Aggregation Behavior of Ethoxylated Phytosterol Surfactants in Different Protic Solvents: An Insight from Dielectric Relaxation Studies.

The micellar aggregation behavior of biocompatible surfactants, phytosterol ethoxylates (BPS-, is the oxyethylene (EO) chain length), containing polyoxyethylene chains in four organic solvents (glycerol (G), ethylene glycol (EG), formamide (FA), and ,-dimethylformamide (DMF)) was studied by dielectric spectroscopy in the frequency range of 40 Hz to 110 MHz. Only the BPS-/EG and BPS-/G systems show distinct dielectric loss peaks near 10 Hz, indicating that BPS- forms micellar aggregates in EG and G solvents, and the interfacial polarization (IP) between the aggregates and solvents leads to this relaxation. The dielectric spectra were analyzed based on the IP theory and a columnar dispersion model.

Desalination behavior analysis of interior-modified carbon nanotubes doped membrane by dielectric spectrum and molecular simulation.

Carbon nanotube (CNT)-doped polyamide (PA) membranes have attracted much attention in reverse osmosis (RO) membranes due to their significant advantages of water flux and desalination. In this study, we synthesized multi-walled carbon nanotube (MWNT)/PA RO membrane by 12-oxodidodecanoic acid methyl ester group interior-modified MWNTs (MWNT-CHO). Then, their mechanism of desalination behavior was successfully analyzed by combining dielectric relaxation spectrum (DRS) and molecular dynamics (MD) simulation.

Broadband dielectric properties of honey: effects of temperature.

Dielectric properties of jujube honey were investigated at 298-358 K by broadband dielectric measurements. Four relaxation processes were observed and analyzed, which are caused by long range correlation of density fluctuation, cooperative motions of molecules, rotational polarization of bound water and collective reorientation of free water, respectively. The results of temperature dependence of dielectric parameters show that with increasing temperature, the interaction among the molecules e.

Dielectric Analysis of Microcapsule-Immobilized Composite Capsules Suspension: Substances Release.

Dielectric spectroscopy has unique advantages in monitoring drug release. In this work, a dielectric measurement was carried out on the release of the substances of microcapsule-immobilized composite capsules, which were fabricated by encapsulating the extract-loaded gum Arabic/gelatin microcapsules (PaE: GA/GE-MCs) in calcium alginate hydrogel (PaE: CA/GA/GE-CCs). We established the dielectric model of PaE: CA/GA/GE-CCs and got in-depth information on the systems.

Phase transition and electrical properties of aggregations of ethoxylated phytosterol surfactants by dielectric spectroscopy.

The aggregation behaviors of the bio-friendly nonionic phytosterol ethoxylated (BPS-n) surfactants, in water were investigated by dielectric spectroscopy over a frequency range from 40 Hz to 110 MHz. Only the BPS-5 solution system observes dielectric relaxation and we judge this is because due to the difference in the chain length of BPS-n surfactants. Then we further analyze the BPS-5 solution system.

Effect of grafting density on conformation of poly(acrylic acid) in solution by dielectric spectroscopy.

The effect of grafting density of poly(ethylene oxide) and dodecyl groups on the conformation of poly(acrylic acid) in solution was clarified by dielectric relaxation spectroscopy over a frequency range from 40 Hz to 110 MHz. Two distinct dielectric relaxations were found after the elimination of electrode polarization, and valuable information about the conformations and interfacial electrokinetic properties of molecules was obtained by analyzing the dielectric spectra based on a refined double-layer polarization model. The critical aggregation concentration was determined by the concentration dependency of dielectric parameters.

Dielectric Insights into the Microcosmic Behavior of Ionic Liquid-Based Self-Assembly-Microemulsions/Micelles.

