Cac Value Research Articles

Amphiphilic cellulose: Surface activity and aqueous self-assembly into nano-sized polymeric micelles

The aim of the present study was to design amphiphilic cellulose that can self-assemble into polymeric vesicle or as nontoxic surfactants. Sulfate was firstly introduced as hydrophilic groups, then the hydrophobic groups for three cellulose derivatives. Effects of the hydrophobic length on the surface tension and critical aggregate concentration (cac) were investigated by the conventional Wilhelmy plate method. Results showed that the cac value decreased from 0.28 to 0.08 wt% and the corresponding surface tension increased from 44 to 55 mN/m when the hydrophobic chain length changed from C 8 to C 18. The aqueous self-assembly of the modified polymer was investigated using transmission electron microscopy (TEM) and dynamic laser scattering (DLS). Results showed that three cellulose derivatives were capable of forming polymeric micelles in water with an average particle diameter ranging from 20 to 67 nm. And the diameter of the nano-micelles was proportional to the length of hydrophobic chain under the experimental conditions. These amphiphilic polymers showed more remarkable shear shinning rheological behavior as expected since higher shear rates lead to disruptions of hydrophobic associations. These data suggest that the amphiphilic cellulose derivative may form nano-micelles and might find use as surfactant or a potential drug carrier.

Recovery of ionic liquids from wastewater: Aggregation control for intensified membrane filtration

Based on the hypothesis that ionic liquids should show a similar behaviour as surfactants in membrane filtration, this research work analyses the potential of aggregation control to improve the performance of downstream membrane separations, applied to the system 3-octyl-1-methylimidazolium chloride (OMIM-Cl), water and iron(III) chloride (FeCl 3). It was obtained that the addition of FeCl 3 has an important effect on CAC value and its increase has consequences on the design of the corresponding membrane filtration system.

Interaction of Ethylene Oxide−Propylene Oxide Copolymers with Ionic Surfactants Studied by Calorimetry: Random versus Block Copolymers

The present study used calorimetric techniques to follow the interaction of random and block ethylene oxide (EO)-propylene oxide (PO) copolymers with ionic surfactants. Features such as the intensity of the interaction (evaluated through their critical aggregation concentrations) and the profile of the isothermal titration calorimetry (ITC) curves were comparatively analyzed for random and block copolymers with similar composition (number of EO and PO units). Random copolymers displayed an interaction similar to that observed with other hydrophilic homopolymers with the additional characteristic that the intensity of the interaction increased with the increase in the copolymer hydrophobicity (as determined by its PO content), revealing that these copolymers display an intermediate behavior between PEO and PPO. For nonaggregated block copolymers (unimers) with large enough EO blocks (molar mass above 2000 g mol-1), ITC curves revealed that the anionic surfactant sodium dodecylsulfate (SDS) interacts with the PO and EO blocks almost independently, being more favorable with the PO block, which controls the critical aggregation concentration (cac) value. Effects of temperature and of the nature of the ionic surfactants on their interaction with these copolymers were found to agree with the previously reported trends.

Self-assembly properties of some chiral N-palmitoyl amino acid surfactants in aqueous solution

Various chiral N-palmitoyl amino acid surfactants (AAS) derived from methionine, proline, leucine, threonine, phenylalanine and phenylglycine were prepared and converted to their sodium salt. The properties of the aggregates formed in aqueous solution were studied for both the optically-active compounds and their racemic mixture. Characterization was made by surface tensiometry, fluorimetry, dynamic light scattering, circular dichroism (CD) and transmission electron microscopy. It appeared that most of the AAS studied in this work spontaneously formed different types of aggregates, including micrometer-sized aggregates. No significant difference could be found between the critical aggregation concentration (cac) value of pure enantiomers and that of the racemic forms. CD spectra did not reveal any aggregation-induced chirality.

