A Novel Soft Contact Piezo-Controlled Liquid Cell for Probing Polymer Films under Confinement using Synchrotron FTIR Microspectroscopy

Natalie L. Benbow,Mark J. Tobin,Tracey T. M. Ho,Jitraporn Vongsvivut,Marta Krasowska,Jessie L. Webber,Piotr Pawliszak,David A. Beattie,Damien A. Sebben

doi:10.1038/s41598-018-34673-4

Natalie L. Benbow, Mark J. Tobin + Show 7 more

Open Access

https://doi.org/10.1038/s41598-018-34673-4

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Abstract

Soft polymer films, such as polyelectrolyte multilayers (PEMs), are useful coatings in materials science. The properties of PEMs often rely on the degree of hydration, and therefore the study of these films in a hydrated state is critical to allow links to be drawn between their characteristics and performance in a particular application. In this work, we detail the development of a novel soft contact cell for studying hydrated PEMs (poly(sodium 4-styrenesulfonate)/poly(allylamine hydrochloride)) using FTIR microspectroscopy. FTIR spectroscopy can interrogate the nature of the polymer film and the hydration water contained therein. In addition to reporting spectra obtained for hydrated films confined at the solid-solid interface, we also report traditional ATR FTIR spectra of the multilayer. The spectra (microspectroscopy and ATR FTIR) reveal that the PEM film build-up proceeds as expected based on the layer-by-layer assembly methodology, with increasing signals from the polymer FTIR peaks with increasing bilayer number. In addition, the spectra obtained using the soft contact cell indicate that the PEM film hydration water has an environment/degree of hydrogen bonding that is affected by the chemistry of the multilayer polymers, based on differences in the spectra obtained for the hydration water within the film compared to that of bulk electrolyte.

Highlights

Polyelectrolyte multilayers (PEMs) are a versatile and useful soft matter system, whose properties, including film thickness, density, surface charge and hydration content, can be controlled
The results demonstrated that Fourier-transform infrared (FTIR) spectroscopy possessed a unique capability to probe the polymer characteristics and simultaneously monitor changes in hydration water within the PEMs6,19,21
The buildup of a subsequent layers of poly(sodium 4-styrenesulfonate) (PSS)/poly(allylamine hydrochloride) (PAH) film was confirmed in streaming potential experiments, where the determined zeta potential had a negative value for a multilayer terminated with polyanion, and a positive value

Summary

Introduction

Polyelectrolyte multilayers (PEMs) are a versatile and useful soft matter system, whose properties, including film thickness, density, surface charge and hydration content, can be controlled. Beattie et al.[19] used synchrotron Fourier-transform infrared (FTIR) microspectroscopy along with a custom built solid−solid contact cell to probe the structure of boundary lubricant layers confined between two solid surfaces This method, lacked the precise control of pressure applied during the contact formation and was restricted to soft/flexible solid surfaces (i.e. mica, which is not ideal for FTIR studies due to its anisotropic optical properties). The geometry of the ATR crystal (curved under surface for contact) ensures that the application of pressure (of practical/relevant magnitude) is gentle and non-destructive Such a unique design allows in situ monitoring of the hydration of the confined film under different (and controlled) degrees of compression

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