Aggregation and Adsorption Behavior of Cationic Surfactants (Cetyltrimethylammonium Bromide and Dodecyltrimethylammonium Bromide) in Aqueous Solutions of Antibiotic Drug (Amikacin Sulphate) at Different Temperatures

Conductivity and spectroscopy techniques have been accomplished to comprehend the mechanism of supramolecular assembly of cetyltrimethylammonium bromide (CTAB) and dodecyltrimethylammonium bromide (DTAB) in aqueous solution of amikacin sulphate (0.001, 0.005, and 0.010 mol kg⁻¹). For CTAB, the normal boost of the CMC value with rise in temperature manifests the significant role of aquaphilic dehydration. However, the aquaphobic dehydrations become prominent with temperature and depict typical U-shaped behavior of CMC for DTAB. The thermodynamic parameters of micellization have been derived from CMC values. The outcomes have been conferred in terms of solvation of hydrophobic part of surfactants by hydrophobic part of amikacin sulphate and micellization becomes more favorable for surfactant with more hydrophobic character in the presence of drug. The alteration in micro-environment of the ternary (drug/surfactant/water) system has been explained in terms of fluorescence emission intensity of surfactant solutions which has been found to decrease by the addition of drug. The obtained absorbance spectrum by varying concentrations of surfactant/drug affords noteworthy information regarding the diverse interactions in studied systems. Moreover, the exhaustive understanding of surfactant micellar behavior have been discussed in consideration of use of surfactants as drug delivery agents and hence to amplify drug bioavailability consequently remodeling its treatment efficacy.     

Counterion Effect on Krafft Temperature and Related Properties of Octadecyltrimethylammonium Bromide

In the present work, we have investigated the effect of some counterions on the Krafft temperature (T _K) and the micelle formation of octadecyltrimethylammonium bromide (OTAB) in aqueous solution. The results showed that the ions with more chaotropic nature increase the T _K while those with a kosmotropic, hydrotropic and less chaotropic nature lower the T _K of the surfactant. More chaotropic SCN^? and I^?, being weakly hydrated, form contact ion pairs with the octadecyltrimethylammonium ion and reduce the electrostatic repulsion between the surfactant molecules. As a result, these ions exhibit salting out behavior and raise the T _K of the surfactant. On the other hand, less chaotropic Cl^? and NO₃ ^?, kosmotropic SO₄ ^2? and F^? and hydrotropic benzoate and salicylate ions increase the solubility of the surfactant, with a consequent decrease in the T _K. SO₄ ^2?, F^?, benzoate and salicylate cannot form contact ion pairs with the weakly hydrated cationic part of OTAB. Rather, being extensively hydrated and kosmotropic in nature, these ions do not show any tendency to shed their hydrated water molecules to form contact ion pairs with the weakly hydrated octadecyltrimethylammonium ion and therefore, stay apart. As a result, the T _K of the surfactant decreases significantly in the presence of these ions. The critical micelle concentration (CMC) of the surfactant decreases significantly in the presence of these ions due to screening of the micelle surface charge by the added counterions. Consequently, the surfactant molecules attain better packing because of substantial reduction in the electrostatic repulsion between the charged head-groups, showing a significant decrease in the CMC.     

Studies on Solution Behavior of Aqueous Mixtures of Nonionic Polymer in Presence of Cationic Surfactants

