CTAB Micelles Research Articles

Influence of supramolecular self-assembly of oppositely charged Co- and Sn-porphyrins on the their spectral-luminescent properties in aqueous and aqueous micellar media of ionic surfactants

The processes of supramolecular self-assembly of Co(III)-meso-tetra-(4-trimethylammoniophenyl)porphyrin (CoP) and bis-(4-(1-imidazolyl)-phenol)-Sn(IV)-meso-tetra(4-sulfophenyl)porphyrin (SnP) were studied using electronic, steady-state and time-resolved fluorescence, one- and two-dimensional NMR spectroscopy in aqueous media. The main product of such interaction at a 2:1 M ratio of Co and Sn porphyrinates was found to be supramolecular porphyrin trimer CoP–SnP–CoP formed due to donor-acceptor, hydrogen and electrostatic interactions. The distinctive features of the resulting trimer are: significant distortion of the spatial structure of the Co-porphyrin fragments and strong quenching of the Sn-porphyrin macrocycles fluorescence (by 70 %). The distortion of the spatial structure of Co porphyrinates is in good agreement with the quantum chemical calculations as well as with the electronic and NMR spectroscopy data. Adding surfactants – both anionic (Cetyltrimethylammonium bromide - CTAB) and cationic (Sodium dodecyl sulfate - SDS) – even at concentrations below the critical micelle concentration (CMC) leads to the supramolecular trimer destruction. In solutions of ionic surfactants, supramolecular trimer destruction is caused by the interaction of either the peripheral macrocycles of the trimer (CoP) with SDS micelles (premicellar aggregates) or the central macrocycle (SnP) with CTAB micelles (premicellar aggregates). This process is prolonged and the rate of trimer destruction depends on the surfactant concentration. The sizes of the CTAB and SDS micelles solubilized with porphyrin molecules were established by dynamic light scattering. In general, surfactant additions lead to an increase in the SnP fluorescence at least due to the destruction of the supramolecular self-assembly, as well as due to the changes in the state of its microenvironment.

Effects of synthesis conditions on particle size and pore size of spherical mesoporous silica

The particle size and pore size of spherical mesoporous silica materials play significant roles in their application. However, relatively limited systematic research has been conducted on how preparation conditions influence these properties. In particular, the effects of some important factors have not been adequately studied, including reaction time, reaction temperature, and organic solvent type. In this work, octane and water were used as solvents, and tetraethyl orthosilicate was used as the silicon source to systematically study the effects of reaction time, reaction temperature, different organic solvents, octane/water mass ratio, styrene template concentration, and surfactant (cetyltrimethylammonium bromide, CTAB)/H2O mass ratio on the particle morphology, particle size, and pore size of silica. The results suggest that the above-mentioned neglected factors exert a substantial influence on both particle size and pore size. In the experimental temperature range, the pore diameter decreases and the particle size increases with increasing temperature. The maximum particle size and pore size are achieved after a reaction time of 3 h, and a further increase in reaction time leads to a smaller particle size and pore size. As the number of carbon atoms in the organic solvent decreases, the pore size also gradually increases. Styrene and organic solvents that dissolve in CTAB micelles are crucial factors in pore formation, while the aggregation of the swollen CTAB micelles influences the particle size. The changes in the pore structure stability and hydroxyl density of the synthesized samples in water were also studied. After undergoing water treatment at temperatures ranging from 20 to 60 °C for 72 h, both the pore structure and morphology remain relatively unchanged. When the temperature increases, the surface hydroxyl density exhibits a more pronounced increase in the presence of water. After water treatment for 5 h, the surface hydroxyl density reaches saturation.

