Light absorbing scattering techniques in soft matter

There exist different micro-rheological techniques for studying the structural and dynamical properties of complex fluids at a supramolecular level. Among these we find the lightscattering techniques: Dynamic Light Scattering (DLS and Diffusing Wave Spectroscopy (DWS). Both of them work as a complementary technique of the other one, in this case because we can get a wider landscape of the viscoelastic spectrum of the studied systems. These light scattering techniques take advantage of the Brownian motion of probe particles embedded into the fluid, which scatter the incident light in all directions. Retrieving the scattered light, it is possible to estimate the mean square displacement of the particles (MSD) by means of the correlation function generated by the photons that reach the detector. It is important to note that the fluid medium to be analyzed should be transparent to the incident light, but using a resent technique developed by Prahl for medical applications and studied and applied by Sarmiento-Gomez et al., it is possible to extent the DWS technique to light absorbent fluids. This technique also allows the possibility of extent in time the MSD response, becoming a complementary technique when backscattering DWS is difficult to set up. In this work we show some preliminary microrheological results of a system of worm- like micelles made by the self-assembly of 1, 4 poly (1, 3-butadiene)-polyethylene oxide diblock copolymer in water solution and preliminary rheological results of a system of single wall carbon nanotubes (SWNT) dispersed in Poly(acrylic acid) as a function of a variation of its pH.