Jens Rieger

Organic Nanoparticles in the Aqueous Phase—Theory, Experiment, and Use

Many active organic compounds and organic effect materials are poorly soluble in water, or even insoluble. Aqueous forms of application thus require special formulation techniques to utilize or optimize the physiological (pharmaceuticals, cosmetics, plant protection, nutrition) or technical (varnishes, printing inks, toners) action. The most interesting properties of nanodispersions of active organic compounds and effect materials include the impressive increase in solubility, the improvement in biological resorption, and the modification of optical, electrooptical, and other physical properties which are achievable only with particle sizes in the middle or lower nanometer range (50-500 nm). Hence in addition to economic and ecological constraints there are also technical demands which appear to urgently require the development of new processes for the production of organic nanoparticles as alternatives to the established mechanical milling processes. In this context attention is drawn to the recent increase in research activities which have as their objective the continuous, automatic preparation of nanodispersed systems by precipitation from molecular solution. In this review the current state of knowledge of the fundamentals of particle formation from homogeneous solution and the effect of solvent and polymer additives on the morphology and supramolecular structure of the nanoparticle will be discussed. The practical implementation of this new formulation technology will be explored in detail for the carotenoids, a class of compounds of both physiological and technical interest.

Organische Nanopartikel in wässriger Phase – Theorie, Experiment und Anwendung

Viele organische Wirk- und Effektstoffe sind in Wasser schwer loslich oder sogar unloslich. Wassrige Anwendungsformen erfordern daher besondere Formulierungsverfahren, um die physiologische (Pharma, Kosmetik, Pflanzenschutz, Ernahrung) oder technologische Wirkung (Lacke, Druckfarben, Toner) nutzen zu konnen oder zu optimieren. Zu den interessantesten Eigenschaften nanodisperser Verteilungen organischer Wirk- und Effektstoffe gehoren die drastische Erhohung der Loslichkeit, die Verbesserung der biologischen Resorption sowie die Modifizierung optischer, elektrooptischer und anderer physikalischer Eigenschaften, die erst mit Teilchengrosen im mittleren und unteren Nanometerbereich (50–500 nm) erzielbar sind. So sind es neben okonomischen und okologischen Zwangen auch technologische Herausforderungen, die als Alternative zu den etablierten mechanischen Zerkleinerungsverfahren die Entwicklung neuer Verfahren zur Herstellung organischer Nanopartikel als dringend geboten erscheinen lassen. In diesem Sinne sind in jungster Zeit vermehrt Forschungsaktivitaten zu verzeichnen, die die kontinuierliche, automatisierte Herstellung nanodisperser Systeme durch Fallung aus molekularer Losung zum Ziel haben. Im vorliegenden Aufsatz wird der aktuelle Kenntnisstand zu den Grundlagen der Partikelbildung aus homogener Losung, zum Einfluss des Losungsmittels und polymerer Additive auf die Morphologie und auf die supramolekulare Struktur der Nanopartikel dargestellt. Anhand der sowohl physiologisch als auch technologisch interessanten Stoffklasse der Carotinoide wird die praktische Umsetzung dieser neuen Formulierungstechnologie eingehend erlautert.

Formation of Nanoparticles and Nanostructures—An Industrial Perspective on CaCO3, Cement, and Polymers

Nanotechnology enables the design of materials with outstanding performance. A key element of nanotechnology is the ability to manipulate and control matter on the nanoscale to achieve a certain desired set of specific properties. Here, we discuss recent insight into the formation mechanisms of inorganic nanoparticles during precipitation reactions. We focus on calcium carbonate, and describe the various transient stages potentially occurring on the way from the dissolved constituent ions to finally stable macrocrystals-including solute ion clusters, dense liquid phases, amorphous intermediates, and nanoparticles. The role of polymers in nucleating, templating, stabilizing, and/or preventing these structures is outlined. As a specific example for applied nanotechnology, the properties of cement are shown to be determined by the formation and interlocking of calcium-silicate-hydrate nanoplatelets. The aggregation of these platelets into mesoscale architectures can be controlled with polymers.

Analysis of the Nucleation and Growth of Amorphous CaCO3 by Means of Time-Resolved Static Light Scattering

The formation of amorphous calcium carbonate particles from supersaturated aqueous solution is relevant to many processes in nature and industry. The present work introduces time-resolved static light scattering as a new tool to investigate the initial stage of this process. The process is initiated by mixing a solution of Na(2)CO(3) with a CaCl(2) solution or, alternatively, by mixing solutions of the dimethyl ester of carbonic acid and CaCl(2) with solutions of NaOH. Particle formation was analyzed by recording scattering curves as a function of time. Scattering data indicate the formation of compact spheres with diameters close to 360 nm. In the case of particle formation induced by ester hydrolysis, nucleation sets in after a certain lag time. Particle size is homogeneous, and the growth mechanism corresponds to an addition of ions or small constituent particles to a constant number of growing spheres. An increase of the NaOH concentration, which triggers ester hydrolysis, decreases the lag period prior to the onset of particle formation. An increase of the solution temperature also decreases this lag period. The temperature and NaOH dependent duration of the lag time could successfully be interpreted in terms of the kinetics of the ester hydrolysis. The work establishes time-resolved static light scattering as an efficient tool to investigate the particle formation process of amorphous calcium carbonate.

