Wetting-autophobicity

K. Shull, Wetting autophobicity of polymer melts, Faraday Discuss., 98, 203 [1994],... 

When a surface-active agent is present in a liquid droplet, it can adsorb to the surface, lower the surface energy, and cause the liquid contact angle to increase. This phenomenon, known as autophobicity, was postulated by Zisman many years ago [78, 79]. Autophobicity is quite striking in wetting films on clean... 

The observation of liquid drops on top of a film of the same substance is often referred to as pseudo-partial [ 1 ] or autophobic wetting. This behavior is not surprising in this... 

Fig. 11 a, b. Autophobic wetting of mica by carbosilane dendrimer with OH end groups [73]... 

Another explanation has been offered for the observed maximum in spreading area with concentration, based on the concept of autophobicity, i.e., the existence of an adsorbed layer of surfactant at the liquid-solid interface that is not wetted by its own kind [44]. However, the short time scale of the spreading ( 2 seconds in the high concentration regime) requires that this autophobic layer is laid down in this short period, which is unlikely considering the kinetic limitations on reorientation of molecules [50]. 

The dendrimer droplets were used as a tool to examine surface heterogeneity on the nanoscale [319]. Figure 32 shows two pairs of SFM images of the droplets deposited on mica (a,b) and a copolymer film (c,d), respectively. On mica, the hydroxyl terminated dendrimer showed the autophobic or pseudo-partial wetting behaviour as the droplets sit on a thin film of the same material [312,320]. 

Fig. 32. Amplitude (a,c) and phase (b,d) SFM micrographs demonstrate autophobic wetting of mica (a,b) and semifluorinated copolymer (c,d) by carbosilane dendrimer with hydroxyl end groups. Fluid droplets with a contact angle of about 8.7 degrees in (a) and 18.5 degrees in (c) were determined after 24 h equilibration at room temperature from cross sectional profiles recorded along the reference lines indicated on the (a) and (b) respectively. Reproduced from [319]...

Fig. 34. SFM amplitude images of the oligo(hexafluoropropene) substituted PMA films on mica after annealing at room temperature for 50 h [324]. Depending on the number ol HFPO units, polymers exhibit either a autophobic wetting behaviour for HFP05 or b stable coverage with a 10 nm thick film for HFP03...

Therefore, the inverse gas chromatography method allows us to determine the model of long-chain aliphatic alcohol distribution on the surface of porous silica gel if the amount of alcohol on adsorbent surface is equal or exceeds the monolayer capacity, then the monolayer is composed of alcohol molecules oriented their polar moieties to the adsorbent surface. The monolayer, in a solid-condensed state, is stable up to 81°C. At this temperature the monolayer transfers into a liquid-expanded state. The threedimensional excess of alcohol, because the autophobicity phenomenon, does not wet the monolayer surface. 

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