Molecular coatings

Details Molecular coatings Molecular coatings

2001-01-26

2003-05-13

Barr, Michael (Department: 1762)

Coating processes

Electrical product produced

Reexamination Certificate

active

06562398

ABSTRACT:

FIELD OF THE INVENTION
This invention relates broadly to molecular coatings or articles to, for example, protect surface of the article or to alter the surface characteristics such as its hydrophilicity or hydrophobicity.
Background of the Invention
The field of surface science has gained increasing technological importance over recent-decades due to the ongoing reduction in dimensions of e.g. integrated circuits, micromechanical machines and sensors. Therefore, surface properties become increasingly important as many of the characteristics of such devices are determined ultimately by processes that occur at surfaces of or interfaces between thin coatings of the relevant materials. As such, for example the control of the surface properties of the outermost surfaces (i.e. at the device to environment interface) are critical in designing such devices. Surface coatings therefore play an important role in thin film device technology. As part of this technology the characteristics of monolayer films/coatings on a variety of surfaces have been extensively researched. One class of monolayers is referred to as self-assembling monolayers (SAMs) which are organised monolayers that can be prepared via spontaneous adsorption from neat or dilute solution. An overview of self-assembling monolayers can be found in “Self-assembling Monolayers in the Construction of Planned Supramolecular Structures and as Modifiers of Surface Properties”, R. Maoz et al., Journal de Chimie Physique, 1988, 85, No. 11/12 1059-1065, and “Pattern transfer: Self-assembled monolayers as ultrathin resists”, Y. Xia et al., Microelectronic Engineering 32 (1996) 255-268. In the former document it is described that surface-bound monolayers prepared by self-assembly may be used to modify the chemical nature of a substrate surface in two different ways, a) that the monolayer forming molecules are oriented on the surface with the desired functional group pointing outwards or b) that the desired functional group is introduced via in situ chemical modification of the pre-assembled SAMs.
It has been one of the main criteria of self-assembled monolayers to produce a close packed, highly oriented array of long chain hydrocarbon molecules on a substrate, the long chain hydrocarbon molecules embedded between a bottom functional group that can be used to attach the molecule to a substrate and a top, surface functional group that may be used to alter the surface characteristics. The structure of the SAM molecules determine the permeability characteristics and/or stability characteristics of the SAM. Up to date it has been believed that in order to optimise the properties/usefulness of SAMs it is desired to increase the crystallinity of the SAMs in order to provide stable ordered, close packed, two-dimensional arrangements of the surface groups. To utilise the (for example) protective or insulating properties of a SAM most effectively, it was believed to be necessary to minimise the defects in the SAMs (i.e. to increase their crystallinity) to take full advantage of the properties attributable to a “pure” SAM. However, the defect free properties of the SAM will ultimately be influenced by the surface on which the SAMs are formed. Most surfaces comprise defects such as monoatomic steps, kinks or facets which may transfer defects to the SAM formed on those surfaces. Therefore, the attempt to improve the SAM properties/applications by increasing their crystallinity has a preset limit forced onto the SAM by the substrate. In particular in more commercially oriented applications of SAMs, this limit constitutes a significant draw back in the application of SAMs, as preparation of substrate surfaces with a negligible amount of surface defects on a large scale can be economically difficult if not impossible at this stage.
Apart from he applications of coatings described above, such coatings are also applicable to various other surfaces comprising surfaces of fabrics to make the fabrics water resistant/repellent. In such applications even more so than in the surface scientific applications any influence of the surface of the substrate on the performance of the coatings constitutes a major disadvantage, as fabrics are non-crystalline substrates.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention there is provided an article comprising a molecular coating which comprises a layer having a liquid crystalline phase property.
By “article” we mean an object which has at least one is other function in addition to carrying the molecular layer, i.e. the article has utility or is intended to have utility other than just supporting the layer, e.g. a utilitarian article. For example an “article” may comprise a fabric (which can be used to make clothing), electronic devices such as integrated circuits on silicon wafers, micromachines, sensors, membranes, etc.
A coating formed from molecules having a liquid crystalline phase property preferably results in a coating whose structural properties are to a large extent independent of the structural properties of the underlying substrate. This is useful where the coating is used to for example protect the underlying substrate, i.e. a continuous, undamaged coating is desirable. If the structural properties of the coating are strongly dependent on the structural properties/defects of the substrate (i.e. the coating is crystalline), the coating may exhibit cracks or discontinuities caused by those defects. As it is almost impossible to create substrates which are completely free of any defects, molecular coatings which are formed from molecules having the liquid crystalline phase property can preferably be used to form continuous coatings free of defects induced by the substrate. The applicants have found that molecular layers having the liquid-crystalline chase property show surprisingly good protective and insulating properties which were previously believed to be achievable only with crystalline molecular layers.
Preferably, the layer is a self-assembling layer. Self-assembling layers can be prepared via spontaneous absorption from organic solutions and can be used to modify the surface properties of a substrate or protect a substrate.
The self-assembling layers may be used to make the surface of a substrate more hydrophobic or hydrophilic, or to form a coating which has particular permeability characteristics and/or stability characteristics.
Advantageously, the molecules have a structure of
wherein group A are groups which confer the liquid-crystalline phase property on to the self-assembling layer, groups B are groups which confer structural stability onto the molecule, groups X are functional groups that are chosen so that the molecule can be attached to a surface, and groups Y are functional groups that are chosen to alter a property other than the liquid-crystalline phase property of the self-assembling layer.
In other embodiments, the molecules may have a structure of
wherein groups A are groups which confer the liquid-crystalline phase property to the self-assembling layer, groups B are groups which confer structural stability onto the molecule, groups X are functional groups that are chosen so that the molecule can be attached to a surface, groups Y are functional groups that are chosen to alter a property other than the liquid-crystalline phase property of the self-assembling layer, and groups Z are functional groups that are chosen to join different groups within one molecule.
Advantageously, groups Z are functional groups that are further chosen to stabilise the self-assembling layer.
Preferably, groups B are further chosen to contribute to the liquid-crystalline phase property of the self-assembling layer.
The self-assembling layer may be a self-assembling monolayer.
The molecular coating may be a multi-layered coating comprising a layer having the liquid crystalline phase property. In other words, the molecular coating could be formed from more than one layer, at least one of which has the liquid-crystalline phase property.
The molecular coating may be a multi-lay

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