Contraction of weak polyelectrolyte multilayers in response to organic solvents

Abstract

Weak polyelectrolyte multilayers (PEMs) prepared by the layer-by-layer assembly technique have recently been found to demonstrate a unique contraction upon exposure to organic solvents. This response is dependent upon which organic solvent is employed, and fundamental questions have not been clarified regarding the correlation of the magnitude of the film contraction with solvent type. In this work, we used solubility parameters to analyze the response of branched poly(ethylene imine)/poly(acrylic acid) (BPEI/PAA) multilayers when exposed to a variety of solvents. BPEI/PAA multilayers were immersed in a series of 16 different organic solvents and solvent mixtures. Immersion in organic solvent caused film dehydration and therefore contraction and also induced changes in the mechanical properties of PEMs. The film thickness was the best predictor of how a film swelled in water or contracted in organic solvent when using different batches of commercially available polyelectrolytes, rather than polyelectrolyte assembly pH conditions. The degree of film contraction was correlated with Hansen and Kamlet-Taft solubility parameters as well as solvent dielectric constant. In most cases, the hydrogen bonding ability of solvents is the primary factor to determine the magnitude of film contraction. For these solvents, increasing the temperature which corresponds to decreasing the strength of hydrogen bonding, also decreases the ability to dehydrate the films. For solvents that do not follow these trends with the strength of hydrogen bonding, a stronger correlation was found between contraction and dielectric constant, indicating that both traditional solvent quality arguments and electrostatics are important to understanding the contraction of PEMs in organic solvents.

Fast Self‐Healing of Polyelectrolyte Multilayer Nanocoating and Restoration of Super Oxygen Barrier

“…Nanocoating thickness was measured in different environments as a function of the number of BL deposited (Figure S2, Supporting Information). A swelling ratio of 52% was observed for an 8‐BL PEI/PAA nanocoating when immersed in water, which agrees well with a previous study . The film shrinks to its original thickness (≈700 nm for 8‐BL) after drying at 70 °C for 30 min.…”

“…A swelling ratio of 52% was observed for an 8-BL PEI/PAA nanocoating when immersed in water, which agrees well with a previous study. [51] The film shrinks to its original thickness (≈700 nm for 8-BL) after drying at 70 °C for 30 min. It has been reported that this reversible swelling-drying cycle can be repeated at least ten times without damaging the multilayer nanocoating.…”

Thickness‐dependent swelling of molecular layer‐by‐layer polyamide nanomembranes

“…We have successfully applied a new swelling model, a model based on Painter‐Shenoy for gel‐like swelling that incorporates the Leibler‐Sekimoto theory for Langmuir sorption, to extract the network parameters of the polyamide thin films. We anticipate that this proposed model can be applied to a variety of heterogeneous polymeric materials where swelling behavior is a function of physical properties, such as polyelectrolyte layer‐by‐layer films, polymer brushes, nanophase segregated materials, as well as polymer glasses.…”

Ultrathin Single Bilayer Separation Membranes Based on Hyperbranched Sulfonated Poly(aryleneoxindole)

“…The exact reasons for this SA‐induced performance improvement are still unknown. It may be speculated that this SA process helps to remove loose polymer structures or rearranges polymer chains by dehydration . SA can also prevent the collapse of pores in the support and facilitate the solvent entrance into the pores .…”