丙烯酸类共聚物对纳米Y-TZP水悬浮液性质的影响

高固含量、低粘度的稳定浆料是陶瓷胶态成型的关键。目前人们常采用调节浆料pH值或加入分散剂等方法来改善浆料稳定性。共聚物类分散剂因其优异的分散性能而成为研究的热点。目前已有关于共聚物分散TiO2和Al2O3悬浮液的报道。本文研究了丙烯酸－丙烯酸酯共聚物在纳米Y－TZP粉体上的吸附状况,悬浮液的ζ电位、有效粒径等随分散用量及pH值的变化,并采用原子力显微镜直接测量了颗粒间相互作用。     

聚己内酯型超分散剂对磁浆流变行为和分散效果的影响

研究了磁性悬浮体（磁浆）的流变行为和分散稳定性，在磁浆中加入聚己内酯型超分散剂可显著降低体系的剪切粘度，提高分散体的稳定性，超分散剂的分散效果与溶化链分子量和锚固基团种类密切相关，当溶剂化链分子量为７００、锚固基团为氨基和羧基混合物，分子结构为“梳状”时，超分散剂的分散效果最佳。     

壳聚糖大分子链的形态调控及其在微悬浮聚合中的分散稳定作用

以易去除可回用的壳聚糖(CS)为分散剂,通过微悬浮聚合制备微米级的软硬质聚合物胶粒.考察不同酸碱度下水相介质中CS大分子链的质子化程度、亲疏水性和形态结构,及其对油水界面处CS存在形态的影响,进而评估其对剪切均质化所制单体液滴的分散稳定作用.发现通过调节体系pH值可较容易地控制CS大分子链的质子化程度、亲疏水性以及在单体液滴表面的吸附效率和铺展程度,进而可在弱酸性环境下调控微悬浮聚合体系中CS的分散能力和稳定效果.特别是当pH值在6.0左右时,CS大分子链质子化程度和亲疏水性适中,链内易形成具有一定内聚密度的高分子链收缩构象、链间易形成由多根CS链缠结而成的疏松聚集状态.在此状态下的CS链对苯丙单体液滴具有较强的分散能力和稳定作用,因而通过微悬浮聚合可制得形态结构规整、分散状态良好的聚合物粒子.进一步与微悬浮聚合常用的无机粉末类和高分子类分散剂进行应用效果比较,发现CS具有形态调控性好、分散稳定效率高、易去除能回用、特别适合制备软质微米胶粒等优点,是一种有别于无机粉末类和高分子类分散剂的新型微悬浮聚合分散剂.     

部分水解聚丙烯酰胺/柠檬酸铝胶态分散凝胶体系的剪切稠化现象

一般认为 ,能够产生剪切稠化现象的体系为分散稳定的固 -液浓悬浮体 ,分散相 (固相 )体积分数 30 %～ 6 0 % [1～ 4] .最近 ,我们在研究固含量仅为 0 .0 3%的部分水解聚丙烯酰胺 (简称PHPA) /柠檬酸铝胶态分散凝胶体系流变性时 ,也发现了剪切稠化现象 .胶态分散凝胶( CDG)主要由交联剂在单个聚合物分子中通过内交联形成[5,6] ,形成条件是低聚合物质量分数 (一般为 0 .0 1 %～ 0 .1 2 % )和低交联剂 /聚合物质量比 (一般为 1∶ 2 0～ 1 0 0 ) .由于不能象常规凝胶一样形成三维网络结构 ,因而 CDG的分子结构状态介于常规聚合物凝胶和自由…     

甲基丙烯酸甲酯悬浮聚合实验教学的改进

选用氢氧化镁为分散剂,甲基丙烯酸甲酯(MMA)为单体,进行悬浮聚合反应,研究了分散剂用量、引发剂用量、水和单体比、搅拌速度、反应温度及反应时间对聚合物珠粒大小、均匀程度和产率的影响。结果表明:与目前高分子实验教材普遍选用的以聚乙烯醇(PVA)为分散剂的悬浮聚合反应相比,以氢氧化镁为分散剂,具有操作简单、聚合时间短、体系稳定性高等优点,可代替原有的悬浮聚合反应实验,作为高分子化学实验的教学课程内容。     

超细改性碳酸钙浓悬浮体的正负触变性

以超细改性碳酸钙、氧化钙、邻苯二甲酸二辛脂组成的浓悬浮体为对象,用触变性和屈服应力来探测悬浮体的内部结构,结合悬浮体的分散稳定性能,讨论了正负触变性的形成、稳定性和可逆转变及触变性结构的强度,并考察了游离脂肪酸对悬浮体正负触变性转化的影响.     

