▪ Abstract Biofilms can be defined as communities of microorganisms attached to a surface. It is clear that microorganisms undergo profound changes during their transition from planktonic (free-swimming) organisms to cells that are part of a complex, surface-attached community. These changes are reflected in the new phenotypic characteristics developed by biofilm bacteria and occur in response to a variety of environmental signals. Recent genetic and molecular approaches used to study bacterial and fungal biofilms have identified genes and regulatory circuits important for initial cell-surface interactions, biofilm maturation, and the return of biofilm microorganisms to a planktonic mode of growth. Studies to date suggest that the planktonic-biofilm transition is a complex and highly regulated process. The results reviewed in this article indicate that the formation of biofilms serves as a new model system for the study of microbial development.

Biofilm Formation as Microbial Development

A global perspective on the use, sales, exposure pathways, occurrence, fate and effects of veterinary antibiotics (VAs) in the environment

There is a special reason for reviewing this book at this time: it is the 50th edition of a compendium that is known and used frequently in most chemical and physical laboratories in many parts of the world. Surely, a publication that has been published for 56 years, withstanding the vagaries of science in this century, must have had something to offer. There is another reason: while the book is a standard fixture in most chemical and physical laboratories, including those in medical centers, it is not as frequently seen in the laboratories of physician's offices (those either in solo or group practice). I believe that the Handbook can be useful in those laboratories. One of the reasons, among others, is that the various basic items of information it offers may be helpful in new tests, either physical or chemical, which are continuously being published. The basic information may relate

Handbook of Chemistry and Physics

Introduction PART I: THEORY Lifshitz-van der Waals (LW) Interactions Relation Between the Hamaker Constant and the Apolar Surface Tension Component Polar or Lewis Acid-Base Interactions Electrical Double Layer Interactions Brownian Movement Forces-Osmotic Interactions of Polymers Rate of Decay with Distance PART II: INTERFACIAL PROPERTIES AND STRUCTURE OF LIQUID WATER Lifshitz-van der Waals and Lewis Acid-Base Properties of Liquid Water-Physical and Physico-Chemical Effects Role of Water in Hydrophobic Attraction Role of Water in Hydrophilic Repulsion The Water-Air Interface PART III: EXPERIMENTAL MEASUREMENT METHODS Contact Angle and Surface Tension Determination and Preparation of Solid Surfaces Interfacial Tension Determination-Influence of Macroscopic- and Microscopic-Scale Interactions Different Approaches for Interpreting Contact Angles and Determining the Surface Tension and Surface Tension Components of Solids Electrokinetic Methods Direct Measurement Methods, Treating the Force Balance in Particular PART IV: ASSOCIATED PHENOMENA AND APPLICATIONS Surface Tension Components and Parameters of Liquids and Solids Attractive LW- and AB-Forces: Hydrophobic Interactions-Osmotic Pressures of PEO Solutions Repulsive AB-Forces: Hydrophilic Interactions The Primary and Secondary Interactions Phase Separation in Polymer Solutions Coacervation and Complex Coacervation Solubility of Polymers and Other Solutes Cell and Particle Stability Adsorption and Adhesion in Aqueous Media, Including Ligand-Receptor Interactions Kinetics and Energetics of Protein Adsorption onto Metal Oxide Surfaces List of Symbols Used References Index

Interfacial Forces in Aqueous Media

Recently, polymer nanocomposites reinforced with lower volume fraction of nanoceramics and carbon nanotubes have attracted steadily growing interest due to their peculiar and fascinating properties as well as their unique applications in commercial sectors. The incorporation of nanoceramics such as layered silicate clays, calcium carbonate or silica nanoparticles arranged on the nanometer scale with a high aspect ratio and/or an extremely large surface area into polymers improves their mechanical performances significantly. The properties of nanocomposites depend greatly on the chemistry of polymer matrices, nature of nanofillers, and the way in which they are prepared. The uniform dispersion of nanofillers in the polymer matrices is a general prerequisite for achieving desired mechanical and physical characteristics. In this review article, current development on the processing, structure, and mechanical properties of polymer nanocomposites reinforced with respective layered silicates, ceramic nanoparticles and carbon nanotubes will be addressed. Particular attention is paid on the structure–property relationship of such novel high-performance polymer nanocomposites.

Structural and mechanical properties of polymer nanocomposites

The interactions of oxytetracycline with model clay adsorbents were investigated as a function of suspension pH. The clay adsorbents used were native montmorillonite (SWy-2), Na-montmorillonite (Na-SWy-2), and hexadecyl trimethylammonium-montmorillonite (HDTMA-montmorillonite). The adsorption of oxytetracycline to the clay could be described by Freundlich-type adsorption isotherms. It was observed that the adsorption of oxytetracycline in the native and sodium forms of montmorillonite decreases with increasing pH in the order pH 1.5 > 5.0 > 8.7 > 11.0. This trend is consistent with cationic exchange interactions that are dominant at lower pH values when oxytetracycline has a net positive charge. On the other hand, hydrophobic interactions when oxytetracycline is zwitterionic (at pH 5.0) are predominant over other mechanisms, as evident from the FT-IR spectrum of the HDTMA-montmorillonite and humic acid-montmorillonite adsorbed with oxytetracycline. The presence of a large amount of dissolved organic matter (DOM) was also found to decrease the sorption of oxytetracycline to clay, suggesting that DOM may increase its mobility in the natural environment. Several mechanisms of interaction of oxytetracycline in clay are proposed based on the adsorption isotherms and the results from X-ray diffraction (XRD) and Fourier transform-infrared (FT-IR) analyses.

