水蒸气诱导聚电解质刷的构象转变

我们把Flory-Huggins模型(association models)推广应用到暴露于水蒸气中的聚电解质刷体系,考虑聚电解质-水氢键(P-W氢键)与水-水氢键(W-W氢键)、形成氢键与聚电解质链构象的耦合特性,研究水蒸气诱导的聚电解质刷构象转变的机理.研究发现,当P-W氢键效应起主导作用时,随着水蒸气浓度的增加,聚电解质刷会单调溶胀;P-W和W-W两种氢键效应,则会导致随着水蒸气浓度的增加,聚电解质刷的构象首先塌缩,然后开始溶胀的反常转变行为.基于本文的分析,可以预言,由于P-W氢键效应,聚电解质刷可以吸附水蒸气,吸附能力随聚电解质链长的增加而增强;当聚电解质链接枝密度足够高时,由于P-W和W-W两种氢键效应,增加体系中的水蒸气,会在聚电解质刷体系中形成由P-W氢键和W-W氢键交错链接的三维网络状凝胶结构.     

水蒸气诱导聚电解质刷的构象转变

我们把 Flory−Huggins 模型(association models)推广应用暴露于水蒸气中的聚电解质刷体系,考虑聚电解质-水氢键(P-W氢键)与水-水氢键(W-W氢键)、形成氢键与聚电解质链构象的耦合特性,研究水蒸气诱导的聚电解质刷构象转变的机理.研究发现,当 P-W 氢键效应起主导作用时,随着水蒸气浓度的增加,聚电解质刷会单调溶胀;P-W 和 W-W 两种氢键效应,则会导致随着水蒸气浓度的增加,聚电解质刷的构象首先塌缩,然后开始溶胀的反常转变行为。基于本文的分析,可以预言,由于 P-W 氢键效应,聚电解质刷可以吸附水蒸气,吸附能力随聚电解质链长的增加而增强;当聚电解质链接枝密度足够高时,由于 P-W 和 W-W 两种氢键效应,增加体系中的水蒸气,会在聚电解质刷体系中形成由 P-W 氢键和 W-W 氢键交错链接的三维网络状凝胶结构。     

高分子凝胶体积相变中的氢键作用

我们把关联模型(association models)推广应用到高分子凝胶体系,研究高分子与溶剂分子间的氢键和溶剂分子与溶剂分子间的氢键在高分子凝胶体积相变中的作用.首先通过分析凝胶体积分数与温度的关系发现,由于两种氢键作用,随着温度变化高分子凝胶出现连续、不连续体积相变,结果表明在体积相变过程中两种氢键都起着重要作用.其次,对不同氢键分数条件下的旋节线的研究发现,对于高分子凝胶体积相变中出现的UCST和LCST(上临界共溶温度和下临界共溶温度)现象也是由于高分子与溶剂分子间氢键和溶剂分子与溶剂分子间氢键共同作用的结果.     

分子动力学模拟方解石和白云石润湿性

利用分子动力学模拟研究油水分子在方解石和白云石表面的吸附,分析体系的平衡构型、相对浓度、径向分布函数和吸附能,研究方解石和白云石的亲水性并对比二者差异.根据油水分子吸附规律分析方解石/白云石-油水体系作用机理.研究表明：白云石-油水体系更易达到热力学稳定状态并且体系更加稳定;方解石和白云石表面均能够优先吸附水分子并在表面形成双层结构的水膜.其中,白云石表面对水分子吸附强度大于方解石;稳定吸附过程分为两步：范德华力、静电力和O（CaCO₃,CaMg（CO₃）₂）-H（H₂O）氢键共同影响下水分子向晶体表面移动并吸附形成紧密吸附层;O（H₂O）-H（H₂O）氢键作用下游离的H₂O向晶体表面靠近形成扩散层.从分子尺度解释方解石/白云石亲水特性,为碳酸盐岩储层润湿性研究奠定理论基础.     

Structures and Hydrogen Bonding Interactions in Urea-water System Studied by All-atom MD Simulation and Chemical Shifts in NMR Spectrum

采用分子动力学模拟方法结合核磁共振化学位移和粘度对尿素水溶液在稀浓度范围内的结构和弱相互作用进行研究. 从径向分布函数(RDF)分析看出,尿素水溶液中存在着几种不同类型、不同氢键形成能力的传统氢键. 氢键网络分析发现尿素水溶液体系在水富集区域,水分子倾向于自身缔合形成稳定的分子簇结构,而随着尿素浓度的逐渐增加,水的有序结构受到破坏,水分子和尿素分子发生了交叉缔合作用形成氢键,尿素分子有形成自身缔合的趋势. 分子动力学统计的平均氢键数与核磁共振化学位移和粘度数据结果进行比较,发现它们的变化趋势一致,证明了实验和理论结果有很强的可靠性.     

