Silica and borosilicate glass matrix composites containing carbon nanotubes

Due to their remarkable properties and unique dimensions, carbon nanotubes (CNTs) are considered as an exciting nano-reinforcement in a variety of inorganic matrix composites. However, published data is unable to clearly define the role of CNTs on the properties of these composites, in particular, the mechanical properties including hardness, stiffness, strength and fracture toughness. This lack of knowledge is due in part to manufacturing issues, such as the dispersion of CNTs, densification of composites and microstructural changes during sintering. Moreover, interest in the electrical and thermal properties of inorganic matrix composites demands a comprehensive functional property evaluation. The still unexplored technological properties of these composites, such as thermal shock, ageing, friction and wear resistance, also deserve particular attention, in order to identify the extent of improvement that can be achieved due to CNTs. The microstructural characterisation including the nature of CNT distribution and their embedded morphology in brittle and amorphous matrices is still unclear, together with the nature of the CNT/matrix interface. Finally, the effect of different CNT aspect ratios on properties is yet to be investigated in order to choose the most suitable CNT sizes for desired composite performance. The present study is, therefore, aimed at developing a model composite system of uniformly dispersed CNTs of different sizes and loadings in a dense, brittle and amorphous matrix, and exploring the real effect of CNTs on physical, mechanical, functional and technological properties of these composites together with their microstructural and interfacial characterisation. Indigenously synthesised and functionalised multiwalled carbon nanotubes (MWCNTs) of four different aspect ratios (~31-65) were used as reinforcement, up to 10wt% (13.2vol%) loadings, while silica (SiO2) glass was chosen as an inorganic matrix. Heterocoagulation upon colloidal mixing provided composite powders with homogeneously dispersed MWCNTs while pressureless sintering produced dense (96-99%) composites. The randomly oriented MWCNTs in the glass matrix showed a mechanical MWCNT/glass interface due to the interlocking of MWCNTs with the matrix. The indentation fracture toughness was improved, by up to ~100%, but hardness and stiffness decreased by 21-38% and 20-37%, respectively. The electrical conductivity increased by >11 orders of magnitude but the thermal conductivity showed limited improvement, i.e. 41-48%. The effect of different MWCNT sizes on the mechanical properties, such as hardness, elastic modulus and indentation fracture toughness, could not be determined due to the decrease in the densities of the composites containing higher aspect ratio MWCNTs; however, the functional properties, such as electrical and thermal conductivity, increased in proportion to the MWCNT size. The presence of MWCNTs in the thermal shock resistant silica glass matrix did not produce thermal cracking after a single quench to 20oC from 1200oC or multiple quenches from 1000oC; however, devitrification of the glass was observed. During the thermal ageing of composites (up to 1000oC for up to 96h), no significant degradation was observed at lower temperatures (500oC) except limited surface MWCNT oxidation. However, at 750oC, considerable MWCNT oxidation was noticed, and at 1000oC, cristobalite was also formed producing surface cracking on cooling. The decarburisation depth due to MWCNT oxidation increased with time and temperature, and completely porous composites were obtained after oxidation of all of the embedded MWCNTs. The friction coefficient decreased with increase in MWCNT content, while the formation of a stable graphitic layer in composites containing 10wt% MWCNTs reversed the otherwise increasing wear rate. Finally, the established composite processing route was applied to a commercial borosilicate glass system containing up to 10wt% (17vol%) MWCNTs. The microstructure along with the resulting mechanical and functional properties ensured the applicability of the developed model system, which is believed to serve as a guide in future for preparation of other technically relevant inorganic matrix composites containing CNTs for improved properties

Processing and characterisation of inorganic matrix composites containing carbon nanotubes

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A New Route to Fluorescent SWNT/Silica Nanocomposites: Balancing Fluorescence Intensity and Environmental Sensitivity

