Mechanical and Thermal Properties of Poly(Tetrahydrofurfuryl Methacrylate) Nano-Composites

To obviate the brittleness and improve the mechanical properties of poly(tetrahydrofurfuryl methacrylate) (PTHFMA), clay mineral nano-composites of PTHFMA with two different montmorillonites (MMT), Cloisite® 20A and Cloisite® 30B, were prepared. The mechanical properties were investigated by dynamic mechanical analysis (DMA) and nanoindentation. The thermal properties of the nano-composites were studied using thermogravimetric analysis (TGA). According to the DMA results, tanδ was increased by addition of the clay, leading to the improvement in the mechanical properties which was also confirmed by the nanoindentation results. TGA thermograms showed better thermal stability for the nano-composites compared to that of the homopolymer. Considering all results, the clay mineral polymer nano-composites (CPN) with Cloisite® 20A exhibited better properties compared to those with Cloisite® 30B. Transmission electron microscopy (TEM) micrographs, and X-ray diffraction (XRD) patterns validated intercalation-exfoliation of the clay mineral layers for the Cloisite 20A and intercalation of the Cloisite 30B in the polymer matrix.     

Effect of clay silylation on curing and mechanical and thermal properties of unsaturated polyester/montmorillonite nanocomposites

This work focuses on the chemical modification of montmorillonite (MMT) (Cloisite® Na) with compatible silanes, vinyltriethoxysilane (CVTES) and γ-methacryloxypropyltrimethoxysilane (CMPS) in order to prevent agglomeration and to improve montmorillonite interaction with an unsaturated polyester resin matrix seeking to achieve a multifunctional composite. Clays were dispersed in the resin by mechanical stirring and sonication and the nanocomposites were prepared by resin transfer into a mold. The mechanical, morphological, thermal and flammability properties of the obtained composites were compared with those prepared using commercial Cloisite® 30B (C30B) and Cloisite® 15A (C15A) clays. Advantages of using silane-modified clays (CVTES and CMPS) as compared with organic-modified clays (C30B and C15A) can be summarized as similar flexural strength and linear burning rate but higher storage modulus and improved adhesion to the polyester resin with consequent higher thermal deflection temperature and reinforcement effectiveness at higher temperatures. However, organic modified clays showed better dispersion (tendency to exfoliate) and consequently delayed thermal volatilization due to the clay barrier effect.     

Preparation and properties of polyurethane/MMT nanocomposite actuators

This study dealt with the electrostrictive response of a polyurethane (PU)/clay nanocomposite film, which was a promising candidate for a material to be used in polymer actuators. The nanocomposites were produced by using three types of montmorillonites (MMTs) such as natural MMT (Cloisite^®Na⁺), hydrophobic MMT (Cloisite^® 20A), and hydrophilic MMT (Cloisite^® 30B). The nanometer-scale silicate layers of organo-clay were completely exfoliated in PU for the cases of 1, 3 and 5 wt% PU/MMT nanocomposites as confirmed by wide X-ray diffraction (WAXD) profiles. Actuation tests indicated that the displacement of PU/MMT nanocomposite actuator was larger than pure PU actuator, caused by an increase in dielectric constant. Especially, PU/MMT nanocomposite actuator with Cloisite^® 30B had the largest displacement and it became possible to operate at low voltage.     

低场固体NMR研究纳米复合凝胶结构与动力学

纳米复合水凝胶复杂的微观结构和动力学决定了其宏观性能,阐明其结构和动力学的非均匀性对揭示凝胶相变机理、认识其宏观物理和化学性质和设计新型高分子凝胶都具有重要意义.通过合成不同粘土含量的系列聚异丙基丙烯酰胺(PNIPAm)/锂藻土纳米复合水凝胶,运用多种先进的低场固体NMR技术详细研究了凝胶微观结构和动力学的非均匀性.首先建立了分析多组分凝胶体系中刚性和柔性高分子组分相对含量的计算方法,然后在不同粘土含量下,通过测量凝胶FID信号和质子T1定量研究了凝胶中刚性和柔性高分子组分的相对含量;通过偶极滤波双量子NMR实验,研究了体系中与交联密度关联的残余偶极作用参数随黏土含量的变化.结果表明:在纳米复合水凝胶中,随着粘土含量的增加,凝胶中聚合物的刚性相增加,而柔性相下降,当粘土含量达到12%(Wclay/Wwater)时体系中的刚性相含量趋于平衡.多量子实验结果表明,随着粘土含量的增加,纳米复合水凝胶中高分子链的残余偶极作用参数逐渐增大,反映了体系中高分子链的受限运动和二维无机纳米片层形成的物理交联密度增大的趋势.     

