Confinement effects on the dynamic behavior of poly(d, l -lactic acid) upon incorporation in α-cyclodextrin

M. T. Viciosa, N. M. Alves, T. Oliveira, M. Dionísio, J. F. Mano

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8 Citations (Scopus)

Abstract

Inclusion complexes (ICs) composed of α-cyclodextrin (α-CD) and poly(d,l-lactic acid) (PDLLA), with 10/24 (IC1) and 15/46 (IC2) (% w/w) of PDLLA incorporated/initial PDLLA weight percentage, were prepared and characterized mainly by dielectric relaxation spectroscopy (DRS). Bulk PDLLA was also analyzed for comparison. DRS was revealed to be a suitable tool to distinguish the dynamical response of the PDLLA regions constrained in between α-CD channels from the fraction incorporated inside channels. While the cooperative α-process undergoes a dramatic depletion shifting to higher temperatures (∼4.5°C) for the PDLLA interchannels portion, it is suppressed for PDLLA chains inside pores. It was demonstrated that the broad secondary relaxation of bulk PDLLA is the Johari-Goldstein process (βJG-process). The detection of its analogue in the ICs at higher frequencies, to a greater extent in IC1, is interpreted as a true confinement effect where the dimensions of the α-CD channels interfere with the length scale of the βJG-process. The limit predicted in the framework of the coupling model, where the α-relaxation transforms in the βJG-process, seems to be reached in the ICs. Furthermore, it was found that the length scale of the additional γ process only detected in the ICs is inferior to inter- or intrachannel dimensions.

Original languageEnglish
Pages (from-to)6972-6981
Number of pages10
JournalJournal of Physical Chemistry B
Volume118
Issue number24
DOIs
Publication statusPublished - 19 Jun 2014

Keywords

  • DIELECTRIC-RELAXATION SPECTROSCOPY
  • GLASS-TRANSITION DYNAMICS
  • THIN POLYMER-FILMS
  • POLY(L-LACTIC ACID)
  • INCLUSION COMPLEXES
  • TEMPERATURE-DEPENDENCE
  • STRUCTURAL RELAXATION
  • POLY(LACTIC ACID)
  • SECONDARY RELAXATIONS
  • COOPERATIVITY LENGTH

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