Laser speckle analysis on correlation between gelation and phase separation in aqueous methyl cellulose solutions

Structure formation by coupling between formation of crosslinking points and liquid–liquid phase separation was investigated for aqueous methyl cellulose solution by small‐angle X‐ray scattering (SAXS) and light scattering (LS) techniques. The sol–gel phase diagram and the SAXS results suggested that the liquid–liquid phase separation occurred before gelation. By LS measurements, the structure due to the liquid–liquid phase separation was directly observed. By applying speckle analysis on the LS profiles, it was suggested that the gelation and the phase separation strongly coupled each other: the increase in the apparent molecular weight by crosslinking induced the liquid–liquid phase separation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 168–174, 2010     

丝素蛋白-聚氨酯水凝胶的制备和性能

以异佛尔酮二异氰酸酯（IPDI）、聚乙二醇（PEG）、聚氧化丙烯二醇（PPG）等为主要原料,合成了一系列—NCO封端的水性聚氨酯（PU）预聚体,与自制的丝素蛋白（SF）水溶液混合进行交联反应,制备出丝素蛋白-聚氨酯（SF-PU）水凝胶。研究了SF-PU水凝胶的合成工艺,对SF-PU水凝胶进行了红外和电镜表征及性能测试,...     

Preparation of the Cationic Dendrimer-Based Hydrogels for Controlled Heparin Release

We introduce a cationic polyamidoamine (PAMAM) dendrimers and tetronic (Te) based hydrogels in which precursor copolymers were prepared with simple methods. In the synthetic process, tyramine-conjugated tetronic (TTe) was prepared via activation of its four terminal hydroxyl groups by nitrophenyl chloroformate (NPC) and then substitution of tyramine (TA) into the activated product to obtain TTe. Cationic PAMAM dendrimers G3.0 functionalized with p-hydroxyphenyl acetic acid (HPA) by use of carbodiimide coupling agent (EDC) to obtain Den-HPA. ¹H-NMR confirmed the amount of HPA and TA conjugations. The aqueous TTe and Den-HPA copolymer solution rapidly formed the cationic hydrogels in the presence of horseradish peroxidase enzyme (HRP) and hydrogen peroxide (H₂O₂) at physiological conditions. The gelation time of the hydrogels could be modulated ranging from 7 to 73 secs, when the concentrations of HRP and H₂O₂ varied. The hydrogels exhibited minimal swelling degree and low degradation under physical condition. In vitro cytotoxicity study indicated that the hydrogels were highly cytocompatible as prepared at 0.15 mg/mL HRP and 0.063 wt% of H₂O₂ concentration. Heparin release profiles show that the cationic hydrogels can sustainably release the anionic anticoagulant drug. The obtained results demonstrated a great potential of the cationic hydrogels for coating medical devices or delivering anionic drugs.     

Synthesis of Hydrogels from Polyallylamine with Carbon Dioxide as Gellant: Development of Reversible CO2 Absorbent

Hydrogels were successfully synthesized utilizing CO₂ as a gellant. A cross‐linking reaction of polyallylamine (PAA) with CO₂ in the presence of 1,8‐Diazabicyclo[5,4,0]‐undec‐7‐ene (DBU) provided hydrogels bearing urea cross‐linking points and residual amino groups in the side chains. The obtained hydrogels absorbed CO₂ at 25 °C and gave a maximum absorption four times larger than that of PAA aqueous solution and 2.8 times larger than that of the most commonly used absorbent, monoethanolamine. The PAA hydrogels desorbed the absorbed CO₂ completely under a N₂ atmosphere at 120 °C, and could be repeatedly recycled without loss of efficiency, indicating their potential application as recyclable CO₂ absorption materials.

     

Ultrastretchable,Tough, and Notch‐Insensitive Hydrogels Formed with Spherical Polymer Brush Crosslinker

Spherical polymer brushes, poly(acrylic acid) (PAA)‐grafted polystyrene nanoparticle (PAA@PS), are employed as the macro‐crosslinker to prepare PAA hydrogels. Benefitting from the innumerable hydrogen bonds between highly entangled PAA chains both in bulk and on the polymer brush, the PAA/PAA@PS hydrogels combine desirable stretchability, toughness, and notch‐insensitivity. The uniaxial tensile tests show a very high fracture elongation up to 9.1 × 10³% while the fracture toughness reaches 3.0 MJ m⁻³ and the maximum swelling ratio of the hydrogel can be 2.0 × 10³ as well. After being loaded with silver nanoparticles, the PAA/PAA@PS hydrogels are employed as a recyclable catalyst successfully.     