Dielectric relaxation spectra of ([Bmim][BF]/TX-100/ p-xylene) microemulsions and ([Bmim][BF]/TX-100) micelles were measured. A specific dielectric relaxation changing with the concentration of ionic liquids (ILs) was observed in the range of 10-10 Hz. When dielectric parameters were combined with the Einstein displacement equation and Bruggeman's effective-medium approximation, the interaction between [Bmim][BF] and p-(1,1,3,3-tetramethylbutyl) phenoxypolyoxyethyleneglycol (TX-100) in microemulsions/micelles was presented: because of the electrostatic interaction and van der Waals force, [Bmim][BF] is bound around the polyethylene oxide (PEO) chains of TX-100, and once the electric field is added, ions of [Bmim][BF] will move along the PEO chain.

Dielectric Behavior and Phase Behavior of Block Copolymer PEO-PPO-PEO Aqueous Solution.

Dielectric spectroscopy can be applied to study the structure and dynamics of block polymer. In this work, dielectric measurements of block copolymer Pluronic L64 solution are carried out in the frequency range between 40 Hz and 110 MHz with variable temperatures and concentrations. We analyze the phase behavior of the PEO-PPO-PEO (Pluronic L64) aqueous system according to the concentration/temperature-dependence of direct current conductivity.

Chain conformation of poly(acrylic acid)-graft-poly(ethylene oxide)-graft-dodecyl in solution: an anomalous counter-ions condensation.

A dielectric spectroscopy study on a polyelectrolyte in aqueous solutions, which contains hydrophobic groups in part of the side chains poly(acrylic acid)-graft-poly(ethylene oxide)-graft-dodecyl (PAA-g-PEO-g-dodecyl) is reported. A refined double layer polarization model was proposed to analyze the double dielectric relaxations in the dielectric spectra. Various electrical and structural parameters of the copolymers were obtained.

Insight into the effect mechanism of urea-induced protein denaturation by dielectric spectroscopy.

Dielectric relaxation spectroscopy was applied to study how urea affects the phase transition of a thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPAM), which has been widely used as a protein model. It was found that there is a pronounced relaxation near 10 GHz for the ternary system of PNIPAM in urea aqueous solution. The temperature dependence of dielectric parameters indicates that urea can reduce the lower critical solution temperature (LCST) of PNIPAM, i.

How side chains affect conformation and electrical properties of poly(acrylic acid) in solution?

To better understand the effect of side chains on the chain conformation and electrical properties of polyelectrolytes, dielectric measurements were carried out on solutions of poly(acrylic acid) (PAA), poly(acrylic acid)-graft-dodecyl (PAA-g-dodecyl), and poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) over a wide concentration range. Double dielectric relaxations with counterion distribution were observed for these polymers and a refined double-layer polarization model was proposed to analyze these, by which valuable information about conformations and interfacial electrokinetic properties was obtained. The transitional concentrations for the overlapping and entanglement of chains were identified from results for the dielectric increment and relaxation time.

Concentration dependent phase behavior and collapse dynamics of PNIPAM microgel by dielectric relaxation.

The dielectric behavior of thermo-sensitive poly-(N-isopropylacrylamide) (PNIPAM) microgel with three different concentrations was investigated for the frequencies ranging from 40 Hz to 110 MHz as a function of temperature from 10 to 60 °C. Two remarkable and temperature-dependent relaxation processes were observed. The slow relaxation originates from the segmental motion over the whole temperature range.

Dielectric analysis based on spherical-shell model for cationic and anionic spherical polyelectrolyte brushes.

We report here a dielectric study on cationic and anionic spherical polyelectrolyte brush (SPB) (consisting of a polystyrene (PS) core and poly (2-aminoethylmethacrylate hydrochloride (PAEMH) chains or poly (acrylic acid) (PAA) chains grafted onto the core) suspensions over a frequency range of 40 Hz-110 MHz. The relaxation behavior of the suspensions shows significant changes in the brush layer properties when changing the particle mass fraction or pH of the system. After eliminating the electrode polarization effect at a low frequency, two definite relaxations related to interfacial polarization, around 100 kHz and 10 MHz respectively, are observed.

