蒸汽相转化法原位诱导沸石化制备Y-ZSM-5双沸石复合物

针对Y型沸石在ZSM-5沸石干胶制备及晶化过程中易于溶解、坍塌的问题,采用葡萄糖在水热处理条件下对Y沸石进行包膜处理,提高了Y沸石在高温、高碱度环境中的稳定性,并采用蒸汽相转化法制备了同时含有Y和ZSM-5的双沸石复合物。对影响沸石复合物形成的因素如Y沸石表面碳包膜改性、凝胶碱度、晶化时间等进行了详细讨论。采用X射线衍射(XRD)、扫描电子显微镜(SEM)、傅立叶变换红外(FT-IR)、N2吸附-脱附,能谱(EDS)以及NH3-TPD等手段对制备的材料进行了表征。结果表明通过蒸汽相转化法能获得Y和ZSM-5两相共存的双沸石复合物,产物中的ZSM-5沸石相前驱体随蒸汽处理时间的延长逐渐从蠕虫状无定型向纳米多晶ZSM-5沸石转变,纳米多晶聚集体与Y型沸石晶粒之间紧密相连,相互包埋。在异丙苯催化裂化反应中,合成的沸石复合物的活性和稳定性介于Y和ZSM-5之间,优于对应的机械混合物。     

MoS2/g-C3N4复合材料的制备及可见光催化性能

首先在N-甲基吡咯烷酮溶液中超声剥离得到少层的MoS₂,将其与石墨相氮化碳（g-C₃N₄）复合,制得MoS₂/g-C₃N₄复合材料。采用X射线衍射（XRD）,扫描电镜（SEM）,X射线光电子能谱（XPS）,傅里叶变换红外光谱（FTIR）,Raman光谱,紫外-可见漫反射吸收光谱（DRS）和光致荧光（PL）技术对复合材料进行表征。可见光下考察MoS₂/g-C₃N₄复合材料光催化降解罗丹明B（RhB）的活性,结果表明：将少量MoS₂与g-C₃N₄复合可明显提高光催化活性,且1%（w/w）MoS₂/g-C₃N₄复合物的光催化活性最高,可能的原因是MoS₂和g-C₃N₄匹配的能带结构,增大了界面间电荷的传输,降低了光生电子-空穴的复合,进而提高了光催化活性。     

Design of novel morphing structures based on bistable composites with piezoceramic actuators

Instead of attempts to avoid the large out-of-plane deformations of multilayered fiber-reinforced composites caused by residual stresses, these deformations can be advantageously used for technical applications such as novel morphing structures, where only a discontinuous energy impulse of an actuator is necessary to change the configuration of the structure. For the design of such innovative morphing structures with piezoelectric actuators, novel nonlinear semi-analytical and numerical simulation models have been developed and verified experimentally. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 4, pp. 475–494, July–August, 2006.     

Stability in Shells

This paper charts the various ways in which a close working relationship with Michael Thompson, during our early years within the Stability Research Group at UCL, came to have such a profound influence on the direction of my own research activities. In particular, his fascination with energy and its use in providing a systematic framework for looking at the initial post-buckling of systems was especially contagious, opening up for me new ways of approaching the interpretation of shell buckling. In a sense my own work moved from chaos to stability in shells while Mike's was the reverse.     

Simultaneous synthesis of silver nanoparticles and poly(2,5‐dimethoxyaniline) in poly(styrene sulfonic acid)

Silver nanoparticles were formed in situ along with poly(2,5‐dimethoxyaniline) (PDMA) in an interconnected network matrix (reactor), comprising the electronic conductive polymer, PDMA, and a polyelectrolyte, poly(styrene sulfonic acid) (PSS), through the simultaneous reduction of Ag⁺ ions and polymerization of 2,5‐dimethoxyaniline. In situ ultraviolet‐visible spectroscopy showed that peaks corresponding to the plasmon resonance of silver nanoparticles at 411 nm and the polaronic transition of PDMA at 438 nm provided evidences for the simultaneous formation of silver nanoparticles and PDMA. Transmission electron microscopy and size distribution analysis revealed the presence of spherical silver nanoparticles with an average diameter of 12 nm in the composite. X‐ray photoelectron spectroscopy showed that the amine units in PDMA changed to imine units upon the formation of silver nanoparticles. A comprehensive mechanism for the formation of the PDMA‐PSS‐Ag nanocomposite is proposed. A 10‐fold increase in the conductivity was noticed for the PDMA–PSS–Ag nanocomposite (1 S/cm) in comparison with the PDMA–PSS composite (0.1 S/cm). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3843–3852, 2006     

Polymer‐nanofiber composites: Enhancing composite properties by nanofiber oxidation

Nanocomposites of styrene and vinyl phenol copolymers, which contain varying (10, 20, and 40 mol %) vinyl phenol content, were prepared with 1 wt % unoxidized, 1 wt % oxidized, and 5 wt % oxidized carbon nanofibers. Dynamic mechanical analysis and differential scanning calorimetry indicate that the composites prepared from oxidized nanofibers exhibit improved thermal and structural properties relative to those prepared from unoxidized nanofibers. The optimum enhancement in the mechanical and thermal properties was observed for the composite containing oxidized nanofibers and the 20% vinyl phenol copolymer. These results are in excellent agreement with our previous work on carbon nanotube–polymer composites and suggest that the presence of intermolecular interactions between the copolymer matrix and nanofibers are responsible for the observed property enhancement. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3053–3061, 2006     

