Hydrophobic recovery

Bar, G., Delineau, L., Hafele, A. and Whangbo, M.H., Investigation of the stiffness change in, the indentation force and the hydrophobic recovery of plasma-oxidized polydimethyl-siloxane surfaces by tapping mode atomic force microscopy. Polymer, 42(8), 3627-3632 (2001). 

Fritz JL, Owen MJ (1995) Hydrophobic recovery of plasma-treated poly-dimethylsiloxane. J Adhesives 54 33... 

Hillborg, H., N. Tomczak, A. Olah, H. Schonherr, and G.J. Vansco. 2004. Nanoscale hydrophobic recovery A chemical force microscopy study of UV/ozone-treated cross-linked poly(dimethylsiloxane). Langmuir 20 785-794. 

FIGURE 2.33 Creation of a hydrophilic PDMS channel with hydrophobic sealing, (a) The native PDMS surface with methyl groups, (b) After treatment with a 02-plasma, a hydrophilic surface with exposed OH-groups is obtained, (c) The hydrophilic PDMS surface is in mechanical contact with a native PDMS surface, (d) Rearrangement of the PDMS surface leads to its hydrophobic recovery, (e) A hydrophilic channel with hydro-phobic sealing is obtained [267], Reprinted with permission from Elsevier Science. 

The surface modification is applied on hydrophobic polymers in this case, and the complication due to change of bulk phase due to water immersion is small. The decay of hydrophilic characteristics or hydrophobic recovery is similar to that occurring in air. 

Thus, the driving force for the reverse process is much less than for the wetting process. Consequently a simple drying of the wetted sample does not cause a significant hydrophobic recovery of the surface. From the viewpoint of interaction forces, the repulsive force between fluorine atoms and water molecules is not replaced by the attractive force in the similar magnitude, but the repulsive force is merely removed. The reverse process, therefore, may be more appropriately considered as a redistribution process of certain chemical moieties, which is driven by the local differential chemical potential of each species. 

Mortazavi M, Nosonovsky M. A model for diffusion-driven hydrophobic recovery in plasma-treated polymers. Appl Surf Sci 2012 258(18) 6876—83. 

Hydrophobic recovery. Plasma and corona modified surfaces... 

Polymer surface restructuring has become a topic of considerable interest in recent years. It is of particular interest in efforts to increase the surface energy of relatively hydrophobic materials including silicone polymers. This can give benefits such as improved adhesion, better wettability, etc. but such efforts are often frustrated by a progressive hydrophobic recovery once the treatment ceases. The two most important areas of this type in the organosilicon polymer field are plasma treatment and corona discharge treatment. These two treatments are closely related. The former is often used to improve adhesion of... 

A wide variety of analytical techniques has been applied to shed light on the mechani sm of this hydrophobic recovery process including XPS, ATR - FTIR, GPC, SIMS, DMA, SEM, and contact angle. Our experience and that of others (for example, Triolo and Andrade °) is that the combination of XPS, SEM, and contact angle is a powerful surface analytical strategy for silicone polymer surfaces. We believe that many aspects of the preceding list of possible mechanisms are involved in this complex phenomenon and also that it is impossible to generalize as some silicone polymer systems behave quite differently to others. 

We have also carried out some unpublished studies on the temperature dependence of hydrophobic recovery of plasma treated PDMS. The activation energy of this thermal restructuring process is 44 kJ/mol. This is more than the activation energy of viscous flow of PDMS (15 kJ/mol) 2 but much less than the only similar measurement of which we are aware for a carboxylic acid functionalized polyethylene surface (210 kJ/mol). ... 

UV irradiation and plasma treatment. However, it has been observed that the water contact angle of the treated polymer surfaces increases gradually with time, thereby making them hydrophobic and less biocompatible. The phenomenon is called hydrophobic recovery of polymeric biomaterials and is being addressed in detail [36]. 

Fig. 9. Surface energy and its PC of biaxially oriented iPP modified by corona discharge during long-term hydrophobic recovery a - surface energy, b - PC of the SFE...

Fig. 14 Variation of the relative change in the strength of the adhesive joint modified iPP -polyvinyl acetate during long-term hydrophobic recovery a - biaxiaUy oriented, b -extruded iPP.

Novak, I. Florian, S. (2004). Investigation of long-term hydrophobic recovery of plasma modified polypropylene. /. Mater. Sci, VoL 39, pp. 2033-2036, ISSN 0022-2461. 

The hydrophilic stability of surface-modified PDMS was described by Bodas et al. [13]. Three different modification processes, namely, conventional oxygen-plasma treatment, two-step modification using O2 -I- C2F6, and chemical modification using HEMA, were considered in the study. AU of the surfaces were characterized using static contact angle measurements and ATR-FTIR spectroscopy. Oxygen-plasma modification resulted in hydrophilic stability for about 2 days. The hydrophobic recovery in this case... 

Surface treatments and surface interactions are the challenges ahead for the research community in relation to the development of advanced, sophisticated microfluidic devices. Stuface modification techniques need to be optimized for various applications and particularly for disposable microfluidic devices. PDMS will be a popular material for future microfluidic devices, and some issues associated with most of the currently employed treatments, such as the hydrophobic recovery of PDMS surfaces, need to be adequately addressed. 

The H2 plasma was used to prepare poly(ether ether ketone)-polyurethane membranes (Salerno et al. 2009) before ammonia plasma treatment. Such pretreatment cross-links and stabilizes the surface of the membrane before grafting of the A-groups, so that the hydrophobic recovery of the flnal surface is signiflcantly reduced. 

Hillborg, H. Tomczak, N. Olah, A. Schonherr, H. Vancso, G. J., Nanoscale Hydrophobic Recovery A Chemical Force Microscopy Study of UV/ Ozone-Treated Cross-Linked Poly(dimethylsiloxane). Langmuir 2004, 20, 785-794. 

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