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SUMMARY:Mechanics of Polymer Brushes - Prof Srikantha Anasavarapu\, Depart
 ment of Mechanical Engineering\, University of British Columbia\, Vancouve
 r\, BC\, CANADA
DTSTART:20190614T130000Z
DTEND:20190614T140000Z
UID:TALK126193@talks.cam.ac.uk
CONTACT:Hilde Hambro
DESCRIPTION:: A brush-like structure emerges from the stretching of long p
 olymer chains\, densely grafted on to the surface of an impermeable substr
 ate. This structure is due to a competition between the conformational ent
 ropic elasticity of grafted polymer chains\, and the intra and interchain 
 excluded volume repulsions. Polymer brushes occur in biology: neurofilamen
 ts\, articulate cartilage\, extra cellular biopolymers etc. This seminar w
 ill examine the reversible mechanical stresses in such soft active matter.
  We begin with  experiments on a thermoresponsive brush grafted onto a sof
 t beam\, which showed the surface stress is on the order of −10 N/m and 
 its magnitude decreases gradually\, and reversibly\, upon increasing solve
 nt temperature. Strong stretching theory (SST) from polymer physics is the
 n combined with continuum mechanics to obtain stress variation in a neutra
 l brush with Gaussian chains. This theory predicts that the normal stress\
 , parallel to the substrate\, is a quartic function of the distance from t
 he grafting surface with a maximum at the grafting surface. Idealizing the
  brush as a continuum elastic surface layer with a residual stress\, close
 d-form expressions for surface stress and surface elasticity as a function
  of molecular weight and graft density are derived. At a higher graft dens
 ity\, a more refined (semi) analytical SST with Langevin chain elasticity 
 is advanced. Theoretical predictions are assessed by molecular dynamics si
 mulation of a brush using bead-spring model. The seminar will conclude wit
 h the theoretical advances made and opportunities for further progress in 
 theory\, experiments\, and technological applications of polymer brushes.\
 nKey References:\n(1) Manav\, M.\, Ponga\, M.P.\,  Phani\, A.S.\, 2019\, S
 tress in a polymer brush\, Journal of the Mechanics and Physics of Solids\
 , 127\, pp 125--150\, https://doi.org/10.1016/j.jmps.2019.03.009\n(2) Mana
 v\, Anil Kumar\, P.\, Phani\, A.S.\, 2018\, Mechanics of polymer brush bas
 ed soft active materials -- theory and experiments\, 121\, 296--312\, http
 s://doi.org/10.1016/j.jmps.2018.06.021\n(3) Zou\, Y.\, Lam\, A.\, Brooks\,
  D.E.\, Phani\, A.S.\, Kizhakkedathu\, J.N.\, 2011\, Bending and stretchin
 g actuation of soft materials through surface-initiated polymerization\,  
 50(22)\, 5116-5119\,   \nhttps://doi.org/10.1002/anie.201008252\n
LOCATION:Oatley Seminar Room\, Department of Engineering
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