Effects of Solution Composition (salts, PH, Dielectric Constant) on Polyelectrolyte Complex (PEC) Formation and Their Properties PDF Download

Author: Huan Zhang (Polymer engineer)
Publisher:
ISBN:
Category : Photoelectrochemistry
Languages : en
Pages : 0

Get Book Here

Book Description
Polyelectrolyte complexes (PECs) are formed based on the strong association of oppositely charged polyelectrolytes, a process driven by a combination of enthalpy and entropy, but often with entropic considerations dominating. PEC based materials including polyelectrolyte coacervates, precipitates, and multilayers (PEMs), exhibit promising application in a variety of areas. These abundant applications of PECs are made possible by their highly controllable/tailorable properties upon exposure to different stimuli like pH, salt, organic solvent, and so on. It is important to understand how these different parameters affect the complexation of polyelectrolytes and the structures of PECs. In this dissertation, the main goal is to investigate the effects of solution composition including salt content, pH of solution, and solvent quality on the properties of polyelectrolyte coacervate, precipitate and multilayers. Based on these studies, the potential of applications of PEC materials in self-healing, 3D printing under ethanol and adhesive were studied. Firstly, the interactions between various types of salt and polyelectrolytes were studied. The energetics of the binding process between salt and polyelectrolytes were investigated. Various types of cations and anions were employed in this study, including alkali metal, alkaline earth metal ions, transition metal ions and a Hofmeister series of anions. Based on the different interactions between these ions and polyelectrolytes, the salts present different effects on the properties of PECs. Salt effects on coacervate, especially coacervate stability, are summarized in Chapter III. Chapter IV shows the study of salt effects on the properties of PEMs including the growth and swelling/deswelling behaviors. In Chapter V, the effects of salt and pH on the self-healing ability of bulk PEC materials were studied. The rheological properties of hydrated, bulk PEC material are strongly influenced by salt and pH treatment, which directly controls the crosslink density in the material, chain mobility, and therefore self-healing ability. Alkali metal ions and transition metal ions show different effects on the self-healing ability of the BPEI/PAA complex. The effects of these two different types of salts on complex are reversible, which presents a possible way to control the material properties, ranging from self-healing to completely unable to do so. Due to changes in charge density of weak polyelectrolytes in response to pH, the self-healing of weak PECs can be enhanced by pH treatment as well. In Chapter VI, the effects of ethanol on the complexation of polyelectrolytes, rheological properties and structure of polyelectrolyte precipitates were investigated. The complexation of polyelectrolytes is inhibited by the presence of ethanol due to the weakening interactions between polycation and polyanion under low dielectric constant environment. For the polyelectrolyte precipitate formed from higher ethanol content mixture, the precipitate shows a smaller modulus and larger loss angle. In comparison, by immersing polyelectrolyte precipitate in a higher ethanol content mixture, the precipitate shows an increased modulus. This enhancement of mechanical properties is mainly due to the dehydration of the polyelectrolyte precipitate, which results in an enhanced interaction between BPEI and PAA (lowering the dielectric constant surrounding ion pairs strengthens them). The precipitate formed from high ethanol content mixture (vol% of ethanol > ~ 40%) can be dissolved in water to form a highly viscous polyelectrolyte coacervate, which shows potential applications in 3D printing under ethanol. In Chapter VII, electrophoretic deposition (EPD) was used to fabricate polyelectrolyte complex films, and it was shown to create thicker films than those created by the simple deposition of polyelectrolyte complexes in the absence of external electrical fields. A pulsed EPD with controlled pulse ON time and pulse OFF times can effectively suppress the formation of these bubbles. The mobility and zeta potential of BPEI/PAA complexes are modulated by the ratio of BPEI to PAA and pH of complexes, which will affect the thickness of deposited complex film. Regardless of different pulsed mode, by changing the electric field strength, the maximum thickness of BPEI/PAA complex film is obtained at a moderate electric field strength. High electric field strength will result in the dissolution of BPEI/PAA complexes due to formation of air bubbles and the high pH environment near the working electrode. In contrast, by using strong polyelectrolyte complex pair, PDAC/PSS, a proportional relationship between the thickness of complex film and electric field strength is observed. Therefore, the local pH change near working electrode is an important factor in the deposition of weak polyelectrolyte pairs. Moreover, ionic strength of the complex solution influences the charge density and stability of BPEI/PAA polyelectrolyte complexes. This work also shows the fabrication of polyelectrolyte complex-dye films using EPD. The loading of dye in complex films can be enhanced using proper EPD method.