表面活性剂对TiO2水悬浮体稳定及流变性质的影响

在陶瓷的制备过程中,通常需将陶瓷粉末分散于水中形成陶瓷浆后再浇铸成型.研究表明[1],陶瓷浆的分散、稳定及流变性质直接影响到成品的性能.因此,研究分散稳定剂对该浆料性质的影响有着重要意义.本文利用电泳和流变学方法研究了TiO2在表面活性剂的水溶液中浓浆体的分散稳定性及流变性质.     

高分子型炭黑分散剂的合成及其性能研究

研究了嵌段型分分子颜料分散剂的合成及其有炭黑分散体系中的分散稳定作用。结果表明，高分子嵌段分散剂在炭黑分散体系中能明显改善分散稳定性。同时发现，嵌段分散剂的组成、结构及分子量对分散作用有综合影响。     

悬浮态乳液聚合

对一种新的聚合方法－－悬浮态乳液聚合的研究进展进行了综述。通过对比悬浮聚合，乳液聚合和悬浮态乳液聚合方法的异同，突出了悬浮态乳液聚合的优点。讨论了悬浮态微液聚合的机理，以及分散剂，表面活性剂，水油比等对聚合物颗粒形态的影响。     

悬浮聚合实验的教学探索

结合高分子化学实验课程的开设情况,对悬浮聚合实验的教学内容进行了探讨。在悬浮聚合实验的教学中,应充分提高学生的学习兴趣,提高教学效果,与理论课相衔接。实验的内容可以从三个方面进行改进,开展分散剂的影响研究、悬浮聚合对单体的选择和与竞聚率相结合的研究。     

Correlation between Dispersion Stability of Concentrated Ceramic Suspension and Capillary Suction Time

Dispersion stability of highly concentrated ceramic suspensions using different dispersants required for colloidal processing can be assessed by measuring capillary suction time (CST). A systematic evaluation of dispersibility characteristics of colloidal alumina suspension is reported in the presence of three commonly used dispersants, namely, Dispex N 100, Darvan C, and Aluminon by employing the CST technique. The correlation between dispersibility of ceramic suspension and capillary suction time has been established. It has been found that higher the CST value of a suspension, the greater is the stability of the suspension and viceversa. In this investigation, this technique is employed both to choose suitable dispersant and to characterize the suspension. It has been concluded that higher the dispersion ratio (DR) of a suspension above unity the better is the stability and the lower the DR value below unity, the better is the aggregation tendency of the suspension. Quantitative estimation of dispersibility of an aqueous suspension is reported in terms of dispersion ratio. The CST technique has been found to be very useful and suitable for obtaining information for assessing stability of ceramic suspensions and characterizing concentrated ceramic slurry.     

NOVEL DISPERSANTS OF SILICON CARBIDE AND ALUMINUM NITRIDE

Recent advances in ceramics processing indicate that significant materials improvements can be attained by control of dispersion and colloid theology. New results are presented, where natural and synthetic lipopeptide surfactants were discovered to be excellent dispersants of ceramic powders in toluene. Relatively low concentrations of the lipopeptides promoted rapid dispersion of colloidal 0-silicon carbide (SiC) and aluminum nitride (AlN) at slurry concentrations of up to 40 wt% solids. Gravity settling produced up to 5 fold densification improvement over common industrial agents. The new dispersants may find application in a variety of ceramic, pharmaceutical and colloidal processes where superior control of dispersion, slurry rheology and product density are required.     

