Ordered structure constructed from C2-symmetric hexa-peri-hexabenzocoronene linked with oligo(dimethylsiloxane)

The preparation of sub-5-nm ordered structures is very important to the development of today's nanotechnology. Block molecules have the potential to form structures with significantly small characteristic dimensions. Herein two novel organic-inorganic block molecules composed of a hexa-peri-hexabenzocoronene (HBC) core and two oligo(dimethylsiloxane) (ODMS) tails with C₂ symmetry are reported. A hierarchical lamello-columnar structure with a two-dimensional rectangular lattice where HBC cores adopt a tilted arrangement was obtained from their bulk self-assembly. The feature sizes are all below 5 nm and can be regulated via the number of ODMS chains. Sub-5-nm line structures were obtained through spin-coating of the block molecules onto silicon substrates modified with poly(dimethylsiloxane). As organic-inorganic hybrid materials, these block molecules may be further applied in sub-5-nm nanopatterning.

Magnetic hybrid materials in liquid crystals

The integration of nanoparticles with magnetic, ferroelectric or semiconducting properties into liquid crystals (LCs) has attracted great interest both for fundamental investigations and for technological applications. Here, an overview of hybrid materials based on magnetic nanoparticles (MNPs) and thermotropic LCs is given. After a general introduction to thermotropic LCs and LC-MNP hybrid materials, various preparation methods established by us are presented. The synthesis of shape-(an)isotropic MNPs, their functionalization by tailored (pro)mesogenic ligands with linear or dendritic structures and their integration into LC hosts are discussed. The characterization of the MNPs, (pro)mesogenic ligands and resulting MNP-LC hybrid materials is described to show the influence of MNP functionalization on the MNP-LC interactions including aspects such as colloidal stability and structuring in the LC host. Overall, we show that the physical properties of the hybrid material are significantly influenced not only by the MNPs (i.e., their size, shape and composition) but also by their surface properties (i.e., the structure of the (pro)mesogenic ligands).

Dielectric behaviour of magnetic hybrid materials

The objectives of this work include the analysis of electrical and magnetic properties of magneto-elastic hybrid materials with the intention of developing new techniques for sensor and actuator applications. This includes the investigation of dielectric properties at both low and high frequencies. The behaviour of capacitors whose dielectrics comprise magnetic hybrid materials is well known. Such interfacial magnetocapacitance can be varied according to magnetic content, magnetic flux density and the relative permittivity of the polymer matrix together with other dielectric content. The basic function of trapping electrical charges in polymers (electrets) is also established technology. However, the combination of magnetoactive polymers and electrets has led to the first electromagnetic device capable of adhering to almost any material, whether magnetically susceptible or not. During the course of this research, in addition to dielectrics, electrically conductive polymers based on (PDMS) matrices were developed in order to vary the electrical properties of the material in a targeted manner. In order to ensure repeatable results, this demanded new fabrication techniques hitherto unavailable. The 3D printing of silicones is far from being a mature technology and much pioneering work was necessary before extending the usual 3 d.o.f. to include orientation about and diffusion of particles in these three axes, thus leading to the concept of 6D printing. In 6D printing, the application of a magnetic field can be used during the curing process to control the particulate distribution and thus the spatial filler particle density as desired. Most of the devices (sensors and actuators) produced by such methods contain levels of carbonyl iron powder (CIP) embedded magnetic filler of up to 70 wt%. Contrary to this, a hitherto neglected research area, namely magnetoactive polymers (MAPs) having significantly lower magnetic particle concentrations (1 to 3 wt% CIP) were also investigated. With filler concentrations lower than 3 wt%, structures are formed which are completely absent at higher filler levels. CIP concentrations in the range of 1wt% demonstrate the formation of toroidal structures. Further development of coherent rings with a compact order results as filler concentrations increase towards 2 wt%. Above 3 wt% the structure eventually disintegrates to the usual random order found in traditional MAP with higher CIP content. Structured samples containing 1%–3 wt% CIP were investigated with the aid of X-ray tomography where solitary ring structures can be observed and eventually the formation of capillary doubles. Over wavelengths ranging from 1 to 25 µm, spectroscopic analysis of thin film MAP samples containing 2 wt% CIP revealed measurable magnetic-field-dependent changes in IR absorption at a wavenumber 2350 (λ = 4.255 µm). This was found to be due to the diamagnetic susceptibility of atmospheric carbon dioxide (CO2). Consequently, the first potential application for sparse matrix MAPs was found.

Room-Temperature, Strain-Tunable Orientation of Magnetization in a Hybrid Ferromagnetic Co Nanorod-Liquid Crystalline Elastomer Nanocomposite

Hybrid nanocomposites based on magnetic nanoparticles dispersed in liquid crystalline elastomers are fascinating emerging materials. Their expected strong magneto-elastic coupling may open new applications as actuators, magnetic switches, and for reversible storage of magnetic information. We report here the synthesis of a novel hybrid ferromagnetic liquid crystalline elastomer. In this material, highly anisotropic Co nanorods are aligned through a cross-linking process performed in the presence of an external magnetic field. We obtain a highly anisotropic magnetic material which exhibits remarkable magneto-elastic coupling. The nanorod alignment can be switched at will at room temperature by weak mechanical stress, leading to a change of more than 50 % of the remnant magnetization ratio and of the coercive field.

Superparamagnetic amorphous iron oxide nanowires self-assembled into ordered layered structures

The thermal decomposition of μ3-oxo trinuclear iron(iii) acetate in presence of dodecylamine and oleic acid, in trichloroacetic acid at 320 °C was optimized to obtain iron oxide nanoparticles with pure nanowire morphology.

Strain-induced macroscopic magnetic anisotropy from smectic liquid-crystalline elastomer-maghemite nanoparticle hybrid nanocomposites

We combine tensile strength analysis and X-ray scattering experiments to establish a detailed understanding of the microstructural coupling between liquid-crystalline elastomer (LCE) networks and embedded magnetic core-shell ellipsoidal nanoparticles (NPs). We study the structural and magnetic re-organization at different deformations and NP loadings, and the associated shape and magnetic memory features. In the quantitative analysis of a stretching process, the effect of the incorporated NPs on the smectic LCE is found to be prominent during the reorientation of the smectic domains and the softening of the nanocomposite. Under deformation, the soft response of the nanocomposite material allows the organization of the nanoparticles to yield a permanent macroscopically anisotropic magnetic material. Independent of the particle loading, the shape-memory properties and the smectic phase of the LCEs are preserved. Detailed studies on the magnetic properties demonstrate that the collective ensemble of individual particles is responsible for the macroscopic magnetic features of the nanocomposite.

Liquid-crystalline nanoparticles: Hybrid design and mesophase structures

Liquid-crystalline nanoparticles represent an exciting class of new materials for a variety of potential applications. By combining supramolecular ordering with the fluid properties of the liquid-crystalline state, these materials offer the possibility to organise nanoparticles into addressable 2-D and 3-D arrangements exhibiting high processability and self-healing properties. Herein, we review the developments in the field of discrete thermotropic liquid-crystalline nanoparticle hybrids, with special emphasis on the relationship between the nanoparticle morphology and the nature of the organic ligand coating and their resulting phase behaviour. Mechanisms proposed to explain the supramolecular organisation of the mesogens within the liquid-crystalline phases are discussed.