BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:Contr. Talk 9 - Poised between order and disorder: sheared DNA sol utions across the Isotropic-Nematic transition DTSTART;VALUE=DATE-TIME:20181211T134000Z DTEND;VALUE=DATE-TIME:20181211T140000Z DTSTAMP;VALUE=DATE-TIME:20260523T191805Z UID:indico-contribution-491@lindico453.srv.lu.se DESCRIPTION:Speakers: Giuliano Zanchetta (University of Milano)\nHydrogels built from DNA are an attractive class of materials\, whose structure and mechanical properties can be tuned by the design of “physical” cross- links based on selective Watson-Crick base pairing [Pan\, Soft Matter 12\, 5537 (2016)]. Even simple systems of entangled DNA helices can display com plex mechanical response\, such as shear banding [Boukany\, Soft Matter 5\ ,780 (2009)] and strain hardening [Orakdogen\, Macromolecules 43\, 1530 (2 010)]\; however\, in discussing such intriguing features\, it is often dis regarded that long DNA strands also undergo a transition to Nematic (N) li quid crystalline phase at concentrations as low as few mg/ml [Merchant\, B iophys.J. 73\,3154 (1997)].\nWe investigate the correlation among phase be haviour\, structure and rheological properties in DNA helices of thousands of base pairs. In a wide concentration range\, the solutions are viscoela stic while also displaying a continuous transition from Isotropic to N\, w ithout detectable phase separation. These solutions exhibit very low degre e of ordering at rest\, but strong\, transient birefringence when sheared. \nWe measure the mechanical and optical response to continuous\, oscillato ry and step deformations across the transition region. To this aim\, we co mbine rheology to real-space measurement of shear-induced alignment in a m icroscope shear cell\, or through polarized reflection directly on the rhe ometer [Mykhaylyk\, J. Polym. Sci. B 54\,2151 (2016)]. Furthermore\, throu gh rheo-SAXS experiments we gain access to the local degree of alignment a nd structure. \nWe find that both shear stress and birefringence relax wit h two different time scales\, a slow decay related to spontaneous disentan glement and a faster one\, which we interpret as the result of the frustra ted phase separation and local heterogeneity of the system. Regions with l arger N order are more easily aligned and fluidized than the isotropic\, v iscoelastic matrix in which they are embedded\, resulting in a faster opti cal and mechanical relaxation.\n\nhttps://lindico453.srv.lu.se/event/67/co ntributions/491/ LOCATION:Elite Hotel Ideon Tera URL:https://lindico453.srv.lu.se/event/67/contributions/491/ END:VEVENT END:VCALENDAR