Chemical Contrast on a Microphase-Separated Block Copolymer Surface Observed by Scanning Force Microscopy

Abstract

tween the aligned MoO 6 octahedra, forming a sinusoidal pattern in a plane perpendicular to the oxide sheets; the phenyl rings, however, are tipped away from this plane about a dihedral angle of about ±13. This model was used in fitting the 1D data shown in Figure 2, and will also be used in our further studies to simulate the 2D Sync MAS data. Significantly, the polymer structure within the layers is similar to that of the oligoaniline ªpentamerº (five phenyl-ring molecule) determined by crystallographic studies. [14] The structure of PANI itself is not known, owing to its insolubility and lack of crystallinity.The 2 H NMR results provide substantial detail concerning the polymer in (PANI) 0.24 MoO 3 , as these show that order is not determined solely by the oxide layers, but is manifested by the polymer between the layers as well. The oxide host acts as a highly anisotropic 2D ªcageº that can be readily aligned on glass slides, which in turn can be oriented in the magnetic field. This allows the structure of the PANI chains to be probed as a function of orientation of the oxide host. Such a study is only possible in the nanocomposite, as bulk PANI cannot be oriented in a similar fashion. The combination of 1D and 2D Sync MAS 2 H NMR provides unique and irrefutable evidence as to the preferential orientation of polyaniline within the molybdenum trioxide host lattice. We add that the heterogeneity of the local carbon site environments along the polymer chain made characterization of order using high-resolution 13 C cross polarization (CP) MAS NMR fruitless. In contrast, solid-state 2 H NMR is uniquely suited to providing this information, by virtue of the large quadrupolar local field that dominates the spectra. Thus, 2 H NMR studies of polymers intercalated within transition metal oxide hosts can provide important and unique information about the structure of the polymer that cannot be obtained by other methods. Further investigations of these materials, including two-dimensional NMR experiments to better characterize the distribution [15] and electrochemical and NMR studies of lithium insertion in these materials, are ongoing. [5] Solid-state NMR spectra of perdeuterated polyaniline nanocomposites were performed at 11.7 T, for which the 2 H Larmor frequency was 76.77 MHz. The quadrupole echo pulse sequence was used, with 90 pulse widths of 2.0±2.2 ms when radio-frequency pulses of approximately 450 W were applied. As well, a much shorter pulse (0.5± 1.0 ms) was used for the initial excitation of the spins, with no difference due to finite pulse width effects evident in the spectra when compared to those obtained with the traditional 90±90 sequence. Acquisition was initiated before the peak of the quadrupole echo with subsequent left-shifting of the free-induction decay to ensure the peak of the echo was correctly obtained. Spectral widths of 1 MHz were used, corresponding to dwell times of 1 ms between each of the 8192 complex time-domain points collected.

Encapsulation of ZnS:Mn2+ nanocrystals with diblock copolymers

“…The relation between the photoluminescence and the structure of the PS‐PVP encapsulated ZnS:Mn NCs was confirmed by changing the solvent quality. In contrast to the case in toluene, there is little preferential driving force in chloroform for PVP segregation to the nanocrystals because chloroform is a nonselective solvent 29–31. Thus, such self‐assembled structures as observed in DLS measurements were not obtained for ZnS:Mn NCs and PS‐PVP .059 in chloroform.…”

Amorphous‐Crystalline PSnPEOn Heteroarm Star Copolymers: Crystallinity and Crystallization Kinetics

“…[21][22][23][24][25] However the order-disorder transition, T ODT , was higher for the heteroarm star copolymers than the diblock counterparts having equal arm (block) molecular weights, implying a stronger phase-segregation for the former. This effect has been attributed to the non-Gaussian stretching of the branched chains of the star polymer.…”

New Developments in Polymer Analytics II

“…Of fundamental importance was the finding that energy, transferred to the film, caused local heating which melted the crystalline phase and induced rubbery behaviour on the amorphous phase. Recently, cross sections of microphase separated block copolymers of polystyrene and poly(2-vinyl pyridine) have been investigated by LFM regarding friction coefficients depending on the chemical structure of the tips [427]. A few studies have been performed on thin polymer layers with regards to their lubrication performance [115, 428,429].…”