Disintegration Of Micelles Research Articles

Influence of temperature and organic acid on self-assembly behavior of pluronic F127

Temperature dependent micellization of 5 wt% F127 has been studied below and above its critical micellization temperature (CMT) using isothermal titration calorimetry. Monomer and micelle dissolution enthalpies are used to calculate solute–solute and solute–solvent interactions. Significant differences are observed at different temperatures indicating a difference in solvent re-structuring around the monomers and micelles. Variation in partial molar enthalpy of the solvent with change in solute concentration is found to be small, in passing from monomer dissolution regime at 288 K to micelle dissolution regime. Enthalpy measurement for the de-micellization process of aqueous F127 has indicated subsequent oligomer (or monomolecular micelle) formation in presence and absence of solubilized salicylic acid (SA). Significant reductions in critical micelle concentration (cmc) and enthalpy of micellization have been observed for F127 with solubilization of SA. Solution behavior of SA solubilized F127 system has been treated using regular solution theory and a decrease in the interaction parameter is observed with increased concentration of solubilized SA indicating its existence in the core region rather than corona.

Mixed micelles formulation for carvedilol delivery: In-vitro characterization and in-vivo evaluation

Carvedilol (CAR) is a widely studied, beta and alpha-1 blocker, antihypertensive drug due to its poor water solubility and low oral bioavailability (25–35%). The aim of this work is to improve poor water solubility and the pharmacokinetic parameters of carvedilol by using an optimized and self-assembly prepared micelle formulation. Optimized micelle formulation composed of Pluronic® F127, D-α-tocopheryl polyethylene glycol 1000 succinate, L-cysteine HCl in a ratio of 4:3:3. Micellar size, polydispersity index, zeta potential, morphology, critical micelle concentration, thermal behaviors, in-vitro dissolution of micelles and pharmacokinetic parameters in rats were characterized in this study. Carvedilol aqueous solubility increased (up to 271-fold) as a result of its encapsulation within a mixed micelle formulation. The measured micellar sizes of blank and carvedilol loaded mixed micelles are lower than 30 nm with size distributions of 26.69 ± 2.93 nm and 24.16 ± 4.89 nm, respectively. Transmission electron microscopy revealed that the micelles were spherically shaped. There is a significant enhancement of carvedilol dissolution compared to commercially available tablet formulation (f2 < 50). The in-vivo test demonstrated that the t1/2 and AUC0–∞ values of micelles were approximately 10.89- and 2.65-fold greater than that of the commercial tablets, respectively. Based on our study, bring such applications into being may provide effective new drugs for treatment armamentarium of cardiovascular diseases and hypertension in near future.

Reduction‐sensitive carrier containing disulfide bond based on Pluronic F68 with cholesterol for drug delivery

AbstractThe reduction‐sensitive amphiphilic polymer chol‐SS‐F68‐SS‐Chol (F68‐CDEC. chol, SS and F68 represent cholesterol, disulfide bond and Pluronic F68, respectively) was easily synthesized by two steps of esterification reactions. The self‐assembly behavior of the polymer was studied by fluorescence spectrophotometry, dynamic light scattering and TEM. Impressively, the critical micelle concentration of F68‐CDEC was 58‐fold smaller than that of F68. Besides, the drug loading content (LC = 20.25%) was higher than that of F68 (LC = 13.42%). In vitro release experiments showed that the reductant dithiothreitol triggered rapid disintegration of micelles with an accumulated drug amount of 55%, compared with an accumulated drug amount of 20% in phosphate‐buffered saline solution. These good abilities were further proved by cell uptake experiments. More importantly, almost no cytotoxicity was observed by 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) colorimetric assay and immunofluorescence staining experiments. There are reasons to believe that the polymer F68‐CDEC can be used as a reduction‐sensitive drug delivery material. © 2020 Society of Industrial Chemistry

Effect of genipin cross-linking on the structural features of skim milk in the presence of ethylenediaminetetraacetic acid (EDTA)