Preparation and Property of Poly(N-isopropylacrylamide) (PNIPAAm)/Clay/Linear Polyacrylamide (PAAm) Nanocomposite Hydrogels

In this study, a linear polyacrylamide (PAAm) with an average viscosimetric molecular weight 3.97 × 10³ kg mol^?1 was added to the prereaction solution for the preparation of poly(N-isopropylacrylamide) (PNIPAAm)/clay nanocomposite hydrogels. The effects of the linear PAAm on the optical transparency and tensile property of the resulting PNIPAAm/clay/linear PAAm hydrogels were systematically investigated. The results revealed that the optical transparency and mechanical tensile properties of the resultant hydrogels strongly depended on the linear PAAm content. In particular, 5 wt% loading of linear PAAm led to almost fivefold decreases of transmittance at 25°C and a onefold increase of the tensile elongation at break. These characteristic changes were explained by a typical interpenetrating microstructure, which was formed by PNIPAAm due to the incorporation of linear PAAm in the PNIPAAm/clay network. The dynamic rheological test and infrared spectroscopy analysis on the mixed solutions consisting of linear PAAm and clay platelets further confirmed the interaction.     

Effect of biotite content of hydrogels on enhanced removal of methylene blue from aqueous solution

A series of chitosan-g-poly(acrylic acid)/biotite (CTS-g-PAA/BT) hydrogels with unique clay biotite (BT) were prepared and used to remove cationic dye methylene blue (MB) from aqueous solution by batch adsorption experiments. Variables of the system including BT content, initial pH, contact time, initial concentration, and temperature affecting the adsorption efficiency of MB by CTS-g-PAA/BT hydrogels were investigated. Kinetic studies indicated that the adsorption data well followed pseudo-second-order kinetics. Langmuir and Freundlich isotherm models were applied to experimental equilibrium data of MB adsorption depending on temperature. The adsorption equilibrium data obeyed Langmuir isotherm, and the monolayer adsorption capacity calculated from the Langmuir isotherm was 2,125.70 mg/g for CTS-g-PAA/10% BT at 30 °C. The adsorption capacity was much higher compared with other hydrogels with the same content of other clays. The introduction of BT into the hydrogel could effectively improve its adsorption properties and reduce the cost. Thermodynamic parameters were evaluated for the dye-adsorbent systems and revealed that the adsorption process was spontaneous and exothermic in nature. All the information gave an indication that CTS-g-PAA/10% BT could potentially be applied as an efficient adsorbent for cationic dye removal from aqueous solution.     

P(NIPAM-co-AA)/Clay nanocomposite hydrogels exhibiting high swelling ratio accompanied by excellent mechanical strength

In this paper, a series of P(NIPAM-co-AA)/Clay composite hydrogels (abbreviated as NAC gels) with high swelling ratio and excellent mechanical strength were synthesized and characterized by DMA, SEM, and IR. In NAC gels composed of a unique organic P(NIPAM-co-AA)/inorganic (clay) network, the inorganic clay acts as a multifunctional cross-linker in place of an organic cross-linker as used in the conventional chemically cross-linked hydrogels (abbreviated as OR gels). The NAC gels exhibit excellent swelling ratio, and there was no detectable change in properties on altering the concentration of clay, while the swelling ratio tends to decrease slightly when C _clay increases up to 25 wt%, which was revealed in swelling measurements. IR spectra show that clay has been intercalated by copolymers. Furthermore, results of DMA reveal that the composite hydrogel has an excellent mechanical strength by using a wide range of clay concentration, while the moduli improve with increasing C _clay.     

