TY - JOUR
T1 - Mechanistic study of the formation of fiber-like micelles with a π-conjugated oligo(p-phenylenevinylene) core
AU - Tao, Daliao
AU - Cui, Yinan
AU - Huang, Xiaoyu
AU - Lu, Guolin
AU - Manners, Ian
AU - Winnik, Mitchell A.
AU - Feng, Chun
PY - 2020/2/15
Y1 - 2020/2/15
N2 - Hypothesis: Crystallization-driven self-assembly (CDSA) of block copolymers (BCPs) with a crystallizable core-forming oligo(p-phenylenevinylene) (OPV) segment can be a powerful strategy for the preparation of uniform fiber-like nanostructures containing a π-conjugated core with controlled dimension and composition. However, the self-assembly landscape can be complex, and our understanding of the nucleation and growth processes in the CDSA of BCPs with a crystalline π-conjugated segment is limited. Experiments: We used fluorescence spectroscopy and 1H NMR to follow the self-assembly of oligo(p-phenylenevinylene)-b-poly(N-isopropyl acrylamide) (OPV5-b-PNIPAM49), a typical π-conjugated-coil BCP, as solution of the BCP in ethanol is cooled from 80 °C to 23 °C and allowed to age, µDSC to monitor the crystallization exotherm, and DLS and TEM to follow micelle growth. We see a striking difference in the experiments that monitor unimer in solution comparing to those that monitor micelle growth. We see nearly complete disappearance of unimer within 30 min upon cooling. In contrast, the micelles continue to grow, increasing in length by a factor of ten over the next several hours. We are able to exclude growth by end-to-end coupling. Findings: We propose a self-assembly mechanism in which short semi-crystalline rod-like micelles form upon cooling, accompanied by small amorphous aggregates. Unimers that dissociate from these aggregates subsequently deposit on the growing ends of the core-crystalline micelles. We also find that the length of the PNIPAM block affects the elongation kinetics of OPV5-b-PNIPAM.
AB - Hypothesis: Crystallization-driven self-assembly (CDSA) of block copolymers (BCPs) with a crystallizable core-forming oligo(p-phenylenevinylene) (OPV) segment can be a powerful strategy for the preparation of uniform fiber-like nanostructures containing a π-conjugated core with controlled dimension and composition. However, the self-assembly landscape can be complex, and our understanding of the nucleation and growth processes in the CDSA of BCPs with a crystalline π-conjugated segment is limited. Experiments: We used fluorescence spectroscopy and 1H NMR to follow the self-assembly of oligo(p-phenylenevinylene)-b-poly(N-isopropyl acrylamide) (OPV5-b-PNIPAM49), a typical π-conjugated-coil BCP, as solution of the BCP in ethanol is cooled from 80 °C to 23 °C and allowed to age, µDSC to monitor the crystallization exotherm, and DLS and TEM to follow micelle growth. We see a striking difference in the experiments that monitor unimer in solution comparing to those that monitor micelle growth. We see nearly complete disappearance of unimer within 30 min upon cooling. In contrast, the micelles continue to grow, increasing in length by a factor of ten over the next several hours. We are able to exclude growth by end-to-end coupling. Findings: We propose a self-assembly mechanism in which short semi-crystalline rod-like micelles form upon cooling, accompanied by small amorphous aggregates. Unimers that dissociate from these aggregates subsequently deposit on the growing ends of the core-crystalline micelles. We also find that the length of the PNIPAM block affects the elongation kinetics of OPV5-b-PNIPAM.
KW - Crystallization-driven self-assembly (CDSA)
KW - Elongation mechanism
KW - Fiber-like micelle
KW - Oligo(p-phenylenevinylene) (OPV)
KW - π-conjugated-coil block copolymer
UR - http://www.scopus.com/inward/record.url?scp=85073461839&partnerID=8YFLogxK
U2 - 10.1016/j.jcis.2019.10.014
DO - 10.1016/j.jcis.2019.10.014
M3 - Article (Academic Journal)
C2 - 31639564
AN - SCOPUS:85073461839
SN - 0021-9797
VL - 560
SP - 50
EP - 58
JO - Journal of Colloid and Interface Science
JF - Journal of Colloid and Interface Science
ER -