UV ozone exposure

Fig. 4.9 CFM of droplets appearing with time after 30 min of UV/ozone exposure (a) height, (b) maximum adhesive forces, and (c) adhesion hysteresis. The color scales indicate the height [bright (0 nm) to dark (10 nm] maximum adhesive force [dark (6 nN) to bright (17 nN)] and hysteresis [dark (0.2 x 10-17 J) to bright (1.2 x 10-17 J)]. (d) Representative force-distance curves. Adapted with permission from [28]. Copyright 2004. American Chemical Society.

To more clearly confirm the correlation between catalytic activity and the amount of surface oxide layer formed on two different-sized Rh nanoparticles, we carried out the CO oxidation reaction as a function of UV-ozone exposure time. Figure 7.5a shows that the catalytic activity of the 2 and 6.5 nm Rh nanoparticles... 

The manufacture of base discs for laser recording material is realized by covering of the plastic substrates surface with solid polymer layer possessing directing channels and/or signal holes. The surface of the plastic substrate is preliminary cleaned by UV/ozone exposure before the formation of the hardened polymer layer [128],... 

Ultraviolet (UV) or UV/ozone exposure (UVO) is another class of techniques extensively used to modify PDMS surface. Previously, it was reported that when exposed to UV light or a combination of UV and ozone, silicone rubbers underwent drastic surface chemical changes similar to the result of oxygen plasma [29]. However, the UV and UVO modification processes are nearly an order of magnitude slower than the modification by plasma techniques and provide much deeper modification of PDMS surface without cracking or mechanically weakening the PDMS [30]. The treatment results showed that a hydrophilic SiO -like layer formed, and such gradual surface reconstruction of PDMS layer is directly related to the duration of the exposure time [31]. 

With rubber base adhesives, it is necessary to prevent their properties from changing during service life. Oxidative changes induced by thermal, ozone exposure and UV light can dramatically affect service life of rubber base adhesives. More precisely, the rubber and the resin are quite susceptible to oxidative degradation. Environmental and physical factors exert detrimental effects on rubber base adhesive performance. These effects can be mitigated by the incorporation of low levels of stabilizers during the fabrication process of the adhesive. 

Ormrod, D.P., Landry, L.G., and Conklin, P.L., Short-term UV-B radiation and ozone exposure effects on aromatic secondary metabolite accumulation and shoot growth of flavonoid-deficient Arabidopsis mutants, Physiol Plant., 93, 602, 1995. 

These human medical problems do not necessarily spell disaster—most skin cancers can be cured, eye damage can often be corrected, and we may come to regard the dry, wrinkled skin of a former tanning enthusiast as beautiful. However, the great unknown factor is the effect of increased UV-B and UV-C exposure on ecosystems at large. Already, it is a matter of common experience worldwide that frogs and other amphibians have suddenly become scarce although no causal connection with ozone layer... 

A significant number of papers take advantage of the fact that oxidation of PDMS (either by exposure to UV-ozone or to oxygen plasma) can create a stiff silica-like material [17, 40, 43], During the oxidation process, up to 50% of PDMS in the topmost layer is converted into silica [40], Oxygen plasma treatment was first applied by B owden and coworkers [ 16] to create such a surface layer and use a thermal shrinkage process to create wrinkles. They found patterns with wavelengths between fractions of a micron and 10 p.m. They also reported the appearance of cracks which arise due to the brittle nature of the silica material. 

Fig. 4.10 Histograms of the pull-off forces and corresponding adhesion images of (a) unexposed PDMS and oxidized PDMS after (b) 0.1 day after exposure to 60 min of UV/ ozone. In the adhesion images, the color scales are individually scaled from dark (low pull-off) to bright (high pull-off). Reproduced with permission from [28]. Copyright 2004. American Chemical Society...

To make samples for the adhesion experiments, a crosslinked PDMS elastomer substrate was oxidized by a 30 min exposure to UV/ozone [21-24], using a Jelight Company Model 42 UVO-Cleaner. A thin layer of polystyrene (M = 38000 g mol ) with a trimethoxysilyl end group was spin-cast onto this oxidized elastomer from a solution in toluene. These functionalized chains were grafted onto the oxidized PDMS surface by annealing for 1.5 h at 125 °C, and the excess polystyrene chains were removed by rinsing the sample in toluene... 

For OTFT measurement, a heavily doped p-Si wafer wifh an overlayer of Si02 (300nm, Q—llnF/cm ) was used as fhe subsfrafe. The subsfrafe was cleaned sequentially using ethanol and acetone in ultrasonic bath, followed by an exposure to UV-ozone for 20 min [73]. During fhe organic film deposition, the substrate was kept at 60°C. The thickness of fhe organic layer was 100 nm. In the case of NPB, 20 nm of tungsten oxide x 2-3) was ther-... 

Fair to good aging Cured products often will outperform natural rubber products, but uncured products made from emulsion polymers can degrade rather quickly if not compounded for UV, ozone, and oxygen resistance. Block copolymers are typically better in the uncured state than standard SBR, but still require protectant additives for extended exposure conditions. 

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