Parametric Studies on the Grafting of Poly(Methyl Methacrylate) onto Organophilic Montmorillonite Using Silylated Clay Platelets

Poly(methyl methacrylate) (PMMA)/organophilic montmorillonite (Cloisite 30B) nanocomposites were synthesized by the chemical grafting of PMMA onto Cloisite 30B via solution polymerization of methyl methacrylate (MMA) with vinyl-modified organoclay. The effects of different parameters such as clay weight percent (CWP), solvent per monomer volume ratio, and dispersion time on the properties of the PMMA grafted Cloisite 30B were investigated using the Taguchi experimental design method. This method gives a much-reduced variance for the experiments with optimum setting of control parameters and provides a set of minimum experiments compared to the conventional methods. Qualitative evidence for the chemical grafting of the PMMA onto Cloisite 30B was confirmed by Fourier transform infrared spectroscopy (FT-IR). X-ray diffraction (XRD) was used to investigate interlayer changes of the clay in the grafted nanoplatelets. The exfoliated/intercalated morphology of the nanocomposites was confirmed by XRD. Furthermore, thermal properties were measured by thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA). Statistical analysis of results revealed that clay weight percent and solvent per monomer ratio had significant effects on the properties of final products. The percent of grafted PMMA and storage modulus of PMMA/30B nanocomposites decreased with increasing clay content due to better dispersion of the clay at lower loadings. On the other hand, because of a tendency to formation of homopolymer and oligomers at higher solvent loadings; the percent of grafted PMMA, storage modulus and glass transition temperature of PMMA/30B nanocomposites decreased with an increase in solvent per monomer volume ratio. However, the obtained PMMA/30B nanocomposites at the optimum conditions, was exhibited a higher glass transition temperature, higher storage modulus and better thermal stability than the pure PMMA.     

The Role of Organoclay on Microstructure Development and Rheological Properties of Poly(Butylene Terephtalate)/Epoxy/Organoclay Hybrid Systems

The main objective of the present work was to study the role of organoclay on the microstructure development and rheological properties of poly(butylene terephtalate)/ epoxy/organoclay (Cloisite® 30B) hybrid nanocomposites. The effects of feeding order and curing of the epoxy were also investigated. The hybrid nanocomposite samples were prepared by melt compounding in a laboratory internal mixer at a temperature of 240°C. The samples were prepared by three feeding routes; (1) simultaneous feeding, (2) PBT/organoclay based master batch feeding, and (3) epoxy/organoclay based master batch feeding. The XRD results evidenced a highly intercalated microstructure for all the samples. The linear viscoelastic results obtained for uncured samples, prepared by the first and second feeding routes, exhibited a pronounced low-frequency nonterminal behavior whose extent was found to be increased in the cured samples. These results suggested that the major part of the nanoclay tactoids and/or platelets were dispersed in the PBT matrix, with higher nanoclay concentration in the sample prepared by the second feeding route. However, the samples prepared through epoxy/organoclay based master batch did not exhibit an appreciable low-frequency solid body response. This suggests that the process of migration of the nanoclay tactoids and/or platelets from epoxy droplets to PBT matrix was the time consuming process due to the high aspect ratio of the nanoclay and the high viscosity of the PBT matrix. From linear and nonlinear viscoelastic measurements, it could be deduced that the curing process does not play an important role in determining the extent of intercalation and dispersion of the nanoclay, but it can enhance the interfacial interaction between the two phases in the nanocomposite.     

