Interface modifier

VI. PROBING MOLECULAR TRANSFER AT LIQUID-GAS INTERFACES AND LIQUID INTERFACES MODIFIED WITH LANGMUIR MONOLAYERS... 

Table 4.1 Intermolecular Interactions at the Solid-water Interface (Modified from Westall, 1987)...

Benatar, A. and Gutowski, T.G. (1986). Effects of moisture on interface modified graphite epoxy composites. Polym. Composites 7, 84-90. 

Inorganic NPs exhibit higher surface to volume ratios than their bulk counterparts. Thus, electrochemical interfaces modified with inorganic NPs will provide a higher electrochemically active area and therefore lead to higher detection sensitivity. 

Electrochemical interfaces modified with inorganic NPs behave as nanoelectrode ensembles. In principle, the electroanalytical detection limit at a nanoelectrode ensemble can be much lower than that at an analogous macrosized electrode because the ratio between the faradaic and capacitive currents is higher.19-23... 

Figure 7.18a Dissolved and particulate 210Po profiles in a permanently anoxic fjord (Framvaren, Norway), illustrating that 210Po is largely controlled by the intense cychng of sulfur microorganisms at the O2/H2S interface. (Modified from Swarzenski et al.,...

If this assumption is true the decrease of the ignition time can be avoided by suitable interface modification, which, however, should preserve the advantageous charring activity of nanofillers having catalytic effects. This challenging concept could not be realized by any conventional interface modifier. A polymeric interlayer, which has not yet been studied in this respect, may provide a solution. 

Monomers and prepolymers that are useful to form shellwalls were reacted with interface modifying molecules to create novel surfactants in-situ leading to stable emulsions [23], The reactions are designed to create polymers with surfactant properties rather than encapsulating shellwalls at the OAV interface. The emulsions were formed without conventional emulsifiers, and were shown to have long term stability without creaming. Absence of classical emulsifiers reduces the tendency toward foaming. 

A nanofilm of a plasma polymer could be used as an interface modifier, which joints two distinctively different materials, or could be used as the top layer of a material, which would become a part of new interface when the material is placed in a different environment such as biological tissues, bloodstream, etc. (SAIE in biomedical materials is described in Chapter 35). 

Another example of the presence of a surface altering the course of a reaction is provided by the studies of Wasteneys and Borsook (08). It has already been mentioned (Section VI) that the presence and nature of an oil-water interface modified considerably the acid- and basecombining properties of the complex derivatives whose formation from peptides and an enzyme was catalyzed by an emulsion of oil. 

Figure 1. Schematic presentation of some polar lipids and their orientation at an air-water or oil-water interface, modified from Carey and Small (1970). (a) Lecithin, (b) lysolecithin, (c) ionized fatty acid, (d) bile salt, (e) cholesterol.

Counter-ions diffuse rapidly compared with the surface active species, but the build-up of the electric fields at the interface modifies the transport in such a way that it accelerates the slowly diffusing species and decelerate the rapidly diffusing ones so that finally the fluxes of each are equal. Thus, the condition of approximate equality of the currents of adsorbing ions and counter-ions is provided by the appearance of an excessive surface charge the sign of which coincides with that of the fast-diffiising ions. 

For the evaluation of the diffusion constant D at a time t, the potential difference relative to the potential of the intact, electrolyte-free metal/adhesive interface is fitted with respect to Eq. (22). For the ingress of sodium chloride from an aqueous solution of 0.5 m NaCl into the defect area as shown in Fig. 31.2, a diffusion coefficient of 1 x 10 cm s is calculated, even for highly stable adhesive/metal interfaces modified with an aminosilane adhesion promoter. Performing the diffusion measurement with other metal hahde solutions shows that an effective diffusion coefficient of the hydrated ion-pair, is measured by this method. This could be shown by changing the size of either the hydrated cation or anion, which resulted in a corresponding change in the measured diffusion coefficient (with smaller hydrated ions diffusing faster). 

Furthermore, the absorption of water by the interphasal polymer can reduce its yield strength below the interfacial bond strength. Thus, the apparent interfacial shear strength will be reduced, and a yield front, rather than a debond, will propagate along the fibre interface modifying the stress transfer micromechanics at a fibre break. A consequence is that the stress concentrations in adj acent fibres to the fibre break will be reduced, and the probability of the formation of a flaw of critical dimensions is also reduced. The number of interacting fibre breaks associated with a flaw of critical dimensions will increase. 

Experimental studies of the adhesion between thermoset and thermoplastic phases are also of interest. For example, the energy per unit area required to fracture an epoxy-polystyrene interface modified with a carboxylic acid terminated deuterated polystyrene could be increased by as much as 25 times, depending on grafting density and chain length [138]. 

Surface segregation, which is also a common phenomenon in other materials, has received limited attention and most of the studies applied this concept for the control of the surface chemical composition. Moreover, surface segregation has been typically considered as a non-desirable effect. This is particularly true in the case of materials with precise bulk properties provided by the presence of different additives such as plasticizers or UV-absorbers. The segregation of these additives towards the interface modifies the bulk properties and can provoke large variatiOTis on their mechanical behavior. Several contributions have explored this phenomenon in order to reduce the amount of oligomers/polymeric additives that bloom to polymer surfaces [13]. However, in many other applications it is desirable to have surface properties that vary to a large extent from those found in the bulk. For example, to favor adhesion or increase the wettability, or the opposite, i.e., increase the hydrophobicity, to improve the biocompatibility of commercial polymers or to enhance the chemical resistance. 

Moisture Permeation of Polymer Sealants and Interface Modifying Films... 

Materials selected as interface modifiers for surface passivation were chosen by their potential to react with surface oxides and hydroxyls where moisture would likely interact. The three which were ultimately tested are polyphenylsilsesquioxane (PSS), hexamethyldisilazane (HMDS), and N- 3-(N-vinyIbenzylamino) ethyl-7-aminopropyl-trimethoxysilane-monohydrogen chloride ("silane ). The last material proved to be corrosive to the test nichrome resistors due to the chloride part of the molecule. Therefore, most of the study centered around the first two materials. 

Several such interface modifiers were found to have the potential of meeting the requirements of hermeticity and repairability. One, however, was outstanding in both categor ies. A plasma-polymer ized hexamethyldisilazane (HMDS) coating provided effective protection for nichrome thin film resistors in high temperature and humidity, power-on conditions for 1,000 hours. HMDS was a very thin coating (approximately 1000 A) which was easily removed for repair purposes. 

Further tests of interface modifiers and their use on hybrids for passivation is the focus of the next phase of this project. 

P. wh. Schuessler and B.L. Rathbun, "Hydrophobic Resins and Interface Modifiers , NASC Phase II Report, February 1982. 

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