Piezoelectric poly(lactide) stereocomplexes with a cholinium organic ionic plastic crystal

abstract

This paper describes a novel method to produce poly(lactic acid) (PLA) stereocomplex (SC) crystallites directly from high molecular weight PLLA by incorporation of small quantities of choline dihydrogen phosphate ([Ch][DHP]), at room temperature. Combined results of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) confirm the formation of the PLA SC crystals. H-1 NMR spectroscopy indicates a modification of the short range structural environment of choline in the blend with PLA in good agreement with the major long-range structural changes suggested by XRD, both suggesting a direct role of the choline in the PLA stereocomplexation. The electrical conductivity of these membranes measured using impedance spectroscopy is in the 6 x 10(-7)-4 x 10(-6) S cm(-1) range, which increases with increasing choline content and with increasing relative humidity (RH). The dependence on RH is weaker than for pure PLA, thus suggesting that the SC enhances the hydrophobic character of PLA, in agreement with contact angle measurements. Atomic force microscopy (AFM) and piezoresponse force microscopy (PFM) reveal a new phase with piezoelectric properties at the microsphere interfaces, with d(33) corresponding to similar to 60% of d(33) of a periodically poled lithium niobate reference, which is directly related to the formation of SC crystalline domains. This first report of intrinsic piezoelectricity in PLA stereocomplexes opens the possibility for the development of new types of bio-based piezoactive polymers.

keywords

MOLECULAR-WEIGHT POLYLACTIDE; DIHYDROGEN PHOSPHATE; LACTIC-ACID; LIQUIDS; FILMS; BEHAVIOR; PHASE

subject category

Materials Science; Physics

authors

Barbosa, P; Campos, J; Turygin, A; Shur, VY; Kholkin, A; Barros-Timmons, A; Figueiredo, FM

Groups

G1 - Porous Materials and Nanosystems
G2 - Photonic, Electronic and Magnetic Materials
G3 - Electrochemical Materials, Interfaces and Coatings

Projects

CICECO - Aveiro Institute of Materials (UID/CTM/50011/2013)

UnirCell - Sistema combinado de célula de combustível/ electrolisador para fornecimento eficiente de enregia renovável: dos materiais ao dispositivo (SAICTPAC/0032/2015)

acknowledgements

FCT/MEC is acknowledged for the financial support to the CICECO-Aveiro Institute of Materials (Ref. FCT UID/CTM/50011/2013, POCI-01-0145-FEDER-007679) and to project UniRCell (Ref. SAICTPAC/0032/2015, POCI-01-0145-FEDER-016422), through national funds and when applicable co-financed by FEDER under the PT2020 Partnership Agreement. FCT also supports the individual grants IF/01174/2013, SFRH/BPD/96665/2013 and SFRH/BPD/85811/2012. The choline dihydrogen phosphate, [Ch][DHP], was kindly supplied by Joao A. P. Coutinho's research group at the CICECO-Aveiro Institute of Materials, Portugal. The authors would like to appreciate Artur Silva from the Chemistry Department of the University of Aveiro for the helpful discussion of the ¹H NMR spectra.