ,由tanδ不依赖于ω的判据求出了海藻酸钠水溶液随浓度变化发生Sol gel转变、出现物理凝胶化的凝胶化点溶液浓度cgel和临界指数n .cgel=7 6wt%~ 8 0wt% ,基本与分子量无关 ;分子量较高的 3个试样的n =0 32~ 0 38,而分子量低的试样的n =0 6 1.该结果表明 ,物理凝胶化主要是由大分子重复单元间的相互作用决定 ,分子链越长则凝胶化点的交联结构越完善 相似文献
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Javvaji V Baradwaj AG Payne GF Raghavan SR 《Langmuir : the ACS journal of surfaces and colloids》2011,27(20):12591-12596
Biopolymers such as alginate and pectin are well known for their ability to undergo gelation upon addition of multivalent cations such as calcium (Ca(2+)). Here, we report a simple way to activate such ionic gelation by UV irradiation. Our approach involves combining an insoluble salt of the cation (e.g., calcium carbonate, CaCO(3)) with an aqueous solution of the polymer (e.g., alginate) along with a third component, a photoacid generator (PAG). Upon UV irradiation, the PAG dissociates to release H(+) ions, which react with the CaCO(3) to generate free Ca(2+). In turn, the Ca(2+) ions cross-link the alginate chains into a physical network, thereby resulting in a hydrogel. Dynamic rheological experiments confirm the elastic character of the alginate gel, and the gel modulus is shown to be tunable via the irradiation time as well as the PAG and alginate concentrations. The above approach is easily extended to other biopolymers such as pectin. Using this approach, a photoresponse can be imparted to conventional biopolymers without the need for any chemical modification of the molecules. Photoresponsive alginate gels may be useful in creating biomaterials or tissue mimics. As a step toward potential applications, we demonstrate the ability to photopattern a thin film of alginate gel onto a glass substrate under mild conditions. 相似文献
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Maneval JE Bernin D Fabich HT Seymour JD Codd SL 《Magnetic resonance in chemistry : MRC》2011,49(10):627-640
The formation of heterogeneous structures in biopolymer gels is of current interest for biomedical applications and is of fundamental interest to understanding the molecular level origins of structures generated from disordered solutions by reactions. The cation-mediated physical gelation of alginate by calcium and copper is analyzed using magnetic resonance measurements of spatially resolved molecular dynamics during gel front propagation. Relaxation time and pulse-field gradient methods are applied to determine the impact of ion front motion on molecular translational dynamics. The formation of capillaries in alginate copper gels is correlated to changes in translational dynamics. 相似文献
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A novel approach was developed to prepare a superporous hydrogel with superior mechanical and elastic properties. According to this method, a synthetic monomer was polymerized and crosslinked in the presence of a water-soluble alginate polymer. Later in the process, the alginate part of the synthesized hydrogel was treated with metal cations, which resulted in a hydrogel hybrid with an interpenetrating network structure. In this article, a hydrogel hybrid of acrylamide and alginate is highlighted because of its unique swelling and mechanical properties. This hydrogel hybrid shows resilience and a rubbery property in its fully water-swollen state, which not previously been reported. To help understand the underlying mechanism responsible for such unique properties with hydrogel hybrids, the ionotropic gelation of the alginate polymer was also studied in more detail. 相似文献
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海藻酸钠溶液溶胶-凝胶相转移的温度效应及IR光谱研究 总被引:1,自引:0,他引:1
考察了3wt%海藻酸钠溶液中加入Cu2+、Co2+后,体系的粘度、电导与离子浓度、温度的关系,结合IR光谱对海藻酸钠溶液在溶胶-凝胶相转移过程中的分子结构与构型变化进行了解剖。 相似文献
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Giulia Remaggi Ovidio Catanzano Fabiana Quaglia Lisa Elviri 《Molecules (Basel, Switzerland)》2022,27(3)
3D-printed hydrogels are particularly advantageous as drug-delivery platforms but their loading with water-soluble active compounds remains a challenge requiring the development of innovative inks. Here, we propose a new 3D extrusion-based approach that, by exploiting the internal gelation of the alginate, avoids the post-printing crosslinking process and allows the loading of epirubicin-HCl (EPI). The critical combinations of alginate, calcium carbonate and d-glucono-δ-lactone (GDL) combined with the scaffold production parameters (extrusion time, temperature, and curing time) were evaluated and discussed. The internal gelation in tandem with 3D extrusion allowed the preparation of alginate hydrogels with a complex shape and good handling properties. The dispersion of epirubicin-HCl in the hydrogel matrix confirmed the potential of this self-crosslinking alginate-based ink for the preparation of 3D-printed drug-delivery platforms. Drug release from 3D-printed hydrogels was monitored, and the cytotoxic activity was tested against MCF-7 cells. Finally, the change in the expression pattern of anti-apoptotic, pro-apoptotic, and autophagy protein markers was monitored by liquid-chromatography tandem-mass-spectrometry after exposure of MCF-7 to the EPI-loaded hydrogels. 相似文献