Abbas Khan

Synthesis, Characterization, and Silver Nanoparticles Fabrication in N-isopropylacrylamide-Based Polymer Microgels for Rapid Degradation of p-Nitrophenol

Multiresponsive poly(N-isopropylacrylamide-co-methacrylic acid) microgels were synthesized by precipitation polymerization in aqueous medium. Then silver-poly(N-isopropylacrylamide-co-methacrylic acid) hybrid microgels were prepared by in-situ reduction of silver ions. Formation of microgels was confirmed by Fourier transform infrared spectroscopic analysis. pH and temperature sensitivity of microgel was studied by dynamic light scattering. Hydrodynamic radius of microgels decreases with increase in temperature at pH 8.20 and show volume phase transition temperature around 45°C. At pH 2.65, hydrodynamic radius decreases with increase in temperatures upto 35°C but further increase in temperature causes aggregation and microgel becomes unstable due to increase of hydrophobicity. With increase in pH of medium, the hydrodynamic radius of microgels increases sigmoidally. Formation of silver nanoparticles inside microgel and pH dependence of surface plasmon resonance wavelength of the hybrid microgels were investigated by ultraviolet-visible spectroscopy. The value of surface plasmon resonance band and absorbance associated with surface plasmon resonance band increases with increases in pH of the medium. The apparent rate constant of reduction of p-nitrophenol was found to be linearly dependent on volume of hybrid microgels used as catalyst. The system has a potential to be used as effective catalyst for rapid degradation of industrial pollutant.

Intermolecular Interactions of Polymer/Surfactants Mixture in Aqueous Solution Investigated by Various Techniques

The interaction between diblock copolymer with ionic surfactants in aqueous solution were studied employing surface tensiometery, electrical conductivity, steady-state fluorescence spectroscopy and dynamic laser light scattering at 303 K. Surface tension measurements were used to determine critical micelle concentration (CMC) and, thereby, its free energy of micellization (ΔGm), free energy of adsorption (ΔGads), surface excess concentration (Γ), and minimum area per molecule (A). The negative values of (ΔGm) both in case of SDS and CTAB confirmed the spontaneity of the processes. Conductivity measurements were used to determine critical micelle concentration (CMC), critical aggregation concentration (CAC), polymer saturation point (PSP), degree of ionization (α), and counterion binding (β). Addition of polymers could effectively reduce the CMC value of surfactants and, thus increase the detergency. Dynamic light scattering experiments were performed to check the changes in physiochemical properties of the block copolymer micelles take place due to the interactions of diblock copolymer with ionic surfactants. The ratio of (I1/I3) indicates the polarity of the pyrene micro environment and confirms the detection of micelle as well as polymer-surfactant interactions. Aggregation number (N), number of binding sites (n), and free energy of binding (ΔGb) for pure surfactants as well as for polymer-surfactant mixed micellar systems were determined by fluorescence quenching method.

Effect of Hydrophilic/Hydrophobic Block Ratio and Temperature on the Surface and Associative Properties of Oxyethylene and Oxybutylene Diblock Copolymers in Aqueous Media

Recent development in dispersion science and technology demands block copolymers with a variable block length and composition. To highlight that purpose, the surface active, associative, colloidal, and thermodynamic behavior of three diblock copolymers having different hydrophilic to hydrophobic ratio is reported here. Using surface tension and light scattering measurements, the micellization and adsorption behavior of polyoxyethylene and polyoxybutylene diblock copolymers of the type EmBn have been analyzed. Critical micelle concentration (CMC) and related thermodynamic parameters like free energy (ΔGmic), enthalpy (ΔHmic), and entropy (ΔSmic) of micellization were calculated from CMC value using the closed association model. Likewise, the surface active parameters, like surface excess concentration (Γ2), area per molecule (A2), and thermodynamic parameters such as free energy (ΔGads), enthalpy (ΔHads), and entropy (ΔSads) of adsorption of polymer at the air/water interface, were also calculated at various temperatures. Static and dynamic light scattering techniques were employed for the determination of the weight-average molar (Mw), association number (Nw), polymer–water interaction (A2), and micellar size in terms of hydrodynamic radii (Rh) of copolymer micelles. The effect of block length and solution temperature on the surface and micellar properties of these copolymers was also investigated. GRAPHICAL ABSTRACT

Fabrication of silver nanoparticles in pH responsive polymer microgel dispersion for catalytic reduction of nitrobenzene in aqueous medium

