title: Probing sub-nano level molecular packing and correlated positron annihilation characteristics of ionic cross-linked chitosan membranes using positron annihilation spectroscopy.
abstract: Chitosan, CS, cross-linked with bivalent palladium has shown enhanced mechanical and thermal properties depending on the transformation of the structure at a microscopic scale. In the present study, CS directly cross-linked by palladium cation membranes (CS-cr-PM) was prepared through a solution-casting method. Mobility of chitosan chains were greatly reduced after crosslinking, making a great reduction in the swelling ratio studied by a water-swelling degree measurement, which led to an improvement in molecular chain rigidity. In order to investigate the chain packing at the molecular level in the ionic cross-linked CS system, the structure of chemically-crosslinked CS is investigated by means of the combined use of wide angle X-ray diffraction (WAXD) and infrared measurements, and a combination of positron annihilation lifetime spectroscopy (PALS) and simultaneous coincidence Doppler broadening (CDB) spectroscopy offers coherent information on both the free-volume related sub-nano level molecular packing and the chemical surrounding of free volume nanoholes in CS-cr-PM as a function of palladium salt loading. The variations in the free volume size and size distribution have been determined through the ortho-positronium (o-Ps) lifetime and its lifetime distribution. The studies showed that a strong interaction between CS molecules and palladium cations results in the change in crystallinity in formed CS-cr-PM leading to variational chain packing density. Meanwhile, significant inhibition effects on positronium formation due to doping are observed, which could be interpreted in terms of the existence of chloride ions. Applications of positron annihilation spectroscopy to study the microstructure and correlated positron annihilation characteristics of an ionic cross-linked CS system are systematically discussed.
authors.affiliation: Key Lab for Magnetism and Magnetic Materials of Ministry of Education, School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China and Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China. caoxzh@ihep.ac.cn.
authors.forename: Rui
authors.initials: R
authors.lastname: Xia
authors.affiliation: Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China. caoxzh@ihep.ac.cn.
authors.forename: Xingzhong
authors.identifier: http://orcid.org/0000-0001-5011-5912
authors.initials: X
authors.lastname: Cao
authors.affiliation: Key Lab for Magnetism and Magnetic Materials of Ministry of Education, School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China.
authors.forename: Meizhen
authors.initials: M
authors.lastname: Gao
authors.affiliation: Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China. caoxzh@ihep.ac.cn.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhang
authors.affiliation: Zhejiang Key Laboratory of Alternative Technologies for Fine Chemicals Process, Shaoxing University, Shaoxing 312000, China.
authors.forename: Minfeng
authors.initials: M
authors.lastname: Zeng
authors.affiliation: Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China. caoxzh@ihep.ac.cn.
authors.forename: Baoyi
authors.initials: B
authors.lastname: Wang
authors.affiliation: Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China. caoxzh@ihep.ac.cn.
authors.forename: Long
authors.initials: L
authors.lastname: Wei