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SUMMARY:Keynote 5 - Combining in-situ\, time-resolved SANS\, SAXS/WAXS and
  SALS\, to study molecular and crystal alignment in bottlebrushes polymers
  during uniaxial deformation
DTSTART;VALUE=DATE-TIME:20181211T080000Z
DTEND;VALUE=DATE-TIME:20181211T084000Z
DTSTAMP;VALUE=DATE-TIME:20260523T152608Z
UID:indico-contribution-484@lindico453.srv.lu.se
DESCRIPTION:Speakers: Carlos Lopez-Barron (ExxonMobile Chemical Company\, 
 USA)\nMolecular bottlebrushes are branched polymers with very high graft d
 ensity which results in very rigid backbones. This conformation provides u
 nique rheological properties compared to linear polymer melts. For instanc
 e\, their very large entanglement molecular weight (Me) results in very lo
 w elastic modulus\, which could be used to produce super-soft elastomers [
 Pakula et al.\, Polymer 47\, 7198 (2006)]. Despite the growing interest in
  bottlebrush polymers\, very few studies have been devoted to their linear
  viscoelastic response\, whereas\, to our knowledge\, no study has been re
 ported on their extensional rheology or their response to cold-drawing. We
  synthesized a series of ultra-high molecular weight (UHMW) a-olefin molec
 ular bottlebrushes by organometallic coordinative insertion polymerization
  of 1-alkenes with lengths ranging from 8 to 18 carbons. The molecular wei
 ght of these polymers are in the order of a few million g/mol\, which allo
 ws accurate measurement of their rubbery plateau modulus (GN0) and their M
 e values. The latter is an increasing function of the side chain length (N
 sc) and takes values ranging from 25 kg/mol (for poly(1-octene)) to 115 kg
 /mol (for poly(1-octadecene)). Therefore\, our bottlebrush polymers are hi
 ghly-entangled and have sufficient melt strength to perform extensional rh
 eology measurements using a commercial Sentmant extensional rheometer (SER
 ). Bottlebrush chain alignment was measured using a novel method that comb
 ines the use of a SER with time-resolved small-angle neutron scattering (S
 ANS) measurements [López-Barrón et al.\, J Rheol. 61\, 697 (2017)]. The 
 latter uses state of the art methods of neutron time stamping in the SANS 
 detector and deconvolution protocols that yields scattering data with time
  resolutions of the order of seconds [López-Barrón et al.\, Phys. Rev. L
 ett. 108\, 258301\; Calabrese et al.\, Soft Matter 12\, 2301 (2016)]. Thos
 e measurements were used to confirm the direct correlation between extensi
 onal stress and bottlebrush chain alignment. Complementary\, in situ wide-
  and small-angle X-ray scattering measurements reveal that chain alignment
  is concomitant of self-assembly of the bottlebrush molecules into hexagon
 al packed cylinder (HEX) phases induced by uniaxial extension. This work r
 eports the first direct evidence of strain-induced alignment and packing o
 f molecular bottlebrushes and their relation with the macroscopic rheologi
 cal and mechanical responses.\n\nhttps://lindico453.srv.lu.se/event/67/con
 tributions/484/
LOCATION:Elite Hotel Ideon Tera
URL:https://lindico453.srv.lu.se/event/67/contributions/484/
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