Mesoporous GeOx/Ge/C as a Highly Reversible Anode Material with High Specific Capacity for Lithium-Ion Batteries.

Nanostructured Ge is considered a highly promising material for Li-ion battery applications as Ge offers high specific capacity and Li-ion diffusivity, while inherent mesoporous nanostructures can contribute resistance against capacity fading as typically induced by high volume expansion in bulk Ge films. Mesoporous GeOx/Ge/C films are synthesized using K4Ge9 Zintl clusters as a Ge precursor and the amphiphilic diblock copolymer polystyrene-block-polyethylene oxide as a templating tool. As compared to a reference sample without post-treatment, enhanced surface-to-volume ratios are achieved through post-treatment with a poor-good azeotrope solvent mixture. High capacities of over 2000 mA h g-1 are obtained with good stability over 300 cycles. Information from morphological and compositional characterization for both reference and post-treated sample suggests that the good electrochemical performance originates from reversible GeO2 conversion reactions.

Comparing the backfilling of mesoporous titania thin films with hole conductors of different sizes sharing the same mass density.

Efficient infiltration of a mesoporous titania matrix with conducting organic polymers or small molecules is one key challenge to overcome for hybrid photovoltaic devices. A quantitative analysis of the backfilling efficiency with time-of-flight grazing incidence small-angle neutron scattering (ToF-GISANS) and scanning electron microscopy (SEM) measurements is presented. Differences in the morphology due to the backfilling of mesoporous titania thin films are compared for the macromolecule poly[4,8-bis-(5-(2-ethyl-hexyl)-thio-phen-2-yl)benzo[1,2-b;4,5-b']di-thio-phene-2,6-diyl-alt-(4-(2-ethyl-hexyl)-3-fluoro-thieno[3,4-b]thio-phene-)-2-carboxyl-ate-2-6-diyl)] (PTB7-Th) and the heavy-element containing small molecule 2-pinacol-boronate-3-phenyl-phen-anthro[9,10-b]telluro-phene (PhenTe-BPinPh). Hence, a 1.7 times higher backfilling efficiency of almost 70% is achieved for the small molecule PhenTe-BPinPh compared with the polymer PTB7-Th despite sharing the same volumetric mass density. The precise characterization of structural changes due to backfilling reveals that the volumetric density of backfilled materials plays a minor role in obtaining good backfilling efficiencies and interfaces with large surface contact.

Nanoscale crystallization of a low band gap polymer in printed titania mesopores.

The crystallization behavior of the low band gap polymer poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3'''-di(2-octyldodecyl)2,2';5',2'';5'',2'''-quaterthiophen-5,5'''-diyl)] (PffBT4T-2OD) induced in printed mesoporous titania films with different pore sizes is studied to optimize the crystal orientation for an application in hybrid solar cells. The correlation between the crystal structure of PffBT4T-2OD and the titania pore size is investigated with a combination of grazing incidence wide-angle X-ray scattering (GIWAXS) and grazing incidence small-angle X-ray scattering (GISAXS). For comparison, poly(3-hexylthiophene) (P3HT) is also backfilled into the same four types of printed titania mesoporous scaffolds. Both, lattice constants and crystal sizes of edge-on oriented P3HT crystals decrease with increasing the titania pore size. Similarly and irrespective of the crystal orientation, a denser stacking of PffBT4T-2OD chains is found for larger pore sizes of the titania matrix. For an edge-on orientation, also bigger PffBT4T-2OD crystals are favorably formed in smaller pores, whereas for a face-on orientation, PffBT4T-2OD crystals increase with increasing size of the titania pores. Thus, the best ratio of face-on to edge-on crystals for PffBT4T-2OD is obtained through infiltration into large titania pores.

Hydration and Solvent Exchange Induced Swelling and Deswelling of Homogeneous Poly(N-isopropylacrylamide) Microgel Thin Films.

