Doping of salt ions within stoichiometric polyelectrolyte complex coacervates (PECs) is modeled with a theory that includes polymer ion pairing and counterion adsorption as equilibrium reactions along with Flory−Huggins free energy and electrostatic correlations that capture the effects of polyelectrolyte charge connectivity. The model shows at low salt concentration a region in which the salt content in the PEC depends linearly on the salt concentration in the (external) supernatant, consistent with the experimental observations of the Schlenoff group. We find that only in the limit of strong salt ion adsorption are all salt ions in the PEC bound to polyelectrolytes; for binding free energies up to several k B T per ion, a significant fraction of the salt ions in the PEC are free (or unbound), even at the lowest salt concentration. When the salt concentration in the supernatant is increased to higher values beyond this linear regime, the PEC strongly swells with water and free salt ions, similar to that observed experimentally. The model also predicts that the partitioning behavior of salt ions into the PEC is primarily governed by ion-specific effects, which manifest themselves in the strength of salt ion adsorption and polyelectrolyte ion-pairing, in agreement with observations of Schlenoff and co-workers. With an appropriate choice of parameters, the theory provides good agreement with experimental doping and phase behavior data in the literature.

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Overcharging in complex coacervation, in which a polyelectrolyte complex coacervate (PEC) initially containing equal moles of the cationic and anionic monomers absorbs a large excess of one type of polyelectrolyte...

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A macroscopic thermodynamics-based theory that can quantitatively describe the behavior of water confined between hydrophobic solutes has so far remained elusive. In this work, we progress toward this goal by comparing the predictions of macroscopic theory with the results from computer simulations. We have determined free energy profiles of water confined between two nanometer-sized surfaces of varying hydrophobicity using molecular simulations and have estimated thermodynamic properties such as contact angle, line tension, and size of the critical vapor tube from independent simulations. We show that the scaling of free energy barrier to evaporation is fairly well captured by the factor (D/2 + λ/ϒLV)2, where D is the confinement gap and λ/ϒLV is the ratio of line-tension and liquid–vapor surface tension. The radius of the critical vapor tube necessary for nucleating evaporation scales by the factor (D/2 + λ/ϒLV). Exclusion of the line-tension term from thermodynamic theory leads to a qualitative disagreement between theoretical predictions and results from molecular simulations. We also demonstrate that macroscopic theory that includes the line-tension term is able to quantitatively match the entire free energy profile associated with the formation of a vapor-tube inside the confined region for conditions when the vapor state is the most stable state. The match is however only qualitatively correct for the conditions when the liquid state is more stable. Overall, the conclusion is that the inclusion of line-tension in macroscopic theory is necessary to describe the behavior of water under nanoscale confinement between two hydrophobic solutes.

In order to examine allelopathic effect of Cannabis sativa L. on germination capability and seedling growth of Lactuca sativa L., a study was performed in laboratory conditions. Treatments were set up in randomised block design in four replications for each of four concentration ranges of 25, 50, 75 and 100 % of aqueous extract made of shoot parts and 4 identical extract concentrations made of root of cannabis. Control variant was lettuce seed treated by distilled water. During the studies shoot and seminal root length of lettuce seedlings were measured after treatments with different concentrations of extracts made of root and shoot parts of cannabis, and the obtained values were compared with the control. The obtained results suggest that the extract from the shoot parts of cannabis in high concentrations of 75 and 100% had inhibiting effect to the germination indices while the extract from the root had no statistically significant effect on germination of lettuce seeds. Extract made of root part of cannabis showed also stimulatory effect to shoot and seminal root length of lettuce seedlings in extract concentrations of 50, 75 and 100 %. V laboratorijskih razmerah je bil preučevan alelopatičen učinek navadne konoplje (Cannabis sativa L.) na kalitev semen in rast kalic vrtne solate (Lactuca sativa L.). Obravnavanja so bila izvedena kot naključni bločni poskus v štirih ponovitvah z vsako od štirih koncentracij, 25, 50, 75 in100 %, vodnega izvlečka poganjkov in korenin konoplje. V kontrolnem poskusu so bila semena vrtne solate tretirana na enak način z distilirano vodo. Poleg indeksa kalitve sta bili v poskusi merjeni še dolžina poganjkov in semenskih korenin kaleče solate. Rezultati so pokazali, da je imel izvleček poganjkov konoplje v večjih koncentracijah, 75 in 100 %, inhibitorni učinek na kalitveni indeks, medtemko izvlečki iz korenin niso imeli statistično značilnega vpliva na iste merjene parametre. Izvleček iz korenin konoplje je imel stimulativni učinek na dolžino poganjkov in semenskih korenin vrtne solate pri koncentracijah 50, 75 in 100 %.

We use all-atom molecular dynamics simulations to extract ΔGeff, the free energy of binding of potassium ions K+ to the partially charged polyelectrolyte poly(acrylic acid), or PAA, in dilute regimes. Upon increasing the charge fraction of PAA, the chains adopt more extended conformations, and simultaneously, potassium ions bind more strongly (i.e., with more negative ΔGeff) to the highly charged chains to relieve electrostatic repulsions between charged monomers along the chains. We compare the simulation results with the predictions of a model that describes potassium binding to PAA chains as a reversible reaction whose binding free energy (ΔGeff) is adjusted from its intrinsic value (ΔG) by electrostatic correlations, captured by a random phase approximation. The bare or intrinsic binding free energy ΔG, which is an input in the model, depends on the binding species and is obtained from the radial distribution function of K+ around the charged monomer of a singly charged, short PAA chain in dilute solutions. We find that the model yields semi-quantitative predictions for ΔGeff and the degree of potassium binding to PAA chains, α, as a function of PAA charge fraction without using fitting parameters.

We review theories of polyelectrolyte (PE) coacervation, which is the spontaneous association of oppositely charged units of PEs and phase separation into a polymerdense phase in aqueous solution. The simplest theories can be divided into "physicsbased" and "chemistry-based" approaches. In the former, PEs are treated as charged, long-chain, molecules, defined by charge level, chain length, and chain flexibility, but otherwise lacking chemical identity, with electrostatic interactions driving coacervation. The "chemistry-based" approaches focus on the local interactions between the species for which chemical identity is critical, and describe coacervation as the result of competitive local binding interactions of monomers and salts. In this article, we show how these approaches complement each other by presenting recent approaches that take both physical and chemical effects into account. Finally, we suggest future directions toward producing theories that are made quantitatively predictive by accounting for both long range electrostatic and local chemically specific interactions.