Utilising thermoporometry to obtain new insights into nanostructured materials

Thermoporometry is a relatively new method of characterising porous properties of nanostructured materials based on observation of solid–liquid phase transitions of materials confined in pores. It provides several advantages over the conventional characterisation methods, mercury porosimetry and gas sorption. The advantages include possibility of using short measurement times, non-toxic chemicals and wet samples. In addition, complicated sample preparation and specialised instruments are not required. Therefore, it has a great potential of becoming a widely utilised characterisation method, although its potential has not yet been widely realised. In recent years, there has been a significant increase in research activities regarding the method. In the first part of the review, we introduce thermoporometry and review related results of the confinement effects on materials and their solid–liquid phase transition.     

Switching Properties of a Spiropyran–Cucurbit[7]uril Supramolecular Assembly: Usefulness of the Anchor Approach

A nitrospiropyran, which was modified with a cadaverine‐derived anchor, was investigated with respect to its thermally induced isomerizations, hydrolytic stability of the merocyanine form, and photochromic ring closure. The host–guest complexation of the anchor by the cucurbit[7]uril macrocycle, evidenced by absorption titration, NMR spectroscopy, and electrospray ionization mass spectrometry, produced significant improvements of the switching properties of the photochrome: 1) appearance of the merocyanine form about 70 times faster, 2) practically unlimited hydrolytic stability of the merocyanine (two and a half days without any measureable decay), and 3) fast, clean, and fatigue‐resistant photoinduced ring closure back to the spiro form. The importance of an adequate molecular design of the anchor was demonstrated by including control experiments with spiropyrans with a shorter linker or without such structural asset.     

All-photonic molecular half-adder

One molecule acts as both an AND and an XOR Boolean logic gate that share the same two photonic inputs. The molecule comprises a half-adder, adding two binary digits with only light as inputs and outputs, and consists of three covalently linked photochromic moieties, a spiropyran and two quinoline-derived dihydroindolizines. The AND function is based on the absorption properties of the molecule, whereas the XOR function is based on an off-on-off response of the fluorescence to the inputs that results from interchromophore excited-state quenching interactions. The half-adder is simple to operate and can be cycled many times.     

Information Processing with Molecules—Quo Vadis?

Information processing at the molecular level is coming of age. Since the first molecular AND gate was proposed about 20 years ago, the molecular interpretation of binary logic has become vastly more sophisticated and complex. However, the field is also at a crossroads. While cleverly designed molecular building blocks are abundant, difficult questions remain. How can molecular components be flexibly assembled into larger circuits, and how can these components communicate with one another. The concept of all‐photonic switching with photochromic supermolecules has shown some interesting potential and is discussed in this review. Although the field of molecular logic was originally discussed mainly in terms of a technology that might compete with solid‐state computers, potential applications have expanded to include clever molecular systems and materials for drug delivery, sensing, probing, encoding, and diagnostics. These upcoming trends, which are herein illustrated by selected examples, deserve general attention.     

Utilising thermoporometry to obtain new insights into nanostructured materials

Thermoporometry is a relatively new method of characterising porous properties of nanostructured materials based on observation of solid–liquid phase transitions of materials confined in pores. It provides several advantages over the conventional characterisation methods, mercury porosimetry and gas sorption. The advantages include possibility of using short measurement times, non-toxic chemicals and wet samples. In addition, complicated sample preparation and specialised instruments are not required. Therefore, it has a great potential of becoming a widely utilised characterisation method, although its potential has not yet been widely realised. In recent years, there has been a significant increase in research activities regarding the method. In the second part of the review, results and conclusions of the recent studies about thermoporometry are surveyed and discussed focusing on the application of thermoporometry in extracting various structural information from the porous materials.     

Some comments and corrections regarding the calculation of electrostatic potential derivatives using the Ewald summation technique

A review of the literature on the calculation of electrostatic potentials, fields, and field gradients in systems consisting of charges and dipoles using the Ewald summation technique is presented. Discrepancies between the previous formulas are highlighted, and an error in the derivation of the reciprocal contributions to the electrostatic field and field gradient is corrected. The new formulas for the field and field gradient are shown to exhibit a termwise identity with the ones for the electrostatic energy.     

