鞣酸改性纳米二氧化硅对UV固化涂料性能的影响

通过在纳米二氧化硅-乙醇悬浮液中加入一定量鞣酸的方法,在纳米二氧化硅表面引入羟基等活性基团对纳米二氧化硅进行表面改性,并用SEM、FTIR和TG等手段对鞣酸表面改性纳米二氧化硅的改性机理进行研究。利用交流阻抗图谱(EIS)研究包覆后二氧化硅对UV固化涂料的防腐蚀性能。结果表明:鞣酸是以化学键合的方式接枝到纳米二氧化硅表面,改性后的纳米二氧化硅分散良好,鞣酸改性纳米SiO2能极大提高UV固化涂层防腐蚀效果。     

纳米二氧化硅包覆云母氧化铁及其对UV固化涂料防腐性能的影响

采用溶胶-凝胶法在云母氧化铁表面上包覆纳米二氧化硅对其进行改性。采用红外光谱(FTIR)、能谱(EDS)和热重分析(TG)确定纳米二氧化硅是否包覆于云母氧化铁表面;扫描电镜(SEM)观察了云母氧化铁包覆前后的表观形貌变化;利用EIS技术研究了云母氧化铁经改性后对涂层耐腐蚀性的影响。结果表明:包覆在云母氧化铁表面的SiO_2颗粒大小一致,粒径大小约为40 nm;纳米SiO_2包覆云母氧化铁后使其表面具有纳米材料特性,从而提高了云母氧化铁的耐热性和疏水性,因此极大地增强了涂层的耐腐蚀性能。     

刺激响应型过氧化氢凝胶的制备与性能

通过低温震荡方法制备了过氧化氢凝胶。研究了微米和纳米级颗粒状二氧化硅对过氧化氢的胶凝行为及其所形成凝胶的刺激响应性。用R／S软物质测定仪研究了某过氧化氢凝胶配方的触变性能。结果表明,二氧化硅的粒度与表面性质直接影响其胶凝能力,亲水性纳米二氧化硅比亲水性微米二氧化硅具有更好的胶凝能力,而疏水性微米和纳米二氧化硅不能胶凝过氧化氢。亲水性纳米二氧化硅的过氧化氢凝胶具有显著的温度／剪切双重刺激响应性,并随过氧化氢浓度的增加而增强。在实验的基础上,提出了凝胶形成和刺激触变的可能机理。实验发现,加入微量表面活性剂与氢氟酸,能够有效提高凝胶的稳定性。     

纳米二氧化硅的制备与表征

通过购买市售的几种不同生产厂家的纳米二氧化硅,分别对其做扫描电镜(SEM)分析、红外光谱(IR)分析和X射线衍射(XRD)分析,以了解纳米二氧化硅的表面及内部微观结构信息。分别用化学沉淀法和溶胶—凝胶法制备粒径在70 nm左右的二氧化硅粉末,并对两种方法的优缺点和制得的产品质量进行比较。改变反应物浓度、乙醇水体积比和表面活性剂的种类等条件,比较制得的二氧化硅粉末质量,以确定最优的制备方法。     

纳米二氧化硅改性超疏水性汽车蜡的研究

将表面修饰有高疏水链结构的纳米二氧化硅微粒加入到汽车蜡中,制备出了具有疏水性的纳米复合涂层,利用接触角测定仪、扫描电子显微镜(SEM)考察了其性能。结果表明,当纳米微粒添加到5%时,涂层的接触角达到了150°以上,具有超疏水性,SEM观察了表面形貌。     

胶粉中二氧化硅的原位生成及其在天然橡胶中的应用

通过溶胶-凝胶法在胶粉中原位生成纳米二氧化硅网络,经傅里叶变换红外光谱和热重分析,结果证实在溶胶-凝胶反应中于胶粉表面过渡层中可原位生成质量分数约3%～5%的类似二氧化硅的网络结构.改性胶粉表现出更好的热稳定性,失重5%的温度比未改性时提高了约30%.将50份(质量)改性胶粉填充到天然橡胶中后,所得天然橡胶/改性胶粉复合材料仍具有较好的物理机械性能和动态力学性能.     