Casein nanogels formed using genipin as a cross-linking agent were studied by dynamic light scattering (DLS), transmission electron microscopy (TEM), small angle X-ray and neutron scattering (SAXS, SANS). The size, substructure, and stability of casein nanogel particles at various genipin concentrations were investigated upon the addition of ethylenediaminetetraacetic acid (EDTA) up to a concentration of 30 mM. Particle size was retained up to 30 mM EDTA for particles with a genipin concentration of 2.5 mM or greater. In contrast, small casein aggregates were formed with size of ∼20−30 nm as a result of casein micelle disintegration on adding EDTA. SAXS revealed that, for both control and cross-linked milks, the homogeneity within the casein protein matrix is increased upon EDTA addition. SANS confirmed that the colloidal calcium phosphate (CCP) particle is an amorphous calcium phosphate core stabilized by a protein shell. Adding EDTA into milk induced a complete solubilisation of the CCP. In the genipin cross-linked milk only the amorphous calcium phosphate core is dissolved, while the protein shell surrounding the CCP is kept intact. These results demonstrate that genipin cross-linking can maintain the structural integrity of the casein protein matrix and the protein shell layer surrounding the CCP particles.

Influence of surfactant on the penetration time of hydrophilic microparticles impacting into the gas–liquid interface at low impact velocities

The micro-mechanics of particle-interface collision is fundamental for revealing the separation mechanism of gas-borne particles in the bubble column. This study further investigates the particle penetration time under different concentrations of anionic and nonionic surfactant solutions at low impact velocities (up0 ≤ 0.5 m/s) utilizing high-speed imaging technique. The results show that the penetration time exhibits a power function to the particle size, which remains constant with increasing the concentration of surfactants. The variation of interfacial deformation width wi and three-phase contact line dTPCL controls the cavity shape and capillary force exerted on the particle, further influencing the penetration time. The increased concentration of surfactant slightly improves the particle surface wettability, while the interfacial deformation width wi exhibits quite different features before and after reaching the critical micelle concentration (CMC). When csurfactant < CMC, the impact cavity will cause the uneven distribution of interfacial concentration and induce the Marangoni effect. When csurfactant> CMC, the disintegration of micelles can supply the monomers and eliminate the Marangoni effect. The model of penetration time has been extended to include the variation of surfactant at pre- and post- CMC.

Structural characterization of heat-induced protein aggregates in model infant milk formulas

Heat treatments induce structural modifications of bovine milk proteins. In this study, we aimed to investigate how these structural modifications are affected by the whey protein profile of infant milk formulas (IMFs) and heat treatment parameters. Three model IMFs (1.3% of proteins; casein:whey protein ratio 40:60) differing by the whey protein profile (1:3.37 α-lactalbumin (α-LA):β-lactoglobulin (β-LG), 1:3.26:1.80 α-LA:β-LG:lactoferrin (LF) or 1:0.13:0.40 α-LA:β-LG:LF), were heated at 67.5 °C or 80 °C to reach an akin whey protein denaturation extent of 65%. Protein structures were analyzed by asymmetrical flow field-flow fractionation coupled with multiangle light scattering and differential refractometer, transmission electron microscopy and electrophoresis. The unheated IMFs were used as reference. The results showed that LF addition in IMFs induced partial casein micelle disintegration before heating. In the absence of added LF, the heat-denatured whey proteins either formed soluble whey protein aggregates or casein micelle-bound whey protein aggregates. The latter were favored at the expense of soluble aggregates in the heated IMFs with the LF content increase and the concomitant β-LG content decrease. Consequently, the casein micelle structure was strongly dependent on the β-LG and LF amounts in IMFs and on the heating temperature. In the IMFs containing β-LG and LF and at temperature greater than the β-LG denaturation temperature, the casein micelles exhibited filamentous appendages on its surface after heating. Below the denaturation temperature of β-LG and in IMFs containing trace β-LG amount, the heated casein micelles were perfectly spherical with a smooth surface.