Dispersant adsorption and viscoelasticity of alumina suspensions measured by quartz crystal microbalance with dissipation monitoring and in situ dynamic rheology

Adsorption behavior and water content of adsorbed layers of four dispersants for aqueous ceramic processing were studied by quartz crystal microbalance with dissipation monitoring (QCM-D) on alumina surfaces. The dispersants were a poly(acrylic acid), a lignosulfonate, and two hydrophilic comb copolymers with nonionic polyoxyethylene chains of different molecular weights. A Voigt model was applied to analyze the viscoelastic behavior of the adsorbed dispersant layers. The results from QCM-D were compared with viscoelastic properties determined by in situ dynamic rheology measurements of highly concentrated alumina suspensions during slip casting. The QCM-D results showed that both the poly(acrylic acid) and the lignosulfonate adsorbed in low amounts and in a flat conformation, which generated thin, highly rigid layers less than 1 nm thick. The water content of these layers was found to be around 30% for the lignosulfonate and 35% for the poly(acrylic acid). High casting rate and strength in terms of storage modulus were observed in the final consolidate of the suspensions with the two polyelectrolytes. In contrast, the high molecular weight comb copolymer adsorbed in a less elastic layer with a thickness of about 6 nm, which is enough to provide steric stabilization. The viscous behavior of this layer was attributed to high water content, which was calculated to be around 90%. Such a water-rich layer gives a lubrication effect, which allows for reorientation of particles during the consolidation process, resulting in a high final strength of the ceramic material. During consolidation, the suspension showed a slow casting rate, most likely due to rearrangement facilitated by the lubricating layer. The short-chain comb copolymer adsorbed in a 1.5 nm thick, rigid layer and gave low final strength to the consolidated suspension. It is likely that the poor consolidation behavior is caused by flocculation due to insufficient stabilization of the dispersion.     

Adsorption Mechanism of Comb Polymer Dispersants at the Cement/Water Interface

Comb polymers are commonly used as dispersants to stabilize highly concentrated cement suspensions. The effectiveness of such polymeric additives to stabilize these suspensions is determined to a large extent by the amount adsorbed. In this study we investigated the adsorption characteristics of various comb dispersant containing different graft densities on surfaces of cement particle. The effect of inorganic salts on their adsorption was also examined in order to elucidate their adsorption mechanism. The results show that the adsorption of comb polymer dispersants on cement surface conforms approximately to Langmuir's adsorption isotherm and the characteristic plateau A _s and adsorption free energy ΔG_ads are largely dependent on the anionic group content of the comb polymers. The A _s and ΔG_ads increase with increasing anionic group content. This information suggests that the adsorption of comb polymers on cement surfaces is dominated by electrostatic interaction between COO-groups on the comb polymers and the positive surface of the cement. This conclusion is supported by effects of inorganics such as calcium and sulfate ions, and diffuse reflectance FTIR spectroscopy. The implication of results for tuning polymers for the required performance in cement manufacture should be noted.     

Modeling the effect of molecular architecture of comb polymers on the behavior of Al2O3 dispersions using charge/composition factors (CCF)

In this work, we study the effect of periodicity and PEO side-chain length in four PMAA-PEO (sodium salt) comb polymers with known molecular architecture on Al₂O₃ colloidal dispersions in DI water. We introduce here charge composition factors (CCF) representing charge density of the comb polymers defined as (number of charged units in a repeating unit)/(molecular weight of a repeating unit). We find, for the first time to our knowledge, that the CCF can be used along with dispersant dosage to obtain explicit functions predicting the conductivity of the dispersants in solution, the zeta potential behavior during dispersant titrations, and the isoelectric point (IEP) of the dispersions. In addition, the dosage normalized by the CCF provides a basis for comparison for the dispersants to elucidate the trends found in adsorption and potentiometric titrations. Thus, the CCF can be used as a tool for the design of improved and new comb polymer molecular architectures.     

Colloidal stabilization of nanoparticles in concentrated suspensions

The stabilization of nanoparticles in concentrated aqueous suspensions is required in many manufacturing technologies and industrial products. Nanoparticles are commonly stabilized through the adsorption of a dispersant layer around the particle surface. The formation of a dispersant layer (adlayer) of appropriate thickness is crucial for the stabilization of suspensions containing high nanoparticle concentrations. Thick adlayers result in an excessive excluded volume around the particles, whereas thin adlayers lead to particle agglomeration. Both effects reduce the maximum concentration of nanoparticles in the suspension. However, conventional dispersants do not allow for a systematic control of the adlayer thickness on the particle surface. In this study, we synthesized dispersants with a molecular architecture that enables better control over the particle adlayer thickness. By tailoring the chemistry and length of these novel dispersants, we were able to prepare fluid suspensions (viscosity < 1 Pa.s at 100 s-1) with more than 40 vol % of 65-nm alumina particles in water, as opposed to the 30 vol % achieved with a state-of-the-art dispersing agent. This remarkably high concentration facilitates the fabrication of a wide range of products and intermediates in materials technology, cosmetics, pharmacy, and in all other areas where concentrated nanoparticle suspensions are required. On the basis of the proposed molecular architecture, one can also envisage other similar molecules that could be successfully applied for the functionalization of surfaces for biosensing, chromatography, medical imaging, drug delivery, and aqueous lubrication, among others.     

