丙烯酰胺聚合物与氧化铝晶体相互作用的分子动力学模拟

将丙烯酰胺单体分别与丙烯酸(AA)、阳离子单体丙烯酰氧乙基二甲基乙基溴化铵(DMB)、疏水性单体丙烯酸十八酯(OA)共聚,分别得到阴离子聚丙烯酰胺P(AA-co-AM)、阳离子聚丙烯酰胺P(DMB-co-AM)、非离子聚丙烯酰胺P(AM)和疏水性聚丙烯酰 胺P(OA-co-AM)等四种丙烯酰胺高分子絮凝剂. 用分子动力学方法,模拟计算了四种聚丙烯酰胺絮凝剂与氧化铝晶体(012)晶面的相互作用,以获得相应的形变能,结合能及理论排序,为阐释四种高分子絮凝剂的絮凝作用机理提供理论依据. 研究结果表明：四种聚合物分子相对Al₂O₃(012)面的初始位置均已贴近Al₂O₃(012)面,且絮凝剂分子中的O原子与Al₂O₃(012)面的Al原子之间存在强烈的相互作用;与Al₂O₃(012)晶面结合的高分子絮凝剂发生扭曲变形,但形变能远小于相应的非键作用能. Al₂O₃(012)晶面结合能的大小排序为P(DMB-co-AM)>P(OA-co-AM)>P(AA-co-AM)>P(AM), 显示四种絮凝剂中P(DMB-co-AM)的絮凝性能最佳,PAM絮凝效果最差.     

Photoluminescence of water-soluble CdSe/ZnS nanoparticles in complexes with cationic and anionic polyelectrolytes

The data on the influence of polyelectrolytes on the photon emission probability of water-soluble CdSe/ZnS nanoparticles are obtained. The decrease in the photoluminescence quantum yield of nanoparticles occurring upon their transfer to aqueous solutions from toluene (in the course of solubilization) depends on the ionic nature of an agent applied for the replacement of trioctylphosphine oxide residues on the surface of nanoparticles. It turns out that such a cationic modifying agent as cysteamine leads to an insignificant (～10%) decrease in the photoluminescence quantum yield of nanoparticles. The use of such an anionic agent as mercaptoacetic acid causes a significant (～80%) decrease in the quantum yield and the average decay time of photoluminescence. For nanoparticles modified by mercaptoacetic acid (anionic nanoparticles), this decrease is partially compensated if these particles interact with polyelectrolytes whose backbone is oppositely charged (cationic polyelectrolytes), such as polyallylamine and polydiallyldimethylammonium chloride. In this case, the photoluminescence quantum yield shows a reverse increase by 40%, remaining the same within a matter of months or longer. In contrast to this, cationic nanoparticles, only slightly quenched by cysteamine at the stage of solubilization, are appreciably degraded in complexes with anionic polyelectrolytes in solutions and upon immobilization of complexes on a substrate, so that their photoluminescence quantum yield irreversible decreases to zero within a few days. Possible mechanisms of the effects observed are discussed and their consideration in polyelectrolyte-based molecular lithography.     

An Electroacoustic Investigation of Concentrated Aqueous Suspensions of Calcium Pyrophosphate

The zeta potential of concentrated suspensions of calcium pyrophosphate were investigated using electroacoustics. The particles were negatively charged over the entire pH range studied. It proved impossible to reduce the pH of the suspension below 1.8, but the iso electric point could be estimated to occur at approximately pH 1. Two commercially available dispersants (one cationic and one anionic) were then added in small increments to the suspension in order to follow the change in zeta potential as the dispersants adsorbed onto the particles. From the shape of the curve it was possible to estimate the optimum adsorbed amount of dispersant required to fully coat the particles. The cationic dispersant adsorbed strongly and the optimum dosage was estimated at 2.5 ml of active polymer/kg of powder. Anionic dispersants are known to adsorb onto negatively charged ceramic oxide particles, but the anionic dispersant used in this study did not adsorb onto the negatively charged calcium pyrophosphate particles.     