We investigate the relationship between photoluminescence (PL) intensity and environmental sensitivity of surfactant-wrapped single walled carbon nanotubes (SWNTs). SWNTs were studied under a variety of conditions in suspension as well as encapsulated in silica nanocomposites, which were prepared by an efficient chemical vapor into liquids (CViL) sol-gel process. The dramatically improved silica encapsulation process described here has several advantages, including fast preparation and high SWNT loading concentration, over other encapsulation methods used to prepare fluorescent SWNT/silica nanocomposites. Further, addition of glycerol to SWNT suspensions prior to performing the CViL sol-gel process allows for the preparation of freestanding fluorescent silica xerogels, which to the best of our knowledge is the first report of such nanocomposites. Our spectroscopic data on SWNTs suspended in aqueous surfactants or encapsulated in silica show that achieving maximum PL intensity results in decreased sensitivity of SWNT emission response to changes imparted by the local environment. In addition, silica encapsulation can be used to "lock-in" a surfactant micelle structure surrounding SWNTs to minimize interactions between SWNTs and ions/small molecules. Ultimately, our work demonstrates that one should consider a balance between maximum PL intensity and the ability to sense environmental changes when designing new SWNT systems for future sensing applications

Synergistic enhancement of cancer therapy using a combination of docetaxel and photothermal ablation induced by single-walled carbon nanotubes

Lei Wang1, Mingyue Zhang1, Nan Zhang1, Jinjin Shi1, Hongling Zhang1, Min Li1, Chao Lu2, Zhenzhong Zhang1 1School of Pharmaceutical Sciences, Zhengzhou University, Zhengzhou, People’s Republic of China; 2University of Maryland, College Park, MD, USA Background: Single-walled carbon nanotubes (SWNT) are poorly soluble in water, so their applications are limited. Therefore, aqueous solutions of SWNT, designed by noncovalent functionalization and without toxicity, are required for biomedical applications. Methods: In this study, we conjugated docetaxel with SWNT via p-p accumulation and used a surfactant to functionalize SWNT noncovalently. The SWNT were then conjugated with docetaxel (DTX-SWNT) and linked with NGR (Asn-Gly-Arg) peptide, which targets tumor angiogenesis, to obtain a water-soluble and tumor-targeting SWNT-NGR-DTX drug delivery system. Results: SWNT-NGR-DTX showed higher efficacy than docetaxel in suppressing tumor growth in a cultured PC3 cell line in vitro and in a murine S180 cancer model. Tumor volumes in the S180 mouse model decreased considerably under near-infrared radiation compared with the control group. Conclusion: The SWNT-NGR-DTX drug delivery system may be promising for high treatment efficacy with minimal side effects in future cancer therapy. Keywords: single-walled carbon nanotubes, docetaxel, NGR peptide, tumor-targeting, near-infrared radiatio

Carbon Nanotube Doped Tellurite Glasses

In the past it was observed that buck ball doped glasses showed enhanced optical nonlinearities. However, carbon nanotubes are much more stable than buck ball and should be a better choice for that purpose. Therefore we decided to investigate the possibility to produce carbon nanotubes doped tellurite glasses and measured their optical nonlinearities. Tellurite glasses already have a larger nonlinearity compared to silica, and other, glasses. We produced TeO 2-ZnO tellurite family glasses doped with multi wall Carbon Nanotube (CNT). The CNTs acquired from Carbolex were vigorously mechanically mixed with the tellurite glass precursors and melted in platinum crucible around 650°C in a controlled atmosphere inside an electrical induction furnace. We used the lowest temperature possible and controlled atmosphere to avoid the CNT oxidation. The glass melt was cast in a stainless steel and thermally treated at 300°C for 5 hours to relieve internal stresses. The samples were than cutted and polished to perform the optical characterization. We measured refractive index and thermo physical properties, such as vitreous transition Tg, crystallization onset Tx and melting Tf temperatures. Raman spectroscopy showed the possible presence of CNTs.6890Iijima, S., (1991) Nature, 354, p. 56http://www.ati.surrey.ac.uk/news/n, onlinearDiMaio, J., Rhyne, S., Yang, Z., Fu, K., Czerw, R., Xu, J., Webster, S., Ballato, J., (2003) Information Sciences, 149, p. 69Aoki, Y., Okubo, S., Kataura, H., Nagasawa, H., Achiba, Y., (2005) Chem. Lett, 34 (4), p. 562Misra, S.K., Watts, P.C.P., Valappil, S.P., Silva, S.R.P., Roy, I., Boccaccini, A.R., (2007) Nanotechnology, 18, p. 07570