Immobilizing au nanoparticles with polymer single crystals, patterning and asymmetric functionalization.
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Crystallization↗
Biomedical subjects
Christopher Y Li
Publications and source records attributed to Christopher Y Li.
Polymer crystallization-driven, periodic patterning on carbon nanotubes.
We report herein a unique means to periodically pattern polymeric materials on individual carbon nanotubes (CNTs) using a controlled polymer crystallization method. One-dimensional (1D) CNTs were periodically decorated with polymer lamellar crystals, resulting in nano-hybrid shish-kebab (NHSK) structures. The periodicity of the polymer lamellae varies from 20 to 150 nm. The kebabs are approximately 5-10 nm thick (along CNT direction) with a lateral size of approximately 20 nm to micrometers, which can be readily controlled by varying crystallization conditions. Both polyethylene and Nylon 66 were successfully decorated on single-walled carbon nanotubes (SWNTs), multiwalled carbon nanotubes (MWNTs), as well as vapor grown carbon nanofibers (CNFs). The formation mechanism was attributed to "size-dependent soft epitaxy". Because NHSK formation conditions depend on CNT structures, it further provides a unique opportunity for CNT separation. The reported method opens a gateway to periodically patterning polymers and different functional groups on individual CNTs in an ordered and controlled manner, an attractive research field that is yet to be explored.
Journal Article↗
Patterning polyethylene oligomers on carbon nanotubes using physical vapor deposition.
Periodic patterning on one-dimensional (1D) carbon nanotubes (CNTs) is of great interest from both scientific and technological points of view. In this letter, we report using a facile physical vapor deposition method to achieve periodic polyethylene (PE) oligomer patterning on individual CNTs. Upon heating under vacuum, PE degraded into oligomers and crystallized into rod-shaped single crystals. These PE rods periodically decorate on CNTs with their long axes perpendicular to the CNT axes. The formation mechanism was attributed to "soft epitaxy" growth of PE oligomer crystals on CNTs. Both SWNTs and MWNTs were decorated successfully with PE rods. The intermediate state of this hybrid structure, MWNTs absorbed with a thin layer of PE, was captured successfully by depositing PE vapor on MWNTs detached from the solid substrate, and was observed using high-resolution transmission electron microscopy. Furthermore, this hybrid structure formation depends critically on CNT surface chemistry: alkane-modification of the MWNT surface prohibited the PE single-crystal growth on the CNTs. We anticipate that this work could open a gateway for creating complex CNT-based nanoarchitectures for nanodevice applications.
Microscopy, Atomic Force↗
Perforated layer structures in liquid crystalline rod-coil block copolymers.
We report a novel observation of the tetragonal perforated layer structures in a series of rod-coil liquid crystalline block copolymers (BCPs), poly(styrene-block-(2,5-bis[4-methoxyphenyl]oxycarbonyl)styrene) (PS-b-PMPCS). PMPCS forms rigid rods while PS forms the coil block. Differential scanning calorimetry (DSC), polarized light microscopy (PLM), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and transmission electron microscopy (TEM) techniques were used to investigate these rod-coil molecules, and a perforated layer structure was observed at f(PMPCS) approximately 0.37 in relatively low molecular weight (M(w)) samples and approximately 0.5 in high M(w) PS-b-PMPCS. This substantial phase boundary shift was attributed to the rod-coil nature of the BCP. The perforation obeys a tetragonal instead of hexagonal symmetry. The "onset" of perforation was also observed in real space in sample PS(272)-b-PMPCS(93) (f(PMPCS) approximately 0.52), in which few PS chains punctuate PMPCS layers. A slight increase in f(PS), by blending with PS homopolymer, led to a dramatic change in the BCP morphology, and uniform tetragonal perforations were observed at f(PMPCS) approximately 0.48.
Journal Article↗
Onset of tethered chain overcrowding.
We proposed an approach to precisely control the density of tethered chains on solid substrates using PEO-b-PS and PLLA-b-PS. As the crystallization temperature Tx increased, the PEO or PLLA lamellar crystal thickness d(L) increased as well as the reduced tethering density sigma; of the PS chains. The onset of tethered PS chains overcrowding in solution occurs at sigma(*) approximately 3.7-3.8 as evidenced by an abrupt change in the slope between (d(L))(-1) and Tx. This results from the extra surface free energy created by the tethered chain that starts to affect the growth barrier of the crystalline blocks.
Journal Article↗