One of the key parameters controlling polymer mechanical and
optical behavior is how the polymer chains arrange or ‘stack’ relative to each
other. Chemically, polymers with regular, repeating structures tend to stack
more closely into crystalline forms than polymers which have irregular structures
where steric hindrance prevent the chains from getting to close to one another.
Additionally, the speed and conditions at which the polymers solidify (either
from solvent or melt) as well as any mechanical drawing force play a role in
crystalline domain formation. The more time the chains have to rearrange, the
more they tend to crystallize and, if there is an applied force, they tend to
crystallize parallel to the direction of the force. Recently, researchers from Université
d’Orléans (France) utilized PLLA (PolyVivo AP006 and PolyVivo AP050) from
PolySciTech (www.polyscitech.com) to
perform fundamental research on the effect processing conditions have on
crystalline PLLA film formation. This research holds promise for the
development of mechanically robust or optically clear components for use in
biomedical applications. Read more: Vayer, Marylène, Alain Pineau, Fabienne
Warmont, Marjorie Roulet, and Christophe Sinturel. "Constrained
crystallization of poly (L-lactic acid) in thin films prepared by dip
coating." European Polymer Journal (2018)., https://www.sciencedirect.com/science/article/pii/S0014305717322413
“Abstract: Dip coating process used at various withdrawing
speeds showed a great ability to control the crystalline structure of thin
films of poly(L-lactic acid) which can be of great importance for applications
where mechanical or optical properties are involved. Thin films were studied by
Atomic Force Microscopy and Grazing Incidence Angle X-ray Diffraction.
Withdrawing the silicon substrate in the draining regime (at high speed) led to
amorphous films with flat surface whatever the solvent and the molar mass. At
low speeds (capillary regime), AFM demonstrated the presence of spherulites or
hedrites in the films depending on the solvent and the molar mass. GIXRD showed
that spherulites were less crystallized than hedrites. This difference was
attributed to solvent evaporation rate. Highlights: PLLA thin films were prepared
by dip coating solutions. The thin films were investigated using AFM and GIXRD.
Withdrawal at high speed led to amorphous films. Withdrawal at low speed led to
partially crystallized films. The nature of solvent and molecular mass
influenced the crystalline structure of the films.”
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