The mechanical properties of interfaces separating two immiscible fluids have a substantial influence on the dynamics of numerous in vivo and industrial systems such as cells, lung alveoli, emulsions, and foams. Since the ability of complex interfaces to withstand stresses can govern the macroscopic behavior of such systems, an instrument allowing for the quantification of the interfacial shear dynamic moduli (viscous and elastic modulus) is an excellent tool to study this kind of materials.

In this webinar, we are discussing the fundamentals and functionalities of the ISR Flip. We are explaining the physics of the instrument, where a mobile magnetic trap along with a magnetic needle is used to impose a controlled shear deformation on a given interface. The acquisition of the raw data and the integrated method of analysis is discussed too, which will allow us to enumerate the main benefits of this technology. Then, we are paying attention to how the instrument should be operated, from the calibration procedure to the use of different operation modes. In the final part of the webinar, we are sharing some recent results on the rheological characterization of Langmuir monolayers.

The development of nanostructured materials based on the self-assembly of simple constituents mediated by wet chemistry methods has been demonstrated to be an efficient and scalable bottom-up strategy. A particularly versatile approach is the use of spherical nanoparticles as building blocks. The existence of well-established synthesis methods to obtain monodisperse batches using a disparity of materials, combined with the inherent tendency of spheres to self-assemble into ordered 2D or 3D lattices, has resulted in a wealth of examples where, depending on the size, material, and surface structure and chemistry, nanoparticles have been employed to build photonic materials, functional
substrates, or biosensors, just to name a few.

Among the different methods that have been proposed to control the self-assembly of nanoparticles, Langmuir–Blodgett (LB) deposition stands out. Originally developed for the transfer of insoluble surfactants previously organized at the water/air interface, its use has been extended to the deposition of supramolecular entities and hard nanomaterials.

Structured thin films such as ordered monolayers or multilayers of nanoparticles are particularly well-suited to be prepared by the LB technique, and have been employed for the preparation of photonic materials or as templates to improve the tribological properties of substrates. Additionally, noble metal nanoparticles are widely used in biosensing thanks to their plasmon resonance that enhances scattered signals of adsorbed biomolecules. Raman spectroscopy is one of the most used for molecule identification and Surface-Enhanced Raman Scattering (SERS) leverages the plasmonic effects to increase by orders of magnitude the efficiency of an otherwise very inefficient process.

Langmuir monolayer (LM) at the air-water (A/W) interface can mimic a classical two dimensional system. It is essential to have amphiphilic molecules for the formation of a stable LM at the A/W interface. However, there are several purely hydrophobic materials which can form a stable LM at the A/W interface. In this talk, the LM and Langmuir-Blodgett films of some interesting technologically important hydrophobic materials will be discussed.

Sustainable and environment benign materials are the core attention in research for next generation applications. Cellulose nanofiber (CNF) is a green material obtain from biomass is a unique choice owing to its earth abundance, biodegradability and nontoxicity¹. Chemically, it is composed of a repeating unit with two anhydroglucose ring connected with a glycosidic linkage between C₁ and C₄ carbon (figure 1(a)). In the plant cell wall, cellulose nanofibers (CNF) are the main component of multiple cellulose chain. They have thickness 3-4 nm and length in several microns². In this study, cellulose nanofiber (CNF) nanosheets were developed by Langmuir–Blodgett (LB) technique. The CNF was obtained from sulfuric acid hydrolysis of commercially available microfibrillated cellulose. The sulfate-grafted negatively charged needle like CNF maintained at the air–water interface, assisted by amphiphilic polymer, poly(N-dodecyl acrylamide) (pDDA) (figure 1(b)). The CNF produced a stable monolayer and the surface pressure increased steadily with a high collapse pressure of 50 mNm^-1 when spread with formic acid and pDDA. The composite monolayers were transferred onto solid substrates as Y-type LB films using a vertical dipping method. The transfer ratio of the films was unity and 0.85 for upstroke and downstroke respectively, indicating that full coverage was achieved by the monolayer even for more than 200 layers. The various spectroscopic and microscopic studies reveal that CNF nanosheets possess well-defined layer structure with average monolayer thickness of 5.3 nm. The nanosheets were optically transparent to visible light and exhibited hydrophobicity³. Robust and free standing nanosheets were possible with this technique which produced the thinnest CNF film so far.

Join Susanna Laurén for a one-hour practical training on Langmuir and Langmuir-Blodgett films. The training is for those at the beginning of their Langmuir and Langmuir-Blodgett journey, to get a head start on the experiments. During the training, Susanna will go through the most important steps of the experiment, starting from the cleaning of the trough and spreading of the monolayer to isotherm formation and deposition. After the training session, you will have a chance to ask questions.

Carbonaceous and silica particles are accounted as the most common pollutants in the modern. This makes necessary a careful examination of their potential effect on lipid membranes, e.g. tear films, lung surfactant or skin. This work proposes to analyze the impact of different types particles on Langmuir monolayers of 1,2-Dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and a commercial lung surfactant preparation as first step for understanding the potential toxicity of this type of pollutants on human health. For this purpose, the effect of the particles on the ability for reducing the surface tension upon static and dynamics condition was explored due to the importance of the surface tension reduction on the physiological performance of lipid membranes. The results show that the insertion of particle into the lipid film results in an exclude area-like effect which modifies the cohesion and packing of the molecules, which in turn reduces the ability of the lipid film to reduce the surface tension.  Furthermore, the analysis of the response of the systems against mechanical stresses evidenced a worsening of the performance of the lipid layers, which may alter both their functional and structural roles. It is expected that these results can contribute to deepen on the understanding of the potential toxicological effects of the air pollution on the physiological performance of cellular barriers and biofluids.

Matthew Paige completed a PhD in chemistry at the University of Toronto in the field of protein aggregation and a postdoctoral fellowship at Stanford University studying single-molecule fluorescence spectroscopy.  He joined the Department of Chemistry at the University of Saskatchewan as a faculty member.  He is currently the Thorvaldson Professor and serves as Department Head.  The University of Saskatchewan is located on Treaty 6 Territory and the homeland of the Métis. 

We will present the main results of the group where we use Langmuir monolayer to investigate the action of drugs and other bioactive compounds in lipidic interfaces that mimic the first barrier that drug finds to enter the cell. Also, we will present the assembly of nanostructures based on enzymes and adjuvants (carbonaceous materials, nanoparticles, etc.) formed by means of the LB technique.