Simultaneous one-dimensional fluorescence lifetime measurements of OH and CO in premixed flames

A method for simultaneous measurements of fluorescence lifetimes of two species along a line is described. The experimental setup is based on picosecond laser pulses from two tunable optical parametric generator/optical parametric amplifier systems together with a streak camera. With an appropriate optical time delay between the two laser pulses, whose wavelengths are tuned to excite two different species, laser-induced fluorescence can be both detected temporally and spatially resolved by the streak camera. Hence, our method enables one-dimensional imaging of fluorescence lifetimes of two species in the same streak camera recording. The concept is demonstrated for fluorescence lifetime measurements of CO and OH in a laminar methane/air flame on a Bunsen-type burner. Measurements were taken in flames with four different equivalence ratios, namely ? = 0.9, 1.0, 1.15, and 1.25. The measured one-dimensional lifetime profiles generally agree well with lifetimes calculated from quenching cross sections found in the literature and quencher concentrations predicted by the GRI 3.0 mechanism. For OH, there is a systematic deviation of approximately 30 % between calculated and measured lifetimes. It is found that this is mainly due to the adiabatic assumption regarding the flame and uncertainty in H₂O quenching cross section. This emphasizes the strength of measuring the quenching rates rather than relying on models. The measurement concept might be useful for single-shot measurements of fluorescence lifetimes of several species pairs of vital importance in combustion processes, hence allowing fluorescence signals to be corrected for quenching and ultimately yield quantitative concentration profiles.     

Atmospheric pressure chemical vapour synthesis of silicon–carbon nanoceramics from hexamethyldisilane in high temperature aerosol reactor

Silicon–carbon nanoceramics have been synthesised from hexamethyldisilane (HMDS) by the atmospheric pressure chemical vapour synthesis (APCVS). Direct aerosol phase synthesis enables continuous production of high purity materials in one-stage process. The particle formation is based on the decomposition of the precursor in a high temperature reactor. Reaction of the gas phase species leads to homogeneous nucleation and formation of the nanoparticles with a narrow size distribution (geometric mean diameter range of particle number size distribution 160–200 nm with 1.5–1.6 geometric standard deviation at reaction temperatures 800–1200 °C). A systematic investigation of the influence of the process temperature on the powder characteristics, including the particle size, crystallinity, chemical structure, surface and bulk composition and surface morphology, was carried out. At the reactor temperature of 800 °C, the synthesised nanoparticles were amorphous preceramics containing mostly SiC₄, Si–CH₂–Si and Si–H units. The composition of the powder turned towards nanocrystalline 3C–SiC (crystal size under 2 nm) when the reaction temperature was increased to 1200 °C. The reaction temperature appeared to be a key parameter controlling the structure and properties of the synthesised powders.     

Aerosol characterization and lung deposition of synthesized TiO2 nanoparticles for murine inhalation studies

This study presents a novel exposure protocol for synthesized nanoparticles (NPs). NPs were synthesized in gas phase by thermal decomposition of metal alkoxide vapors in a laminar flow reactor. The exposure protocol was used to estimate the deposition fraction of titanium dioxide (TiO₂) NPs to mice lung. The experiments were conducted at aerosol mass concentrations of 0.8, 7.2, 10.0, and 28.5 mg m^?3. The means of aerosol geometric mobility diameter and aerodynamic diameter were 80 and 124 nm, and the geometric standard deviations were 1.8 and 1.7, respectively. The effective density of the particles was approximately from 1.5 to 1.7 g cm^?3. Particle concentration varied from 4 × 10⁵ cm^?3 at mass concentrations of 0.8 mg m^?3 to 12 × 10⁶ cm^?3 at 28.5 mg m^?3. Particle phase structures were 74% of anatase and 26% of brookite with respective crystallite sized of 41 and 6 nm. The brookite crystallites were approximately 100 times the size of the anatase crystallites. The TiO₂ particles were porous and highly agglomerated, with a mean primary particle size of 21 nm. The specific surface area of TiO₂ powder was 61 m² g^?1. We defined mice respiratory minute volume (RMV) value during exposure to TiO₂ aerosol. Both TiO₂ particulate matter and gaseous by-products affected respiratory parameters. The RMV values were used to quantify the deposition fraction of TiO₂ matter by using two different methods. According to individual samples, the deposition fraction was 8% on an average, and when defined from aerosol mass concentration series, it was 7%. These results show that the exposure protocol can be used to study toxicological effects of synthesized NPs.