Relaxations and phase transitions during the collapse of a dense PNIPAM microgel suspension-thorough insight using dielectric spectroscopy.

The dielectric behavior of a thermo-sensitive poly-(N-isopropylacrylamide) (PNIPAM) microgel suspension with a dense concentration was investigated over the frequency range of 40 Hz to 110 MHz in a wide temperature window of 10-60 °C. By successfully removing the electrode polarization effect from the original data, two remarkable and temperature-dependent relaxation processes were observed. Both of the two-phase transition processes, i.

Insight into the electrical properties and chain conformation of spherical polyelectrolyte brushes by dielectric spectroscopy.

We report here a dielectric study on three kinds of anionic spherical polyelectrolyte brush (SPBs, consisting of a polystyrene (PS) core and three different poly (acrylic acid) chains grafted onto the core) suspensions over a frequency ranging from 40 Hz to 110 MHz. The relaxation behavior of the SPB suspensions shows significant changes in the brush-layer properties when the mass fraction of SPBs and the pH of the suspensions change. Two definite relaxations related to the interfacial polarization are observed around 100 kHz and 10 MHz.

Dielectric Analysis for the Spherical and Rodlike Micelle Aggregates Formed from a Gemini Surfactant: Driving Forces of Micellization and Stability of Micelles.

The self-aggregation behavior of Gemini surfactant 12-2-12 (ethanediyl-1,2-bis(dimethyldodecylammonium bromide)) in water was investigated by dielectric relaxation spectroscopy (DRS) over a frequency range from 40 Hz to 110 MHz. Dielectric determination shows that well-defined spherical micelles formed when the concentration of the surfactant was above a critical micelle concentration CMC1 of 3 mM and rodlike micelles formed above CMC2, 16 mM. The formation mechanism of the spherical micelles and their transition mechanism to clubbed micelles were proposed by calculating the degree of counterion binding of the micelles.

Influence of the structure on the collapse of poly(N-isopropylacrylamide)-based microgels: an insight by quantitative dielectric analysis.

The collapse of poly(N-isopropylacrylamide)/poly(acrylic acid) semi-interpenetrating polymer network (PNIPAM/PAA SIPN) and poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AA)) microgel suspensions is studied by dielectric spectroscopy in a frequency range from 40 Hz to 110 MHz as a function of temperature. Dielectric measurements show that the structure affects the relaxation behavior of microgels: two relaxations (micro-Brownian motion and interfacial polarization at low frequency and counterion polarization at high frequency) are observed in the SIPN microgel whose charges mainly exist in domains and one relaxation (interfacial polarization) is observed in the copolymer microgel whose charges distribute in the whole network. A dielectric model is proposed to describe the collapsed microgel suspensions, from which some parameters, such as the volume fraction and the permittivity of microgels, were calculated using Hanai's equation.

Anomalous Volume Phase Transition Temperature of Thermosensitive Semi-Interpenetrating Polymer Network Microgel Suspension by Dielectric Spectroscopy.

A new experimental result from dielectric spectroscopy of poly(N-isopropylacrylamide)/poly(acrylic acid) semi-interpenetrating polymer network (PNIPAM/PAA SIPN) microgel, which undergoes significant volume phase transition, is reported. Two significant dielectric relaxations were observed around 0.1-0.

Dielectric Relaxation of Spherical Polyelectrolyte Brushes: Movement of Counterions and Electrical Properties of the Brush Layer.

Dielectric behaviors of spherical polyelectrolyte brush (SPB) suspensions under various mass fractions of SPB and the pH of solution were investigated in a frequency range of 40 Hz to 110 MHz. The SPB consists of a polystyrene (PS) core grafted with poly(acrylic acid) (PAA) chains. Two unique relaxations were found at either about 10 kHz or 1-10 MHz, respectively, with the former due to the diffusion of counterions and the latter resulting from the interfacial polarization.

The chain conformation and relaxation dynamics of poly(acrylic acid)-graft-poly(ethylene oxide)-graft-dodecyl in water: effect of side-chains and distribution of counterions.

