Structure of poly(N-isopropylacrylamide) brushes and steric stability of their grafted cellulose nanocrystal dispersions

Usha D Hemraz; Ang Lu; Rajesh Sunasee; Yaman Boluk

doi:10.1016/j.jcis.2014.05.011

Structure of poly(N-isopropylacrylamide) brushes and steric stability of their grafted cellulose nanocrystal dispersions

J Colloid Interface Sci. 2014 Sep 15:430:157-65. doi: 10.1016/j.jcis.2014.05.011. Epub 2014 May 19.

Authors

Usha D Hemraz¹, Ang Lu², Rajesh Sunasee³, Yaman Boluk⁴

Affiliations

¹ Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, Canada; National Institute for Nanotechnology, National Research Council of Canada, Edmonton, AB, Canada.
² Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, Canada.
³ Department of Chemistry, State University of New York at Plattsburgh, Plattsburgh, NY, USA.
⁴ Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, Canada; National Institute for Nanotechnology, National Research Council of Canada, Edmonton, AB, Canada. Electronic address: yaman.boluk@ualberta.ca.

PMID: 24998068
DOI: 10.1016/j.jcis.2014.05.011

Abstract

Thermo-responsive poly(N-isopropylacrylamide) (poly(NIPAAm)) brushes were grafted from the surface of cellulose nanocrystals (CNC) via living radical polymerization (LRP) using different initiator and monomer concentrations. The dry film thickness of the poly(NIPAAm) layer around CNC was calculated based on Scanning Electron Microscopy (SEM) and dynamic light scattering (DLS) measurements. The wet film thicknesses of grafted poly(NIPAAm) brushes in water were calculated to be 15 and 9nm for NIPAAm-CNC-1 and NIPAAm-CNC-2, respectively. Grafted chain densities and wet film thicknesses at below and above the critical temperature (T=34°C) of polyNIPAAm were calculated by applying mean-field analytical theory. The non-ionic poly(NIPAAm) brushes screened the surface charges of CNC particles, leading to a significant decrease in the absolute zeta potential values for the poly(NIPAAm) grafted CNCs compared to the unmodified and initiator modified CNC samples. Nevertheless, the colloidal stability of poly(NIPAAm) grafted CNC particles were still maintained by steric stabilization below the critical temperature On the other side, hydrophobic attractions among poly(NIPAAm) grafted CNC rods above 34°C lead to coagulation and phase separation. While both poly(NIPAAm) grafted CNC samples showed thermo-responsive behavior, the reversibility of this temperature triggered property was dependent on grafting density.

Keywords: Brushes; Cellulose nanocrystals; Colloids; Grafting; Poly(N-isopropylacrylamide); Rod like particles; Stability; Steric.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Acrylic Resins / chemical synthesis*
Acrylic Resins / chemistry*
Cellulose / chemistry*
Nanoparticles / chemistry*

Substances

Acrylic Resins
poly-N-isopropylacrylamide
Cellulose