Jan van Stam

Ibuprofen loading into mesostructured silica using liquid carbon dioxide as a solvent

It has been demonstrated that the pharmaceutical molecule, Ibuprofen, can be loaded into mesoporous silica using liquid (near-critical) carbon dioxide as the solvent, and that the resulting material had a high Ibuprofen content (300 mg Ibuprofen/g SiO2). A high enrichment (300 times) of Ibuprofen in the pores was observed in comparison to the Ibuprofen concentration in the solution. When similar experiments were performed in CO2 (l) mixed with minor amounts (5 mol-%) of other organic cosolvents (cyclohexane, acetone or methanol), a significantly lower loading capacity of Ibuprofen into the mesoporous material was achieved. The drug-loaded mesoporous silica material was analyzed with Thermogravimetric Analysis (TGA), confocal Raman microscopy, X-ray Powder Diffraction (XRPD) and Scanning Electron Microscopy (SEM). It was found that the Ibuprofen loaded into the mesoporous silica host was amorphous and that Ibuprofen was present both at the surface and in the centre of the mesoporous silica particles. Furthermore, the SEM images did not reveal any large flakes of Ibuprofen molecules outside the mesoporous silica particles.

Naphthalene Complexation by-Cyclodextrin: Influence of Added Short Chain Branched and Linear Alcohols

Naphthalene forms 1 : 1 complexes with β-cyclodextrin (β-CD)in water. The binding constant is 377 ± 35 M-1. Addition of linear or branched alcohols causes a reduction in the apparent strength of naphthalene binding (Kapp) compared to the value in the absence of additives. For example, 1% 1-pentanol reduces Kapp to 184 ± 31 M-1. Branching does not alter Kapp much for a given number of carbon atoms, e.g., it is 113 ± 9 M-1for 2-pentanol and 116 ± 8 M-1for 3-pentanol. The exception to this is tert-butanol for which Kapp is 577 ± 40 M-1. The variation in Kapp as a function of [1-pentanol] yields values for the individual equilibrium constants contributing to Kapp. This reveals that a ternary complex forms involving naphthalene, the CD and 1-pentanol. The constant for formation of the ternary complex is 99 ± 29 M-2. NaI quenching of naphthalene fluorescence indicates that the CD cavity partially protects the naphthalene excited state fromthis water phase quencher. Interestingly, the Stern–Volmer constant is lower in the presence of 1-pentanol than in its absence, although there should be more unbound (and therefore more NaI accessible) naphthalene in the former system than in the latter. These apparently contradictory results are discussed in terms of ternary complex formation.

Synchrotron XRR study of soft nanofilms at the mica–water interface

We describe here the design of a liquid cell specific for synchrotron X-ray reflectometry (XRR) characterisation of soft matter nanofilms at the mica–water interface. The feature of the cell is a “bending mica” method: by slightly bending the mica substrate over an underling cylinder the rigidity of the mica sheet along the bending axis is enhanced, providing sufficient flatness along the apex of the cylinder as required by XRR measurements. Using this cell, we have performed XRR measurements for a number of systems and in this article we show example results: (1) a cationic surfactant, C16TAB; (2) a zwitterionic surfactant, C12H25PC; (3) a semi-fluorinated surfactant, F4H11(d)TAB; and (4) surface complex of an anionic fluorinated surfactant, CsPFN, and a positively charged polymer, PEI. For the data analysis we have taken into account the mica crystal truncation rod, i.e. the reflectivity from the mica substrate, and fitted the data with a custom Java™ based software package. Our results unravel detailed structural information of these soft nanofilms, indicating that this method is suitable for XRR measurements of a wide range of soft matter structures at the mica–water interface.

Observation of α-terthiophene excited dimer fluorescence in aqueous solutions of γ-cyclodextrin

Observation of .alpha.-terthiophene excited dimer fluorescence in aqueous solutions of .gamma.-cyclodextrin

On the use of dynamic fluorescence measurements to determine equilibrium and kinetic constants. The inclusion of pyrene in .beta.-cyclodextrin cavities

Abstract An analysis of the kinetic identifiability of two-state excited-state processes goves the conditions which have to be fulfilled to make it possible to estimate the ground-state equilibrium constant from dynamic fluorescence data. For the aqueous system β-cyclodextrin:pyrene it turns out that the only kinetic parameters which can be estimated are (i) the deactivation rate constant of pyrene dissolved in the aqeuous mbulk, (ii) the rate of formation of a β-cyclodextrin:pyrene inclusion complex in the excited-state, which is negligibly slow, and (iii) the sum of the rate constats for deactivation to the ground-state and for exclusion into the aqueous bulk of the excited pyrene participating in inclusion complex formation. This sum cannot be separated into its individual rate constant contributions, and it is impossible to determine the ground-state equilibrium constant for the formation of β-cyclodextrin:pyrene inclusion complexes solely from fluorescence decay data, a fact not taken into account in the literature.

