Early-stage compositional segregation in polymer-blend films

The existence of a transient period during the surface enrichment of a binary polymer blend by one of its components has been suggested by previous theoretical and experimental studies as well as computer simulations. Taking advantage of the high depth resolution of neutron reflectivity and the slow dynamics of polymers near their glass transition, we investigate this early-stage surface compositional enrichment in a phase separating polymer blend for the first time. Two stages of surface enrichment layer growth are observed. A rapid local surface enrichment at the chain segmental level occurs first, followed by a slower growth of a diffuse layer having a scale on the order of the bulk correlation length and the radius of gyration of the surface enriching polymer chains

Intracellular Nanoparticle Dynamics Affected by Cytoskeletal Integrity

The cell interior is a crowded chemical space, which limits the diffusion of molecules and organelles within the cytoplasm, affecting the rates of chemical reactions. We provide insight into the relationship between non-specific intracellular diffusion and cytoskeletal integrity. Quantum dots entered the cell through microinjection and their spatial coordinates were captured by tracking their fluorescence signature as they diffused within the cell cytoplasm. Particle tracking revealed significant enhancement in the mobility of biocompatible quantum dots within fibrosarcoma cells versus their healthy counterparts, fibroblasts, as well as in actin destabilized fibroblasts versus untreated fibroblasts. Analyzing the displacement distributions provided insight into how the heterogeneity of the cell cytoskeleton influences intracellular particle diffusion. We demonstrate that intracellular diffusion of non-specific nanoparticles is enhanced by disrupting the actin network, which has implications for drug delivery efficacy and trafficking

Polymer and spherical nanoparticle diffusion in nanocomposites

Nanoparticle and polymer dynamics in nanocomposites containing spherical nanoparticles were investigated by means of molecular dynamics simulations. We show that the polymer diffusivity decreases with nanoparticle loading due to an increase of the interfacial area created by nanoparticles, in the polymer matrix. We show that small sized nanoparticles can diffuse much faster than that predicted from the Stokes-Einstein relation in the dilute regime. We show that the nanoparticle diffusivity decreases at higher nanoparticle loading due to nanoparticle-polymer interface. Increase of the nanoparticle radius slows the nanoparticle diffusion

Effects of oncological treatments on semen quality in patients with testicular neoplasia or lymphoproliferative disorders.

Pretherapy sperm cryopreservation in young men is currently included in good clinical practice guidelines for cancer patients. The aim of this paper is to outline the effects of different oncological treatments on semen quality in patients with testicular neoplasia or lymphoproliferative disorders, based on an 8-year experience of the Cryopreservation Centre of a large public hospital. Two hundred and sixty-one patients with testicular neoplasia and 219 patients with lymphoproliferative disorders who underwent chemotherapy and/or radiotherapy and pretherapy semen cryopreservation were evaluated. Sperm and hormonal parameters (follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone, inhibin B levels) were assessed prior to and 6, 12, 18, 24 and 36 months after the end of cancer treatment. At the time of sperm collection, baseline FSH level and sperm concentration were impaired to a greater extent in patients with malignant testicular neoplasias than in patients with lymphoproliferative disorders. Toxic effects on spermatogenesis were still evident at 6 and 12 months after the end of cancer therapies, while an improvement of seminal parameters was observed after 18 months. In conclusion, an overall increase in sperm concentration was recorded about 18 months after the end of cancer treatments in the majority of patients, even if it was not possible to predict the evolution of each single case ‘a priori'. For this reason, pretherapy semen cryopreservation should be considered in all young cancer patients

Exercise Reduces DNA Damage, Inflammation and Apoptotic Markers in the Brain of High Fat Fed Animals

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Block copolymer adsorption from a homopolymer melt to an amine-terminated surface

Using neutron reflectometry, the adsorption of diblock copolymers from a neutral polystyrene (PS) matrix is studied as a function of substrate type and non-adsorbing block degree of polymerization. The block copolymer is poly(deutero styrene)-block-poly(methyl methacrylate) and the substrates are silicon oxide, SiOx, and SiOx functionalized with (3-aminopropyl)triethoxysilane (APTES). We have determined the equilibrium volume fraction-depth profiles for such films, and compared them with volume fraction profiles generated by self-consistent mean-field (SCMF) theory and find good agreement between the experimental and theoretical data. SCMF calculations show that the segmental interaction energy between PS matrix chains and APTES is two orders of magnitude stronger than that between PS and SiOx

Dispersion of PMMA-grafted, mesoscopic iron-oxide rods in polymer films

This study investigates the parameters that affect the dispersion of polymer grafted mesoscopic iron-oxide rods (FeMRs) in polymer matrices. FeMRs (212 nm long by 36 nm in diameter) are grafted with poly(methyl methacrylate) (PMMA) at three different brush molecular weights: 3.7 kg mol, 32 kg mol, and 160 kg mol. Each FeMR sample was cast in a polymer thin film consisting of either PMMA or poly(ethylene oxide) (PEO) each at a molecular weight much higher or much lower than the brush molecular weight. We find that the FeMRs with 160 kg mol brush disperse in all matrices while the FeMRs with 32 kg mol and 3.7 kg mol brushes aggregate in all matrices. We perform simple free energy calculations, taking into account steric repulsion from the brush and van der Waals attraction between FeMRs. We find that there is a barrier for aggregation for the FeMRs with the largest brush, while there is no barrier for the other FeMRs. Therefore, for these mesoscopic particles, the brush size is the main factor that determines the dispersion state of FeMRs in polymer matrices with athermal or weakly attractive brush-matrix interactions. These studies provide new insight into the mechanisms that affect dispersion in polymer matrices of mesoscopic particles and therefore guide the design of composite films with well-dispersed mesoscopic particles

Glass Transition Dynamics and Fragility of Ultrathin Miscible Polymer Blend Films

We use cooling-rate-dependent <i>T</i>_g measurements (CR-<i>T</i>_g) to indirectly probe the relaxation dynamics and fragility of thin films of polystyrene (PS)/poly­(2,6-dimethyl-1,4-phenylene oxide) (PPO) blends. Thin films of this miscible blend have a single glass transition temperature (<i>T</i>_g) that can be systematically shifted over 100 K simply by varying the composition of the blend. This study shows that the <i>T</i>_g of these blends decreases below the bulk <i>T</i>_g as the film thickness is decreased. Additionally, the degree of change in <i>T</i>_g strongly depends on the cooling rate of the experiment. We show that the <i>T</i>_g of 16 nm films of a 50% PS blend is 15 K lower than that of bulk at a cooling rate of 1 K/min but decreases only 4 K at a cooling rate of 120 K/min. By analyzing the cooling rate dependence of the <i>T</i>_g for various thicknesses of the 50% PS blend, we demonstrate that the fragility of these blends decreases with film thickness. This behavior is similar to what is observed in ultrathin films of polystyrene, which suggests that the deviations from bulk dynamics in PS/PPO blends are due to enhanced mobility near the free surface. Similar to pure PS, if extrapolated to higher temperatures, the dynamics of thin films intersect the bulk dynamics at a temperature a few degrees above bulk <i>T</i>_g. The presence of this temperature (<i>T</i>*) can help explain why some experiments fail to see <i>T</i>_g depression in thin films of these blends. Lastly, we show that while the fragility of the bulk blend changes due to differences in the fragility of the homopolymers, ultrathin films (<i>h</i> <i> = </i> 16 nm) have identical average dynamics and fragilities regardless of the blend composition at the same temperature relative to T_g. This result implies that enhanced mobility near the free surface affects the dynamics of these blend thin films similarly