Topology sorting: Separating linear/star polymer blend components by imbibition in nanopores.

We report the imbibition and adsorption kinetics of a series of symmetric linear/star cis-1,4-polyisoprene blends within the long channels of self-ordered nanoporous anodic aluminum oxide (abbreviated: AAO). Using in situ nanodielectric spectroscopy, we followed the evolution of the longest chain modes in the blends with a judicious selection of molar masses for the constituent components. We demonstrated differences in the imbibition kinetics of linear and star components based on the relative viscosities (e.g., polymers with lower zero-shear viscosity penetrated first the nanopores). Following the complete imbibition of the pores, the adsorption time, τads, of each component was evaluated from the reduction in the dielectric strength of the respective chain modes. In the majority of blends, both components exhibited slower adsorption kinetics with respect to the homopolymers. The only exception was the case of entangled stars mixed with shorter linear chains, the latter acting as a diluent for the star component. This gives rise to what is known as topology sorting, e.g., the separation of linear/star blend components in the absence of solvent. Moreover, a simple relation (τads ∼ 10 × tpeak; tpeak is the time needed for the complete filling of pores) was found for linear polymers and stars. This suggested that the characteristic timescale of imbibition (tpeak) governs the adsorption process of polymers. It further implied the possibility of predicting the adsorption times of high molar mass polymers of various architectures by the shorter imbibition times.

A Terrylene-Anthraquinone Dyad as a Chromophore for Photothermal Therapy in the NIR-II Window.

A terrylenedicarboximide-anthraquinone dyad, FTQ, with absorption in the second near-infrared region (NIR-II) is obtained as a high-performance chromophore for photothermal therapy (PTT). The synthetic route proceeds by C-N coupling of amino-substituted terrylenedicarboximide (TMI) and 1,4-dichloroanthraquinone followed by alkaline-promoted dehydrocyclization. FTQ with extended π-conjugation exhibits an optical absorption band peaking at 1140 nm and extending into the 1500 nm range. Moreover, as determined by dielectric spectroscopy in dilute solutions, FTQ achieves an ultrastrong dipole moment of 14.4 ± 0.4 Debye due to intense intramolecular charge transfer. After encapsulation in a biodegradable polyethylene glycol (DSPE-mPEG2000), FTQ nanoparticles (NPs) deliver a high photothermal conversion efficiency of 49% under 1064 nm laser irradiation combined with excellent biocompatibility, photostability, and photoacoustic imaging capability. In vitro and in vivo studies reveal the great potential of FTQ NPs in photoacoustic-imaging-guided photothermal therapy for orthotopic liver cancer treatment in the NIR-II window.

Non-equilibrium Effects of Polymer Dynamics under Nanometer Confinement: Effects of Architecture and Molar Mass.

The non-equilibrium dynamics of linear and star-shaped cis-1,4 polyisoprenes confined within nanoporous alumina is explored as a function of pore size, d, molar mass, and functionality (f = 2, 6, and 64). Two thermal protocols are tested: one resembling a quasi-static process (I) and another involving fast cooling followed by annealing (II). Although both protocols give identical equilibrium times, it is through protocol I that it is easier to extract the equilibrium times, teq, by the linear relationships of the characteristic peak frequencies with time and rate, respectively, as log(fmax) = C1 - k log(t) and log(fmax) = C2 + λ log(ß). Both thermal protocols establish the existence of a critical temperature (at Tc, where k → 0 and λ → 0) below which non-equilibrium effects set-in. The critical temperature depends on the degree of confinement, 2Rg/d, and on molecular architecture. Strikingly, establishing equilibrium dynamics at all temperatures above the bulk, Tg, requires 2Rg/d ∼ 0.02, i.e., pore diameters that are much larger than the chain dimensions. This reflects non-equilibrium configurations of the adsorbed layer that extent away from the pore walls. The equilibrium times depend strongly on temperature, pore size, and functionality. In general, star-shaped polymers require longer times to reach equilibrium because of the higher tendency for adsorption. Both thermal protocols produced an increasing dielectric strength for the segmental and chain modes. The increase was beyond any densification, suggesting enhanced orientation correlations of subchain dipoles.

Layers of Distinct Mobility in Densely Grafted Dendrimer Arborescent Polymer Hybrids.

Melts of multiarm stars of 1,4-polybutadiene (dendrimer arborescent hybrids) with very high branching functionality (f) and small arm molar mass behave as jammed colloids and show distinct layers of segmental mobility. Three mobility layers were identified, comprising outer, intermediate, and near-core segments, all displaying a Vogel-Fulcher-Tammann temperature dependence. The respective glass temperatures increase as f^{1/2}. Our findings pave the way for further progress in this field by reconsidering previous theoretical treatments based on a single friction coefficient in hybrid nanoparticles such as densely grafted stars.