Copolymer microgels based on N-isopropylacrylamide (NIPAM) and methacrylic acid (MAA) have been synthesized by free radical emulsion polymerization using N,N-methylenebisacrylamide (BIS) as a cross-linker. Synthesized microgels were characterized by Fourier transform infrared spectroscopy (FTIR). Then silver nanoparticles were fabricated in the synthesized microgels by in-situ reduction of AgNO3 with NaBH4. The formation of silver nanoparticles was confirmed by UV–Vis spectroscopy. The pH sensitivity of the copolymer microgels was investigated using dynamic light scattering technique (DLS). Hydrodynamic radius of P (NIPAM–MAA) microgels increases with increase in pH of the medium at 25°C. Surface plasmon resonance wavelength (λSPR) of silver nanoparticles increases with increase in hydrodynamic radius due to change in pH of the medium. The catalytic activity for the reduction of nitrobenzene (NB), an environmental pollutant, into aniline was investigated by UV–Vis spectroscopy in excess of NaBH4 using hybrid microgels as catalyst. The value of apparent rate constant (kapp) of the reaction was calculated using pseudo first order kinetic model and it was found to be linearly related to the amount of catalyst. The results were compared with literature data. The system was found to be an effective catalyst for conversion of NB into aniline.

Effect of Temperature, Polymer, and Salts on the Interfacial and Micellization Behavior of 3-Dodecyl-1-Methyl-1H-Imidazol-3-Ium-Bromide: A Dispersion of a Long-Chain Ionic Liquid

Owing to low melting point (<100°C), negligible vapor pressure, and broad spectrum of applications, ionic liquids have gained much attention in the recent years. In this paper, the effects of temperature, polyvinyl pyrrolidone (PVP) polymer, and salts on the interfacial and bulk properties of aqueous solution of long-chain ionic liquid [i.e., 3-dodecyl-1-methyl-1H-imidazol-3-ium-bromide (C12mimBr)] were investigated using tensiometry. This long-chain ionic liquid was found to behave like a conventional surfactant, and thus it can be called surface active ionic liquid (SAIL). An inflection point in surface tension versus concentration curve at specific concentration was observed, which is termed the critical micelle concentration (CMC) of C12mimBr. The pre-micellar region was used to calculate various surface active parameters whereas the CMC was used to investigate its micellar behavior. Both surface activity and CMC of SAIL increased with the increase in temperature. No prominent effect was observed with the addition of PVP, whereas NaCl and CuNO3 addition distinctly changed the CMC. Similarly, surface effectiveness (πcmc) of C12mimBr decreased with the addition of NaCl and increased with the addition of CuNO3, whereas addition of PVP showed no effect on it. It shows that PVP has negligible interaction with C12mimBr. Further, the process of micellization was found to be entropy driven. GRAPHICAL ABSTRACT

A COMPARATIVE STUDY OF THERMODYNAMIC PROPERTIES OF STRUCTURALLY RELATED PHENOTHIAZINE DRUGS IN AQUEOUS SOLUTION

ABSTRACT Association characteristics of amphiphilic phenothiazine drugs Fluphenazine and Trifluperazine dihydrochloride in water have been examined and their thermodynamic parameters have been calculated using conductometry. The electrical conductivity was measured as a function of concentration at various temperatures and cmc was calculated in the temperature range of 20-50°C. Thermodynamic parameters i.e. standard free energy of micellization, G m ∆ ° , standard enthalpy of micellization, H m ∆ ° and standard entropy of micellization, S m ∆ ° were calculated from cmc value using closed association model. e-mail. m_sidiq12@yahoo.com INTRODUCTION A large number of drugs exhibit colloidal behavior and their properties mainly depend on the nature of aromatic ring system of hydrophobic moiety. They are useful in probing the relationship between molecular structure and physicochemical properties. One of the mechanisms to serve this purpose is to study the thermodynamics of their aggregation and the factors governing this process

Characterization of Surfactant-Diblock Copolymer Interactions and Its Thermodynamic Studies

The interaction of nonionic diblock copolymer poly(ethylene oxide butylene oxide) (E62B22) with a cationic surfactant cetyl trimethyl ammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulphate (SDS) were studied using surface tension, conductivity, and dynamic laser light scattering techniques. Surface tension measurements were used to determine critical micelle concentration and thereby its free energy of adsorption (ΔGads), free energy of micellization (ΔGm), surface excess concentration (Γ), and minimum area per molecule (A). Conductivity measurements were used to determine critical micelle concentration (CMC) critical aggregation concentration (CAC) at different temperatures, enthalpy of micellization (ΔHm), free energy of micellization and entropy of micellization (ΔSm). Changes in physicochemical properties of the micellized block copolymer were studied by using dynamic laser light scattering. The effect of surfactant on the size and properties of block copolymer has also been discussed.

