Search results for "Chemical engineering"
showing 10 items of 5892 documents
Switching of Polymer Brushes
1999
Polymer coatings of brushlike monolayers composed of two different polymers, polystyrene and poly(2-vinylpyridine), are grafted by radical polymerization on the surface of silicon wafers. Thickness, grafting density, molecular weight of grafted chains, and the composition of the coatings were regulated by grafting time, monomer concentration, and additional initiator in solution. A typical dry film thickness is between 10 and 100 nm, and the molecular weights of the components range from 100 to 300 kg/mol. The fabricated coatings turn out to be sensitive to the composition of the environment. For instance after exposition to toluene the layer becomes hydrophobic and the top of the layer is …
Biological evaluation of PLLA membranes, with different pore diameters, to stimulate cell adhesion and growth in vitro
2015
Polymeric membranes prepared via DIPS (Diffusion Induced Phase Separation) are widely studied and utilized as scaffolds for the regeneration of tissue. In this work, poly (L)-lactide membrane are prepared through a DIPS protocol starting from a ternary solution made of polymer, dioxane (solvent) and water (non-solvent). A three-dimensional, porous and mechanically stable membrane is desirable for ingrowth of human bronchial epithelial cells. Polymeric membranes prepared via DIPS (Diffusion Induced Phase Separation) are widely studied and utilized as scaffolds for the regeneration of tissue. In this work, poly (L)-lactide membrane are prepared through a DIPS protocol starting from a ternary …
Metal-Oxide-Free Methylammonium Lead Iodide Perovskite-Based Solar Cells: the Influence of Organic Charge Transport Layers
2014
Metal-oxide-free methylammonium lead iodide perovskite-based solar cells are prepared using a dual-source thermal evaporation method. This method leads to high quality reproducible films with large crystal domain sizes allowing for an in depth study of the effect of perovskite film thickness and the nature of the electron and hole blocking layers on the device performance. The power conversion efficiency increases from 4.7% for a device with only an organic electron blocking layer to almost 15% when an organic hole blocking layer is also employed. In addition to the in depth study on small area cells, larger area cells (approx. 1 cm(-2)) are prepared and exhibit efficiencies in excess of 10…
Mixed polymeric monolayers and Langmuir-Blodgett multilayers with functional low molecular weight guest compounds
2008
Abstract Mixed monolayers and Langmuir-Blodgett multilayers of functional low molecular weight guest compounds, especially nonlinear optical (NLO) dyes, within the matrix of an amphotropic spacer polymer have been prepared. The polymer matrix enabled the transfer of guest compounds not capable of self-organizing at the air-water interface by themselves. The structure of the LB multilayers and the transfer process were studied by small angle X-ray scattering and UV-visible spectroscopy. Good NLO coefficients were found in the mixed films.
Self-Diffusion in Concentrated Colloid Suspensions Studied by Digital Video Microscopy of Core−Shell Tracer Particles
1998
Optical video microscopy and digital image processing have been used to study the self-diffusion of colloidal particles with a hard-sphere potential. The colloid particles consist of cross-linked polymers and are dispersed in a good solvent to avoid aggregation. To investigate single particle motion in highly concentrated dispersions, a host−tracer system, consisting of two different kinds of polymer particles, has been designed: the host particles are made of poly-t-butylacrylate (with ethanedioldiacrylate as cross-linker) and have the same refractive index as the employed solvent, 4-fluorotoluene. The tracer particles have a core−shell structure with a polystyrene core (cross-linked with…
THERMOTROPIC HOMOPOLYESTERS. IV. STUDY OF FIBER FORMATION.
1983
We report a melt spinning and viscosity study of two semiflexible homopolyesters containing both rigid and flexible segments in the repeating unit. Single filaments of the polyesters formed from 4,4′-diacetoxybiphenyl and azelaic acid (PB7) and sebacic acid (PB8), and from 4′-hydroxyphenyl-4-hydroxycinnamate and azelaic acid (C7), were spun at temperatures between 205 and 255°C. The temperature dependence of the Newtonian melt viscosity of PB7 and C7 was investigated, and a range of molecular weights was studied for PB7. The spinning parameters, fiber characteristics, and viscosity-temperature behavior are related to the type of mesophase formed. The mechanical properties of fibers spun fro…
Distribution of molecularly imprinted polymer layers on macroporous silica gel particles by STEM and EDX
2005
Abstract Using transmission electron microscopy (TEM) in parallel and scanning mode (STEM) combined with energy dispersive X-ray spectroscopy (EDX) the distribution of molecularly imprinted polymer layers covalently grafted on the inner and outer surface of macroporous silica gel particles was observed. The grafting was achieved using a special initiator system ( iniferter ) and applied on a well known model system producing molecularly imprinted layers with l -phenyl alanine analide ( l -PA) as template. By staining the sample with RuO 4 before its embedment in epoxy resin and cutting ultra thin slices it was possible to identify the stained grafted polymer on the silica matrix by EDX. Bas…
Interaction between a water-in-oil microemulsion and a linear-dendritic poly(propylene oxide)–polyglycerol block copolymer
2011
We present small angle scattering and dielectric spectroscopy results on the influence of an amphiphilic diblock copolymer on the structure and dynamics of a microemulsion. We use a water-in-oil (w/o) droplet microemulsion based on the anionic surfactant AOT (sodium bis(2-ethylhexyl) sulfosuccinate), that forms spherical water droplets coated by a monolayer of AOT dispersed in the continuous oil matrix. The studied polymer consists of a hydrophobic poly(propylene oxide) (PPO) block and a hydrophilic hyperbranched polyglycerol with 74 glycerol units (NG74). Combining small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) we find that the droplet structure is preserved …
Natural Anti-oxidants for Bio-polymeric Materials
2017
In this work, three different bio-polymers, i.e. a commercial starch-based polymer (Mater-Bi®) a bio-polyester (PLA), and a bio-polyether (PEO) were additivated with quercetin, a natural flavonoid antioxidants, in order to formulate biobased films for eco-sustainable packaging and outdoor applications. The photo-oxidation behavior of unstabilized and quercetin stabilized films has been evaluated and compared with that of films additivated with a commercial synthetic light stabilizer. Obtained results show that quercetin molecules are able to slow down the photodegradation rate of all investigated bio-polymeric films, opening new avenues in the formulation of fully renewable polymer-based sy…
Biopolymer interactions affect the functional properties of edible films based on agar, cassava starch and arabinoxylan blends
2009
Abstract Edible films based on the binary combination of agar (AG), cassava starch (CAS) and arabinoxylan (AX) were studied with regard to their microstructure, moisture barrier and mechanical properties. Though the films appear macroscopically homogeneous, electron microscopy observations reveal a phase separation and dispersion, respectively, in AG–CAS and AG–AX blend film structures, whereas the structure of CAS–AX blend films seems homogeneous. In case high moisture (84% and 99% RH), neither the combination of AG and CAS nor the addition of AX into CAS can improve film moisture barrier properties, except at a lower RH (57%). Conversely, water vapor permeability (WVP) of AG based film is…