光散射技术在高分子表征研究中的应用

光散射技术是高分子领域中重要的表征手段之一.静态光散射和动态光散射的结合能够获得丰富的关于高分子的信息,如重均分子量、回转半径、第二维里系数、流体力学半径、尺寸分布、分子链构象等.除合成高分子外,光散射技术同样适用于研究生物大分子、微生物、胶体、纳米粒子、病毒、囊泡等在溶液或悬浮液中的行为.本综述重点介绍稀溶液中静态光...     

疏水缔合聚丙烯酰胺在盐水中的自组装行为

使用静态光散射、动态光散射以及原子力显微镜(AFM)研究了疏水缔合聚丙烯酰胺(HAPAM)在盐水溶液中的自组装行为.研究了聚合物分子在不同盐浓度中的表观重均分子量(Mw,a),均方根回转半径(),流体力学半径(),第二维里系数(A2)的变化,并根据/的比值得出聚合物分子的聚集形态.实验结果表明:随着盐浓度的增强,聚合物溶液的分子链由舒展变得卷曲.     

光散射技术在蛋白质晶体生长研究中的应用和进展

光散射技术广泛应用于生物大分子的晶体生长研究中,它包括静态光散射和动态光散射两种。利用静态光散射可以测定蛋白质溶液渗透的第二维里系数;利用动态光散射可以测定蛋白质溶液的平动扩散系数,获得溶液中蛋白质粒子的流体力学半径及分布情况,分离蛋白质结晶的成核与生长过程,研究大分子的聚集行为和晶体生长的动力学。借助光散射技术可以实现蛋白质晶体生长过程的动态控制。近些年光散射仪器向着小型化、轻便化的方向发展,光散射技术不断得到改进,日益完善,不仅用于地面实验,也应用于空间领域蛋白质晶体生长的研究中。     

P(NIPAM-co-NVP)共聚物分子链水溶液中的可逆聚集研究

用溶液聚合方法合成了线型聚(N-异丙基丙烯酰胺-co-N-乙烯基吡咯烷酮)共聚物,通过弹性光散射(elastic light scattering,ELS)、荧光光谱与动态光散射研究了共聚物水溶液分子链可逆聚集的温度和时间依赖性.研究表明,升温时,ELS强度增加,分子链聚集;降温时,ELS强度降低,聚集的分子链解离.荧...     

线形、梳形和星形高分子静态和动态性质的模拟

以梳形高分子为纽带,基于粗粒化分子动力学模拟方法,研究了线形、梳形和星形拓扑结构高分子的静态和动态性质,以揭示稀溶液中高分子链行为与链拓扑结构依赖关系的一般性规律.研究结果表明,随着线形-梳形-星形的链拓扑结构转变,回转半径的标度关系由仅依赖分子聚合度转变为同时依赖链聚合度与臂数或侧链数.分析了星形高分子和梳形高分子的静态和动态性质的特征规律.星形高分子的臂数增加使其尺寸迅速减小,形状则由长椭球形转变为类球形,且扩散系数也随之增加;其均方回转半径(〈R_g〉)和扩散系数(D)与分子聚合度(N)及臂数(f)的标度规律为〈R_g〉~N~(0.581)f~(-0.402),D~N~(-0.763)f~(0.227).梳形高分子的静态与动态性质与分子聚合度及侧链数的依赖关系为〈R_g〉~N~(0.597)f~(-0.212)(每个支化点只有一条侧链)和〈R_g〉~N~(0.599)f~(-0.316)(每个支化点有多条侧链).     

梳状共聚物水泥分散剂构效关系研究进展

梳状共聚物水泥分散剂(由聚电解质主链和非离子型聚乙二醇侧链组成)是建筑化学外加剂领域的研究热点。关于梳状共聚物分子结构-吸附-分散及分散保持的构效关系已经基本明晰,而从梳状共聚物构象和水泥早期水化的研究才刚刚起步。本文结合课题组在梳状共聚物方面的最新研究成果,详细总结了梳状共聚物溶液构象、界面吸附构象、分散及分散保持性能、早期水化历程等构效关系方面的最新研究进展,并提出了今后在基础和产品开发方面的重点研究方向。     

激光光散射表征寡链聚苯乙烯微胶乳粒子的方法

本文阐述了利用激光光散射表征寡链（ｐａｕｃｉ－ｃｈａｉｎ）聚苯乙烯微胶乳的方法。在静态光散射中，可测得微胶乳粒子的重均摩尔质量，结合粒子内所含高分子链的重均分子量，进而计算出每个微胶乳粒子内高分子链的平均数目；在动态光散射中，通过对时间相关光谱的拉普拉斯反演求出粒子的平动扩散系数分布Ｇ（Ｄ），进而得到流体力学半径（Ｒｈ）及分子量的分布。通过综合分析静态与动态光散射的结果，建立了计算球形粒子密度的光散射方法，并发现，寡链聚苯乙烯微胶乳的密度低于通常的胶乳粒子以及本体聚苯乙烯的密度     