Synthesis and Properties of a Novel Class of Gemini Pyridinium Surfactants

A novel class of gemini pyridinium surfactants with a four-methylene spacer group was synthesized, and their surface-active properties and interactions with polyacrylamide (PAM) were evaluated by surface tension, fluorescence, and viscosity measurements. A comparison between the gemini pyridinium surfactants and their corresponding monomers was also made. The cmc's of gemini pyridinium surfactants are much lower than those of the corresponding monomeric surfactants. The C20 value is about one order of magnitude lower than that of corresponding monomers, and the longer the hydrophobic chains of the surfactants, the lower the cmc value. Surface tension measurements of the surfactant-PAM mixed systems show that the critical aggregation concentration (cac) value is much lower than the cmc value of the surfactant system alone. Viscosity measurements of the surfactant-PAM mixed systems show that the relative viscosity of the surfactant-PAM system decreased with increasing concentration of surfactant. Additionally, fluorescence measurements of the surfactant-PAM mixed system suggest the formation of surfactant-polymer aggregates, and the gemini pyridinium surfactant with longer hydrophobic chains have a stronger interaction with PAM, owing to the stronger hydrophobic interaction.

Fluorescence, Circular Dichroism, Light Scattering, and Microscopic Characterization of Vesicles of Sodium Salts of Three N-Acyl Peptides

Aggregation behavior of three N-acyl peptide surfactants, sodium N-(4-n-dodecyloxybenzoyl)-L-alyl-L-valinate (SDBAV), L-valyl-L-alaninate (SDBVA), and L-valyl-L-valinate (SDBVV), were investigated. The amphiphiles have very low critical aggregation concentration (cac). Fluorescence anisotropy studies using 1,6-diphenyl-1,3,5-hexatriene (DPH) as a fluorescent probe indicated formation of bilayer aggregates in dilute solution. Transmission electron micrographs showed the existence of large vesicles in dilute solution. Circular dichroism spectra suggested formation of helical aggregates. The vesicle formation was found to be more favored at neutral pH. Dynamic light scattering was used to measure hydrodynamic radius of the vesicles. The microviscosity of the vesicles formed by the amphiphiles was determined by use of fluorescence anisotropy and the lifetime of the DPH probe. The vesicles formed by the surfactants are stable at temperatures above body temperature and for a long period of time. Fluorescence probe studies, however, indicated transformation of vesicles to rod-like micelles at surfactant concentrations much higher than the cac value. Addition of sodium chloride also transformed the vesicles to rod-like micelles.

Synthesis and aggregates of cellulose-based hydrophobically associating polymer

A novel cellulose-based hydrophobically associating water-soluble polymer-cellulose octaonate sulfate (COS) was synthesized in this paper. The basic physico-chemical properties such as surface tension and the critical aggregation concentration ( cac) were measured by the conventional Wilhelmy plate method. The obtained cac value was compared with environmental scanning electron microscopy (ESEM) and Rheology data. All these results indicated that cac of this amphiphilic polymer was between the range 0.04 and 0.2 wt% and the corresponding surface tension was around 55 mN/m. The conformation of aggregates and size of particles in aqueous solution were carefully investigated by ESEM and dynamic laser scattering (DLS) measurements. When the concentration is around 0.04 wt%, loose aggregates are formed; around 0.5 wt%, network structure formed. DLS results indicated that average size of particle was increased from 54.7 nm to 73 nm and finally to 168.1 nm with the increase of concentration from 0.04% to 0.1% and even to 0.2%. These results suggested that almost all of micelles in aqueous solution aggregated at the experimental concentration range 0.04–0.5 wt%. Rheological properties of this polymer were similar to hydrophobically associating polymers’ (HMP). As the shear rate increased, the solution passed through a shear-thickening region before exhibiting a sharp decrease in viscosity, eventually exhibited Newtonian behavior.

