Surface spontaneous

If, when a liquid drop is placed on a smooth surface, the forces of adhesion between the solid and the liquid are greater than the forces of cohesion of the liquid, then the liquid will spread and will perfectly wet the surface spontaneously. If the forces reach an intermediate balance determined by the interfacial energies ylv, ysj and ysv, then the liquid drop will form a definite contact angle (0) with the solid surface (Figure 4.12). 

Compound Condition of Stainless Steel Surface Spontaneous Ignition Temp., ° F. 

The stoneware surface is usually provided with the so-callcd salt glaze which is formed on the surface spontaneously, as a result of sodium chloride being introduced into the kiln at the end of firing. In the presence of water vapour, sodium chloride vapour reacts with Si02 and the other components producing a smooth silicate layer. Feldspar glazes represent the other alternative. 

When a Pt(100) surface is subjected to ultrahigh vacuum conditions, the clean surface spontaneously reconstructs [84] from the (1 x 1) structure to the reconstructed state at room temperature by the adsorption of impurities, such as water molecules to the (5x20) structure [84]. The present (lxl) structure means that the state of the sample treated this way, which gave an LEED pattern of the (100) plane without further treatment under vacuum, has a satisfactory initial crystallographic surface structure from an LEED point of view for the electrochemical experiment. 

Stabilization of BLMs at the surface of electrodes has been reported by a number of groups [28-30]. For example, the tip of a Teflon-coated platinum microelectrode was cut in situ with a scalpel while immersed in a lipid solution (lipid in a hydrocarbon solvent). Upon immersion of the wire into an aqueous solution of 0.1 M KCl, the phospholipid coating adhering to the metal surface spontaneously thinned to form a BLM directly adjacent to the electrode surface... 

In chemical etching (Fig. 16b) neutrals react with the surface spontaneously to yield product. An example is etching of silicon with F atoms. Rapid surface fluori-nation leads to SiF4 which desorbs into the gas. 

Besides being used as adsorbent for gas molecules, both SWCNTs and MWC-NTs can be cast as a random network or a porous thin film on metal electrodes [57-59] or used as a three-dimensional scaffold [41,42] for biosensors. CNTs serve both as large immobilization matrices and as mediators to improve the electron transfer between the active enzyme site and the electrochemical transducer. Various enzymes, such as glucose oxidase and flavin adenine dinucleotide (FAD) can adsorb onto the CNT surface spontaneously and maintain their substrate-specific enzyme activity over prolonged times [57]. Recently, cells have been grown on CNT scaffolds which provide a three-dimensional permeable environment, simulating the natural extracellular matrix in a tissue [60-62]. 

A structural instability of the 4-PyS modified electrode prepared from the solutions of 4-PySSPy and 4-PySH has been reported [70]. This instability manifests itself as a decrease in the ability of the modified surfaces to facilitate the electrode reaction of cyt. c with an increase of immersion time in the precursor solutions. The modified surfaces spontaneously decompose to yield an adlayer composed largely of adsorbed atomic and oKgomeric sulfur. 

The wettability, and hence ability to bond, of oxidized polyethylene decreases quickly upon heating it to 85°C (66). Apparently, oxygen-containing groups in the surface spontaneously turn inward toward the bulk of the sample, so that the surface energy of the material is reduced and the hydrocarbon character of the surface is increased. At room temperature, the loss of bondability is slower since the chains have less mobility for this redistribution. 

In the case of woven textiles the interactions with liquids are more complex. They involve several physical phenomena, such as wetting of the fiber surfaces, spontaneous flow of a liquid into an assembly of fibers driven by capillary forces (wicking), adsorption on the fiber surface, and possibly diffusion of the liquid into the interior of the fibers [101]. In general, fiber assembly-liquid interactions depend on the wettability of the fibers, their surface geometry, the capillary geometry of the fabric, the nature of the test liquid, and external forces (applied pressure) [101]. 

If the liquid molecules are much more attracted to each other thau they are to the solid - such as water on polyethene - they will ball up to form droplets sitting on the surface. This prefereuce cau be measured by the angle, 0 > 90°. If the liquid molecules are much more attracted to the solid than they are to each other, the liquid will spread out completely and wet the surface spontaneously, e.g. acetone on clean glass, and 0 is 0°. At intermediate values of 0, i.e. between 90° and 0°, the liquid will spread aud wet the surface if force is used to expand the drops. It takes energy to stretch the skin and make more surface. 

The Cyclol Theory.—Protein molecules are composed largely, if not entirely, of amino acid residues, and contain many — NH—CO— linkages but few free — NHg groups, apart from those found in side-chains. The general uniformity of the protein type su ests a uniformity of general structure. Many proteins are easily denatured, and when spread on a suitable surface spontaneously form insoluble monolayers. 

The wettability, and hence ability to bond, of oxidized polyethylene decreases quickly upon heating it to 85°C (66). Apparently, oxygen-containing groups in the surface spontaneously turn inward toward the bulk of the sample. 

---