蠕虫状链模型下梳状共聚物分子的均方回转半径的理论分析及其在聚羧酸系减水剂分子中的应用

利用蠕虫状链模型对梳状共聚物分子的均方回转半径进行了理论分析,建立了回转半径与主链轮廓长度、主链持久长度、侧链轮廓长度、侧链持久长度、侧链数目以及侧链沿主链的分布情况(均匀分布和梯度分布)之间的定量数学关系.在此基础上,以被称为"第一代聚羧酸系高性能减水剂"(以下简称为MPEG-type PCE)的甲基丙烯酸(MAA)/烯酸甲酯(MAA-MPEG)梳状共聚物分子为研究对象,结合实验数据,对其聚电解质主链的持久长度进行了分析,并考察了主侧链长度、刚柔性、侧链分布、接枝密度等分子结构参数对PCE回转半径的影响,最后对模型的局限性作简要说明.梳状共聚物分子的蠕虫状链模型物理图像简洁,参数意义明确,应用于PCE分子体系时较之前所报道的柔性链模型要更为合理,能够为分析PCE的分子结构与溶液构象和吸附构象之间的关系提供更科学的视角.     

具有温度响应壳层的金纳米粒子的制备

利用可逆-加成断裂链转移聚合得到全亲水性的嵌段共聚物(PEO-b-PNIPAM), 通过"grafting to"使其接枝到金纳米粒子表面. 通过透射电子显微镜、 紫外-可见吸收光谱、 能谱分析及动态光散射研究了杂化的金纳米粒子的壳层结构及温度响应行为. 实验结果表明, 得到核壳结构的金纳米粒子, 同时其壳层具有温度响应行为. 随着温度的升高, 其流体力学半径略有减小. 在整个升温过程中, 由于外层PEO链段的抑制作用, 没有发生粒子间的聚集.     

葡萄糖基N-异丙基丙烯酰胺共聚物合成及其温敏性

采用酶促法合成了可聚合的葡萄糖乙烯酯衍生物6-O-乙烯己二酰-D-葡萄糖(OVAG),通过自由基聚合法将N-异丙基丙烯酰胺和OVAG共聚,制备出了温敏含糖共聚物poly(OVAG-co-NIPAAm),通过1H NMR对聚合物的结构进行了表征,用凝胶色谱测定共聚物的相对分子质量。用可见光吸收法测定了poly(OVAG-co-NIPAAm)的低临界溶解温度(LCST),动态光散射测定了聚合物在水溶液中的流体力学直径,静态光散射测定了共聚物在水溶液中的均方旋转半径。结果表明,采用自由基聚合制备的温敏含糖共聚物在水溶液中自组装成近似球形的纳米粒子,其LCST由N-异丙基丙烯酰胺均聚物的32℃提高至39℃,粒径在60 nm左右,粒径分布较窄。     

Synthesis and Characterization of Star Polymer with Comb-like Poly(lauryl methacrylate) Arms by Atom Transfer Radical Polymerization via One-pot ‘Arm-First’ Method

Atom transfer radical polymerization (ATRP) was used to prepare core crosslinked star polymers with comb-like poly (lauryl methacrylate) (LMA) arms by one-pot “arm-first” method, involving the synthesis of comb-like PLMA arms, followed by their crosslinking, using a mixture of LMA monomer and ethylene glycol dimethacrylate (EGDMA) crosslinker. By adjusting the feeding time and level of EGDMA, a series of star-like polymers with various comb-like arms length and number can be obtained. The molecular architecture including radius of gyration (Rg), hydrodynamic radius (Rh) and intrinsic viscosity (η_i) etc. were characterized by a triple-detector gel permeation chromatography (GPC) equipped with a refractive index detector, viscometer detector and a multi-angle static laser light scattering (MALLS) detector. The thermal property and shearing stability of these star-like polymers were also investigated.     

LIGHT-SCATTERING STUDY OF POLYELECTROLYTE HOLLOW CAPSULES

Silver halide (AgX) microcrystal was used as template to synthesize hollow polyelectrolyte capsules. These hollow capsules were characterized by laser light scattering (LLS) used to measure the size of the capsules in solution. The ratio of hydrodynamic radius (Rh) from dynamic LLS to the radius of gyration (Rg) from static LLS is almost unity, revealing that the entities are hollow in solution. The results suggest that the LLS method can be regarded as a good complement to the confocal laser scanning microscopy (CLSM) method for the characterization of small hollow capsules, and it possesses the advantage of not needing fluorescence labeling.     

