Preparation of polymer/inorganic nanoparticles composites through ultrasonic irradiation

In this paper, ultrasonic induced encapsulating emulsion polymerization was first used to prepare the novel polymer/inorganic nanoparticles composites. The behaviors of several inorganic nanoparticles (SiO₂, Al₂O₃, TiO₂) under ultrasonic irradiation, such as dispersion, crushing, and activation, were studied. The dispersion stability, morphology, and structure of the ultrasonic irradiated nanoparticles were characterized by means of transmission electron microscopy (TEM), Fourier transform infrared (FTIR), and spectrophotometry, respectively. The results show that the inorganic nanoparticles in the aqueous solution can redisperse more effectively by ultrasonic irradiation than by conventional stirring. This is the basis for preparation of polymer/inorganic nanoparticles composites. By this technique, the long‐term stable latex, which mainly consists of polymer/inorganic nanoparticles composite latex particles, were successfully prepared. TEM, FTIR, thermogravimetric analysis, X‐ray photoelectron spectroscopy, spectrophotometry, and element analysis confirmed that well‐dispersed nanoparticles were encapsulated by the formed polymer, and the thickness of encapsulating polymer layer was in the range of 5–65 nm. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1478–1488, 2001     

Polymer/carbon nanotube composite emulsion prepared through ultrasonically assisted in situ emulsion polymerization

In this study, ultrasonic irradiation and in situ emulsion polymerization were combined to prepare stable poly(methyl methacrylate‐co‐n‐butyl acrylate) (P(MMA‐BA))/carbon nanotubes (CNTs) composite emulsion, which solves the dispersion problem of CNTs in the latex. Two stages were adopted. In Stage I, ultrasonically initiated in situ emulsion polymerization was conducted to disperse CNTs and prepare the seed emulsion containing polymer coated CNTs. In Stage II, conventional in situ emulsion polymerization was conducted to further enhance the monomer conversion and solid content. The dispersion behavior of MWCNTs in aqueous solution under ultrasonic irradiation was investigated by spectrophotometry. The effects of CNTs content on the emulsion stability and mechanical properties of composite film were studied. The results suggest that in the composite emulsion the long CNTs with a diameter of 20–40 nm are separated and dispersed by the formed polymer latex nanoparticles with a size of 20–40 nm. The spherical polymer latex nanoparticles adhere to the wall of CNTs to form a structure like “grapes on the twig.” The smooth, uniform, and flexible polymer/CNTs composite films were prepared from the composite emulsion. The CNTs can be individually dispersed in P(MMA‐BA)/CNTs composite film. Tensile tests suggest that with the increase in the CNTs content, the Young's modulus and the yield strength of the film increase. Only at 1 wt % CNTs, the Young's modulus increases from 124 to 289 MPa, and the yield strength is improved about ～14%. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3123–3130, 2006     

Synthesis and characterization of nanosilica/polyacrylate composite latex

The nanosilica/polyacrylate organic–inorganic composite latex was synthesized by in‐situ emulsion polymerization of methyl methacrylate (MMA) and butyl acrylate (BA) in the presence of silica nanoparticles, which were modified by silane coupling agent. The surface properties and dispersibility of silica nanoparticles modification, chemical structure, Zeta potential, diameter distribution of the composite latex prepared, surface roughness, and thermal stability of the hybrid film formed by the composite latex were investigated by fourier transform infrared spectrometer (FTIR), transmission electron microscopy (TEM), Zeta meter, ZetaPlus apparatus (dynamic light scattering method), atomic force microscopy (AFM), and thermogravimetric analysis (TGA), respectively. After modification with silane coupling agent, silane was grafted onto the surface of silica nanoparticles to form the organic layers, which was able to efficiently prevent the silica nanoparticles from aggregating to individually homogeneous disperse in the in‐situ emulsion polymerization system and improve the compatibility of silica nanoparticles with the acrylate monomers. The nanosilica/polyacrylate organic–inorganic composite latex prepared had the properties of silica nanoparticles and pure polyacrylate latex but was not simply a combination. Strong chemical bonding tethered the silica and acrylate chains to form the core/shell structural composite latex. Consequently, the hybrid film formed by nanosilica/polyacrylate composite latex exhibited a smooth surface and better thermal properties than the pure polyacrylate film. POLYM. COMPOS. 27:282–288, 2006. © 2006 Society of Plastics Engineers     

Nanocomposite particles with core–shell morphology III: preparation and characterization of nano Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–poly(styrene–methyl methacrylate) particles via miniemulsion polymerization

