Dynamic light scattering and small-angle neutron scattering studies on phenolic resin solutions

Solution properties of unfractionated phenolic resins prepared by polycondensation of phenol and formaldehyde using oxalic acid as a catalyst were investigated by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The hydrodynamic radius, obtained by DLS experiments with 1 vol % solution in acetone, and the correlation length, ξ, of the Ornstein-Zernike equation, obtained by SANS experiments with 10 vol % solution in tetrahydrofuran, obey a power-law relation as a function of z-average molecular weight estimated by gel permeation chromatography, with scaling exponents of 0.57 and 0.27, respectively. These behaviors are unaffected by polymerization conditions, such as initial phenol-to-formaldehyde molar ratio in the range from 0.9 to 1.5, catalyst concentration with oxalic acid-to-phenol molar ratio from 0.01 to 0.1, and reaction time within the period in which the polymer remains soluble. SANS curves for polymers prepared under different conditions are sufficiently superimposed onto a single curve with the reduced variables, ξ⁻²I(q) and ξq. These results indicate that unfractionated phenolic resins have a self-similar structure with respect to the molecular weight.     

Dynamic light scattering from polymer gels: spring-rotor model

Dynamic light scattering behaviour in the form of periodic oscillating correlation functions has been found from measurements on both physically and chemically crosslinked hydrogels. The former were aqueous methyl cellulose at the thermal gelation temperature and the latter were poly(N,N-dimethylacrylamide-co-methyl methacrylate-co-ethylene dimethacrylate) at swelling equilibrium in water. In order to explain the oscillating behaviour, a spring-rotor model is proposed in which the molecular motions inside a gel are modelled as vibrations of springs having various frequencies. These frequencies are equivalent to the rotational frequencies when the free rotor theory was used to process the oscillating correlation functions by a modified CONTIN computer program. The validity of this model is supported by experimental data in three ways. (1) The model fits the experimental data almost perfectly. (2) The main peak positions of the obtained frequency distribution are not affected by the scattering angle. (3) For the chemically crosslinked hydrogels differing only in content of ethylene dimethacrylate, the mean vibrational frequency of the gel spring is higher the shorter the spring, i.e. the lower the average molecular mass between crosslinks. © 1998 SCI     

Microgelation of unsaturated polyester resins by static and dynamic light scattering

The microgelation phenomenon during the curing of unsaturated polyester resin was investigated by both static and dynamic light scattering before gelation. The results of static light scattering revealed that the polymer molecular weight increased with degree of curing. The second virial coefficient, A₂, decreased slowly in the initial stage of curing and decreased dramatically at a conversion around α ∼ 8.7%, indicating a drastic decrease of compatibility between the polyesters and styrene. Two modes of the size distribution of the microgel particles during curing were observed by dynamic light scattering. The small particles consist of primary unsaturated polyester molecules. The large ones consist of microgel particles formed by linking adjacent polyester molecules. The sizes of the microgel particles increased in the initial stage of curing, then decreased slightly at a conversion of α ∼ 8.7%, which was due to the intramolecular crosslink reaction of the microgel particles. The experimental results revealed that the compatibility between polyesters and the styrene monomer became worse as the intramolecular crosslinking reaction inside the microgel particles caused a tight packing of the micro-gel molecules. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 871–878, 1998     

合成混合物中NaOH含量对MCM - 22分子筛的合成及其特性的影响

本文用硅溶胶、异丙醇铝、六亚甲基亚胺(HMI)、NaOH和H2O反应体系动态水热合成法合成MCM-22分子筛,并采用XRD、SEM测试手段对所制样品进行表征。结果表明:NaOH含量直接影响水热合成的周期,其含量越高,合成周期越短,同时合成混合物中六亚甲基亚胺也相应增加。     

Dynamic light scattering of dilute PVA-borax aqueous solutions

Poly(vinyl alcohol)-borate (PVA-borate) complexes in dilute aqueous solutions were investigated by dynamic light scattering (DLS). Two relaxation modes obtained, were scattering vector-q² dependent and diffusive. The amplitude of slow mode was independent of borax concentration. In the very dilute PVA concentration regime ( [PVA] < 5 g/L), the PVA di-diol-borate complexation was dominated by intra-molecular reaction, and the fast mode correlation length ς_f which corresponds to the polymer chain dimension increased rapidly with borax concentrations lower than 0.06 M, and reached an asymptote in the higher borax concentration regime. However, for a dilute PVA aqueous solution with higher PVA content (i.e., [PVA] = 9 g/L), both intra-and inter-molecular PVA di-diol-borate complexations might happen. The chain expansion and shrinkage of PVA-borate complex with increasing borax concentration was observed due to the balance between the electrostatic repulsion of the charged diol-borate complexes and the intra-molecular crosslink induced by the intra-molecular di-diol-borate complexation.     