GIUSAXS and AFM Studies on Surface Reconstruction of Latex Thin Films during Thermal Treatment

The structural evolution of a single-layer latex film during annealing was studied via grazing incidence ultrasmall-angle X-ray scattering (GIUSAXS) and atomic force microscopy (AFM). The latex particles were composed of a low-Tg (-54 degrees C) core (n-butylacrylate, 30 wt %) and a high-Tg (41 degrees C) shell (t-butylacrylate, 70 wt %) and had an overall diameter of about 500 nm. GIUSAXS data indicate that the q(y) scan at q(z) = 0.27 nm(-1) (out-of-plane scan) contains information about both the structure factor and the form factor. The GIUSAXS data on latex films annealed at various temperatures ranging from room temperature to 140 degrees C indicate that the structure of the latex thin film beneath the surface changed significantly. The evolution of the out-of-plane scan plot reveals the surface reconstruction of the film. Furthermore, we also followed the time-dependent behavior of structural evolution when the latex film was annealed at a relatively low temperature (60 degrees C) where restructuring within the film can be followed that cannot be detected by AFM, which detects only surface morphology. Moreover, compared to AFM studies GIUSAXS provides averaged information covering larger areas.

Buckling-induced structural transition during the drying of a polymeric latex droplet on a solid surface

The structural evolution in the center of a droplet of a dialyzed styrene–n-butyl acrylate copolymer latex dispersion on a solid surface during drying was studied by means of an in situ synchrotron ultra small-angle X-ray scattering technique. During water evaporation, as the droplet shrinks the shell yields and thickens, as evidenced by the appearance of diffraction peaks at the early stage combined with TGA measurement. As the droplet dried further, colloidal crystalline structure transformation is identified. The transition is attributed to the collapse of the thin shell made of densely packed particles at the surface of the droplet caused by capillary forces that drive the deformation of the shell. As there is a small amount of water remaining beneath the surface layer, charged particles are able to explore new configurations to reestablish a stable structure after leaving the initially formed face-centered cubic structure. Finally, a torus-shaped solid film with a central flat thin film is produced.

Structural Reorganization of a Polymeric Latex Film During Dry Sintering at Elevated Temperatures

Structural rearrangement in a latex powder during dry sintering at temperatures higher than the minimum film formation temperature was investigated by means of synchrotron small-angle X-ray scattering. Two major effects were identified: (1) Deformation of latex particles leads to a closure of voids between them and an extensive perfectioning of the face centered cubic colloidal crystalline ordering. Such an improvement of the colloidal crystalline structure involves preferential crystal growth along certain crystallographic directions as was evidenced by the measured unmatched relative diffraction intensity distribution of the crystallographic (111) and (220) planes. (2) Interdiffusion of polymeric chains between adjacent particles promotes a nanometer sized aggregation of nonpolymeric materials previously located in the interstices between particles. Size and size distribution of the aggregates at different dry sintering conditions were evaluated by using a model considering spheres dispersed in the system.

Shear free and blotless cryo-TEM imaging: a new method for probing early evolution of nanostructures.

Cryogenic transmission electron microscopy (cryo-TEM) is a powerful method to image native state morphologies of nanoscale soft and hard objects suspended in solvents. Sample preparation is a critical step toward producing images at length and time scales of interest. We demonstrate a nearly shear-free sample thinning method which simultaneously allows imaging of evolving nanostructures at subsecond time scales. This device breaks the trade-off between high shear and short time scales typical in current cryo-TEM sample preparation methods. We demonstrate the low-shear feature of the new method by imaging wormlike micelles, showing an interconnected network, in contrast to the traditional sample preparation method which shows aligned micelles at similar time points. The time resolution of this method is demonstrated by imaging morphologies of calcium carbonate (formed through the reaction of calcium chloride with sodium carbonate) at subsecond time scales, capturing its evolution from an amorphous to a crystalline state. The impact of hyperbranched polyglycerol additives on the amorphous to crystalline transition in calcium carbonate at short times is examined. Early images at low shear provide unique fundamental insights into mechanisms of nanostructure evolution, thus offering a new paradigm for research in materials sciences, soft matter, and biological sciences.

Facile preparation of macroscopic soft colloidal crystals with fiber symmetry

A facile, efficient way to fabricate macroscopic soft colloidal crystals with fiber symmetry by drying a latex dispersion in a tube is presented. A transparent, stable colloidal crystal was obtained from a 25 wt % latex dispersion by complete water evaporation for 4 days. The centimeter-long sample was investigated by means of synchrotron small-angle X-ray diffraction (SAXD). Analysis of a large number of distinct Bragg peaks reveals that uniaxially oriented colloidal crystals with face-centered cubic lattice structure were formed. The measurement of evaporation rates under different conditions indicates that the water evaporates primarily through the optically clear regions (i.e., via the solid material) even when the region is more than 2 mm thick.

Conformational statistics of polymers: a unifying approach comprising broken rods, blobs, and simple random walks

Abstract Various approaches have been proposed for the conformational behaviour of macromolecules with mixed statistics, i.e. chain molecules which are described by different statistics on different length scales. An example is the concentration blob model where the chain experiences excluded volume effects on a small length scale whereas these effects are screened on large length scales. In the present work, I propose a generic model for the description of chain statistics which includes the blob model as a special case. The chain is treated as a succession of n segments. These segments are steps of an uncorrelated random walk. The conformational behaviour of each segment is determined by the exponent ν relating the average extension of the segment to its contour length. Explicit expressions are given for the mean squared end-to-end distance R 2 and the radius of gyration R g of the chain for arbitrary n and ν. For ν = 1 the transition from rigid rod ( n = 1) to broken rod ( n > 1) behaviour is described. The case 1 2 yields a general description of chain statistics in the blob model. The models proposed comprise two cases: model I, where all subsegments have the same length; and model II, where the breaking points between two segments are distributed randomly along the chain. It is shown under which conditions the widely used relation R g 2 = R 2 /6 loses its validity.