The interactions of two gemini surfactants (16–s–16, s = 5, 6) and their conventional counterpart cetyltrimethylammonium bromide (CTAB) with polyethylene glycols (PEG 3000 and PEG 35000) have been investigated using conductivity, steady state fluorescence, viscosity and TEM techniques. The results indicate that there is no interaction between the PEG 3000/CTAB complex at lower polymer concentrations. However, a very weak interaction is observed at higher concentrations (0.5 and 1.0 wt% PEG 3000), while PEG 3000 and PEG 35000 interact with the gemini surfactants. Both critical aggregation concentration (CAC) and critical micelle concentration (CMC) increases with polymer concentration but are independent of the polymer molecular weight. From steady state fluorescence it is found that the addition of PEG results in no drastic decrease in the aggregation number (N) for all surfactants. This suggests that the atmosphere surrounding the polyion-bound micelles, with respect to the influence on the forces acting at the micelle surface, is equivalent to the counterion/water atmosphere surrounding free micelles. The relative viscosity (η _r) results show an enhancement in η _r for all the surfactants. The increase in η _r is quite significant with gemini surfactants. Polymer-surfactant interaction also depends on the polymer molecular weight. Also, the interaction seems to affect both inter polymer–polymer association as well as chain expansion. Additionally the surfactant induced changes in the polymer conformation depicted by TEM study at the micro structural level confirmed previously observed interactions determined by different analytical techniques.     

Aggregation Behavior of Sodium Dodecyl Sulfate and Cetyltrimethylammonium Bromide Mixtures in Aqueous/Chitosan Solution at Various Temperatures: An Experimental and Theoretical Approach

A conductometric study of the mixed micellization behavior between cetyltrimethylammonium bromide (CTAB, a cationic surfactant) and sodium dodecyl sulfate (SDS, an anionic surfactant) was carried out in the absence/presence of various percentages of chitosan in the temperature range of 298.15–318.15 K. The deviations of critical micelle concentration (cmc) from the ideal values indicate the interaction between CTAB and SDS. The micellar mole fraction values according to different proposed models X₁^Rub (Rubingh), X₁^M (Motomura), X₁^Rod (Rodenas), and X₁^id (ideal mole fraction) were estimated and the results obtained reveal the high contribution of CTAB in the mixed micellization, which enhances with the increase of the mole fraction of CTAB. The negative magnitudes of indicate the spontaneous formation of mixed micelles between CTAB and SDS. The values of activity coefficients (f₁ and f₂) were less than unity and the values of the interaction parameter (β) are negative in all cases, which indicate the attractive interaction between CTAB and SDS. The negative values of excess free energy of micellization (ΔG_ex) signify the stability of the mixed micelles. The negative values of in the chitosan systems indicate that micellization is exothermic. The values of were found to be positive in all cases.     

Effect of Electrolytes on the Krafft Temperature of Cetylpyridinium Chloride in Aqueous Solution

This paper presents the effect of some electrolytes on the Krafft temperature (T_K) of cetylpyridinium chloride in aqueous solution. The results show that more chaotropic anions raise while less chaotropic anions lower the T_K of the surfactant. More chaotropic Br^?, SCN^? and I^? form contact ion pairs with the cetylpyridinium ion and reduce the electrostatic repulsion between the surfactant molecules. As a result, these ions exhibit salting‐out behavior, showing an increase in the T_K of the surfactant. On the other hand, less chaotropic NO₃^? increase the solubility of the surfactant, with a consequent decrease in the T_K. Surface tension data of the salt solutions reveal that more chaotropic ions show a relatively less molar increase in surface tension compared to less chaotropic ions. This indicates that less chaotropic ions have a preferential tendency to be negatively adsorbed at the air–water interface as well as hydrocarbon–water interface and thereby disturb the hydration of the surfactant. SO₄^2? being a strong kosmotrope cannot form contact ion pairs with the cationic part of the surfactant. Rather this ion preferentially remains in the bulk because of its strong tendency for hydration and thereby stays apart. As a result, SO₄^2? also causes a significant lowering of the T_K of the surfactant. Thus it appears that contrary to the usual trend SO₄^2? behave like a chaotrope showing salting‐in effect of the surfactant.     