Role of methyl in the phase transition of poly(N-isopropylmethacrylamide)

Poly(N-isopropylmethacrylamide) (PiPMA) has one more methyl group at each monomeric unit than poly(N-isopropylacrylamide) (PiPA). By use of laser light scattering (LLS) and ultrasensitive differential scanning calorimetry (US-DSC) we have investigated the association and dissociation of PiPMA chains in water. LLS studies reveal that PiPMA chains form larger aggregates at a temperature above its lower critical solution temperature (LCST) as the chain molar mass (Mw) decreases. In comparison with PiPA aggregates, PiPMA aggregates show a larger ratio of average radius of gyration to average hydrodynamic radius (/), indicating that PiPMA aggregates are looser. US-DSC studies show PiPMA chains have smaller enthalpy change (DeltaH) and entropy change (DeltaS) than PiPA chains during the phase transition, indicating that PiPMA chains have smaller conformational change. Our experiments demonstrate that the additional methyl groups in PiPMA chains restrain the intrachain collapse and interchain association, leading the phase transition to occur at a higher temperature.     

Microstructural characterisation and behaviour in different salt solutions of sodium polymethacrylate-g-PEO comb copolymers

Different polycarboxylate polymers (PCPs) have been characterised and their microstructure investigated by size exclusion chromatography, ¹H and ¹³C nuclear magnetic resonance spectroscopy. These polymers are comb-like with a sodium polymethacrylate backbone (PMAANa) on which poly(ethylene oxide) (PEO) chains are randomly grafted as shown by ¹³C NMR measurements. Since they are mostly used as superplasticisers in cementeous applications, their behaviour has been investigated at high pH in various salt solutions; average radii were determined at room temperature by static and dynamic light scattering and phase diagrams were determined as a function of temperature. We tried to evaluate the influence of different parameters (ion valence, cations, anions, PCP molecular weight, PEO length and grafting degree). A few experiments on homopolymers (PEO and PMAANa) have been equally performed in order to better understand the behaviour of PCPs in solution.     

pH-Responsive Self-assembled Nanoparticles of Simulated P(AA-co-SA)-g-PEG for Drug Release

Simulated graft copolymer of poly(acrylic acid-co-stearyl acylate) [P(AA-co-SA)] and poly(ethylene glycol) (PEG) was synthesized, where acrylic acid, stearyl acylate and PEG was employed as the pH-sensitive, hydrophobic and hydrophilic segment, respectively. Polymeric nanoparticles prepared by the dialysis of simulated graft copolymer solution in dimethylformamide against citrate buffer solution with different pH values were characterized by transmission electron microscopy (TEM), fluorescence technique and laser light scattering (LLS). TEM image revealed the spherical shape of the self-aggregates, which was further confirmed by LLS measurements. The critical aggregation concentration increased markedly (10 to 150 mg/L) with increasing pH (4.6 to 7.0), consistent with the de-protonation of carboxylic groups at higher pH. The hydrodynamic radius of polymeric nanoparticles decreased from 118 nm at pH 3.4 to 90 nm at pH 7.0. The controlled release of indomethacin from those nanoparticles was investigated, and the self-assembled nanoparticles exhibited improved performance in controlled drug release.     

Study of ethidium bromide effect on dsDNA separation by capillary zone electrophoresis and laser light scattering

The effect of ethidium bromide (EB) on dsDNA separation was studied by using capillary zone electrophoresis (CZE) and laser light scattering (LLS). By increasing the concentration from 1 to 15 microg/mL, EB showed significant influence on the separation of pBR322 HaeIII in terms of resolution, speed, and signal-over-noise ratio. The physicochemical properties of DNA, such as mobility under electric field, charge-over-size ratio, and hydrodynamic radius, showed two declines, a sharp drop followed by a relaxed decrease, with increasing EB concentration. Such observations could be explained by using two modes of the dye binding process: intercalation and outside binding. The combination of results obtained from CZE and LLS also confirmed the existence of outside binding. Compared with intercalation, outside binding showed a weaker dye concentration dependence in neutralizing the negative charges on the DNA fragments. Static light scattering showed that and of DNA in 1xTris-borate-EDTA (TBE) were increased with increasing EB concentration. / of DNA with dye had a value larger than 1.5, suggesting a random coil conformation.     