Filling two needs with one deed: Differential sensing of anthrax biomarker dipicolinic acid and bovine serum albumin using binary ensemble based on 1,8-naphthalimide Schiff base and cationic surfactant

Keeping in mind the severities of anthrax disease caused by bacteria Bacillus anthracis and side effects of abnormal levels of a nonmetalloprotein bovine serum albumin (BSA), their early diagnosis was highly required. The existing lanthanide based sensors for their detection are not up to the mark due to their potential disadvantages of genetic toxicity, bio-migration, supply shortages, low atom utilization and poor stability. To address these issues, a binary ensemble OHNP@CTAB was fabricated in aqueous medium by encapsulation of 1,8-naphthalimide derived Schiff base (OHNP) in the micelles of a cationic surfactant CTAB. Significant changes were observed in the absorption and emission spectrum of OHNP@CTAB in the presence of DPA and BSA mainly due to electrostatic interaction among positively charged receptor and negatively charged guest species. Limit of detection (LOD) values of OHNP@CTAB towards DPA and BSA were calculated to be 1.19 and 0.11 µM, respectively from fluorescence spectral titration data. Moreover, the binary ensemble OHNP@CTAB efficiently detected BSA and DPA in real samples viz. packaged milk, gulkand and candy.

Behavior of Curcumin in micellar biomimetic systems and its protolytic and tautomeric equilibria elucidated by multivariate analysis

Curcumin (CUR), a natural compound originating from Asia, has found widespread application in the field of biomedicine. CUR shows significant results in its applications, despite its high hydrophobicity and low bioavailability. In general, success depends mainly on the interaction between CUR and the target cell, microbial membrane, cell wall, or protein capsule. Associated with this, solid tumors, gastric or stomach regions, as well as regions affected by wounds, have very different pH conditions. In this scenario, micellar biomimetic systems obtained from cationic (CTAB), anionic (SDS), zwitterionic (HPS), and non-ionic (TX-100) surfactants emerge as an interesting alternative within this type of investigation. Thus, in the present study, the interaction of CUR with CTAB, SDS, HPS, and TX-100 micelles was evaluated first under physiological conditions (pH 7.4). The results showed that CUR interacts very well with the most distinct environments, as demonstrated by experimental and computational analysis. The binding constant, Kb, was higher for TX-100 micelles and lower for SDS in the presence or absence of the ionic strength control, appointing the influence of hydrophobic and electrostatic effects. The spectral properties show the efficient incorporation of CUR in micelles, also confirmed by in-silico assays. Multivariate analysis based on Q-Imbrie's factor and the K-matrix method on the electronic absorption spectroscopy data in different pHs ranging from 0 to 14 allowed for the understanding of the complex protolytic/tautomeric equilibrium, and the influence of the microenvironment on the CUR at each pH. Thus, the CUR tends to prevail in the photolytic form of better interaction, a chemically explained fact here called the “chameleon effect”. So, in SDS the pKa values tend to increase to favor the interaction between CUR0 and SDS-. On the other hand, in CTAB the pKa values tend to decrease to favor the interaction between CUR-1/CUR-2 and CTA+. The multivariate analysis also allowed the pure spectra separation and the molar absorptivity determination of each species. These interactions were also confirmed by the estimated electrical potential ψo from ΔpKa-el determined using the Boltzmann equation.

Interaction of anti-inflammatory drug nimesulide with ionic and non-ionic surfactant micelles: Insights from spectral and bioinformatics approach