The Influence of an Organic Salt on Micellization Behavior of Tetradecyltrimethylammonium Bromide in Aqueous Solutions of Trisubstituted Ionic Liquid [Odmim][Cl]

The influence of sodium benzoate (Na-Bz) on micellization behavior of the cationic surfactant tetradecyltrimethylammonium bromide (TTAB) in aqueous media of trisubstituted imidazolium-based ionic liquid (IL), 1,2-dimethyl-3-octylimidazolium chloride [odmim][Cl], was investigated using conductometry, tensiometry, fluorescence,¹H NMR, Dynamic Light Scattering (DLS), and Rheology techniques. It was observed that with an increase in salt concentration, the critical micelle concentration (CMC) values of the system decrease. The CMC and various thermodynamic parameters like standard Gibbs free energy of micellization (), standard enthalpy change (), and standard entropy change () were calculated using conductometry and surface parameters such as surface pressure at the interface (П_cac), maximum surface excess concentration (Г_max), minimum surface area per molecule (A_min), and pC₂₀ (adsorption efficiency) were calculated using the tensiometry technique. The aggregation number (N_agg) was calculated using fluorescence measurements. ¹H NMR spectra shed light on interactions between the salt and the cationic surfactant in 0.1 wt% IL. DLS gives information about the size distribution of micelles in solution at different concentrations of salt.     

The Effect of Methanol on the Micellar Properties of Dodecyltrimethylammonium Bromide (DTAB) in Aqueous Medium at Different Temperatures

The micellar properties of dodecyltrimethylammonium bromide (DTAB) in water and methanol water mixtures at different temperatures have been studied by conductivity and surface tension measurements. The critical micelle concentrations (CMC), degree of ionization (α), standard Gibbs free energy of micellization (), standard enthalpy of micellization (), standard entropy of micellization () and free energy of transfer () were evaluated from conductivity data. The CMC, maximum excess surface concentration ( ), area occupied per surfactant molecule ( ), surface pressure at the CMC ( ), packing parameter (P) and standard free energy interfacial adsorption ) were estimated from surface tension measurements. The CMC of DTAB was found to increase with increasing volume fraction of methanol and increasing temperature. Thermodynamic parameters and surface properties revealed that the addition of methanol changes the relevant physicochemical properties which affect the process of micellization.     

Effects of Molecular Structure and Temperature on Micellization of Cationic Ammonium Gemini Surfactants in Aqueous Solution

Micellization of four cationic quaternary ammonium gemini surfactants, having a diethyl ether or hexyl spacer with the alkyl chain lengths of 12 and 16 carbon atoms, was studied using isothermal titration microcalorimetry (ITC) and electrical conductivity measurements in the temperature range from 298.15 to 313.15 K. In this temperature range, where surfactants are normally applied, the temperature almost does not influence the critical micelle concentration (CMC) and the degree of micelle ionization (α) values of the gemini surfactants, and the replacement of a hexyl spacer by a diethyl ether spacer leads to a slight decrease in the CMC and α values. However, as the alkyl chain length increases from 12 to 16 carbon atoms, the CMC values significantly decrease from 0.99–1.19 mM to 0.020–0.057 mM. In particular, the enthalpy of micellization (ΔH_mic ) and the associated thermodynamic parameters show obvious changes with varying temperature and molecular structure. ΔH_mic becomes much more exothermic at higher temperature or for the surfactants with a more hydrophilic spacer. Moreover, the heat capacity change of micellization (ΔC _{P, mic} ) is less exothermic for the surfactants with a more hydrophilic spacer or a longer alkyl chain. The enthalpy–entropy compensation data show that the surfactants with longer alkyl chains have a more stable micellar structure.     

Influence of Some Hofmeister Anions on the Krafft Temperature and Micelle Formation of Cetylpyridinium Bromide in Aqueous Solution

