Nanostructured block copolymers. Page: 4 of 9
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RESULTS AND DISCUSSION
Self Assembly of OPVn-PEGm In Organic Solvents
The OPVn-PEGm diblock copolymers undergo self assembly in organic solvents,
such as chloroform and tetrahydrofuran (THF). The Small Angle Neutron Scattering
(SANS) data of OPV13-PEGm in dg-THF showed a form factor typical of infinitely long
rod-like micelles. With modified Guinier analysis for rod-like objects, which involves
plotting ln[QxI(Q)] versus Q2, the radius of the rod is obtained as R = 2 x (-2xslope).
The averaged radius of OPV13-PEG45 under several different concentrations gave a value
of 7.9 nm. There are two possible ways for OPVn-PEGm diblock copolymers to self-
assemble in THF, i.e., the OPV segment can be either the outer shell or the inner core.
Based on the hydrophobicity of the OPV segment and the hydrophilicity of both PEG and
solvent THF, the expected packing consists of a hydrophobic OPV inner core and a
hydrophilic PEG outer shell. In order to verify the model, we carried out a contrast
matching experiment. The neutron and x-ray scattering length densities of the solvent
and block copolymer segments are listed in the following Table.
Table 1. Neutron and X-ray scattering
length density (1010 cm 2Compound Neutron X-ra
THE - 8.35
dg-THF 6.35 -
PEG 0.58 9.40
OPV 0.79 8.80
d-PEG 6.26 -Sopv opv ,
PEG
d-THF d-THF
Figure 1 Schematic representation of
neutron scattering (see text).In deuterated THF, SANS measures the contributions from both OPV and PEG
due to the contrast difference (Table 1 and Figure 1 Left). With fully deuterated PEG
segment (d-PEG), the neutron scattering density of d-PEG is comparable to that of the dg-
THF solvent and neutron scattering measures the OPV contribution only (Table 1 and
Figure 1 Right). If OPV is the outer shell of the rod-like micelle, OPV-d-PEG will give a
radius about the same as that of the OPV-PEG. However, if OPV is the inner core, OPV-
d-PEG will reflect a much smaller radius. SANS measurements on OPV13-d-PEG2 in dg-
THF gave a radius of 5.2 nm that was significantly smaller than 7.9 nm of OPV13-PEG45.
The result clearly indicated that the OPV-PEG micelles consisted of OPV inner cores
with PEG outer shells, and the radii of the OPV13 inner cores are 5.2 nm. The contrast
difference among OPV, PEG, and THF, under x-ray scattering condition is small but
measurable with the strong synchrotron source. We modeled the small angle x-ray
scattering (SAXS) data of OPV13-PEG45 in THE solution with a core-shell cylinder and
an elliptical cross section. The two semi axes are approximately 50 and 100 A with a
shell thickness of -20 A. The neutron and x-ray scattering intensity versus scattering
vector plots as well as modeling have been published previously. [4]
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Wang, H. H.; Wang, H.; Yu, L.; Han, C. Y.; Csencsits, R.; Willing, G. A. et al. Nanostructured block copolymers., article, July 9, 2002; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc738396/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.