Encapsulation of inorganic nanoparticles (as a core) by polymers (as a shell) is one of the interesting research subjects that lead to the synthesis of nanocomposite. These materials include properties of not only the organic polymer (e.g. optical properties, toughness, processability, flexibility, etc.) but also the inorganic nanoparticles (e.g. mechanical strength, thermal stability, etc.). Some of the applied preparative methods are dry-spray, dispersion, suspension, emulsion and miniemulsion polymerization techniques. Here, miniemulsion polymerization technique was used in order to obtain white-color nanocomposite latex particles containing nano-alumina (40–47 nm) encapsulated by copoly [styrene (St)–methyl methacrylate (MMA)] under high-shear ultrasonic irradiation. At first, bare nano-alumina was encapsulated with the copolymer to obtain latex particles. In another attempt and in order to investigate the effect of compatiblizing system, alumina nanoparticles were coated with oleic acid in order to form modified alumina core. Then miniemulsion polymerization was performed in the minidroplets including modified alumina, St and MMA for obtaining core/shell nanocomposite particles. The progress of encapsulation polymerization was followed by different instrumental techniques such as FT-IR spectra, thermal gravimetric analysis, dynamic light scattering, induced-coupled plasma, TEM and SEM.     

Preparation of poly(butyl methacrylate)/γ‐Al2O3 nanocomposites via ultrasonic irradiation

A new technique (ultrasonic irradiation) has been employed to prepare poly(n‐butyl methacrylate) PBMA/γ‐Al₂O₃ nanocomposites, taking advantages of the multiple effects of ultrasonic irradiation, such as dispersion, pulverization and activation. When subjected to ultrasonic irradiation, n‐butyl methacrylate (BMA) is polymerized to form poly(n‐butyl methacrylate) (PBMA) latex without any chemical initiators, and the monomer conversion reaches 72.5% in 25 min. At an appropriate pH, surfactant bilayers are formed through electrostatic interactions between γ‐Al₂O₃ nanoparticles and the anionic surfactant sodium dodecyl sulfate (SDS), which adsorb BMA. After ultrasonic induced polymerization of BMA in the presence of nanoparticles of γ‐Al₂O₃, the γ‐Al₂O₃ nanoparticles are encapsulated by PBMA shells formed. The influence of factors such as pH, surfactant concentration and the nanoparticle content is investigated. The FTIR spectra show that there are still polymers tightly adsorbed by nanoparticles even after extraction by acetone for 72 h. The difference observed in the XPS spectra of nanocomposite residues and the pure γ‐Al₂O₃ nanoparticles may indicate some interactions between γ‐Al₂O₃ nanoparticles and the PBMA matrix. Furthermore, the feasibility of SDS bilayer formation and encapsulating polymerization is proven by XPS characterization. © 2001 Society of Chemical Industry     

Growth mechanism and pH-regulation characteristics of composite latex particles prepared from Pickering emulsion polymerization of aniline/ZnO using different hydrophilicities of oil phases

A Pickering emulsion polymerization of aniline, using different hydrophilicities of oil phases, was stabilized by ZnO nanoparticles and performed to synthesize composite latex particles of polyaniline/ZnO. Ammonium peroxydisulfate (APS) was used as an oxidizing agent. The morphologies and growth mechanisms of the resulted composite latex particles were studied. The pH-regulation capacity of the composite latex particles was discussed. When toluene was used as the oil phase, the composite latex particles showed hollow structure, irregular morphology, and hundreds of nanometer in size. It was ascribed to the polymerization of aniline on the interfaces of droplets/water. ZnO nanoparticles, with 50-100 nm in size, acted as surfactants to stabilize the emulsion. When THF was used as an oil phase, the composite latex particles showed spherical morphology and enwrapping ZnO nanoparticles. It was attributed to the homogeneous nucleation of polyaniline in the aqueous phase. ZnO nanoparticles acted as templates for the polyaniline particles. The stability of the Pickering emulsion polymerization was affected by the volume ratio of the oil phase to water. The aqueous solution with pH 3-9 could simply be regulated to about pH 7 by the composite latex particles. It was contributed by the dissolution of ZnO nanoparticles and doping-dedoping of polyaniline in the acidic and alkaline aqueous solutions.     