The investigation of the response kinetics of smart colloidal microgel films is crucial for their optimization to enable advanced applications. We study the classical thermoresponsive microgel model system N-isopropylacrylamide cross-linked with N,N'-methylenebisacrylamide. Without the typically used polyelectrolyte coating of the substrate, thin microgel films are prepared in a single spin-coating step. Atomic force microscopy measurements reveal an extremely dense packing, resulting in a homogeneous compact thin film of microgel particles. The hydration kinetics of these films in H2O and D2O atmospheres as well as the kinetics of the solvent exchange between both water species are investigated with in situ time-of-flight neutron reflectometry (TOF-NR) and in situ Fourier-transform infrared (FTIR) spectroscopy. With accounting for a nonconstant humid atmosphere, the intrinsic diffusion dynamics of water molecules into the thin microgel film are modeled and the specific time constant τ and the effective Flory-Huggins interaction parameter χeff are determined. Comparing the results in H2O and D2O atmospheres, TOF-NR and FTIR spectroscopy results show an increased affinity of the microgel films toward H2O as compared to D2O. From the FTIR spectroscopy data, we further identify different kinetics of intermolecular processes and order them according to their temporal evolution.

In Situ Monitoring Mesoscopic Deformation of Nanostructured Porous Titania Films Caused by Water Ingression.

Nanostructured porous titania films are used in many energy-related applications. In this work, the temporal evolution of the mesoscopic deformation of mesoporous titania films synthesized via block copolymer-assisted sol-gel chemistry is investigated with in situ grazing incidence small-angle neutron scattering (GISANS) during exposure to D2O vapor. Two types of mesoporous titania films are compared, which have a different degree of structural stability, depending on the applied annealing temperature (400 °C vs 600 °C) in a nitrogen atmosphere. Water ingression causes a gradual structure deformation in terms of decreasing center-to-center distances and broadening of the size distribution of the titania nanostructures. Based on the evolution of the mesopore size obtained from in situ GISANS measurements, the results show that structures synthesized at lower temperature undergo a stronger deformation because of the lower elastic modulus originating from larger pores, despite having a higher degree of order.

Morphology Tuning of ZnO/P3HT/P3HT- b-PEO Hybrid Films Deposited via Spray or Spin Coating.

Hybrid films of zinc oxide (ZnO) and poly(3-hexylthiophen-2,5-diyl) (P3HT) show promising characteristics for application in hybrid bulk-heterojunction solar cells (HBSCs). However, the incompatibility of ZnO and P3HT may lead to a reduced interface area, thus reducing the probability of exciton separation and consequently lowering solar cell efficiencies. Here, a diblock copolymer P3HT- b-poly(ethylene oxide) (PEO) is introduced to improve the interface between ZnO and P3HT. ZnO is synthesized via a block copolymer assisted sol-gel approach, and the used zinc precursor is directly incorporated into the PEO blocks. Thus, the possibility of aggregation is reduced for both the inorganic and the organic components, and a good intermixing is ascertained. Two deposition methods, namely, spray and spin coating, are compared with respect to the resulting film structure, which is investigated with scanning electron microscopy and time-of-flight grazing-incidence small-angle neutron scattering measurements. Both the surface and inner morphologies reveal that the spin coated samples possess smaller and less diverse domain sizes than the sprayed films. Due to the advantage of spray coating in large-scale production, the morphology of the sprayed samples is tailored more meticulously by changing the weight fraction of ZnO in the films. The sprayed hybrid films show smaller domains and less aggregation with decreasing the amount of ZnO. This reveals that both the deposition method and composition of the ZnO/P3HT/P3HT- b-PEO hybrid films play an important role for tailoring the film morphology and thus for improving the performance of HBSCs in future application.

Amphiphilic diblock copolymer-mediated structure control in nanoporous germanium-based thin films.

