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Synthesis of Monodisperse Cylindrical Nanoparticles via Crystallization-driven Self-assembly of Biodegradable Block Copolymers
Published on: June 20, 2019
Square grains in asymmetric rod-coil block copolymers
Bradley D Olsen1, Michael F Toney, Rachel A Segalman
1Department of Chemical Engineering, University of California, Berkeley, California 94720, USA.
Langmuir : the ACS Journal of Surfaces and Colloids
|January 29, 2008
Summary
Square grains in block copolymer thin films form due to molecular packing. This hierarchical structuring, driven by a tetragonal lattice, leads to unique grain shapes in poly(2,5-di(2'-ethylhexyloxy)-1,4-phenylene vinylene)-b-polyisoprene (PPV-b-PI).
Area of Science:
- Materials Science
- Polymer Science
- Nanotechnology
Background:
- Soft materials typically form rounded grains.
- Block copolymers exhibit microphase separation into nanodomains.
- Hierarchical structuring influences material morphology.
Purpose of the Study:
- To investigate the formation of square grains in thin films of a rod-coil block copolymer.
- To understand the molecular mechanisms behind the observed grain morphology.
- To determine the conditions necessary for square grain formation.
Main Methods:
- Thin film preparation of poly(2,5-di(2 eal-ethylhexyloxy)-1,4-phenylene vinylene)-b-polyisoprene (PPV-b-PI).
- Analysis of microphase-separated lamellar structures.
- Investigation of molecular packing and crystalline lattice effects.
Main Results:
- Observed square grains of microphase-separated lamellae, unlike typical rounded grains.
- Square grains are oriented with lamellar layers parallel to the film interface.
- Formation is linked to a tetragonal crystalline lattice within rod-rich nanodomains and occurs within a specific coil volume fraction range (around 72%).
Conclusions:
- Hierarchical structuring from molecular packing of rods dictates square grain formation.
- The tetragonal lattice within PPV-b-PI nanodomains drives the orthogonal growth.
- Grain formation is sensitive to coil volume fraction, exhibiting kinetic barriers and lattice disordering, and is nucleation-limited.
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