Switching Transport through Nanopores with pH-Responsive Polymer Brushes for Controlled Ion Permeability

Several nanoporous platforms were functionalized with pH-responsive poly(methacrylic acid) (PMAA) brushes using surface-initiated atom transfer radical polymerization (SI-ATRP). The growth of the PMAA brush and its pH-responsive behavior from the nanoporous platforms were confirmed by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). The swelling behavior of the pH-responsive PMAA brushes grafted only from the nanopore walls was investigated by AFM in aqueous liquid environment with pH values of 4 and 8. AFM images displayed open nanopores at pH 4 and closed ones at pH 8, which rationalizes their use as gating platforms. Ion conductivity across the nanopores was investigated with current–voltage measurements at various pH values. Enhanced higher resistance across the nanopores was observed in a neutral polymer brush state (lower pH values) and lower resistance when the brush was charged (higher pH values). By adding a fluorescent dye in an environment of pH 4 or pH 8 at one side of the PMAA-brush functionalized nanopore array chips, diffusion across the nanopores was followed. These experiments displayed faster diffusion rates of the fluorescent molecules at pH 4 (PMAA neutral state, open pores) and slower diffusion at pH 8 (PMAA charged state, closed pores) showing the potential of this technology toward nanoscale valve applications

Thin Polymer Brush Decouples Biomaterial's Micro-/Nano-Topology and Stem Cell Adhesion

Surface morphology and chemistry of polymers used as biomaterials, such as tissue engineering scaffolds, have a strong influence on the adhesion and behavior of human mesenchymal stem cells. Here we studied semicrystalline poly(ε-caprolactone) (PCL) substrate scaffolds, which exhibited a variation of surface morphologies and roughness originating from different spherulitic superstructures. Different substrates were obtained by varying the parameters of the thermal processing, i.e. crystallization conditions. The cells attached to these polymer substrates adopted different morphologies responding to variations in spherulite density and size. In order to decouple substrate topology effects on the cells, sub-100 nm bio-adhesive polymer brush coatings of oligo(ethylene glycol) methacrylates were grafted from PCL and functionalized with fibronectin. On surfaces featuring different surface textures, dense and sub-100 nm thick brush coatings determined the response of cells, irrespective to the underlying topology. Thus, polymer brushes decouple substrate micro-/nano-topology and the adhesion of stem cells

Monovalent cation selective crown ether containing poly(arylene ether ketone)/SPEEK blend membranes

Blend membranes of sulfonated poly(ether ether ketone) (SPEEK) and poly(arylene ether ketone) (PAEK) derivatives containing crown ether units in the main chain (CPAEK) were prepared and characterized in terms of water swelling and ion exchange capacity (IEC). The miscibility of the polymers was verified by DSC and HR-SEM. Ion transport characteristics of the membranes were established for the monovalent ions Li+ and K+ and the separation of these ions by the cation exchange membranes was investigated. Diffusion experiments for aqueous KCl, LiCl and their mixtures were carried out with pure SPEEK membranes as well as with the CPAEK/SPEEK membranes. Blending significantly decreased the ion permeability due to cation-crown ether complexation and increased the hydrophobicity of the matrix. The K+ over Li+ selectivity of the SPEEK membrane was enhanced by blending SPEEK with CPAEK by a factor of nearly 4, indicating that the presence of a crown ether polymer changes the relative transport of the ions in the membrane

Quantitative estimation of the strength of specific interactions in polyurethane elastomers, and their effect on structure and properties

Two sets of segmented polyurethane (PU) elastomers were prepared from crystalline MDI, butanediol and a polyester or a polyether polyol, respectively. The molar mass of both polyols was 1000 g/mol. The –OH functional group ratio of polyol/total diol was kept constant at a value of 0.4, while the ratio of the isocyanate and hydroxyl groups (NCO/OH) changed between 0.90 and 1.15 in the polyester, and 0.94 and 1.15 in the polyether polyurethanes, respectively. One step bulk polymerization was carried out in an internal mixer and the samples were compression molded for testing. Advanced molecular modeling was used to estimate the strength of various specific interactions quantitatively in the polymers studied. Fifteen different specific interactions were identified in polyester while thirteen in polyether PU considering only hydrogen bonds. Estimated binding enthalpy changes between 11 and 26 kJ/mol. The results proved that hard–soft and not hard–hard segment interactions control phase separation of linear segmented polyurethanes. A new model was developed to quantify the relative importance of specific interactions acting between the two types of segments. The calculations predicted better solubility of the soft phase in hard domains in polyester than in polyether polyurethanes. Besides the mutual solubility of the phases, their size and mechanical properties also depend on these interactions shown by the study of phase structure using a novel combination of various methods in a wide length scale. Properties are determined by different aspects of morphology. Transparency depends on the amount of ordered hard phase, stiffness and hardness on phase composition, while ultimate properties on stoichiometry, which determines molecular weight and the number of physical cross-link point

Ion-selective Ionic Polymer Metal Composite (IPMC) actuator based on crown ether containing sulfonated Poly(Arylene Ether Ketone)

This study introduces the concept of ion selective actuation in polymer metal composite actuators, employing crown ether bearing aromatic polyether materials. For this purpose, sulfonated poly(arylene ether ketone) (SPAEK) and crown ether containing SPAEK with molar masses suitable for membrane preparation are synthesized. The synthesized polymers are characterized using Nuclear magnetic resonance (NMR) and fourier transform infrared spectroscopy (FTIR) spectroscopy, thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). Ionic polymer metal composite (IPMC) actuators are fabricated by electroless chemical deposition of a platinum (Pt) layer on both sides of SPAEK and crown-ether containing SPAEK membranes, resulting in electrode layers of around 120 nm thickness. Actuation experiments demonstrate cation specific responses and bending degrees of the IPMC actuators. Incorporation of crown ether units in the polymer backbone results in an improved and ion-selective bending displacement compared with SPAEK actuators. S(25)C(50)PAEK actuators show an increased bending displacement of 28% for Na+ and 20% for K+ ions