Surface release properties

Surface release properties A smooth surface tends to discourage the adhesion of cohesive, damp, wet, or fatty solids, although when the avoidance of such behaviour is important, the surface cohesion of optional surfaces should be measured by tests. Surface cohesion is shown on a graph, whereby the force promoting shp is plotted versus the normal load. The intercept on the slip force axis shows the measure of surface cohesion. A bright, polished surface is not normally required for surface cleanliness or to... 

In 1954 the surface fluorination of polyethylene sheets by using a soHd CO2 cooled heat sink was patented (44). Later patents covered the fluorination of PVC (45) and polyethylene bottles (46). Studies of surface fluorination of polymer films have been reported (47). The fluorination of polyethylene powder was described (48) as a fiery intense reaction, which was finally controlled by dilution with an inert gas at reduced pressures. Direct fluorination of polymers was achieved in 1970 (8,49). More recently, surface fluorinations of poly(vinyl fluoride), polycarbonates, polystyrene, and poly(methyl methacrylate), and the surface fluorination of containers have been described (50,51). Partially fluorinated poly(ethylene terephthalate) and polyamides such as nylon have excellent soil release properties as well as high wettabiUty (52,53). The most advanced direct fluorination technology in the area of single-compound synthesis and synthesis of high performance fluids is currently practiced by 3M Co. of St. Paul, Minnesota, and by Exfluor Research Corp. of Austin, Texas. 

When considering relea.se mechanisms, the physical and chemical heterogeneity of the adhesive/release interface cannot be ignored. At its most basic level, roughness of the release and PSA surface, the stiffness of the PSA and the method in which the PSA and release surface are brought together define the contact area of the interface. The area of contact between the PSA and release material defines not only the area over which chemical interactions are possible, but al.so potential mechanical obstacles to release. In practice, a differential liner for a transfer adhesive can be made to depend in part on the substrate roughness for the differences in release properties [21],... 

Siloxane containing interpenetrating networks (IPN) have also been synthesized and some properties were reported 59,354 356>. However, they have not received much attention. Preparation and characterization of IPNs based on PDMS-polystyrene 354), PDMS-poly(methyl methacrylate) 354), polysiloxane-epoxy systems 355) and PDMS-polyurethane 356) were described. These materials all displayed two-phase morphologies, but only minor improvements were obtained over the physical and mechanical properties of the parent materials. This may be due to the difficulties encountered in controlling the structure and morphology of these IPN systems. Siloxane modified polyamide, polyester, polyolefin and various polyurethane based IPN materials are commercially available 59). Incorporation of siloxanes into these systems was reported to increase the hydrolytic stability, surface release, electrical properties of the base polymers and also to reduce the surface wear and friction due to the lubricating action of PDMS chains 59). 

In a series of papers, Gupta et al. (109-112) studied the in vitro release properties of heat-stabilized BSA microspheres containing adriamycin. The biphasic release of drug was attributed to its location in the microsphere. The initial release results from surface desorption and diffusion through pores, while the later release arises from drug within the microsphere, which becomes available as the microsphere hydrates. 

The property that makes polyanhydrides unique is their surface hydrophobic-ity. Due to this high hydrophobicity, polyanhydride matrices do not facilitate water absorption. Consequently, hydrolytic degradation is restricted to the surface—a property that is termed as surface erosion. This type of degradation allows for zero-order release of drugs, i.e., the drug release profile is independent of the residual concentration of the drug in the matrix. 

Important practical aspects related to the surface composition and morphology of Z coatings are their release properties with various adhesives and antigraffiti and easy cleanability performances in regard to many chemicals. 

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. 

Films of the complexes are stable in water at a pH of 7 while they dissolve at pH 5. This can be explained by the pKa value of retinoic acid, which is, for example, 6.05 in 150 mM NaCl and 6.49 in 5 mM NaCl [163]. Therefore, the anionic retinoic moieties within the complexes will be protonated at pH values lower than the pKa which lead to the cleavage of the ionic bonds in the complexes. The first experiments to evaluate the release properties of retinoic acid from thin films of the complexes were performed by using FTIR and surface tension measurements. Films were immersed in solutions of 0.15 m sodium chloride at pH 5 for both methods. The increase of the absorbance at 1255 cm-1 (C-0 stretch vibration) [186] in the FTIR spectra was used as a qualitative measure for the release of retinoic acid from the PEI-retinoate complexes. For comparison, the spectra of the complex and of the non-com-plexed retinoic acid are shown at wave numbers around 1255 cm 1 (Fig. 26, insert curves a and b). The time-dependency of the absorbance, which is a relative measure of the amount of released retinoic acid, is shown in Fig. 26. It can be seen that the increase of the absorbance, and therefore the release... 

The major mineral groups commonly found in soil include (1) aluminosilicates, (2) oxides, and (3) organic matter. Through their surface electrochemical properties, these soil minerals control adsorption, transformation, and release behavior of chemical constituents (e.g., nutrients and contaminants) to water or soil solution. Soil-surface electrochemical properties vary between soil types and depend on factors such as parent material, climate, and vegetation (Table 3.1). Generally, the overall makeup of soil is (Fig. 3.1)... 

In contrast to the advantageous nature of CDs for molecular inclusion, their surface makes it more difficult for the highly hydrophilic CD molecule to interact with lipophilic biological membranes. For this reason, natural CDs have been chemically modified to alter their water solubility, interaction with biological membranes, and drug release properties. 

---