Swelling behaviour of alginate-chitosan microcapsules prepared by external gelation or internal gelation technology

Swelling behaviour is one of the important properties for microcapsules made by hydrogels, which always affects the diffusion and release of drugs when the microcapsules are applied in drug delivery systems. In this paper, alginate-chitosan microcapsules were prepared by different technologies called external or internal gelation process respectively. With the volume swelling degree (S-w) as an index, the effect of properties of chitosan on the swelling behaviour of both microcapsules was investigated. It was demonstrated that the microcapsules with low molecular weight and high concentration of chitosan gave rise to low S-w. Considering the need of maintaining drug activity and drug loading, neutral pH and short gelation time were favorable. It was also noticed that S-w of internal gelation microcapsules was lower than that of external gelation microcapsules, which was interpreted by the structure analysis of internal or external gelation Ca-alginate beads with the aid of confocal laser scanning microscope. (C) 2004 Elsevier Ltd. All rights reserved.

Preparation of uniform calcium alginate gel beads by membrane emulsification coupled with internal gelation

With the objective of making calcium alginate gel beads with small and uniform size, membrane emulsification coupled with internal gelation was proposed. Spherical gel beads with mean size of about 50 mum, and even smaller ones in water, and with narrow size distribution were successfully obtained. Experimental studies focusing mainly on the effect of process parameters on bead properties were performed. The size of the beads was mainly dependent on the diameter of the membrane pores. High transmembrane pressure made for large gel beads with wide size distribution. Low sodium alginate concentration produced nonspherical beads, whereas a high concentration was unsuitable for the production of small beads with narrow distribution. Thus 1.5% w/v was enough. A high surfactant concentration favored the formation of small beads, but the adverse effect on mass transfer should be considered in this novel process. (C) 2002 Wiley Periodicals, Inc.

Finite element simulation of the physical gelation of rennet casein(酶凝干酪素物理凝胶化过程的有限元模拟)

以酶凝干酪素的凝胶化过程为对象,利用有限元方法数值分析了在凝胶化过程中温度场的空间分布和时间演变规律.在此基础上,基于一阶的凝胶化动力学方程,数值模拟了凝胶体系的复剪切模量场,进而分析了材料配方、体系尺寸与冷却方案对复剪切模量场的影响规律.模拟结果表明,由于热阻的差异,体系表面的冷却速率大于内部,表面首先发生凝胶化;而由于预凝胶化阶段的平均冷却速率决定了无穷复剪切模量的值,最终体系内部的复剪切模量超过表面的.

Performance inhomogeneity of gelatin during gelation process

The structural and performance inhomogeneities of gelatin gel can directly affect its application as a kind of functional material. The structural inhomogeneity of gelatin caused by the uneven and unstable temperature field has been analyzed by the finite element method in our previous work. Further in this paper, the performance inhomogeneity of gelatin which is closely connected with the actual application is numerically analyzed during the gelation process, which includes the inhomogeneities of the optical and mechanical properties of gelatin gels. The time required for reaching the gel point at different spatial grids is exhibited and discussed. The calculated results also show that the equilibrium shear modulus of gelatin is dependent on the thermal history.

Effects of polar group saturation on physical gelation of Amphiphilic polymer solutions

Monte Carlo simulation on the basis of the comblike coarse grained nonpolar/polar (NP) model has been carried out to study the polar group saturation effect on physical gelation of amphiphilic polymer solutions. The effects of polar group saturation due to hydrogen bonding or ion bridging on the sol-gel phase diagram, microstructure of aggregates, and chain conformation of amphiphilic polymer solutions under four different solvent conditions to either the nonpolar backbone or the polar side chain in amphiphilic polymer chains have been investigated. It is found that an increase of polar group saturation results in a monotonically decreased critical concentration of gelation point, which can be qualitatively supported by the dynamic theological measurements on pectin aqueous solutions. Furthermore, various solvent conditions to either the backbone or the side chain have significant impact on both chain conformation and microstructure of aggregates. When the solvent is repulsive to the nonpolar backbone but attractive to the polar side chain, the polymer chains are collapsed, and the gelation follows the mechanism of colloidal packing; at the other solvent conditions, the gelation follows the mechanism of random aggregation.

