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Surface Modification

Making a surface interact with formulation components to trigger a chemical or physical change, or modifying a surface with a functional coating on a temporary or permanent basis, are fertile areas for technological innovation.

Let me use my experience of physical chemistry, organic chemistry and materials science to assist you in making best use of surface properties in your products.

Making surfaces perform a function

Often it is not necessary to give much attention to the properties of a surface, other than selecting a known material that is fit for the purpose.

But the most innovative of products will often consider the surface in a more creative way, by modifying it to deliver properties that are advantageous to the application. Developing such surfaces is a fertile area for technological innovation, and it’s a field I’ve had considerable experience with.

Using surfaces to trigger change

The properties of a surface can be used to induce a variety of chemical or physical changes in an applied formulation. The two examples below show how surfaces can be used both to trigger an irreversible reaction and to reversibly control molecular alignment – using differences between metal electropotentials and van der Waals interactions with liquid crystals, respectively.

Example:
Repairing microparticle defects by redox-enabled epoxy polymerisation

Electrically conductive adhesives are used to bond electrical components to each other and to PCBs, and the simplest versions comprise a liquid or paste containing silver-coated copper microspheres. However, the silver coating is often imperfect, exposing areas of copper that can lead to corrosion in the final product. How can these be reliably sealed off en masse?

While working at Henkel, we applied the principles used in electrodeless plating to design and patent cure engines that triggered the polymerisation of an epoxy formulation only on the copper (see also thislater study on the underlying principles). As a result of this innovation, inexpensive microparticles can now be easily treated to improve their quality before they are dispersed in the host matrix.

Example:
Vapour-deposited alignment layers for liquid crystal displays

The ultra-thin ‘alignment layers’ used in liquid crystal displays are essential for inducing directionality (bias) to the liquid crystal molecules that they’re in contact with. Convenient ways to deposit such layers on large substrates are much in demand.

To address this need, when I was in the team at Loctite we developed (and patented) an approach in which we used the well-known volatility of cyanoacrylates to vapour-deposit a uniform, transparent layer across an optically transparent electrode. Rubbing this layer gave the subsequently added liquid crystal mixture a high tilt angle – a feature that is an important attribute of certain fast switching displays.

Modifying coatings to provide surface protection

Being able to make a surface passive, whether on a temporary or permanent basis, has a variety of uses. Temporary polymeric coatings are found in applications including wound care products, cosmetic products, solder masks, photoresists, and coatings for metal parts. Permanent coatings often provide additional functionality, such as resistance to staining, corrosion or scratching, as well as haptic, antistatic, non-reflective, antibacterial and antiviral properties.

Anti-reflective coatings are ubiquitous on optical devices from solar cells to lenses, and are just one example of modifying surface properties using coatings.

Inspiration and advice on surface modification

Considering functional surfaces as a part of a product range is fast becoming essential, rather than an ‘optional extra’. Let me share some ideas with you about how to leverage various technologies in new product development.

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