Micellar parameters of diblock copolymers and their interactions with ionic surfactants

The interactions of non-ionic amphiphilic diblock copolymer poly(oxyethylene/oxybutylene) (E39B18) with anionic surfactant sodium dodecyl sulphate (SDS) and cationic surfactant hexadecyltrimethylammonium bromide (CTAB) were studied by using various techniques such as surface tension, conductivity, steady-state fluorescence and dynamic light scattering. Surface tension measurements were used to determine the critical micelle concentration (CMC) and thereby the free energy of micellization (ΔGmic), free energy of adsorption (ΔGads), surface excess concentration (Γ) and minimum area per molecule (A). Conductivity measurements were used to determine the critical micelle concentration (CMC), critical aggregation concentration (CAC), polymer saturation point (PSP), degree of ionization (α) and counter ion binding (β). Dynamic light scattering experiments were performed to check the changes in physiochemical properties of the block copolymer micelles taken place due to the interactions of diblock copolymers with ionic surfactants. The ratio of the first and third vibronic peaks (I1/I3) indicated the polarity of the pyrene micro environment and was used for the detection of micelle as well as polymer-surfactant interactions. Aggregation number (N), number of binding sites (n) and free energy of binding (ΔGb) for pure surfactants as well as for polymer-surfactant mixed micellar systems were determined by the fluorescence quenching method.

Kinetic investigation and lifetime prediction of Cs–NIPAM–MBA-based thermo-responsive hydrogels

This study attempted to clarify the influence of a cross-linker, N,N-methylenebisacrylamide (MBA), and N-isopropylacrylamide (NIPAM) on the non-isothermal kinetic degradation, solid state and lifetime of hydrogels using the Flynn-Wall-Ozawa (F-W-O), Kissinger, and Coats-Redfern (C-Red) methods. The series of dual-responsive Cs-PNIPAM-MBA microgels were synthesized by soapless-emulsion free radical copolymerization in an aqueous medium at 70 °C. The thermal properties were investigated using thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) under nitrogen atmosphere. The apparent activation energy using the chosen Flynn-Wall-Ozawa and Kissinger methods showed that they fitted each other. Meanwhile, the type of solid state mechanism was determined using the Coats-Redfern method proposed for F1 (pure Cs) and F2 (Cs-PNIPAM-MBA hydrogel series) types, which comprise random nucleation with one nucleus reacting on individual particles, and random nucleation with two nuclei reacting on individual particles, respectively. On average, a higher Ea was attributed to the greater cross-linking density of the Cs hydrogel.

Light scattering and surface tensiometric studies of tip-modified PEO-PBO diblock copolymers in water

The micellar and associative properties of four diblock copolymers, Me2N(CH2)2OE79B34 (denoted DE80B34), I−Me3N+(CH2)2OE79B34 (denoted TE80B34), I−Me3N+(CH2)2OE48B22 (denoted TE49B22), and HO(CH2)2OE62B22 (denoted E62B22), in aqueous solution and at various concentrations and temperatures, were investigated by surface tensiometry and dynamic and static laser light scattering. Surface tension measurements enabled the critical micelle concentration (CMC) to be determined at different temperatures, and thus the enthalpy of micellization (ΔHomic), the free energy of micellization (ΔGomic), and the entropy of micellization (ΔSomic) to be ascertained. Dynamic and static light-scattering measurements allowed the micellar parameters to be calculated and the extent of hydration of the copolymer micelle to be obtained qualitatively. The experimental results provided by these techniques are discussed in the terms of the variation in the hydrophilic to hydrophobic (E/B) ratio and end-group modification. Micellar parameters such as the weight-average molar mass (Mw), the association number (Nw), the thermodynamic radius (rt), and the hydrodynamic radius (rh) obtained from light-scattering data show that the micelles formed by the conventional EmBn and dimethylamino-tipped (DEmBn) copolymers are harder than those of trimethylammonium-tipped (TEmBn) copolymers. This difference in micellar properties is considered to be due to differences in polarity and charge effect at the hydrophilic ends of the tip-modified copolymers. The high value of rh for DEmBn and TEmBn copolymers as compared to E62B22 is an indication of micellar aggregation.