Purity of samples used for film preparation is examined with the use of a gradient HPLC system composed of two pumps Model 6000 of Waters, Millipore Corp. (Milford MA, USA) and a home made gradient controller as well as a UV-vis detector type SPD10A of Shimadzu Corp. (Tokyo, Japan) or a home made electrochemical detector. These samples are purified, if needed, by using a semi-preparative mode of this HPLC system.
Mono- and multilayer Langmuir films floating on aqueous subphase solutions are prepared and their spreading properties investigated by using a rectangular trough (see photo), type BAM 601 of Nima Technology, Ltd. (Coventry, UK). During the film compression and expansion, surface pressure and surface potential is simultaneously measured with a Nima PS-4 surface pressure sensor and an integrated 320C-H-CE non-contact voltmeter with 3250 probe of Trek, Inc. (New York, USA) working as surface potential sensor, respectively. Moreover, the film surface is continuously imaged with 2 µm lateral resolution, during the compression-expansion cycling, with a Brewster angle microscope type EP3-BAM of NFT-Nanofilm Technologie, GmbH (Göttingen, Germany). This microscope can also be used for imaging of the Langmuir-Blodgett (LB) films transferred onto solid substrates.
With a Nima D1L linear dipper, the Langmuir films are vertically transferred, by using the Langmuir-Blodgett (LB) technique, onto solid substrates, such as quartz slides, indium-tin oxide optically transparent electrodes (OTE-ITO) or highly oriented pyrolytic graphite (HOPG) specimens, or onto quartz crystal oscillators for the UV-vis spectroscopy, UV-vis spectro-electrochemistry and simultaneous electrochemical and piezoelectric microgravimetrical characterization, respectively. Moreover, the monolayer films are prepared on solid substrates by self-assembly while multilayer films by electrochemical polymerization, dip- or spin-coating, drop casting, electrochemical polymerization, or either electrophoretic or vacuum vapor deposition.
Preparation of thin films well adhering to the substrate surface requires preceding thorough cleaning of this surface. Surface cleanness is important both for transfer of the Langmuir-Blodgett films and deposition of polymer films by electropolymerization. The plasma cleaner Model ZEPTO of Diener electronic GmbH (Ebhausen, Germany) allows for this cleaning. For that, the oxygen or argon plasma is generated. Moreover, the cleaner can generate mixed plasma of two gases of defined composition.
With a Vertex 80v FT-IR spectrophotometer of Bruker (Ettlingen, Germany), equipped with the PMA50 accessory, a polarization-modulated infrared reflection-absorption spectra of the LB films and those self-assembled on the solid substrates can be measured. It is also possible to record typical transmission IR spectra of samples in KBr pellets with 0.08 cm-1 resolution.
With a Monolayer/Grazing Angle Accessory for FT-IR Spectroscopy of Graseby Specac, Ltd. (Kent, UK) the IR spectra are recorded with a 170SX FT-IR spectrometer of Nicolet (Madison, WI, USA) of either floating Langmuir films or those transferred onto solid substrates by using the LB technique.
With the UVISEL spectroscopic ellipsometer of Horiba-Jobin-Yvon (Longjumeau, France), working in the spectral range 245 to 2100 nm, thickness as well as optical parameters of single- and multilayer organic and inorganic films can be determined. With the automated sample stage it is also possible to map both sample thickness and optical properties.
A UV-vis Recording Spectrophotometer type UV2501PC of Shimadzu (Kyoto, Japan), equipped with the reflection mode, integrating sphere accessory and linear dichroism attachments, serves for the UV-vis spectroscopy and UV-vis spectro-electrochemistry studies on thin films.
For simultaneous piezoelectric microgravimetry and electrochemistry measurements electrochemical quartz crystal microbalances of the Institute of Physical Chemistry (Warsaw, Poland) are used. The 10-MHz quartz crystal oscillators serve for operation under batch (EQCM 5710) or flow-through (EQCM 5610) conditions. The EQCM 5610 microbalance features a flow-through quartz crystal holder suitable for simultaneous piezoelectric microgravimetry and electrochemical detection measurements in flow analytical techniques, such as flow injection analysis (FIA) and micro-bore column HPLC. A unique feature of the EQCM 5710 microbalance is its capability of the simultaneous voltammetric, chronoamperometric, chronocoulometric, or galvanostatic measurement and frequency or frequency changes and dynamic resistance measurement allowing thus for measurement of both mass and viscoelastic changes during an electrochemical process.
Visco-elastic properties in solutions of films and mass changes are also simultaneously examined by analyzing components of electromechanical impedance of the film-coated quartz crystal oscillators both under batch and flow-through solution conditions. For that purpose, an 8712E RF Network Analyzer of Agilent Technologies (Englewood CO, USA) is used, along with dedicated VEE software, either in a transmission (in air) or reflection (in air and in solution) mode of operation. Analysis of the visco-elastic film properties along with the film mass changes can be performed under electrochemical conditions if the Autolab electrochemistry system (see below) is connected.
For surface plasmon resonance (SPR) measurements a double-channel ESPRIT SPR instrument of Eco Chemie (Utrecht, The Netherlands) equipped with open-structure electrochemical cuvette as well as an autosampler is used. The instrument is applied for studying kinetics and thermodynamics of interactions between analytes in solutions and a receptor film. With an additional potentiostat/galvanostat, this instrument can be used for simultaneous measurements of the current and SPR signal change during typical electrochemical experiments.
Electroanalytical measurements on films are carried out with a driven by dedicated GPES 4.5 software three Autolab electrochemical systems of Eco Chemie (Utrecht, The Netherlands), equipped with cards of a PGSTAT20 potentiostat, BIPOT bipotentiostat, ECD microelectrode unit, and FRA frequency response analyzer. The latter is used for measurements of electrochemical impedance spectroscopy (EIS). Moreover, voltammetric and chronoamoperometric measurements on the films with the use of a home-made the rotating ring-disk electrode (RRDE) are performed.
Preparation of the air- and moisture-sensitive samples as well as electrochemical experiments in an anaerobic and moisture-free environment is possible with the LabStar glove box of MBraun (Garching, Germany).
Surfaces of the studied films, deposited either on conducting (electrode) or non-conducting substrates, are imaged using a MultiMode microscope of Veeco (Santa Barbara CA, USA). This microscope (see photo) is configured to enable visualization with the atomic force microscopy (AFM), scanning tunneling microscopy (STM), magnetic force microscopy (MFM), or electric force microscopy (EFM), and more, modes of imaging. The microscope is equipped with electrochemical mini cells for surface imaging in the course of an electrochemical experiment. Moreover, it is equipped with a set for optical CCD camera imaging. This set allows for both very precise positioning of the scanning tip on the spot to be imaged and visualization of a sample in the course of an experiment.