Free Space Makes the Polymer “Dead Layer” Alive

The effect of free space on molecular motion inside the polymer “dead layer” or adsorbed nanolayers on solid surfaces is investigated. Free space is introduced into the nanolayer by choosing a polymer with a relatively big side group, poly n-butyl methacrylate (PnBMA), and polarization-resolved single-molecule fluorescence microscopy is adopted as the method. The rotational motion of the doped fluorescent probes is found to be considerably excited at moderate temperatures, attributed to the free space brought by the side group of the PnBMA. The development of the adsorbed nanolayer by the prolonged annealing of the parent film is carefully monitored, together with the evolution of the molecular motion and the glass transition temperature (Tg). The Tg values of the exposed nanolayers are considerably lower than that of the bulk system, while they become higher than those in the bulk situation when the nanolayer is covered with a polymer top layer. The experimental evidence has demonstrated that the free space made available by the side group and the air–polymer interface has considerably promoted the molecular motion inside the adsorbed nanolayers, even under the situation of overwhelming surface attraction

Visualization 1: High-spatial-resolution localization algorithm based on cascade deconvolution in a distributed Sagnac interferometer invasion monitoring system

Video waveform 1. Originally published in Applied Optics on 10 October 2016 (ao-55-29-8180

Response of a Permanently Charged Polyelectrolyte Brush to External Ions: The Aspects of Structure and Dynamics

Structure and dynamics inside permanently charged polyelectrolyte brushes, sodium polystyrene sulfonate brushes, during their response to the introduction of external ions (NaCl) are investigated by neutron reflectivity and dielectric spectroscopy. Neutron reflectivity measurements show that the segmental density of the inner part of the brushes decreases and that of the outer part increases when the salt level is tuned from the salt-free condition to a moderate level (<10^–2 M)the brushes swell further compared with the salt-free condition. This is attributed to the breakup of the multiplets formed by dipole–dipole pairs, and by this process, the previously constrained chain segments by the multiplets are released. Dielectric spectroscopy discovers a giant dipole by the charge separation of the adsorbed counterions and the PSS^– chains, induced by electric field. The dynamics of the induced giant dipole is accelerated with the increase of external salt, as a result of the charge regularization by elevated salt level. At high-enough salt level, the screening effect reduces the electrostatic repulsion between the neighboring chains and makes the brushes shrink

Counterion Cloud Expansion of a Polyelectrolyte by Dilution

It has long been documented that the reduced viscosity of polyelectrolyte has an anomalous dependence on its concentration, i.e., the Fuoss law. To explore the molecular mechanism, the counterion distribution of sodium polystyrenesulfonate (NaPSS) as a function of concentration is investigated at the single-molecule level. By examination of the fluorescence resonance energy transfer (FRET) between a fluorescence donor on NaPSS chain and an acceptor in the counterions using single-molecule fluorescence spectroscopy, an increase of average counterion–chain distance is discovered upon dilution, indicating the expansion of counterion cloud. By photon counting histogram, an increase of effective charge of the NaPSS chain during dilution is exposed. The variation of these parameters agrees well with that of the reduced viscosity, helping to shed light on the molecular mechanism of the Fuoss law: the expansion of the counterion cloud increases hydrodynamic friction, and the increase of effective charges of NaPSS due to desorption of counterions brings about the stronger interchain coupling

Conformational Transition of Poly(<i>N</i>‑isopropylacrylamide) Single Chains in Its Cononsolvency Process: A Study by Fluorescence Correlation Spectroscopy and Scaling Analysis

Fluorescence correlation spectroscopy (FCS) has been adopted to investigate the conformational transition of poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) single chains with moderate molecular weights in the cononsolvency process. A practical approach of performing accurate FCS measurements with the presence of the refractive index mismatch was developed. The practical and reliable FCS calibration facilitates the acquisition of the hydrodynamic radius (<i>R</i>_H) of PNIPAM single chains with the change of the water–ethanol composition. By using the synthesized PNIPAM samples covering a range of degrees of polymerization (<i>N</i>), the scaling analysis in the relationship of <i>R</i>_H ∼ <i>N</i>^ν exhibits a progressive, re-entrant change of the scaling index (ν) between good solvent (0.57) and poor solvent (∼1/3) condition, which is a reflection of a re-entrant conformational transition of the polymers. Furthermore, the highly asymmetrical feature of the cononsolvency process of single PNIPAM chains was unveiled, which indicates a much stronger effect or interaction of the ethanol molecules to the PNIPAM chain. Comparisons of the present results with previous reports provided new information to the mechanism model of the PNIPAM cononsolvency

Cyclometalated Platinum Complexes with Aggregation-Induced Phosphorescence Emission Behavior and Highly Efficient Electroluminescent Ability

Aggregation-induced emission (AIE) materials can exhibit intense luminescence in the aggregated or solid state, which are highly desirable for OLED application. However, only limited research results on developing AIE-active Pt^II complexes in electroluminescence (EL) application have been reported so far. Herein, a series of AIE-active Pt^II(C^N)­(N-donor ligand)Cl complexes have been developed. Their chemical structures have been determined by NMR, MS, and X-ray crystallography characterization. Theoretical results including the frontier molecular orbitals, the simulated UV–vis spectra, and natural transition orbitals (NTO) have been employed to insightfully interpret their photophysical properties. It has also been found that a much higher degree of molecular aggregation in these Pt^II complexes should be required to induce phosphorescent AIE than that for the fluorescent AIE behavior. These AIE-active Pt^II complexes can exhibit very strong emission in poly­(methyl methacrylate) (PMMA) films with the phosphorescence quantum yield (Φ_p) of ∼72.0%, while that in dilute solution is just about 4.7%. Accordingly, on the basis of these AIE-active Pt^II complexes, the optimized OLEDs fabricated by the simple solution-processed strategy can achieve high EL efficiencies with a maximal external efficiency (η_ext) of 28.4%, a maximal current efficiency (η_L) of 75.9 cd A^–1, and a maximal power efficiency (η_P) of 62.7 lm W^–1. Considering the rarity for EL investigations of the AIE-active Pt^II complexes, the concerned results realized by these Pt^II(C^N)­(N-donor ligand)Cl complexes should provide valuable clues for exploring AIE-active Pt^II phosphorescent complexes with high EL performance

Resolving the Difference in Electric Potential within a Charged Macromolecule

The difference of the electric potential between the middle and end of polystyrenesulfonate (PSS^–) chain is discovered experimentally. Using a pH-responsive fluorophore attached to these two locations on the PSS^– chain, the local pH value was determined by single molecule fluorescence technique: photon counting histogram (PCH). By the observation of a very high accumulation of proton (2–3 orders of magnitude in concentration) at the vicinity of the PSS^– as a result of the electrostatic attraction between the charged chain and protons, the electric potential of the PSS^– chain is determined. A higher extent of counterion adsorption is discovered at the middle of the PSS^– chain than the chain end. The entropy effect of the counterion adsorption is also discoveredupon the dilution of protons, previously adsorbed counterions are detached from the chain

K⁺ concentration changes in each group during storage.

<p>#: <i>P</i><0.05 and *: <i>P</i><0.01 compared with untreated group.</p

TUG1-miR590-5p-PBRM1 contribute to the development of clear cell renal cell carcinoma

Four most frequently mutation genes can distinct ccRCC from other tumor. UG1 and has-miR590-5p in regulating PBRM1 RNA expression contribute to the development of ccRCC

Change in MCV over time during storage at 4°C.

<p>Change in MCV over time during storage at 4°C.</p