MSN/PMAA核/壳纳米材料的制备及其性质表征

采用溶胶—凝胶法制备出单分散性好、粒径均一(直径约为90~100 nm)有规则孔道的介孔二氧化硅纳米粒子(Mesoporous silica nanoparticles,MSN)。利用硅烷偶联剂(MPS)对MSN进行表面改性,使其表面带有氨基,同时,将α-甲基丙烯酸(MAA)聚合为PMAA后采用原位聚合法聚集在MSN的表面,得到MSN/PMAA核壳材料。采用透射电镜(TEM)、红外光谱(IR)、X射线衍射(XRD)对样品MSN/PMAA核/壳材料进行性质表征。结果表明:所制备的介孔二氧化硅纳米粒子具有规则的孔道,并且聚合物PMAA成功包覆在了介孔二氧化硅纳米粒子的表面。     

纳米二氧化硅团聚特性对水泥水化硬化性能的影响

以团聚粒径很大的沉淀二氧化硅(PS)和团聚粒径较小的纳米二氧化硅(NS)为原材料,研究了纳米二氧化硅团聚特性对水泥水化硬化特性的影响。结果表明:与NS相比,虽然PS团聚粒径很大,后期火山灰活性较低,其早期火山灰活性却较大,对水泥水化的促进作用也更明显。扫描电子显微镜分析表明,NS和PS的火山灰反应产物的胶结作用有限,其与水泥水化产物本体之间甚至存在明显的界面过渡区。压汞分析表明:掺PS和NS均可有效降低硬化水泥石毛细孔率;与掺PS相比,掺NS对减小20 nm～10μm的凝胶孔和毛细孔体积更有利。掺纳米二氧化硅对硬化水泥石微观结构的影响主要是由于团聚颗粒对水泥分散体系的填充效应和吸水效应所致,与晶核效应无关。     

碳酸钙／二氧化硅纳微复合粒子的高能球磨制备

采用高能球磨法制备了碳酸钙(纳米)/二氧化硅(微米)复合粒子.用X射线衍射(XRD)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、能谱分析仪(EDS)和傅里叶变换红外光谱仪(FT-IR)研究了球磨过程中复合粉体的相组成和微观组织;对碳酸钙/二氧化硅复合粒子的粒径、形态、结构进行了测定与表征.结果表明随着球磨时间的延长,复合粉体在强烈的冲击、挤压作用下逐渐细化和均匀化;球磨240 min可形成结合紧密的碳酸钙/二氧化硅复合粒子,并使之球形化;纳米碳酸钙均匀复合于二氧化硅的表面及其空隙,复合过程中没有产生新物质;强烈的机械力作用,使纳米碳酸钙表面晶体结构发生畸变,颗粒表面无定形化程度增加.     

纳米二氧化硅催化剂催化Michael加成反应

脱水活化后的纳米二氧化硅颗粒能有效催化Michael加成反应,研究了不同温度及六甲基二硅氮烷(HMDS)处理改变二氧化硅表面性质后催化剂的催化性能改变。结果表明,随着热处理温度的升高,二氧化硅催化活性降低;HMDS能够覆盖其表面的单独硅羟基,从而降低二氧化硅催化活性。研究表明,二氧化硅表面的硅羟基是催化活性中心,催化活性与硅羟基浓度相关。不同溶剂对反应活性影响明显,DMF为反应的最佳溶剂,反应收率最高可达71%。     

可分散性纳米SiO2对甲基乙烯基硅橡胶结构与性能的影响

考察了原位改性法制备的可分散性DNS-2型纳米SiO2对甲基乙烯基硅橡胶(MVQ)结构与性能的影响,并与气相法白炭黑填充MVQ进行了比较。结果表明,DNS-2-1型、DNS-2-2型和DNS-2-3型纳米SiO2为类球形颗粒,其表面改性的有机物质量分数分别为6.0%,3.9%,3.1%;DNS-2型纳米SiO2填充MVQ的加工性能及力学性能均优于气相法白炭黑填充MVQ;填充DNS-2型纳米SiO2后,MVQ的结晶温度降低,熔融吸热减小,在低温下不易硬化;DNS-2型纳米SiO2与MVQ的相容性及其在硅橡胶中的分散性优于气相法白炭黑。     

Morphology and rheology of immiscible polymer blends filled with silica nanoparticles

The effect of silica nanoparticles on the morphology and the rheological properties of an immiscible polymer blend (polypropylene/polystyrene, PP/PS 70/30) was investigated. Two types of pyrogenic nanosilica were used: a hydrophilic silica with a specific surface area of 200 m²/g and a hydrophobic silica having a specific surface area of 150 m²/g. First, a significant reduction in the PS droplet volume radius, from 3.25 to nearly 1 μm for filled blends with 3 wt% silica, was observed. More interestingly, image analysis of the micrographs proved that the hydrophilic silica tends to confine in the PS phase whereas hydrophobic one was located in the PP phase and at the PP/PS interface (interphase thickness ≈ 100-200 nm). Furthermore, a migration of hydrophilic silica from PP phase toward PS domains was observed.An analysis of the rheological experimental data was based on the framework of the Palierne model, extended to filled immiscible blends. Due to the partition of silica particles in the two phases and its influence on the viscosity ratio, limited cases have been investigated. The rheological data obtained with the hydrophobic silica were more difficult to model since the existence of a thick interphase cannot be taken into account by the model. Finally, the hypothesis that hydrophilic silica is homogeneously dispersed in PS droplets and that hydrophobic silica is dispersed in PP matrix was much closer to the actual situation. It can be then concluded that stabilization mechanism of PP/PS blend by hydrophilic silica is the reduction in the interfacial tension whereas hydrophobic silica acts as a rigid layer preventing the coalescence of PS droplets.     

