Use of Polyguanidine-Derivatives-Based Biocides for Microbial Growth Inhibition and for the Development of a Novel Polyethylene-Based Composite Material Resistant to the Formation of Multispecies Microbial Biofilms

This study aimed to investigate the dependence of the biocidal activity of polyguanidine (co)polymers on their structure during the formation of biofilms by active PE-degrading cultures of model microorganisms. The Bc-2 copolymer of methacryloyl guanidine hydrochloride (MGHC) and diallyldimethylammonium chloride (DADMAC), which suppressed both the formation of biofilms and the growth of planktonic cultures, exhibited the highest activity. When PE was exposed in tropical soil, the composition of the microbial community on the PE surface differed significantly from that of the community in the surrounding soil. In particular, the proportion of Actinobacteria increased from 7% to 29%, while the proportion of Bacteroidetes decreased from 38% to 8%. Keywords: biofilms, polyhexamethylene guanidine salts, dynamics of biofilm formation, antibiofilm effect, composite materials

Cyclic Methacrylate Tetrahydropyrimidinones: Synthesis, Properties, (Co)Polymerization

During radical polymerization of novel biocidal methacrylate guanidine monomers, a cyclic byproduct was discovered and identified as 2-imino-5-methyltetrahydropyrimidin-4(1H)-one (THP). Its methacrylate salt (MTHP) was synthesized and characterized via 1H and 13C NMR and pyrolysis chromatography. Synthesis conditions of both THP and MTHP were optimized to high yields, and both MTHP homopolymerization (in aqua) and copolymerization with diallyldimethylammonium chloride (in aqua in salt form) were successfully carried out with middle to high yields, providing a promising platform for potential tailored biocide polymers.

Interfacial Behavior of Solid- and Liquid-like Polyelectrolyte Complexes as a Function of Charge Stoichiometry

We systematically investigate in this work the surface activity of polyelectrolyte complex (PECs) suspensions as a function of the molar charge ratio Z (= [-]/[+]) from two model systems: the weakly and strongly interacting poly (diallyldimethylammonium chloride)/poly (acrylic acid sodium salt) (PDADMAC/PANa) and poly (diallyldimethylammonium chloride)/poly (sodium 4- styrenesulfonate) (PDADMAC/PSSNa) pairs, respectively. For both systems, the PEC surface tension decreases as the system approaches charge stoichiometry (Z = 1) whenever the complexation occurs in the presence of excess PDADMAC (Z < 1) or excess polyanion (Z > 1) consistent with an increased level of charge neutralization of PEs forming increasingly hydrophobic and neutral surface-active species. The behavior at stoichiometry (Z = 1) is also particularly informative about the physical nature of the complexes. The PDADMAC/PANa system undergoes a liquid–liquid phase transition through the formation of coacervate microdroplets in equilibrium with macroions remaining in solution. In the PDADMAC/PSSNa system, the surface tension of the supernatant was close to that of pure water, suggesting that the PSSNa-based complexes have completely sedimented, consistent with a complete liquid–solid phase separation of an out-of-equilibrium system. Besides, the high sensitivity of surface tension measurements, which can detect the presence of trace amounts of aggregates and other precursors in the supernatant, allows for very accurate determination of the exact charge stoichiometry of the complexes. Finally, the very low water/water interfacial tension that develops between the dilute phase and the denser coacervate phase in the PDADAMAC/PANa system was measured using the generalized Young–Laplace method to complete the full characterization of both systems. The overall study showed that simple surface tension measurements can be a very sensitive tool to characterize, discriminate, and better understand the formation mechanism of the different structures encountered during the formation of PECs.

Pattern Formation upon Evaporation of Sessile Droplets of Polyelectrolyte/Surfactant Mixtures on Silicon Wafers

The formation of coffee-ring deposits upon evaporation of sessile droplets containing mixtures of poly(diallyldimethylammonium chloride) (PDADMAC) and two different anionic surfactants were studied. This process is driven by the Marangoni stresses resulting from the formation of surface-active polyelectrolyte–surfactant complexes in solution and the salt arising from the release of counterions. The morphologies of the deposits appear to be dependent on the surfactant concentration, independent of their chemical nature, and consist of a peripheral coffee ring composed of PDADMAC and PDADMAC–surfactant complexes, and a secondary region of dendrite-like structures of pure NaCl at the interior of the residue formed at the end of the evaporation. This is compatible with a hydrodynamic flow associated with the Marangoni stress from the apex of the drop to the three-phase contact line for those cases in which the concentration of the complexes dominates the surface tension, whereas it is reversed when most of the PDADMAC and the complexes have been deposited at the rim and the bulk contains mainly salt.

ZrO2 Nanoparticles and Poly(diallyldimethylammonium chloride)-Doped Graphene Oxide Aerogel-Coated Stainless-Steel Mesh for the Effective Adsorption of Organophosphorus Pesticides

A novel sorbent based on the ZrO2 nanoparticles and poly(diallyldimethylammonium chloride)-modified graphene oxide aerogel-grafted stainless steel mesh (ZrO2/PDDA-GOA-SSM) was used for the extraction and detection of organophosphorus pesticides (OPPs). Firstly, the PDDA and GO composite was grafted onto the surface of SSM and then freeze-dried to obtain the aerogel, which efficiently reduced the accumulation of graphene nanosheets. It integrated the advanced properties of GOA with a thin coating and the three-dimensional structural geometry of SSM. The modification of ZrO2 nanoparticles brought a selective adsorption for OPPs due to the combination of the phosphate group as a Lewis base and ZrO2 nanoparticles with the Lewis acid site. The ZrO2/PDDA-GOA-SSM was packed into the solid-phase extraction (SPE) cartridge to extract OPPs. According to the investigation of different factors, the extraction recovery was mainly affected by the hydrophilic-hydrophobic properties of analytes. Effective extraction and elution parameters such as sample volume, sample pH, rate of sample loading, eluent, and eluent volume, were also investigated and discussed. Under the optimal conditions, the linearity of phoxim and fenitrothion was in the range of 1.0–200 μg L−1, and the linearity of temephos was in the range of 2.5–200 μg L−1. The limits of detection were ranged from 0.2 to 1.0 μg L−1. This established method was successfully applied to detect OPPs in two vegetables. There was no OPP detected in real samples, and results showed that the matrix effects were in the range of 46.5%–90.1%. This indicates that the ZrO2/PDDA-GOA-SSM-SPE-HPLC method could effectively extract and detect OPPs in vegetables.