Disintegration of Surfactant Micelles at Metal–Water Interfaces Promotes Their Strong Adsorption

We have studied the adsorption behavior of micelles of cationic surfactants at metal-water interfaces via fully atomistic simulations. We show that the micelles experience a free energy barrier to adsorption. Near the metal surface, surfactant molecules in the micelles slowly rearrange, leading to complete disintegration of the micelles. The disintegration of the micelles results in much stronger adsorption. After the disintegration, surfactant molecules adsorb by lying flat on the metal surface. Additional simulations performed by treating the micelles as rigid bodies result in only weak adsorption. This confirms our result that disintegration of the micelles is necessary for their strong adsorption.

A pH-Sensitive Polymer for Cancer Targeting Prepared by One-Step Modulation of Functional Side Groups

Nanocarriers with pH-sensitive functionality are of great interest in the development of pH-dependent drug release compounds in acidic tumor microenvironments. A new polyelectrolyte block copolymer, poly[(benzyl-L-aspartate)-co-(N-(3-aminopropyl) imidazole-L-aspartamide)]-poly(ethylene glycol) (PABI-PEG), was prepared by one-step modulation to produce pH-sensitive nanocarriers. PABI-PEG formed a stable nanocarrier at pH values above 7.4 and was destabilized in acidic conditions (pH 6.5) through the protonation of the imidazole groups. Docetaxel loaded micelle (DLM) exhibited pH-dependent drug release through structural conversion due to the protonation of the imidazole groups on the PABI block. The critically low micelle concentration of PABI-PEG at physiological pH and the pH-dependent drug release would result to high stability and restrict drug loss during systemic circulation which may lower the toxicity of normal tissue to physiological pH. Additionally, the extracellular tumor pH (<7.0) and early endosomal pH (<6.5) environments triggered the disintegration of micelles, producing higher drug release compared to other normal tissues and blood (pH 7.4). Therefore, PABI-PEG may be a pHsensitive drug delivery method for cancer chemotherapy.

Hydration of diblock copolymer micelles: Effects of hydrophobicity and co-solvent.

Diblock polymer micelles dispersed in an aqueous environment are being actively investigated for various applications, but there is only a qualitative understanding of the effect of the chemical structure on the micelle hydration and water dynamics as these properties are difficult to assess experimentally. Using all-atom molecular dynamics simulations, we investigate aqueous solutions of three comparable in size diblock copolymer micelles with core-forming blocks of different hydrophobicity: polybutadiene (PB), polycaprolactone (PCL), and polytetrahydrofuran (pTHF) with the same hydrophilic block, polyethylene oxide (PEO). We found that core-block hydrophobicity and ability to form hydrogen bonds with water strongly affect the water dynamics near the core: water molecules spend considerably less time in contact with the PB block than with PCL and pTHF blocks. We obtained polymer and solvent volume fraction profiles and determined that the interfacial width systematically increases with a decrease of core block hydrophobicity with water penetration into the core being negligible for PB-PEO and PCL-PEO micelles, while for pTHF-PEO micelles the interface is more diffuse and there is a noticeable penetration of water (17% by volume). For PCL-PEO micelles, which are commonly used in biomedical applications, we also investigated tetrahydrofuran (THF) penetration into the micelles from mixed THF:water solution at early stages of micelle dissolution. We found an inhomogeneous solvent distribution with a maximum of THF volume fraction in the interfacial core-corona region and partial exclusion from the PEO corona, which slows down micelle dissolution. These results can have important implications for micelle stability and use in biomedical applications.

Bloodstream Stability Predetermines the Antitumor Efficacy of Micellar Polymer-Doxorubicin Drug Conjugates with pH-Triggered Drug Release.