Preparation and structure control of hollow polymer particles: Influence of seeded emulsion polymerization and alkalization treatment process

Hollow polymer latex particles containing a hydrophilic core were prepared by seeded emulsion polymerization with MAA/BA/MMA/St as comonomers, followed by stepwise alkalization treatment with ammonia. The size and morphology of composite latex particles was determined by TEM. The effects of the seeded emulsion polymerization conditions and alkalization treatment on the size and hollow structure of latex were investigated. The results showed that the optimum content of crosslinking agent in the shell polymers was about 0.5–1.0 wt %, emulsifier was about 0.8–1.1 wt %, and the core/shell weight ratio was 1/7. To obtain uniform hollow latex particles with large size, the starved feeding technique should be adopted in seeded emulsion polymerization, and the neutralization temperature should equal to the T_g of the shell polymer. Then, the obtained polymer particles under this condition had an excellent hollow structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Development of morphology in latex particles: The interplay between thermodynamic and kinetic parameters

A thermodynamic analysis and a mathematical model were developed to describe the free energy changes corresponding to various possible morphologies in composite latex particles. Two experimental composite latex systems were used to verify and establish limitations of the model. The two latex systems were based on polystyrene/poly(methyl methacrylate), one prepared by conventional seeded emulsion polymerization and the second system by direct emulsification of a solution of a blend of the two polymers. The influence of several experimental parameters on latex particle morphology was investigated. These included monomer/polymer ratio, surfactant type, and initiator type in the seeded emulsion polymerization system. The influence of local viscosity, shear effects, and molecular weights of polymers were investigated in the artificial latex system.     

Preparation of crosslinked composite nanoparticles

Crosslinked composite nanoparticles were prepared by adding a trifunctional monomer (trimethyol propane trimethacrylate) or a difunctional monomer (divinyl benzene) as a crosslinker into the emulsion polymerization system of styrene in the presence of inorganic nanosilica. A coupling agent, 3‐methacryloxypropyltrimethoxysilane (MPS), was added along with the monomer, crosslinker, and silica to improve the interfacial interaction between silica and polymer and thus to obtain high binding efficiency. The role of MPS was examined. The effects of crosslinkers on the kinetics of emulsion polymerization, monomer conversion, and yield were investigated. The morphology of the composite particles was observed by TEM. The particle size and size distribution of composite latex particles were measured by the dynamic light scattering method. The binding efficiency and swelling ratio were determined by reluxing the sample in xylene using a Soxhlet extraction apparatus. FTIR spectra and TGA verified the participation of crosslinker and silica. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1538–1544, 2005     

纳米TiO2/PSB复合乳液的制备与性能研究

为了提高丁苯乳液涂膜力学性能,用硅烷偶联剂(KH-570)改性纳米TiO2,采用半连续种子乳液聚合法,制备TiO2/聚丁苯(PSB)复合乳液。采用FT-IR、TEM表征TiO2/PSB复合乳液乳胶粒子结构,结果表明合成了以TiO2为核的核壳结构纳米TiO2/PSB乳胶粒子。探讨了纳米TiO2、乳化剂、电解质、引发剂及增稠剂用量、聚合时间与温度、单体配比等对TiO2/PSB复合乳液性能的影响。确立了适宜的聚合工艺条件:纳米TiO2、乳化剂用量分别为总质量的0.5%和3.5%,电解质和引发剂用量为单体质量的0.4%,聚合温度和时间分别为64℃和3.5 h,可制备出高固高黏且性能优良的复合乳液。经纳米TiO2改性的PSB复合乳液涂膜性能较未改性的,在黏度、硬度、耐冲击性、耐洗刷性、附着力及耐水性等方面均有明显改善。     

高分子表面活性剂存在下超声辐照引发苯乙烯乳液聚合的研究

采用高分子表面活性剂(CMC-A9)和十二烷基硫酸钠(SDS)做乳化剂,用超声辐照乳液聚合方法制备了相对分子质量高(>106)的寡链聚苯乙烯纳米粒子。研究结果表明,在适当的反应条件下,CMC-A9的加入使反应速率大大提高,反应60min单体转化率能达到85%,制得直径30～60nm的聚苯乙烯胶乳粒子,乳胶粒子中含平均分子链数为3～20。CMC-A9或SDS质量浓度提高,能降低乳胶粒径和乳胶中所含的平均分子链数,增加聚合物相对分子质量。超声波输出功率对乳胶粒径影响不大。     