紫外光引发模板聚合阳离子聚丙烯酰胺及其污泥脱水应用

阳离子聚丙烯酰胺是污水和污泥处理中常用的一种絮凝剂,传统方法制备的阳离子聚丙烯酰胺因阳离子单体随机分布, 电荷过于分散, 导致其在絮凝时不能充分发挥阳离子单体的电中和作用,为此本研究尝试使用一种新型方法制备阳离子聚丙烯酰胺,即以二甲基二烯丙基氯化铵(DMDAAC)和丙烯酰胺(AM)为单体,分别以两种不同分子量的聚丙烯酸钠(PAAS)为模板,使用紫外光引发模板聚合法制得模板聚合物TPDA1和TPDA2,同时使用紫外光引发聚合法制得非模板聚合物(NTPDA)作为对比。使用红外光谱(FTIR)、氢核磁共振图谱(1H NMR)、扫描电镜(SEM)等方法对制得的聚合物进行表征,并通过污泥脱水试验研究其污泥脱水效率。波谱分析结果表明,添加模板提高了DMDAAC单体的活性,促使聚合物分子中形成DMDAAC连续分布的阳离子单体嵌段结构,从而提高了聚合物的絮凝性能,尤其是电中和作用;SEM扫描显示模板聚合物的具有较大的比表面积和分形维数;污泥脱水试验表明,模板聚合物具有较好的污泥脱水性能和较宽pH应用条件,当模板聚合物TPDA1投加量为50 mg·L-1,污泥pH为8时,其具有最佳污泥脱水效率,污泥含水率降至最低值72.5%。模板分子量对聚合物属性也存在影响,分子量较低的模板制得的聚合物具有相对较好的污泥脱水效率。     

Debye-Hückel theory for interfacial geometries

The Debye-Hückel theory for bulk electrolyte solutions is generalized to planar interfacial geometries, including screening effects due to mobile salt ions which are confined to the interface and solutions with in general different salt concentrations and dielectric constants on the two sides of the interface. We calculate the general Debye-Hückel interaction between fixed test charges, and analyze a number of relevant special cases as applicable to charged colloids and charged polymers. Salty interfaces, which are experimentally realized by monolayers or bilayers made of cationic and anionic surfactants or lipids, exert a strong attraction on charged particles of either sign at large separations from the interface; at short distances image-charge repulsion sets in. Likewise, the effective interactions between charged particles are strongly modified in the neighborhood of such a salty interface. On the other hand, charged particles which are immersed in a salt solution are repelled from the air (or a substrate) interface, and the interaction between two charges decays algebraically close to such an interface. These general results have experimentally measurable consequences for the adsorption of charged colloids or charged polymers at monolayers, solid substrates, and interfaces.     

Anionic nonconjugated polyelectrolyte as an anode interfacial layer for polymer solar cells

Since the most high-performing donor polymers in polymer solar cells (PSCs) possessed the deep highest occupied molecular orbital (HOMO) level, interfacial engineering on anode contact is becoming increasingly important. Herein, we demonstrated efficient PSCs using an anionic poly(styrene sulfonate) (PSS) as an anode interfacial layer (AIL). With the formation of the dipole layer, the effective work function (WF) of indium tin oxide (ITO) electrode is significantly increased from 4.8 to 5.3 eV, providing favorable energetic alignment to the quasi-Fermi level of various donor polymers. Moreover, by incorporating cationic polyelectrolytes as a cathode interfacial layer, a pair of electric dipole layers induces a strong built-in electric field across the photoactive layer to drive efficient sweep-out of photogenerated charges. Consequently, the device with PSS AIL exhibited high power conversion efficiencies of 9.2 and 14.8% in PTB7-Th:PC₇₁BM- and PM6:Y6-based PSCs, respectively, both of which are higher than those of the devices with PEDOT:PSS.     

Monte carlo study of coulombic criticality in polyelectrolytes

The role of charges in determining the water solubility of polyelectrolytes, a question of considerable relevance to biology, is currently unresolved. We use computer simulations to study the purely Coulombic phase separation of flexible polyelectrolytes with monovalent counterions in an athermal solvent. In agreement with recent theories we find that the critical temperature for this transition increases with chain length, but that the critical density remains unchanged. We therefore stress that the phase behavior of polyelectrolytes is qualitatively different from uncharged polymers, where the critical density decreases towards zero for long chains.     