Herein, the biodegradable micelle-forming amphiphilic N-(2-hydroxypropyl) methacrylamide (HPMA)-based polymer conjugates with the anticancer drug doxorubicin (Dox) designed for enhanced tumor accumulation were investigated, and the influence of their stability in the bloodstream on biodistribution, namely, tumor uptake, and in vivo antitumor efficacy were evaluated in detail. Dox was attached to the polymer carrier by a hydrazone bond enabling pH-controlled drug release. While the polymer-drug conjugates were stable in a buffer at pH 7.4 (mimicking bloodstream environment), Dox was released in a buffer under mild acidic conditions modeling the tumor microenvironment or cells. The amphiphilic polymer carriers differed in the structure of hydrophobic cholesterol derivative moieties bound to the HPMA copolymers via a hydrolyzable hydrazone bond, exhibiting different rates of micellar structure disintegration at various pH values. Considerable dependence of the studied polymer-drug conjugate biodistribution on the stability of the micellar structure was observed in neutral, bloodstream-mimicking, environment, showing that a faster rate of the micelle disintegration in pH 7.4 increased the conjugate blood clearance, decreased tumor accumulation, and significantly reduced the tumor:blood and tumor:muscle ratios. Similarly, the final therapeutic outcome was strongly affected by the stability of the micellar structure because the most stable micellar conjugate showed an almost similar therapeutic outcome as the water-soluble, nondegradable, high-molecular-weight starlike HPMA copolymer-Dox conjugate, which was highly efficient in the treatment of solid tumors in mice. Based on the results, we conclude that the bloodstream stability of micellar polymer-anticancer drug conjugates, in addition to their low side toxicity, is a crucial parameter for their efficient solid tumor accumulation and high in vivo antitumor activity.

Kinetics of Photocontrollable Micelles: Light-Induced Self-Assembly and Disassembly of Azobenzene-Based Surfactants Revealed by TR-SAXS.

The kinetics of micelles involving photosensitive surfactants is still not well understood. In this work, we unravel the mechanistic pathways involved in the micelle formation and dissolution of photocontrollable micelles. We focus on the fast self-assembly processes of photosensitive cationic azobenzene-containing surfactants (AzoTMA) that display a change in hydrophobicity induced by a reversible cis-trans conformational transition upon exposure to light. By combining both in situ time-resolved small-angle X-ray scattering (SAXS) and light scattering, we characterized the detailed structure and phase behavior of AzoTMA in mixtures of water and dimethylformamide (DMF). Time-resolved synchrotron SAXS with monochromatic light as a trigger enabled us to observe the nonequilibrium formation and dissolution process of micelles (demicellization) directly on the nanoscale with a time resolution starting from milliseconds. The structural results show that in pure water UV-light illumination leads to a 12% reduction of the aggregation number of the micelles and more than a 50% increase in the critical micelle concentration (CMC). Close to the CMC, adjusted by the addition of DMF, UV light illumination leads to a complete dissolution of the micelles, while shining blue light reverses the process and leads to the reformation of micelles. The UV-triggered dissolution follows a two-step mechanism; the first and rapid (second time scale) release of unimers is followed by a slower decomposition of the micelles (over tens of seconds) as a result of an increase in temperature due to optical absorption. Similarly, the reverse process, i.e., micelle formation, occurs rapidly upon photoconversion to trans conformers under blue light, and micelles are disrupted at long exposure time due to the optical absorption and corresponding increase in temperature. Interestingly, the coexistence of unimers with regular micelles is found at all times, and no other transient assemblies could be detected by SAXS.

