Mechanical properties of epoxy resin toughened with cornstarch

We investigated the effect of starch modification on the mechanical properties of phenolic epoxy resin (EP). Corn starch admixture of 2.5, 5, 7.5, and 10 wt% were added into the EP. The tensile strength, elongation at break, and elastic modulus of different corn starch contents were compared. The containing of corn starch showed a positive effect on the toughness of the epoxy but showed little effect on strength when the additive content was less than 10 wt%. The strength and elastic modulus increased first and then decreased with the increase in starch content and reached their maximum values at a content of 2.5 wt%. The enhancement effect might be due to corn starch’s mechanical properties, dispersibility, and interfacial interaction. With the increase in starch content, starch granules quickly contact each other, causing self-aggregation sedimentation and a decrease in strength and elastic modulus. The scanning electron micrographs of the toughened EP specimens showed ductile failure because of the starch particles. The surface morphology of the blend resin specimens was full of staggered and stepped cracks caused by the shearing damage, which is shown by obvious plastic fracture characteristics with plastic deformation ability. The initiation of micro-cracks in the EP matrix was induced by the incorporation of starch particles, which caused localized stepped shear damage in the matrix. More energy would be absorbed during this process, and the toughness of the EP would be enhanced. It is recommended that the best corn starch content should be 2.5 wt% to obtain excellent strength and good toughness.

Interaction of cationic surfactant with acid yellow dye in absence/presence of organic and inorganic additives: conductivity and dye solubilization methods

In the present study, the conductometric and dye-solubilization techniques have been utilized to investigate the interaction between an anionic dye (acid yellow 23 [AY]) and a cationic surfactant (cetyltrimethylammonium bromide [CTAB]) in presence of organic (ethanol)/inorganic (NaCl) additives. From the conductometric method, two critical micelle concentrations (cmc) were found for AY + CTAB mixture in an aqueous system and the cmc values were found to undergo a change with the variation of AY concentrations. The cmc values of AY + CTAB systems were observed higher in the alcoholic medium, while the same was found to be lower in the NaCl solutions. The change in cmc of AY + CTAB systems shows an U-like curve with an increase of temperature. The negative free energy of micellization ( Δ G m o ${\Delta}{G}_{m}^{o}$ ) for the AY + CTAB systems has indicated a spontaneous micelle formation in all of the cases studied. The enthalpy ( Δ H m o ${\Delta}{H}_{m}^{o}$ ), as well as the entropy of micellization ( Δ S m o ${\Delta}{S}_{m}^{o}$ ) for the AY + CTAB systems, were assessed and discussed with proper reasoning. Additionally, the enthalpy-entropy compensation parameters were also investigated and illustrated. The solubility of AY and C D was observed to rise linearly with an increase in the concentration of CTAB/NaCl solution. The solubilization capacity (χ) of AY, the molar partition coefficient (K M) amongst the micellar and the aqueous phase, and free energy of solubilization ( Δ G S o ${\Delta}{G}_{S}^{o}$ ) were evaluated and discussed in detail. The former parameters undergo an increase with an increase of NaCl concentrations.

Impact of salts on the phase separation and thermodynamic properties of mixed nonionic surfactants in absence/attendance of polyvinyl alcohol

Mixed surfactant systems are used in different applied fields like pharmaceutical formulation rather than single surfactant. Therefore, the determination of the clouding nature of the triton X-100 (TX-100) + Tween 80 (TW-80) mixture was carried out in H2O and polyvinyl alcohol (PVA). In the occurrence of PVA, the cloud point (CP) values of TX-100 initially enhance with enhancing the concentration of PVA and tend to decrease after a certain concentration. For different ratios of TX-100 and TW-80 mixture having the same concentration of both solutions, CP values increase through the decreasing ratios of TX-100 with/without PVA. In the presence of polymer, at higher ratios of TX-100 than TW-80, the CP values are higher in magnitudes in comparison to the aqueous medium but at lower ratios of TX-100, the value of CP are lower in magnitudes in comparison to the aqueous system. The CP values of the TX-100 + TW-80 mixture in the salt system are lower in magnitudes than the aqueous medium in both the absence/presence of PVA. However, a reduction of CP values was obtained to a large extent for Na2SO4 over NaCl in the case of lower volume ratios of TX-100. Various thermodynamic variables (standard free energy ( Δ G c o ${\Delta}{G}_{c}^{o}$ ), standard enthalpy ( Δ H c o ${\Delta}{H}_{c}^{o}$ ), standard entropy ( Δ S c o ${\Delta}{S}_{c}^{o}$ ) change, thermodynamic parameters of transfer (free energy of transfer ( Δ G c , t o ${\Delta}{G}_{c,t}^{o}$ ), and transfer of enthalpies ( Δ H c , t o ${\Delta}{H}_{c,t}^{o}$ )) of phase transition) were also determined.