氘代溶剂对丙烯酰胺溶剂化作用的NMR研究

用¹H NMR谱研究了丙烯酰胺（AM）分别在氘代氯仿（CDCl₃）和氘代二甲基亚砜（DMSO-d₆）溶剂以及在不同比率的混合溶剂中,AM的烯键C上的反式两个质子的谱峰位置开始相向移动,重叠,后又反向交错以致形成“类似镜像”的现象,用溶剂化作用讨论了成因;混合溶剂中,随着DMSO-d₆摩尔分数的增加,－NH₂质子和溶剂残余水质子的化学位移逐渐都向低场移动,这与－NH₂和DMSO之间形成氢键,－NH₂和水质子之间既有氢键生成又有质子交换有关.     

三种二元水溶液体系中氢键对拉曼线宽的影响

采用显微共聚焦拉曼光谱对三种二元水溶液(乙腈/水、二甲基亚砜(DMSO)/水和丙酮/水)进行测量,得到含有氢键作用的水溶液体系拉曼频移和线宽随浓度的变化规律。应用混合模型和相互作用体系的线宽经验公式对实验结果进行了分析。结果表明,含有氢键作用的水溶液体系中,氢键作用越强线宽越大,并且线宽随单位浓度变化率大;同种氢键体系中,线宽不仅受浓度浮动的影响,氢键作用也是一个重要的影响因素,定量分析证明线宽与浓度、氢键作用关系很好地符合Ojha等提出的线宽公式。     

亲水性两性离子聚合物刷的构象与结构

本文应用分子场理论,研究暴露于水蒸气中的亲水性两性离子聚合物(HP)刷的构象与结构.理论模型考虑HP-水(P-W)氢键和水-水(W-W)氢键效应,以及HP单体之间的偶极-偶极相互作用.研究发现,P-W与W-W氢键决定着HP的水合性,P-W氢键形成,会诱导HP刷溶胀.我们通过考察HP单体间的偶极-偶极相互作用发现,随着偶极-偶极相互作用增强,HP链在垂直培基表面沿着链方向,形成了结节状结构.这是由于HP单体之间的偶极-偶极静电吸引作用导致单体间汇聚结节,这种结节在刷内产生了较强的排斥体积作用,因此,这种HP刷具有抗污性能.在较高的接枝密度环境下,由于HP链间单体之间的偶极-偶极静电吸引作用,会形成链间单体-单体的结节,在刷内形成结节网络状凝胶结构,这种结构的出现,会使得HP刷呈现极强的抗污性.另外,当体系中水蒸气浓度增加、水合相互作用增强时,增加的P-W氢键将平衡HP单体之间的偶极-偶极相互作用,使得结节解开,聚合物链伸展.我们的理论结果符合实验观测,由此表明,P-W氢键效应,以及HP单体之间的偶极-偶极相互作用决定着HP刷的构象转变和结构特性,刷内出现的两性离子聚合物链内单体间的结节和链间单体结节状凝胶结构,是两性离子聚合物刷呈现较强抗污性的本质特性.     

水蒸气诱导两性离子聚合物刷的构象转变

我们把Flory Huggins模型(association models)推广应用到暴露于水蒸气中的两性离子聚合物刷体系,考虑两性离子聚合物-水氢键(P-W氢键)与两性离子聚合物链间两亲离子单体-单体键合(zwitterions complex)、形成氢键与两性离子聚合物链构象的耦合特性,研究水蒸气诱导的两性离子聚合物刷构象转变的机理和相行为.研究发现,随着水蒸气浓度的增加,P-W氢键效应会使得两性离子聚合物刷溶胀;两亲离子单体-单体键合效应会导致水分子将会被排出刷外,并会导致两性离子聚合物刷塌缩.通过分析两性离子聚合物刷的相图发现,P-W氢键效应在决定两性离子聚合物刷的相行为中起到主导作用,在水蒸气增加过程中两性离子聚合物刷将会单调溶胀.基于本文的分析,可以预言,由于P-W氢键效应,两性离子聚合物刷可以吸附水蒸气,当两性离子聚合物链接枝密度足够高时,两性离子聚合物刷内的水分子将会被排出,并会形成两亲离子单体-单体键合连接的凝胶状结构.     

