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O texto abaixo representa uma contribuição solicitada para a proposta de Laboratório Associado "I3N - INSTITUTO de NANOTECNOLOGIAS, NANOMATERIAIS e NANOCIÊNCIAS" recentemente apresentada à FCT-MCIES.

Nano-scale systems research

The research activity of the Polymeric and Mesomorphic Materials group covers several aspects of the molecular, mesoscopic (nano and micro scale) and macroscopic properties and behaviour of soft materials and complex fluids, namely polymer liquid crystals and biomaterials. Theoretical, computational, and experimental techniques are used, the later including Rheo-NMR, Rheology, AFM, etc. The current trend of this research is to increase the activity in the mesoscopic scale, and in this context the group plans, for the next five years (2005-2009), to develop projects in the following areas:

a) Thin-film surface patterning: A technique to produce extremely regular micro- and nano-corrugations in the surface of some elastomeric thin films has been recently developed in our laboratory [1], which will be applied in the design of components for flexible information displays (reflective and anti-reflective coatings, alignment layers, etc.). The same corrugated films will be used as substrates for the orientation of protein micro-crystals [2] and for cell dynamics experiments.

b) Nanoscale rheology of the erythrocyte: The equilibrium shapes of the human red blood cells (RBC) have been intensively studied for more than thirty years and are now fairly well understood. Quantitative models for the rheology (deformation and flow) of RBCs in large vessels and in capillaries are still missing. We plan to use Rheo-NMR [3] and computational mesoscale modelling techniques, e.g. dissipative particle dynamics [4], to obtain essential information for the establishment of such models and the formulation of a constitutive equation for blood properly taking into account the RBCs deformability and aggregation. These results should then help elucidating some pathologies of the vascular system, e.g. the diabetic retinopathy. Within this framework we will also address the problem of blood-wall vessel interaction at the mesoscopic scale in order to get new insight on the formation and rupture of saccular aneurysms in the cerebrovascular system.

c) Nematic nanotube gels and active viscoelastic materials: Isolated carbon nanotubes possess remarkable mechanical properties and most of their potential materials applications require collective alignment of the nanotubes in some matrix. Gels containing large domains of oriented carbon nanotubes (i.e. showing nematic liquid crystal order) have been recently obtained [5] and deserve further investigation. A different class of novel nanomaterials are active gels of polar filaments, like the cytoskeleton of eukaryotic cells. In active systems, energy is continuously supplied by internal or external sources and internally consumed; they are out of equilibrium systems. Cytoskeleton networks, in particular, are made of molecular motors (at the cross links of the network) interacting with filaments that polymerize at one end while depolymerising at the other end. We plan to investigate the rheological properties of both passive and active nematic gels.

d) Tissue engineering: three-dimensional cell scaffolds with inverted colloidal crystal geometry will be prepared and used for tissue engineering [6].

References:

[1] M.H. Godinho, J.G. Fonseca, A.C. Ribeiro, L.V. Melo and P. Brogueira, Macromolecules 35, 5932 (2002).

[2] J. Caldeira, J.L. Figueirinhas, C. Santos and M.H. Godinho, J. Magn. Resonance 170, 213 (2004).

[3] A.F. Martins, P. Esnault and F. Volino, Phys. Rev. Lett. 57, 1745 (1986); A.F. Martins, in: Physical Properties of Liquid Crystals, vol.1: Nematics, book ed. by D.A. Dunmur, A. Fukuda and G.R. Luckhurst, EMIS Datareviews Series, INSPEC, London, pp. 405-413 (2001).

[4] A. Polimeno, A. Gomes and A.F. Martins, in: Computer Simulations of Liquid Crystals and Polymers, ed. by P. Pasini, C. Zannoni and S. Zumer, NATO ASI series [Kluwer Dordrecht, 2004], pp135-147 .

[5] M.F. Islam et al., Phys.Rev. Lett. 92, 088303-1 (2004).

[6] N.A. Kotov et al., Langmuir 20, 7887 (2004).

(AFM-041101)