纳米复合水凝胶的力学行为与刺激响应性

纳米复合水凝胶（nanocomposite hydrogels,NC凝胶）由于其简便的制备方法、独特的组成、优异的力学性能、高光学透明度以及良好的溶胀/去溶胀性等,引起了广泛的关注.近年来,本课题组在NC凝胶的力学行为及刺激响应性NC凝胶的制备方面取得了可喜的研究成果.观察到新合成的和溶胀平衡的聚N-异丙基丙烯酰胺（PNIPAm）-锂藻土LaponiteNC凝胶的超拉伸性,发现了在大应变下的应变硬化现象;发现利用Mooney-Rivlin方程可以描述NC凝胶的压缩应力-应变,但不能描述较大的应变硬化;Creton模型能很好地描述NC凝胶在大形变下的应力-应变曲线,特别是凝胶的应变硬化;从NC凝胶小应变下的平衡剪切模量得到了有效交联密度,观察到NC凝胶形变-回复过程的迟滞现象,测定了NC凝胶的松弛指数.我们认为NC凝胶具有超拉伸性的原因是其较低的交联密度和适度的松弛速率;在响应性NC凝胶的制备方面,发现了溶胶型Laponite的水分散液的稳定窗口,避免了加入离子性单体引起的聚集沉淀;通过共聚制备了具有超拉伸性、pH响应或温度和pH双响应的透明NC凝胶.本文主要综述了我们课题组在NC凝胶力学行为及响应性NC凝胶领域的一些研究进展,并分析了NC凝胶研究领域仍然未解决的科学问题,以及今后可能的发展方向.     

医用壳聚糖膜的制备和性能研究

研究了壳聚糖膜的制备方法和性能。探讨了壳聚糖浓度、甘油和戊二醛用量对壳聚糖膜性能的影响,并考察了膜的体外降解过程。结果表明w=．02的壳聚糖溶液成膜效果较好;甘油和戊二醛能王著改善壳聚糖膜的力学性能和尺寸稳定性能;溶茼酶-林格氏液中浸泡40d后膜的降解率为41．98％。满足引导组织再生材料的基本要求。该膜作为一种潜在的生物医用材料,将具有较广阔的应用前景。     

Experimental study of a diffusion-controlled reaction involving a chain molecule with terminal reactive sites

Diffusion-controlled reaction of electron transfer from diphenylsilane radical anions to the series of α- and α,ω-bromoalkanes with alkane chain length up to 18 atoms has been studied in n-dodecane solutions. At room temperature, reaction rate constants have been determined and corresponding reaction radii have been evaluated. It has been shown that a not-too-long chain molecule, which contains two terminal reaction sites and participates in the diffusion-controlled reaction, may be considered as a rapidly rotating pair of reacting sinks with a distance between their centers equal to the mean-square end-to-end distance of the molecule.     

Enhanced Corrosion Resistance and Discharge Performance of Mg-MnO2 Battery by Na2SiO3 Additive

Corrosion resistance and delayed action are major obstacles that severely limit the practical application of Mg alloy in battery fields. In this work, the effects of Na2SiO3 on the electrochemical behavior of the AZ31B Mg alloy in MgSO4-Mg(NO3)2 composite solution[0.14 mol/L MgSO4,1.86 mol/L Mg(NO3)2] were investigated. Electrochemical tests were carried out using electrochemical impedance spectroscopy, galvanostatic discharge, and linear sweep voltammograms. The results indicate that the impedance value increases by nearly fourfold, and the delayed time decreases from 2.1 s to 0.6s. Battery perfoniiance test reveals that the addition of Na2SiO3 significantly improves the discharge specific capacity of Mg-MnO2. The surface morphology and composition of corrosion products from Mg alloys were studied by scanning electron microscopy(SEM) and Fourier translonn infrared spectroscopy(FTIR), respectively. The SEM images of the AZ31B Mg alloys in composite solution with or without Na2SiO3 additive have an evident distinction due to the ionnation of new insoluble compound.FTIR result confirms that the corrosion products accumulated on the alloy surface in the electrolyte containing Na2SiO3 are mainly composed of Mg(OH)2, MgCO3, and MgSiO3.     

利用二氧化碳的缓慢释放控制聚丙烯酰胺在含柠檬酸铬水溶液中的粘度

Partially hydrolyzed polyacrylamide (HPAM) has been widely used for water shut-off and profile control to enhance oil recovery. Herein, we reported a novel technique by which the crosslinking between HPAM and Cr³⁺ in aqueous solutions at 60 ℃ can be delayed effectively. Citric acid was selected as an organic complexing agent of Cr³⁺ so that the crosslinking between HPAM and Cr³⁺ can be prevented completely. Due to the decomposition of the bicarbonate (HCO₃^-) embedded in solution, CO₂ released from solution and the pH value of solution increased gradually. The degree of ionization of HPAM and its ability to complex with Cr³⁺ increased accordingly. When the complexation of Cr³⁺ with HPAM is stronger than that with citric acid, the viscosity of the HPAM solution increased significantly. Under the closed condition, together with the existence of potassium dihydrogen phosphate (KH₂PO₄), the release of CO₂ was very slow and the condition was highly controlled so that the ionization of HPAM was prevented initially. Furthermore, the hydrogen bonding interactions between HPAM and melamine embedded in solution previously also postponed the ionization of HPAM. As a result, the crosslinking between HPAM and Cr³⁺ can be delayed for almost one month, completely meeting the requirements for deep water shut-off and profile control to enhance oil recovery.     