Polymorphism of nylon‐6 in multiwalled carbon nanotubes/nylon‐6 composites

The effects of pristine and amino‐functionalized multiwalled carbon nanotubes (MWNTs) on the crystallization behaviors of nylon‐6 were investigated by differential scanning calorimetry and X‐ray diffraction. The results indicate the presence of polymorphism in nylon‐6 and its composites, which is dependent on the MWNTs concentration and the cooling rate. More MWNTs and slow cooling from the melt favors the formation of α crystalline form. With the increase in cooling rates, the crystallinity of neat nylon‐6 decreases, and that of the composites decreases initially but increases afterward. Moreover, the degree of crystallinity of the composites is higher than neat nylon‐6 under high cooling rates, counter to what is observed under low cooling rates. The heterogeneous nucleation induced by MWNTs and the restricted mobility of polymer chains are considered as the main factors. Furthermore, addition of MWNTs increases the crystallization rate of α crystalline form but amino‐functionalization of MWNTs weakens this effect. The influence of thermal treatment on the crystalline structure of MWNTs/nylon‐6 composites is also discussed. A γ–α phase transition takes place at lower temperature for MWNTs/nylon‐6 composites than for nylon‐6. The annealing peaks of the composites annealed at 160 °C are higher than that of neat nylon‐6, and the highest annealing peak is obtained for amino‐functionalized MWNTs/nylon‐6 composites. This phenomenon is closely related to the different nucleation and recrystallization behaviors produced by various MWNTs in confined space. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1499–1512, 2006     

Low-velocity impact of sandwich composite plates

In this paper we investigate impact and compression after impact properties of plain weave carbon fiber sandwich composites. Impact tests were conducted on different sample types to obtain information about absorbed energy and maximum impact force. The different samples consisted of foam-filled and hollow honeycomb cores with four-layer carbon fiber facesheets on one or both sides. The impact and compression after impact data provided valuable information to allow for comparisons between the different sample types. Also, the compression after impact tests were conducted in order to determine the reduction in compressive strength when comparing impacted to non-impacted samples. In conclusion, a two-degrees-of-freedom spring/mass model was compared to experimental results. The comparison helped illustrate the limitations of current impact theory. This paper was presented, in part, at a symposium honoring Dr Christian P. Burger, Novel Applications of Experimental Methods in Mechanics, held at the 2003 SEM Annual Conference and Exposition on Experimental and Applied Mechanics, June 2–4, 2003, Charlotte, North Carolina.     

Computer simulation of crystallization kinetics and morphology in fiber-reinforced thermoplastic composites. I. Two-dimensional case

A body of experimental evidence suggests that reinforcing fibers influence both the crystallization kinetics and morphology of those composite materials that are based on crystallizable thermoplastics. The absence of an analytical model to predict the effect of fibers on crystallization has hindered data analysis. A new approach, using computer simulation of polymer crystallization, makes it possible to study the influence that reinforcing fibers have on the crystallization kinetics and morphology of semicrystalline polymers. Fibers depress the crystallization rate relative to an unreinforced polymer since they constrain spherulitic growth by an impingement mechanism. On the other hand, reinforcing fibers can also enhance crystallization rate by providing added surface nucleation sites. This work describes a two-dimensional simplification of the crystallization process that occurs in bulk materials. It is demonstrated that the relative bulk and fiber nucleation densities, in addition to the fiber fraction, fiber diameter, and spherulitic growth rate control the crystallization kinetics and also the spherulitic and transcrystalline morphologies that develop in reinforced thermoplastic composites. © 1993 John Wiley & Sons, Inc.     

Intercalation of solvent and polymer in galleries of mobile clay platelets by a Monte Carlo simulation

The intercalation of solvent particles and polymer chains of concentration C_w = 0.2 and C_p = 0.2, respectively, in a layer of (4) clay platelets is studied by a Monte Carlo simulation on a cubic lattice. Polymer chains and platelets are modeled by bond fluctuations. Besides the excluded volume, a set of polymer-clay (cs) and solvent-clay (ws) interactions with (i) cs = 1, ws = −2, (ii) cs = −2, ws = 1 and (iii) cs = ws = −2 are considered. The global dynamics of platelets is constrained due to the presence of three components, i.e., solvent, polymer, and platelets, which retain their interstitial spacing with well-defined galleries. Intercalation of solvent particles and polymer chains (low molecular weight) occurs with their attractive interaction with the platelets, which further reinforces the layered clay morphology. The density profiles of the solvent particles are similar to previous studies with platelets in a mobile solvent. The density profile of polymer chains differs considerably from the platelets in a polymer matrix alone, particularly with its attractive interaction (ii). For the same attractive interaction of solvent and polymer chains with the clay platelets (iii), the solvent particles (the smallest constituents) intercalate the fastest in the clay galleries, whereas the intercalation of polymer chains decreases with their molecular weight. The polymer density profiles, both longitudinal (x) and transverse (y), show maxima peaks around outer platelets (surface) of the layer and decay sharply both in the adjacent galleries and in the bulk. The amplitude of oscillation in the transverse density profiles, a measure of the degree of intercalation, decreases with increasing molecular weight of the polymer. The intercalation of the polymer is driven by its attractive interaction at the low molecular weight, but reduces considerably at high molecular weight because of both entanglement and larger radius of gyration. Variations of the gyration radius of the diffusing polymer chains with molecular weight and interaction with the clay are consistent with the results of their corresponding density profiles. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2487–2500, 2009