Dispersion of nano-silicon carbide (SiC) powder in aqueous suspensions

The dispersion characteristics of nanosize silicon carbide (SiC) suspension were investigated in terms of surface charge, particle size, rheological measurement and adsorption study. Ammonium polycarboxylate has been used as dispersant to stabilize the suspension. It was found that the isoelectric point (iep) of SiC powder was pH_iep (4.9). The surface charge of powder changed significantly in presence of the ammonium polycarboxylate dispersant and iep shifted significantly towards lower acidic pH (3.6). The shift in iep has been quantified in terms of ΔG ⁰ _SP, the specific free energy of adsorption between the surface sites and the adsorbing polyelectrolyte (APC). The values of ΔG ⁰ _SP (−10.85 RT unit) estimated by the electro kinetic data compare well with those obtained from adsorption isotherms (−9.521 RT unit). The experimentally determined optimum concentration of dispersant required for maximizing the dispersion was found to be 2.4 mg/g of SiC (corresponding to an adsorbed amount of 1.10 mg/g), at pH 7.5. This is much below the full monolayer coverage (corresponding to adsorbed amount of 1.75 mg/g) of the particles surface by the dispersant. The surface charge quantity, rheological, pH, electro kinetic and adsorption isotherm results were used to explain and correlate the stability of the nanosize silicon carbide in aqueous media. At pH 7.5, where both SiC surface and APC are negatively charged, the adsorption of APC was low because of limited availability of favourable adsorption sites. In addition, the brush-like configuration of the adsorbed polymer prevented close approach of any additional dispersant; hence stabilization of the slurry happens at a comparatively lower concentration than the monolayer coverage.     

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.     

聚羧酸盐在洗衣粉中的应用性能研究

将5种聚羧酸盐和羧甲基纤维素钠（CMC）分别配入洗衣粉中,用卧式去污机做去污实验和20次循环洗涤实验,结果表明：在无磷洗衣粉中加入聚羧酸盐,去污力比加入CMC提高了7．73％～12．20％,灰分沉积比不含聚羧酸盐的降低了49．77％～65．08％,白度保持比不含聚羧酸盐的提高了2．43％～4．02％．在5种聚羧酸盐中,3种不同分子量的聚丙烯酸钠KT-3、PA25CL和445N均可用作无磷洗衣粉的抗再沉积剂,其中KT-3更优．     

Adsorption Properties of Comb-Shaped Polycarboxylate Dispersant onto Different Crystal Pyraclostrobin Particle Surfaces

The stability of the suspension system of the two crystal forms of pyraclostrobin is evaluated using multiple light technology, and the adsorption performance of polycarboxylate dispersant on the surface of two different crystalline pyraclostrobin particles is compared in combination with XRD, FTIR, XPS, and SEM from the microscopic view. The adsorption kinetics and thermodynamics studies of 2700 on the surfaces of different crystalline forms of pyraclostrobin particles show that the adsorption process of 2700 on the surfaces of pyraclostrobin crystal forms II and IV conform to pseudo-second-order kinetic adsorption model. The Ea values for crystal forms II and IV are 12.93 and 14.39 kJ∙mol⁻¹, respectively, which indicates that both adsorption processes are physical adsorption. The adsorption models of 2700 on the surfaces of pyraclostrobin crystal forms II and IV are in accordance with Langmuir adsorption isotherms. The ∆G_ad values of crystal forms II and IV are negative and the ∆S_ad values are positive at different temperatures. Therefore, the adsorption processes are spontaneous and accompanied by entropy increase. The results of this study provide an important theoretical basis for the selection of polycarboxylate dispersants in the suspension of pyraclostrobin. This study also provides a reference for the research of polycrystalline pesticide suspension concentrate.     

Research on synthesis and action mechanism of polycarboxylate superplasticizer

The relationship between the structure and performance of polycarboxylate superplasticizer was analyzed. The respective functions of the structure units of the main and branched chains were discussed. The progress of synthesis and molecular structure design and synthesis of polycarboxylate superplasticizer were reviewed according to the difference in the structure unit of the main chain. Results indicated that their performance is related to the structure unit of the main and branched chains, as well as the position and species of functional groups. The polycarboxylate superplasticizer, which had suitable graft and block polymers of polyethylene glycol or polyoxyethylene, and a suitable sulfonic group, had small slump loss besides high water-reducing performance. On the other hand, the hydroxyl group at the end of the chain causes gelation easily. On the basis of the items mentioned above, as well as the source and cost of raw materials, esterification of polyethylene glycol and acrylic acid were first adopted using para-toluene sulfonic acid as catalyst, then polymerized with sodium sulfonate methacrylate. A certain amount of acrylic was added in order to regulate both the polymerization degree of the main chain and the ratio of carboxyl and sulfonic groups in the branched chain. As a result, the high performance superplasticizer has been synthesized (was obtained). The divergence of the cement plasma is about 200 mm when the addition amount of superplasticizer is 0.16%–0.20% of cement weight, and the ratio of the water and cement is 0.29. Translated from Journal of Wuhan Uniwersity of Technology, 2006, 28(9): 18–20 [译自: 武汉理工大学学报]     

聚羧酸系高效减水剂减水机理研究

重点叙述了聚羧酸高效减水剂的特点、研究和发展的状况,并就聚羧酸减水剂的减水机理、分子结构对减水率的影响、减水剂在水泥中的化学作用等因素进行了较详细的综述,分析了影响减水率的规律和可能的作用机理。     