Calcium and phosphorus equilibria during acidification of skim milk at elevated temperature

The solubilisation of calcium and phosphorus from casein micelles was studied during skim milk acidification with glucono-delta-lactone. Dynamic measurements of storage modulus (G′) as a function of time were recorded during the formation of acid milk gels with a final pH of 4.6. An abnormal change in slope of G′ (G′shoulder) as a function of time was observed at 50 and 60 °C with decreasing pH. During the appearance of G′shoulder immediately after onset of gelation there was a large change in the concentrations of serum and micellar calcium and phosphorus for change of 0.1 pH units. The onset of gelation at pH values, where the colloidal calcium phosphate is not fully solubilised, is coupled to casein micelle disintegration, and will create increased bonding between caseins forming the final acid gel with a concomitant and sudden solubilisation of calcium and phosphorus from the casein micelles.

Influence of photo-cross-linking on emulsifying performance of the self-assemblies of poly(7-(4-vinylbenzyloxyl)-4-methylcoumarin-co-acrylic acid).

Polymeric micelles could be used as model polymeric particulate emulsifiers to elucidate the correlation between the micellar structure and their emulsifying performance. Photo-cross-linkable and pH-responsive micelles were prepared with amphiphilic random copolymers, poly(7-(4-vinylbenzyloxyl)-4-methylcoumarin-co-acrylic acid) (PVMAA), via the self-assembly in selective-solvent DMF/H2O and then used as polymeric particulate emulsifiers to stabilize toluene-in-water emulsions. Primary micelles, based on PVMAA with 12 mol % of hydrophobic composition, were chosen as model to investigate the influence of photo-cross-linking on the emulsifying performance. The larger shrinkage degree by photo-cross-linking (SDC) the micelles have, the lower emulsifying efficiency the micelles exhibit. Furthermore, the structural transitions of micelles with SDC of 0% and 95% in response to pH change were comparatively confirmed by a combination of electrophoresis, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The micelles of various states, manipulated by photo-cross-linking and pH changes, were used as emulsifiers to stabilize toluene-in-water or styrene-in-water emulsions. For the un-cross-linked micelles, polymer chains gradually protrude from micelles with pH increasing, which benefits the increase in the emulsifying efficiency of micelles. However, as pH elevated over 8, the stability of emulsions significantly decreases due to the disintegration of micelles. On the contrary, micelles with SDC of 95% keep their structural integrity and become more rigid as pH increase, leading to lower emulsifying efficiency of micelles and worse stability of the emulsions. This paper provides a new insight into the principles governing the extremely high emulsifying efficiency of polymeric particulate emulsifiers and pH-dependent or pH-responsive properties of the formed emulsions.

Dual location disulfide degradable interlayer-crosslinked micelles with extended sheddable coronas exhibiting enhanced colloidal stability and rapid release

Amphiphilic block copolymer-based micellar nanocarriers hold great promise as a drug delivery platform; however, the colloidal stability of nanoassemblies upon intravenous injection remains a significant challenge. Further, enhanced/controlled release of encapsulated drugs by cleavage of dynamic covalent linkages in response to external stimuli is highly desired. Herein, we report new polylactide (PLA)-based triblock copolymers (PssDL) possessing thiol-responsive dynamic disulfide linkages at dual locations using a combination of ring opening polymerization and controlled radical polymerization techniques. These well-defined PssDL copolymers are designed to self-assemble to form aqueous micellar aggregates having multiple pendant disulfide linkages in a hydrophobic interlayer as well as single disulfides at interfaces of the interlayer and PLA core, surrounded by hydrophilic coronas. Through thiol-responsive cleavage of these dually located disulfide linkages, novel interlayer-crosslinked micelles (ICMs) with a crosslinkable and sheddable extended corona can be formed, thus combining the enhanced colloidal stability of crosslinked nanocarriers with rapid destabilization or disintegration of micelles typically found with sheddable systems. This dual location degradation process results in enhanced colloidal stability, along with controlled release of encapsulated anticancer drugs to promote the inhibition of cell proliferation after internalization into cancer cells.

