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Self-regenerating Functional Surfaces – Towards a Technology Platform for New Materials and Devices

Periodic Reporting for period 3 - Regenerate (Self-regenerating Functional Surfaces – Towards a Technology Platform for New Materials and Devices)

Reporting period: 2018-05-01 to 2019-10-31

The aim for this research project is a technology platform that allows the self-regeneration of surface properties. In current technology, many devices fail when their surfaces are contaminated. We therefore wanted to develop a material that can selectively and sequentially shed its contaminated or defective layers, like a reptile shedding its skin, and present a fresh, functional one.
The target material consists of discrete, non-interpenetrating, alternating layers of functional and degradable polymers. When the upper functional layer is contaminated or damaged, the layer underneath is degraded. This enables shedding of the entire topmost functional layer. Due to a degradability gradient through the stack, only the top degradable layer should be removed, so that the stack can be “skinned” sequentially. The selective and sequential shedding of polymer layers from a multi-stack, with the aim of obtaining functionally intact successive layers, is so far an unresolved and therefore extremely attractive, fundamentally important concept, both from a basic science and an application point of view. Solving this problem would open up a new field in materials science.
We want to demonstrate the feasibility of our concept with two research objectives: Objective 1: Sequential regeneration of a functional surface property, exemplified by antimicrobial activity; Objective 2: Regeneration of the activity of a functional device, exemplified by a glucose sensor.
For Objective 1, we first had to compiled a “toolbox” of polymers with different degradation rates to enable sequential and selective layer shedding. The synthesis and polymer characterization of these polymers are finished; the polymer degradation rates have been quantified usind three methods specifically developed for this project. The polymers had degradation rates that differed by a factor of 25, which is suitalbe for their applications in a multilayer system. We also synthesized novel functional polymers for Objective 1, including cross-linkable and fluorescent ones. We then assembled these different components to build the target system, a polymer multistack. With a series of experiments, we demonstrated under which conditions such a stack can shed layers, and where such shedding fails.

The results so far achieved, particular in the cases were layer shedding did not work, demonstrated that delamination from a polymer multilayer stack is significantly more difficult than anticipated. For the polymer multistack systems here considered, the following has been be learnt: First, it will be more difficult to delaminate one polymer layer from another one than from a hard substrate as both materials are comparatively soft and elastic. As such, they can adjust to interfacial changes, provided these changes do not induce sudden, dramatic stresses. Second, it is not sufficient to consider the local molecular interactions between the polymer layers. Instead, these layers must be considered as a polyvalent system. To break the adhesion between two such layers, a sufficient amount of bonding interactions must be broken simultaneously. In the initial design of the systems studied by us (WP 1.2) it was anticipated that shedding could be achieved by simply removing any kind of sacrificial layer. However, some of the results of demonstrate that the top and bottom layer surrounding the interfacial layer can adjust and re-form bonding interactions that prevent shedding under certain conditions. Thus, the time scale of delamination, i.e. the kinetics of disintegration of the sacrificial layer, plays a vital role. In nature, when reptiles shed their skin, molecular processes take place that remove bonding interactions between the old hide and the emerging skin layer. Yet as in our model system, this is insufficient to shed the hide – for this, the reptile has to rub against stones. This indicates that mechanical stresses are play an important role for shedding and should also be the path to success in our polymerlayer multistack.
• Three methods to study degradation of surface-attached (polymer) films.
• Synthesis of several novel monomers and polymers.
• Novel methods to selectively and sequentially shed polymer layers from a multistack.
Concept of layer shedding