Khosrow Rahimi

Anisotropic Charge Transport in Spherulitic Poly(3-hexylthiophene) Films

Poly(3-hexylthiophene) (P3HT) is one of the most important semiconducting polymers for organic photovoltaics and optoelectronics.[1] Yet, because of the structural complexity of semicrystalline polymers, comparatively little is known conclusively about the relationship between charge transport and microstructure in P3HT-containing semiconductors.[2–9] This lack of information arises mainly from an inability to manufacture samples with spontaneous long-range crystalline order approaching macroscopic dimensions, that allow characterisation in a similar fashion to inorganic single crystals. We have overcome this limitation and grown well-ordered P3HT spherulites, sufficiently large to measure charge transport within single oriented crystal domains, enabling measurements of the charge mobility both parallel and perpendicular to the characteristic π-stacked nanocrystalline lamellae and across spherulite boundaries. The importance of local order and molecular orientation in determining the electronic properties of polymer semiconductor films is now well established.[3] In the case of the poly(alkylthiophenes) (PAT)s an edge-on orientation of the molecules, such that the alkyl sidechains (a-axis) stand vertically and both the chain backbone (c-axis) and π-stacking direction (b-axis) lie in the plane of the film, is critical in achieving high in-plane

Controllable Processes for Generating Large Single Crystals of Poly(3‐hexylthiophene)

Sowing the seeds: A simple strategy based on self-seeding allows large single crystals of long regioregular poly(3-hexylthiophene) chains to be grown from solution. When appropriately crystallized, materials differing in their degrees of regioregularity and molecular weights formed monoclinic form II crystals with interdigitated hexyl side groups (see picture).

Nacre-mimetics with synthetic nanoclays up to ultrahigh aspect ratios

Nacre-mimetics hold great promise as mechanical high-performance and functional materials. Here we demonstrate large progress of mechanical and functional properties of self-assembled polymer/nanoclay nacre-mimetics by using synthetic nanoclays with aspect ratios covering three orders in magnitude (25-3,500). We establish comprehensive relationships among structure formation, nanostructuration, deformation mechanisms and mechanical properties as a function of nanoclay aspect ratio, and by tuning the viscoelastic properties of the soft phase via hydration. Highly ordered, large-scale nacre-mimetics are obtained even for low aspect ratio nanoplatelets and show pronounced inelastic deformation with very high toughness, while those formed by ultralarge nanoplatelets exhibit superb stiffness and strength, previously only reachable for highly crosslinked materials. Regarding functionalities, we report formerly impossible glass-like transparency, and excellent gas barrier considerably exceeding earlier nacre-mimetics based on natural nanoclay. Our study enables rational design of future high-performance nacre-mimetic materials and opens avenues for ecofriendly, transparent, self-standing and strong advanced barrier materials.

Light absorption of poly(3-hexylthiophene) single crystals

We report the local UV-Vis absorption behaviour of single crystals of conjugated poly-3-hexylthiophene (P3HT), obtained by crystallization in dilute solutions at elevated temperatures based on a self-seeding approach and characterized by high internal structural order.

Nerve Cells Decide to Orient inside an Injectable Hydrogel with Minimal Structural Guidance

Injectable biomaterials provide the advantage of a minimally invasive application but mostly lack the required structural complexity to regenerate aligned tissues. Here, we report a new class of tissue regenerative materials that can be injected and form an anisotropic matrix with controlled dimensions using rod-shaped, magnetoceptive microgel objects. Microgels are doped with small quantities of superparamagnetic iron oxide nanoparticles (0.0046 vol %), allowing alignment by external magnetic fields in the millitesla order. The microgels are dispersed in a biocompatible gel precursor and after injection and orientation are fixed inside the matrix hydrogel. Regardless of the low volume concentration of the microgels below 3%, at which the geometrical constrain for orientation is still minimum, the generated macroscopic unidirectional orientation is strongly sensed by the cells resulting in parallel nerve extension. This finding opens a new, minimal invasive route for therapy after spinal cord injury.

Cubosomes from hierarchical self-assembly of poly(ionic liquid) block copolymers.