高分子溶液中物理凝胶化的Monte Carlo模拟和小角中子散射研究

高分子凝胶广泛地存在于自然界以及日常生活中，按其形成作用力不同分为化学凝胶和物理凝胶两大类。由于高分子物理凝胶具有凝胶化的可逆性及其对环境条件强烈的响应性，因此，在近半个世纪的研究与应用中受到极大的关注。高分子溶液中的物理凝胶因其结构及形成机制复杂，在实验方面，除了散射技术及流变技术能够有效地揭示它的部分信息外，其它的实验手段很难用于这个领域的研究；在理论方面，化学凝胶的理论已经比较成熟，而物理凝胶的粘弹性质以及凝胶化是一个远离平衡态的松弛过程，除了一些特征的标度指数外，人们还没有得到适用于高分子物理凝胶的普适规律。当前，由于计算机模拟理论及模拟方法的发展，使得计算机模拟成为除了实验和理论研究方法之外的第三个重要的研究方法。但是，由于物理凝胶化行为的复杂性，用实验和理论获得的信息很难较好地描述凝胶化过程，而计算机模拟的高度透明性及反映信息的完整性，有助于理解这一复杂过程中所涉及的物理本质。因此，利用计算机模拟结合实验及理论方法深入研究高分子物理凝胶的形成机制、结构与性能关系已成为目前最有效的手段之一。 本论文主要运用Monte Carlo模拟方法，并结合小角中子散射（Small-Angle Neutron Scattering, SANS）和流变（Rheology）等实验手段从多个角度探讨了以下几类典型的高分子溶液物理凝胶化行为。 1. 温度对遥爪型三嵌段共聚物在选择性溶剂中的自组装及凝胶化行为影响的研究：采用二维简单方格子Monte Carlo模拟方法，结合逾渗（Percolation）理论，建立了溶胶－凝胶转变相图在统计热力学中的确定方法；甄别了具有特征构象的链，讨论了链及胶束的聚集，明晰了相互作用（体现为约化温度）、构象转变、聚集与凝胶化的一致的关联关系；提出了构象转变模型，进而明确了此体系的凝胶化过程，在微观尺度上表现为桥型链和环型链之间的竞争。 2. 模拟模型改进及其应用到持续长度对稀溶液中高分子链构象影响的研究：考虑到原始八位置键涨落模型效率低，实现复杂且不能应用到复杂的高分子体系，对该模型进行了改进，使其实现简单、效率高，并拓宽了该模型的应用范围。然后，以刚性对均聚物构象的影响为例，发现随着刚性增加，均聚物构象从球形椭球到棒状椭球的转变，并对比了自由连接链（Free Joint Chain, FJC）模型和蠕虫链（Wormlike Chain, WLC）模型在不同刚性范围内对高分子链末端距预测的偏差，首次给出了这两个经典模型的半定量的适用边界。 3. 溶剂尺寸对遥爪型三嵌段共聚物在选择性溶剂中的自组装及凝胶化行为影响的研究：用改进后的八位置键涨落Monte Carlo模型，研究了遥爪型三嵌段共聚物在选择性溶剂条件下的聚集和凝胶化对溶剂尺寸的依赖性，发现溶剂尺寸效应对凝胶化的作用是非单调的。由一个均聚物体系的对比模拟证明这种作用主要是由熵驱动的，并给出了中分子溶剂的半定量定义。在均聚物和嵌段共聚物溶液中，不同尺寸的溶剂分子可以使溶液由于高分子聚集不同而具有不同的微结构，并影响高分子链构象和溶液的性质。从多个角度研究了三嵌段共聚物在不同尺寸溶剂的溶液中所遵循的三种不同的凝胶化机理。 4. 聚氧化乙烯－氧化丙稀－氧化乙烯三嵌段共聚物（poly(ethylene oxide)-poly (propylene oxide)-poly-(ethylene oxide), PEO-PPO-PEO）重水溶液凝胶化的小角中子散射（SANS）和Monte Carlo研究：结合Pluronic F127（EO65PO99EO65）/D2O三嵌段共聚物溶液的特征，对照SANS数据，用改进后的八位置键涨落模型成功地从模拟中获得了F127/D2O的溶胶－凝胶转变相图。详细地考察了体系的微观结构，提出此类高分子溶液中形成的物理凝胶包含高分子逾渗网络的生成，以及被束缚溶剂（Bound Solvent）必须超过离散组分体系逾渗的临界体积分数的机理。着重研究了一定浓度的F127水溶液随温度升高引起的溶胶－凝胶转变以及凝胶－溶胶转变的Reentrant相行为，发现体系在低温区域的溶胶－凝胶转变遵循相同的机理，而在中等温度和较高温度以及不同浓度区域中的凝胶－溶胶转变遵循不同的机理。 5. 极性基团饱和度和溶剂条件对两亲性聚合物在溶液中的聚集行为和凝胶化影响的研究：用改进后的八位置键涨落模型，针对两亲性聚合物在不同溶剂条件的溶液建立了粗粒化模型，以两亲性聚合物中极性基团的饱和度，溶剂条件和高分子浓度为变量，考察了其对链构象、聚集及其凝胶化的影响。 6. 多糖水溶液凝胶化的流变和小角中子散射研究：用流变和SANS考察了两个多糖水溶液中物理凝胶化过程，针对由氢键主导的水基凝胶体系的典型特征进行了讨论，从分子链构象，聚集体结构及其关联以及流变特征等方面对聚强电解质角叉胶（Carrageenan）水溶液和聚弱电解质明胶（Pectin）水溶液进行了详细的讨论。考察了不同多糖的种类（聚合物链的电荷密度），盐的种类和浓度，溶液温度等对凝胶化和凝胶结构的影响，分析了不同多糖溶液的凝胶化机理。