In this work, the effect of some Hofmeister anions on the Krafft temperature (T_K) and micelle formation of cetylpyridinium bromide (CPB) have been studied. The results show that more chaotropic anions increase, while the less chaotropic ones lower the T_K of the surfactant. More chaotropic I^? and SCN^? form contact ion pairs with the cetylpyridinium ion and reduce the electrostatic repulsion between the CPB molecules. As a result, these ions show salting‐out behavior, with a consequent increase in the T_K. In contrast, less chaotropic Cl^? and NO₃^? increase the activity of free water molecules and enhance hydration of CPB molecules, showing a decrease in the T_K. A rather unusual behavior was observed in the case of SO₄^2? and F^?. These strong kosmotropes shift from their usual position in the Hofmeister series and behave like moderate chaotropes, lowering the T_K of the surfactant. Because of the high charge density and the strong tendency for hydration these ions preferentially remain in the bulk. Rather than forming contact ion pairs, these ions stay away from the CPB molecules, decreasing the T_K of the surfactant. In term of decreasing the T_K, the ions follow the order NO₃^? > SO₄^2? > Cl^? > F^? > Br^? > SCN^? > I^?. The critical micelle concentration (CMC) of the surfactant decreases significantly in the presence of these ions due to the screening of the micelle surface charge by the excess counterions. The decreasing trend of the CMC in the presence of the salts follows the order SCN^? > I^? > SO₄^2? > NO₃^? > Br^? > Cl^? > F^?.     

The Effect of NaCl on the Krafft Temperature and Related Behavior of Cetyltrimethylammonium Bromide in Aqueous Solution

This paper presents the effect of NaCl on the Krafft temperature (T _K), surface adsorption and bulk micellization of cetyltrimethylammonium bromide (CTAB) in aqueous solution. The critical micelle concentration (CMC) of CTAB in the presence of NaCl increased and then decreased with increasing temperature. Thus, the CMC–temperature data can be represented by a bell-shaped curve. The micellar dissociation (fraction of counterion binding) and energetic parameters (free energy, enthalpy and entropy changes) of both adsorption and micellization were calculated. The processes were found to be both enthalpy and entropy controlled and appeared to be more and more enthalpy driven with increasing temperature. An enthalpy–entropy compensation rule was observed for both adsorption and micelle formation. The T _K of the surfactant decreased significantly in the presence of NaCl, which is a sharp contrast to the usual behavior of the effect of electrolytes on the T _K of classical ionic surfactants. The surface excess concentrations decreased with increasing temperature. However, the values were much higher in the presence of NaCl compared to the corresponding values in pure water. The solubilization behavior of a water-insoluble dye, Sudan red B (SRB), in the micellar system was studied by the UV–visible spectrophotometric technique. The molar solubilization ratio in the presence of NaCl was found to be about three times higher than that in pure water, indicating that the solubilization of SRB in the CTAB micelles significantly increases in the presence of NaCl.     

Influence of Additives and Temperature on the Interaction of Acid Red 151 Dye with Cetyltrimethylammonium Bromide: A Conductometric Study

The interaction of an anionic textile dye, acid red 151 (AR), with a cationic surfactant, cetyltrimethylammonium bromide (CTAB), in aqueous electrolyte medium (e.g., KCl, NaCl) and in H₂O + ethanol medium was observed using the conductometric method. Two critical micelle concentrations (CMC) were found for the AR + CTAB system in water and H₂O + ethanol medium, but only one CMC was detected for AR + CTAB in salt+H₂O media and for pure CTAB in all solutions. The change in CMC behavior of CTAB in the presence of AR indicates the occurrence of strong interaction between AR and CTAB. The extent of solubility increases with an increase of temperature, which disfavors micellization. The CMC values in NaCl solution are comparatively lower than those found in KCl solution, which signifies that the micelle formation is more favorable in attendance of NaCl. In aqueous ethanol solution, two CMC values were also observed for AR + CTAB that are higher than those obtained in water. The free energy of micellization () was negative, which illustrates a thermodynamically spontaneous micellization process. The values of enthalpy () and entropy () of micellization show that the process was entirely entropically driven at a lower temperature; but, enthalpic events are favored at elevated temperature in electrolyte medium, whereas both enthalpy and entropy are reduced in attendance of ethanol. In aqueous medium, the thermodynamic parameters signify the presence of electrostatic interaction between AR and CTAB at higher temperatures, while the hydrophobic interaction is the main driving force at a lower temperature. A linear expression of as a function of demonstrates enthalpy-entropy compensation over the experimental conditions employed in this study.     

