Micelles
with perfect monodispersity in terms of the aggregation
number (N
agg) have recently been discovered,
whose values of N
agg interestingly always
coincide with the vertex or face number of regular polyhedral structures
(i.e., Platonic solids). Owing to the monodispersity of the micelles,
named Platonic micelles, we could expect them to exhibit unprecedented
aggregation behavior. In this study, the effects of alkyl chain length
on micellar aggregation behavior were characterized using small-angle
scattering techniques such as small-angle X-ray scattering and asymmetrical
flow field-flow fractionation coupled with multi-angle light scattering,
as well as analytical ultracentrifugation measurements. The N
agg of Platonic micelles discretely and discontinuously
increased when increasing the alkyl chain length, which differs markedly
from the findings for conventional micelles. This aggregation behavior
could be reasonably explained by the relationship between the thermodynamic
stability of the micelles and the coverage density defined by one
of the unsolved mathematical problems: the Tammes problem.
Poly(2-methoxyethyl acrylate) (PMEA) is known to exhibit excellent thromboresistance, i.e., hardly causing blood-clot formation on its surface. Hence, PMEA and its analogues have been commercially used for blood-contacting materials in medical devices. In this study, we investigated the conformation and solvation state of PMEA in mixtures of tetrahydrofuran (THF) and water with various water volume fractions (ϕ water ) by viscosity, sedimentation equilibrium, small-angle X-ray scattering (SAXS), and dielectric relaxation measurements. We also comparatively investigated those of poly[2-(2methoxyethoxy)ethyl methacrylate] (PMe2MA) and polystyrene (PS). For all of these, THF is a good solvent and water is a nonsolvent or poor solvent. PMe2MA and PMEA show equally good thromboresistance, while PS does not at all. The solution properties of PMe2MA and PMEA were found to be quite different from PS. There are clear attractive interactions (or correlation) between the PMEA chain (or PMe2MA) and the waters in the vicinity of the chain despite their water insolubility. These correlated waters give additional scattering and the angular dependence of SAXS was analyzed in terms of the hydration layer model that has been used in protein solution scattering. The hydration is related to increasing both the chain stiffness and excluded volume. These distinctive properties are likely related to the origin of its good thromboresistance.
The monodisperse micellar aggregation number remains constant at 12 when increasing the alkyl chain length from C4 to C6, which is unique behaviour of Platonic micelles.
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