Spherical Micelles with Nonspherical Cores: Effect of Chain Packing on the Micellar Shape

Abstract

Self-assembly of amphiphilic polymers into micelles is an archetypical example of a “self-confined” system due to the formation of micellar cores with dimensions of a few nanometers. In this work, we investigate the chain packing and resulting shape of C n -PEOx micelles with semicrystalline cores using small/wide-angle X-ray scattering (SAXS/WAXS), contrast-variation small-angle neutron scattering (SANS), and nuclear magnetic resonance spectroscopy (NMR). Interestingly, the n-alkyl chains adopt a rotator-like conformation and pack into prolate ellipses (axial ratio ϵ ≈ 0.5) in the “crystalline” region and abruptly arrange into a more spheroidal shape (ϵ ≈ 0.7) above the melting point. We attribute the distorted spherical shape above the melting point to thermal fluctuations and intrinsic rigidity of the n-alkyl blocks. We also find evidence for a thin dehydrated PEO layer (≤1 nm) close to the micellar core. The results provide substantial insight into the interplay between crystallinity and molecular packing in confinement and the resulting overall micellar shape.

Encapsulation of miRNA and siRNA into Nanomaterials for Cancer Therapeutics

“…Recently, cationic micelles have been broadly investigated for the delivery of drugs and RNAi-based mixes [7]. These micelle structures are framed by amphiphilic copolymers and are absolutely nanoscopic [90]. Micellar networks have been shown to be the most appropriate for drug delivery applications because of their tunable properties as per the specific region.…”

Surface Charged Polymeric Micelles─A Tunable Model System Studied by SANS

“…The PEO chains in the corona are highly swollen with water and exhibit a radially decaying density profile ∝ r −4/3 , in agreement with theoretical predictions. 49,50 It should be mentioned that we have not used the aspherical core− shell model introduced recently by Konig et al 36 to account for the effect of n-alkyl chain packing because of neglibible contributions to the scattering profile under full contrast conditions. I blob (Q) represents the so-called "blob" scattering originating from the internal structure of the coronal PEO chains and is added incoherently.…”

“…Digit 5 denotes the PEO molar mass in kg/mol. Structural properties of micelles formed by the OH-terminated block copolymer have been thoroughly studied and published earlier. − Since carboxylic acids are weak acids, the number of surface charges can be conveniently varied by adjusting the pH. Thus, we are able to systematically investigate properties of sterically and electrostatically stabilized soft colloids.…”