Crystallization of Polymers Under 1D Confinement
Crystallization of polymers becomes tremendously sluggish upon confinement at the nanoscale level, where a severe reduction in the overall crystallization rate is commonly observed. In extreme cases, below a critical thickness (usually on the order of few
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Abstract Crystallization of polymers becomes tremendously sluggish upon confinement at the nanoscale level, where a severe reduction in the overall crystallization rate is commonly observed. In extreme cases, below a critical thickness (usually on the order of few tens of nm) polymer chains do not crystallize. This phenomenon has attracted a considerable technological interest. Being able to suppress, or at least to reduce, the crystallization rate would yield, for example, a tremendous increase in safety of those amorphous drugs where the crystalline form has non-negligible toxicity, and a neat improvement the lifetime of polymer-based nanodevices where the presence of crystals affects materials properties. While most of the work on crystallization on confinement focused on the investigation of the formation of crystalline structures, less is known on the molecular origin of the confinement effects of the slower kinetics. Unveiling the nature of the changes in crystallization rate requires the use of experimental approaches, as broadband dielectric spectroscopy, permitting to achieve information also on molecular relaxation processes taking place in the noncrystalline component. In this chapter, we will summarize the outcome of the investigation of the cold crystallization of thin polymer films (1D confinement) via Broadband Dielectric Spectroscopy (BDS). After discussing the experimental protocol necessary to perform such measurements, we will show how BDS can be employed to disentangle the nucleation and the growth component of the kinetics. Finally, we will discuss on the interplay between chain adsorption and crystal growth in thin films and introduce a general picture of the competition between the two phenomena affecting mass transport at the nanoscale level. Keywords Thin polymer films · 1D confinement · Dielectric spectroscopy · Segmental mobility · Crystallization · Irreversible adsorption
S. Napolitano (B) Polymer and Soft Matter Dynamics, Experimental Soft Matter and Thermal Physics (EST), Faculté des Sciences, Université Libre de Bruxelles (ULB), 1050 Ixelles, Brussels, Belgium e-mail: [email protected] © Springer Nature Switzerland AG 2020 T. A. Ezquerra and A. Nogales (eds.), Crystallization as Studied by Broadband Dielectric Spectroscopy, Advances in Dielectrics, https://doi.org/10.1007/978-3-030-56186-4_9
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Abbreviations BDS C G h LN2 PEO PEN PET PHB PLLA tcry TFA Tg Tm ε ξ
Broadband Dielectric Spectroscopy Capacitance Crystal growth rate Film thickness Liquid nitrogen Polyethylene oxide Poly(ethylene 2,6-naphthalate) Poly(ethylene terephthalate) Poly(3-hydroxy butyrate) Poly(L-lactide acid) Crystallization time Trifluoroacetic acid Glass transition temperature Melting temperature Dielectric strength Stokes–Einstein exponent
1 Introduction Nanoconfinement affects the crystallization of polymers [1]. For long chains, same as in the case of smaller molecules [2], the complex set of mechanisms leading to the formation of ordered structures is affected by both finite size
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