Intensification and optimization of the process for thyme oil in water nanoemulsions preparation using subcritical water and xanthan gum

Intensified process based on subcritical water conditions (120 °C and 1.5 atm, for 2 h) was utilized to prepare thyme oil in water (O/W) nanoemulsions. In this technique, water and xanthan gum, as green solvent and natural microbial emulsifier, were utilized. Results of gas chromatography revealed that Thymol and Carvacrol were two main bioactive compounds of the extracted thyme oil. Effects of amounts of xanthan gum (0.05–0.25 g) and thyme essential oil (0.2–0.8 mL) on size of oil nanodroplets and polydispersity index (PDI) of the resulted nanoemulsions were evaluated using response surface methodology. Results demonstrated that the produced thyme O/W nanoemulsion by 0.242 mL thyme oil and 0.140 g xanthan gum had smallest average nanodroplet size (150 nm) and PDI (0.088). Furthermore, monodispersed and spherical in shape thyme oil nanodroplets were provided in the nanoemulsion using these optimal conditions with zeta potential value of −10.1 mV and antioxidant activity of 17.4%. Results also indicated that this prepared nanoemulsion had high fungicidal and bactericidal activities toward Penicillium digitatum and Escherichia coli, respectively.

Synthesis and Antiplatelet Potential Evaluation of 1,3,4-Oxadiazoles Derivatives

A novel series of 2-(3-methyl-1,6-diphenyl-1H-pyrazolo[3,4-b]pyridin-4-yl)-5-aryl-1,3,4-oxadiazoles (4a–4h) has been synthesized from corresponding hydrazones (3a–3h) and evaluated their antiplatelet aggregation effect induced by arachidonic acid and collagen. Spectral data and elemental evaluation were used to confirm the structure of the compounds while molecular docking against cyclooxygenase 1 and 2 (COX1 & COX2) and quantitative structure-activity relationship (QSAR) were performed in describing their antiplatelet potential. All synthesized compound exhibited more than 50% platelet aggregation inhibition against both arachidonic acid and collagen. Antiplatelet activities results showed that 4b and 4f compounds have highest % inhibition against arachidonic acid. High Egap and ionization potential values showed that the compound 4d, 4e and 4f were supposed to be more active and good electron donor while 4b, 4c, 4d, 4e, 4g and 4h might be more active due to more electrophilic sites. Interaction with more than one residues in the binding pocket of COX-1 in comparison with aspirin and ligand efficacy (LE) consequences showed that compounds have excellent action potential for COX-1. Computational evaluations are in good agreement with antiplatelet activities of the compounds. All compounds might be promising antiplatelet agents especially 4b, 4f and helpful in the synthesis of new drugs for the treatment of cardiovascular diseases (CVDs).

On the Thermodynamics of Micellizationof Oppositely Charged Surfactants in the Presence of Organic Additives in the Aqueous Medium

