Tethered oils

In this paper, we report two methods to control oil depletion from silicone foul release coatings ablative networks and tethered incompatible oils. The synthesis of ablative and tethered diphenyldimethylsiloxane oils, the incorporation of such oils into the silicone room temperature vulcanized (RTV) network and the foul release properties of RTV coatings containing the ablative and tethered oils are discussed. The residence time of radiolabeled diphenyldimethylsiloxane oils in silicone RTV topcoats is also addressed. Synthesis of the radiolabeled diphenyldimethylsiloxane oil and incorporation of the radiolabeled oil into the silicone network are discussed. In addition, the environmental partitioning of the radiolabeled oils in both freshwater and marine systems is presented with the material balance. 

The incorporation of ablative and tethered oils into the silicone topcoat of fouling release coatings is a desirable mechanism for slow, controlled release of the silicone oil from the RTV topcoat. Once incorporated into the silicone network, the hydrolytically unstable Si-O-C bond in the ablative oil (Figure 3) should slowly degrade in water. Conversely, the tethered oil is chemically bonded into the silicone network and one end (the non-miscible portion) should phase separate to the surface of the PDMS. Both ablative and tethered oils contain diphenyldimethylsiloxane functionality, based on previous studies of the free oil. The approach was to synthesize both ablative and tethered diphenyldimethylsiloxane copolymers, incorporate the copolymers into the RTV topcoat and then measure the foul release performance of the coatings. Both oils are shown below in Figure 3. 

Incorporation of Ablative and Tethered Oils into Silicone Network... 

From the foul release results of the ablative and tethered oils, we can conclude that free oil is necessary in the silicone coating for optimal foul release performance. In... 

The spectroscopic data for 2 support the proposed structure. In particular, the 29Si NMR chemical shift of 37.17 ppm as a doublet of doublets (Jp,.Si = 1281.6 Hz, JSi-p(i xm)= 148.82 Hz, /sl-pc ) = 12.80 Hz) is close to the literature values for cis-PtSizPz complexes.6 Compound 2 was found to be a good precursor for the double-silylation reaction.7 Thus, thermolysis of a toluene solution of 2 and 1-hexyne at 120 °C afforded complex 3 as a colorless oil. A key feature in the H NMR spectrum of 3 is a singlet at 6.24 ppm assigned to the vinyl proton. A characteristic low-frequency l3C NMR resonance at 5 138.50 provides evidence for a tethered carbon atom of the two silicon moieties8 (Scheme 1). 

The cells tethered to the surface of the optically flat capillary are observed using a Nikon Optiphot (or similar) microscope with a lOOx oil immersion phase contrast objective using light >950 nm to image the cells (18). 

The time-dependent behaviour is different in the two types of highly oriented, chain-extended polymer fibres. Table 1 gives the results of studies in FIBRE TETHERS 2000 (1995), which were made because creep rupture is a concern in deep-water mooring of oil-rigs. The low-load creep in aramid fibres is due to a straightening of the initial. structure. It reduces in rate, even on a logarithmic scale, with time and is not a source of creep rupture. In Vectran, the creep is less and is absent after 10 days under load. 

EXAMPLE 22.4 Acid dissociation near an oil/water interface. Consider an acid group in water near a dielectric interface. For example, an acidic group may be tethered to an uncharged bilayer membrane in contact with water. Suppose that the intrinsic pX of the acid in the bulk solution is pKa (°o) = 4.6. What is the pKa of the same acidic group as a function of the tethering distance from the oil interface ... 

Mechanisms for Oil Retention in RTVll Topcoat Ablative Networks and Tethered Incompatible Oils... 

Figure 3. Summary of Ablative (1) and Tethered (2) Diphenyldimethylsiloxane Oils...

The tethered diphenyldimethylsiloxane oil was prepared by a kinetically controlled anionic ring opening polymerization of hexamethylcyclotrisiloxane (D3) and hexaphenylcyclotrisiloxane (Dj ) in the presence of n-BuLi (Figure 5) (7). Once the lithium salt of D3 and 03 6 was formed in a two step process, it was then quenched with water to give a silanol terminated diphenyldimethylsiloxane product (2). 

Likewise, the tethered diphenyldimethylsiloxane oil was also incorporated at 10 wt % into the PDMS network (Figure 7). The silanol endgroups of 2 condense with TEOS in the presence of Sn(IV) to give the triethoxy-terminated copolymer, which subsequently condense with the silanol-terminated RTVll to form a crosslinked network. The incompatible butyl-terminated diphenyldimethyl fragment should phase separate to the surface of the PDMS network. 

Figure 7. Incorporation of Tethered Diphenyldimethylsiloxane Oil into RTV Network...

RTV topcoats containing either the ablative or tethered diphenyldimethylsiloxane copolymers were applied to steel panels previously coated with the epoxy and a tie layer developed at NRL (8), After the panels were allowed to cure for one week, they were deployed at both northeast and southeast static test sites for 9 months. Controls of RTV 11 and RTV 11 containing 10% free diphenyldimethyl siloxane oil were also immersed in these marine environments. The overall fouling coverage was recorded for the northeast site and barnacle adhesion values were measured for the southeast site. Results are shown below in Figures 8 and 9. 

The model therefore displays the correct thermodynamic behavior and interfadal fluctuations. It can also be extended to model amphiphilic mixtures by introducing dimers consisting of tethered A and B particles. If the A and B components of the dimers participate in the same collisions as the solvent, they behave like amphiphilic molecules in binary oil-water mixtures. The resulting model displays a rich phase behavior as a function of pF and the number of dimers, Ad. Both the formation of droplets and micelles, as shown in Fig. 5 (left panel), and a bicontinuous phase, as illustrated in Fig. 5 (right panel), have been observed [45]. The coarse-grained nature... 

---