Structural and rheological properties of hydrophobically modified alkali‐soluble emulsion solutions

Scattering and rheological experiments were carried out on hydrophobically modified alkali‐soluble emulsion solutions at pH ～ 7.3 as a function of the polymer concentration. The light scattering experiments revealed the existence of a liquidlike order for concentrations below approximately 0.1 × 10^?2g cm^?3 corresponding approximately to the close packing of microgels particles. Above this concentration, the zero‐shear viscosity rose sharply, whereas the ordering disappeared progressively. The results are discussed within the framework of gelation models of associating polymers. Diffusing wave spectroscopy experiments provided estimates of the high‐frequency modulus. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1985–1994, 2002     

可注射水凝胶的制备与应用

可注射水凝胶在再生医学和药物控释等方面有着广泛的用途,是近年来生物医用材料领域新的研究方向.本文综述了近年来人们在可注射水凝胶制备和应用方面的研究进展,最后展望了其发展前景.     

Comparison of Critical Exponents Determined by Rheology and Dynamic Light Scattering on Irreversible and Reversible Gelling Systems

Summary: The sol-gel transition of a radical chain cross-linking copoly-merization system [N-vinylcaprolactam/2-hydroxylethyl methacrylate/allyl-methacrylate] and various thermoreversible gelling systems (mixtures made of xanthan gum and locust bean gum as well as gelatin) have been studied using in-situ time-resolved dynamic light scattering (DLS) and in-situ rheology. A critical dynamical behavior was observed near the sol-gel transition, which is characterized by the presence of a power-law spectra in the time-intensity correlation function g₂(t)−1 ∝ t^−µ and in the low-amplitude oscillatory shear experiment G′(ω) ∝ G″(ω) ∝ ωⁿ. A comparison of the obtained critical dynamical exponents µ and n were made according to the theory by Doi and Onuki. This theory predicts a relation between these exponents, but up to now no detailed experimental comparison was done in the past. It was found that for all investigated systems n > µ.     

均一沉淀法云母片被覆TiO2

利用硫酸氧钛和的均一沉淀反应法，在天然矿物云母上被覆ＴｉＯ２薄膜，讨论了薄膜形成主影响膜层结构的工艺因素，分阶段控制反应温度和时间有利于控制析出粒子形态和膜最，可获得均匀致密切的膜，不同厚度的膜层因光学干涉效应显示出各种色彩。     

Gelation Studies on a Radical Chain Cross‐Linking Copolymerization Process: Comparison of the Critical Exponents Obtained by Dynamic Light Scattering and Rheology

Summary: The sol–gel transition of a radical chain cross‐linking copolymerization system [N‐vinylcaprolactam/2‐hydroxylethyl methacrylate/allyl methacrylate] has been studied using in situ time‐resolved dynamic light scattering (DLS) and in situ rheology. A critical dynamic behavior was observed near the sol–gel transition, which was characterized by the presence of a power‐law spectra over three decades in the time–intensity correlation function g₂(t) − 1 ∼ t^−μ and over two decades in the oscillatory shear experiment G′(ω) ∼ G″(ω) ∼ ωⁿ. A comparison of the obtained critical exponents μ ≈ 0.62 and n ≈ 0.75 was made. The theory predicts a relationship between these exponents, but up to now no experimental comparison has been done. The experimental results favor the percolation model, with a fractal dimension d_f of the gel clusters of 1.67.

Double‐logarithmic plot of time–intensity correlation functions g₂(t) − 1 versus the delay time t.     

共轭聚合物水凝胶的制备与应用进展

共轭聚合物水凝胶是利用共轭聚合物制备的水凝胶材料,兼备水凝胶的力学性质、溶胀性质和共轭聚合物优异的电化学特性.共轭聚合物水凝胶的制备方法多样,主要有原位聚合、直接填充、物理交联和化学交联等.同时,在面对环境和能源领域的应用挑战时,共轭聚合物水凝胶具备良好的发展潜能,可广泛应用于药物释放、能量转换、能量储存、传感器、组织损伤修复和污水处理等诸多领域.本文系统归纳了共轭聚合物水凝胶的制备方法和应用,对其研究目前存在的主要问题以及未来发展方向进行了分析.     

均匀沉淀法制备单分散纳米ZnS及发光性能

采用均匀沉淀法,乙酸锌和硫代乙酰胺(TAA)分别提供Zn源和S源,无水乙醇为分散介质,十八胺(ODA)为分散剂,成功制备了小于50nm的单分散ZnS纳米颗粒,并就反应温度、分散剂浓度、溶液浓度和陈化时间对ZnS纳米颗粒粒径的影响进行系统研究。用SEM、激光纳米粒度仪、XRD、PL、EL对样品进行了表征,结果表明:维持一定的分散剂和溶液浓度于0℃陈化24h,样品粒径最小且结晶度佳,干燥和退火后的发光样品在275nm的紫外光激发下发射出490nm左右的蓝绿光,在2kV(样品厚度1mm)激励下发射出520nm的绿光。     

