Fabrication of "hairy" colloidosomes with shells of polymeric microrods

Novel colloidosome microcapsules with aqueous gel cores and integral shells of rodlike polymeric particles have been prepared and characterized. The synthesis is based on templating water-in-oil emulsions stabilized by rodlike particles followed by gelling of the aqueous phase, dissolution of the oil phase in ethanol, and redispersion of the obtained colloidosome capsules in water. Such capsules may find applications as vehicles for delivery and controlled release of drugs, cosmetics, and food supplements.     

Thermal desorption of Ag from oxidized W

Thermal desorption spectra (TDS) of Ag condensates deposited at two substrate temperatures T_s = 300 K and T_s = 779 K have been obtained. A shift of the temperature T_m of the maximum of the desorption flux R_e was observed. It was established that the shift of the maximum depends on the value of the initial coverage σ₀. A significant difference was found to exist between TDS of silver condensates deposited on oxidized and clean W substrates due to differences in the mechanism of condensation. Silver condensates were deposited on oxidized W at different initial conditions (T_s, impingement rates R_i, etc.) but equal σ₀. The corresponding TDS were compared and a conclusion has been drawn that the shift of T_m is due to the different structure of Ag condensates. TDS of Ag condensates deposited at room temperature (T_s = 300 K) were interpreted using the method of Bauer et al. [J. Appl. Phys. 45 (1974) 5164: Surface Sci. 53 (1975) 87]. The dependence of the desorption flux R_e on the substrate temperature T_s and coverage σ was treated on the basis of the Polanyi-Wigner equation and some parameters of the condensation process were evaluated.     

Adsorption of sterically stabilized latex particles at liquid surfaces: effects of steric stabilizer surface coverage, particle size, and chain length on particle wettability

A series of five near-monodisperse sterically stabilized polystyrene (PS) latexes were synthesized using three well-defined poly(glycerol monomethacrylate) (PGMA) macromonomers with mean degrees of polymerization (DP) of 30, 50, or 70. The surface coverage and grafting density of the PGMA chains on the particle surface were determined using XPS and (1)H NMR spectroscopy, respectively. The wettability of individual latex particles adsorbed at the air-water and n-dodecane-water interfaces was studied using both the gel trapping technique and the film calliper method. The particle equilibrium contact angle at both interfaces is relatively insensitive to the mean DP of the PGMA stabilizer chains. For a fixed stabilizer DP of 30, particle contact angles were only weakly dependent on the particle size. The results are consistent with a model of compact hydrated layers of PGMA stabilizer chains at the particle surface over a wide range of grafting densities. Our approach could be utilized for studying the adsorption behavior of a broader range of sterically stabilized inorganic and polymeric particles of practical importance.     

Growth Mode on an Adsorbate Precovered Substrate

Simple lattice model is used to consider the influence of adsorption on the thin film growth mode. It is found that the presence of an adsorbate in a heterogeneous system does not change the general form of the Wulff-Kaischew theorem provided the surface sensitive quantities are correctly defined. An extended criterion for the layer-by-layer growth mechanism is obtained. Contrary to the Bauer's 3-σ rule in the generalized criterion enter interfacial free energies only whereby all surface free energies are absent. As a consequence the change of the growth mode (3D → 2D) upon adsorption could be explained by purely thermodynamic reasons. It is shown also that the adsorbate changes drastically the chemical potential of the underlying layer rendering it close to the chemical potential of the infinitely large three-dimensional crystal. Therefore, the growth on a preadsorbed foreign substrate takes place practically as on an own substrate. An exchange process between incoming atoms and adsorbate particles keeps the adsorbate predominantly on the top of the growing surface rather than in the bulk of the film. The driving force of this process is the free energy difference between “in bulk” and “on surface” configurations of the system. The phenomenon reveals the thermodynamic principle that the spontaneous processes lower the free energy and render the system to its ground state.     

Scalable Formation of Concentrated Monodisperse Lignin Nanoparticles by Recirculation-Enhanced Flash Nanoprecipitation

A highly controllable and scalable process for fabrication of large amounts of concentrated lignin nanoparticles (LNPs) is reported. These lignin core nanoparticles are formed through flash nanoprecipitation, however, scaling up of the fabrication process requires fundamental understanding of their operational formation mechanism and surface properties. It is shown how a semicontinuous synthesis system with a recirculation loop makes it possible to produce flash precipitated lignin nanoparticles in large amounts for practical applications. The roles of the process parameters, including flow rates and lignin concentration, are investigated and analyzed. The results indicate that the LNPs are formed by a process of continuous burst nucleation at the point of mixing without diffusive growth, which yields nanoparticles of highly uniform size following a modified LaMer nucleation and growth mechanism. This mechanism makes possible facile process control and scale-up. Effective control of the resulting nanoparticle size is achieved through the initial concentration of lignin in the injected solution. The impressive capability to produce suspensions of any predesigned multimodal distribution is demonstrated. The resulting nanofabrication technique can produce large volumes of concentrated LNP suspensions of high stability and tightly controlled size distributions for biological or agricultural applications.     

A novel technique for preparation of monodisperse giant liposomes

A novel technique for the preparation of monodisperse giant liposomes has been developed based on a combination of micro-patterning of ITO glass slides with lipid solution and electroformation. The average diameter of the produced liposomes is determined by size of the micro-pattern features.     

Assembling carbon nanotubosomes using an emulsion-inversion technique

Novel micro-capsules (carbon nanotubosomes) have been fabricated by cross-linking shells of amine-functionalized multi-walled carbon nanotubes (MWNTs) produced by their adsorption on water-in-oil emulsion drops followed by an emulsion-inversion.     

Novel surface tension isotherm for surfactants based on local density functional theory

In this Letter we report a new general method for calculating of surface tension isotherms in the presence of surfactants, based on a local density functional. We illustrate this method by deriving the interfacial tension isotherm for nonionic surfactants at an air-water or oil-water interface by using the self-consistent field theory of polymer brushes. We consider a particular case of local density functional to calculate explicitly how the interfacial tension and the surfactant adsorption depend on the surfactant bulk concentration. Experimental data for the surface tension and the surfactant adsorption isotherm for nonionic surfactants were interpreted with the help of the new isotherm. Very good agreement between the adsorption of n-dodecyl pentaoxyethylene glycol ether (C12E5) at an air-water interface, calculated from the surface tension isotherm and small-angle neutron-scattering is obtained.     

Massenspektrometrische untersuchungen der kondensation von dünnen schichten auf fremden unterlagen: I. Kinetik der adsorption und der desorption von Ag auf W

The adsorption and desorption kinetics of silver on clean polycrystalline tungsten were investigated with a mass-spectrometric technique. The deposition up to about 2 monolayers occurred without two-dimensional phase transformation. The thermal accommodation coefficient was found to be unity. The desorption energy and frequency factor for different coverages were determined. The bonding of silver atoms in the first monolayer was found to be localized. Additionally, thermal desorption experiments with linear heating rate were carried out.