基于氢键作用的几种二元水溶液的表面张力特性及拉曼光谱研究

氢键效应作为溶液中典型的微观特性直接影响溶液微观结构,并对物理和化学性质产生重要影响。对氢键作用的研究是水科学研究的重要突破口,也使得通过氢键研究水溶液性质成为一种极具优势的研究方法。通过测量不同浓度下的表面张力以及各体系拉曼光谱,研究二甲基亚砜/水、乙腈/水、丙酮/水三种具有典型氢键作用的二元溶液体系。研究了表面张力的变化规律和各体系中的氢键作用,讨论了溶液体系的微观结构变化,解释了氢键作用对表面张力的影响机制。     

Preparation and Characterization of Chemically Crosslinked Polyvinyl Alcohol/Carboxylated Nanocrystalline Cellulose Nanocomposite Hydrogel Films with High Mechanical Strength

Chemically crosslinked polyvinyl alcohol (PVA)/carboxylated nanocry-stalline cellulose (PVA/CNCC) nanocomposite hydrogel films were fabricated by film-casting of PVA/CNCC mixture solutions and subsequent thermal-curing of the PVA with the CNCC. Gel fractions of the hydrogel films were measured to confirm the occurrence of crosslinking. Morphologies of the hydrogel films were characterized by polarized light microscopy and scanning electron microscopy (SEM). Thermal properties, swelling behavior and mechanical properties of the hydrogel films were investigated to evaluate the influence of CNCC content (10～30% of PVA mass). Equilibrium water content of the hydrogel films was in the range of 40～49%. At swelling equilibrium, the hydrogel films could be stretched to 3～3.4 times their original length, and their tensile strength was in the range of 7.9～11.6 MPa. The results show that the PVA/CNCC nanocomposite hydrogel films were both extensible and highly tough.     

Preparation and Properties of Polyvinyl Alcohol/Collagen Hydrogel

Hydrogel scaffolds based on poly(vinyl alcohol) (PVA) collagen films were prepared by a chemical cross-linking method. The effects of the contents of PVA and cross-linker on compressive strength and swelling ratio were studied, and the effect of the pH value of the immersion medium on the swelling ratio was also investigated. The results showed that the introduction of PVA improved the compressive strength of PVA/collagen hydrogel, and the swelling ratio of the hydrogel scaffold increased with increasing PVA content in the blends. With increasing cross-linker content, the swelling ratio decreased; however, the compressive strength increased. The swelling ratio of PVA/collagen scaffold increased when pH was decreased. In conclusion, swelling ratio and compressive strength in PVA/collagen blends can be controlled by variation of their contents, cross-linking agent content, and pH value.     

Microstructure and Thermal and Tensile Properties of Poly(vinyl alcohol) Nanocomposite Films Reinforced by Polyacrylamide Grafted Cellulose Nanocrystals

Abstract

Polyacrylamide grafted cellulose nanocrystals (CNC-g-PAM) were incorporated into poly(vinyl alcohol) (PVA) by a solution casting method to fabricate nanocomposite films with enhanced thermal and tensile properties. The microstructure and the thermal and tensile properties of the PVA/CNC-g-PAM nanocomposite films were investigated as a function of CNC-g-PAM content. Infrared spectroscopy corroborated the presence of hydrogen bonds between PVA and the PAM on the surface of the CNC. Polarized optical microscopy and scanning electron microscopy revealed good dispersion of the CNC-g-PAM in the PVA matrix and good interfacial compatibility. Accordingly, the initial degradation temperature of the nanocomposite films was elevated slightly compared to pristine PVA film. The glass transition temperature, melting temperature, and crystallinity of the PVA also varied slightly after the incorporation of the CNC-g-PAM. At both 0% and 50% RH, the nanocomposite films showed an obvious increase of elastic modulus, no apparent change of breaking strength and a drastic reduction of elongation at break with increasing CNC-g-PAM content.     

Synthesis and Properties of Polyacrylamide-Based Conducting Gels with Enhanced Mechanical Strength

A nanocomposite conducting hydrogel, polyacrylamide/MWNT/clay (abbreviated as PAM/MWNT/clay), prepared through in situ free radical aqueous polymerization and crosslinked by both clay, as a functional physical crosslinker, and N,N′-methylenebisacrylamide (MBA) as a chemical crosslinker, is reported. The morphology of the gels was characterized by scanning electron microscopy (SEM). The mechanical properties and electrical conductivity were also studied. The results show that the prepared hydrogels had the expected chemical components, with a highly porous structure, and the gels also showed high mechanical strength. The mechanical strength and electrical conductivity value increased with increasing content of multi-walled nanotube (MWNT), and decreased with increasing content of water.     

Gelation and Swelling Behavior of Semi-Interpenetrating Polymer Network Hydrogels Based on Polyacrylamide and Poly(vinyl alcohol)

Novel semi-Interpenetrating Polymer Network (semi-IPN) hydrogels based on partially Hydrolyzed Polyacrylamide (HPAM) and Poly(Vinyl Alcohol) (PVA) were prepared by solution crosslinking using chromium triacetate. Effects of PVA content on the gelation process and swelling behavior in tap water and different electrolyte solutions were investigated. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the semi-IPN gels decreased with increasing PVA content. It was also found that increasing the PVA content increases the loss factor, indicating that the viscous properties of this gelling system increase more strongly than the elastic properties. The swelling ratio of the semi-IPN gels in tap water decreased as the concentration of the PVA increased. However, the semi-IPN gels showed lower salt sensitivity factor in synthetic oil reservoir water as compared with HPAM gels. Therefore, they are potentially good candidates for enhanced oil recovery applications.     

