2Institute of Ceramics and Glass-CSIC, 28049 Madrid, Spain RHEOLOGICAL BEHAVIOUR OF CARBON NANOTUBES SUSPENSIONS WITH BIOMEDICAL APPLICATIONS Arisbel Cerpa Naranjo1, Begoña Ibañez Martínez1, Isabel Lado Touriño1, Rodrigo Moreno Botella2, Paloma Ballesteros García3, Sebastián Cerdán García-Esteller4 1Department of Industrial and Aerospatial Engineering, Universidad Europea de Madrid, C/Tajo s/n, 28670 Villaviciosa de Odón, Spain 2Institute of Ceramics and Glass-CSIC, 28049 Madrid, Spain 3Laboratory of Organic Synthesis and Molecular Imaging by Magnetic Resonance, Faculty of Sciences, UNED, 28040 Madrid, Spain 4LIERM, Institute of Biomedical Research “Alberto Sols”, CSIC, 28029 Madrid, Spain arisbel.cerpa@universidadeuropea.es 1. INTRODUCTION 2.3. Rheological behaviour The rheological behaviour of different carbon nanotubes suspensions in the dilute regime was evaluated. Suspension of non-functionalized multi-walled carbon nanotubes (MWCNTs Com), multi-walled carbon nanotubes oxidized with nitric acid under reflux for 24 hours in our laboratory (MWCNTs Oxi) and commercial multi-walled carbon nanotubes with carboxylic groups (MWCNTs Com-Oxi) were studied. The study was performed in two dispersing media: water and fetal bovine serum (FBS). In addition, the results were compared with the results of the rheological behaviour of single-walled carbon nanotubes suspensions obtained in previous works [1, 2]. Structural characterization was performed with different techniques: XRD, IR, TGA, TEM, SEM and AFM. To study the colloidal behaviour, the zeta potential of suspensions was determined at pH values ​​between 6 and 8, close to physiological pH. Rheological measurements were carried out with a rotational rheometer using a double-cone and plate system. The measurements were done for different concentrations of suspensions (1 and 1.5 mg/ml), temperatures from 25 to 37 C, and water and FBS as solvents. 2.3.1. Effect of kind and concentration of CNTs The change of concentration in the suspension prepared with FBS does not cause significant changes in the viscosity values while in the aqueous suspensions the viscosity increases with increasing concentration (Figure 3). It is observed that the viscosity values of multiwalled carbon nanotubes suspensions are larger than the viscosity values of single-walled carbon nanotubes suspensions when water is used as a solvent. The viscosity values of multiwalled carbon nanotubes suspensions are between 2 and 6 mPa.s for the concentrations studied. Nevertheless, the viscosity values of single-walled carbon nanotubes suspensions are less than 3 mPa.s. 2. RESULTS 2.1. Structural characterization The IR spectra shown in Figure 1 confirmed the presence of carboxylic groups with the stretching band of the (C=O) group at ca. 1700 cm−1, the stretching (C–O) vibration of the carboxylic group around 1200 cm−1 and the O–H stretching band at ca. 3400 cm-1. The peak around 1570 cm−1 was assigned to the C═C stretching of the carbon skeleton. TEM images show the classical carbon nanotubular structure and MWCNT bundles. MWCNTs Com have lengths from 1 to 5 m, while the MWCNTs Oxi and MWCNTs Com-Oxi present a length distribution between 100-400 nm and 400 nm-1.5 m respectively. 24 h Figure 3. Viscosity vs shear rate for different carbon nanotubes suspensions of different concentrations. a) water and b) FBS. 2.3.2. Effect of temperature and dispersion medium Figure 1. (a) Infrared spectrum and (b) Transmission Electron Microscopy (TEM) of the studied multi-walled carbon nanotubes. Figure 4. Viscosity vs temperature for different carbon nanotubes suspensions to 1 mg/ml of concentration. a) water and b) FBS. Figure 2 shows the high tendency to aggregation of the carbon nanotubes with the bovine serum albumin (BSA) protein present in the fetal bovine serum. This behaviour was also observed by modelling simulations using molecular dynamics calculations. 3. CONCLUSIONS The diameter of the carbon nanotube bundles in FBS increases due to the interaction between the BSA protein present in the fetal bovine serum and the carbon nanotubes. The colloidal stability of carbon nanotubes changes with type, size of CNTs and dispersing media. The suspensions show a Newtonian flow behaviour. Depending on the type of solvent and carbon nanotubes the viscosity changes. The viscosity values of multi-walled carbon nanotubes suspensions (2 and 6 mPa.s) are larger than those of single-walled carbon nanotubes suspensions (they are less than 3 mPas) when water is used as a solvent. The change of concentration in the suspension prepared with FBS does not cause significant changes in the viscosity values while in the aqueous suspensions the viscosity increases with increasing concentration. Depending on the solvent, the decreasing viscosity values with the temperature are different, being smaller in FBS than in water. (a) (b) (c) Figure 2. AFM, Tridimensional representation (3D) of (a) fetal bovine serum (FBS), (b) MWCNTs and (c) SWCNTs oxidized for 24 hours in FBS suspensions. 2.2.Colloidal stability The zeta potential of different multi-walled carbon nanotubes was measured using two dispersing media: water and fetal bovine serum (FBS). The suspensions in water are slightly more stable than in FBS and have a negative zeta potential between -10 to -18 mV whereas for FBS, they vary from -6 to -18 mV for pH= 6-8. Nevertheless, the zeta potential for FBS is around –20 mV. The same behaviour was observed for single-walled carbon nanotubes [2]. The kind and size of carbon nanotubes influence the zeta potential values. 4. REFERENCES [1] Arisbel Cerpa, Mariana Köber, Daniel Calle, Viviana Negri, José María Gavira, Antonio Hernanz, Fernando Briones, Sebastián Cerdán, and Paloma Ballesteros. Med. Chem. Com 473 (2013) 270. [2] A. Cerpa, O. Quiroga, R. Moreno, I. Lado, M.P. Ros, V. Negri, S. Cerdán, P. Ballesteros. DIAM 2014. International Conference on Diamond and Carbon Materials. Madrid (2014). ACKNOWLEDGEMENTS This work was supported by: Project UEM14 (European University of Madrid) and MICINN CTQ2010-20960-C02-01 (BQU), MINECO CTQ2013-47699-R