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Abstract: Over the past two decades, nanocarriers prepared through ionic crosslinking of polyelectrolytes have been explored in a wide range of applications, including drug delivery, medical imaging and food science. The design and use of these materials require control over their size distributions, stability, and payload uptake and release properties. To this end, we focus on recent progress made towards understanding the physical and colloid chemistry underlying the formation and properties of ionically crosslinked nanocarriers and provide commentary on some unresolved problems. [Copyright &y& Elsevier]

Mixtures of polyelectrolytes andmultivalent counterions can self-assembleinto colloidal complexes. These complexes attract widespread interestin applications such as medicine, household product formulations,and separation processes. To facilitate the development of these colloidaldispersions, we examined isothermal titration calorimetry (ITC) asan automated screening tool for identifying the polymer and multivalentcounterion compositions that (1) form ionically cross-linked colloidalcomplexes and (2) lead to their rapid coagulation (and macroscopicphase separation). By studying various polyelectrolyte/multivalentcounterion mixtures, we have identified and generalized the featuresin the ITC data that indicate colloidal complex formation and coagulation.The limitations of this calorimetric screening method were also elucidated.These analyses suggest that ITC can be effective for screening theshort-term colloidal behavior of polyelectrolyte/multivalent counterionmixtures but are unreliable in revealing their long-term (equilibrium)properties. [ABSTRACT FROM AUTHOR]

Mixtures of oppositely charged surfactants and polyelectrolytes self-assemble into a variety of nanostructured complexes. With the view of developing simpler and cleaner alternatives to synthetic nanomaterials, self-assembled nanostructures can be prepared from bioderived surfactant/polyelectrolyte mixtures. These complexes can be designed to vary their phase behavior and structure in response to external stimuli, and are simpler and cleaner to prepare than conventional synthetic copolymers (e.g., block or graft). Yet, some potential applications of surfactant/polyelectrolyte complexes are limited by their lower stability. Here, we overcome this limitation by covalently coupling the surfactant head group to the polymer chain. Visual observations and small-angle X-ray scattering (SAXS) reveal that covalent coupling dramatically improves stability at both the macroscopic and mesoscopic lengthscales. This suggests that, through covalent conjugation, stability of nanostructured surfactant/biopolymer complexes can be made to rival that of synthetic copolymers, thereby extending their use to applications that require long-lasting nanostructured materials. [ABSTRACT FROM AUTHOR]

Stimulus-responsive polyelectrolyte particles are used in a wide array of scientific and technological applications, such as foods, personal care products, pharmaceutics, and separation processes. Depending on their method of preparation, they range from tens of nanometers to millimeters in size, assume a variety of morphologies, and respond to a range of external stimuli. Despite their broad utility, however, literature describing their preparation and properties remains fragmented. To this end, this article presents a broad and unifying review on their formation and properties. Specifically, it surveys the molecular mechanisms by which polyelectrolytes associate and methods by which their assemblies are shaped into particulate matter. It also discusses how particle properties can be tuned by varying their preparation methods and the molecular properties of their constituents, and review some of their applications. [ABSTRACT FROM AUTHOR]

Abstract: Mixtures of oppositely charged surfactants and polyelectrolytes are commonplace in household products, whose performance depends on surfactant/polyelectrolyte binding. Many of these formulations contain multiple surfactant species. Although polyelectrolyte interactions with ionic/nonionic surfactant mixtures have been characterized in detail, literature on polyelectrolyte interactions with mixtures of anionic or cationic surfactants remains limited. To address this, we used UV–vis spectroscopy and gel swelling experiments to study the competitive binding of two anionic surfactants, sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS), to a cationically derivatized hydroxyethyl cellulose gel (JR-125TM). Because SDBS absorbs UV radiation and SDS does not, UV–vis spectroscopy allowed the effect of SDS on the SDBS binding to be elucidated. The competitive binding of SDBS and SDS to the gel was modeled using a simple, two-species Langmuir isotherm, which yielded fair agreement with the experimental data. Additionally, to address the need for effective separation processes, we demonstrated the use of cationic hydroxyethyl cellulose gels in the removal (and recovery) of surfactants from water. This revealed that densely-crosslinked polyelectrolyte gels are advantageous for surfactant removal because they: (1) increase the surfactant/polyelectrolyte binding strength, and (2) increase the binding capacity of the gel by reducing swelling. The gel-bound surfactant can be recovered and recycled by extraction into a 50/50 water/ethanol mixture. [ABSTRACT FROM AUTHOR]

Underwater adhesion has numerouspotential medical, household,and industrial applications. It is typically achieved through covalentpolymerization and cross-linking reactions and/or the use of highlyspecialized biological or biomimetic polymers. As a simpler alternativeto these covalent and biomimetic strategies, this article shows thatstiff, gel-like complexes that adhere to various substrates underwater can also be prepared through the ionic cross-linking of common,commercial polyelectrolytes. The gels form spontaneously when syntheticpolycations, such as poly(allylamine) (PAH), are mixed with stronglybinding multivalent anions, pyrophosphate (PPi) and tripolyphosphate(TPP). The PAH/PPi and PAH/TPP gels exhibit very high storage moduli(G∞′≈ 400 kPa), self-heal when torn,and adhere to both hydrophilic and hydrophobic substrates under water(with short-term tensile adhesion strengths of 350–450 kPa).Furthermore, these gels can be dissolved on demand (if adhesion needsto be reversed) by changing the ambient pH, which controls the ionizationstate of the polyelectrolyte and ionic cross-linker. These propertiessuggest that synthetic polycations cross-linked with PPi and TPP ionscould provide a simple, inexpensive, and scalable platform for underwateradhesion. [ABSTRACT FROM AUTHOR]

When oppositely-charged polymers are mixed in water they self-assemble into polyelectrolyte complexes (PECs). These complexes have numerous technological applications that require control over their shape. To this end, we show how PEC geometry can be tailored through photodirected assembly. A commonly-used weak polycation, poly(allylamine) (PAH), was co-dissolved in a basic solution (significantly above its effective pKa) with a commonly-used polyanion, poly(styrene sulfonate) (PSS), and a photoacid generator (diphenyliodonium nitrate). The solution was then irradiated with UV light through photomasks to spatially control the protonation (and therefore the ionization) of PAH. The ionization resulted in the formation of insoluble PECs, whose shapes were predictably tuned by varying the photoirradiation pattern. Also analyzed were the phase behavior of PAH/PSS/diphenyliodonium nitrate mixtures, and the kinetics and spatial resolution limits of their photodirected assembly. This revealed that pH-mediated photodirected assembly works well for macroscopic structures (i.e., larger than about a millimeter in size), but is impeded by ion diffusion when smaller irradiation sites are used. [ABSTRACT FROM AUTHOR]