| 1. |
- Cautela, Jacopo, et al.
(författare)
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Supracolloidal Atomium
- 2020
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 14:11, s. 15748-15756
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Tidskriftsartikel (refereegranskat)abstract
- Nature suggests that complex materials result from a hierarchical organization of matter at different length scales. At the nano- and micrometer scale, macromolecules and supramolecular aggregates spontaneously assemble into supracolloidal structures whose complexity is given by the coexistence of various colloidal entities and the specific interactions between them. Here, we demonstrate how such control can be implemented by engineering specially customized bile salt derivative-based supramolecular tubules that exhibit a highly specific interaction with polymeric microgel spheres at their extremities thanks to their scroll-like structure. This design allows for hierarchical supracolloidal self-assembly of microgels and supramolecular scrolls into a regular framework of “nodes” and “linkers”. The supramolecular assembly into scrolls can be triggered by pH and temperature, thereby providing the whole supracolloidal system with interesting stimuli-responsive properties. A colloidal smart assembly is embodied with features of center-linker frameworks as those found in molecular metal–organic frameworks and in structures engineered at human scale, masterfully represented by the Atomium in Bruxelles.
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| 2. |
- Chae, Soosang, et al.
(författare)
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Stretchable Thin Film Mechanical-Strain-Gated Switches and Logic Gate Functions Based on a Soft Tunneling Barrier
- 2021
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Ingår i: Advanced Materials. - : Wiley-Blackwell. - 0935-9648 .- 1521-4095. ; 33:41
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Tidskriftsartikel (refereegranskat)abstract
- Mechanical-strain-gated switches are cornerstone components of material-embedded circuits that perform logic operations without using conventional electronics. This technology requires a single material system to exhibit three distinct functionalities: strain-invariant conductivity and an increase or decrease of conductivity upon mechanical deformation. Herein, mechanical-strain-gated electric switches based on a thin-film architecture that features an insulator-to-conductor transition when mechanically stretched are demonstrated. The conductivity changes by nine orders of magnitude over a wide range of tunable working strains (as high as 130%). The approach relies on a nanometer-scale sandwiched bilayer Au thin film with an ultrathin poly(dimethylsiloxane) elastomeric barrier layer; applied strain alters the electron tunneling currents through the barrier. Mechanical-force-controlled electric logic circuits are achieved by realizing strain-controlled basic (AND and OR) and universal (NAND and NOR) logic gates in a single system. The proposed material system can be used to fabricate material-embedded logics of arbitrary complexity for a wide range of applications including soft robotics, wearable/implantable electronics, human-machine interfaces, and Internet of Things.
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| 3. |
- Erik, Johansson
(författare)
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Molecular Interactions in Thin Films of Biopolymers, Colloids and Synthetic Polyelectrolytes
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of the layer-by-layer (LbL) technique has turned out to be an efficient way to physically modify the surface properties of different materials, for example to improve the adhesive interactions between fibers in paper. The main objective of the work described in this thesis was to obtain fundamental data concerning the adhesive properties of wood biopolymers and LbL films, including the mechanical properties of the thin films, in order to shed light on the molecular mechanisms responsible for the adhesion between these materials.LbLs constructed from poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA), starch containing LbL films, and LbL films containing nanofibrillated cellulose (NFC) were studied with respect to their adhesive and mechanical properties. The LbL formation was studied using a combination of stagnation point adsorption reflectometry (SPAR) and quartz crystal microbalance with dissipation (QCM-D) and the adhesive properties of the different LbL films were studied in water using atomic force microscopy (AFM) colloidal probe measurements and under ambient conditions using the Johnson-Kendall-Roberts (JKR) approach. Finally the mechanical properties were investigated by mechanical buckling and the recently developed SIEBIMM technique (strain-induced elastic buckling instability for mechanical measurements).From colloidal probe AFM measurements of the wet adhesive properties of surfaces treated with PAH/PAA it was concluded that the development of strong adhesive joints is very dependent on the mobility of the polyelectrolytes and interdiffusion across the interface between the LbL treated surfaces to allow for polymer entanglements.Starch is a renewable, cost-efficient biopolymer that is already widely used in papermaking which makes it an interesting