DETECTION OF FORMATION AND DISINTEGRATION OF MICELLES BY OBLIQUE-INCIDENCE REFLECTIVITY DIFFERENCE MICROSCOPY

An oblique-incidence reflectivity difference (OI-RD) scanning microscope was developed for label-free detection of the formation and disintegration of micelles upon solid substrates. Micelles are made of polymers with hydrophilic heads in contact with the surrounding solvent and hydrophobic tails in the micelle center. This characteristic makes them very efficient drug carriers. Streptavidin molecules were first printed on glass slides for capturing biotinylated polymers. Micelles were formed when the concentration of polymers was higher than a critical value. The formation of micelles resulted in an increase in the oblique-incidence reflectivity difference signals. As the concentration of polymers decreased below the critical value, micelles were disintegrated, and a corresponding decrease in the oblique-incidence reflectivity difference signals was observed. This microscope was employed for the real-time monitoring of the formation and disintegration of two different micelles. The critical concentration above which micelles were formed was determined to be around 0.0006 mg/mL for micelles made of PEG5KCA8 polymers. The results suggest that this microscope would have practical application in testing the efficiency and durability of micellar drug carriers.

Perspective on Improving Passive Human Intestinal Absorption

Methods such as pH adjustment, cosolvency, complexation, and micellization are routinely used to increase the concentration of dissolved drug in the gastrointestinal (GI) lumen over that of a saturated solution. However, these solubilizing agents also reduce the membrane-water distribution coefficient so that the membrane transport rate is not changed. Also, dilution of a formulation upon administration results in: (1) a pH change toward that of the GI fluid, (2) an exponential decrease in cosolvency, and (3) disassociation of complexes and the disintegration of micelles. As a result, these solubilizing agents cannot be expected to produce any increase in membrane transport-limited drug absorption over that of a suspension of unformulated drug.

Multifunctional pH-Disintegrable micellar nanoparticles of asymmetrically functionalized β-cyclodextrin-Based star copolymer covalently conjugated with doxorubicin and DOTA-Gd moieties

We report on a novel type of multifunctional pH-disintegrable micellar nanoparticles fabricated from asymmetrically functionalized β-cyclodextrin ( β-CD) based star copolymers covalently conjugated with doxorubicin (DOX), folic acid (FA), and DOTA- Gd moieties for integrated cancer cell-targeted drug delivery and magnetic resonance (MR) imaging contrast enhancement. Asymmetrically functionalized β-CD, ( N 3) 7- CD-( Br) 14, which possesses 7 azide functionalities and 14 α-bromopropionate moieties in the upper and lower rim of rigid toroidal β-CD core, respectively, was synthesized at first. The subsequent atom transfer radical polymerization (ATRP) of N-(2-hydroxypropyl) methacrylamide (HPMA), conjugation with DOX and FA, and click reaction with alkynyl-(DOTA- Gd) complex afforded (DOTA- Gd) 7- CD-(PHPMA- FA- DOX) 14 star copolymer comprising of 7 DOTA- Gd complex moieties and 14 PHPMA arms covalently anchored with DOX and FA via acid-labile carbamate linkages and ester bonds, respectively. The covalent conjugation with ∼13 DOX molecules onto PHPMA arms per star copolymer (∼14 wt% loading content) endows the initially hydrophilic one with amphiphilicity, leading to the self-assembly into micellar nanoparticles of several tens of nanometers in aqueous solution at pH 7.4. In vitro DOX release profile from micellar nanoparticles is highly pH-dependent, and over a time period of 42 h, cumulative releases of ∼10%, 53%, and 89% conjugated DOX at pH 7.4, 5.0, and 4.0, respectively, were observed. Most importantly, the pH-modulated release of conjugated DOX from micellar nanoparticles is accompanied with the micelle disintegration due to the loss of amphiphilicity of the star copolymer scaffold. In vitro cell viability assays revealed that (DOTA -Gd) 7- CD-(PHPMA 15) 14 star copolymer is almost non-cytotoxic up to a concentration of 0.5 g/L, whereas DOX-conjugated micellar nanoparticles of (DOTA- Gd) 7- CD-(PHPMA- FA- DOX) 14 can effectively enter and kill HeLa cells at a concentration higher than ∼80 mg/L. In vitro MR imaging experiments indicated a considerably enhanced T 1 relaxivity ( r 1 = 11.4 s −1 mM −1) for micellar nanoparticles compared to that for the small molecule counterpart, alkynyl-DOTA-Gd ( r 1 = 3.1 s −1 mM −1). In vivo MR imaging assay in rats revealed considerable accumulation of micellar nanoparticles within rat liver and kidney and prominent positive contrast enhancement. The integrated design of diagnostic and therapeutic functions of multifunctional pH-disintegrable micellar nanoparticles augurs well for their practical applications in the field of image-guided cancer chemotherapy.

