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We investigate the mass transfer and membrane growth processes during capsule formation by interaction of the biopolymer xanthan gum with CnTAB surfactants. When a drop of xanthan gum polymer solution is added to the surfactant solution, a membrane is formed by coacervation. It encapsulates the polymer drop in the surfactant solution. The underlying mechanisms and dynamic processes during capsule formation are not yet understood in detail. Therefore, we characterized the polymer-surfactant complex formation during coacervation by measuring the surface tension and surface elasticity at the solution-air interface for different surfactant chain lengths and concentrations. The adsorption behavior of the mixed polymer-surfactant system at the solution-air interface supports the understanding of observed trends during the capsule formation. We further measured the change in capsule pressure over time and simultaneously imaged the membrane growth via confocal microscopy. The experiments showed a rapid increase in the capsule pressure during the initial stage of membrane formation. The cross-linking and shrinkage during the membrane formation by coacervation leads to an increasing tensile stress in the elastic membrane, resulting in a rapid pressure rise. Afterwards, the pressure gradually decreases and the capsule shrinks as water diffuses out. This is not only due to the initial capsule overpressure but also due to osmosis caused by the higher ionic strength of the surfactant solution outside the capsule compared to the polymer solution inside the capsule. The influence of polymer concentration and surfactant type and concentration on the pressure changes and the membrane structure are studied in this work, providing detailed insights on the dynamic membrane formation process by coacervation. This knowledge can be used to produce capsules with tailored membrane properties and to develop a suitable encapsulation protocol in technological applications. The obtained insights

We present an experimental approach to studying the kinetics of polymer nanoparticle formation using molecular rotor molecules as fluorescence probes. By combining fluorescence lifetime analysis and fluorescence correlation spectroscopy, it is possible to simultaneously monitor the evolution of the local environment in the nanoparticles and their size. To assess the generality of the method, we select two common but very different methods for nanoparticle preparation: emulsion-solvent evaporation and miniemulsion polymerization. In both cases, three stages of the nanoparticle formation process were identified on the basis of their polymer content. In the initial stage of the process, the polymer content is low. Then it increases rapidly because of solvent evaporation or polymerization during the second stage. Finally, it reaches a plateau value. Furthermore, significant heterogeneities in the final nanoparticles were found that can be attributed to remaining solvent or monomer and the spatial variation of the polymer-free volume.

Contains fulltext : 216143.pdf (publisher's version ) (Open Access), Fast and bioorthogonally reacting nanoparticles are attractive tools for biomedical applications such as tumor pretargeting. In this study, we designed an amphiphilic block copolymer system based on HPMA using different strategies to introduce the highly reactive click units 1,2,4,5-tetrazines (Tz) either at the chain end (Tz-CTA) or statistical into the hydrophobic block. This reactive group undergoes a rapid, bioorthogonal inverse electron-demand Diels-Alder reaction (iEDDA) with trans-cyclooctenes (TCO). Subsequently, this polymer platform was used for the preparation of different Tz-covered nanoparticles, such as micelles and colloids. Thereby it was found that the reactivity of the polymeric micelles is comparable to that of the low molar mass tetrazines. The core-cross-linked micelles can be successfully conjugated at rather low concentrations to large biomacromolecules like antibodies, not only in physiological buffer, but also in human blood plasma, which was confirmed by fluorescence correlation spectroscopy (FCS).

Poly(n-butylacrylate)@polystyrene nanoparticles behaving as a capsule-based sealing nanoadditive are synthesized through an optimized semicontinuous emulsion polymerization protocol. Solid state time-domain 1H-NMR and 13C magic angle spinning (MAS) NMR analysis suggest strong phase separation. Line width of 13C resonances in cross polarization and single pulse experiment MAS-NMR spectra indicates that the peculiar mobility of each phase is preserved at the nanoscale. Atomic force spectroscopy (AFM) shows the permanence of spherical shape in absence of solvent (i.e., subsequent to strong capillary and surface forces) up to moderate external load, as well as the possibility of plastically deforming the polystyrene shell and ultimately triggering the nanoparticle flow at higher force loads. The breakdown characteristic of the nanoparticle shows for the first time baroplastic behavior on a single particle with precise biphasic core@shell morphology.