Fluorescence and UV/VIS absorption spectroscopy studies on polymer blend films for photovoltaics

The quinoxaline-based polymer TQ1 (poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5- diyl]) is a promising candidate as electron donor in organic solar cells. In combination with the electron acceptor [6,6]- phenyl-C71- butyric acid methyl ester (PC70BM), TQ1 has resulted in solar cells with power conversion efficiencies of 7 %. We have studied TQ1 films, with and without PC70BM, spin-casted from different solvents, by fluorescence spectroscopy and UV/VIS absorption spectroscopy. We used chloroform (CF), chlorobenzene (CB), and odichlorobenzene (o-DCB) as solvents for the coating solutions and 1-chloronaphthalene (CN) as solvent additive. CN addition has been shown to enhance photo-conversion efficiency of these solar cells. Phase-separation causes lateral domain formation in the films and the domain size depends on the solvent . These morphological differences coincide with changes in the spectroscopic patterns of the films. From a spectroscopic point of view, TQ1 acts as fluorescent probe and PC70BM as quencher. The degree of fluorescence quenching is coupled to the morphology through the distance between TQ1 and PC70BM. Furthermore, if using a bad solvent for PC70BM, morphological regions rich in the fullerene yield emission characteristic for aggregated PC70BM. Clear differences were found, comparing the TQ1:PC70BM blend films casted from different solvents and at different ratios between the donor and acceptor. The morphology also influences the UV/VIS absorption spectra, yielding further information on the composition. The results show that fluorescence and UV/VIS absorption spectroscopy can be used to detect aggregation in blended films and that these methods extend the morphological information beyond the scale accessible with microscopy.

α-Terthiophene in non-ionic Triton X-100 micelles: biphotonic creation of its radical cation

Abstract α -Terthiophene ( α T) has been photophysically and photochemically investigated in a non-ionic micellar environment. The distribution of α T amongst micelles is poissonian, this distribution determining its photophysical and photochemical reactivity. Neither ground-state α T, nor its triplet, migrates between micelles while the radical cation does so via the aqueous bulk. From transient absorption measurements, with different laser energies, it is concluded that the creation of the radical α T · + is biphotonic, contrary to what has been reported for homogeneous solutions.

Morphology in dip-coated blend films for photovoltaics studied by UV/VIS absorption and fluorescence spectroscopy

Blend thin films, prepared by dip-coating, of polyfluorene (F8 or PFO), acting as an electron donor, and [6,6]-phenyl-C61- butyric acid methyl ester (PC60BM), acting as the electron acceptor, have been characterized by UV/VIS absorption spectroscopy, static and dynamic fluorescence, and atomic force microscopy. Four different solvents were used for the film preparation; the monohalogenated fluorobenzene and chlorobenzene and their dihalogenated counterparts odifluorobenzene and o-dichlorobenzene, respectively. Fluid mechanics calculations were used to determine the withdrawal speed for each solvent, in order to prepare wet films of comparable thicknesses. The resulting dry films were also of similar thicknesses. It was found that the choice of solvent influences the ability for F8 to form its β-phase.

Comparing morphology in dip-coated and spin-coated polyfluorene:fullerene films

When preparing the active layer film for organic optoelectronic devices, e.g., solar cells, spin-coating is often used for the deposition of the solution of electron donor and acceptor molecules. An alternative, among others, is to use dipcoating, where the substrate is dipped into the solution and subsequently withdrawn, all at coordinated speeds and times. In order to develop knowledge on how the final active layer morphology is influenced by preparation parameters, different coating methods are compared. In this contribution, we report on a comparative study of thin deposited films from a model system. The investigated model system is poly(9,9-dioctylfluorene) (F8, also referred to as PFO) as donor and [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) as acceptor. Combining fluorescence and absorption spectroscopy with atomic force microscopy allows us to conclude that dipcoating offers increased possibilities to manipulate the film morphology, that the transition of the glassy F8 α-phase to the more ordered β-phase is influenced by the dipping speed as well as by the blend ratio, and that the long-wavelength emission of F8 cannot stem from the oxidized keto-F8 only.

Fullerene Aggregation in Thin Films of Polymer Blends for Solar Cell Applications

We report on the effects of the film morphology on the fluorescence spectra for a thin film including a quinoxaline-based co-polymer (TQ1) and a fullerene derivative ([6,6]-phenyl-C71-butyric acid methyl ester—PC70BM). The ratio between the polymer and the fullerene derivative, as well as the processing solvent, were varied. Besides the main emission peak at 700 nm in the fluorescence spectra of thin films of this phase-separated blend, a broad emission band is observed with a maximum at 520–550 nm. The intensity of this emission band decreases with an increasing degree of mixing in the film and becomes most prominent in thicker films, films with high PC70BM content, and films that were spin-coated from solvents with lower PC70BM solubility. We assign this emission band to aggregated PC70BM.