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Path-Dependent Preparation of Complex Micelle Packings of a Hydrated Diblock Oligomer.

ABSTRACT: Small-angle X-ray scattering analyses reveal that the hydrated diblock oligomer n-C₁₆H₂₃(OCH₂CH₂)₂₀-OH (C₁₆E₂₀ or Brij 58) forms lyotropic liquid crystals (LLCs) exhibiting face-centered cubic (FCC), body-centered cubic (BCC), Frank-Kasper (FK) A15, and cylindrical (H_I) morphologies over the concentration range 30-65 wt % amphiphile. Heating LLCs comprising 54-59 wt % C₁₆E₂₀ drives the temperature-dependent phase transition sequence: A15 ? BCC ? H_I. However, rapidly quenching the resulting H_I phase from 70 to 25 °C initially forms a BCC phase that isothermally transforms into a complex, tetragonal FK ? phase comprising 30 quasispherical micelles. The metastability of this micellar ? phase is shown to depend on the sample cooling rate, thermal quench depth, and isothermal annealing temperature. We rationalize the preference for the A15 structure at 25 °C in terms of minimizing unfavorable water/hydrophobic contacts, while maximizing local particle sphericity. The symmetry breaking transition kinetics in these micellar LLCs apparently stem from the temperature-dependent activation barriers for phase nucleation and growth, which are intimately coupled to the time scales for micelle reconfiguration by amphiphile chain exchange and their spatial rearrangement. These findings highlight how thermal processing influences nucleation and growth of the self-assembled morphologies of intrinsically reconfigurable, soft spherical particles.

SUBMITTER: Jayaraman A

PROVIDER: S-EPMC6487539 | biostudies-literature | 2019 Apr

REPOSITORIES: biostudies-literature

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Path-Dependent Preparation of Complex Micelle Packings of a Hydrated Diblock Oligomer.

Jayaraman Ashish A Zhang Diana Y DY Dewing Beth L BL Mahanthappa Mahesh K MK

ACS central science 20190228 4

Small-angle X-ray scattering analyses reveal that the hydrated diblock oligomer n-C16H23(OCH2CH2)20-OH (C16E20 or Brij 58) forms lyotropic liquid crystals (LLCs) exhibiting face-centered cubic (FCC), body-centered cubic (BCC), Frank-Kasper (FK) A15, and cylindrical (HI) morphologies over the concentration range 30-65 wt % amphiphile. Heating LLCs comprising 54-59 wt % C16E20 drive ...[more]

PMID: 31041381

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Project description:Polyelectrolyte complex micelles are hydrophilic nanoparticles that self-assemble in aqueous environments due to associative microphase separation between oppositely charged blocky polyelectrolytes. In this work, we employ a suite of physical characterization tools to examine the effect of charged block length mismatch on the equilibrium structure of double diblock polyelectrolyte complex micelles (D-PCMs) by mixing a diverse library of peptide and synthetic charged-neutral block polyelectrolytes with a wide range of charged block lengths (25-200 units) and chemistries. Early work on D-PCMs suggested that this class of micelles can only be formed from blocky polyelectrolytes with identical charged block lengths, a phenomenon referred to as chain length recognition. Here, we use salt annealing to create PCMs at equilibrium, which shows that chain length recognition, a longstanding hurdle to repeatable self-assembly from mismatched polyelectrolytes, can be overcome. Interestingly, D-PCM structure-property relationships display a range of values that vary systematically with the charged block lengths and chemical identity of constituent polyelectrolyte pairings and cannot be described by generalizable scaling laws. We discuss the interdependent growth behavior of the radius, ionic pair aggregation number, and density in the micelle core for three chemically distinct diblock pairings and suggest a potential physical mechanism that leads to this unique behavior. By comparing the results of these D-PCMs to the scaling laws recently developed for single diblock polyelectrolyte complex micelles (S-PCMs: diblock + homopolymer), we observe that D-PCM design schemes reduce the size and aggregation number and restrict their growth to a function of charged block length relative to S-PCMs. Understanding these favorable attributes enables more predictive use of a wider array of charged molecular building blocks to anticipate and control macroscopic properties of micelles spanning countless storage and delivery applications.

Dataset Information

Path-Dependent Preparation of Complex Micelle Packings of a Hydrated Diblock Oligomer.

Publications

Path-Dependent Preparation of Complex Micelle Packings of a Hydrated Diblock Oligomer.

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