Characterization of structure and diffusion behaviour of Ca-alginate beads prepared with external or internal calcium sources

Ca-alginate beads were prepared with either external or internal calcium sources. The structures of both beads were investigated with the aid of scanning electron microscopy (SEM) and confocal microscopy. It was shown that the beads with internal calcium source had a looser structure and bigger pore size than those with external calcium source. The attempts to interpret the difference were carried out by determining the Ca content within the beads at various times, which indicated that it was the different gelation mechanisms that caused the difference of structures of both beads. Furthermore, it was also found that the diffusion rate of haemoglobin (Hb) within the beads with an internal calcium source was faster than that of the beads with an external one, which was consistent with the observation of their structures.

Ultrasound-promoted chiral fluorescent organogel

In this paper, we have described a chiral binaphthyl-based fluorescent organogel. Very interestingly, similar to sonocrystallisation of organics, ultrasound can promote the gelation while it cannot occur spontaneously at relatively high temperature or low concentration. The fluorescence enhancement of the gel obtained via ultrasound irradiation is observed. In solution there exist rapid dynamic equilibria between (S)-1 oligomers. The association interactions both between gelator molecules and between solvent and gelator molecules could together effect the helical growth of distorted (S)-1 nanocrystals.

Application of a New Cyclic Guanidinium Ionic Liquid on Dye-Sensitized Solar Cells (DSCs)

A new cyclic guanidinium ionic liquid OGI (1,3-dimethyl-2-N ''-methyl-N ''-octylimidazoguanidinium iodide) has been used as a quasi-solid-state electrolyte for dye-sensitized solar cells (DSCs), and 6.38% conversion efficiency was achieved at AM 1.5 simulated sunlight (9.81 mW cm(-2)). Further gelation with SiO2 nanoparticles afforded the solid-state electrolyte, which presented overall conversion efficiency of 5.85%. The diffusion properties of these OGI-based electrolytes were investigated. In the meantime, the optimal structure and ion-pairing interaction in OGI have been proposed by density functional theoretical calculation (DFT) at the B3LYP/6-21G(d,p) level.