The present work reports the interaction of anti-inflammatory drug nimesulide with cationic (CTAB, HDPC), anionic (SDS) and non-ionic (Triton X-100) surfactant micelles. The drug-micelles systems were studied by UV–Vis absorption spectroscopy to estimate the binding constant (Kb), partition coefficient (Kx) and the free energy of binding and partition (ΔGb, ΔGx). The values of Kb indicate a stronger interaction between nimesulide and cationic micelles due to cumulative electrostatic and hydrophobic forces. Also, the higher values of Kx obtained for HDPC and CTAB micelles point out a higher drug concentration in cationic micelles than in the surrounding aqueous medium, as against SDS and Triton X-100 micelles. The bioinformatic methods were used to evaluate the pharmacokinetic, pharmacogenomic and pharmacodynamic profiles of the nimesulide, CTAB, HDPC, SDS, and Triton X-100. Our results showed that all compounds exhibit good intestinal absorption, good BBB and CNS permeabilities, and low toxicity features. Also, the ecotoxicity of compounds was quantified. Various pharmacogenomic features of compounds were recorded. Supplementary, we conducted an extensive analysis based on various aspects of the structural and functional features of compounds, such as their electronic (dipole moment, frontiers orbital energies), steric, and hydrophobic features. Experimental and theoretical results show that CATB and HDPC cationic micelles may be better drug delivery agents for nimesulide.

Design and spectral-luminescent properties of a triad consisting of two BODIPY chromophores axially bound to a Sn(IV)-porphyrin in aqueous and aqueous micellar media

In this work, we designed and studied the emissive properties of a triad consisting of two BODIPY chromophores axially bound to a Sn(IV)-porphyrin via a methylphenolate bridge in aqueous and aqueous micellar media. It has been shown that the fluorescent properties of the porphyrin fragment of the triad, due to photoinduced energy transfer from the axial fragments to the macrocycle, are most sensitive to small changes in viscosity in the range from 3 to 6 cP, which corresponds to the viscosity of the blood of a healthy person (4–6 cP). The localization of the triad in the spherical CTAB micelles increases its emission in aqueous media. The structure–property dependencies established in the study can be applied to design molecular devices for sensing local viscosity of aqueous and aqueous micellar media, which could be of great interest for non-contact detection of physical properties of intracellular or lymphatic fluids.

Opto-microfluidic assisted synthesis of photo-protoporphyrin (pPP) conjugated to hollow gold-albumin hybrid nanoshells to enhance the efficiency of photodynamic therapy of triple negative breast cancer cells

IntroductionProtoporphyrin-IX (PpIX), a photosensitizer used in photodynamic therapy, has limitations due to its hydrophobicity, rapid photobleaching, and low absorption peak in the red region. These limitations make the use of PpIX less effective for photodynamic therapy treatments. In this study, we harnessed the power of microfluidic technology to manipulate the properties of PpIX and quickly synthesize albumin-based hybrid nanoshells with high reproducibility. Methods and materialTo begin with, we designed a microfluidic chip with SolidWorksⓇ software; then the chip was fabricated in Poly(methyl methacrylate) (PMMA) material using micromilling and thermal bonding. We synthesized PpIX-loaded CTAB micelles and subsequently transformed the PpIX structure into photo-protoporphyrin (PPP,) by opto-microfluidic chip (Integrating a microfluidic chip with a light source). Simultaneously with CTAB-PPP synthesis complex, we trapped it in binding sites of bovine serum albumin (BSA). Afterward, we used the same method (without irradiating) to generate a hybrid nanostructure consisting of hollow gold nanoshells (HGN) and BSACTAB-PPP. Then, after physical characterization of nanostructures, the photodynamic effects of the agents (HGNs, CTAB-PpIX, BSA-CTABPpIX, HGN-BSA-CTAB-PpIX, CTAB-PPP, BSA-CTAB-PPP, and HGNs-BSA-CTAB-PPP) were evaluated on MDA-MB-231 and 4T1 cells and the cytotoxic properties of the therapeutic agents after treatment for 24, 48, and 72 hours were investigated using MTT assay. Finally, we analyzed the findings using GraphPad Prism 9.0 software. ResultsResults revealed that the opto-microfluidic assisted synthesis of HGN-BSA-CTAB-PPP is highly efficient and reproducible, with a size of 120 nm, a zeta potential of -16 mV, and a PDI index of 0.357. Furthermore, the cell survival analysis demonstrated that the HGNBSA-CTAB-PPP hybrid nanostructure can significantly reduce the survival of MDA-MB-231 and 4T1 cancer cells at low radiation doses (< 10 J/cm2) when exposed to an incoherent light source due to its strong absorption peak at a wavelength of 670 nm. ConclusionThis research indicates that developing albumin-based multidrug hybrid nanostructures using microfluidic technology could be a promising approach to design more efficient photodynamic therapy studies.

