Imperial College London
Alternate

Professor DameJuliaHiggins

Faculty of Engineering, Department of Chemical Engineering

Emeritus Professor Distinguished Research Fellow
 
 
 
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Contact

 

+44 (0)20 7594 5565j.higgins

 
 
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Assistant

 

Mrs Sarah Payne +44 (0)20 7594 5567

 
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Location

 

337Roderic Hill BuildingSouth Kensington Campus

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Summary

 

Publications

Citation

BibTex format

@article{Arrighi:2018:10.1021/acs.macromol.8b00397,
author = {Arrighi, V and Gagliardi, S and Ganazzoli, F and Higgins, JS and Raffaini, G and Tanchawanich, J and Taylor, J and Telling, MTF},
doi = {10.1021/acs.macromol.8b00397},
journal = {Macromolecules},
pages = {7209--7223},
title = {Effect of chain length and topological constraints on segmental relaxation in cyclic PDMS},
url = {http://dx.doi.org/10.1021/acs.macromol.8b00397},
volume = {51},
year = {2018}
}
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RIS format (EndNote, RefMan)

TY  - JOUR
AB  - We present a detailed investigation of local dynamics of linear and cyclic poly(dimethylsiloxane) (PDMS) covering a wide range of molar masses. To aid interpretation of the experimental data, QENS measurements in the time scale from 2 to 200 ps and at Q = 0.3 to 1.8 Å–1 are complemented by theoretical calculations. These make use of a methodology developed by us elsewhere applicable to both simple chain models and real chains and applied here, for the first time, to cyclic PDMS. Analysis of the incoherent dynamic structure factor at T < Tm shows that the rotational motion of the methyl groups is unaffected by polymer topology. At higher temperatures, the QENS data are described by a model that consists of two dynamic contributions: methyl group rotation and segmental motion, the latter described by a stretched exponential function. Relaxation times of both linear and cyclic PDMS increase with increasing molar mass. Several features predicted by theory are also reproduced by the experimental data. We show, unambiguously, that rings have higher relaxation times for the segmental motion compared to linear chains of the same number of monomer units. Theoretical calculations support the idea that such slowing down of local dynamics is due to the topological constraint imposed by the ring closure, a constraint which becomes negligible for very large molar masses. Our calculations suggest that due to its albeit small conformational rigidity, cyclic PDMS undergoes an additional constraint which further increases the relaxation time, producing a shallow maximum for N ≈ 50 repeat units. A similar feature is also observed in the experimental QENS data. Values of activation energy, Ea, are derived from analysis of the temperature dependence of the quasi-elastic broadening and are found to be in agreement with viscosity measurements reported in the literature. Although the pronounced molar mass dependence of Ea for linear PDMS is certainly linked to the pres
AU  - Arrighi,V
AU  - Gagliardi,S
AU  - Ganazzoli,F
AU  - Higgins,JS
AU  - Raffaini,G
AU  - Tanchawanich,J
AU  - Taylor,J
AU  - Telling,MTF
DO  - 10.1021/acs.macromol.8b00397
EP  - 7223
PY  - 2018///
SN  - 0024-9297
SP  - 7209
TI  - Effect of chain length and topological constraints on segmental relaxation in cyclic PDMS
T2  - Macromolecules
UR  - http://dx.doi.org/10.1021/acs.macromol.8b00397
UR  - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000445971800022&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
UR  - http://hdl.handle.net/10044/1/69980
VL  - 51
ER  -
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