Effect of the chemical characteristics of mesoporous silica MCM‐41 on morphological,thermal, and rheological properties of composites based on polystyrene

Mesoporous silica nanoparticles (MCM‐41) with an average diameter of ～ 20 nm were synthesized by a sol‐gel method using binary surfactant system. Polystyrene (PS) composites containing mesoporous silica nanoparticles were prepared by in situ polymerization of styrene monomers. Similar in situ polymerized PS composites were prepared based on the modified silica functionalized with methyl and vinyl groups. The effects of silylation on thermal and rheological properties of the PS/silica composites are investigated. Of particular importance is that the in situ polymerization of monomers within the mesoporous silica may trap some polymer chains, if not all, thereby affording a greater physical interaction between polymer and the porous fillers, whereas the chemical modification of silica surface promotes the polymer–filler interaction, which in turn enhances the thermal stability of composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Unique behavior of in-situ generated nanosilica particles on physico-mechanical properties of fluoroelastomer

Fluoroelastomer (FKM) rubber containing different weight percentage of in-situ generated nanosilica particles have been prepared by sol-gel method using tetraethoxysilane (TEOS) as precursor and n-butyl amine as catalyst. FKM rubber with precipitated silica particles have also been prepared to compare the effect of in-situ generated nanosilica particles and precipitated silica particles on the physico-mechanical properties of FKM rubber. It is interesting to note that the FKM rubber containing in-situ generated nanosilica particles display excellent tensile stress-strain properties, rheological properties and thermal properties in comparison to the FKM rubber containing precipitated silica particles. The better performance of the in-situ generated nanosilica particles has been attributed to the good dispersion of in-situ generated nanosilica particles in FKM rubber matrix when compared to the precipitated silica particles. The fourier transform infrared (FTIR) spectroscopy clearly confirms the existence of chemical interaction between the FKM rubber chains and the in-situ generated nanosilica particles which leads to the good dispersion of the nanosilica particles in the rubber matrix. Strain sweep studies confirm the presence of more rubber-filler interaction in FKM rubber filled with in-situ generated nanosilica particles. On the other hand, strain sweep studies confirm the presence of more filler-filler aggregation in FKM rubber filled with precipitated silica particles. The dispersion of the in-situ generated nanosilica particles and precipitated silica particles in the surface and bulk of FKM rubber has been studied by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Selected samples have been cured to understand the effect of curing on the efficiency of in-situ generated nanosilica particles and precipitated silica particles on the physico-mechanical properties of FKM rubber.     

Rheological behavior of hydrophilic silica dispersion in polyethylene glycol

The rheological properties of hydrophilic fumed silica dispersed in polyethylene glycol (PEG) were investigated. The dispersion was prepared by dispersing the fumed silica in PEG with various concentrations. The reversible sol–gel transition was observed over 5 wt % of silica concentration as a function of temperature. The gelation temperature was found to depend on the applied shear stress and silica concentration, and the high shear stress was found to lead to the decrease of sol–gel transition temperature of the dispersion with the same silica concentration. As the silica concentration increases, the sol–gel transition shifts to the lower temperature. © 2006 Wiley Periodicals, Inc. J Apple Polly Sci 103: 2481–2486, 2007     

Beneficial role of “sol–gel” synthesized mesoscale silica networks on the performance of liquid silicone elastomer

This piece of contribution highlights the profound effect of unique mesoscale morphology of tailor made nanosilica assembly (SS‐Silica), synthesized by sol–gel route, on the mechanical and dynamic rheological properties of platinum catalyzed addition‐cured silicone elastomers. While commercial colloidal nanosilica (CS Silica) is used as the control nanofiller representing particulate morphology, the tailor‐made SS‐Silica having highly percolated network structure offers 10‐fold increase in storage modulus of the uncured reactive PDMS precursor nanocomposite with stable dynamic rheological behavior and more than 180% enhancement in tensile strength of resulting liquid silicone rubber (LSR) produced on curing, as compared to colloidal silica of commercial origin. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40125.     

