Humidity-Driven Transparent Holographic Free-Standing Polyelectrolyte Films

Abstract

In the present work, transparent holographic poly­(diallyldimethylammonium chloride) (PDADMAC)/heparin and PDADMAC/poly­(styrenesulfonate) (PSS) films were synthesized via polyelectrolyte coacervates. PDADMAC/heparin films were obtained without temperature treatment. Thin holographic free-standing films with a 1 μm grating period and uniform surface of a polyelectrolyte complex were readily and quickly made by pressing polyelectrolyte coacervate, the hydrated viscoelastic fluid-like form of polyelectrolyte complex precursor, between a flat surface and holographic mask. Heparin replaces PSS in film composition to prepare the sheer film. Thus, the PDADMAC/heparin holographic film demonstrates transparency and reversible response for humidity under diffraction detection. In addition to diffraction humidity signal measurements, the cobalt­(II) chloride was impregnated in polyelectrolyte coacervate to make an additional colorimetric signal response. In this case, the free-standing film serves both as the substrate for the hygroscopic salt and as a diffraction humidity sensor. The PDADMAC/heparin/Co­(II) chloride film demonstrates a linear humidity range from 50 to 90%. Additionally, due to hydrated inorganic salt ion size, cobalt chloride prevents film porosity, which initiates under film swelling. Based on the results and calculations obtained, the study proposes the mechanism of water incorporation, including the reptation model and polyelectrolyte complex behavior. Results of density functional theory calculations prove that binding of cobalt aqua complexes [Co­(H2O)6]2+ with the dimeric associates heparin/PDADMAC via noncovalent interactions (hydrogen bonds) additionally is much more energetically favorable compared with the alternative association of heparin/PDADMAC with water molecules.

Relaxation Times of Solid-like Polyelectrolyte Complexes of Varying pH and Water Content

“…Aqueous solutions of oppositely charged polyelectrolytes (PEs) phase separate upon mixing, leading to the formation of a dilute supernatant and a polymer-rich phase known as a polyelectrolyte complex (PEC). PECs are formed due to electrostatic attractions between oppositely charged PEs and the entropic release of counterions and water. − PECs can exist as solid-like complexes or liquid-like coacervates, − and the physical properties are affected by salt, temperature, water, pH, and hydrophobicity of the PEs. − This leads to applications of PECs in drug delivery systems, humidity sensors, separation membranes, electrochemistry, and many more. − However, there is little information regarding the impact of complexation pH and water content on the mechanical properties and relaxation of PECs.…”

Polyelectrolyte Complex Membranes via Salinity Change Induced Aqueous Phase Separation

“… 31 − 35 Porous saloplastic materials are obtained by centrifugation 31 , 36 and electrospinning 37 of coacervate phases or by desalting a homogeneous PE solution in between semipermeable membranes. 38 In addition, doped PECs can be extruded to obtain dense materials in various shapes (tape, tube, rod, and fiber) 32 , 33 or spin-coated, 34 , 39 cast, 40 , 41 or pressed in between templates 42 , 43 to obtain transparent films. Moreover, some of the saloplastics show self-healing behavior which can operate under room temperature and tuned by type of salt.…”

Recent Progress of Layer‐by‐layer Assembly, Free‐Standing Film and Hydrogel Based on Polyelectrolytes

“…One such example is a poly (diallyldimethylammonium chloride)/heparin film modified with cobalt chloride ( Figure 5 a). [ 70 ] Nikolaev et al. [ 70 ] showed that even in such a simple system, complex, competitive thermodynamically favorable molecular hydration reactions proceed.…”

“…[ 70 ] Nikolaev et al. [ 70 ] showed that even in such a simple system, complex, competitive thermodynamically favorable molecular hydration reactions proceed. The incorporation of redox molecules, such as ferrocene, into the polystyrene sulfonic acid matrix, allows nitric oxide redox detection.…”

“…Reproduced with permission. [ 70 ] Copyright 2020, American Chemical Society. b) Photo of silver melamine thin film as flexible platform 2 wt% (upper pattern) 0.2 wt% (below the pattern), correspondingly.…”