添加剂对罗丹明B和吖啶黄在SDS溶液中能量转移的影响

罗丹明B(RB)和吖啶黄(AY)在十二烷基硫酸钠(SDS)水溶液中浓度小于临界胶团浓度时,就能发生有效的能量转移,能够反映出SDS形成预胶团的聚集状况。非离子表面活性剂Tween 60,使两种染料分子之间的能量转移受到抑制,分析表明,加入Tween 60后聚集体变小,由于Tween 60的极性头基较大,所以其预胶团结构较紧密,不利于能量转移的发生。在溶液中加入无机盐NaCl和Na2SO4后,虽然聚集体变小,但体系中染料分子仍可以发生有效的能量转移,表明体系中预胶团内部结构较疏松,而且盐的浓度越高,能量转移效率越低,加入无机盐种类不同,能量转移效率也不同,说明无机盐的种类对聚集体的形态有一定影响。     

Counter-ion Effect on Micellization of Ionic Surfactants: A Comprehensive Understanding with Two Representatives, Sodium Dodecyl Sulfate (SDS) and Dodecyltrimethylammonium Bromide (DTAB)

Various micelle parameters viz., critical micelle concentration (CMC), counter-ion binding (β), aggregation number (N), hydrodynamic radius (R _h), micelle zeta potential (ζ) and energetic parameters, free energy of micellization ( $ \Updelta G_{\text{m}}^{0} $ ), enthalpy of micellization ( $ \Updelta H_{\text{m}}^{0} $ ) and entropy of micelle formation ( $ \Updelta S_{\text{m}}^{0} $ ) were determined for sodium dodecylsulfate, and dodecyltrimethylammonium bromide in the presence of NaCl for the former and NaBr for the latter. Conductometry and calorimetry methods were used for the measurements of CMC and energetic parameters. The fluorimetric (static quenching) method was employed to determine N and dynamic light scattering to estimate R _h and ζ. The conductometrically determined β was verified from the CMC values by calorimetry using the Corrin–Harkins equation. The results found for the two surfactants of identical tails but different head groups have been presented and discussed. A detailed report on the salt effect using salts containing counter-ions the same as those in the surfactant is found only limitedly in the literature.     

Volumetric, Compressibility, and Surface Tension Studies on Micellization Behavior of SDS in Aqueous Medium: Effect of Sugars

The densities , velocities of sound , and surface tension , of anionic surfactant sodium dodecyl sulfate in presence of aqueous saccharides (fructose and maltose) with concentrations 0.01 and 0.10 mol kg^?1 have been reported over a wide temperature range (293.15–313.15 K) at an interval of 5 K. The apparent molar volume , isentropic compressibility , and apparent molar adiabatic compression values have been calculated using densities and velocities of sound data. Both, and vary non‐linearly at lower concentration of surfactant and tend to achieve linearity at higher concentration of surfactant in presence of saccharides. From the surface tension data, parameters like surface excess , minimum area occupied by the surfactant molecule at the saturated air/solution interface and surface film pressure have been computed. The effect of additives on these parameters has been discussed in terms of different types of the interactions pertaining in the micellar system. An attempt has also been made to draw an inference regarding the effect of these additives on the critical micelle concentration of the surfactant.     

Effect of Temperature on Probe Tack Adhesion: Extension of the Dahlquist Criterion of Tack

