Application overview

Changes in the chemical composition of the Langmuir film, including:

• Chemical composition of thin films: Chemical composition can be detected from thin films that are just one molecule thick.
• Adsorption/desorption and surface reactions in mono- and multilayers:  Studying interaction of biomolecules using cell membrane models can provide the means to understand reactions related to drug delivery and the membrane behavior itself. These kinds of model systems are employed in several application areas, such as drug development, food technology, and biological and biochemical research.
• Hydration/hydrogen bonding: The PM-IRRAS peak position shifts dramatically when the hydration stage changes. This allows the observation of a film’s structural response due to changing external condition such as pH or temperature.
• Presence of functionalized nanoparticles: In multi-component Langmuir films, the presence of functionalized nanoparticles can be examined both at air-water interfaces and after deposition at air-solid interfaces to verify their presence and chemical activity in the films.

Changes in the molecular orientation in the Langmuir film, including:

• Molecular-scale quantitative analysis of molecular orientation: The orientation changes of molecules at the air-water interface or at reflective solids can be detected from the PM-IRRAS peak intensity. This enables, for example, observation of the effect of Langmuir film packing density as well as Langmuir Blodgett coating orientation.
• Phase transitions in thin films. Monolayer phase transitions can be detected with PM-IRRAS. A typical example would be protein denaturation at the interface or deposited layer.

 Features & benefits

• KSV NIMA PM-IRRAS is based on the polarization modulation IR absorption technology that makes it possible to characterize both chemical composition and molecular orientation of even single-molecule thin layers.
• Specifically designed for Langmuir film characterization the system features easy integration with KSV NIMA L & LB Troughs enabling characterization with controlled surface pressure and molecular packing. KSV NIMA PM-IRRAS is suitable for characterizing both floating monolayers on the liquid surface and nanoscale solid surfaces.
• The instrument has a user-friendly and open design with simple angle (40°-90°) and height adjustments. It takes only minutes to setup an experiment and it is  easy to combine with an external UV light source, heater or other complementary equipment.
• The polarization modula­tion method eliminates background signals from environmental factors such as water vapor and CO₂. There is no need for protective gasses or having the optical part of the FTIR spectrometer in a vacuum. It also allows longer measurement times, because changes in light source intensities or water surface height do not affect the final spectrum.
• The capability to perform transmission measurements.

 Product details

KSV NIMA PM-IRRAS is a state-of-the-art compact Fourier Transform IR-spectrometer. By positioning the spectrometer and detector on a goniometer above the surface the experimental setup is greatly simplified and provides results within minutes instead of days as in traditional IRRAS systems. The open design allows combined use of other comple­mentary equipment such as external UV light sources and heating. The instrument can be positioned above a fully equipped analytical KSV NIMA Langmuir Trough, facilitating accurate monolayer studies without restrictions.

PM-IRRAS technology allows the measurement of surface specific FT-IR spectra in materials by recording the differences in the reflection of p- and s-polarized light from interfaces enabling detection of chemical compositions and molecular orientation from interfacial films down to films one molecule thick.

For more information about the technology, see:

• PM-IRRAS (FTIR Reflection Spectroscopy)

Reflectance measurement

In reflectance measurement mode the instrument delivers infrared spec­tra from an air-water interface or IR-reflective surface. The air-liquid measurement allows observation of any changes in thin film func­tional groups at the interface. This can be due to structural changes caused by chemical reaction, phase transition or other phenomena. With IR-reflective samples the s-polarization
disappears and allows direct ac­cess to molecular orientation of the coating. Due to the open design, polymerization reactions on solid surfaces initiated with temperature or UV- light can be easily performed.

Transmittance measurements

Traditional transmittance measurements, such as the study of KBr pel­lets, are possible due to the flexibility of the goniometer. Measuring non-modulated polarized or non-polarized IRRAS is also possible by turning off polarization.

 Application examples

Polarization modulated infrared spectroscopy of thin films at the nanometer scale

PM-IRRAS is an excellent method for FT-IR experi­ments of nanometer scale thin films. It was possible to acquire FT-IR spectrums of films of around 2 nm thick, and also deduce molecular orientation from the experiments. Linear correlation between LB layer number and peak intensities was discovered. This demonstrates that the KSV NIMA PM-IRRAS is a powerful tool for thin film charac­terization and analysis. The measurements are fast and simple to perform thanks to KSV NIMA PM-IRRAS unique design.

For more information, see:

• Application Note 2 — Polarization Modulated Infrared Spectroscopy of Thin Films at the Nanometer Scale

PM-IRRAS spectra of SA Langmuir-Blodgett films of increasing thickness on gold at (A) pH 2 and (B) pH 6 in the C-H stretch region.

Real-time PM-IRRAS study of ultra-thin film photopolymerization

Polymerization kinetics were calculated for ultrathin layers of monomers by using data from PM-IRRAS measurements. In this study it was shown that the obtained kinetic data could be placed in the regular exponential growth equation of polymerization and that it
was possible to obtain the activation energy for the epoxy polym­erization that corresponded well with known values. The bleaching of porphyrin can also be monitored with the method and it was shown that a polymerized layer bleached slower than a polymerized one.