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Ansan, South Korea

Kuang Q.,Harbin Institute of Technology | Zhang D.,Harbin Institute of Technology | Yu J.C.,Hanyang University | Yu J.C.,Hepce Chemical Co. | And 4 more authors.
Journal of Physical Chemistry C | Year: 2015

Elastomers such as polyurethanes usually possess low stiffness, and the addition of traditional fillers typically results in a moderate improvement. Aramid nanofibers (ANFs) represent one of the most promising nanoscale building blocks for high-performance nanocomposites. In this work, waterborne polyurethanes (PUs) have been reinforced with ANFs using two solution processing methods, namely, layer-by-layer (LBL) assembly technique and the vacuum-assisted flocculation (VAF) method. Record-high modulus of 5.275 GPa and ultimate strength of 98.02 MPa are obtained among all the reported PU based nanocomposites. We attribute such achievement to the similar molecular structures of ANFs with PUs which ensures a high affinity made possible by the manifold interfacial interactions. The formation of multiple hydrogen bonds due to the presence of amide groups with appropriate spacing in both components is confirmed by the computer simulation. Compared with the VAF method, it is found that LBL assembly allows a better load transfer, resulting in higher ultimate strength and stiffness. The VAF method shows advantages in improving the ultimate strength at low loadings of ANFs. We believe our work may not only lead to a new practical combination within the field of composite materials but also provide important implications for the future design of nanocomposites based on the innovative nanofillers. © 2015 American Chemical Society. Source

Yang M.,University of Michigan | Alvarez-Puebla R.,Hepce Chemical Co. | Kim H.-S.,University of Vigo | Aldeanueva-Potel P.,Hepce Chemical Co. | And 3 more authors.
Nano Letters | Year: 2010

Development of multifunctional drug delivery vehicles with therapeutic and imaging capabilities as well as in situ methods of monitoring of intracellular processes will greatly benefit from a simple method of preparation of plasmonic Au structures with nanometer scale gaps between sharp metallic elements where the so-called SERS hot spots can be formed. Here the synthesis of gold lace capsules with average diameters ca. 100 nm made of a network of metallic branches 3-5 nm wide and separated by 1-3 nm gaps is reported. Biocompatible amphiphilic polyurethanes (PUs) were used as template for these particles. The unusual topology of the produced gold lace shells somewhat reminiscent of Fabergé eggs is likely to reflect the network of hydrophobic and hydrophilic domains of PU globules. The gold lace develops from initial open weblike structures by gradual enveloping the PU template. The diameter of gold lace shell is determined by the size of PUs in water and can be adjusted by the molecular mass of PUs. The close proximity between branches makes them excellent supports for surface-enhanced Raman spectroscopy (SERS), which was demonstrated using 1-naphthalenethiol upon excitation with photons with different wavelengths. The loading and releasing of pyrene as a model of hydrophobic drugs and the use of SERS to monitor it were demonstrated. © 2010 American Chemical Society. Source

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