To investigate the effect of additives urea and thiourea, on the micellization behavior of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), detailed conductance measurements were carried out in aqueous media at different temperatures. The critical micelle concentration (CMC), determined from the discontinuity in the plots of molar conductance versus square root of concentration, indicated an inhibitory effect of urea and thiourea on micelle forming ability of the surfactants SDS and CTAB in the range of composition studied. The demicellizing effect of urea has been found to be more pronounced in SDS than CTAB. These observations are further augmented by the evaluation of thermodynamic parameters of micellization. A negative change in enthalpy of micellization ( Δ H m ∘ $\Delta{\text{H}}_{\text{m}}^{\circ}$ ) indicates a strong interaction between water and the additives and a positive change observed in entropy of micellization ( Δ S m ∘ $\Delta{\text{S}}_{\text{m}}^{\circ}$ ) manifest, that the micellization is an entropy-driven process. Further Δ H m ∘ $\Delta{\text{H}}_{\text{m}}^{\circ}$ and Δ S m ∘ $\Delta{\text{S}}_{\text{m}}^{\circ}$ change in mutually compensating manner, so that Δ G m ∘ < 0 $\Delta{\text{G}}_{\text{m}}^{\circ} < 0$ is not significantly affected. Finally, the counterion binding values (β) obtained for SDS and CTAB remain practically constant from 0.6 to 0.8 between 25 °C and 45 °C indicate that the size and shape of micelle remain essentially constant. Moreover, the increase in Δ G II ∘ $\Delta{\text{G}}_{{\text{II}}}^{\circ}$ values, which represent the effect of co-solvent or additive on micellization, substantiates the above observations. Many early works has investigated the micellization behavior of surfactants using a fixed additive composition. However, in this study, variable aqueous compositions of urea (0.30–1.78 wt%) and thiourea (0.24–1.41 wt%) have been considered.

Temperature Dependent Solubility of Benzoic Acid in Aqueous Phase and Aqueous Mixtures of Aliphatic Alcohols

The benzoic acid solubility in aqueous phase and in various aqueous mixtures of methanol, ethanol and 2-propanol was determined at temperatures ranging from 303 to 333 K by an analytical technique. The results showed that the solubility of the acid in alcohols-water binary mixtures is high as compared to pure aqueous phase. The addition of alcohols to water favors the dissolution of benzoic acid which increases further with the increase in alcohols content of water within the investigated temperature range. The benzoic acid solubility in water alone and aqueous mixtures of the selected alcohols was in the order of; 2-propanol in water > ethanol in water > methanol in water > pure water. It is also observed that within the investigated temperature range, the acid solubility increases with rise in temperature in both the aqueous phase and alcohols-water binary solvents. The logarithm of the mole fraction of the acid’s solubility also showed a linear trend against the temperature. The experimental results obtained in the current study were compared with the reported literature for the studied acid and other organic acids in various solvents and showing a good agreement. The study will have implications in the processes involving separation, crystallization and pharmaceutical formulation in various industries.

Solubility and Solution Thermodynamics of Baricitinib in Six Different Pharmaceutically Used Solvents at Different Temperatures

The preset study was undertaken to determine solubility and solution thermodynamics of a novel anticancer drug baricitinib in some pharmaceutically used mono/pure solvents including “water, ethanol, polyethylene glycol-400 (PEG-400), ethyl acetate (EA), dichloromethane (DCM) and dimethyl sulfoxide (DMSO)” at “T = 298.2 K to 323.2 K” and “p = 0.1 MPa”. The solubility of baricitinib after equilibrium (saturation state) was analyzed spectrophotometrically by applying an isothermal technique. Characterization of solid phases of initial and equilibrated baricitinib was confirmed with the help of differential scanning calorimetry (DSC). Measured solubilities of baricitinib were regressed using “van’t Hoff and Apelblat models”. DSC spectra of baricitinib showed no change in physical state of baricitinib after equilibrium. Solubilities of baricitinib (as mole fraction) were estimated highest in DMSO (1.65 × 10−1) followed by PEG-400 (1.42 × 10−1), DCM (1.29 × 10−3), ethanol (7.41 × 10−4), EA (4.74 × 10−4) and water (1.76 × 10−4) at “T = 323.2 K” and same tendencies were also noted at other temperatures studied. With the help of theoretical solubilities of baricitinib, activity coefficients were estimated. The estimated data of activity coefficients indicated higher molecular interactions in baricitinib-DMSO and baricitinib-PEG-400 as compared with baricitinib-water, baricitinib-EA, baricitinib-DCM and baricitinib-ethanol. Thermodynamic treatment of solubility values of baricitinib showed “endothermic and entropy-driven dissolution” of baricitinib in all pharmaceutically used solvents evaluated.