Reversible Binding Interfaces Made of Microstructured Polymer Brushes.

The polymer brush architecture of the end-tethered polymer molecules is one of the most widely used efficient methods to regulate interfacial interactions in colloidal systems found in live matter and manufactured materials. Emerging applications of polymer brush structures require solutions to new tasks in the control of interfacial interactions. The rapid development of live cell manufacturing relies on scalable and efficient cell harvesting methods. Stimuli-responsive surfaces made of surface-grafted poly(N-isopropylacrylamide) (PNIPAM) can bind and detach the adherent cell upon changes in temperature and have been used for cell growth and harvesting. The applications are limited by the requirement to satisfy a range of PNIPAM coating characteristics that depend on the dimensions of the integrin complex in the cell membrane and the basal surface. The analysis of the microstructured surfaces, when adhesive and disjoining functions of the microdomains are decoupled, shows that many limitations of PNIPAM one-component coatings can be avoided by using a much broader range of structural characteristics of the microstructured interfaces composed of alternating disjoining PNIPAM domains and adhesive polymeric domains with cell-affinity functional groups. Temperature-controlled reversible adhesion to such microstructured interfaces is studied here experimentally with model systems of solid spherical particles and by employing simulations for solid and soft membranes interacting with the microstructured surfaces to mimic interactions with soft and solid disk-like particles.

Scalable Fabrication of Thermally Conductive Layered Nacre-like Self-Assembled 3D BN-Based PVA Aerogel Framework Nanocomposites.

In this study, three-dimensional (3D) polyvinyl alcohol (PVA)/aligned boron nitride (BN) aerogel framework nanocomposites with high performance were fabricated by a facile strategy. The boron nitride powder was initially hydrolyzed and dispersed with a chemically crosslinked plasticizer, diethyl glycol (DEG), in the PVA polymer system. The boron nitride and DEG/PVA suspensions were then mixed well with different stoichiometric ratios to attain BN/PVA nanocomposites. Scanning electron microscopy revealed that BN platelets were well dispersed and successfully aligned/oriented in one direction in the PVA matrix by using a vacuum-assisted filtration technique. The formed BN/PVA aerogel cake composite showed excellent in-plane and out-of-plane thermal conductivities of 0.76 W/mK and 0.61 W/mK with a ratio of BN/PVA of (2:1) in comparison with 0.15 W/mK for the pure PVA matrix. These high thermal conductivities of BN aerogel could be attributed to the unidirectional orientation of boron nitride nanoplatelets with the post-two days vacuum drying of the specimens at elevated temperatures. This aerogel composite is unique of its kind and displayed such high thermal conductivity of the BN/PVA framework without impregnation by any external polymer. Moreover, the composites also presented good wettability results with water and displayed high electrical resistivity of ~1014 Ω cm. These nanocomposites thus, with such exceptional characteristics, have a wide range of potential uses in packaging and electronics for thermal management applications.

Effects of the Pre-Consolidated Materials Manufacturing Method on the Mechanical Properties of Pultruded Thermoplastic Composites.

The choice of a manufacturing process, raw materials, and process parameters affects the quality of produced pre-consolidated tapes used in thermoplastic pultrusion. In this study, we used two types of pre-consolidated GF/PP tapes-commercially available (ApATeCh-Tape Company, Moscow, Russia) and inhouse-made tapes produced from commingled yarns (Jushi Holdings Inc., Boca Raton, FL, USA)-to produce pultruded thermoplastic Ø 6 mm bars and 75 mm × 3.5 mm flat laminates. Flat laminates produced from inhouse-made pre-consolidated tapes demonstrated higher flexural, tensile, and apparent interlaminar shear strength compared to laminates produced from commercial pre-consolidated tapes by as much as 106%, 6.4%, and 27.6%, respectively. Differences in pre-consolidated tape manufacturing methods determine the differences in glass fiber impregnation and, thus, differences in the mechanical properties of corresponding pultruded composites. The use of commingled yarns (consisting of matrix and glass fibers properly intermingled over the whole length of prepreg material) makes it possible to achieve a more uniform impregnation of inhouse-made pre-consolidated tapes and to prevent formation of un-impregnated regions and matrix cracks within the center portion of the fiber bundles, which were observed in the case of commercial pre-consolidated tapes. The proposed method of producing pre-consolidated tapes made it possible to obtain pultruded composite laminates with larger cross sections than their counterparts described in the literature, featuring better mechanical properties compared to those produced from commercial pre-consolidated tapes.

Hydrolysis rate constants and activation parameters for phosphate- and phosphonate-bridged phthalonitrile monomers under acid, neutral and alkali conditions.

Hydrolysis data for Bis(3-(3,4-dicyanophenoxy)phenyl) phenyl phosphate and Bis(3-(3,4-dicyanophenoxy)phenyl) phenylphosphonate under pH 4, 7 and 10 are presented. Conversion/time plots collected by HPLC analysis, typical chromatograms and NMR spectra of the reactions products are given. Pseudo-first order rate constants are determined for both substrates at 25, 50 and 80 °C. Activation parameters were calculated from Arrhenius equation.