Conformational,optical, electro-optical,and dynamic characteristics of cross-linked poly(N-acryloyl-11-aminoundecanoic acid)

Polymerizable surfactants now attract a great interest due to high potential of their practical application as components of pseudostationary phase in micellar chromatography, drug carriers, and “building blocks” for molecular design of nanoparticles and nanostructured polymer materials, for encapsulation of various biological preparations. In the present work, we have studied poly(N-acryloyl-11-aminoundecanoic acid) (cross-linked comb-like polymer). Cross-linked polymers were obtained via copolymerization of the surfactant bearing double bond in hydrophobic tail with hydrophobic bifunctional cross-linker in micellar solution. Of special interest was the comparison between cross-linked and non-cross-linked polymers and influence of alkaline medium on characteristics of these samples. Non-cross-linked polymers were obtained by hydrolysis of the cross-linked product (treating with NaOH). The mixture of cyclohexanol and dioxane (1:1 volume ratio) was used as a solvent. Detailed studies of the obtained polymers by viscometry, dynamic light scattering, flow birefringence, and equilibrium and non-equilibrium electric birefringence were performed. It was established that during cross-linking process, two types of bonds are formed (the ones inside individual molecules and between several polymer chains). It was shown that cross-linked macromolecular nanoparticles can be transformed into comb-like polymers.     

Dilute solution properties of poly(dimethyldiallylammonium chloride) in aqueous sodium chloride solutions

MW fractions of poly(dimethyldiallylammonium chloride) (PDMDAAC) were prepared by preparative size-exclusion chromatography and characterized by static and dynamic light scattering, viscometry, size-exclusion chromatography, and electrophoretic light scattering, in 0.50M NaCl solution. The behavior of fractions with MW < 2 × 10⁵ was as expected for a strong polyelectrolyte in a good solvent, with a Mark-Houwink exponent of ca. 0.8, and MW-dependencies of the hydrodynamic radius and the radius of gyration of corresponding magnitude. At higher MW, curvature appears in the MW-dependencies, which can be best explained by the presence of branching. While this notably lowers the intrinsic viscosity at high MW, the electrophoretic mobility is unchanged regardless of molar mass. Thus, the branched polymers display the electrophoretic free-draining behavior characteristic of linear polyelectrolytes. ©1995 John Wiley & Sons, Inc.     

Effect of counterions on comb-like polycarboxylate conformation in aqueous solutions

Laser light scattering (LLS) and conductivity experiments were performed to investigate the effect of counterions on the conformation of polycarboxylate comb-like copolymers (PCEs) in aqueous solutions. The addition of monovalent ions (i.e., Na⁺ and K⁺) to dilute polycarboxylate comb-like copolymer solutions induced a slight shrinking of the molecular chains because of the screening of electrostatic intramolecular repulsion. Varying complexation phenomena, such as the formation of intramolecular complexation at certain Ca²⁺ concentrations and a transition between intermolecular and intramolecular complexations at different Ca²⁺ concentrations, were closely associated with Ca²⁺ concentration. Therefore, Ca²⁺ exerted a more complex influence on the conformation of PCEs with side chains containing polyethylene oxide (PEO) with different grafting densities. In addition, various combination types of Ca²⁺ with carboxylic groups were confirmed by theoretical simulation.     

Kinetics of pH-Induced formation and dissociation of polymeric vesicles assembled from a water-soluble zwitterionic diblock copolymer

The kinetics of pH-induced formation and dissociation of vesicles self-assembled from a biocompatible zwitterionic diblock copolymer, poly(2-(methacryloyloxy)ethyl phosphorylcholine)-b-poly(2-(diisopropylamino)ethyl methacrylate) (PMPC- b-PDPA), was investigated in detail via a combination of stopped-flow light scattering and laser light scattering (LLS). Upon jumping from pH 2 to 10, stopped-flow light scattering reveals three distinct relaxation processes for the early stages of vesicle self-assembly (0-40 s). Kinetic sequences associated with the obtained three characteristic relaxation times have been tentatively proposed. Moreover, the kinetics of vesicle formation in the later stage (from 3 min onward) was investigated by dynamic LLS. It was found that both the intensity-averaged hydrodynamic radius, R h, and the polydispersity, mu2/Gamma (2), decrease exponentially, yielding a characteristic relaxation time of approximately 350 s. To our knowledge, this is the first report on the kinetics of the unimer-to-vesicle transition of a stimulus-responsive diblock copolymer. The kinetics of vesicle dissociation for a pH jump from 12 to 2 was also investigated. The breakdown of polymeric vesicles is extremely fast and is independent of polymer concentration; it is complete within approximately 5 ms and is in marked contrast to the much slower rate of vesicle formation.