微波技术在沸石分子筛材料合成中的应用研究进展

综述微波技术在多种常规沸石分子筛、纳米沸石分子筛以及分子筛膜合成过程中的研究进展。微波较常规水热合成能够大大缩短反应时间,有利于生成晶粒尺寸更小的晶体。对国内外开展微波合成沸石分子筛材料的反应设备进行简述,结合作者前期开展的微波合成β分子筛试验,分析并讨论微波和常规水热合成之间的主要区别以及反应机理,对微波加热技术未来应用于实际工业生产进行展望。     

Dynamic light scattering studies on random cross-linking of polystyrene in semi-dilute solution

The random cross-linking of appropriately functionalized polystyrene in semi-dilute toluene solution (c = 0.01–0.05 g/mL) was studied by time-dependent measurements of dynamic light scattering. Macroscopic gelation occurred from concentrations as low as 0.02 g/mL. The gelation time, determined from the first appearance of fluctuations of the scattering intensity and the initial amplitude of the intensity correlation function (ICF), decreases markedly from about 100 min to 10 min with an increase of polymer concentration or cross-linker content. After the gel point, the ICFs display a characteristic power-law decay. The power-law exponent, n = 0.75 ± 0.06, does not change with (i) extent of reaction, (ii) polymer concentration, and (iii) cross-linker concentration, within the inspected ranges. This universal behavior is traced back to the fact that gelation took place as a result of random cross-linking of existent macromolecules, whose state of solution does not change markedly during conversion.     

硬模板法合成分子筛研究进展

综述了近年来以各种碳材料(如碳纳米管、炭气凝胶、介孔碳、炭黑)、生物质及其它材料(如聚苯乙烯微球、CaCO3等)为硬模板合成分子筛的研究进展,介绍了各种模板剂的使用特点和效果,最后总结了利用硬模板法合成分子筛面临的一些问题。     

Laser light scattering studies of ternary polymer solutions

Ternary polymer solutions [polystyrene and poly(methylvinylether) dissolved in a single solvent] have been studied to investigate the thermodynamic compatibility of the polymers and the solvents, and also to facilitate the investigation of the self-diffusion of polystyrene to greater polymer concentration. Both good and poor quality solvents have been used in this study. The self-diffusion coefficient of the polystyrene has been measured by dynamic light scattering and by pulsed field gradient NMR where appropriate. The self-diffusion data are also used to critically examine the recent theoretical developments in this field. Important confirmation of theory has been demonstrated for good solvent solutions and intriguing discrepancies have been discovered for poor solvent solutions.     

Dynamic light scattering and viscoelasticity of semidilute polystyrene/cyclohexane solutions

In the present work, dynamic light scattering (DLS) measurements from polystyrene in cyclohexane semidilute solutions were carried out at 60 °C with scattering angles varied from 30° to 120°. The correlation functions were analyzed with the double KWW function and the CONTIN program. The amplitude of the fast mode A_f of the field correlation function g¹(t) was used to calculate the longitudinal stress modulus M_o using Wang’s theory. A comparison between M_o calculated from DLS data and the shear stress modulus G obtained from mechanical measurement was made.     

有机胺在沸石合成中的作用

综述了有机胺有沸石合成中的作用。总结了沸石合成常用的有机胺。     

动态水热法制备Silicalite-1分子筛膜包覆多孔缺陷Al2O3微球

采用晶种涂覆-预晶化-晶化成膜的动态水热法成功在具有多孔缺陷的氧化铝微球上合成Silicalite-1分子筛膜。以乙醇作为润湿试剂在氧化铝表面涂覆一层晶种,将涂覆过晶种的载体加入到分子筛合成液中预晶化,一层分子筛完全覆盖载体并与载体结合牢固。预晶化后的载体在动态水热条件下处理3天,得到致密分子筛膜包覆的Al₂O₃微球。运用X射线衍射（XRD）和扫描电镜（SEM）对所得材料进行表征。结果表明,包覆的分子筛膜具有典型的MFI结构,晶粒交互生长,厚度约为3μm。考察了TPAOH用量和水量对分子筛膜微观结构的影响,结果发现TPAOH用量主要影响Silicalite-1分子筛膜的形貌,当TPAOH用量为0.17时,合成的Silicalite-1分子筛膜连续致密,而水量对分子筛膜微观结构的影响较小。这种晶种涂覆-预晶化-晶化成膜的方法有助于在多孔缺陷的Al₂O₃微球上制备高质量的分子筛膜。     

The synthesis of colloidal zeolite TPA–silicalite-1

The synthesis of colloidal TPA–silicalite-1 from a clear xTPAOH–yH₂O–TEOS precursor sol, with x=0.01–0.443 and y=20–80, has been studied at 115°C. Both the starting sol and the reaction products at various times were examined by dynamic light scattering (DLS) to determine the size of the colloidal (or sub-colloidal) particles presented. In addition, the pH of the system has been measured. The observations made with the DLS were consistent with the literature results. In essence, uniform particles of colloidal zeolite were formed during the reaction, and their size grew linearly with reaction time. At the same time, sub-colloidal particles smaller than 5 nm were also observed that persisted throughout the process. The measured pH, on the other hand, could be satisfactorily modeled by the equilibrium theory, suggesting that an equilibrium distribution of dissolved silicates was established before the reaction, and a different equilibrium was attended when colloidal zeolites, as well as the co-existing sub-colloidal particles, were observed. The number density of the colloidal particles ρ was found to depend on the 3.4 power of the silica concentration and the ratio x.     