Effect of controlled electron beam irradiation on the rheological properties of nanosilica‐filled LDPE‐EVA based thermoplastic elastomer

The effect of controlled electron beam irradiation on the rheological properties of a model LDPE‐EVA thermoplastic elastomer (TPE) system filled with silica nanoparticles is explored in this article. The pristine silica particles were mixed with LDPE‐EVA system in molten condition by varying the sequence of addition and amount of nanosilica. In one composition, Si69 was used to improve the state of dispersion of nanosilica. The rheological behavior of irradiated TPE systems is influenced remarkably by irradiation dose, loadings of silica, variation of sequence, and addition of Si69. All filled TPE systems register an increase in elastic response with increasing frequency and with increase in irradiation dose. Upon irradiation, melt viscosity increases when compared with the unirradiated samples because of the crosslinking effect and improvements in interfacial bonding. The viscoelastic response varies markedly with the temperature. The radiation sensitizing effect of silica is reflected from the rheological data. The dynamic and steady shear rheological properties do not follow a simple correlation. Finally, the rheological behavior is correlated with the morphology of the irradiated systems processed at various shear rates. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Viscoelasticity of shell-crosslinked core–shell nanoparticles filled polystyrene melt

Shell-crosslinked core–shell nanoparticles (SCCSN) of 63–104 nm in diameter and containing 79.1 wt% crosslinked polystyrene (PS) shell of 16.5–37.0 nm in thickness were prepared by miniemulsion polymerization of styrene in the presence of silane modified nanosilica. The PS shell was crosslinked using divinyl benzene in order to anchor the shell on the nanoparticle surface, to segregate the silica core from the matrix and to avoid entanglement between the shell PS and the matrix macromolecules in SCCSN filled PS composites. Steady and dynamic rheologies of SCCSN filled PS were compared with bare silica filled PS. The SCCSN filled PS composites exhibited exceedingly good rheological stability than silica filled ones during annealing. Both bare silica and SCCSN introduced a non-terminal dynamic rheology while they did not introduce additional mechanism responsible for origination of nonlinear steady flow except for macromolecular disentanglement of the PS matrix. The reinforcement of SCCSN to PS was related to the silica core even though the crosslinked shell could effectively eliminate filler aggregation as the case of silica filled PS.     

Viscoelastic behaviors of shell‐crosslinked core–shell nanoparticles suspended in polystyrene solutions

Shell‐crosslinked core–shell nanoparticles (SCCSNs) were prepared via miniemulsion polymerization of styrene in the presence of silane‐modified inorganic silica. The polystyrene (PS) shell of 58.6% in weight fraction was crosslinked using divinylbenzene. SCCSNs were spherical with a diameter distribution from 32 to 98 nm determined by dynamic light scattering. Dynamic rheology of SCCSNs suspended in PS/toluene solution was compared with that of suspensions of naked silica. The critical strain for onset of rheological nonlinearity was independent of SCCSN concentration above a concentration threshold, which differs from the silica suspensions. Linear dynamic rheological investigation revealed that SCCSN suspensions with a PS volume fraction of 20% were fluid‐like at low particle concentrations while suspensions containing 4.2 vol% SCCSNs formed a gel‐like structure. On the contrary, the silica suspensions with 20.0 vol% PS underwent a fluid‐to‐solid‐like transition with increasing silica concentration. Reasons for the different rheological behaviors of the naked silica and SCCSN suspensions are discussed. Copyright © 2012 Society of Chemical Industry     

Preparation and properties of thermosensitive organic‐inorganic hybrid gels containing modified nanosilica

A series of thermosensitive organic–inorganic hybrid gels containing nanosilica or modified nanosilica were prepared from N‐isopropylacrylamide (NIPAAm), and N,N′‐methylene‐bis‐acrylamide (NMBA) and nanosilica (AE200) or modified AE200 (mAE200); and NIPAAm, NMBA, 3‐(trimethoxysilyl) propyl methacrylate (TMSPMA) as coupling agent and AE200 or mAE200 in this study. The effect of inorganic nanosilica on the swelling behaviors and mechanical properties were investigated by adding different amount of nanosilica and modified nanosilica. Results showed that the swelling ratios of the hybrid gels decrease with increasing nanosilica content. Existence of silane coupling agent would also reduce the swelling ratios of the hybrid gels. Adding coupling agent or nanosilica would improve the gel strength. Modification of nanosilica by grafting amino‐silane via sol–gel process was carried out and the effect of addition of modified silica on gel properties was also investigated. Results showed that the hybrid gels containing modified silica would have higher swelling ratios and moduli than those containing unmodified silica. Gels containing both silane coupling agent and silica would have higher crosslinking density because the silica would be better crosslinked with coupling agent. POLYM. COMPOS., 31:1712–1721, 2010. © 2010 Society of Plastics Engineers.