candidate for the formation of LbL films in practical systems. It was shown, using SPAR and QCM-D, that LbL films can be successfully constructed from cationic and anionic starches on silicon dioxide and on polydimethylsiloxane (PDMS) substrates. Colloidal probe AFM measurements showed that starch LbL treatment have potential for increasing the adhesive interaction between solid substrates to levels beyond those that can be reached by a single layer of cationic starch. Furthermore, it was shown by SIEBIMM measurements that the elastic properties of starch-containing LbL films can be tailored using different nanoparticles in combination with starch.LbL films containing cellulose I nanofibrils were constructed using anionic NFC in combination with cationic NFC and poly(ethylene imine) (PEI) respectively. These NFC films were used as cellulose model surfaces and colloidal probe AFM was used to measure the adhesive interactions in water. Furthermore, PDMS caps were successfully coated by LbL films containing NFC which enabled the first known JKR adhesion measurements between cellulose/cellulose, cellulose/lignin and cellulose/glucomannan. The measured adhesion and adhesion hysteresis were similar for all three systems indicating that there are no profound differences in the interaction between different wood biopolymers. Finally, the elastic properties of PEI/NFC LbL films were investigated using SIEBIMM and it was shown that the stiffness of the films was highly dependent on the relative humidity.
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| 4. |
- Feicht, Patrick, et al.
(författare)
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Systematic evaluation of different types of graphene oxide in respect to variations in their in-plane modulus
- 2017
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Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 114, s. 700-705
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Tidskriftsartikel (refereegranskat)abstract
- Graphene oxide samples prepared in various laboratories following a diversity of synthesis protocols based on Brodie's (BGO) and Hummers/Offeman's (HGO) methods were compared in respect of their in plane moduli. A simple wrinkling method allowed for a spatial resolution <1.5 pm by converting the wrinkling frequency. Quite surprisingly, a drastic variation of the in-plane moduli was found spanning the range from 600 GPa for the best BGO types, which is in the region of chemically derived graphene, all the way down to less than 200 GPa for HGO types. This would suggest that there are no two equal GO samples and GO should not be regarded a compound but rather a class of materials with very variable physical properties. While large differences between Brodie's and Hummers/Offeman's types might have been expected, even within the group of Hummers/Offeman's types pronounced differences are observed that, based on C-13 solid-state NMR, were related to over-functionalization versus over-oxidation.
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| 5. |
- Marais, Andrew, 1988-
(författare)
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Tailored cellulosic materials by physical adsorption of polyelectrolytes
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The growing interest in using bio-based resources has made forest-based cellulose (used as fibre and nanofibril building elements) a good candidate for the development of new materials. In order to be used in commercial applications, cellulose must however be processed and/or functionalized to provide the final material with specific properties. This thesis presents (a) a way to improve the mechanical properties of traditional cellulose-based materials (paper), (b) an investigation into the structural and adhesive properties of the self-assembled hyaluronic acid thin films used to tailor the mechanical properties of paper materials, and (c) the preparation and functionalization of cellulose aerogels.In the first part of this thesis, the adsorption of polyelectrolytes onto pulp fibres (either as a monolayer or as multilayers) was studied as a way to improve the mechanical properties of paper materials. It was found that low amounts of adsorbed cationic amines were able to significantly improve the tensile properties of sheets made from treated fibres. Tensile testing of fibre crosses and microtomography revealed that this improvement in mechanical properties was due to an increase in both the interfibre joint strength and the interfibre contact area. By building up polyelectrolyte multilayers of hyaluronic acid (HA) and polyallylamine hydrochloride (PAH) onto the fibres, a threefold increase in both strain at break and tensile strength was achieved.Finally, wet-resilient porous cellulose aerogels were developed by freezedrying and crosslinking cellulose nanofibrillar gels. This material with high porosity and a high specific surface area was then used as a template to build three dimensional (3D) energy-storage devices using the Layer-by-Layer approach. Thin films of conductive materials were ivdeposited into the bulk of the material, and 3D-interdigitated supercapacitors and batteries were built. The devices showed high capacitance and operated under extreme conditions of compression and bending, opening up numerous possibilities in the field of flexible electronics.