Spectroelectrochemical Studies of CTAB Adsorbed on Gold Surfaces in Perchloric Acid.

The behaviour of CTAB adsorbed on polycrystalline gold electrodes has been studied using a combination of spectroelectrochemical methods. The results indicate that the formation of the layer is the consequence of the precipitation of the CTAB micelles on the electrode surface as bromide ions, which stabilize the micelles, are replaced by perchlorate anions. This process leads to the formation of CTA+ layers in which perchlorate ions are intercalated, in which the adlayer suffers a continuous rearrangement that leads to the formation of micro-dominions of different types of hydrogen-bonded water populations throughout the adlayer. After prolonged cycling, a stable situation is reached. Under these conditions, water molecules permeate through the adlayer toward the electrode surface at potentials positive of the potential of zero charge, due to the repulsion between the CTA+ layer and the positive charge of the electrode.

Dynamics of CTAB micelle mediated reaction of fuchsin degradation in alkaline medium

Abstract Cetyltrimethylammonium bromide (CTAB) micelles catalyzed the degradation of fuchsin in the entire surfactant concentration range investigated. The pseudo first order rate constants increased with CTAB concentrations. However, there was a decrease in the rate constant at higher concentrations of CTAB. Increase in the rate constant was attributed to the incorporation of fuchsin and hydroxide ion in the stern layer of the CTAB micelles. The kinetics involved the removal of the π-conjugation in fuchsin due to its attack by hydroxide ion on the central C atom of the planar ring which led to the formation of carbinol. The reaction showed first order each to fuchsin and OH-. Menger-Portnoy and Piszkiewicz cooperative models were used to explain the micellar and kinetic effects.

Room temperature luminescence and ferromagnetism from transition metal ions: Mn-, Co- and Ni-doped ZnS nanoparticles

ZnS nanoparticles (NPs) and transition metal ions (TMIs) doped ZnS NPs were synthesized by the chemical precipitation method facile via aqueous CTAB micelles. The structural properties, crystallography, morphology, composition analysis, photoluminescence (PL), and magnetic properties of samples were characterized by Fourier transform infrared spectrum (FTIR), X-ray diffraction (XRD) analysis, Field emission scanning electron microscope (FESEM), Energy dispersive X-ray (EDX) spectroscopy, Fluorescence spectroscopy, and Vibrating sample magnetometer (VSM). All the synthesized NPs exhibited a cubic zinc-blende single-phase crystal structure with crystallite size in 2–8 nm range, which indicates the TMIs ions substituted the lattice site of Zn2+ ions, due to almost similar ionic radii of Zn2+ and TMIs (Mn2+, Co2+, and Ni2+), i.e., 0.074, 0.083, 0.069, and 0.065 nm, respectively. PL peak intensity enhanced with TMIs doping causes an excited state to the ZnS NPs, resulting in PL spectra turning into the visible region. ZnS NPs show mixed dominant diamagnetic and weak ferromagnetic behavior. TMIs ions doped ZnS NPs show the well-defined ferromagnetic behavior at room temperature (RT).

Investigating Growth of Gold Nanorods by Simultaneous Small‐Angle X‐Ray and Neutron Scattering (Part. Part. Syst. Charact. 3/2022)

In article number 2100172, Unruh and co-workers study the scattering signal of organic cetrimonium bromide (CTAB) structures and inorganic gold nanorods, which are measured and correlated directly by simultaneously impinging the same sample volume with X-rays and neutrons. This way, the structure of the organic CTAB micelles and gold nanoparticle stabilization layer can be correlated directly with the size and polydispersity evolution of growing gold nanorods.