Monitoring the Dynamics of Concentrated Suspensions by Enhanced Backward Light Scattering

The shear-induced flocculation of kaolin-polymer flocs in a stirred tank is investigated at medium to high solids concentrations (ϕ=1−10% w/w). The evolution of the average floc size is monitored by the change in intensity of laser light scattered in the 180° direction. The measurements reflect the change in particle number concentration as flocculation proceeds. As flocculation begins, coagulation dominates and the floc size increases (total particle number decreases) and then levels off at a steady state value as fragmentation becomes significant and balances coagulation. At steady state, the measurements indicate the extent of flocculation. Increasing the shear rate increases the coagulation and fragmentation rates, resulting in smaller floc sizes at steady state. Increasing the flocculant concentration increases the steady state floc size by strengthening the bonds between primary particles to resist fragmentation. At constant shear rate and flocculant concentration, increasing the solids fraction decreases the steady state floc size indicating formation of weakly bonded flocs. Flocculant mixing was the most important factor for flocculation efficiency at high solids concentrations.     

Flocculation Properties of Some Cationic Polysaccharides

Flocculation of a clay suspension model using some cationic polysaccharides has been studied by turbidity measurements. The investigated polyelectrolytes contain quaternary ammonium salt groups, N-ethyl-N, N-dimethyl-2-hydroxypropylene ammonium chloride, attached to a dextran backbone. The flocculation efficiency was studied as a function of the polycation charge density and some flocculation parameters (polycation dose, settling time, concentration of both clay suspension and parent solution of polymer). All investigated cationic polysaccharides showed high flocculating efficiency at optimum flocculant doses, which correlated well with the charge density of the polycations: the higher charge density, the lower the amount of dextran derivative was required for reaching the maximum clarity degree (of about 100%). This finding is consistent with the neutralization mechanism for a flocculation process. The residual turbidity values also varied with the settling time and the concentrations of clay suspension and parent solution of polymer. Possible reasons for these dependences are discussed.     

Enhanced Dewatering of Waste Sludge With Polyacrylamide/Montmorillonite Composite and Its Conditioning Mechanism

In order to improve the waste sludge dewaterability of polyacrylamide (PAM), the composite conditioner of PAM/montmorillonite (MMT) was prepared. The structure and intermolecular hydrogen bonding of the composite were studied, and the effects of PAM/MMT weight ratio and dosage on the dewaterability of the waste sludge were systematically investigated. The results revealed that the MMT platelets were in an exfoliated state in the PAM matrix, and hydrogen bonding between –OH groups of MMT and –NH groups of PAM led to relatively high elastic modulii (G') values and low tan δ values, indicating the possible formation of a physically cross-linked network in aqueous solution. The addition of MMT significantly reduced the specific resistance to filtration (SRF) of the waste sludge, with a minimum value being achieved at a 1:1 PAM/MMT weight ratio. The UV transmittance and the turbidity of the supernatant of the waste sludge were also improved at a proper PAM/MMT weight ratio. The synergistic effect of the two components in the composite through the charge neutrality and bridging action of PAM as well as the adsorption capacity of MMT resulted in an enhanced dewaterability of waste sludge.     

Electronic effect of ionic‐pair substituents

For conventional organic substituents, an almost linear relationship can be established between the para Hammett constants in aqueous solutions and chemical shifts or natural population analysis charges (NPA charges). Based on these correlations, the Hammett constants of six synthesized ionic‐pair substituents were estimated via the chemical shifts, which were well in agreement with the results calculated by NPA charges. The para Hammett constants of 89 different ionic‐pair substituents (77 anion‐cationic and 12 cation‐anionic) were therefore calculated in the gas phase based on the density functional theory method. The results show that both the anion‐cationic and cation‐anionic substituents are electron‐withdrawing groups and the different cation–anion combinations could tune the Hammett constants of the ionic‐pair substituents in a range from 0.03 to 0.77. Copyright © 2013 John Wiley & Sons, Ltd.     

考虑电离作用的淤泥异向絮凝三维数值模拟

鉴于试验观察淤泥絮凝结构的技术难度,本文尝试以布朗动力学为基础,采用蒙特卡洛方法动态模拟电离作用下颗粒成长为絮团的过程.为结合实际情况,泥沙颗粒初始位置由颗粒粒径和淤泥密度决定,颗粒初始速度按照相应条件下高斯随机分布给定.边界条件用和实际符合较好的循环边界.在模拟数据分析的基础上,讨论并比较了颗粒粒径和淤泥密度对絮凝时间以及絮团开放程度的影响.另一方面,讨论了电离作用后颗粒电荷量对絮团生长的影响.解释了泥沙颗粒表面电荷密度变化对絮凝过程和絮团结构的影响,模拟结果和实际情况较为一致.     