Swelling and Drying Mechanisms of Freeze-Thawed Polyvinyl Alcohol/Egg White/Montmorillonite Bionanocomposite Hydrogels

Abstract

Polyvinyl alcohol and egg white bionanocomposite hydrogels loaded with montmorillonite clay were fabricated by a freezing-thawing technique. The bionanocomposite hydrogels showed an exfoliated morphology and they had a more interconnected and dense network as compared with the clay-free sample. The montmorillonite layers acted as multifunctional crosslinkers and the bionanocomposite hydrogels had nanoscale, slit-shaped pores. The swelling ratios of the bionanocomposite hydrogels were increased either by decreasing the content of incorporated montmorillonite or by increasing the pH of the swelling medium. It was found that the bionanocomposite hydrogels having a higher content of montmorillonite exhibited a slightly slower drying process with a longer drying duration. Using the Ritger-Peppas model, it was shown that the swelling and drying mechanisms for all bionanocomposite hydrogels were non-Fickian diffusion. According to the Peppas-Sahlin model, it was found that the absorption of the swelling agent molecules during the swelling process and also the removal of water molecules during the drying process in the early stages of the processes occurred mostly due to their diffusion. At higher swelling or drying times, the contribution of the relaxation (for swelling) and shrinkage (for drying) of the polyvinyl alcohol polymeric chains and egg white protein chains was increased.     

pH刺激响应水凝胶微观结构动力学的超快红外光谱研究

本文合成了甲基丙烯酸二甲氨基乙酯/丙烯酸共聚水凝胶,并在不同pH条件下表征其宏观溶胀行为. 以硫氰酸根阴离子作为局部红外探针,结合傅里叶变换红外光谱和超快红外光谱学研究了pH刺激响应水凝胶的微观结构动力学. 超快红外光谱数据表明,当水凝胶体系的pH从2.0变为12.0时,硫氰酸根探针的振动弛豫时间常数从(14±1) ps增加到(20±1) ps. 转动各向异性测量结果进一步表明,硫氰酸根探针的转动受到水凝胶中形成的三维网络结构的限制. 尤其是在pH为7.0时,SCN探针的旋转不会衰减到零.     

Effect of surface treatment of nanoclay on the mechanical properties of epoxy/glass fiber/clay nanocomposites

A new method of silane treatment of nanoclays is reported where in the clay is nanodispersed in hydrolyzed silanes. The surface functionalization of Cloisite^® 15A nanoclay has been carried out using two different silane coupling agents: 3-aminopropyltriethoxy silane and 3-glycidyloxypropyltrimethoxy silane using varied amounts of silane coupling agents, e.g. 10, 50, 200, and 400 wt% of clay. The surface modification of Cloisite^® 15A has been confirmed by Fourier transform infrared spectroscopy. The modified clays were then dispersed in epoxy resin, and glass fiber-reinforced epoxy clay laminates were manufactured using vacuum bagging technique. The fiber-reinforced epoxy clay nanocomposites containing silane modified clays have been characterized using small angle X-ray scattering, transmission electron spectroscopy and differential scanning calorimetry. The results indicate that the silane treatment of nanoclay aided the exfoliation of nanoclay and also led to an increase in mechanical properties. The optimized amount of silane coupling agents was 200 wt%. The nanocomposites containing clay modified in 200 wt% of silanes exhibited an exfoliated morphology, improved tensile strength, flexural modulus, and flexural strength. The improved interfacial bonding between silane modified nanoclays and epoxy matrix was also evident from significant increase in elongation at break.     

Clay‐induced Preferred Orientation in Polyethylene/Compatibilized Clay Nanocomposites

Nanocomposites of the organically modified clay Cloisite^® 15A (CL15A) dispersed in HDPE‐g‐MA were prepared by melt‐compounding. Microcomposites of the same clay with HDPE were also obtained with similar procedures. The spherulitic morphology of the polymer matrix was evidenced by optical microscopy in thin films, whereas the structure of the up to 2‐mm–thick, compression‐molded samples was investigated by WAXD and SAXS. Preferred orientation of both the clay and the HDPE crystallites were evidenced in the microcomposites and, to a greater extent, in nanocomposites, whereas in HDPE and HDPE‐g‐MA control specimens hardly any anisotropy was detected. The degree of orientation of PE crystals increases with CL15A concentration, but also with clay exfoliation, with lower cooling rates and decreasing sample thickness. The orientation of the clay platelets parallel to the compression‐molded surface appears to be determined by the platelets anisotropy and by shear in the mixing and the compression‐molding procedures. In turn, it determines the preferred uniaxial orientation of HDPE crystals, which have their crystallographic a axis orthogonal, while b and c are coplanar, to the sample surface, as already reported in the literature for melt‐crystallized HDPE films with thickness below 0.3 μm. It is proposed that the HDPE orientation results from confined crystallization between parallel clay platelets which are on average less than 0.1 μm apart. Simple models, qualitatively accounting for the observed orientation of HDPE, are discussed. Organized architectures resulting from confined crystallization of the polymer matrix in nanocomposites with appropriate anisotropic fillers may be a general feature, important in determining key properties of these systems.     

