Swelling and Drying Mechanisms of Freeze-Thawed Polyvinyl Alcohol/Egg White/Montmorillonite Bionanocomposite Hydrogels

Abstract

Polyvinyl alcohol and egg white bionanocomposite hydrogels loaded with montmorillonite clay were fabricated by a freezing-thawing technique. The bionanocomposite hydrogels showed an exfoliated morphology and they had a more interconnected and dense network as compared with the clay-free sample. The montmorillonite layers acted as multifunctional crosslinkers and the bionanocomposite hydrogels had nanoscale, slit-shaped pores. The swelling ratios of the bionanocomposite hydrogels were increased either by decreasing the content of incorporated montmorillonite or by increasing the pH of the swelling medium. It was found that the bionanocomposite hydrogels having a higher content of montmorillonite exhibited a slightly slower drying process with a longer drying duration. Using the Ritger-Peppas model, it was shown that the swelling and drying mechanisms for all bionanocomposite hydrogels were non-Fickian diffusion. According to the Peppas-Sahlin model, it was found that the absorption of the swelling agent molecules during the swelling process and also the removal of water molecules during the drying process in the early stages of the processes occurred mostly due to their diffusion. At higher swelling or drying times, the contribution of the relaxation (for swelling) and shrinkage (for drying) of the polyvinyl alcohol polymeric chains and egg white protein chains was increased.     

Enthalpy Relaxation Study of Poly(Vinyl Chloride) Films Based on the Time-Temperature Superposition Principle

Abstract

In the enthalpy relaxation of poly(vinyl chloride), a decrease in enthalpy upon the isothermal ageing was measured using the differential scanning calorimetry method as a function of ageing time (t_A) and ageing temperature. The range of the ageing temperature was from 56?°C (T_g ? 25?°C) to 72?°C (T_g ? 9?°C) where T_g denotes the glass transition temperature. The limiting value of the decrease in enthalpy was determined by applying a stretched exponential function to the measured enthalpy data. The relaxation function (?) was derived from the measured enthalpy and the construction of a master curve was tried by shifting the ? ? t_A curves of the respective ageing temperatures horizontally. Although there was no agreement between the shift factors (a_T) and the relaxation times of the ? ? t_A curves, the superposition was successfully constructed and the a_T values obtained for the poly(vinyl chloride) sample were found to be comparable to those reported for viscoelastic experiments over a broad temperature range above and below T_g carried out for different polymers. The origin of the decrease in enthalpy was briefly discussed in terms of the chain dynamics in the isothermal condition.     

Transition‐Metal‐Free Trifluoromethylthiolation of N‐Heteroarenes

A general and efficient methodology for the direct transition metal free trifluoromethylthiolation of a broad range of biologically relevant N‐heteroarenes is reported employing abundant sodium chloride as the catalyst. This method is operationally simple, exhibits high functional group tolerance, and does not require protecting groups.     

基于有序介孔碳的氯离子选择性电极的制备及其在手持传感系统中的应用

以有序介孔碳(OMC)球为离子-电子转换层,制备了固态氯离子选择性电极,构建了基于离子敏感的场效应晶体管(ISFET)的手持式传感系统,用于检测人体血清中的氯离子。优化了OMC前驱体的碳化温度,探究了OMC形貌结构对电极传感性能的影响;电极柔性化制备后考察了其在手持系统中对氯离子的检测效果。结果表明,最优条件下,电极在5.12×10^-4~1.02 mol/L的浓度范围呈现线性响应,响应斜率为60 mV/decade。该柔性电极在手持传感系统中展现出高灵敏度和重现性,可用于人体血清样品中氯离子的检测,其回收率为96.3%~104.9%。     

胆碱氧化酶功能化室温磷光量子点的制备及其对氯化胆碱的定量检测

环境友好型纳米生物传感器能够提高传统生物分子传感器的检测性能，在实际应用中具有重要的应用价值。本研究以胆碱氧化酶（ChOx）为模板，在室温（25 ℃）下通过矿化作用制备了一种ChOx功能化的室温磷光（RTP）量子点（QDs）（ChOx RTP QDs）纳米生物传感器，并利用ChOx与氯化胆碱的特异性酶-底物反应和光诱导的电子转移（PIET）实现了对氯化胆碱（Cho）的RTP定量检测。该纳米生物传感器对氯化胆碱检测的线性范围为0.05~20 mmol/L，检出限为0.02 mmol/L。该方法基于QDs的RTP性质，可以有效地避免生物样品背景荧光的干扰，且无需复杂的样品前处理过程，因此该方法较适合于生物样品中氯化胆碱的定量检测。     

高温水解-离子色谱法测定钴酸锂中氯

使用高温水解-离子色谱法对钴酸锂中痕量的氯进行分析测定。样品在1 100℃高温下通入氧气与水蒸气进行水解反应,生成氯化氢气体随载气带出,经冷凝后接收,并通过离子色谱法对氯的含量进行测定。以NaHCO3(4.5mmol/L)与Na2CO3(2.7mmol/L)的混合溶液为淋洗液,经SH-AG-1保护柱及SH-AC-1分离柱分离,Cl-在0.05~5.00mg/L范围内浓度与峰面积呈线性关系,检出限(3S)为0.010mg/L。方法测定氯的加标回收率在92%~96%,相对标准偏差(n=11)在3.0%~5.3%,方法准确、可靠。     

Unusual 4‐arsonoanilinium cationic species in the hydrochloride salt of (4‐aminophenyl)arsonic acid and formed in the reaction of the acid with copper(II) sulfate,copper(II) chloride and cadmium chloride