Investigating Growth of Gold Nanorods by Simultaneous Small‐Angle X‐Ray and Neutron Scattering

Increased usage of gold nanorods (AuNRs) in various biosensing and medical applications requires tight size and morphology control. This is often achieved by tuning the aggregation behavior of the stabilizing ligand cetrimonium bromide (CTAB). Because the role of CTAB during AuNR growth is still a matter of debate, simultaneous small‐angle X‐ray and neutron scattering experiments (SAXS/SANS) and measurements are performed. The SAXS/SANS measurements have enabled an instantaneous correlation between the size of evolving AuNR and the nanostructure of guiding CTAB moieties. Upon modifying the aggregation behavior of CTAB micelles by adding hexanol or pentanol as inert additives in the precursor solution, a marked change in reaction kinetics is observed. Alcohol‐modified CTAB nanostructures have improved AuNR size uniformity compared to those prepared in alcohol‐free CTAB solutions, which are attributed to different growth modes. The change in reaction kinetics is linked to a changed stabilization mechanism of reactants and nascent AuNR facilitated by CTAB micelles.

Modulating the thermodynamics, kinetics and photochemistry of 7-diethylamino-4'-dimethylaminoflavylium in water/ethanol, SDS and CTAB micelles.

The thermodynamics and kinetics of compound 7-diethylamino-4'-dimethylaminoflavylium were studied in water : ethanol (1 : 1) and water in the presence of SDS and CTAB micelles. The blue flavylium cation is in equilibrium with the pink protonated flavylium cation defined by pKAH2+/AH+ and the yellow trans-chalcone, defined by pKAH+/Ct. The difference between these two pKs gives the pH domain of the flavylium cation, ΔpK = 1.95 in CTAB, ΔpK = 5.6 in water/ethanol (1 : 1) and ΔpK = 8.5 in SDS micelles. On the other hand, the pH domain of the trans-chalcone is limited by pKAH+/Ct and pKCt/Ct-. It is lower in SDS micelles ΔpK = 2.7, increases in ethanol/water (1 : 1) ΔpK = 5.1 and is maximum in CTAB micelles, ΔpK = 6.8. All these effects can be explained by the electric charge present at the micellar surface. Relative energy level diagrams that allow for the explanation of the driving forces for any pH stimuli or light absorption were constructed from the calculated equilibrium constants. Irradiation of the trans-chalcone at 466 nm leads to the formation of the flavylium cation. In water : ethanol (1 : 1), the photochemistry is residual with Φ < 0.00002, while in SDS micelles at pH = 7 light increases the rate of the spontaneous conversion of trans-chalcone to the flavylium cation, with quantum yield Φ = 0.002; photochromism from trans-chalcone to give the flavylium cation with the same quantum yield is also observed in CTAB micelles.

Unfolding of Tryptophanoctyl Ester and Elastic Deformation of Host Micelles via RR'3 N+ ⋅⋅⋅π Interaction: Conceivable Relevance to Wrapping Process of Receptor Mediated Endocytosis.

The interfacial properties of the mixed amphiphiles are modified by a stronger cation-π interaction between the quaternary ammonium head group of CTAB and the π-face of TROE, compared to the tyrosine analogue (TYOE). This eventually triggers a morphology transition through elastic deformation of the spherical micelles of CTAB to cylindrical/wormlike micelles. The unfolding of TROE and the molecular interactions in the nanoenvironment have been recognized by NMR spectroscopy and the physical characteristics of the entangled wormlike micelles are investigated by high resolution transmission electron microscopy (HRTEM), whereas the complex fluidic feature is examined by dynamic rheological measurements. Morphology tuning of the soft nanoaggregates of zwitterionic dodecylphosphocholine by the tryptophan analogue via choline-π interaction has unique biological consequences and we consider the significance of such interactions in facilitating endocytosis of a virion/nano particle(NP) in terms of a quantitative model. The implication in future research on drug development strategies is discussed.