Fabrication of Multifunctional Composite Nanofibers by Green Electrospinning

The present work takes advantage of green electrospinning to create novel composite multifunctional nanofibers (NFs) bearing inorganic nanoparticles (NPs), more specifically quantum dots (QDs), cerium oxide nanoparticles (CeO₂ NPs) and iron oxide nanoparticles (Fe₃O₄ NPs). This is achieved by first encapsulating the desired inorganic NPs into polymer particles by the use of miniemulsion polymerization, and second, spinning the hybrid polymer particles using polyvinyl alcohol (PVA) as template polymer. It is proved that using green electrospinning, it is not only possible to ensure an excellent distribution and encapsulation of the inorganic NPs along the NFs, but also allows to control and change the concentration, size, and type of the inorganic NPs without altering the NFs size, a fact that is not possible by conventional solution electrospinning. As proof of concept, NFs with up to three different types of inorganic NPs have been created in a single electrospinning step, but this technology allows to incorporate as much inorganic NPs as desired without altering the NFs morphology and ensuring a good distribution and encapsulation of the NPs. This paper demonstrates that green electrospinning is a powerful and attractive technology to create multifunctional NFs that are promising materials for sensing and biomedical applications.     

Preparation of polystyrene/poly(vinyl acetate) nanocomposites with a core–shell structure via emulsifier‐free emulsion polymerization

Polystyrene/poly(vinyl acetate) latex nanoparticles with a core–shell morphology in an emulsifier‐free emulsion polymerization system were prepared with purified styrene and vinyl acetate (VAc) as monomers and 2,2′‐azo bis(2‐amino propane) dihydrochloride (ABA,2HCl) as the initiator and emulsifier. The optimized conditions of polymerization of VAc, on top of the already‐formed polystyrene as a core polymer, with a core–shell morphology were obtained using various parameters such as volume ratio of the first and second stages, type of process, and reaction time. The morphologic structure of the nanoparticles was studied by scanning electron microscopy and transmission electron microscopy. The latex nanoparticles and polymers were characterized by differential scanning calorimetry. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2409–2414, 2006     

Synthesis and characterization of poly(fluorinated acrylate)/silica hybrid nanocomposites

The nanocomposite particles (NPs) with inorganic silica as core and fluorinated polymer shell have been in situ synthesized via emulsion polymerization. The chemical composition and core‐shell structure were characterized by Fourier‐transform infrared spectrometry and transmission electron microscopy. The results showed that silica nanoparticles were encapsulated in latex particles, with single‐ and multicore morphologies coexisting. Thermal gravimetric analysis also suggested the successful encapsulation of silica into NPs with enhanced thermal stability. The surface properties of the latex films produced from the core‐shell particles were also investigated by contact angle method and water absorption measurement. Both fluorinated polymer and silica contributed to less water absorption ratio and lower surface‐free energy, which was composed of larger polar component and smaller disperse component, just reversed as usual. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

有机-无机杂化核壳型乳胶粒的制备及其粒径控制

以苯乙烯乳液聚合合成种子,再在种子外生成苯乙烯与甲基丙烯酸-3-三甲氧基硅丙酯（MPS）的共聚物,利用MPS中硅氧烷基的水解-缩合反应,形成交联的壳,得到有机-无机杂化型核壳乳胶粒.然后用溶剂将聚苯乙烯模板溶解,可得到空心微胶囊.通过透射电镜（TEM）和动态光散射粒径仪（DLS）观测乳胶粒及微胶囊的形态.并研究了乳化剂种类、介质pH值、MPS用量和加入方式对粒径、粒子数和体系稳定性的影响.发现非离子型乳化剂、酸性或碱性介质、MPS用量过多均促进乳胶粒子数减少,减弱了乳液稳定性.而采取连续滴加MPS的方法则可提高乳液的稳定性,且粒径可控.     

核壳型醋丙乳液胶黏剂的制备及其性能研究

乳胶粒子形态控制是聚合物乳液研究的重要领域,几十年中在聚合物材料、涂料、胶黏剂等诸多领域的成功的应用使得核壳结构聚合物复合粒子备受关注。采用种子乳液聚合法,采用复配乳化剂体系合成了以醋酸乙烯酯为核,醋酸乙烯酯和丙烯酸丁酯为壳的乳液,并重点研究了单体滴加速率、SDS与OP-10质量比、引发剂用量对乳液性能的影响,通过透射电镜和红外光谱仪表征了乳胶粒子核壳结构的存在。     

