Polymer dynamics under cylindrical confinement featuring a locally repulsive surface: A quasielastic neutron scattering study.

We investigated the effect of intermediate cylindrical confinement with locally repulsive walls on the segmental and entanglement dynamics of a polymer melt by quasielastic neutron scattering. As a reference, the corresponding polymer melt was measured under identical conditions. The locally repulsive confinement was realized by hydrophilic anodic alumina nanopores with a diameter of 20 nm. The end-to-end distance of the hydrophobic infiltrated polyethylene-alt-propylene was close to this diameter. In the case of hard wall repulsion with negligible local attraction, several simulations predicted an acceleration of segmental dynamics close to the wall. Other than in attractive or neutral systems, where the segmental dynamics is slowed down, we found that the segmental dynamics in the nanopores is identical to the local mobility in the bulk. Even under very careful scrutiny, we could not find any acceleration of the surface-near segmental motion. On the larger time scale, the neutron spin-echo experiment showed that the Rouse relaxation was not altered by confinement effects. Also the entanglement dynamics was not affected. Thus at moderate confinement conditions, facilitated by locally repulsive walls, the dynamics remains as in the bulk melt, a result that is not so clear from simulations.

Magnetically responsive biopolymeric multilayer films for local hyperthermia.

We present a proof of concept on the use of thermomagnetic polymer films (TMFs) as heating devices for magnetic hyperthermia in vitro. The TMFs were prepared through spray assisted layer-by-layer assembly of polysaccharides and magnetic iron oxide nanoparticles, yielding an alternate magnetic-polymer multilayer structure. By applying a remote alternating magnetic field (AMF) (f = 180 kHz; H = 35 kA m-1) we increased the temperature of the TMFs in a thickness-dependent way, up to 12 °C within the first 5 minutes. To test our films as heating substrates for magnetic hyperthermia, a series of in vitro experiments were designed using human neuroblastoma SH-SY5Y cells, known by their tolerance to thermal stress. The application of two AMF cycles (30 minutes each) showed that the exogenous magnetic hyperthermia resulted in an 85% reduction of cell viability. This capacity of the TMFs of hyperthermia-mediated cell killing using a remote AMF opens new options for the treatment of small and superficial tumor lesions by means of remotely-triggered magnetic hyperthermia.

Nanopatterned PMMA-Yb:Er/Tm:Lu2O3 composites with visible upconversion emissions.

Nanopillars, nanotubes and nanofibers of transparent polymethyl methacrylate (PMMA) polymer with Yb:Ln:Lu2O3 (Ln = Er or Tm) nanoparticles (NPs) (≈30-35 nm average size) have been prepared by infiltration of anodized aluminum oxide hexagonally nanopatterned templates. The outer diameter of these nanostructures is in the 330-400 nm range, with lengths up to 50 µm and a period distance of 430 nm. These nanostructures show visible upconversion (UC) emissions under excitation with 978 nm light. The steady state temperature of the polymer nanostructures is optically evidenced by the Er(3+) UC emission and optically controlled around the PMMA glass transition temperature by the excitation light, introducing a new method for NP storage in a solid and potential optically induced particle release. Full color emission is shown in tridoped (Yb:Er:Tm) samples.

Novel hydrogels of chitosan and poly(vinyl alcohol)-g-glycolic acid copolymer with enhanced rheological properties.

Poly(vinyl alcohol) (PVA) has been grafted with glycolic acid (GL), a biodegradable hydroxyl acid to yield modified poly(vinyl alcohol) (PVAGL). The formation of hydrogels at pH = 6.8 and physiological temperature through blending chitosan (CS) and PVAGL at different concentrations has been investigated. FTIR, DOSY NMR and oscillatory rheology measurements have been carried out on CS/PVAGL hydrogels and the results have been compared to those obtained for CS/PVA hydrogels prepared under the same conditions. The experimental results point to an increase in the number of interactions between chitosan and PVAGL in polymer hydrogels prepared with modified PVA. The resulting materials with enhanced elastic properties and thixotropic behavior are potential candidates to be employed as injectable materials for biomedical applications.

Effect of nanoconfinement on polymer dynamics: surface layers and interphases.

