A Study of the Buffer Capacity of Polyelectrolyte Microcapsules Depending on Their Ionic Environment and Incubation Temperature

The Buffer Capacity of Polyelectrolyte Microcapsules Depends on the Type of Template

One of the key physicochemical parameters of polyelectrolyte microcapsules (PMCs) is their buffer capacity (BC). The BC of the microcapsules allows for an assessment of the change in protonation state across the entire polyelectrolyte system, which directly impacts the buffer barrier of PMCs, as well as the stability and physical properties of their shell. However, the buffer capacity of PMCs and their behavior under changes in ionic strength and temperature can differ depending on the type of core used to form the microcapsules. As part of this study, we revealed the buffer capacity (BC) of polyelectrolyte microcapsules formed on polystyrene cores (PMCPs) and studied the influence of ionic strength and environmental temperature on the BC of these capsules. We found that the buffer capacity of PMCPs differs from the BC of water at a pH above 8; the addition of sodium chloride leads to an increase in buffer capacity in alkaline conditions, and conversely, thermal treatment leads to its decrease at a pH of 9. The results obtained are different from the BC of polyelectrolyte microcapsules formed on CaCO3 cores, which suggests a difference in the physicochemical properties of these types of capsules. The buffer capacity of polyelectrolyte microcapsules depends on the type of template used.

Sorption of Salts of Various Metals by Polyelectrolyte Microcapsules

Anthropogenic activity negatively affects the environment by polluting it with the salts of various metals. One of the ways to reduce this influence is to use water purification methods for the salts of various metals. Water purification methods based on nanomaterials are promising. In this regard, we proposed to study polyelectrolyte microcapsules (PMC) as a promising sorption agent for the salts of various metals. It was found that the polystyrene sulfonate-polyallylamine (PSS-PAH) polyelectrolyte complex and polyelectrolyte microcapsules of different compositions are not able to adsorb salts CuSO₄, Pb(NO)₃, FeCl₃, and CuCl₂. At the same time, it was found that all types of capsules, except for (PSS/PAH)₂/PSS, are capable of sorbing about 420 µg of K₃[Fe(CN)₆] and about 500 µg of K₄[Fe(CN)₆] from solution. The adsorption of polyelectrolyte microcapsules has an electrostatic nature which is confirmed by increases in the sorption capacity of PMC of K₃[Fe(CN)₆] and K₄[Fe(CN)₆] with decreases in the pH of the solution. Also, It was confirmed that the sorption process of PMC of K₃[Fe(CN)₆] and K₄[Fe(CN)₆] is concentration dependent and has the limitation of the number of binding sites.

Short-Term Stability of Electrochemical Properties of Layer-by-Layer Coated Heterogeneous Ion Exchange Membranes

Layer-by-layer adsorption allows the creation of versatile functional coatings for ion exchange membranes, but the stability of the coating and resulting properties of modified membranes in their operation is a frequently asked question. This paper examines the changes in voltammetric curves of layer-by-layer coated cation exchange membranes and pH-metry of desalination chamber with a studied membrane and an auxiliary anion exchange membrane after short-term tests, including over-limiting current modes. The practical operation of the membranes did not affect the voltammetric curves, but enhanced the generation of H⁺ and OH^- ions in a system with polyethylenimine modified membrane in Ca²⁺ containing solution. It is shown that a distinction between the voltammetric curves of the membranes modified and the different polyamines persists during the operation and that, in the case of polyethylenimine, there is an additional zone of growth of potential drop in voltammetric curves and stronger generation of H⁺ and OH^- ions as indicated by pH-metry.

A Study of the Buffer Capacity of Polyelectrolyte Microcapsules Depending on Their Concentration and the Number of Layers of the Polyelectrolyte Shell

Polyelectrolyte microcapsules are used in the development of new forms of targeted delivery systems, self-healing materials, sensors, and smart materials. Nevertheless, their buffer capacity has not been practically studied, although that characteristic makes it possible to estimate the change in the state of protonation of the entire polyelectrolyte system. This is necessary both for creating a buffer barrier system for pH-sensitive compounds (metals, enzymes, polyelectrolytes, drugs) and for the correct interpretation of the results of research and studying of the PMC structure. The buffer capacity of a PMC can be affected by the concentration of microcapsules in solution and the number of shell layers since the listed parameters affect other physicochemical properties of the PMC shell. This includes, for example, the electrical conductivity, permeability (of ions), osmotic pressure, charge density, etc. In this regard, we studied the change in the buffer capacity of polyelectrolyte microcapsules depending on their concentration and the number of shell layers. As a result, it was found that with an increasing concentration of microcapsules, the buffering capacity of the PMC increases, but at the same time, in the pH range from 4 to 5.5, the calculated buffering capacity of 1 billion capsules decreases with increasing their concentration. This effect may be associated with a decrease in the available -NH2 groups of the PMC’s shell. In addition, it was found that the main contribution to the buffer capacity of a PMC is made by the entire shell of the microcapsule and not just its surface. At the same time, the buffer capacity of the capsules has non-linear growth with an increase in the number of PMC shell layers. It is presumably associated either with a decrease in the polyelectrolyte layer with an increase in their number or with a decrease in the permeability of hydrogen protons.