Blends of poly(epsilon-caprolactone) and intermediate molar mass polystyrene as Langmuir films at the air/water interface

Crystallization of Poly(l-lactic acid) on Water Surfaces via Controlled Solvent Evaporation and Langmuir-Blodgett Films

Solvent evaporation is one of the most fundamental processes in soft matter. Structures formed via solvent evaporation are often complex yet tunable via the competition between solute diffusion and solvent evaporation time scales. This work concerns the polymer evaporative crystallization on the water surface (ECWS). The dynamic and two-dimensional (2D) nature of the water surface offers a unique way to control the crystallization pathway of polymeric materials. Using poly(l-lactic acid) (PLLA) as the model polymer, we demonstrate that both one-dimensional (1D) crystalline filaments and two-dimensional (2D) lamellae are formed via ECWS, in stark contrast to the 2D Langmuir-Blodgett monolayer systems as well as polymer solution crystallization. Results show that this filament-lamella biphasic structure is tunable via chemical structures such as molecular weight and processing conditions such as temperature and evaporation rate.

Evaluating polymeric biomaterial-environment interfaces by Langmuir monolayer techniques

Polymeric biomaterials are of specific relevance in medical and pharmaceutical applications due to their wide range of tailorable properties and functionalities. The knowledge about interactions of biomaterials with their biological environment is of crucial importance for developing highly sophisticated medical devices. To achieve optimal in vivo performance, a description at the molecular level is required to gain better understanding about the surface of synthetic materials for tailoring their properties. This is still challenging and requires the comprehensive characterization of morphological structures, polymer chain arrangements and degradation behaviour. The review discusses selected aspects for evaluating polymeric biomaterial-environment interfaces by Langmuir monolayer methods as powerful techniques for studying interfacial properties, such as morphological and degradation processes. The combination of spectroscopic, microscopic and scattering methods with the Langmuir techniques adapted to polymers can substantially improve the understanding of their in vivo behaviour.

Vertical phase separation and liquid-liquid dewetting of thin PS/PCL blend films during spin coating

Thin films of an amorphous polymer, polystyrene (PS), and a crystalline polymer, poly(ε-caprolactone) (PCL), blend were prepared by spin coating a toluene solution. Surface chemical compositions of the blend films were measured by X-ray photoelectron spectroscopy (XPS), and the surface and interface topographical changes were followed by atomic force microscopy (AFM). By changing the PS concentration and keeping the PCL concentration of the solution at 1 wt %, a great variety of morphologies were constructed. The results show that the morphology of the blend films can be divided into three regions with increasing PS concentration. In region I, PS island domains are embedded in PCL crystals when the PS concentration is lower than 0.3 wt % and the size of the PS island increases with increasing PS concentration. In region II, holes with different sizes surrounded by a low rim are obtained when the concentration of PS is between 0.35 and 0.5 wt %. After selectively washing the PS domains, we studied the interface morphology of PS/PCL and found that the upper PS-rich layer extended into the bottom PCL layer, forming a trench surrounding the holes. In region III, an enriched two-layer structure with the PS-rich layer on top of the blend films and the PCL-rich crystal layer underneath is obtained when the concentration of PS is higher than 0.5 wt %. Last, the formation mechanism of the different surface and interface morphologies is further discussed in terms of the vertical phase separation to a layered structure, followed by liquid-liquid dewetting and crystallization processes during spin coating.

Cobalt nanoparticle Langmuir-Schaefer films on ethylene glycol subphase

The Langmuir-Schaefer (LS) technique was applied to prepare two-dimensional films of tridodecylamine (TDA)-stabilized Co nanoparticles. Ethylene glycol was used as the subphase because the Co nanoparticles spread better on it than on water. Surface pressure-area isotherms provided very little information on the floating films, and Brewster angle microscopy (BAM) was needed to characterize the film formation in situ. In addition to the subphase, various other experimental factors were tested in the LS film preparation, including solvent and presence of free TDA ligands and poly(styrene-b-ethylene oxide) (PS-b-PEO) in the nanoparticle dispersion. LS films deposited from dispersions from which the excess TDA ligands had been removed by washing the Co nanoparticles with 2-propanol consisted of hexagonally organized particles in rafts that were organized in necklace structures. The addition of PS-b-PEO to the deposition dispersion resulted in small nanoparticle rafts evenly distributed over the substrate surface. The best Co-nanoparticle-PS-b-PEO films were obtained with a mass ratio of 20:1 between Co (9 nm) and block copolymer (38 200 g/mol, PEO content 22 mass %). These films were successfully transferred onto Formvar-coated TEM grids and characterized by transmission electron microscopy (TEM) and a superconducting quantum interference device (SQUID) magnetometer. At room temperature the films showed superparamagnetic behavior with a saturation magnetization M(s) of 100 emu/g (Co). Our work indicates that it is possible to obtain thin superparamagnetic LS films of TDA-stabilized Co nanoparticles. This is an important result as the TDA-stabilized Co nanoparticles show a very good resistance to corrosion.