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Hydroxypropyl cellulose as a green polymer for thermo-responsive aqueous foams † †Electronic supplementary information (ESI) available: Additional data measured with UV/vis spectroscopy, foam analyzer and dynamic light scattering. See DOI: 10.1039/c9sm00093c

Authors
  • Weißenborn, Eric
  • Braunschweig, Björn
Type
Published Article
Journal
Soft Matter
Publisher
The Royal Society of Chemistry
Publication Date
Mar 07, 2019
Volume
15
Issue
13
Pages
2876–2883
Identifiers
DOI: 10.1039/c9sm00093c
PMID: 30843017
PMCID: PMC6438354
Source
PubMed Central
License
Green

Abstract

Hydroxypropyl cellulose (HPC) is a surface active polymer that can change its solubility as a function of temperature. This makes HPC interesting for responsive foams, where macroscopic properties need to be reversibly changed on demand. Analysis of aqueous HPC foams as a function of temperature showed a moderate decrease in foam half-life time from 9000 to 4000 s, when the temperature was increased. However, within a narrow temperature range of ±2 °C a dramatic decrease in half-life time to <120 s was observed at 43 °C in the absence and at 31 °C in the presence of 0.7 M NaCl. These drastic changes are highly reversible and are associated to the lower critical solution temperatures (LCST) of HPC in aqueous solutions. In fact, dynamic light scattering experiments indicate that HPC molecules form aggregates at temperatures >31 °C (0.7 M NaCl) and >43 °C (0 M NaCl), which shrink in size when the temperature is increased further. From these results, we conclude that the LCST of 1 MDa HPC is at 43 °C when no salt is present and is at 31 °C in aqueous solutions with 0.7 M NaCl. In addition, shear rheology of bulk solutions and surface tensiometry indicate that the solution's viscosity and the surface pressure dramatically change at the respective LCSTs. Obviously, the solvent's viscosity triggers substantial changes in foam drainage at the LCST, which is shown to be the main driving force for the temperature responsiveness of HPC foams.

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