Synthesis of polycationic nanoparticles for microbial inhibition and killing.

Antimicrobial polymers (AMP) appear to be a promising candidate to deal with the current scenario of bacterial resistance against conventional drugs and antibiotics as they mainly depend on disrupting the bacterial membrane. This work investigates the effect of polycations bearing aromatic and aliphatic pendant cationic groups on the antimicrobial performance of AMP. A radical polymerization strategy was adopted to synthesize two different copolymers and convert them into polycations upon post-modification. Polyelectrolytes were converted into nanoparticles by nanoprecipitation and named PE1 and PE2. Polymers were analyzed by NMR, FT-IR, and gel permeation chromatography (GPC). PE1 and PE2 nanoparticles were uniform, spherical particles from FESEM, size, and zeta potential measurements. The antimicrobial properties of polyelectrolytes were determined against pathogenic Escherichia coli (E. coli), Bacillus Subtilis (B. Subtilis), Bacillus Amyloliquefaciens (B. Amyloliquefaciens) and Citrobecter Freundii (C. Freundii) bacterias. The biocidal activity determination studies showed that polyelectrolyte PE2 with aromatic pendant units outperformed PE1 with the aliphatic pendant group. This work highlights the remarkable effect of aromatic segmentation, which provides microbial inhibition, and killing is demonstrated as an antibacterial surface coating.

Alkyl-chain-grafted hexagonal boron nitride nanoplatelets as oil-dispersible additives for friction and wear reduction.

Hexagonal boron nitride (h-BN), an isoelectric analogous to graphene multilayer, can easily shear at the contact interfaces and exhibits excellent mechanical strength, higher thermal stability, and resistance toward oxidation, which makes it a promising material for potential lubricant applications. However, the poor dispersibility of h-BN in lube base oil has been a major obstacle. Herein, h-BN powder was exfoliated into h-BN nanoplatelets (h-BNNPs), and then long alkyl chains were chemically grafted, targeting the basal plane defect and edge sites of h-BNNPs. The chemical and structural features of octadecyltriethoxysilane-functionalized h-BNNPs (h-BNNPs-ODTES) were studied by FTIR, XPS, XRD, HRTEM, and TGA analyses. The h-BNNPs-ODTES exhibit long-term dispersion stability in synthetic polyol ester lube base oil because of van der Waals interaction between the octadecyl chains of h-BNNPs-ODTES and alkyl functionalities of polyol ester. Micro- and macrotribology results showed that h-BNNPs-ODTES, as an additive to synthetic polyol ester, significantly reduced both the friction and wear of steel disks. Elemental mapping of the worn area explicitly demonstrates the transfer of h-BNNPs-ODTES on the contact interfaces. Furthermore, insight into the lubrication mechanism for reduction in both friction and wear is deduced based on the experimental results.