Surface properties controlled release

The recovery of petroleum from sandstone and the release of kerogen from oil shale and tar sands both depend strongly on the microstmcture and surface properties of these porous media. The interfacial properties of complex liquid agents—mixtures of polymers and surfactants—are critical to viscosity control in tertiary oil recovery and to the comminution of minerals and coal. The corrosion and wear of mechanical parts are influenced by the composition and stmcture of metal surfaces, as well as by the interaction of lubricants with these surfaces. Microstmcture and surface properties are vitally important to both the performance of electrodes in electrochemical processes and the effectiveness of catalysts. Advances in synthetic chemistry are opening the door to the design of zeolites and layered compounds with tightly specified properties to provide the desired catalytic activity and separation selectivity. 

An alternative route to hybrid nanostructures with controlled release or mass transfer properties entails the modification of the pore network surface with photo-isomerizable molecules such as azobenzene (Fig. 18.5a). Azobenzene exists in two conformations, trans (the most stable isomer) and cis irradiation with light... 

Mesoporous silica containers can be used as inhibitor hosts with controlled release properties triggered at the beginning of the corrosion process in response to local pH changes. For instance, mesoporous silica nanoparticles covered with polyelectrolyte layers can be loaded with an inhibitor (2-(benzothiazol-2-ylsulfanyl)-succinic acid) prior to introduction into a hybrid zirconia-silica sol-gel film. This hierarchical design avoids spontaneous release of the inhibitor by the formation of a polyelectrolyte shell over the container s outermost surface. 

The pH sensitivity of halloysite can be enhanced by using retardant polymers, a cationic coating for the formation of a pH-sensitive polyelectrolyte shell on the nanotubes after their saturation with corrosion inhibitor. To equip the halloysite nanotubes with controlled release properties, the surface of the nanotubes was first loaded with benzotriazole and subsequently modified by LbL deposition of two polyelectrolyte bilayers, thus blocking the tubes openings with polyelectrolytes. 

Bosquillon, C., et al. (2004) Aerosolization properties, surface composition and physical state of spray-dried protein powders. Journal of Controlled Release, 99 p. 357-367. 

Electrochemical polymerisation produces films on an electrode surface.. Under controlled conditions uniform films up to a few mm thick, which carl be removed from the electrode for subsequent study, can be prepared. Physical properties can be modified by choice of the counterions (dopants) included in the film during growth. It is, however, more difficult to control chain structure and crosslinking than in chemical methods. Electrochemically produced polymers are, therefore, less well characterised than the best directly-synthesised polymers. While this is less satisfactory for fundamental investigations, it is of less concern for applications such as battery electrodes, artificial muscles and drug release agents. The two main approaches, direct-synthesis and electrochemical, are described in the following two sections. 

Despite the long list of requirements, a variety of chemical fmishes have been used to produce textiles with demonstrable antimicrobial properties. These products can be divided into two types based on the mode of attack on microbes. One type consists of chemicals that can be considered to operate by a controlled-release mechanism. The antimicrobial is slowly released from a reservoir either on the fabric surface or in the interior of the fibre. This Teaching type of antimicrobial can be very effective against microbes on the fibre surface or in the surrounding enviromnent. However, eventually the reservoir will be depleted and the finish will no longer be effective. In addition, the antimicrobial that is released to the enviromnent may interfere with other desirable microbes, such as those present in waste treatment facilities. 

This second example demonstrates that the SU-8-based micro/ nanostructured surfaces allow for rapid binding and manipulation of hydropho-bically modified DNA at SU-8 surfaces and its controlled release by lipid film spreading. Using a combination of nano- and micro-meter-sized SU-8 patterns, DNA concentration gradients in solution can be created d3mamically. Moreover, other molecules with different hydrophobicites can likely be used such that the hydrophobicity of the molecules can be exploited as a sorting tool to modify surface properties of SU-8. It is, furthermore, possible to heat... 

Sheskey and Hendren in 1999 studied the effect of roll surface configuration on the drug release and physical properties of a HPMC matrix controlled-release dosage form. ° Smooth and axial-grooved roll surface designs were studied using a Vector Model... 

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