Structures having the unusual protonated 4‐arsonoanilinium species, namely in the hydrochloride salt, C₆H₉AsNO₃⁺·Cl⁻, (I), and the complex salts formed from the reaction of (4‐aminophenyl)arsonic acid (p‐arsanilic acid) with copper(II) sulfate, i.e. hexaaquacopper(II) bis(4‐arsonoanilinium) disulfate dihydrate, (C₆H₉AsNO₃)₂[Cu(H₂O)₆](SO₄)₂·2H₂O, (II), with copper(II) chloride, i.e. poly[bis(4‐arsonoanilinium) [tetra‐μ‐chlorido‐cuprate(II)]], {(C₆H₉AsNO₃)₂[CuCl₄]}_n , (III), and with cadmium chloride, i.e. poly[bis(4‐arsonoanilinium) [tetra‐μ‐chlorido‐cadmate(II)]], {(C₆H₉AsNO₃)₂[CdCl₄]}_n , (IV), have been determined. In (II), the two 4‐arsonoanilinium cations are accompanied by [Cu(H₂O)₆]²⁺ cations with sulfate anions. In the isotypic complex salts (III) and (IV), they act as counter‐cations to the {[CuCl₄]²⁻}_n or {[CdCl₄]²⁻}_n anionic polymer sheets, respectively. In (II), the [Cu(H₂O)₆]²⁺ ion sits on a crystallographic centre of symmetry and displays a slightly distorted octahedral coordination geometry. The asymmetric unit for (II) contains, in addition to half the [Cu(H₂O)₆]²⁺ ion, one 4‐arsonoanilinium cation, a sulfate dianion and a solvent water molecule. Extensive O—H…O and N—H…O hydrogen bonds link all the species, giving an overall three‐dimensional structure. In (III), four of the chloride ligands are related by inversion [Cu—Cl = 2.2826 (8) and 2.2990 (9) Å], with the other two sites of the tetragonally distorted octahedral CuCl₆ unit occupied by symmetry‐generated Cl‐atom donors [Cu—Cl = 2.9833 (9) Å], forming a two‐dimensional coordination polymer network substructure lying parallel to (001). In the crystal, the polymer layers are linked across [001] by a number of bridging hydrogen bonds involving N—H…Cl interactions from head‐to‐head‐linked As—O—H…O 4‐arsonoanilinium cations. A three‐dimensional network structure is formed. Cd^II compound (IV) is isotypic with Cu^II complex (III), but with the central CdCl₆ complex repeat unit having a more regular M —Cl bond‐length range [2.5232 (12)–2.6931 (10) Å] compared to that in (III). This series of compounds represents the first reported crystal structures having the protonated 4‐arsonoanilinium species.     

Polyvinyl alcohol-modified graphene oxide as a support for bimetallic Pt–Pd electrocatalysts to enhance the efficiency of formic acid oxidation

The aim of this research was to study the efficiency of polyvinyl alcohol (PVA)-modified graphene oxide (GO) as a supporting material for catalysts that oxidize formic acid. The active metal catalysts (e.g., Pt and Pd) were electrodeposited on PVA/GO surfaces. The morphologies of the prepared catalysts were characterized by scanning electron microscopy and transmission electron microscopy, while their chemical compositions were identified by X-ray diffraction and X-ray photoelectron spectroscopy. The results show that compared with the other catalysts on GO, the prepared active PtPd alloy catalyst nanoparticles with 11.49–20.73 nm sizes were well dispersed on the PVA/GO surfaces. Electrochemical results indicate that the activities of the catalysts with PVA provided a higher current density than that of the catalysts without PVA. The bimetallic 3Pt3Pd/PVA/GO catalyst showed the greatest catalytic activity, stability, and CO oxidation when compared to those of other catalysts. The electronic, morphological, and structural properties promote the mass-charge transfer through the interaction. These results indicate that the PVA-modified GO provides a suitable site for active bimetallic catalyst surfaces, resulting in excellent formic acid oxidation and high CO elimination. The 3Pt3Pd/PVA/GO electrocatalyst is promising for enhancing formic acid oxidation.     

Super-Strong Hydrogel Composites Reinforced with PBO Nanofibers for Cartilage Replacement

Cartilage replacement materials exhibiting a set of demanding properties such as high water content, high mechanical stiffness, low friction, and excellent biocompatibility are quite difficult to achieve. Here, poly(p-phenylene-2,6-benzobisoxazole) (PBO) nanofibers are combined with polyvinyl alcohol (PVA) to form a super-strong structure with a performance that surpasses the vast majority of previously existing hydrogels. PVA–PBO composites with water contents in the 59–76% range exhibit tensile and compressive moduli reaching 20.3 and 4.5 MPa, respectively, and a coefficient of friction below 0.08. Further, they are biocompatible and support the viability of chondrocytes for 1 week, with significant improvements in cell adhesion, proliferation, and differentiation compared to PVA. The new composites can be safely sterilized by steam heat or gamma radiation without compromising their integrity and overall performance. In addition, they show potential to be used as local delivery platforms for anti-inflammatory drugs. These attractive features make PVA–PBO composites highly competitive engineered materials with remarkable potential for use in the design of load-bearing tissues. Complementary work has also revealed that these composites will be interesting alternatives in other industrial fields where high thermal and mechanical resistance are essential requirements, or which can take advantage of the pH responsiveness functionality.     

氢氧化钡与氯化铵反应实验中结冰成功的关键

对氢氧化钡晶体与氯化铵晶体吸热反应进行实验改进,在反应物中加少量的水,反应小烧杯上面倒扣上一个大一点的烧杯等,使得实验中水结冰成功率高,结冰快,且结冰量增大。结冰水中加入酚酞溶液,结出的冰为红色,既能检验氨的生成,又增添了实验的趣味性。