We present neutron spin echo experiments that address the much debated topic of dynamic phenomena in polymer melts that are induced by interacting with a confining surface. We find an anchored surface layer that internally is highly mobile and not glassy as heavily promoted in the literature. The polymer dynamics in confinement is, rather, determined by two phases, one fully equal to the bulk polymer and another that is partly anchored at the surface. By strong topological interaction, this phase confines further chains with no direct contact to the surface. These form the often invoked interphase, where the full chain relaxation is impeded through the interaction with the anchored chains.

Magnetic hydrogels derived from polysaccharides with improved specific power absorption: potential devices for remotely triggered drug delivery.

We report on novel ferrogels derived from polysaccharides (sodium alginate and chitosan) with embedded iron oxide nanoparticles synthesized in situ and their combination with thermally responsive poly(N-isopropylacrylamide) for externally driven drug release using AC magnetic fields. Samples were characterized by Raman spectroscopy, transmission electron microscopy, and magnetic measurements. The obtained nanoparticles were found to be of ∼10 nm average size, showing magnetic properties very close to those of the bulk material. The thermal response was measured by power absorption experiments, finding specific power absorption values between 100 and 300 W/g, which was enough for attaining the lower critical solution temperature of the polymeric matrix within few minutes. This fast response makes these materials good candidates for externally controlled drug release.

Direct observation of confined single chain dynamics by neutron scattering.

Neutron spin echo has revealed the single chain dynamic structure factor of entangled polymer chains confined in cylindrical nanopores with chain dimensions either much larger or smaller than the lateral pore sizes. In both situations, a slowing down of the dynamics with respect to the bulk behavior is only observed at intermediate times. The results at long times provide a direct microscopic measurement of the entanglement distance under confinement. They constitute the first experimental microscopic evidence of the dilution of the total entanglement density in a polymer melt under strong confinement, a phenomenon that so far was hypothesized on the basis of various macroscopic observations.

Structure of Poly(vinyl alcohol) Cryo-Hydrogels as Studied by Proton Low-Field NMR Spectroscopy.

The network structure of poly(vinyl alcohol) (PVA) hydrogels obtained by freezing-thawing cycles was investigated by solid-state (1)H low-field NMR spectroscopy. By the application of multiple-quantum NMR experiments, we obtain information about the segmental order parameter, which is directly related to the restrictions on chain motion (cross-links) formed upon gelation. These measurements indicate that the network mesh size as well as the relative amount of nonelastic defects (i.e., non-cross-linked chains, dangling chains, loops) decrease with the number of freezing-thawing cycles but are independent of the polymer concentration. The formation of the PVA network is accompanied by an increasing fraction of polymer with fast magnetization decay ( approximately 20 mus). The quantitative study of this rigid phase with a specific refocusing pulse sequence shows that it is composed of a primary crystalline polymer phase ( approximately 5%), which constitutes the main support of the network structure and determines the mesh size, and a secondary population of more imperfect crystallites, which increase the number of elastic chain segments in the polymer gel but do not affect the average network mesh size appreciably. Correspondingly, progressive melting of the secondary crystallites with increasing temperature does not affect the network mesh size but only the amount of network defects, and melting of the main PVA crystallites at approximately 80 degrees C leads to the destruction of the network gel and the formation of an isotropic PVA solution.

One-dimensional magnetopolymeric nanostructures with tailored sizes.

Ultra-high aspect ratio nanofibers composed of poly(vinyl alcohol) and CoFe(2)O(4) nanoparticles (PVA/CoFe(2)O(4)) and moderate aspect ratio nanofibers composed of poly(vinyl chloride) and Fe(3)O(4) nanoparticles (PVC/Fe(3)O(4)) have been prepared. Magnetopolymeric one-dimensional (1D) nanostructures with any diameter and length can be prepared by template synthesis using anodic aluminum oxide (AAO) followed by the replication methods presented in this work. These replication methods are very effective, and allow the nanomoulding of any polymer-nanoparticle 1D composite. A first magnetic characterization of the nanostructured composites reveals a modest magnetic anisotropy. The development of magnetopolymeric nanofibers with adjusted length and diameter opens new opportunities in a wide range of applications.