Supramolecular hydrogels that are formed from low molecular weight gelators are a new class of soft materials which are gaining prominence. Depending on their molecular make up, these soft gel materials are formed based on different triggers, pH being one among them. In order to build applications with pH-triggered supramolecular gelators, it is necessary to understand their structure-property relationships and learn how to predict, control material properties. As explained in chapter 1, this thesis dealt with the above topics via three distinct fronts: Gelation kinetics, predictive modelling and electrochemical patterning....

Metallic pigments are versatile, eye-catching and increasingly utilized materials to create unique effects in plastics. However, these pigments usually show a higher sensitivity to weathering factors like UV light and water in polymer formulations than other pigments. In the particular case of Polyvinyl Chloride (PVC), this is even more evident for pigments containing iron based compounds (the typical red and orange brilliant colors) because they can initiate a degradation processes or catalyze oxidation of the polymer or other components. Thus, an improvement of such formulations for a better long term stability of the final products is needed.The present study was carried out in the Avery Dennison R&D laboratories. It was designed in order to carry out a preliminary test to address the issue of low durability of certain colored PVC based-films containing metallic pigments. Several sensitive pigments were selected as a case study for this project. In particular, the project aims to focus on understanding the effect of water on the surface of colored PVC cast films. Water retention on the surface of the films tends to cause accelerated and localized degradation of the PVC matrix enhanced by the effect of the metal oxides.What was observed for the pigmented PVC films is that as the pigment loading increases, the weathering durability improves. The degradation spots were mostly observed on the sides of the tested films but in some cases degradation spots were observed on the surface as well. The localized degradation on the sides is attributed to the damaged flake/particles of pigments which causes the initiation and propagation of PVC degradation in combination with water retention. After the SEM analysis, the degradation on the surface can be attributed to pigment flakes/particles really close to the films surface or even protruding from it where they can easily come in contact with water.Among all five selected additives (water scavenger, dispersants 1 and 2, fluorinated MICA and anticorrosive pigment), the ones with the best overall performance were the water scavenger and the anti-corrosive pigment. The water scavenger reacts with water avoiding its involvement in the PVC degradation process. Since water is not involved, less free radicals are formed and as a result, the propagation of PVC degradation is delayed. The anti-corrosive pigment increases the overall weathering durability of the system by protecting the sensitive metallic pigments with the Zn content of the anti-corrosive pigment surface treatment conferring sacrificial cathodic protection

Growing importance of hydrogels in various areas of human life has led to increasing need in controlling their properties, which is generally achieved by adjusting hydrogels shape and microstructure. Even though standard microfabrication and microstructuring techniques can be currently applied in hydrogel research, the variety of properties of hydrogel materials makes it difficult to employ any of these techniques universally. Furthermore, to produce hydrogel structures complex enough to mimic biological tissues, several structuring and microfabrication approaches on various length scales would need to be combined. The complexity and diversity of problems associated with such processes raises a whole set of multidisciplinary challenges. This doctoral dissertation explores novel approaches to structuring and fabrication of polymeric and supramolecular hydrogels by combining modern microfabrication techniques with molecular self-assembly and/or exploiting mutual incompatibility of certain hydrophilic polymers.

Self-assembly of amphiphilic block copolymers in aqueous solution provides a versatile tool to create complex and functional micelles with various nanostructures, such as spherical, cylindrical and bilayer structures. As an important class in these structures, nanofibrillar micelles have attracted growing interest due to their unique properties that can potentially mimic biological analogues. For example, a great number of nanofibrillar structures, such as actin filaments and collagen gels with filamentous structures, were found in nature systems and have greatly motivated researchers to mimic these systems with synthetic materials. Besides, precise spatiotemporal control and integration of these nanofibrillar structures will offer a powerful strategy for construction of new soft devices in the future. Therefore, in this thesis, we explore the ultra-long, stiff and quenched micelles of diblock copolymers and develop a hybrid approach combining self-assembly of block copolymers and micro-fabrication methods to manipulate these micelles for building soft devices.

Background: Soft-tissue grip is a challenge in minimally invasive surgery. Grasping instruments used in clinical practice require high pinch forces in order to generate sufficient grip for manipulating soft tissue without slipping.
In nature, several animals employ adhesion in order to grip on, not only hard, but also soft substrates. Among these animals, geckos and tree frogs are of special interest for engineered gripping systems, because of their high body mass. The toe pads of both animals are soft and characterized by a hierarchical pillar structure ranging from micro to nanoscale. Several research groups have mimicked this structure and demonstrated its potential for adhesive grip. Next to pillars, the toe pads of both animals possess a network of stiff inner fibers, which possibly also contributes to (friction) grip.
Aim: Inspired by the inner fiber network of geckos and tree frogs, the aim of this work was to investigate whether reinforcing a soft pad with stiff fibers increases friction on soft substrates as compared to a fiber-less pad. Our hypothesis was that provided that a soft exterior of such a pad establishes adhesive contact with the substrate, stiff fibers at a direction parallel to the substrate reduce the compliance of the pad in this direction, thereby preserving the established contact and thus increase the peak friction force.
Methods: Three experiments were conducted. In Experiment 1, composites consisting of 3D-printed fibers encapsulated in a polydimethylsiloxane (PDMS) pad were fabricated, and their adhesion and friction forces were measured. In Experiment 2, the friction of composites with stiffer 3D-printed fibers than those in Experiment 1 was measured. Lastly, in Experiment 3, the friction of composites consisting of a carbon fiber fabric encapsulated in PDMS of various stiffness degrees were tested. All experiments were conducted on both hard and soft gelatin substrates of various stiffness degrees, the latter functioning as soft-tissue phantoms.
Results: The results showed that, for all substrate types, adding 3D printed fibers with varying degrees of stiffness to a PDMS pad significantly reduced peak friction force, whereas adding a carbon fiber fabric significantly increased peak friction force compared to a fiber-less PDMS pad. The PDMS stiffness did not have a significant effect on friction force.
Conclusion: The results from this research are promising for developing fiber-reinforced composites for gripping to soft substrates, including minimally invasive grasping instruments for soft-tissue grip.