Colloid‐Enhanced Ultrafiltration of Chlorophenols in Wastewater: Part IV. Effect of Added Salt on the Surfactant Leakage in Surfactant Solutions and Surfactant–Polymer Mixtures

The critical aggregation concentration (cac) in surfactant–polymer mixtures approximates a lower limit to the surfactant concentration in the permeate (surfactant leakage) in polyelectrolyte micellar‐enhanced ultrafiltration. Here, the cac was measured at different salinities by using surface tension measurements. It was found that the cac increases slightly with the addition of simple salt, then the cac value decreases at higher salt concentration. The critical micelle concentration (CMC), which approximates surfactant leakage in micellar systems (no polymer), decreases monotonically with increasing salinity for ionic surfactants. The surfactant leakage in colloid‐enhanced ultrafiltration (CEUF) processes is investigated by using a dialysis method in the presence of three phenolic solutes with various degrees of chlorination: 2‐monochlorophenol (MCP), 2,4‐dichlorophenol (DCP), and 2,4,6‐trichlorophenol (TCP). Cetylpyridinium chloride (CPC) or n‐hexadecylpyridinium chloride is used as a cationic surfactant; and sodium poly(styrenesulfonate) (PSS) is used as an anionic polyelectrolyte. The effect of salinity and type of colloid is focused on here. In the absence of added salt, the cac can be over an order of magnitude less than the CMC, as can be surfactant leakage with added polymer. The added salt reduces the surfactant leakage in the micellar solution due to CMC reduction in the presence of electrolyte. In the surfactant–polymer mixture, the surfactant leakage is dramatically affected by salinity.

Investigation of the Interaction between Sodium Dodecyl Sulfate and Cationic Polymers

Aggregation properties of sodium dodecyl sulfate (SDS) on a cationic hydroxyethyl cellulose, Polyquaternium-10 (PQ-10), of low charge density were studied by potentiometric and pyrene fluorescence methods and compared with those of poly(diallyldimethylammomium chloride) (PDADMAC) of high charge density. The critical aggregation concentration (cac) was measured with the potentiometric method and further confirmed with the fluorescence method. The former was found to be more accurate. The value of the cac for the SDS/PQ-10 system was measured at 100, 200, and 400 ppm polymer and at 288.2,298.2, and 308.2 K. They showed almost the same cac value, 0.04 mmol dm-3. The I1/I3 value of the pyrene fluorescence spectrum in the SDS/PQ-10 system at higher SDS concentration was smaller than that in SDS/PDADMAC solution and much larger than that of water. From the binding isotherm by the potentiometric method, the free DS- concentration (Cf) and the bound DS- concentration (Cb) could be evaluated with ease over the SDS concentration range above the cac. The aggregation number of DS- aggregates for both the above polymers was evaluated from the fluorescence quenching method using the values of Cf and Cb from the potentiometric method. Because Cf in the SDS/PQ-10 system above the cac did not maintain a constant value contrary to that in the SDS/PDADMAC system but increased quite a lot, Cb should not be regarded as [SDS] - cac above the cac. The aggregation number in the SDS/PQ-10 system increased almost linearly with increasing total concentration of SDS, while that in the SDS/PDADMAC system reached a plateau. With increasing temperature, the aggregation number of the SDS/PDADMAC system decreased more rapidly than that of the SDS/PQ-10 system.

Thermally responsive core-shell nanoparticles self-assembled from cholesteryl end-capped and grafted polyacrylamides:: drug incorporation and in vitro release

The thermally responsive cholesteryl end-capped poly( N-isopropylacrylamide- co- N,N-dimethylacrylamide) and cholesteryl grafted poly[ N-isopropylacrylamide- co- N-(hydroxymethyl) acrylamide] amphiphilic polymers were synthesized and utilized to encapsulate cyclosporin A (CyA) and indomethacin (IND) within core-shell nanoparticles by a membrane dialysis method. The blank and drug-loaded nanoparticles were characterized using various analytical tools. The blank nanoparticles had a mean diameter less than 100 nm, whereas the drug-loaded nanoparticles were between 100 and 200 nm in diameter. The CAC value of cholesteryl end-capped and grafted polymers in PBS (pH 7.4) was estimated to be 16 and 8.5 mg/l, respectively. The LCST value for both nanoparticle systems in PBS (pH 7.4) was determined to be 33.4°C and 38.3°C, respectively. The presence of proteins in PBS reduced the LCST. The core-shell nanoparticles provided great capacity for drug loading. In particular, the cholesteryl grafted polymer yielded a higher encapsulation efficiency for drugs. Compared to CyA, better entrapment was observed for IDN. A reduced fabrication temperature provided greater drug encapsulation efficiency. An increase in the initial drug content yielded lower drug encapsulation efficiencies at 10°C and 15°C. Increasing the polymer concentration increased drug encapsulation efficiency. The drug-loading process was analyzed to understand the effect of various fabrication parameters on drug encapsulation efficiency. IND release from the nanoparticles was responsive to temperature changes, being faster at a temperature around the LCST than below the LCST.

