Surfactant or block copolymer micelles? Structural properties of a series of well-defined n-alkyl–PEO micelles in water studied by SANS

Abstract

aHere we present an extensive small-angle neutron scattering (SANS) structural characterization of micelles formed by poly(ethylene oxide)-mono-n-alkyl ethers (C n -PEOx) in dilute aqueous solution. Chemically, C n -PEOx can be considered as a hybrid between a low-molecular weight surfactant and an amphiphilic block copolymer. The present system, prepared through anionic polymerization techniques, is better defined than other commercially available polymers and allows a very precise and systematic testing of the theoretical predictions from thermodynamical models. The equilibrium micellar properties were elaborated by systematically varying the n-alkyl chain length (n) at constant PEO molecular weight or increasing the soluble block size (x), respectively. The structure was reminiscent of typical spherical starlike micelles i.e. a constant core density profile, $r 0 , and a diffuse corona density profile, $r À4/3. Through a careful quantitative analysis of the scattering data, it is found that the aggregation number, N agg initially rapidly decreases with increasing PEO length until it becomes independent at higher PEO molecular weight as expected for star-like micelles. On the other hand, the dependency on the n-alkyl length is significantly stronger than that expected from the theories for star-like block copolymer micelles, N agg $ n 2 similar to what is expected for surfactant micelles. Hence the observed aggregation behavior suggests that the C n -PEOx micelles exhibit a behavior that can be considered as a hybrid between low-molecular weight surfactant micelles and diblock copolymer micelles.

Nanoscopic Confinement through Self-Assembly: Crystallization within Micellar Cores Exhibits Simple Gibbs-Thomson Behavior

“…This model system, synthesized by living anionic polymerization, exhibits very low polydispersities, M w =M n ≤ 1.05, and impurities and is therefore well suited for fundamental investigations. This system spontaneously forms spherical starlike micelles in water where the 2-3 nm spherical core consists of n-alkane(s) that may fully or partially crystallize, surrounded by an extended highly swollen, diffuse PEO polymer shell [37,38]. The size of the core, R c , can be varied continuously both through the length of the hydrophobic n-alkyl block and the length of the PEO.…”

SANS study on self-assembled structures of glucose-responsive phenylboronate ester-containing diblock copolymer

“…The neutron scattering length density (SLD) of D 2 O is 6.34×10 -6 Å -2 , of PEG is 0.67 × 10 -6 Å -2 using a mass density of 1.196g mL -1 [23]. The mass density of PPBDEMA was not found; SciFinder R gives a predicted mass density of the monomer, 1.08g mL -1 .…”

Intelligent micellar polymeric nanocarriers for therapeutics and diagnosis

“…The corona also constitutes the interface between the drug reservoir and the release medium; depending on its properties (e.g., microfluidity) and on drug–corona interactions, the drug release can be facilitated or hampered . As the shell‐forming block, several hydrophilic and nonionic polymers, such as poly(ethylene glycol) (PEG), poly(ethylene oxide) (PEO), poly( N ‐vinyl pyrrolidone), poly(2‐oxazoline), poly( N ‐isopropyl acrylamide) (PNIPAAm), and poly(hydroxypropyl methacrylamide), have been reported. Among them, PEG is the most frequently used for several reasons, including the following: (1) its excellent solubility in aqueous media and several organic solvents, which allows for flexibility in preparation procedures; (2) nontoxicity and low immunogenicity; and (3) lack of interaction with biological components; this provides stealthiness and prevents uptake by the reticuloendothelial system and allows longer circulation times in vivo …”

“…of the forming blocks, solvent quality, presence of additives, and solution temperature. For example, the micellization of block copolymers bearing both nonionic hydrophobic and hydrophilic blocks, such as PEO, poly(2‐oxazoline), PNIPAAm, and poly(vinyl ether), is mainly driven by hydrophobic forces; these are largely controlled by the hydrophobic block length . Hydrogen bonding and metal–ligand coordination interactions can also play an important role .…”

“…Nevertheless, a compromise between the chain solubility and micellar core size must be attained by the tuning of the EO and SO block lengths, with an empirical optimal EO–SO ratio found at about 1.5 . Furthermore, the influence of the amount of feeding drug on the encapsulation yield was also largely evidenced …”