Aspects Of Surface Chemistry Research Articles

Ionic Strength and Curvature Effects in Flat and Highly Curved Polyelectrolyte Brushes

Adsorption of poly(tert-butylstyrene)/poly(styrenesulfonate) diblocks on polystyrene latices from water is reported and interpreted with scaling theories to demonstrate the effects of ionic strength and curvature on layer thickness. The adsorbed amount increases with ionic strength from no added salt to 0.1 M, forming a dense polyelectrolyte brush. The influence of particle radius on layer thickness is correlated quantitatively via the Daoud−Cotton model, but the effect on surface coverage is obscured by uncontrolled aspects of surface chemistry. Decreasing the ionic strength dramatically increases the dimensions of polyelectrolyte micelles and adsorbed layers; the sensitivity, while strongly coupled with curvature, is overestimated by all existing theories. A simple scaling theory that accounts for electrostatic excluded volume more appropriately captures the trends qualitatively.

Studies of NiO thin film formation by atomic layer epitaxy

Nickel oxide thin film formation by atomic layer epitaxy (ALE) was studied including aspects of surface chemistry and structure of the prepared films. The applied source materials were Ni(acac) 2, Ni(apo) 2, Ni(dmg) 2 and O 2, H 2O, N 2O, O 3, CH 3COOH for Ni and O, respectively. The thermal behaviour of the Ni-containing precursors was studied by thermogravimetry and by experiments in the ALE reactor. The reactivity of the Ni-precursors towards various oxygen sources was studied at the deposition temperature of 250°C using soda-lime glass substrates. The crystalline rocksalt-type NiO was obtained only when O 3 was used as an oxygen source. The film was in this case (100) oriented NiO independent on the applied Ni-precursor. The NiO ALE process was optimized for the reaction between Ni(acac) 2 and O 3. The surface-saturated growth rate was limited by the steric hindrance of the ligand and was 0.62 Å cycle −1. A slightly increased growth rate (0.72 Å cycle −1) was observed, when H 2O was supplied together with O 3 as an oxygen source. Structure of the deposited films was studied by atomic force microscopy and X-ray diffraction techniques and some structural variations related to high ozone doses were observed.

Physical chemistry of surfaces

Capillarity. The Nature and Thermodynamics of Liquid Interfaces. Surface Films on Liquid Substrates. Electrical Aspects of Surface Chemistry. Long--Range Forces. Surfaces of Solids. Surfaces of Solids: Microscopy and Spectroscopy. The Formation of a New Phase--Nucleation and Crystal Growth. The Solid--Liquid Interface--Contact Angle. The Solid--Liquid Interface--Adsorption from Solution. Frication, Lubrication, and Adhesion. Wetting, Flotation, and Detergency. Emulsions, Foams, and Aerosols. Macromolecular Surface Films, Charged Films, and Langmuir--Blodgett Layers. The Solid--Gas Interface--General Considerations. Adsorption of Gases and Vapors on Solids. Chemisorption and Catalysis. Index.

Flow adsorption microcalorimetry

Flow adsorption techniques are now widely recognised as important methods of studying adsorption/ desorption phenomena at solid/ uid interfaces. Pioneering work by the author some years ago demonstrated the power of a simpleow technique for the determination of the heats of adsorption at solid± liquid interfaces [1] which was, subsequently, used for the measurement of the heats of adsorption of gases and vapours [2]. A new feature in this calorimeter was the use of a single calorimetric cell for the measurement of temperature changes in the adsorbent bed due to adsorption/desorption phenomena, employing the cold junction of thermocouples as the reference sensors. Heat effects produced during surface interactions were rapidly dissipated in the heat sink constituted by a water jacket in direct contact with the glass walls of the calorimetric cell. The reference cold junctions were placed in water adjoining the glass walls, while the measuring heat junctions were in direct contact with the adsorbent. Heat loss from the cell occurred within a few minutes after surface interactions took place and in this way the heats of adsorption/desorption on granulated solids could be measured effectively under isothermal conditions. This type of microcalorimetry has been referred to as diathermal calorimetry and has been adopted by most adsorption calorimeters of Tian±Calvet type [3]. A similar principle, using a single adsorption cell, was used in the ®rst commercial version of a ow macrocalorimeter developed by MICROSCAL [4]. Subsequently SETARAM and LKB companies produced their own versions of ow adsorption calorimeters, the latter being more widely used. The LKB calorimeter is currently available as thermal activity monitor (TAM). An example of its use is provided by the work of Os et al. [5]. In the Microscal instrument thermocouples were replaced by thermistors and the water jacket by a metal block surrounding a small PTFE cell accommodating 0.17 cc of adsorbent bed [4,6]. A schematic diagram of a recent model of this calorimeter is shown in Fig. 1. This paper reviews extensive work by the author with the use of Microscal ow adsorption microcalorimeters, which have led to the discoveries of new aspects of surface chemistry of inorganic solids [7,8] and the behaviour of adsorbates at different surface coverages [9,10]. The work resulted in the development of new selective adsorption processes [11,12], competitive and co-operative adsorption phenomena [10], a better understanding of the role of adsorption in lubrication [13], surface reactions [14,15] dispersion technology [16] and determination of polarand graphitic-surface sites on carbonaceous solids [17,18].

