Development of pendant drop mechanical analysis as a technique for determining the stress-relaxation and water-permeation properties of interfacially polymerized barrier layers

Effects of the Substrate on Interfacial Polymerization: Tuning the Hydrophobicity via Polyelectrolyte Deposition

Interfacial polymerization (IP) has been the key method for the fabrication of the thin film composite (TFC) membranes that are extensively employed in reverse osmosis (RO) and forward osmosis (FO). However, the role of the substrate surface hydrophilicity in the formation of the IP-film remains a controversial issue to be further addressed. This study characterized the IP films formed on a series of polyacrylonitrile (PAN) substrates whose hydrophilicities (from ~38 to ~93 degrees) were varied via different approaches, including the alkaline treatment and the deposition of various polycations. It was revealed that delamination could occur when the IP film was formed on a relatively hydrophilic surface; the integrity of the TFC membranes was substantially improved, owing to the modification of the polyelectrolyte deposition. On the other hand, the characterization indicated that the TFC membrane could have an enhanced efficiency (with a factor of ~2) when the substrate was relatively hydrophilic. It was established that the polyelectrolyte deposition could be exploited to effectively tune the substrate surface hydrophobicity, thereby providing more degrees of freedom for the optimization of the TFC membranes fabrication.

Evaluation of non-traditional visualization methods to detect surface attachment of biofilms

In food safety and food quality, biofilm research is of great importance for mitigating food-borne pathogens in food processing environments. To supplement the traditional staining techniques for biofilm characterization, we introduce several non-traditional imaging methods for detecting biofilm attachment to the solid-liquid and air-liquid interfaces. For strains of Pseudomonas aeruginosa (the positive control), Acinetobacter baumanii, Listeria monocytogenes and Salmonella enterica, the traditional crystal violet assay showed evidence of biofilm attachment to the well plate base as well as inferred the presence of an air-liquid biofilm attached on the upper well walls where the meniscus was present. However, air-liquid biofilms and solid-surface-attached biofilms were not detected for all of these strains using the non-traditional imaging methods. For L. monocytogenes, we were unable to detect biofilms at a particle-laden, air-liquid interface as evidenced through microscopy, which contradicts the meniscus staining test and suggests that the coffee-ring effect may lead to false positives when using meniscus staining. Furthermore, when L. monocytogenes was cultivated in a pendant droplet in air, only microbial sediment at the droplet apex was observed without any apparent bacterial colonization of the droplet surface. All other strains showed clear evidence of air-liquid biofilms at the air-liquid interface of a pendant droplet. To non-invasively detect if and when air-liquid pellicles form in a well plate, we also present a novel in situ reflection assay that demonstrates the capacity to do this quantitatively.

Time-dependent FTIR microscopy for mechanism investigations and kinetic measurements in interfacial polymerisation: a microporous polymer film study

The real-time characterisation of interfacial polymerization is demonstrated by using FTIR-mapping spectroscopy with microscopy to deduce the reaction kinetics.