Spectroscopic studies on the effect of doping with CoBr2 and MgCl2 on some physical properties of polyvinylalcohol films

Filled and unfilled polyvinylalcohol (PVA) films were prepared by the casting technique. Films of equal amounts with various concentrations of two fillers (CoBr₂ and MgCl₂) were prepared. Spectroscopic, structural and some physical properties of these films were studied with different techniques. Fourier-transform infrared (FTIR) revealed that the syndiotacticity structure of the PVA samples causes dense molecular packing in the crystal and also stronger intermolecular hydrogen bonds, which are responsible for the disappearance of the molecular motion. X-ray diffraction (XRD) scans evidenced the presence of some semicrystalline structure of PVA films. The optical absorption spectra suggested the presence of an optical gap (E_g), which depends on filler concentration for all the filling levels. Differential thermal analysis (DTA) suggests that the segmental mobility of an amorphous pure PVA increases as a result of the addition of mixed fillers, becoming less-rigid segments. This indicates that the mixed fillers act as plasticizers.     

合金效应加强水分子在PtRun团簇上的吸附作用

利用第一性原理计算方法,研究合金效应对PtRu_n-1（n=2-14）和H₂O-PtRu_n-1（n=2-14）体系的几何构型、稳定性及吸附水特性的影响.结果表明：铂原子替代钌原子的能量较低,容易与钌团簇形成合金,铂原子喜欢占据配位数较低位置.相对于纯钌团簇,合金效应很大程度上提高了水分子在PtRu_n团簇上的吸附能.考虑范德瓦尔斯力后,水分子在PtRu₇上的吸附能增大,分解势垒降低,水分子可以在PtRu₇上分解.铂钌合金更适合做分解水制取氢气的催化剂.     

Swelling and mechanical properties of radiation crosslinked Au/PVA hydrogel nanocomposites

Hydrogel nanocomposites of polyvinyl alcohol (PVA) filled with gold nanoparticles (Au NPs) were synthesised using gamma irradiation technique. Structural, optical, and morphological characterisation was performed using powder XRD, UV-vis, FESEM, and TEM techniques. Inclusion of Au NPs at the time of crosslinking may have reduced the binding sites of PVA matrix, which resulted in high-swelling capacity of Au/PVA hydrogel nanocomposites. The increase in mechanical stability of the Au/PVA hydrogel nanocomposites has been observed and it may be due to increase in the crystallinity percentage with increased Au NPs in PVA matrix. These nanocomposites may fulfil the increasing demand for multifunctional hydrogel with enhanced swelling and mechanical properties.     

pH-Sensitive Poly(Vinyl Alcohol)/Sodium Carboxymethylcellulose Hydrogel Beads for Drug Delivery

A series of pH-sensitive hydrogel beads were prepared composed of poly(vinyl alcohol) (PVA) and sodium carboxymethylcellulose (CMC) by using Fe³⁺ crosslinking and freeze-thawing (FT) cycle techniques. The mixed solution of CMC and PVA was firstly crosslinked with Fe³⁺ to form beads and then subjected to freezing-thawing cycles for further crosslinking. The formation of hydrogel was confirmed by Fourier transform infrared spectroscopy (FTIR). The gelling rate in ferric solution and the swelling and pH-senstive properties of the hydrogel beads were investigated. The encapsulation efficiency and in-vitro release properties of beads were also evaluated using Bovine serum albumin as model drug. The pH sensitivity and the release rate increased with increasing CMC content. These results suggest that the PVA/CMC hgdrogel beads should be useful as pH-sensitive drug delivery systems for bioactive agents.     

Hydrogen depth profile measurement in a-Si1-xCx:H films by elastic recoil detection

The hydrogen content and depth profile in a-Si_1-xC_x:H films were measured by the elastic recoil detection (ERD) technique. It is shown that the hydrogen content changes from 15 to 50 at% with increasing carbon content x. For x<0.4 the hydrogen content increases mainly due to the increase of the Si-CH₃ contribution and for x > 0.4 due to C-H bonds. By combining the ERD and IR results, the proportionality between the number of Si-CH₃ bonds and the intensity of IR absorption due to the Si-CH₃ rocking mode vibration is ascertained. The proportionality constant is found to be A^roc_Si-CH3 = 5 × 10¹⁹ cm^-2.