Undergraduate Laboratory for Surface Science

Surface science has developed into a multidisciplinary field of research with applications ranging from heterogeneous catalysis to semiconductor etching (1). Aspects of surface chemistry are now included in physical chemistry textbooks (2) and undergraduate curricula (3), but the perceived cost and complexity of equipment has deterred the introduction of surface science methods in undergraduate laboratories (4). Efforts to expose chemistry undergraduates to state-of-the-art surface instrumentation have just begun (5).To provide our undergraduates with hands-on experience in using standard techniques for characterizing surface morphology, adsorbates, kinetics, and reaction mechanisms, we have developed a set of surface science experiments for our physical chemistry laboratory sequence. The centerpiece of the laboratory is an ultrahigh vacuum (UHV) chamber for studies of single crystal surfaces. This instrument, shown in the figure, has surface analysis capabilities including low energy electron diffraction (LEED), Auger spectroscopy, and temperature-programmed desorption (TPD).The laboratory exercises involve experiments on the well-studied Pt(111) surface. Students prepare a previously mounted single crystal sample by sputtering it with an argon ion gun and heating it under O2. Electron diffraction patterns from the cleaned surface are then obtained with a reverse view LEED apparatus (Princeton Instruments). Images are captured by a charge-coupled device (CCD) camera interfaced to a personal computer for easy downloading and subsequent analysis. Although the LEED images from a Pt(111) surface can be readily interpreted using simple diffraction arguments, this lab provides an excellent context for introducing Miller indices and reciprocal lattices (6). The surface chemical composition can be investigated by Auger spectroscopy, using the LEED apparatus as a simple energy analyzer.The temperature programmed desorption experiment, which is nearly complete, will be be added to the curriculum this academic year. This experiment introduces students to the concepts of surface adsorption and desorption kinetics. The sample mount can be both heated to 900 oC and cooled by liquid nitrogen, allowing the study of the desorption of a variety of adsorbates, both chemisorbed and physisorbed. Adsorbed species evolving from the heated surface are detected with a quadrupole mass spectrometer. Initially, students will study the desorption kinetics of CO from a Pt(111) surface for a range of coverages and temperature programming rates in order to obtain rate parameters and to test the validity of Redhead's relationship between the activation energy of desorption and the peak desorption temperature. They then will be introduced to the mechanisms of surface reactions (Langmuir-Hinshelwood) in a study of CO oxidation on this surface.We have also set up a scanning tunneling microscopy (STM) laboratory using a commercially available instrument (Burleigh Instruments, Inc.), which complements the UHV surface structure experiments by introducing the topography of a real surface, for example, with steps and defect sites.With the apparatus now completed, we can explore other possible developments, for example, an applied physics track designed around experiments on semiconductor substrates. Future additions include X-ray photoelectron spectroscopy and completion of a separate surface infrared spectroscopy experiment on supported catalysts.We acknowledge support from the National Science Foundation, Division of Undergraduate Education Instrumentation and Laboratory Improvement (ILI) Program (Grant No. DUE-9352254) and an ATandT Special Purpose Grant.