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| 6. |
- Poehlman, Melanie, et al.
(författare)
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Magnetic microbubbles for multimodality imaging : the importance of the shell structure for low and high frequency mechanics
- 2013
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Konferensbidrag (refereegranskat)abstract
- There is a growing interest in magnetic microbubbles (MBs) for simultaneous enhanced ultrasound (US) and enhanced magnetic resonance imaging (MRI) to support well-established imaging procedures as well as new emerging diagnostic and therapeutic applications. However, the development of hybrid contrast agents is challenging, because their design needs to satisfy a variety of requirements such as a sufficient stability of the probe for the circulation within the cardiovascular system, the production of an adequate US echo signal and a reasonable reduced relaxation time of nearby located protons. The studied magnetic MBs consist of an air-filled core, which is encapsulated by a soft hydrogel-like shell composed of poly(vinyl alcohol) and superparamagnetic iron oxide nanoparticles (SPIONs)[1]. Two strategies were used to combine magnetic nanoparticles with the polymeric shell: SPIONs were either covalently attached to the shell surface via a post-chemical treatment or embedded physically inside the shell during the MBs’ synthesis. In particular, we were interested on the impact of the used SPIONs integration strategy on low and high frequency mechanics of the magnetic MBs. Therefore, we used a straightforward characterization of the MBs on the single particle level to correlate the synthesis with the MBs’ morphological properties and low frequency mechanics that were studied in quasi-static force measurements with atomic force microscopy. High frequency mechanics were investigated by exposure of an ensemble of MBs to an acoustic field. By further correlation of low and high frequency mechanics, we were able to bridge the gap between synthesis and the MBs macroscopic properties relevant for their application. The shown approach offers the possibility to sustainable design and optimize complex probes based on an improved understanding of structure/property relations.
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| 7. |
- Poehlmann, Melanie, et al.
(författare)
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On the interplay of shell structure with low- and high-frequency mechanics of multifunctional magnetic microbubbles
- 2014
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 10:1, s. 214-226
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Tidskriftsartikel (refereegranskat)abstract
- Polymer-shelled magnetic microbubbles have great potential as hybrid contrast agents for ultrasound and magnetic resonance imaging. In this work, we studied US/MRI contrast agents based on air-filled poly(vinyl alcohol)-shelled microbubbles combined with superparamagnetic iron oxide nanoparticles (SPIONs). The SPIONs are integrated either physically or chemically into the polymeric shell of the microbubbles (MBs). As a result, two different designs of a hybrid contrast agent are obtained. With the physical approach, SPIONs are embedded inside the polymeric shell and with the chemical approach SPIONs are covalently linked to the shell surface. The structural design of hybrid probes is important, because it strongly determines the contrast agent's response in the considered imaging methods. In particular, we were interested how structural differences affect the shell's mechanical properties, which play a key role for the MBs' US imaging performance. Therefore, we thoroughly characterized the MBs' geometric features and investigated low-frequency mechanics by using atomic force microscopy (AFM) and high-frequency mechanics by using acoustic tests. Thus, we were able to quantify the impact of the used SPIONs integration method on the shell's elastic modulus, shear modulus and shear viscosity. In summary, the suggested approach contributes to an improved understanding of structure-property relations in US-active hybrid contrast agents and thus provides the basis for their sustainable development and optimization.
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| 9. |
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