Optical manipulation of charged microparticles in polar fluids

In this study, we report a systematic study of the response of a charged microparticle confined in an optical trap and driven by electric fields. The particle is embedded in a polar fluid, hence, the role of ions and counterions forming a double layer around the electrodes and the particle surface itself has been taken into account. We analyze two different cases: (i) electrodes energized by a step‐wise voltage (DC mode) and (ii) electrodes driven by a sinusoidal voltage (AC mode). The experimental outcomes are analyzed in terms of a model that combines the electric response of the electrolytic cell and the motion of the trapped particle. In particular, for the DC mode we analyze the transient particle motion and correlate it with the electric current flowing in the cell. For the AC mode, the stochastic and deterministic motion of the trapped particle is analyzed either in the frequency domain (power spectral density, PSD) or in the time domain (autocorrelation function). Moreover, we will show how these different approaches (DC and AC modes) allow us, assuming predictable the applied electric field (here generated by plane parallel electrodes), to provide accurate estimation (3%) of the net charge carried by the microparticle. Vice versa, we also demonstrate how, once predetermined the charge, the trapped particle acts as a sensitive probe to reveal locally electric fields generated by arbitrary electrode geometries (in this work, wire‐tip geometry).     

Friedel-Crafts Polymers. 8. Friedel-Crafts Polycondensation of β-Resorcylic Acid or Resorcinol with p-Xylylene Dichloride,p,p′-Dichloromethyldiphenyl Ether,and p,p′-Dichloroacetyldiphenyl Ether

Friedel-Crafts polycondensation of β-resorcylic acid (BRA) with p-xylylene dichloride (PXDC) or 4,4′-dichloromethyldiphenyl ether (DDE) in dioxane could be effected without simultaneous decarboxylation of BRA. The similar polycondensation of BRA with PXDC, DDE, or 4,4′-dichloroacetyldiphenyl ether (DADE) in nitrobenzene or in the absence of solvent at 150°C was associated with decarboxylation of BRA. Polymers having structures isomeric with those of the polycondensation product of BRA formed with subsequent in situ decarboxylation were prepared by Friedel-Crafts polycondensation of resorcinol with the above dichlorides. All the polymer samples were characterized, and those with related structures were compared. The ion-exchange properties of the polymer sample prepared from BRA and DDE in dioxane were studied.     

Viscometric Estimation of Unperturbed Chain Dimensions of Polymers

A new expression is proposed to determine the unperturbed dimensions of coil-like polymers viscometrically by use of the Flory and Kratky expression. The unperturbed dimensions so estimated are compared with the results obtained by using different expressions available in the literature. The results are comparable even for stiff chain polymers. The data obtained under theta conditions also fit this expression very well. The effect of molecular weight, its distribution, and that of the solvent has also been studied. It is concluded that the unperturbed dimensions are independent of molecular weight and solvent but depend on the heterogeneity of the system.     

Monitoring nitrite with optical sensing films

A new, low-cost nitrite sensor was developed by immobilizing a direct indicator dye in an optical sensing film for food and environmental monitoring. This sensor was fabricated by binding Safranine O to a cellulose acetate film that had previously been subjected to an exhaustive base hydrolysis. The membrane has good durability (>12 months) and a short response time (<8 s). Nitrite can be determined for the range of 0.005-2.00 μg ml⁻¹ with 3δ detection limits of 0.001 μg ml⁻¹. The method is easy to perform and uses acetylcellulose as a carrier. The reagents used for the activity of the cellulose support are inexpensive, non-toxic and widely available.     

Synthesis and evaluation of nitrated poly(4-hydroxystyrene) microspheres for pH sensing

Lightly crosslinked nitrated poly(4-hydroxystyrene) microspheres were prepared for pH sensing. The first step is to prepare poly(4-acetoxystyrene) microspheres using porous glass membrane emulsification followed by suspension polymerization. The resulting microspheres have diameters between 1 and 2 μm. They hydrolyzed to poly(4-hydroxystyrene) by exposing them to base. This is followed by nitration to nitric acid. The percentage of nitrogen depends on the nitration conditions. Percentages greater than the theoretical percentage for mononitro poly(4-hydroxystyrene) can be obtained at elevated temperatures indicating partial dinitration. These microspheres were cast into hydrogel membranes for use as pH sensors. The membrane is turbid because the refractive index of the microspheres is higher than the hydrogel refractive index. At high pH, deprotonation of the hydroxyl group introduces a negative charge onto the polymer backbone causing it to swell. Swelling is accompanied by a decrease in microsphere refractive index, which is detected as a decrease in membrane turbidity.     

New HPLC-chiral stationary phases for enantiomeric resolution of sulfoxides and selenoxides

Summary Enantiomers of several sulfoxides and some selenoxides can be easily separated by using a new chiral stationary phase (CSP-DACH-DNB) containing the 3,5-dinitrobenzoyl derivative of R,R-(-)1,2-diamino-cyclohexane as selector, covalently bonded to the siliceous matrix. The easy operative conditions and the high enantioselectivity values (α) allow a direct transfer of the analytical separations to a semi-preparative and preparative scale.     

