THE SPECIFIC WORK OF FLOW AS A UNIVERSAL CRITERION FOR ORIENTATION IN POLYMER CRYSTALLIZATION
There are two different morphologies in semicrystalline polymers: a spherulite structure forming at quiescent conditions and a shish-kebab structure appearing under shear. A critical examination of studies on flow-induced crystallization (FIC) finds that the longest chains play a catalytic role in the formation of shish-kebabs recruiting other chains into the formation of this morphology. Flow is responsible for both the orientation of polymer chains, and the stretching of polymer chains. While at shear rates &>1/Td, where Td is a disengagement time, the orientation of primitive path of the polymer chains along the flow can be obtained, at a higher shear rates &> 1/td> 1/tR, where tR is a Rouse time of the polymer chains, a stretching of the molecules into a conformation ideal for crystallization can be achieved as well. It has been proposed in a set of works on FIC in polydisperse systems 1, 2 that shear rates 1/Td would be enough to form oriented nuclei; however, the trend noted in a review 3 suggests that actually higher shear rates, 1/TR, responsible for the stretching of the molecules would be a necessary condition to form shish nuclei. Our recent work on FIC in specially designed and synthesised bidisperse linear-linear hydrogenated polybutadiene blends with known relaxation times has confirmed the later that shear rates inversely proportional to Rouse time of the longest chains in the polymer are required to form oriented nuclei 4. Thus, the chains with longest relaxation time in a polymer ensemble have to be stretched by shear flow to be able to form shish nuclei upon which the bulk of the material could crystallize as kebabs.
O.O.Mykhaylyk P.Chambon R.S.Graham J.P.A.Fairclough P.D.Olmsted A.J.Ryan
Department of Chemistry,University of Sheffield,Sheffield,S3 7HF,United Kingdom School of Physics & Astronomy.University of Leeds,Leeds LS2 9JT,United Kingdom School of Mathematica School of Physics & Astronomy.University of Leeds,Leeds LS2 9JT,United Kingdom
国际会议
International Symposium on Polymer Physics(2008年国际高分子物理学术会议PP2008)
厦门
英文
52-53
2008-06-08（万方平台首次上网日期，不代表论文的发表时间）