一维CuO纳米棒的微乳-均匀沉淀耦合法制备与结构表征

以CuSO4和NH3·H2O为原料,采用微乳-均匀沉淀耦合法制备了一维CuO纳米棒。用XRD、SEM、TEM、HRTEM和FTIR对产物的结构和形貌进行了表征。结果表明:产物为单斜晶相结构的CuO纳米棒,内部具有孔洞结构,其直径为40～110nm,长度为800～3000nm。可通过改变水核比(ω)、反应物的浓度、反应时间、反应温度等条件实现对CuO纳米棒形貌和尺寸的调控。探讨了可能的反应机理,并用热分析方法考察了CuO纳米棒对高氯酸铵(AP)分解的催化作用。     

Dynamic light scattering and small-angle neutron scattering studies on organogels formed with a gelator

Small-angle neutron scattering (SANS) and light scattering studies were carried out on an organogel consisting of a gelator, coded P-1, and dimethyl sulfoxide (DMSO). The gelator was made of an oligosiloxane stem and about eight branches of an amino acid derivative combined with a long alkyl chain. The amino acid part, N-n-pentanoyl-L -isoleucylaminooctadecane, was responsible for intermolecular association via hydrogen bonding between amide groups. After the complete dissolution of P-1 in DMSO at 85 °C, the solution was cooled, and the variations of the scattered light intensity were monitored as a function of the temperature. The scattered intensity increased drastically at about 40 °C when the P-1 concentration (C) was 3.5 g/L, and this indicated gel formation. The SANS results showed that the scattering intensity function was a monotonically decreasing function, regardless of C. A master relationship of the scattering intensity was obtained with respect to C. These scattering studies disclosed the following facts. First, gelation could be monitored as an abrupt increase in the intensity. Second, the gel was composed of randomly oriented bundlelike clusters. Third, the structure factor could be reduced by the gelator concentration, and this indicated the presence of a self-similar structure across the gelation threshold. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1841–1848, 2004     

二乙烯基砜交联的可德胶化学水凝胶的制备与表征

以二乙烯基砜(DVS)作为交联剂通过亲电加成反应制备了可德胶化学水凝胶。采用傅里叶变换红外光谱(FT-IR)、扫描电子显微镜(SEM)和质构分析手段表征了所得凝胶的结构与性能,并对其形貌、溶胀率以及水凝胶的力学性质与制备条件的关系进行了研究。结果表明:所得凝胶网络结构较为致密均匀,溶胀率依赖于交联度。可德胶化学水凝胶的强度和韧性可以通过DVS的用量、可德胶的浓度和碱溶液的浓度进行调控。     

均匀沉淀法制备氧化锌纳米棒

采用均匀沉淀法制备了氧化锌纳米棒,用XRD,TEM,PL等检测手段对样品进行了表征.结果表明:所得样品为长约100 nm,宽约30 nm的纤锌矿结构氧化锌纳米棒,颗粒分布均匀.其在可见光区比紫外区的荧光发射显著增强.     

Preparation of Injectable Composite Hydrogels by Blending Poloxamers with Calcium Carbonate-Crosslinked Sodium Alginate

The effects of calcium carbonate-crosslinked sodium alginate on poloxamer hydrogels have been investigated. The mechanical strength, degradability, and thermal stability of hydrogels were characterized. The chemical and physical crosslinking in the composite hydrogels has resulted in an improvement of the compressive strength and elasticity of the hydrogels. These mixed hydrogels showed improved mechanical properties, elasticity, and stability as well as environmental responsiveness and injectability.     

均相水解法制备金红石含量可控的纳米TiO2

用均相水解法通过调节对甲苯磺酸的添加量制备了金红石含量线性可控的纳米TiO2粒子,相同条件下,没有加入对甲苯磺酸时,制备的TiO02颗粒为纯锐钛矿晶型．制备的纳米TiO2颗粒,其单晶尺寸为19．5mm(金红石),13．5mm(锐钛矿),比表面积72．7m^2／g,通过公式计算得到了制备的TiO2纳米颗粒带隙能为2．83eV,比P25和纯锐钛矿纳米TiO2颗粒的带隙能均低．     

A One Pot,One Step Method for the Preparation of Clickable Hydrogels by Photoinitiated Polymerization

Current preparation methods for hydrogels based on redox or photopolymerization of water soluble monomers are simple to use, and flexible, but have the drawback of requiring additional modification steps for tuning or introducing properties for specific purposes. We have devised a simple and rapid synthetic strategy to prepare hydrogels possessing reactive sites to incorporate any molecules of interest by “Click Chemistry”. The strategy is based on the use of propargyl acrylamide (PAm) as comonomer together with acrylamide (AAm) and N,N′‐methylene bisacrylamide (BAAm) as crosslinker in photoinitiated polymerization. With the selective reactivity of photochemically generated free radicals towards acrylic function of PAm, hydrogels with clickable acetylene groups can be prepared in one pot, one step manner. Based on the acetylene functionality, any molecule possessing azide groups can be conjugated onto hydrogel by “Click Chemistry” as demonstrated on the example of fluoroscent azide functional pyrene.