1 and 2-Photon Fluorescence Anisotropy Decay to Probe the Kinetic and Structural Evolution of Sol-Gel Glasses: A Summary

We review recent 1- and 2-photon fluorescence studies of the formation dynamics and structure of sol-gel glasses, from nanometre-sized particles to clusters, prepared from both aqueous silicates and tetramethylorthosilicate (TMOS), over a broad pH range. Through the careful choice of a fluorescent probe, anisotropy decay has been shown to provide both silica particle size and viscosity information and offers advantages over traditional techniques for silica particle sizing based on small-angle neutron, Xray, or light scattering. Subsequently, we are now able to observe the self-assembly mechanisms (or recently termed kinetic life history) of silica, produced under both acidic and alkaline conditions from sodium silicate solution (water glass) in the case of hydrogels and from alkoxides in the case of alcogels. The controlled preparation of hydrogels, often deemed a blackart, is also discussed in some detail, as are the potential applications and benefits of fluorescence anisotropy decay to industrial sol-gel systems. The insight into the sol-gel process provided by these new interpretations of fluorescence decay data, promises to have implications for both our fundamental understanding and the production of sol-gel systems in general.     

Synthesis and Properties of Polyacrylamide-Based Conducting Gels with Enhanced Mechanical Strength

A nanocomposite conducting hydrogel, polyacrylamide/MWNT/clay (abbreviated as PAM/MWNT/clay), prepared through in situ free radical aqueous polymerization and crosslinked by both clay, as a functional physical crosslinker, and N,N′-methylenebisacrylamide (MBA) as a chemical crosslinker, is reported. The morphology of the gels was characterized by scanning electron microscopy (SEM). The mechanical properties and electrical conductivity were also studied. The results show that the prepared hydrogels had the expected chemical components, with a highly porous structure, and the gels also showed high mechanical strength. The mechanical strength and electrical conductivity value increased with increasing content of multi-walled nanotube (MWNT), and decreased with increasing content of water.     

Flow of clays

Recent experimental and theoretical research into physical phenomena in clays is reviewed. Clays’ present place in the context of modern materials science is briefly discussed, and illustrated through the rich behavior recently displayed in this physical model system. We will show that in order to understand macroscopic flow behaviors in these systems, it is crucial to know the underlying nanostructures in detail. With the clay nanostructural basis at hand, we will review recent advances in clay systems from the geological example of quick clay flows and avalanches, to materials science and the stability, strength and flow of smart electrorheological clay structures. In the case of natural quick clay, there is now hope of establishing a protocol for avalanche preditction based on rheological sample data. In materials science, the use of electric fields together with flow in order to improve the processing of clay composite materials may open new unexplored avenues. We will finally discuss that due to the interplay of van der Waals and electrostatic forces screened by ions at the nanoscale, clays may either form a glass, or a gel and thus give fundamental insights into the elusive questions related to materials universal aging flow dynamics.     

