Frequency-Swept Integrated Solid Effect

The efficiency of continuous wave dynamic nuclear polarization (DNP) experiments decreases at the high magnetic fields used in contemporary high-resolution NMR applications. To recover the expected signal enhancements from DNP, we explored time domain experiments such as NOVEL which matches the electron Rabi frequency to the nuclear Larmor frequency to mediate polarization transfer. However, satisfying this matching condition at high frequencies is technically demanding. As an alternative we report here frequency-swept integrated solid effect (FS-ISE) experiments that allow low power sweeps of the exciting microwave frequencies to constructively integrate the negative and positive polarizations of the solid effect, thereby producing a polarization efficiency comparable to (±10 % difference) NOVEL. Finally, the microwave frequency modulation results in field profiles that exhibit new features that we coin the “stretched” solid effect.National Institute of Biomedical Imaging and Bioengineering (U.S.) (Grant EB-002804)National Institute of Biomedical Imaging and Bioengineering (U.S.) (Grant EB-002026)National Institute of General Medical Sciences (U.S.) (Grant GM095843

Synthesis and Properties of the 5,10,15-Trimesityltruxen-5-yl Radical

The synthesis of a long-lived, truxene-based radical that is highly delocalized and exhibits a narrow EPR absorption is reported. The radical is stable for multiple hours in a solution exposed to air and remains for months in the solid state under inert gas. Characterization and properties are discussed

Defects, Solvent Quality, and Photonic Response in Lamellar Block Copolymer Gels

Stimuli-responsive photonic gels are made from the lamellar block copolymer (BCP) poly­(styrene-<i>b</i>-2-vinylpyridine) (PS–P2VP), where the photonic responses are triggered by swelling/deswelling of the P2VP block with a selective solvent. When compared to isotropic swelling in chemically cross-linked homopolymer gels, the P2VP block in the lamellar BCP shows significantly lower degrees of swelling in alcohol–water cosolvents. The glassy PS layers completely constrain the lateral expansion of the P2VP gel layers and the dislocation defect network that develops during BCP self-assembly provides a counter force to vertical swelling. A model based on Flory–Huggins mixing and dislocation network strain energy is proposed to capture the swelling behavior of the BCP and is then used to estimate the dislocation network density in the lamellar BCP. This work establishes the quantitative relationship between the reflective color of the photonic gel, the effective χ parameter of the swellable block and the solvent, and the defect density of the BCP film and demonstrates the potential utility of these photonic materials as a quick means to measure solvent quality or defect density

Correction: Conformation of bis-nitroxide polarizing agents by multi-frequency EPR spectroscopy

ISSN:1463-9084ISSN:1463-907

Photonic Block Copolymer Films Swollen with an Ionic Liquid

Nonvolatile solvent swollen 1D periodic films were fabricated from lamellae-forming block copolymers with medium molecular weight by infiltrating an ionic liquid. A mixture of imidazole and imidazolium bis­(trifluoromethanesulfonyl)­imide as a room temperature ionic liquid was added after spin-coating of thin films of polystyrene-<i>b</i>-poly­(2-vinylpyridine) (PS–P2VP) block copolymers having an approximately 50/50 composition to create photonic films reflecting in the visible regime. Under normal conditions of temperature and humidity, the films maintained their photonic properties for more than 100 days without perceptible change, stemming from the nonvolatility of the ionic liquid. Transmission electron microscopy revealed the selective swelling of the P2VP nanodomains by the IL and ultrasmall angle X-ray scattering measurements provided quantitative nanostructure information on the periodicities of the films. The wavelength of reflected light from photonic films was tunable by using different molecular weight block copolymers as well as by employing blends of two block copolymers. The experimental wavelength of the reflected light, detected by a fiber-optic spectrophotometer, agreed with values estimated from the Bragg condition and was able to be controlled from about 380 to 620 nm

Leveraging a smartphone to perform time-gated luminescence measurements.

Empowered by advanced on-board sensors, high-performance optics packages and ever-increasing computational power, smartphones have democratized data generation, collection, and analysis. Building on this capacity, many platforms have been developed to enable its use as an optical sensing platform for colorimetric and fluorescence measurements. In this paper, we report the ability to enable a smartphone to perform laboratory quality time-resolved analysis of luminescent samples via the exploitation of the rolling shutter mechanism of the native CMOS imager. We achieve this by leveraging the smartphone's standard image capture applications, commercially available image analysis software, and housing the device within a UV-LED containing case. These low-cost modifications enable us to demonstrate the smartphone's analytical potential by performing tasks ranging from authentication and encryption to the interrogation of packaging, compounds, and physical phenomena. This approach underscores the power of repurposing existing technologies to extend the reach and inclusivity of scientific exploration, opening new avenues for data collection and analysis

Epoxy functionalized multi-walled carbon nanotubes for improved adhesives

Three different types of epoxy-functionalized multi-walled carbon nanotubes (EpCNTs) were prepared by multiple covalent functionalization methods. The EpCNTs were characterized by thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), and Raman spectroscopy to confirm covalent functionalization. The effect of the different chemistries on the adhesive properties was compared to a neat commercial epoxy (Hexion formulation 4007) using functionalized and unfunctionalized multi-walled carbon nanotubes (MWCNT) at 0.5, 1, 2, 3, 5, and 10 wt%. It was found that an EpCNT at 1 wt% increased the lap shear strength, tested using the American Society for Testing and Materials standard test D1002, by 36% over the unfilled epoxy formulation and by 27% over a 1 wt% unmodified MWCNT control sample. SEM images revealed a fracture surface morphology change with the incorporation of EpCNT and a deflection of the crack fronts at the site of embedded CNTs, as the mechanism accounting for increased adhesive strength. Rheological studies showed non-linear viscosity and DSC cure studies showed an alteration of cure kinetics with increased CNT concentration, and these effects were more pronounced for EpCNT.Massachusetts Institute of Technology. Institute for Soldier NanotechnologiesNational Science Foundation (U.S.). Graduate Research Fellowshi

Solvent-Free Dynamic Nuclear Polarization of Amorphous and Crystalline <i>ortho</i>-Terphenyl

Dynamic nuclear polarization (DNP) of amorphous and crystalline <i>ortho</i>-terphenyl (OTP) in the absence of glass forming agents is presented in order to gauge the feasibility of applying DNP to pharmaceutical solid-state nuclear magnetic resonance experiments and to study the effect of intermolecular structure, or lack thereof, on the DNP enhancement. By way of ¹H–¹³C cross-polarization, we obtained a DNP enhancement (ε) of 58 for 95% deuterated OTP in the amorphous state using the biradical bis-TEMPO terephthalate (bTtereph) and ε of 36 in the crystalline state. Measurements of the ¹H <i>T</i>₁ and electron paramagnetic resonance experiments showed the crystallization process led to phase separation of the polarization agent, creating an inhomogeneous distribution of radicals within the sample. Consequently, the effective radical concentration was decreased in the bulk OTP phase, and long-range ¹H–¹H spin diffusion was the main polarization propagation mechanism. Preliminary DNP experiments with the glass-forming anti-inflammation drug, indomethacin, showed promising results, and further studies are underway to prepare DNP samples using pharmaceutical techniques