核壳结构聚硅氧烷/丙烯酸酯复合乳液(Ⅰ)乳化剂对乳液聚合过程及粒径分布和粒子形态的影响

采用种子乳液半连续法合成了具有高有机硅含量的聚硅氧烷/丙烯酸酯核壳结构复合乳液,研究乳化剂的种类、复配比例及质量浓度对有机硅／丙烯酸酯壳核乳液性能与乳胶粒径、分布和结构的影响.结果表明：阴离子乳化剂十二烷基硫酸钠(SDS)、十二烷基磺酸钠(SDS-2)、十二烷基苯磺酸钠(SDBS)所合成的乳胶粒子粒径依次增大,SDS与非离子型乳化剂OP-10复配使用时,随OP-10质量分数的增加,聚合速率和转化率降低,化学稳定性增加,乳胶粒子粒径增大,分布变宽,确定了复合乳化剂的最佳配比.随复合乳化剂浓度的增加,聚合速率加快、转化率增加,乳胶粒子粒径减小而分布加宽.通过改变乳化剂加入方式可减小乳胶粒子的粒径分布.为减少壳层聚合物新粒子的产生,需严格控制乳化剂的浓度,使加入的壳层单体处于“饥饿”状态,在乳胶粒子表面富集、引发聚合,形成表层“过渡层”,最终形成核壳结构复合粒子.     

STUDIES ON SYNTHESIS OF SILICA SOL-ORGANIC POLYMER COMPOSITE EMULSION

An emulsion of polystyrene/poly (butylacrylate-methyl methacrylate acrylic acid) core/shell latex particles (PS/P (BA-MMA-AA)) has been prepared by use of three synthetic methods. The effects of synthetic methods on the distribution of carboxyl groups in latex particles were studied. The results show that the seed emulsion polymerization in which the pre-emulsified monomers were added by dropping method to the second stage is the best technique for obtaining the optimum distribution of carboxyl groups on the surface of the latex particles. Furthermore, by using PS/P (BA-MMA-AA), a type of novel composite emulsion of silica sol-PS/P (BA-MMA-AA) was synthesized with the above method. By observation through transmission EM, the morphology of the latex particles obtained shows that a composite structure has been formed between silica sol particles and organic polymer particles.     

Polymerization of MMA at the surface of inorganic submicron particles

Inorganic submicron particles, such as TiO₂, were modified with titanate coupling agents. The structure and stability of some titanates, both in solution and at the particle surface, were investigated by various methods. The modified titanium dioxide was dispersed in a solution of sodium dodecylsulphate (SDS) in water. The surfactant adsorbs at the now hydrophobic particle surface, thus creating a micellelike structure with an inorganic particle in the centre. In this system an emulsion polymerization of methyl methacrylate was carried out. Product formed at the particle surface is either physically bound by entanglement or chemically bound by covalent bonding to the titanates. In this way a core-shell morphology is obtained with an inorganic core and a polymer shell. The effects of several reaction parameters on the kinetics of the polymerization were studied. The encapsulated TiO₂ particles may offer interesting prospects in those applications where good coupling between polymer matrix and inorganic particles is necessary, such as latex paints and polymer composite materials.     

The preparation and characteristics of poly(methyl methacrylate–methylacrylate acid)/nano-ZnO composite latex particles

In this work, poly(methyl methacrylate-co-methylacrylate acid)/ZnO (poly(MMA–MAA)/ZnO) composite latex particle was synthesized by three steps The first step was to synthesize poly(MMA–MAA) copolymer latex particles by soapless emulsion polymerization. Following the first step, the second step was to polymerize MMA, MAA and 3,3-(trimethoxysilyl) propyl methacrylate (MPS) in the presence of poly(MMA–MAA) seed latex particles to form the poly(MMA–MAA)/poly(MMA–MAA–MPS) core–shell latex particles. In the third step, the poly(MMA–MAA)/poly(MMA–MAA–MPS) latex particles reacted with ZnO nanoparticles, which were synthesized by a traditional sol gel method, to form the polymer/inorganic poly(MMA–MAA)/poly(MMA–MAA–MPS)/ZnO composite latex. In this study, MPS with silanol groups essentially was used as the coupling agent to couple with ZnO nanoparticles, while the results of the study showed that there was not covalent bond existed between ZnO particles and polymer latex. The ZnO particles were adsorbed on the surface of polymer latex by electrostatic interaction. Besides, the linear poly(MMA–MAA)/crosslinking poly(MMA–MAA–MPS) core–shell latex particles which were synthesized in the second step were heated in the presence of ammonia to form the hollow poly(MMA–MAA–MPS) latex particles. The factors of heating time and concentration of crosslinking agent significantly influenced the morphology of hollow poly(MMA–MAA–MPS) latex particles.