Velocity measurement of clay intrusion through a sudden contraction step using a tagging pulse sequence

Magnetic resonance imaging (MRI) with a spatial tagging sequence was used to measure the velocity distribution of clay that was forced past a sudden contraction. A spatial tagging sequence provided magnetic resonance images of clay that allowed measurement of the velocity distribution in the clay, which can provide profound insights on the deformation process of clay during the intrusion process. The experiments were conducted using a specially-designed vessel that could operate at up to 30 MPa. The vessel offers a rectangle test section with a sudden contraction step that had a ratio of contraction of 2:1. The vessel was installed into a commercial magnetic resonance imaging equipment and then the fluid motion of clay flowing into the narrow contracted channel was quantitatively investigated to examine behaviors of flowing clay as non-Newtonian fluid. MRI results are compared with those obtained by computational fluid dynamics (CFD) calculation. Velocity distributions obtained from each tag displacement did not well agree with those predicted by CFD results near the contraction step where the fluid accelerated rapidly. However, a post-processing on calculation results, in which virtual tag displacement is calculated, gave better agreement with experiment and enabled us to compare MRI results with CFD results.     

PVDF-Based Nanocomposite Solid Polymer Electrolytes; the Effect of Affinity Between PVDF and Filler on Ionic Conductivity

Nanocomposite solid polymer electrolytes (NSPEs) based on poly(vinylidene fluoride) (PVDF) were prepared by dispersing two kinds of organoclay (Cloisite^® 30B, Cloisite^® 15A) consisting of silicate layers in the polymer matrix. The effect of affinity between PVDF and organoclay as the filler on ionic conductivity was investigated in relation to its content, dispersed condition of organoclay, and structural changes of nanocomposites. The characterizations of PVDF-based nanocomposites with various organoclay contents were carried out by XRD, TEM, DSC, and DMA. In order to confirm the ion conduction properties of NSPEs with LiCF₃SO₃ at room temperature, ac impedance analyzer and FT-IR spectrometer were used. As a result, a higher ionic conductivity appeared in the case of NSPE with C15A than that with C30B and the maximum conductivity was 1.04 × 10^–3 S/cm for the NSPE containing 5 wt% of C15A and 40 wt% of LiCF₃SO₃.     

Clay dispersion and physical properties of melt-blended PP/organoclay nanocomposites: effect of interfacial interaction

Melt blending of maleic anhydride-grafted polypropylene (PPgMA) and organically modified clay nanocomposites was first carried out in a plasticorder. The structure was investigated with x-ray diffraction (XRD) and transmission electron microscopy (TEM). The interfacial interaction between PB3150 compatibilizer and I30 clay surface was altered with the addition of different loadings of PB3150. It was found at the PB3150 compatiblizer gave rise to a high degree of clay dispersion beyond the PB3150/I30 weight ratio of 3. We then also modified polypropylene/organoclay nanocomposites with different loadings of PB3150 on a twin-screw extruder. When the PB3150 loading exceeded 15 wt%, extensive exfoliation of clay was observed. The relative complex viscosity curves also revealed a systematic trend with the extent of exfoliation and showed promise for quantifying the hybrid structure of the nanocomposites. Mechanical properties and thermal stability were determined by tensile and impact tests and thermogravimeric analysis (TGA), respectively. Although high loading of PB3150 leads to better clay dispersion in the polypropylene nanocomposites, it causes deterioration in both mechanical and thermal properties of the hybrid systems.     

Temperature effect in a montmorillonite clay at low hydration—microscopic simulation

The effect of temperature in the range 0–150°C was studied for homo-ionic montmorillonite clays with Na⁺ and Cs⁺ compensating ions in low hydration states. Monte Carlo and molecular dynamics simulations were employed to provide both static and dynamic information concerning the interlayer ions and water molecules, and emphasis was laid on the temperature activation of the diffusion coefficients. Principal structural changes were limited to the interlayer water phase. In the monohydrated systems, neither of the cations was seen to enter into the hexagonal cavities of the clay. Cs⁺ exhibited clear site-to-site diffusion between sites allowing coordination to six oxygen atoms of the clay sheets, this behaviour persisting to high temperatures. Preferential sites for the Na⁺ counterion were much less well-defined, even at low temperatures. The behaviour of the water phase in the monohydrated states was similar for the two ions. A rapid approach to bulk dynamics was seen in the transition from monohydrated to bihydrated Na-montmorillonite. A detailed quantitative comparison of the temperature activation of diffusion for a two-dimensional water phase and three-dimensional bulk water is presented for the first time.