Dissociation of the DCF-Hb complex in presence of cationic micelles: A spectroscopic and computational approach

Diclofenac sodium (DCF) is a derivative of phenyl acetic acid and a model representative of the family of non-steroidal anti-inflammatory drugs (NSAIDs). It is extensively consumed for treating inflammation and degenerative disorders like rheumatoid arthritis. The micelles or aggregates of surfactants have ability to solubilize poorly soluble drugs thereby increasing bioavailability of the drugs. Thus, in the current study we have shown a systematic approach for the association of diclofenac with haemoglobin and deintercalation of DCF from hemoglobin (Hb) by hexadecyltrimethylammonium bromide (CTAB) micelles by using various spectroscopic techniques. The fluorescence and UV–visible spectral results revealed that DCF interacts with CTAB micelles and resides in its hydrophobic core. Thus, steady fluorescence and UV–visible measurements provides a strong sign for the relocation of DCF molecules from the hemoglobin interior to the micellar interface of CTAB above cmc. The CD results hinted that CTAB micelles do not disturb the structure of hemoglobin, which further supported that CTAB micelles can be applied as a reliable delivery vehicle for DCF. The present study may be significant for the discovery of improved micelle-based vehicles to the delivery of non-steroidal anti-inflammatory drugs in their targeted site.

Investigation of aggregation behavior of ionic surfactant mixture in crystal violet dye solution at different temperatures and solvent compositions: Conductivity and theoretical approach

The conductometric measurement technique was utilized to have an in-depth knowledge on the aggregation behavior of a mixture of two ionic surfactants – sodium dodecyl sulfate (SDS; a common anionic surfactant) and cetyltrimethylammonium bromide (CTAB; a cationic surfactant), in crystal violet (CV) and CV + ethanol (5 and 10% (w/w)) solution media. The related micellar and thermodynamic parameters of the mixed system have been assessed and presented in this paper. The cmc values of pure SDS/CTAB, & their mixture in presence of CV dye, were observed to decrease and thus the insertion of CV favors the micellization of pure and mixed micelle. Also, the cmc values of the mixture of SDS & CTAB undergo a drop with increasing the concentration of CTAB at a specific temperature and these cmc fall in the middle of the detected cmc of SDS & CTAB micelles in all the media studied. The observed values of cmc are lower in magnitude in comparison to the ideal cmc and the numerical values of the interaction parameter (β) are negative, which manifests the existence of attractive interaction between SDS and CTAB surfactants in presence of CV dye. The cmc values are also dependent on the fluctuation of experimental temperature. The micellar mole fraction of component 1 (CTAB) in SDS + CTAB mixture (X1Rub) and the ideal micellar mole fraction (X1id) was obtained to be relatively greater than the related stoichiometric mole fraction (α1) of component 1 (CTAB). The activity coefficients (f1Rub and f2Rub) remained below unity in all test cases, suggesting an attractive interaction in the mixed micellar system. The obtained thermodynamic parameters demonstrate that the single and mixed micellization phenomena are spontaneous and the main driving forces are hydrophobic and exothermic in nature.

Interface and doping in carbon dots influence charge transfer and transport

Nanoscale carbon-based materials have the potential for large-scale optoelectronic and biomedical applications due to their tunable photo-physics. Here, we explore the impact of doping and the role of intervening media on both electron transfer and transport from carbon dots (CD) to an acceptor menadione (MD). In a binary mixture compared to undoped-CD (UCD), the amine-based nitrogen-doped-CD (ACD) reflects significant changes in its photo-physics like excitation-independent fluorescence, enhanced lifetime, along with a distinct drop in electron transfer rate (kET) to MD. With micro-emulsion, kET from UCD to MD is enhanced while a substantial reduction is observed for ACDs, emphasizing the critical role of doping, surface states, encapsulation, and interfaces of CTAB micelles. The impact of doping and Coulombic interaction at interfaces on the charge transport phenomena with redox-active MD is further investigated by current-sensing atomic force microscopy. For similar bias-voltage, ACD reflects a higher conductance than UCD, and the conductance is enhanced in the presence of CTAB micelles. Moreover, at a low voltage regime, the current-voltage curve shows a linear growth, while at higher voltage, Fowler-Nordheim (F–N) tunneling is observed. The presence of MD, however, leads to an abrupt rise in conductivity resulting in a transition from F–N to direct tunneling.