2H NMR and polyelectrolyte-induced domains in lipid bilayers

2H NMR studies of polyelectrolyte-induced domain formation in lipid bilayer membranes are reviewed. The 2H NMR spectrum of choline-deuterated phosphatidylcholine (PC) reports on any and all sources of lipid bilayer surface charge, since these produce a conformation change in the choline head group of PC, manifest as a change in the 2H NMR quadrupolar splitting. In addition, homogeneous and inhomogeneous surface charge distributions are differentiated. Adding polyelectrolytes to lipid bilayers consisting of mixtures of oppositely charged and zwitterionic lipids produces 2H NMR spectra which are superpositions of two Pake sub-spectra: one corresponding to a polyelectrolyte-bound lipid population and the other to a polyelectrolyte-free lipid population. Quantitative analysis of the quadrupolar splittings and spectral intensities of the two sub-spectra indicate that the polyelectrolyte-bound populations is enriched with oppositely charged lipid, while the polyelectrolyte-free lipid population is correspondingly depleted. The same domain-segregation effect is produced whether cationic polyelectrolytes are added to anionic lipid bilayers or anionic polyelectrolytes are added to cationic lipid bilayers. The 2H NMR spectra permit a complete characterization of domain composition and size. The anion:cation ratio within the domains is always stoichiometric, as expected for a process driven by Coulombic interactions. The zwitterionic lipid content of the domains is always statistical, reflecting the systems tendency to minimize the entropic cost of demixing charged lipids into domains. Domain formation is observed even with rather short polyelectrolytes, suggesting that individual polyelectrolyte chains aggregate at the surface to form "superdomains". Overall, the polyelectrolyte bound at the lipid bilayer surface appears to lie flat along the surface and to be essentially immobilized through its multiple electrostatic contacts.     

Ultrathin self-assembled polyelectrolyte multilayer membranes

The paper is concerned with ultrathin membranes prepared upon alternating layer-by-layer adsorption of cationic and anionic polyelectrolytes on a porous substructure. The formation of the polyelectrolyte multilayer membranes is characterised and the transport of gases, liquid mixtures and ions across the membranes is studied. In particular, the use of the membranes for alcohol/water separation under pervaporation conditions, and for the separation of mono- and divalent ions is described. It is demonstrated that upon a suitable choice of polyelectrolytes and substructures, and a careful optimisation of preparation and operation conditions, membranes can be tailored exhibiting an excellent separation capability. Received 4 September 2000     

Effect of counterions on the swelling of spherical polyelectrolyte brushes

We investigate the swelling of colloidal spherical polyelectrolyte brushes in the presence of different counterions. The colloidal particles consist of a solid poly(styrene) core of ca. 100 nm diameter onto which linear polyelectrolyte chains are chemically grafted. Two types of polyelectrolyte chains have been used here: The cationic polyelectrolyte poly(2-(acryloyl)ethyltrimethylammonium chloride)) (PATAC) and the anionic poly(styrenesulfonate) (PSS). Both systems are dispersed in water and the degree of swelling of the surface layer is studied by dynamic light scattering. Adding more and more salt leads to a strong shrinking of the surface layer as expected for polyelectrolyte brushes. It is shown that data obtained at low ionic strength can be collapsed on suitable master curves for monovalent and divalent counterions, respectively. For some ions, however, high salt concentrations may lead to a re-swelling of the brush layer in case of the cationic systems. This points to specific interactions of the counterions with the PATAC chains. This strong specific interaction between the counterions and the attached polyelectrolyte may even lead to flocculation of the particles at intermediate salt concentration. Surprisingly, for iodide and magnesium counterions the solubility increases again if the salt concentration is raised to 1 mol/l. Hence, specific interaction leads to salting-out effects as well as to salting-in effects for these colloidal particles. All specific effects seen at high concentrations of added salt can be explained by the increase of the reduced excluded-volume parameter which is due to the adsorption of salt ions.     