Extraction and characterization of highly pure alumina (α, γ, and θ) polymorphs from waste beverage cans: A viable waste management approach

The recycling and recovery of important materials from inexpensive feedstock has now become an intriguing area and vital from commercial and environmental viewpoints. In the present work, extraction of different single phases of alumina (α, γ, θ-Al₂O₃) having high purity (>99.5 %) from locally available waste beverage cans (～95 % Al) through facile precipitation route calcined at distinct temperatures has been reported. The optimization of process technology was done by a variety of different synthesis parameters, and the production cost was estimated between 84.47-87.45 USD per kg of alumina powder. The as prepared alumina fine particles have been characterized using different sophisticated techniques viz. TG-DTA, WD-XRF, XRD, FT-IR, SEM, DLS-based particle size analysis (PSA) with zeta (ζ) potential measurement and UV–Visible Spectroscopy. X-ray diffractogram confirms the formation of γ-, θ-, and α-alumina at 500–700 °C, 900–1000 °C, and 1200 °C respectively and crystallite size, crystallinity, strain, dislocation density, and specific surface area were measured using major X-ray diffraction peaks which varies with temperature. The SEM studies showed that the as prepared alumina particles were agglomerated, irregular-shaped with particle size (0.23–0.38 µm), pore size, and porosity were calculated from SEM image. ζ-potentials at different pH values as well as isoelectric point (IEP) of α, γ, and θ alumina were calculated in an aqueous medium which changes with temperature. The direct band gap (E_g) energies were found between 4.09 and 5.19 eV of alumina obtained from different calcination temperatures. The synthesized materials can be used in sensors, ceramics, catalysis, and insulation applications.     

Perfectly Encoding π-Conjugated Anions in the RE5(C3N3O3)(OH)12 (RE=Y,Yb, Lu) Family with Strong Second Harmonic Generation Response and Balanced Birefringence

Nonlinear optical (NLO) crystal, which simultaneously exhibits strong second-harmonic-generation (SHG) response and desired optical anisotropy, is a core optical material accessible to the modern optoelectronics. Accompanied by strong SHG effect in a NLO crystal, a contradictory problem of overlarge birefringence is ignored, leading to low frequency doubling efficiency and poor beam quality. Herein, a series of rare earth cyanurates RE₅(C₃N₃O₃)(OH)₁₂ (RE=Y, Yb, Lu) were successfully characterized by 3D electron diffraction technique. Based on a “three birds with one stone” strategy, they enable the simultaneous fulfillment of strong SHG responses (2.5–4.2× KH₂PO₄), short UV cutoff (ca. 220 nm) and applicable birefringence (ca. 0.15 at 800 nm) by the introduction of rare earth coordination control of π-conjugated (C₃N₃O₃)³⁻ anions. These findings provide high-performance short-wavelength NLO materials and highlight the exploration of cyanurates as a new research area.     

A Hydrogen Bonded Supramolecular Framework Birefringent Crystal

Birefringent crystals could modulate the polarization of light and are widely used as polarizers, waveplates, optical isolators, etc. To date, commercial birefringent crystals have been exclusively limited to purely inorganic compounds such as α-BaB₂O₄ with birefringence of about 0.12. Herein, we report a new hydrogen bonded supramolecular framework, namely, Cd(H₂C₆N₇O₃)₂⋅8 H₂O, which exhibits exceptionally large birefringence up to about 0.60. To the best of our knowledge, the birefringence of Cd(H₂C₆N₇O₃)₂⋅8 H₂O is significantly larger than those of all commercial birefringent crystals and is the largest among hydrogen bonded supramolecular framework crystals. First-principles calculations and structural analyses reveal that the exceptional birefringence is mainly ascribed to strong covalent interactions within (H₂C₆N₇O₃)⁻ organic ligands and the perfect coplanarity between them. Given the rich structural diversity and tunability, hydrogen bonded supramolecular frameworks would offer unprecedented opportunities beyond the traditional purely inorganic oxides for birefringent crystals.     

Design and synthesis of polyindole - ZnO nano composite for NLO applications

Present paper mainly focuses on the synthesis, characterization polyindole-ZnO nano composites for third order nonlinear optical applications. Polyindole was synthesized through oxidative polymerization technique and its composites were prepared with different ZnO concentration. Structural morphology of the polymer composite was studied using FESEM, XRD and UV Visible spectroscopic technique. Polymer showed broad absorption with absorption maxima of 395 nm. Newly prepared thin films showed excellent nonlinear absorption with very good optical limiting behaviour when it is exposed to He-Ne laser with maximum optical limiting power of 11 mW along with third-order nonlinear susceptibility χ⁽³⁾ of 2.72 × 10^?3 esu. Hence these polymer composites may be potential candidate for optical limiting applications.