Solubilization of azo dyes by cetyltrimethylammonium bromide micelles as structure control factor at synthesis of ordered mesoporous silicas

Solubilization of anionic azo dyes, methyl red and alizarin yellow, in micelles of cationic surfactant, cetyltrimethylammonium bromide, was studied in aqueous solutions with pH ~ 10 by conductometry and UV–Vis spectroscopy. The electro-conductivity measurements were used to evaluate influence of azo dyes on critical micelle concentration of cetyltrimethylammonium bromide and estimate standard thermodynamic parameters of micellization process. It was found that solubilization of azo dyes by micelles of surfactant is spontaneous process which causes lowering of critical micelle concentration of long-chain quaternary ammonium salt. The phenomenon of azo dyes solubilization by surfactant micelles was confirmed by analysis of the effect of different concentrations of cetyltrimethylammonium bromide on the UV-Vis spectra of azo dyes solutions. Differential spectroscopic technique was employed to obtain quantitative characteristics of azo dyes solubilization in micellar media. The values of binding constant, partition coefficient, and free energy change of partition for azo dyes were calculated. Obtained results proved that methyl red and alizarin yellow incorporate into the CTAB micelle in such a way that their carboxylic groups are lying near by positively charged head group of surfactant and the rest of the molecule is oriented towards center of micelle. Micelles of cetyltrimethylammonium bromide with solubilized azo dyes were used as template in base catalysed hydrothermal-assisted sol-gel synthesis of mesoporous aminosilicas of MSM-41 type. The mesoporous structure of synthesized materials was characterized by low-temperature nitrogen adsorption-desorption and x-ray diffraction analysis. It was proved that incorporation of azo dye additives as solubilizates into the surfactant micelles in sol-gel synthesis leads to the formation of silica materials with improved long-range ordered mesoporous structure.

Effect of surfactant concentration on the formation of Fe2O3@SiO2 NIR-reflective red pigments

High NIR-reflective red pigments were developed by encapsulating Fe2O3 particles in a transparent SiO2 shell layer to form Fe2O3@SiO2 core-shell structures. The pigments were prepared by a sol-gel process and the effect of CTAB surfactant concentration on structural formation and optical properties was investigated. The reaction between CTAB and silica species was found to increase the yield of SiO2 formation, which had a major role to control the SiO2 shell thickness by ranging from 8 to 62 nm when varying CTAB concentration from 0 to 2 mM. After encapsulation, Fe2O3@SiO2 pigments still had the red-brown hue of hematite and the NIR reflectivity improved to 62.7 %–65.3%, or twice that of the uncoated Fe2O3. The pigments prepared using the highest CTAB concertation changed from the original Fe2O3 color (CIE Lab color space coordinates) by only ΔE 8.2% due to the formation of second phase SiO2 microspheres formed from excess CTAB micelles. The NIR-reflective red Fe2O3@SiO2 pigments showed good chemical stability and light resistance, thus they were suitable for use as cool pigments for coating applications.

Increasing resonance energy transfer upon dilution: a counterintuitive observation in CTAB micelles

Stable CTAB micelles loaded with DiI and DiD are prepared, showing RET. Remarkably, the RET efficiency increases upon diluting the sample below the critical micellar concentration, as the dyes cluster around CTAB.