不同聚合物分散剂对Pt/SAPO-11催化剂性能的影响

采用浸渍法制备了经过不同聚合物分散剂处理的Pt/SAPO-11催化剂,并通过X射线衍射(XRD)、透射电子显微镜(TEM)、N₂吸附-脱附和NH₃程序升温脱附(TPD)等对催化剂的组织结构进行了表征。结果表明,分散剂不会破坏催化剂的结构,反而提高了其孔体积、孔径和比表面积,同时改变了沸石的酸强度和酸量,其中以聚乙烯吡咯烷酮处理的Pt/SAPO-11催化剂孔体积、孔径和酸性分布最佳。在固定床反应器上对不同分散剂处理的Pt/SAPO-11催化剂催化性能进行评价,结果表明聚乙烯吡咯烷酮处理的Pt/SAPO-11催化剂也表现出最佳的催化性能,麻风树油的加氢脱氧率高达99.45%,生物航空煤油组分收率和异构烷烃组分(C₈~C₁₆)的选择性分别达到了44.67%和56.37%。     

不同聚合物分散剂对Pt/SAPO-11催化剂性能的影响

采用浸渍法制备了经过不同聚合物分散剂处理的Pt/SAPO-11催化剂,并通过X射线衍射(XRD)、透射电子显微镜(TEM)、N₂吸附-脱附和N_H3程序升温脱附(TPD)等对催化剂的组织结构进行了表征。结果表明,分散剂不会破坏催化剂的结构,反而提高了其孔体积、孔径和比表面积,同时改变了沸石的酸强度和酸量,其中以聚乙烯吡咯烷酮处理的Pt/SAPO-11催化剂孔体积、孔径和酸性分布最佳。在固定床反应器上对不同分散剂处理的Pt/SAPO-11催化剂催化性能进行评价,结果表明聚乙烯吡咯烷酮处理的Pt/SAPO-11催化剂也表现出最佳的催化性能,麻风树油的加氢脱氧率高达99.45%,生物航空煤油组分收率和异构烷烃组分(C₈~C₁₆)的选择性分别达到了44.67%和56.37%。     

不同聚合物分散剂对Pt/SAPO-11催化剂性能的影响

采用浸渍法制备了经过不同聚合物分散剂处理的Pt/SAPO-11催化剂，并通过X射线衍射(XRD)、透射电子显微镜(TEM)、N₂吸附-脱附和NH₃程序升温脱附(TPD)等对催化剂的组织结构进行了表征。结果表明，分散剂不会破坏催化剂的结构，反而提高了其孔体积、孔径和比表面积，同时改变了沸石的酸强度和酸量，其中以聚乙烯吡咯烷酮处理的Pt/SAPO-11催化剂孔体积、孔径和酸性分布最佳。在固定床反应器上对不同分散剂处理的Pt/SAPO-11催化剂催化性能进行评价，结果表明聚乙烯吡咯烷酮处理的Pt/SAPO-11催化剂也表现出最佳的催化性能，麻风树油的加氢脱氧率高达99.45%，生物航空煤油组分收率和异构烷烃组分(C₈~C₁₆)的选择性分别达到了44.67%和56.37%。     

Surface Characterization of NH4PAA-Stabilized Zirconia Suspensions

Ammonium polyacrylate (NH4PAA) stabilized yttria-doped (3 mol%) tetragonal zirconia (Y-TZP) aqueous suspensions were prepared. Surface chemistry of the suspension was investigated by a variety of techniques. Isotherm adsorption of dispersants on ZrO2 particles demonstrated an optimum coverage of 0.25 mg/g at pH 10. The isoelectric point (IEP) of ZrO2 suspensions was shifted to low pH regions with the presence of NH4PAA. Scanning auger microscopy (SAM) and FTIR and UV spectrophotometry were employed to determine the surface properties of ZrO2 suspensions, which confirmed that the surface Zr-O bonds were affected by the adsorbed polymers. Atomic force microscopy (AFM) analysis indicated that the interactions between particles were evidently influenced by polymer dispersants. Copyright 1999 Academic Press.