Dynamics and Microstructures of Nicotine/Water Binary Mixtures near the Lower Critical Solution Temperature

Dynamics of Acrylamide Hydrogels, Polymers, and Monomers in Water Measured with Optical Heterodyne-Detected Optical Kerr Effect Spectroscopy

The ultrafast dynamics of acrylamide monomers (AAm), polyacrylamide (PAAm), and polyacrylamide hydrogels (PAAm-HG) in water were studied using optical heterodyne-detected optical Kerr effect (OHD-OKE) spectroscopy. Previous ultrafast infrared (IR) measurements of the water dynamics showed that at the same concentration of the acrylamide moiety, AAm, PAAm, and PAAm-HG exhibited identical water dynamics and that these dynamics slowed with increasing concentration. In contrast to the IR measurements, OHD-OKE experiments measure the dynamics of both the water and the acrylamide species, which occur on different time scales. In this study, the dynamics of all the acrylamide systems slowed with increasing concentration. We found that AAm exhibits tetraexponential decays, the longest component of which followed Debye-Stokes-Einstein behavior except for the highest concentration, 40% (w/v). Low concentrations of PAAm followed a single power law decay, while high concentrations of PAAm and all concentrations of PAAm-HG decayed with two power laws. The highest concentrations, 25% and 40%, of PAAm and PAAm-HG showed nearly identical dynamics. We interpreted this result as reflecting a similar extent of chain-chain interactions. At low concentrations, PAAm displays non-Markovian, single-chain dynamics (single power law), but PAAm displays entangled chain-chain interactions at high concentrations (two power laws). PAAm-HG has chain-chain interactions at all concentrations that arise from the cross-linking. At high concentrations, the dynamics of the entangled of PAAm become identical within error as those of the cross-linked PAAm-HG.

Ultrasound-triggered nicotine release from nicotine-loaded cellulose hydrogel

Ultrasound (US)-triggered nicotine release system in a cellulose hydrogel drug carrier was developed with three different cellulose concentrations of 0.45 wt%, 0.9 wt%, and 1.8 wt%. The nicotine-loaded cellulose hydrogels were fabricated by the phase inversion method when the nicotine and cellulose mixture in the 6 wt% LiCl/N, N-dimethylacetamide solvent was exposed to water vapor at room temperature. Nicotine was used as the medicine due to its revealed therapeutic potential for neurodegenerative diseases like Alzheimer's and Parkinson's diseases. The behavior of US-triggered nicotine release from nicotine-cellulose hydrogel was studied at 43 kHz US frequency at the changing US output powers of 0 W, 5 W, 10 W, 20 W, 30 W, and 40 W. The significant US-triggered nicotine release enhancement was noted for the hydrogels made with 0.9 wt% and 1.8 wt% cellulose loading. The matrix made with 0.9 wt% cellulose was exhibited the highest nicotine release at the 40 W US power, and differences in nicotine release at different US powers were noticeable than at 0.45 wt% and 1.8 wt% cellulose loadings. For the three cellulose hydrogel systems, the storage modulus (G') values at the 0.01 wt% strain rate were dropped from their initial values due to the US irradiation. This reduction was proportionately decreased when the US power was increased. The deconvolution of FTIR spectra of nicotine-loaded cellulose films before and after US exposure was suggested breakage of cellulose-nicotine and cellulose-water in the matrix; thus, the stimulated nicotine release from the cellulose matrix was promoted by the US irradiation.

Microstructural and Dynamical Heterogeneities in Ionic Liquids

Ionic liquids (ILs) are a special category of molten salts solely composed of ions with varied molecular symmetry and charge delocalization. The versatility in combining varied cation-anion moieties and in functionalizing ions with different atoms and molecular groups contributes to their peculiar interactions ranging from weak isotropic associations to strong, specific, and anisotropic forces. A delicate interplay among intra- and intermolecular interactions facilitates the formation of heterogeneous microstructures and liquid morphologies, which further contributes to their striking dynamical properties. Microstructural and dynamical heterogeneities of ILs lead to their multifaceted properties described by an inherent designer feature, which makes ILs important candidates for novel solvents, electrolytes, and functional materials in academia and industrial applications. Due to a massive number of combinations of ion pairs with ion species having distinct molecular structures and IL mixtures containing varied molecular solvents, a comprehensive understanding of their hierarchical structural and dynamical quantities is of great significance for a rational selection of ILs with appropriate properties and thereafter advancing their macroscopic functionalities in applications. In this review, we comprehensively trace recent advances in understanding delicate interplay of strong and weak interactions that underpin their complex phase behaviors with a particular emphasis on understanding heterogeneous microstructures and dynamics of ILs in bulk liquids, in mixtures with cosolvents, and in interfacial regions.

Temperature and Salting out Effects on Nicotine Dissolution Kinetics in Saline Solutions

The dissolution rate of nicotine in aqueous solutions of sodium chloride (NaCl) was investigated at room temperature and 70 °C by quantitatively visualizing the shrinkage rate of microscopic nicotine droplets. Four different salt concentrations were used: 15 wt % (3.0 M), 20 wt % (4.3 M), 25 wt % (5.7 M), and the saturation NaCl concentration of 26 wt % (6.0 M). These results, together with the Epstein-Plesset mathematical model, provided estimates of nicotine's diffusion coefficient in the NaCl solutions. At room temperature, the dissolution rate of nicotine and diffusion coefficients decreased with increasing NaCl concentration, and below 15 wt %, the dissolution kinetics were too fast to measure accurately via optical microscopy. At the higher temperature of 70 °C, nicotine's dissolution rate showed a decrease for 15 and 20% NaCl. However, at near-saturation 25% NaCl, nicotine's dissolution rate did not exhibit significant change for the two temperatures, and for 26%, dissolution was higher at 70 °C than at room temperature.

Electrochemical sensing of nicotine using CuWO4 decorated reduced graphene oxide immobilized glassy carbon electrode

A novel and selective electrochemical sensing of nicotine is studied using copper tungstate decorated reduced graphene oxide nanocomposite (CuWO₄/rGO) nafion (Nf) immobilized GC electrode (GCE). The CuWO₄/rGO nanocomposite is synthesized using sonication method and characterized by HR-TEM (High resolution transmission electron microscopy), SEM (Scanning electron microscopy), FT-IR (Fourier transform infrared spectroscopy), SAED (Selected area of electron diffraction pattern), XRD (X-ray diffraction), Raman spectroscopy, Thermo gravimetric analysis (TGA) and EDX (Energy dispersive X-ray diffraction) techniques. The CuWO₄/rGO/Nf immobilized GCE shows better electrocatalytic response for the detection of nicotine as compared to bare GCE. A better selectivity and sensitivity is achieved using CuWO₄/rGO/Nf immobilized GCE to detect 0.1 µM nicotine in the presence of 100-fold excess concentrations of different interferents. The present CuWO₄/rGO/Nf immobilized GCE electrochemical sensor exhibits an ample range of sensing from 0.1 µM to 0.9 µM and the low detection limit is found to be 0.035 µM (S/N = 3). Comparable results are achieved for the determination of nicotine in various real samples such as cigarettes (Gold flake and Wills) and urine samples with improved recoveries.