Cubosomes are micro- and nanoparticles with a bicontinuous cubic two-phase structure, reported for the self-assembly of low molecular weight surfactants, for example, lipids, but rarely formed by polymers. These objects are characterized by a maximum continuous interface and high interface to volume ratio, which makes them promising candidates for efficient adsorbents and host-guest applications. Here we demonstrate self-assembly to nanoscale cuboidal particles with a bicontinuous cubic structure by amphiphilic poly(ionic liquid) diblock copolymers, poly(acrylic acid)-block-poly(4-vinylbenzyl)-3-butyl imidazolium bis(trifluoromethylsulfonyl)imide, in a mixture of tetrahydrofuran and water under optimized conditions. Structure determining parameters include polymer composition and concentration, temperature, and the variation of the solvent mixture. The formation of the cubosomes can be explained by the hierarchical interactions of the constituent components. The lattice structure of the block copolymers can be transferred to the shape of the particle as it is common for atomic and molecular faceted crystals.

Social Self-Sorting of Colloidal Families in Co-Assembling Microgel Systems

Colloids are valuable model systems to understand the structure and dynamics of matter, explore new self-assembly concepts, and realize advanced materials. Herein, we demonstrate social self-sorting of co-assembled families of colloids by orthogonal host/guest recognition using cyclodextrins. We show that mixtures of four partners self-sort into their respective families without mutual interference. Additionally, the self-assemblies and their interactions are switchable using orthogonal triggers. This study goes beyond previous features of molecular self-sorting, and opens the design space for future self-sorting colloidal systems via rationally designed molecular recognition.

Supported Molybdenum Catalysts for the Deoxydehydration of 1,4-Anhydroerythritol into 2,5-Dihydrofuran

Efficient deoxygenation strategies are crucial for the valorization of renewable feedstocks. Deoxydehydration (DODH) enables the direct transformation of two adjacent hydroxyl groups into a double bond. Supported molybdenum-based catalysts were utilized for the first time in DODH. MoOx /TiO2 showed superior catalytic activity compared to common molybdenum salts. The catalyst efficiently converted 1,4-anhydroerythritol into 2,5-dihydrofuran in the presence of 3-octanol as reducing agent, showing high reproducibility and stability.

Stimulated Transitions of Directed Nonequilibrium Self-Assemblies

Near-equilibrium stimulus-responsive polymers have been used extensively to introduce morphological variations in dependence of adaptable conditions. Far-less-well studied are triggered transformations at constant conditions. These require the involvement of metastable states, which are either able to approach the equilibrium state after deviation from metastability or can be frozen on returning from nonequilibrium to equilibrium. Such functional nonequilibrium macromolecular systems hold great promise for on-demand transformations, which result in substantial changes in their material properties, as seen for triggered gelations. Herein, a diblock copolymer system consisting of a hydrophilic block and a block that is responsive to both pressure and temperature, is introduced. This species demonstrates various micellar transformations upon leaving equilibrium/nonequilibrium states, which are triggered by a temperature deflection or a temporary application of hydrostatic pressure.

Coacervation of Elastin-Like Recombinamer Microgels

The investigation of the coacervation (self-aggregation) behavior of biomicrogels which can potentially be used as drug carriers is an important topic, because self-aggregation can not only cause loss of activity, but also toxicity and immunogenicity. To study this effect microgels from elastin-like recombinamer are synthesized using miniemulsion technique. The existence of coacervation for such microgels, at different concentrations and temperatures, is studied and proved by cryo-field emission scanning clectron microscopy (cryo-FESEM), cryo-transmission electron microscopy (cryo-TEM), and by a novel (1) H high-resolution magic angle sample spinning (HRMAS), nuclear magnetic resonance (NMR) spectroscopy, and relaxometry methods. The findings by (1) H HRMAS NMR spectroscopy and relaxometry show simultaneous processes of volume phase temperature transition and coacervation with different sensitivity for hydrophobic and hydrophilic amino acid side-chains in the microgel. The coacervation process is more evidential by the behavior of glycine α-CH2 , (1) H NMR peak as compared to the proline β-CH2 .