We present a study on the dielectric behavior of an aqueous solution of an amphiphilic copolymer, poly(acrylic acid)-graft-poly(ethylene oxide)-graft-dodecyl (PAA-g-PEO-g-dodecyl), in the frequency range of 40 Hz to 110 MHz at varying concentrations and temperatures. After eliminating the electrode polarization at low-frequency, three dielectric relaxation processes were observed at about 1.2 MHz, 150 kHz and 30 kHz, whose mechanisms were proved to originate from the fluctuations of free counterions, the fluctuation of condensed counterions, and the rotation of intramolecular aggregates, respectively.

Thermodynamics of micellization of ionic liquids C6mimBr and orientation dynamics of water for C6mimBr-water mixtures: a dielectric spectroscopy study.

The aggregation behavior of C6mimBr and its interaction with water at different concentrations and temperatures have been investigated by dielectric spectroscopy over frequency ranges from 500 MHz to 40 GHz. Dielectric determinations show that micellar aggregations form when the C6mimBr concentration is higher than 0.85 M, and the size of micellar aggregations varies inversely to temperature.

Dielectric relaxations of poly(N-isopropylacrylamide) microgels near the volume phase transition temperature: impact of cross-linking density distribution on the volume phase transition.

Dielectric relaxation behaviors of three types of thermally sensitive poly(N-isopropylacrylamide) (PNIPAM) microgels with different cross-linking density distributions were investigated in a frequency range from 40 Hz to 110 MHz at temperatures from 15 °C to 55 °C. After eliminating the electrode polarization at low frequency, two remarkable relaxations were observed, one in the kHz frequency range and the other in the MHz range. The low-frequency relaxation is attributed to the counterion polarization in the whole measuring temperature range, while the relaxation at high-frequency is probably dominated by different polarization mechanisms depending on below or above the volume phase transition temperature (VPTT): it is considered as micro-Brownian motion of side groups of PNIPAM when T < VPTT and interfacial polarization when T > VPTT.

Electrical transport properties and interaction of heteropolyacid in N,N-dimethylformamide by dielectric spectroscopy.

We present a dielectric spectroscopy study on binary electrolyte solutions composed of N,N-Dimethylformamide (DMF) and heteropolyacid (HPA). The HPA is composed of H(+) and Keggin polyoxometalate anion, [XW12O40](n-)(X = P, Si, with n = 3, 4). Conductivity was used to calculate the transport parameters such as diffusion coefficient and hydrodynamic radius of polyoxometalate (POM) anions.

Aggregation behavior and electrical properties of amphiphilic pyrrole-tailed ionic liquids in water, from the viewpoint of dielectric relaxation spectroscopy.

The self-aggregation behavior of amphiphilic pyrrole-tailed imidazolium ionic liquids (Py(CH₂)₁₂mim⁺Br⁻: Py = pyrrole, mim = methylimidazolium) in water is investigated by dielectric spectroscopy from 40 Hz to 110 MHz. Dielectric determination shows that the critical micelle concentration (CMC) is 8.5 mM, which is lower than that for traditional ionic surfactants.

Effect of side-chain on conformation of poly(acrylic acid) and its dielectric behaviors in aqueous solution: hydrophobic and hydrogen-bonding interactions and mechanism of relaxations.

Dielectric behaviors of poly(acrylic acid) (PAA), poly(acrylic acid)-graft-dodecyl (PAA-g-dodecyl), and poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) solutions were investigated from 40 Hz to 110 MHz at the solution temperature of 26 °C. For PAA and PAA-g-dodecyl solutions, two dielectric relaxations at about 5 MHz and 150 kHz were observed, whose mechanisms were proved to be the fluctuation of free counterions and condensed counterions, respectively. While for PAA-g-PEO solutions, an extra relaxation around 30 kHz was observed, including the two relaxations just mentioned, and it is related to the hydrogen-bonding aggregates in PAA-g-PEO solutions and was attributed to the rotation of the whole molecule.