Micelle Aggregation Research Articles

In situ saxs characterization of thermoresponsive behavior of a poly(ethylene glycol)-graft-(poly(vinyl caprolactam)-co-poly(vinyl acetate)) amphiphilic graft copolymer

We report the thermoresponsive assembly and rheology of an amphiphilic thermosensitive graft copolymer, poly(ethylene glycol)-graft-(poly(vinyl caprolactam)-co-poly(vinyl acetate)) (commercial name Soluplus®), which has been investigated for potential biomedical applications. It has received attention due to is ability to solubilize hydrophobic drugs and for its thickening behavior close to body temperature. Through use of the synchrotron at Brookhaven National Lab, and collaboration with the department of energy, the nanoscale structure and properties can be probed in greater detail. Soluplus® undergoes two structural changes as temperature is increased; the first, a concentration independent change where samples become turbid at 32 °C. Increasing the temperature further causes the formation of physically associated hydrogels. This sol-gel transition is concentration dependent and occurs at 32 °C for 40 wt% samples, and increases to 42 °C for 10 wt% samples. From variable temperature SAXS characterization micelles of 20–25 nm in radius can be seen and maintain their size and packing below 32 °C. A gradual increase in the aggregation of micelles corresponding to a thickening of the material is also observed. Close to and above the gelation temperature, micelles collapse and form a physically associated 3D network. A model is proposed to explain these physical effects, where the poly(vinyl caprolactam) group transitions from the hydrophilic corona at room temperature to the hydrophobic core as temperature is increased.

Theoretical treatment of complex coacervate core micelles: structure and pH-induced disassembly.

Complex coacervate core micelles (C3Ms) are supramolecular soft nanostructures formed by the assembly of a block copolymer and an oppositely charged homopolymer. The coacervation of the charged segments in both macromolecules drives the formation of the core of the C3M, while the neutral block of the copolymer forms the corona. This work introduces a molecular theory (MOLT) that predicts the internal structure and stimuli-responsive properties of C3Ms and explicitly considers the chemical architecture of the polyelectrolytes, their acid-based equilibria and electrostatic and non-electrostatic interactions. In order to accurately predict complex coacervation, the correlations between charged species are incorporated into MOLT as ion-pairing processes, which are modeled using a coupled chemical equilibrium formalism. Very good agreement was observed between the experimental results in the literature and MOLT predictions for the scaling relationships that relate the dimensions of the micelle (aggregation number and sizes of the micelle and the core) to the lengths of the different blocks. MOLT was used to study the disassembly of the micelles when the solution pH is driven away from the value that guarantees the charge stoichiometry of the core. This study reveals that very sharp disassembly transitions can be obtained by tuning the length or architecture of the copolymer component, thereby suggesting potential routes to design C3Ms capable of releasing their components at very precise pH values.

PROPERTIES OF MICELLAR CASEIN AND APPLICATION IN FOOD INDUSTRY

Milk casein has important properties that ensure the widespread use of this protein in industry and increased interest in its study by researchers. Studies of the structure of casein in its native state have revealed its micellar structure. The presence of large ions leads to an increase in the volume of micelles, while acidification results in a decrease. During storage, the ability of MCC to rehydrate and dissolve reduces, aggregation and degradation of the structure are observed, with an increase in storage temperature, these indicators noticeably decrease. Thermal stability is greatest near neutral pH. MCC has gel and foaming properties. In the presence of transglutaminase, the stability of micelles rises. In the same way, under the increased pressure – the coagulation time of micelles increases. The surface activity and hydrophilicity of micellar casein directly depend on the degree of aggregation of micelles, the lower it is, the higher the values of these indicators. The organoleptic characteristics of this additive are favorable. Due to the high content of protein and the peculiarities of its digestibility, MCC is actively used in the production of specialized nutrition, for example, dietary, sports, children's, etc. The process of producing yogurt, desserts, cheeses (processed and hard) is an aggregation of milk casein to varying degrees, the use of commercially available micellar casein makes it possible to make the production process more controlled and improves the quality of final products. In the meat processing industry, functional additives containing milk proteins and casein are actively used, however, there are no data on the introduction of micellar casein into functional mixtures as an individual component. A detailed analysis of the data regarding the physicochemical and technological properties of micellar casein concentrate, such as thermal stability, solubility, waterretaining and gelling abilities, surface-active properties, foaming and influence on the organoleptic properties of products, is given. The existing examples of its application in various fields of the food industry are considered: in the production of high-protein and lowcarbohydrate drinks, sports nutrition, yoghurts and desserts, hard and processed cheeses, as well as in meat processing.