以对苯二氧基二乙酸和咪唑基化合物为配体的镍、镉配合物的合成和晶体结构

以对苯二氧基二乙酸(H₂BDOA)和4,4'-二咪唑基二苯醚(BIDPE)为原料,分别与氯化镍、氯化镉在水热条件下反应,得到2个结构不同的配位聚合物[Ni(BDOA)(BIDPE)(H₂O)]_n(1)和[Cd(BDOA)_0.5(BIDPE)Cl]_n(2)。对它们进行了元素分析、红外光谱分析,并利用X-射线衍射测定了它们的单晶结构。配合物1属于三斜晶系,P1空间群,a=0.93497(8)nm,b=1.03231(9)nm,c=1.35291(12)nm,α=96.3980(10)°,β=90.7290(10)°,γ=102.0270(10)°,V=1.26831(19)nm³,Z=2,M_w=603.22,D_c=1.580g·cm^-3,μ=0.827,F(000)=624,R₁=0.0395,wR₂=0.0895(I>2σ(I))。配合物2也属于三斜晶系,P1空间群,a=1.01751(7)nm,b=1.04299(7)nm,c=1.17338(8)nm,α=68.7230(10)°,β=71.8260(10)°,γ=76.0910(10)°,V=1.09105(13)nm³,Z=2,M_w=562.26,D_c=1.711g·cm^-3,μ=1.163,F(000)=562,R₁=0.0210,wR₂=0.0537(I>2σ(I))。配合物1中镍离子通过2种配体桥联成二维波浪形层状结构,而配合物2中镉离子通过2个Cl离子连接成一个双核Cd₂单元,双核单元再通过2种配体连接成一维链状结构。结果说明了金属离子在配合物组装过程中起着非常重要的作用。此外,研究了它们的荧光性质。     

Effect of hydrophobic units of polycarboxylate superplasticizer on the flow behavior of cement paste

For the tuning of conformation of polycarboxylate (PCE) superplasticizers, hydrophobic groups of different stiffness were incorporated, including styrene (St), methyl methacrylate (MMA), ethyl acrylate (EA), and n-butyl acrylate (n-BA) units. The effect of these hydrophobic groups on the dispersing performance, adsorption process and, rheology of cement paste were investigated. Investigation on the solution conformation and adsorption layer thickness indicated the action mechanism of these groups. High backbone stiffness resulted in a lower extent of conformation condensation from pure aqueous solution to pore solution, and therefore more carboxylic groups could be accessible for adsorption. However, the conformation change after adsorption might also be limited and the size of single molecule after adsorption should be small. Hydrophobic groups always resulted in a coiled PCE conformation in salt solution, which indicated a lower adsorption affinity and thinner adsorption layer for these PCE molecules.     

Effects of cyclodextrin-modified polycarboxylate superplasticizers on the dispersion and hydration properties of cement paste

Abstract

A new series of poly (AA-co-β-CD-A-co-TPEG) (PACDs) copolymers were prepared by the copolymerization of a novel monovinyl β-cyclodextrin monomer (β-CD-A), acrylic acid and isoprenyl oxy polyethylene glycol (TPEG-2400), which could be used as superplasticizers and shown excellent dispersion ability. Therefore, this work mainly investigated the adsorption behavior, dispersing properties as well as hydration behavior of cement pastes. Optical microscopy was employed to describe dispersing performance. X-ray diffraction (XRD) and TGA/DTG were utilized to account for the cement hydration process. We found that the PACDs with β-CD-A exhibited outstanding dispersion ability. In addition, the performances of the PACDs were monitored by evaluating the setting time and fluidity of the cement paste. The results clearly shown that the setting time was longer and slump loss was smaller than that of PACD₀ that without β-CD-A. Therefore, PACDs with the proper content of β-CD pendants had excellent performances due to the steric hindrance of the CD moieties.     

以对苯二氧基二乙酸和咪唑基化合物为配体的镍、镉配合物的合成和晶体结构

以对苯二氧基二乙酸(H₂BDOA)和4,4-二咪唑基二苯醚(BIDPE)为原料,分别与氯化镍、氯化镉在水热条件下反应,得到2个结构不同的配位聚合物[Ni(BDOA)(BIDPE)(H₂O)]_n (1)和[Cd(BDOA)_0.5(BIDPE)Cl]_n (2)。对它们进行了元素分析、红外光谱分析,并利用X-射线衍射测定了它们的单晶结构。配合物1属于三斜晶系,P1空间群,a=0.934 97(8) nm,b=1.032 31(9) nm,c=1.352 91(12) nm,α=96.398 0(10),β=90.729 0(10),γ=102.027 0(10),V=1.268 31(19) nm³,Z=2,M_w= 603.22,D_c=1.580 g·cm^-3,μ=0.827,F(000)=624,R₁=0.039 5,wR₂=0.089 5(I >2σ(I))。配合物2也属于三斜晶系,P1 空间群,a=1.017 51(7) nm,b=1.042 99(7) nm,c=1.173 38(8) nm,α=68.723 0(10)°,β=71.826 0(10)°,γ=76.091 0(10)°,V=1.091 05(13) nm³,Z=2,M_w=562.26,D_c=1.711 g·cm^-3,μ=1.163,F(000)=562,R₁=0.021 0,wR₂=0.053 7(I >2σ(I))。配合物1中镍离子通过2种配体桥联成二维波浪形层状结构,而配合物2中镉离子通过2个Cl离子连接成一个双核Cd₂单元,双核单元再通过2种配体连接成一维链状结构。结果说明了金属离子在配合物组装过程中起着非常重要的作用。此外,研究了它们的荧光性质。