Beta沸石合成研究进展

Beta沸石是一种具有广阔应用前景的催化材料。本文综述了Beta沸石的合成原料、合成工艺路线、多形体和复合型Beta沸石合成的相关进展,着重分析了不同合成工艺路线的优缺点,展望了Beta沸石未来的合成发展趋势。指出从生产原料和合成工艺路线两个方面出发,对其进行优化以降低生产成本是Beta沸石未来发展的必然趋势。同时表明,对于多形体A相关合成方法和具有特殊构效关系的复合型Beta沸石的探索工作将具有重要意义。     

Dynamic light scattering measurements of polystyrene in semidilute theta solutions

Measurements of the co-operative diffusion coefficient, D_c, and a centre of mass translational diffusion coefficient, D_s, have been made by dynamic light scattering for the polystyrene-cyclohexane theta system as a function of molecular weight and concentration. For semidilute solutions it is established that D_s∝N^?2c^?3 which is in agreement with the predictions from scaling arguments for the self-diffusion coefficient. However, if the co-operative mode is interpreted by D_c∝N^xc^y, the results of 0 < x < 0.7 and 0 < y < 0.5 are in disagreement with scaling predictions of D_c∝N⁰c¹. A discussion of the assumptions and potential shortcomings of the blob model which is used in the derivation of the power law predictions and the dynamic scattering equations is included. In addition, monomeric friction coefficients have been obtained from the D_s results within the framework of Doi-Edwards model. A comparison is made of the concentration dependence of the monomeric friction coefficient from the present data to that from similar experiments on a good solvent (tetrahydrofuran) system and from shear relaxation modulus measurements on the polystyrene in Aroclor 1248.     

粉煤灰合成13X型沸石的实验研究

利用工业废渣粉煤灰为原料,探讨了合成13X型沸石分子筛的工艺条件,并对该工艺下制得的13X型沸石分子筛产品进行了分析测试.在合成沸石产品的过程中,晶化温度、晶化时间、反应物液固比、碱液的浓度等对合成产品的质量具有明显影响, 实验确定的最佳工艺条件为:晶化时间8 h,晶化温度100 ℃,NaOH浓度1.4832 mol/L,液固比4∶1.     

沸石催化剂在甲胺合成中的应用

介绍了有关沸石分子筛的择形改性研究及其在甲胺合成工业中的应用和进展。     

基于动态光散射下纳米二氧化硅分散性的影响因素研究

纳米二氧化硅是目前应用最为广泛的一种纳米材料,但其团聚行为对粒径测量和应用效果有不利的影响。为减少纳米二氧化硅颗粒的团聚行为,应用动态光散射粒度分析方法,考察了分散方式、分散剂种类、悬浮液条件对不同纳米二氧化硅的粒径及多分散性指数（PDI）的影响规律。实验结果表明,磁力搅拌条件下,0.1%（质量分数）的PEG-2000对各类纳米二氧化硅均具有较好的分散效果;随着悬浮液pH增大,硅溶胶悬浮液粒径和PDI均呈下降趋势,是因为悬浮液pH影响了硅溶胶的溶解平衡;而固态二氧化硅悬浮液的粒径和PDI则呈先上升后下降的趋势,这是由于悬浮液pH影响了双电层结构。实际测试和应用中应注意悬浮液配制条件和纳米二氧化硅类别对粒径和PDI的影响。     

4A沸石合成工艺研究与产物表征

利用正交优选实验研究了硅铝比、钠硅比、水钠比、反应温度和反应时间等5个因素对水热合成4A沸石的影响,在此基础上还研究了超声波辅助水热合成4A沸石,利用XRD、场发射扫描电子显微镜(FESEM)和钙离子交换能力对4A沸石进行了表征。正交优选实验结果表明:硅铝比是影响4A沸石钙离子交换能力的主要因素,其次是钠硅比和反应时间,水钠比和反应温度的影响最小;水热合成4A沸石的最佳工艺为以硅铝物质的量比为1.5、钠硅物质的量比为2.05、水钠物质的量比为150配制硅铝酸钠凝胶,于130℃下晶化5 h。通过水热合成及超声波辅助水热合成的4A沸石的对比表明:一定时间的超声波辅助水热合成更容易得到较高性能的4A沸石。     

合成分子筛母液及其利用研究

介绍了几种常用分子筛的合成原料、方法及母液组成;综述了合成分子筛母液对后续合成的影响;阐述了几种合成分子筛母液的回收利用工艺及应用,并对其回收利用前景进行了分析和展望。