透光脉动检测仪研究碱度对絮体形成、破碎及再生的影响

为了解碱度对絮体的形成、破碎及再生过程的影响,采用PDA2000型透光脉动检测仪测定不同碱度下投加硫酸铝时高岭土悬浮液的絮凝指数(FI指数),并以强度因子和再生因子评价絮体的强度和再生能力。结果表明,碱度的高低在很大程度上会影响絮体的形成、破碎及再生过程,所形成絮体的颗粒随碱度的增加而减小。混凝剂投量和碱度高低共同决定了絮体的抗破碎强度,碱度越高,混凝剂投量越大,絮体的强度越高。在电中和作用下形成的絮体在低碱度下经一次破碎后恢复程度接近100%,在网捕卷扫作用下形成的絮体,无论碱度高低,从第2次破碎起,FI指数均以大于10%的幅度逐次下降,絮体不可恢复程度显著增大。     

Phosphonated Polyethylenimine‐Coated Nanoparticles: Size‐ and Zeta‐Potential‐Adjustable Nanomaterials

Novel partially phosphonated polyethylenimine polymers are developed in order to control the modification of nanoparticle (NP) surfaces. This polymer is built by an accessible one‐step process. The numerous phosphonate functions assume both a strong covalent anchoring on metal oxide NPs and a modulation of electric charges, while amino groups are associated with dispersion preservation and subsequent biofunctionalization. The zwitterionic nanomaterials obtained display a good stability toward pH and ionic strength. According to the selected percentage of phosphonation and the polymer size, zeta potential, and diameter of the particles are controlled.     

Adsorption of polyelectrolytes on silica and gold surfaces

The results of a study that helps understand the mechanisms of adsorption of polyelectrolytes on particles, using numerical simulation methods, specifically the one known as dissipative particle dynamics are reported here. The adsorption of cationic polyelectrolytes of two different polymerisation degrees interacting with two types of surfaces, one made of gold and the other of silica, is predicted and compared. We find that a more negatively charged wall does not necessarily adsorb more cationic polyelectrolytes because the electrostatic repulsion between the wall and the polyelectrolytes is stronger. Additionally, intra-chain repulsion plays an important role, because the largest polyelectrolyte chains have larger excluded volume than the shorter ones. In regard to the adsorption dependence on the polyelectrolyte polymerisation degree, we find that the excluded volume drives the adsorption throughout the intra-chain electrostatic repulsion, because the SiO₂ surface is strongly negative. These results are expected to be useful for several nanotechnological applications of current interest, such as in gene therapy and in the improvement of drug delivering mechanisms.     

Microstructure of Polyelectrolyte Nanoaggregates Studied by Fluorescence Probe Method

The microstructure of water soluble nanoaggregates based on polyelectrolyte complex formed by the cationic comb-type copolymer poly(acrylamide -co-[3- (methacryloyl-amino)propyl] trimethylammonium chloride)-graft- polyacrylamide [P(AM-co-MAPTAC)-g-PAM] and the anionic linear polyelectrolyte sodium polyacrylate (NaPA) was investigated using the fluorescence probe technique. The fluorescence probe were 1-anilinonaphthalene-8-sulfonic acid (ANS), pyrene (Py) and 1,10-bis(1-pyrene) decane (PD). The fluorescence properties in polyelectrolyte complex solutions, which are sensitive to either micropolarity (ANS, Py) or microviscosity (PD), were related to the quantities obtained in different pure or mixed solvents. Micropolarities were quantified utilizing the polarity common index (Reichardt) E _T(30). ANS and Py showed a variation of the micropolarity with the charge ratio of the two polymers, with the lowest polarity reached at the complex neutralization. The PD probe, by its excimer-to-monomer fluorescence intensities ratio, enabled us to evidence the effect of the composition and the comb-type copolymer grafting density on the microviscosity of the interpolyelectrolytes aggregates. It has been found that the microviscosity increased with the density of the grafting PAM chains.     

Probing particle-particle interactions in flocculated oil-in-water emulsions using ultrasonic attenuation spectrometry

The flocculation of silicone oil-in-water emulsions ( φ = 0.1) containing quasi-monodisperse droplets was studied by ultrasound. The ultrasonic attenuation spectra of emulsions with different particle sizes (200-1600 nm) were measured between 0.5 and 10 MHz using an interferometer. Flocculation was induced by adding excess sodium dodecyl sulphate micelles to the emulsions to increase the attractive forces between the droplets. Droplet flocculation decreased the ultrasonic attenuation at low frequencies because of overlap of the thermal waves caused by the close proximity of the droplets within the flocs. A mean-field model which takes into account this effect was used to determine the droplet volume fraction within the flocs and thus to estimate the distance between the droplets. Received 17 July 2000