Investigating the Molecular Interactions of Oxytetracycline in Clay and Organic Matter: Insights on Factors Affecting Its Mobility in Soil

The terms “hydrophobic” and “hydrophilic” are typically used in a non-specific sense and, as such, they have a limited utility. Surface thermodynamic theory, as described here, allows a natural and potentially powerful definition of these terms. The boundary between hydrophobicity and hydrophilicity occurs when the difference between the apolar attraction and the polar repulsion between molecules or particles of material (1) immersed in water (w) is equal to the cohesive polar attraction between the water molecules. Under these conditions, the interfacial free energy of interaction between particles of 1, immersed in water (ignoring electrostatic interactions), ΔG
 1
 1
 IF
 exactly zero. When ΔG
 1
 1
 IF
 is positive, the interaction of the material with water dominates and the surface of the material is hydrophilic; when ΔG
 1
 1
 IF
 is negative, the polar cohesive attraction between the water molecules dominates and the material is hydrophobic. Thus, the sign of defines the nature of the surface and the magnitude of may be used as the natural quantitative measure of the surface hydrophobicity or hydrophilicity.

The hydrophilicity and hydrophobicity of clay minerals

The cation exchange capacity (CEC) of fine-grained materials, and especially clay minerals, is a fundamental property of these materials, and can be determined routinely. A search of the recent literature illustrates the great interest of this property to researchers. For example, a search of the GeoRef database for references to “cation exchange capacity” for the years 1980 to 1999 yields 2559 citations.

Methods of measurement are based on a determination of the quantity of a particular exchangeable cation, by a variety of means, expressed per 100 g of dry clay. These methods are principally chemical and spectroscopic. The present study describes the results of measurements made primarily on Source Clay minerals using a particularly simple, reliable and inexpensive method developed by Busenberg and Clemency (1973).

The method, in common with other procedures, involves the saturation of exchangeable cation sites with a chemical species, in the present case, ammonium cations. The ammonium-exchanged clay is dispersed in an alkaline solution of sodium hydroxide that releases the ammonium as dissolved ammonia gas. A specific-ion electrode then detects the signal from the ammonia dissolved in solution. Comparison of the signal from the unknown solution with a series of solutions containing known concentrations of ammonia yields the ammonia …

Baseline studies of the clay minerals society source clays: cation exchange capacity measurements by the ammonia-electrode method

A simple method is described for the determination of contact angles (0) on powdered materials such as clay particles. This is done by depositing the particles from a liquid suspension onto glass slides, by sedimentation, followed by drying. The dried thin-layer plates are then subjected to wicking in a number of liquids using the Washhurn equation to determine cos . However, one other unknown in the Washburn equation, i.e. the average interstitial pore radius R, must first be determined. This is done by wicking with low-energy spreading liquids, such as alkanes. It could be shown with spherical monosized polymer particles, as well as with clay particles, that spreading liquids pre-wet the surfaces of the particles over which they subsequently spread. Thus, it can be demonstrated that spreading coefficients, in the sense of Harkins, play no role in this type of spreading and cos 0 equals unity in the Washburn equation for all values of γ1, for all spreading liquids (L). Results were obtained by thin layer...

Determination of contact angles and pore sizes of porous media by column and thin layer wicking

The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory sums the attractive van der Waals and repulsive electrostatic forces as a function of separation distance to predict the interaction between charged particles immersed in a liquid. In aqueous media, however, non-electrostatic polar (electron acceptor/electron donor or Lewis acid/base) forces between particles with high energy surfaces often are comparable to, or greater than, the components of DLVO theory. By means of contact angle measurements on smooth self-supporting clay films, the values of the polar surface forces (AB) and the van der Waals forces (LW) of hectorite were measured. Determinations of ζ were used to derive the electrostatic forces (EL). Calculations based on the values obtained for the EL, LW, and AB forces show that for smooth spheres with a radius of 1 µm in a ≥ 0.1 M NaCl solution a net attraction exists leading to flocculation. At NaCl concentrations of ≤ 0.01 M, a repulsion energy of about +500 to +1300 kT exists at separation distances ≤ 50 A, preventing contact between particles, thus ensuring stability of the colloidal suspension. At these concentrations, theory predicts that small clay particles or edges of clay crystals having an effective radius of curvature ≤ 10 A should be energetic enough to overcome the repulsion barrier which prevents flocculation. Experimentally, for NaCl solution concentrations of ≥ 0.1 M, suspensions of hectorite particles flocculated, whereas at concentrations of ≥ 0.01 M, the suspensions remained stable. These experimental results agree with the predictions made by summing all three forces, but contradict the calculations based on classical DLVO theory.

Rossman F. Giese

Papers

Investigating the Molecular Interactions of Oxytetracycline in Clay and Organic Matter: Insights on Factors Affecting Its Mobility in Soil

The hydrophilicity and hydrophobicity of clay minerals

Baseline studies of the clay minerals society source clays: cation exchange capacity measurements by the ammonia-electrode method

Determination of contact angles and pore sizes of porous media by column and thin layer wicking

DLVO and non-DLVO interactions in hectorite