On low energy surfaces

Besides the spontaneous, complete wetting for some areas of application, e.g., washing and dishwashing, the rewetting of a hydrophobic component on a solid surface by an aqueous surfactant solution is of great importance. The oil film is thereby compressed to droplets which are released from the surface. Hydrophobic components on low-energy surfaces (e.g., most plastics) are only re wetted under critical conditions. For a complete re wetting of a hydrophobic oil on polytetrafluoroethylene (PTFE) by an aqueous solution, the aqueous solution-oil interface tension must be less than the PTFE-oil interface tension... 

Electrochemical deposition of photopolymer films occur on low energy surface states on the metal electrodes. The deposits tend to grow as "pillars" perpendicular to the electrode surface. A smooth coalesced film is observed when... 

The use of biological materials as coatings for piezoelectric crystals was first demonstrated by Shons et al. [237], who immobilized bovine serum albumin (BSA) on a crystal precoated with a 30% solution of Nyebar C, a low-surface energy plastic. The rationale of using this solution as the coating material is that proteins adsorbed on low-energy surfaces retain their antigenic properties. Exposure of the BSA-coated crystal to a solution... 

On low energy surfaces such as polyethylene, polypropylene, or polytetrafluoroethylene many liquids have finite contact angles and Tre values are generally zero (3). On high energy surfaces such as most mineral oxides most liquids have no contact angle, tt6 values are quite appreciable and... 

Wagner, R., Richter, L., Weissmuller, J., Reiners, J., Klein, K.D., Schaefer, D. and Stadtmuller, S. (1997) Silicon-modified carbohydrate surfactants 4. The impact of substructures on the wetting behaviour of siloxanyl-modified carbohydrate surfactants on low-energy surfaces. Appl. Organometallic Chem., 11(7), 617-32. 

R. Wagner, L. Richter, Y. Wu, J. Weissmuller, A. Kleewein, E. Hengge, Appl. Organometal. Chem., 1998, 12(4), 265-276. Silicon-modified carbohydrate surfactants. VII Impact of different silicon substructures on the wetting behavior of carbohydrate surfactants on low-energy surfaces - distance decay of donor-acceptor forces. ... 

This concept of a critical surface tension for spreading on low-energy surfaces is one that was developed by Zisman and coworkers (Fox, 1950 Shafrin, 1960 Zisman, 1964). They demonstrated that, at least for low-energy substrates, in order to wet the substrate the surface tension of the wetting liquid must not exceed a certain critical value that is characteristic of the particular substrate. 

Figure 1. Wetting behavior of hydrogen-bonding liquids on low-energy surfaces of varied surface composition...

Limiting Wetting Behavior of Other Liquids on Low-Energy Surfaces... 

The evidence obtained from measurements of two-liquid adhesion tensions seems to point very strongly to the existence of film pressures of the order of 5 to 10 dynes per cm. on low energy surfaces. In fact, no alternative explanation of the observations suggests itself. Therefore, there follows a discussion of some direct measurements of film pressures which have been reported and which bear on the problem. 

Despite the efforts made, apparently simple questions concerning the rapid spreading of siloxane surfactants on low-energy surfaces remained unsolved. Are single components of the complex surfactant mixtures responsible for the superspreading effect Which physicochemical property qualifies certain molecules Does a synergistic effect exist ... 

If 7Ts 0, as has been suggested for high energy liquids on low energy surfaces (60,61) then equation (8) reduces to... 

Hayes R, Ralston J. (1993) Forced liquid movement on low-energy surfaces. J Colloid Interface Sci 159 429—438. 

Fig. 14. Effect of temperature on the critical surface tension for spreading on low-energy surfaces (A) poly(ethylene terephthalate) (B) polyoxymethylene (C) polyethylene (D) polycarbonate (E) polystyrene (F) silicone (G) and (H) polytetrafluoroethylene and (J) and (K) polytetrafluoroethylene-hexafluoropropylene copolymer.

Like other EO/PO nonionics, they exhibit an inverse %ater-solubility behavior versus temperature (cloud point). Silicone surfactants show excellent wetting capacity on low-energy surfaces. Also, their diluted solutions can considerably decrease the surface tension to below 20 dyn/cm. 

Fowkes, McCarthy and Mostafa (1980) have illustrated that the spreading pressure of methylene iodide (50.8 mN m ) on low energy surfaces like PE and Teflon is zero. 

Fox HW, Zissman WA. The spreading of liquids on low-energy surfaces. II. Modified tet-rafluoroethylene polymers. J Colloid Sci 1952 7 109. 

A lower-energy surface Is usually thought to have a weaker bond with Ice. The observations reported here Indicate that the reason we usually observe lower adhesion of Ice on low-energy surfaces Is not lower molecular bond strength directly but the smaller "real" contact area caused by low-energy surfaces coated with some contamination. 

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