Environmentally responsive polyelectrolytes

The first section of Part One provides a detailed overview of switchable and responsive materials, exploring thermoresponsive polymers (Chapter 1), environmentally responsive polyelectrolytes and zwitterionic polymers (Chapter 2), peptide/protein-based natural responsive materials (Chapter 3), and photonic sensitive switchable materials (Chapter 4). 

Novel responsive controlled release systems based upon polyelectrolyte-grafted membranes have also been reported. Iwata and Matsuda prepared novel environmentally sensitive membranes by grafting poly(acrylic acid) onto poly(vinylidene fluoride) membranes [382, 383]. Under basic conditions, the... 

Another polyelectrolytes such as anionic DNA, cationic PDADMAC (data not presented) show the same effects, although they have different donor and acceptor properties. This indicates that the charge transfer mechanism is not responsible for the observed effects. The observed stabilization of QDs by PAA in aqueous solutions was used earlier [6] and explained as alteration of the environmental polarity of the QDs due to surface charge neutralization. It is obvious that such neutralization must be observed for any combination of opposite charges on QDs surface and. We observed the PL quenching instead of... 

In this chapto, we have illustrated the effects of molecular architecture of polysulfobetaines on solution behavior under specilBc environmental conditions of pH, added electrolytes, and polymer concentration. The nature of the comonomer and amount of incorporation of the sulfobetaine within the polymer chain dictate the polymer solubility and solution behavior. Polyampholyte behavior is realized for acrylamide-based systems containing the sulfobetaine moiety. Polyelectrolyte behavior is coupled with polyampholyte behavior for cyclopolymers containing >40mol% sulfobetaine. Incorporation of the sulfobetaine monomer hinders hydrophobic association for the pH responsive copolymers of series TV at low degrees of ionization. 

To create surfaces that are responsive to environmental cues, polyampholytes, polyelectrolytes, or betaine polymer coatings and/or materials must first be formed through controlled polymerization techniques. There are a number of excellent reviews on polymerization techniques (Barbey et al., 2009 Lowe McCormick, 2002 Matyjaszewski Xia, 2001), so only a brief overview of the most relevant approaches is provided here. 

The second most widely investigated environmental stimulus is salt. This stimulus includes the impacts of both salt concentration and composition and their impact on polyelectrolytes and zwitterionic polymers. In fact, many of the recent studies investigating the ability to control the properties of polyelectrolytes and zwitterionic polymers through pH have also included a component based on salt. However, it is much more challenging to take advantage of the responsiveness to salt for many biomedical applications, so most of the work has focused on one primary apphcation. 

The third environmental stimulus that has been used with polyelectrolytes and zwitterionic polymer systems is temperature. As with pH and salt, the primary temperature-induced response is a change in the conformational state of the polymer structure. The conformational state change is caused by one or more of the monomers passing through its lower critical solution temperature (LCST). This has been demonstrated in polyelectrolytes and zwitterionic polymers, where the charged monomers are responsible for the change, and in systems in which an additional temperature-sensitive monomer is included as a copolymer. 

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