At a molecular level adhesive joint strength of pressure-sensitive adhesives (PSAs) is governed by the ratio between two generally conflicting factors: high energy of cohesive molecular interactions and large free volume. Increase in temperature leads to domination of the free volume contribution over the cohesive strength, affecting mechanisms of the debonding process, examined with a probe tack test. Linear viscoelastic properties and probe tack adhesion of five types of PSAs have been studied: polyisobutylene (PIB); acrylic, styrene-isoprene-styrene (SIS) triblock copolymer; hydrogen-bonded complex of high molecular weight poly(N-vinyl pyrrolidone), PVP; with oligomeric poly(ethylene glycol), PEG; and plasticized polybase—polyacid polyelectrolyte complex (PEC). The transition from solid-like mechanism of debonding to ductile type of adhesive bond failure with fibrillation of adhesive layer has been established to occur for all examined PSAs under temperature increase within the range from ?20 to 80°C. The Dahlquist criterion of tack, which defines the value of the storage modulus, G′, below 0.1 MPa, featured for all the PSAs demonstrating maximum work of debonding, has been found to have a universal character and holds at corresponding temperatures for all the PSAs examined, including both typical and innovative adhesives. In addition to this adhesion predictor we have also established that for all the PSAs the transition from a solid–like debonding mechanism to a ductile type of debonding is observed in the range of G′ = 0.09–0.34 MPa. The value of the dissipation factor, tan δ, is also included in the analysis of correlation between linear viscoelasticity and probe tack behavior.     

Effect of Benzheterazoles on the Micellar Behavior of Sodium Dodecylsulfate in Dimethylsulfoxide: A Conductometric and Spectroscopic Approach

In this article, we report intermolecular interactions in terms of the effect of benzfused heterocyclic compounds, i.e., 2-thioureidobenzimidazole and 2-thioureidobenzoxazole (0.00, 0.01, and 0.05 mol kg⁻¹), on the micellization behavior of sodium dodecylsulphate (SDS) (1–52 mmol kg⁻¹) in dimethylsulphoxide (DMSO) at different temperatures (293.15–313.15 K) through conductometric and spectroscopic investigations. The variation of specific conductance with SDS concentration has been utilized to estimate the critical micelle concentration ( CMC). The above-performed techniques infer that the presence of additives results in a decrease in the CMC values. Various standard thermodynamic parameters such as free energy change (), enthalpy change (), and entropy change () of micellization have been determined using the temperature dependence of CMC. The above calculated parameters and also UV–visible and fluorescence spectroscopy have been used to obtain information regarding the various interactions between the compounds and surfactant aggregates. In addition, an attempt has also been made to examine the minimum inhibitory concentration (MIC) of the heterocompounds, which indicates the effectiveness of these compounds against fungus growth at a particular concentration. These synthetic heterocyclic compounds find increasing applications in material science, medicinal chemistry, and biochemistry due to their antifungal and antioxidant properties.     

A Comparative Study on the Aggregation and Thermodynamic Properties of Anionic Sodium Dodecylsulphate and Cationic Cetyltrimethylammonium Bromide in Aqueous Medium: Effect of the Co-solvent N-Methylacetamide

The effect of co‐solvent N‐methylacetamide (NMA) (0.035, 0.046, 0.127, and 0.258 mol kg^?1) on the micellization behaviour of anionic surfactant sodium dodecylsulphate (SDS) (3.21–10.35 mmol kg^?1) and cationic surfactant cetyltrimethylammonium bromide (CTAB) (0.19–3.72 mmol kg^?1) in aqueous solution was explored by employing conductivity measurements at different temperatures (298.15–313.15 K). The critical micelle concentration (CMC) values for SDS and CTAB in aqueous solutions of NMA were determined from the conductivity versus surfactant concentration plots. The variations in the CMC values of SDS with NMA concentration are in striking contrast to those observed in the case of CTAB. The various relevant thermodynamic parameters of micellization, viz. standard enthalpy change, ΔH_m^o, standard entropy change, ΔS_m^o, and standard Gibbs free energy change, ΔG_m^o, were determined using the temperature variation of the CMC values and counterion binding. The results not only relate these thermodynamic parameters to the consequences of intermolecular interactions but are also able to differentiate between SDS–water–NMA and CTAB–water–NMA systems in terms of contributions from head groups as well as alkyl chains of surfactants.     

