Effects of fluid shear stress on polyelectrolyte multilayers by neutron scattering studies

Journal Article · Tue Feb 17 00:00:00 EST 2015 · Langmuir

DOI:https://doi.org/10.1021/acs.langmuir.5b00037· OSTI ID:1248638

Singh, Saurabh ^[1]; Junghans, Ann ^[1]; Watkins, Erik ^[1]; Kapoor, Yash ^[2]; Toomey, Ryan ^[3]; Majewski, Jaroslaw ^[1]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2. Vision Care R&D, Alcon, Johns Creek, GA (United States)
3. Univ. of South Florida, Tampa, FL (United States)

The structure of layer-by-layer (LbL) deposited nanofilm coatings consists of alternating polyethylenimine (PEI) and polystyrenesulfonate (PSS) films deposited on a single crystal quartz substrate. LbL-deposited nanofilms were investigated by neutron reflectomery (NR) in contact with water in the static and fluid shear stress conditions. The fluid shear stress was applied through a laminar flow of the liquid parallel to the quartz/polymer interface in a custom-built solid–liquid interface cell. The scattering length density profiles obtained from NR results of these polyelectrolyte multilayers (PEM), measured under different shear conditions, showed proportional decrease of volume fraction of water hydrating the polymers. For the highest shear rate applied (ca. 6800 s^–1) the water volume fraction decreased by approximately 7%. The decrease of the volume fraction of water was homogeneous through the thickness of the film. Since there were not any significant changes in the total polymer thickness, it resulted in negative osmotic pressures in the film. The PEM films were compared with the behavior of thin films of thermoresponsive poly(N-isopropylacrylamide) (pNIPAM) deposited via spin-coating. The PEM and pNIPAM differ in their interactions with water molecules, and they showed opposite behaviors under the fluid shear stress. In both cases the polymer hydration was reversible upon the restoration of static conditions. Furthermore, a theoretical explanation is given to explain this difference in the effect of shear on hydration of polymeric thin films.

• Research Organization: Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC52-06NA25396
• OSTI ID: 1248638
• Report Number(s): LA-UR-15-20775
• Journal Information: Langmuir, Vol. 31, Issue 9; ISSN 0743-7463
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE