Oligo(ethylene glycol)-sidechain microgels prepared in absence of cross-linking agent: Polymerization, characterization and variation of particle deformability.

L. Andrew Lyon,Nicole Welsch

doi:10.1371/journal.pone.0181369

L. Andrew Lyon, Nicole Welsch

Open Access

https://doi.org/10.1371/journal.pone.0181369

Copy DOI

Journal: PloS one	Publication Date: Jul 18, 2017
Citations: 23	License type: CC BY 4.0

Affiliation: Georgia Institute of Technology, Chapman University

Abstract

We present a systematic study of self-cross-linked microgels formed by precipitation polymerization of oligo ethylene glycol methacrylates. The cross-linking density of these microgels and, thus, the network flexibility can be easily tuned through the modulation of the reaction temperature during polymerization. Microgels prepared in absence of any difunctional monomer, i.e. cross-linker, show enhanced deformability and particle spreading on solid surfaces as compared to microgels cross-linked with varying amounts of poly(ethylene glycol diacrylate) (PEG-DA) in addition to self-crosslinking. Particles prepared at low reaction temperatures exhibit the highest degree of spreading due to the lightly cross-linked and flexible polymer network. Moreover, AFM force spectroscopy studies suggest that cross-linker-free microgels constitute of a more homogeneous polymer network than PEG-DA cross-linked particles and have elastic moduli at the particle apex that are ~5 times smaller than the moduli of 5 mol-% PEG-DA cross-linked microgels. Resistive pulse sensing experiments demonstrate that microgels prepared at 75 and 80°C without PEG-DA are able to deform significantly to pass through nanopores that are smaller than the microgel size. Additionally, we found that polymer network flexibility of microgels is a useful tool to control the formation of particle dewetting patterns. This offers a promising new avenue for build-up of 2D self-assembled particle structures with patterned chemical and mechanical properties.

Highlights

Microgels are hydrated, cross-linked polymer networks with sizes typically in the colloidal range and, in contrast to solid colloidal particles, are mechanically soft materials
OEGMA-based microgels have been polymerized under precipitation polymerization conditions, i.e. above the volume phase transition temperature (VPTT) of the forming particles, with varying cross-linker content ranging from 0 to 10 mol-% of poly(ethylene glycol diacrylate) (PEG-DA)
This indicates that stable colloidal particles were formed from OEGMA300 and Methacrylic acid (MAA) without poly(ethylene glycol) (PEG)-DA and that chain transfer reactions play a significant role in precipitation polymerization of oligo ethylene glycol methacrylates

Summary

Introduction

Cross-linked polymer networks with sizes typically in the colloidal range and, in contrast to solid colloidal particles, are mechanically soft materials. Oligo(ethylene glycol)-sidechain microgels prepared in absence of cross-linking agent deposition, the glass slides were rinsed with water, dried with nitrogen, and individually placed into wells of a six-well plate containing 25 mM HEPES/150 mM NaCl buffer solution, pH 7.4. AFM images of self-cross-linked microgels prepared at different temperatures (Fig 1B) demonstrate that the temperature is a useful parameter to change the mechanical properties of cross-linker-free hydrogels.

Results

Conclusion