Adsorption Layer Characteristics of Mixed SDS/CnEOm Solutions. 3. Dynamics of Adsorption and Surface Dilational Rheology of Micellar Solutions

The dynamic surface tensions of mixed SDS/C(12)EO(5) and SDS/C(14)EO(8) micellar solutions measured over a wide time range (0.1 ms to 10,000 s) at various mixing ratios are described satisfactorily by a theoretical model for the kinetics of adsorption of surfactant mixtures using the surfactant adsorption parameters obtained for premicellar mixed solutions. Additional relations used for the description of the adsorption kinetics from micellar solutions were expressions of the effective diffusion coefficient of monomers accounting for the disintegration of micelles. The modeled dynamic surface tensions agree well with the experimental data for all studied surfactant mixtures. The rheological behavior of the same mixtures--the dependencies of the viscoelasticity modulus and phase angle--were studied by using the bubble profile method at harmonic bubble surface area oscillations. The theoretical approach employed for data analysis was the same as for the dynamic surface tension behavior. Again, satisfactory agreement between the experimental data and theoretical calculations of the dilational rheological parameters was found.

Salt-induced release of lipase from polyelectrolyte complex micelles

With the aim to gain insight into the possible applicability of protein-filled polyelectrolyte complex micelles under physiological salt conditions, we studied the behavior of these micelles as a function of salt concentration. The micelles form by electrostatically driven co-assembly from strong cationic block copolymers poly(2-methyl vinyl pyridinium)41-block- poly(ethylene oxide)205, weak anionic homopolymers poly(acrylic acid)139, and negatively charged lipase molecules. The formation and disintegration of these micelles were studied with dynamic light scattering (DLS), by means of composition and salt titrations, respectively. The latter measurements revealed differences between disintegration of lipase-filled and normal polyelectrolyte complex micelles. These data, together with small angle neutron scattering (SANS) measurements provide indications that lipase is gradually released with increasing salt concentration. From the SANS data a linear relation between the intensity at q = 0 and the volume of the cores of the micelles at different salt concentrations was derived, indicating a loss of volume of the micelles due to the release of lipase molecules. It was estimated that beyond 0.12 M NaCl all lipase molecules are released.

Adsorption layer characteristics of Triton surfactants: 4. Dynamic surface tension and dilational visco-elasticity of micellar solutions

The presence of micelles in the solution accelerates the adsorption dynamics of Tritons at the solution/air interface, depending on the micelle dissolution rate. Micellar solutions (at CMC and up to about 10× CMC) are studied by maximum bubble pressure tensiometry and oscillating bubble profile tensiometry. The dynamic surface tensions in the time range between 0.1 ms up to 50 s are analysed by a diffusion controlled mechanism. At very short times the effect of molecular reorientation of the Triton molecules at the surface is observed. The dilational elasticity data at low frequencies (0.005–0.2 Hz) provide good agreement with a respective model assuming a very fast micelle dissolution. While for Triton X-45 and X-100 a quantitative agreement with existing theories is observed, the results for Triton X-165 and X-405 agree only qualitatively. This discrepancy is obviously due to the respective composition of the technical surfactants and a quantitative understanding would require an accurate knowledge on the sample composition.