Nanoscale Hydrophobic Recovery:  A Chemical Force Microscopy Study of UV/Ozone-Treated Cross-Linked Poly(dimethylsiloxane)

Abstract

Chemical force microscopy (CFM) in water was used to map the surface hydrophobicity of UV/ozone-treated poly(dimethylsiloxane) (PDMS; Sylgard 184) as a function of the storage/recovery time. In addition to CFM pull-off force mapping, we applied indentation mapping to probe the changes in the normalized modulus. These experiments were complemented by results on surface properties assessed on the micrometer scale by X-ray photoelectron spectroscopy and water contact-angle measurements. Exposure times of < or = 30 min resulted in laterally homogeneously oxidized surfaces, which are characterized by an increased modulus and a high segmental mobility of PDMS. As detected on a sub-50-nm level, the subsequent "hydrophobic recovery" was characterized by a gradual increase in the pull-off forces and a decrease in the normalized modulus, approaching the values of unexposed PDMS after 8-50 days. Lateral imaging on briefly exposed PDMS showed the appearance of liquid PDMS in the form of droplets with an increasing recovery time. Longer exposure times (60 min) led to the formation of a hydrophilic silica-like surface layer. Under these conditions, a gradual surface reconstruction within the silica-like layer occurred with time after exposure, where a hydrophilic SiOx-enriched phase formed < 100-nm-sized domains, surrounded by a more hydrophobic matrix with lower normalized modulus. These results provide new insights into the lateral homogeneity of oxidized PDMS with a resolution in the sub-50-nm range.

Flame treatment of low-density polyethylene: Surface chemistry across the length scales

“…The spring constants of the cantilevers ranged from 0.14 to 0.18 N/m, as obtained by the method of Hutter and Bechhoefer [36] according to the equipartition method which consists of measuring the thermal excitation of the tip to compute its spring constant. The specific details of the CFM procedure were similar to those reported for previous studies [37].…”

Droplet confinement and leakage: Causes, underlying effects, and amelioration strategies

“…25 This means that physical modification is ideally performed on a PDMS device that has had this residual monomer removed or at least depleted. 26 Significantly, the surfactant used in droplet-based microfluidic systems, as well as stabilising the droplet surface, also plays a role in the surface derivatization of the microchannels. Anecdotally, it is well recognised that most PDMS microfluidic devices work better after being conditioned with the continuous phase (containing the surfactant) for a period of time.…”

Effect of Ultraviolet Light Irradiation on Bonding of Experimental Composite Resin Artificial Teeth

“…They can cause molecular bonds to be broken when absorbed in a molecule, a process referred to as photolytic chain scission 14) . The use of ultraviolet (UV) irradiation on the surface of polymers such as poly(dimethyl siloxane) [15][16][17] , polypropylene [18][19][20] , and poly(ethylene terephthalate) 18,21) have been studied in lithography and microelectronics. In terms of advantages, UV irradiation can improve the adhesive property of coatings as well as wettability and printability of polymers by changing the morphology and chemical properties of the polymer surface.…”

“…By means of Fourier transform infrared spectroscopy (FTIR), photolytic chain scission, formation of different functional groups, and degradation of polymer backbone have been observed 15,19) . By means of X-ray photoelectron spectroscopy (XPS), changes in chemical bonding energy have been detected 16,18,19,21) . Then, by means of contact angle measurement, changes in surface hydrophobicity have been monitored 15,16,18,19) .…”