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Thermodynamic Characterization of Free and Surface Water of Colloidal Unimolecular Polymer (CUP) Particles Utilizing DSC.

Authors
  • Geng, Peng1
  • Zore, Ashish1
  • Van De Mark, Michael R1
  • 1 Department of Chemistry, Missouri S&T Coatings Institute, Missouri University of Science and Technology, Roll, MO 65409, USA.
Type
Published Article
Journal
Polymers
Publisher
MDPI AG
Publication Date
Jun 24, 2020
Volume
12
Issue
6
Identifiers
DOI: 10.3390/polym12061417
PMID: 32599952
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Colloidal Unimolecular Polymer (CUP) particles are spheroidal, 3-9 nm with charged groups on the surface and a hydrophobic core, which offer a larger surface water fraction to improve the analysis of its characteristics. Differential scanning calorimetry (DSC) was performed to determine the characteristics of surface water. These properties include the amount of surface water, the layer thickness, density, specific heat of the surface water above and below the freezing point of water, melting point depression of free water, effect of charge density and particle size. The charge density on the CUP surface was varied as well as the molecular weight which controls the particle diameter. The surface water is proportional to the weight fraction of CUP <20%. Analogous to recrystallization the CUP particles were trapped in the ice when rapidly cooled but slow cooling excluded the CUP, causing inter-molecular counterion condensation and less surface water. The density of surface water was calculated to be 1.023 g/mL to 1.056 g/mL depending on the surface charge density. The thickness of surface water increased with surface charge density. The specific heat of surface water was found to be 3.04 to 3.07 J/g·K at 253.15 K and 3.07 to 3.09 J/g·K at 293.15 K. The average area occupied by carboxylate and ester groups on the CUP surface were determined.

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