The hierarchical self-assembly of an amphiphilic block copolymer, poly( N,N-dimethylacrylamide)-block-polystyrene with a very short hydrophilic block (PDMA10-b-PS62), in large granular nanoparticles is reported. While these nanoparticles are stable in water, their disaggregation can be induced either mechanically (i.e., by applying a force via the tip of the cantilever of an atomic force microscope (AFM)) or by partial hydrolysis of the acrylamide groups. AFM force spectroscopy images show the rupture of the particle as a combination of collapse and flow, while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of partly hydrolyzed nanoparticles provide a clear picture of the granular structure. (Chemical Equation Presented).

Blends of chlorinated polyethylene and nylon-6/-6,6/-12 terpolyamide were prepared. The ratio of the two components was systematically varied within the blends. The mechanical behavior of the samples was analyzed with tensile tests and dynamical mechanical analysis showing that, for several ratios, materials with improved mechanical properties typical of thermoplastic elastomers were obtained. In such a mechanical regime, a co-continuous phase-separated morphology was clearly evidenced at the microscopic scale by 3D laser scanning confocal fluorescent microscopy (LSCFM). At blend compositions where plastic tensile behavior is observed, LSCFM reveals dispersed spheres of one component in the other.

Carbon nanoparticles become photoluminescent upon surface passivation with oligomeric polymer chains. In this work, the dependence of the carbon dots photoluminescent properties on the passivation polymer selection has been demonstrated by conjugating polyethylene glycol (PEG) chains, polyethylenimide-co-polyethylene glycol-co-polyethylenimide copolymer, and 4-armed PEG molecules, respectively. The cytotoxicity and cellular internalization of the resulting three types of photoluminescent nanoformulations of carbon dots, named CD2, CD3, and CD4, were evaluated. These nanoformulations exhibited no apparent cytotoxicity on their own and were shown to successfully target cancer cells by conjugation with transferrin. The implication to the use of carbon dots as biocompatible optical nanoprobes for in vitro cancer diagnostics is discussed.

We investigate efficient frequency-doubling of low energy femtosecond pulses in bulk and waveguide nonlinear crystals, thereby demonstrating how to achieve a compact and portable ultrafast blue light Source. Using a femtosecond Cr:LiSAF laser (fundamental wavelength 860 nm) we examine the relative merits of the process of second harmonic generation (SHG) using bulk potassium niobate, bulk aperiodically-poled KTP, periodically-poled and aperiodically-poled KTP waveguide crystals. While SHG conversion efficiencies LIP to 37% were achieved using the waveguides, non-traditional strong focusing in the bulk samples yielded efficiencies of 30%. We have developed several theoretical models to accurately describe the temporal and spectral properties of the generated blue light, as well as the observed saturation behavior of the conversion process in the waveguide structures., QCR 20190211

We demonstrate an effective means of achieving compact, truly portable, and entirely self-contained ultrafast blue light sources. Using a variety of nonlinear media to achieve simple second-harmonic generation of a femtosecond Cr:LiSAF laser, we investigate the relative merits of aperiodically poled bulk and waveguide nonlinear crystals in comparison to periodically poled structures. Such a compact and convenient source of ultrashort laser pulses in the blue spectral region could be of great interest for on-site applications spanning a host of disciplines, such as biomedical imaging, optical micromanipulation, and high-resolution spectroscopy., QC 20100525 QC 20110914

An effective means of achieving a portable, ultrafast blue-light source using a variety of nonlinear media is demonstrated. We investigate the relative merits of aperiodically-poled bulk and waveguide nonlinear crystals in comparison to periodically-poled structures., QC 20141210