Fabrication of porous, foam-like germanium-based (Ge-based) nanostructures is achieved with the use of the amphiphilic diblock copolymer polystyrene-b-polyethylene oxide as structure directing agent. Basic concepts of block copolymer assisted sol-gel synthesis are successfully realized based on the [Ge9]4- Zintl clusters as a precursor for Ge-based thin films. Material/elemental composition and crystalline Ge-based phases are investigated via X-ray photoelectron spectroscopy and X-ray diffraction measurements, respectively. Poor-good solvent pair induced phase separation leads to pore sizes in the Ge-based films up to 40 nm, which can be tuned through a change of the molar mixing ratio between polymer template and precursor as proven by grazing incidence small angle X-ray scattering and scanning electron microscopy.

Deformation of Mesoporous Titania Nanostructures in Contact with D2 O Vapor.

For many applications, mesoporous titania nanostructures are exposed to water or need to be backfilled via infiltration with an aqueous solution, which can cause deformations of the nanostructure by capillary forces. In this work, the degree of deformation caused by water infiltration in two types of mesoporous, nanostructured titania films exposed to water vapor is compared. The different types of nanostructured titania films are prepared via a polymer template assisted sol-gel synthesis in conjunction with a polymer-template removal at high-temperatures under ambient conditions versus nitrogen atmosphere. Information about surface and inner morphology is extracted by scanning electron microscopy and grazing incidence small-angle neutron scattering (GISANS) measurements, respectively. Furthermore, complementary information on thin film composition and porosity are probed via X-ray reflectivity. The backfilling induced deformation of near surface structures and structures inside the mesoporous titania films is determined by GISANS before and after D2 O infiltration. The respective atmosphere used for template removal influences the details of the titania nanostructure and strongly impacts the degree of water induced deformation. Drying of the films shows reversibility of the deformation.

Readily available titania nanostructuring routines based on mobility and polarity controlled phase separation of an amphiphilic diblock copolymer.

The amphiphilic diblock copolymer polystyrene-block-polyethylene oxide is combined with sol-gel chemistry to control the structure formation of blade-coated foam-like titania thin films. The influence of evaporation time before immersion into a poor solvent bath and polarity of the poor solvent bath are studied. Resulting morphological changes are quantified by scanning electron microscopy (SEM) and grazing incidence small angle X-ray scattering (GISAXS) measurements. SEM images surface structures while GISAXS accesses inner film structures. Due to the correlation of evaporation time and mobility of the polymer template during the phase separation process, a decrease in the distances of neighboring titania nanostructures from 50 nm to 22 nm is achieved. Furthermore, through an increase of polarity of an immersion bath the energetic incompatibility of the hydrophobic block and the solvent can be enhanced, leading to an increase of titania nanostructure distances from 35 nm to 55 nm. Thus, a simple approach is presented to control titania nanostructure in foam-like films prepared via blade coating, which enables an easy upscaling of film preparation.

Monitoring the Swelling Behavior of PEDOT:PSS Electrodes under High Humidity Conditions.

Polymer electrodes made of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) are used in many applications but are also sensitive to humidity. We study humidity-induced changes of PEDOT:PSS electrodes as monitored with in situ time-of-flight neutron reflectivity (TOF-NR) measurements under high humidity conditions. The influence of the solvent additive Zonyl and a post-treatment of PEDOT:PSS films with ethylene glycol (EG) serving as electrodes are analyzed with respect to the swelling ratio and water uptake. Depending on the applied PEDOT:PSS treatment, PEDOT and PSS enrichment layers are clearly identified with TOF-NR at the substrate-polymer and polymer-air interface, respectively. The additive Zonyl reduces the water uptake and limits film swelling. EG post-treatment further increases hydrophobicity and thereby water incorporation into the PEDOT:PSS film is strongly suppressed. The characteristic time constants and effective interaction parameters extracted from the kinetic NR data show that additive and post-treatment reduce the sensitivity of the PEDOT:PSS electrodes to humidity.