Effect of Acceptor (Mg) Concentration on the Resistance Degradation Behavior in Acceptor (Mg)-Doped BaTiO3 Bulk Ceramics: I. Impedance Analysis

Degradation behavior of the electrical resistance of acceptor (Mg)-doped BaTiO₃ ceramics was contrasted against different acceptor concentrations. Coarse-grained specimens with uniform grain sizes and different acceptor concentrations were prepared by sintering both in air and a reducing atmosphere. The specimens sintered under both atmospheres showed similar trends in the degradation behavior with a critical dependence on the acceptor concentration. The time to degradation decreased systematically with the increase of acceptor concentration. An impedance spectroscopy study was conducted on these samples at various temperatures. An equivalent circuit analysis of these data was considered, from which bulk and grain-boundary conductivity was determined for each composition as a function of grain size. Attempts were made also to determine the ionic conductivity for the different samples as a function of temperature and doping concentration.     

On the Effect of pH,Temperature, and Surfactant Structure on Bovine Serum Albumin–Cationic/Anionic/Nonionic Surfactants Interactions in Cacodylate Buffer–Fluorescence Quenching Studies Supported by UV Spectrophotometry and CD Spectroscopy

Due to the fact that surfactant molecules are known to alter the structure (and consequently the function) of a protein, protein–surfactant interactions are very important in the biological, pharmaceutical, and cosmetic industries. Although there are numerous studies on the interactions of albumins with surfactants, the investigations are often performed at fixed environmental conditions and limited to separate surface-active agents and consequently do not present an appropriate comparison between their different types and structures. In the present paper, the interactions between selected cationic, anionic, and nonionic surfactants, namely hexadecylpyridinium chloride (CPC), hexadecyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), polyethylene glycol sorbitan monolaurate, monopalmitate, and monooleate (TWEEN 20, TWEEN 40, and TWEEN 80, respectively) with bovine serum albumin (BSA) were studied qualitatively and quantitatively in an aqueous solution (10 mM cacodylate buffer; pH 5.0 and 7.0) by steady-state fluorescence spectroscopy supported by UV spectrophotometry and CD spectroscopy. Since in the case of all studied systems, the fluorescence intensity of BSA decreased regularly and significantly under the action of the surfactants added, the fluorescence quenching mechanism was analyzed thoroughly with the use of the Stern–Volmer equation (and its modification) and attributed to the formation of BSA–surfactant complexes. The binding efficiency and mode of interactions were evaluated among others by the determination, comparison, and discussion of the values of binding (association) constants of the newly formed complexes and the corresponding thermodynamic parameters (ΔG, ΔH, ΔS). Furthermore, the influence of the structure of the chosen surfactants (charge of hydrophilic head and length of hydrophobic chain) as well as different environmental conditions (pH, temperature) on the binding mode and the strength of the interaction has been investigated and elucidated.     

Effect of Acceptor (Mg) Concentration on the Resistance Degradation Behavior in Acceptor (Mg)-Doped BaTiO3 Bulk Ceramics: II. Thermally Stimulated Depolarization Current Analysis

Thermally stimulated depolarization current (TSDC) of acceptor (Mg)-doped BaTiO₃ ceramics was analyzed with different acceptor concentrations for coarse-grained specimens with uniform grain sizes. In all specimens, the increase of the polarization temperature ( T _P) for a fixed condition of polarization field ( E _P) and polarization time ( t _P) increased TSDC peak associated with an oxygen vacancy ( V _O^••) relaxation. When the acceptor concentration is increased, both T _P to generate same magnitude of TSDC and the relaxation temperature ( T _m) of the TSDC peak systematically decreased. On the other hand, the activation energy of the oxygen vacancy relaxation showed roughly constant values of ∼0.9 eV, irrespective of acceptor concentration. Such behavior can be explained by a decrease in the relaxation time constant (τ₀), which is in turn associated with the shape of oxygen vacancy profile in the specimen after polarization. The decrease of T _P, T _m, τ₀, and the little change of activation energy from the TSDC data with the increase of acceptor concentration implies an increase in the oxygen vacancy concentration C ( V _O^••). The experimentally observed behavior of C ( V _O^••) vs acceptor concentration could be explained by the defect chemical model, and from these results, the acceptor ionization energy E _A was estimated to be about 1.0 eV.