Swelling of poly(ethylene oxide) gel in aqueous solutions of sodium dodecyl sulfate with added sodium chloride

The swelling behavior of poly(ethylene oxide) (PEO) gels in aqueous solutions of sodium dodecyl sulfate (SDS) with and without NaCl was investigated. In the absence of NaCl, PEO gels with different degrees of cross-linking began to swell from a concentration lower than the critical micelle concentration (cmc) of SDS, then showed sigmoidal enhancements of swelling in a higher SDS concentration region until the degrees of swelling reached maximum values. The SDS concentration at which the swelling began to appear was in reasonable agreement with the critical aggregation concentration (cac) value reported for the aqueous PEO system. For the cases where NaCl was present, the swelling behavior of PEO gel was different from that when NaCl was absent in the following way. The concentrations where the swelling begins to appear, and hence those where the degree of swelling rises steeply, decreased with an increase in NaCl concentration. The ultimate degrees of swelling at higher concentration regions also decreased with an increase in the NaCl concentration. The lowering of the SDS concentrations at which the PEO gel began to swell is in line with the decreases in the cmc of SDS solutions containing NaCl and also with the decreases in the cac of PEO solution.

Physicochemical Characteristics of Self-Aggregates of Hydrophobically Modified Chitosans

Chitosan derivatives containing 2.8−5.1 deoxycholic acid groups per 100 anhydroglucosamine units of chitosan were synthesized by an EDC-mediated coupling reaction. Physicochemical properties of self-aggregates of the hydrophobically modified chitosans in aqueous media were studied by the dynamic light scattering method and fluorescence spectroscopy. The mean diameter (dH) of DC4.2 self-aggregates in phosphate-buffered saline (PBS) solution (pH 7.2) was 159 nm with unimodal size distribution (variance = 0.082). It seemed that the interparticle interaction between self-aggregates was almost negligible. The mean diameter decreased with increasing degree of substitution (DS), pH, or ionic strength of the medium. The critical aggregation concentration (cac) of self-aggregates was determined from the fluorescence emission spectra of pyrene. The cac value of DC4.2 in PBS solution (pH 7.2) was 2.6 × 10-2 mg/mL. The cac values decreased with increasing DS, pH, or ionic strength of the medium.

Preparation of chitosan self-aggregates as a gene delivery system

Hydrophobically modified chitosan containing 5.1 deoxycholic acid groups per 100 anhydroglucose units was synthesized by an EDC-mediated coupling reaction. Formation and characteristics of self-aggregates of hydrophobically modified chitosan were studied by fluorescence spectroscopy and dynamic light scattering method. The critical aggregation concentration (cac) of the self-aggregate was determined by measuring the fluorescence intensity of pyrene as a fluorescent probe. The cac value in PBS solution (pH 7.2) was 1.7×10 −2 mg/ml. Mean diameter of self-aggregates in PBS solution (pH 7.2) was 162±18 nm with an unimodal size distribution. Charge complex formation between self-aggregates and plasmid DNA was confirmed by electrophoresis on an agarose gel. Migration of DNA on an agarose gel was completely retarded above a charge ratio (+/−) of 4/1 at pH 7.2. The free DNA dissociated from the complexes was observed by electrophoresis above pH 8.0 at a fixed charge ratio of 4/1. An efficient transfection of COS-1 cells was achieved by self-aggregates/DNA complexes.