Influences of Plasma Treatment and 60Co γ-Ray Radiation on the Over-Voltage Positive Temperature Coefficient of High Density Polyethylene/Carbon Black Nano Composites

Argon plasma-pretreated high-density polyethylene (PHDPE) was blended with the conductive nano carbon black (CB) and inorganic flame retardant (magnesium hydroxide, Mg(OH)₂) was added. Influences of the CB content, plasma treatment time, plasma treatment power, and dosage of ⁶⁰Co γ-ray radiation on positive temperature coefficient (PTC) behaviors of composite were studied. In addition, the over-voltage resistance behavior of the composites was also investigated. The free radical of PHDPE was measured by 1,1-diphenyl-2-picryhydrazyl (DPPH) method. The gel contents of composite were measured by solvent extraction method. The results showed that the room-temperature volume resistivity and PTC effect of composite were improved significantly with plasma treatment. The PHDPE composite with ⁶⁰Co γ-ray radiation eliminated the negative temperature coefficient (NTC) effect in the composites effectively, and the PTC intensity of composite was increased. With increasing of radiation dosage from 20 Mrads to 80 Mrads, the gel content of composites increased up to 83.84% and the response temperature of composites shifted to low temperature (127.5 °C to 114.8 °C). In this work, the composites also successfully passed the over-voltage resistance test, and possessed good reproducibility.     

LED诱导延迟荧光技术评价脉冲电场对玉米幼苗抗旱性的影响

脉冲电场(pulsed electric field,PEF)对作物抗旱性的影响是电场生物学效应研究的重要课题,作物叶片延迟荧光动力学参数可以从不同角度灵敏地反映叶片细胞光合系统发生的变化。为了从活体细胞角度揭示脉冲电场对作物幼苗抗旱性的影响及其机理,使用频率为1 Hz、场强为200 kV·m-1、脉宽为80 ms的PEF处理萌发玉米种子,再采用渗透势为-0.1 MPa的PEG-6000溶液形成干旱胁迫,研究了玉米幼苗生长过程中叶片干质量和LED诱导的叶片延迟荧光动力学参数的变化。结果发现,在-0.1 MPa的PEG-6000溶液形成的干旱胁迫下,玉米幼苗叶片干质量逐渐增加,经过PEF处理的玉米幼苗叶片干质量大于对照,相对增长率在5.8%～18.7%之间(p＜0.05)。叶片延迟荧光动力学分析显示,干旱胁迫下玉米幼苗叶片延迟荧光动力学参数初始光子数I₀、相干时间τ、衰减参数β和延迟荧光积分强度I(T)都发生了波动性的变化,这些变化是叶片细胞对干旱胁迫的适应性反应,PEF处理使玉米幼苗叶片延迟荧光各动力学参数和延迟荧光积分强度均明显大于对照组,表明PEF处理使玉米幼苗叶片细胞的光合潜力、组织序性和功能分子之间的相互作用都有所加强,叶片综合光合能力提高了。研究结果为阐明PEF对作物幼苗抗旱性的影响及其机理提供参考。     

The impact of delayed feedback on the pulsating oscillations of class-B lasers

Class-B laser systems can be described by a set of slow-fast differential equations with a small parameter, and they exhibit pulsating oscillations in common. In this paper, the impact of the delayed feedback on the pulsating solutions is investigated. At first, a careful analysis of the local stability and bifurcation shows the existence of a series of Hopf bifurcations and double Hopf bifurcations when the strength of the delayed feedback or the delay increases, by means of stability switches. Then, an application of the geometric singular perturbation theory reveals the evolutional mechanism of the pulsating solutions from transients to stationary states, and the effect of the delayed feedback upon the pulsating solutions is examined.     

First-passage failure of strongly non-linear oscillators with time-delayed feedback control under combined harmonic and wide-band noise excitations

A procedure for studying the first-passage failure of strongly non-linear oscillators with time-delayed feedback control under combined harmonic and wide-band noise excitations is proposed. First, the time-delayed feedback control forces are expressed approximately in terms of the system state variables without time delay. Then, the averaged Itô stochastic differential equations for the system are derived by using the stochastic averaging method. A backward Kolmogorov equation governing the conditional reliability function and a set of generalized Pontryagin equations governing the conditional moments of first-passage time are established. Finally, the conditional reliability function, the conditional probability density and moments of first-passage time are obtained by solving the backward Kolmogorov equation and generalized Pontryagin equations with suitable initial and boundary conditions. An example is worked out in detail to illustrate the proposed procedure. The effects of time delay in feedback control forces on the conditional reliability function, conditional probability density and moments of first-passage time are analyzed. The validity of the proposed method is confirmed by digital simulation.     

一种新型的交联极化聚合物的合成及性能研究

以成膜性能优异、主链上含有多个羟基的聚双酚A二缩水甘油醚-苯胺(BPAN)为骨架,将二阶非线性光学活性发色团分子以键合形式挂接到聚合物主链上,形成新型侧链型聚合物.此聚合物保留了原聚合物体系成膜性好和可进一步交联等优点.极化过程中以含有异氰酸酯基的同种发色团分子作为交联剂,得到发色团含量进一步提高的交联型极化聚合物.采用衰减全反射法(ATR)测得体系的电光系数(r₃₃)为6.7 pm/V(1315 nm).