Effect of gamma-radiation on the thermal and mechanical properties of a commercial poly(butylene adipate-co-terephthalate)

BACKGROUND: Poly(butylene adipate-co-terephthalate) (PBAT) has attracted wide interest as a biodegradable polymer. However, its use is restricted in certain applications due to its low melting point.RESULTS: PBAT was treated using gamma-radiation. The radiation features were analyzed using Soxhlet extraction, and the ratio of chain scission and crosslinking and gelation dose were determined using the classical Charlesby-Pinner equation. The results showed that PBAT is a radiation-crosslinkable polymer. The degree of crosslinking increased with increasing radiation dose; the relation between sol fraction and dose followed the Charlesby-Pinner equation. Differential scanning calorimetry analyses showed that the melting temperature (T-m) and the heat of fusion (Delta H-m) of PBAT exhibited almost no change in the first scan. The second scan, however, showed a decrease in T-m and Delta H-m. The glass transition temperature of irradiated PBAT increased with increasing radiation dose.

Synthesis of Hyperbranched Polymers with Pendent Norbornene Functionalities via RAFT Polymerization of a Novel Asymmetrical Divinyl Monomer

Hyperbranched polymers with numerous pendent norbornene functionalities have been synthesized via the radical polymerization of a novel asymmetrical divinyl monomer hearing a higher reactivity methacrylate group and it lower reactivity norbornene group. Mediated by a rapid reversible addition-fragmentation chain transfer (RAFT) equilibrium, the concentration of polymeric chain radicals is decreased, and thus the gelation did not occur until higher monomer conversions (ca. 90%). An increase in reaction temperature call also significantly promote the formation of the hyperbranched structure owing to the decreased stability of the intermediate radicals derived from the norbornene group, which was confirmed by a model copolymerization system of two single vinyl monomers with similar structures to the vinyl groups in the asymmetrical divinyl monomer. Furthermore, Tri-SEC and conventional Sin-SEC as well as H-1 NMR.

Glycyrrhetinic acid-modified nanoparticles for drug delivery: Preparation and characterization

In this work, glycyrrhetinic acid-modified chitosan (mGA-suc-CTS) used as liver targeted carrier for drug delivery, was prepared via hemisuccinate as a bridged group. The structure of the product was confirmed by IR and NMR methods and the degree of substitution (DS) of glycyrrhetinic acid groups was estimated via elemental analysis. Nanoparticles were formed by ionic gelation methold. The drug-loading and release behavior of the nanoparticles were investigated using BSA as the model drug. The results indicated that the carrier with a highest DS of 5.19% could be got and the DS was controlled by changing reaction temperature or feed ratio. BSA could be entrapped into the nanoparticles with the drug-loading ratio of 26.3% and the encapsulation efficiency of 81.5%. A sustained release over an 11-day period was observed in pH 7.4 in vitro.

Influence of shear on polypropylene crystallization kinetics

Isothermal crystallization kinetics under shear in the melt of iPP was investigated by optical microscopy. It appears that shearing from 200 to the crystallization temperatures enhanced the kinetics, but the shear effect was not obvious if the melt of iPP was sheared only at 200. The experiment results show that relaxation plays an important role during crystallization, and that spherulite growth rates increased with shear rates and were governed by relaxation. The effect of flow on the crystallization kinetics can be understood by considering that the increase of the degree of order due to flow results is an effective change of the melt free energy. The Laurizen-Hoffman theory and the DE-IAA model were used to describe the shear-induced crystallization kinetics of iPP excellently.

Conformation studies on sol-gel transition in triblock copolymer solutions

The gelation of physically associating triblock copolymers in a good solvent was investigated by means of the Monte Carlo simulation and a gelation process based on the conformation transition of the copolymer that was described in detail. In our simulative system, it has been found that the gelation is closely related with chain conformations, and there exist four types of chains defined as free, dangling, loop, and bridge conformations. The copolymer chains with different conformations contribute to the formation of gel in different ways. We proposed a conformational transition model, by which we evaluated the role of these four types of chains in sol-gel transition. It was concluded that the free chains keeping the conformation transition equilibrium and the dangling conformation being the hinge of conformation transition, while the chain with loop conformation enlarges the size of the congeries and the chain with bridge conformations binds the congeries consisted of the copolymer chains. In addition, the effects of temperature and concentration on the physical gelation, the association of the copolymer congeries, and the copolymer chain conformations' distribution were discussed.