Interplay of temperature and calcium content in beta-casein solutions: From controlled self-aggregation of micelles in bulk to the design of stable foams

We describe in this study the aggregation behaviour of β-casein micelles from milk in bulk aqueous solution as function of both temperature and calcium content, and its influence on the foaming properties, in order to test if the different aggregation states of β-casein makes possible the design of proteins-based thermoresponsive foams. First, we characterized the morphology of the self-assembled β-casein molecules in solution by coupling turbidity measurements, Dynamic Light Scattering and Small Angle Neutron Scattering. They self-organize into individual micelles at low temperature (20°C) whatever the calcium content, and transit in a reversible way into aggregates of micelles at large temperature in presence of calcium, with a threshold transition that depend both on temperature and calcium content. The micelles aggregation is driven by the calcium through association with serine phosphate groups localized on the hydrophilic part of the β-casein. In the micelles regime, we demonstrated that the addition of calcium tunes the aggregation number of unimers per micelle in the same way than an increase of temperature through a change of hydrophobic interactions. The hydrophilic chains of the corona are however in a good solvent and interact through excluded volume interactions, even when the β-casein micelles aggregates themselves. The internal molecular structure of the micelles is thus not modified by calcium bridges, which explains the complete reversibility of the aggregation process over temperature cycling. Second, we studied the foam stability versus time as a function of the temperature and calcium content by measuring the kinetic evolution of both the foam volume and the liquid fraction. Foams produced by solutions containing only β-casein micelles were stable in terms of foam volume on a timescale of 1 h at 20°C but drained quickly. However, foams become unstable when the temperature was increased above 20°C. In presence of calcium, the aggregation of β-casein micelles inside the foam liquid channels enabled to increase foam stability at larger temperature by acting as a cork, which slows down the drainage. The increase of foam stability by such aggregates is however not sufficient on the long term to allow the design of thermoresponsive foams.

Investigation on the phase behaviors of aqueous surfactant two-phase systems containing Alkyl polyglucosides (APG) and alkyl polyglucoside sulfosuccinate (APGSS)

The surfactant aqueous two-phase systems have been widely attention because of their mild conditions and easy recovery. The phase behaviors and formation mechanism of an aqueous surfactant two-phase system (ATPS), which was composed of a nonionic surfactant Alkyl polyglucosides (APG) and an anionic surfactant sodium alkyl polyglucoside sulfosuccinate (APGSS), were studied. The phase diagram for APG/APGSS ATPS was illustrated. Merchuk relation was used to correlate the binodal experimental data. Indicating that top phase is APG enriched phase and the bottom phase is APGSS enriched. By measurements of surface tension, electrical conductivity, density, viscosity, transmission electron microscopy, and dynamic light scattering, micelle aggregation behaviors were explored. The formation mechanism of the ATPS was also proposed, which is attributed to the different aggregation behaviors between APG and APGSS molecules leads to different micelle size and morphology. The top phase flocculates due to the presence of asymmetric larger wormlike aggregates, lead to phase separation and the formation of the ATPS.

Spectroscopic analysis of the effect of glycation on casein structure and aggregation and its dependence on lactose concentration

In order to study the effect of glycation on the molecular structure of casein (CN), three groups of simulated milk powders with different lactose (Lac) contents, CN:Lac = 1:1.5, 1:2, and 1:2.5 (m:m), were constructed. The glycation level and the structural changes of CN were analyzed by multiple spectra. The results showed that the interaction between Lac and CN molecules was based on the dynamic quenching of collision. A higher quenching constant, KSV, means that the 1:1.5 group showed more distinct glycation levels. In addition, CN glycation reduced the aggregation of casein micelles caused by heating treatment and repaired the structural damage of CN induced during the heating process. There was no positive correlation found between Lac content and protein glycation; thus, decreasing the Lac content of milk powder is not likely to be an effective method to prolong storage stability.

Heat treatment of milk protein concentrates affects enzymatic coagulation properties

Dairy ingredients with highly concentrated protein contents are high added value products with expanding market. The manufacture of such ingredients includes a succession of unit operations of which heat treatment is a key step to guarantee the microbial safety, that induces major changes in protein structures and thus ingredients functionalities. However, due to an incomplete understanding of phenomena taking place at high protein concentrations, shedding light on their mechanisms is a scientific challenge as well as an industrial need. In this study, the influence of heat treatment (74 °C/ 30 s) of highly concentrated milk protein systems (up to 20 % w/w) on protein denaturation/aggregation and enzymatic coagulation properties was studied using an original semi–industrial approach. 10 % w/w protein solutions constituted with whey protein and casein micelles at milk ratio, standardized in osmosed water or ultrafiltration permeate were used. These protein solutions were processed in different ways prior the manufacture of powders: heat treatment of the 10 % w/w protein solution before vacuum evaporation, heat treatment of the 20 % w/w protein solution after vacuum concentration, two consecutive heat treatments before and after vacuum evaporation. A fourth powder was prepared from unheated 10 % w/w protein solution. An increase in protein concentration led to a higher heat-induced protein denaturation. This phenomenon was reduced when increasing the lactose content. The effect of heat treatment on the extent of protein denaturation was not cumulative. At high protein concentration, interactions between κ-casein and whey protein were modified compared to milk, as mainly micelle-bound aggregates were formed at pH about 6.7. This phenomenon was enhanced at low ionic strength and lactose content. Our study showed that the enzymatic coagulation properties of reconstituted protein powders could be correlated with their physico–chemical compositions. An increase in protein denaturation disrupted the gel reorganization and led to the formation of weaker gels but did not interfere on the micelles aggregation phase and the early gelation. On the contrary, an increase in ionic strength and lactose content led to higher gel time.

Use of Calotropis procera cysteine peptidases (CpCPs) immobilized on glyoxyl-agarose for cheesemaking

Calotropis procera cysteine peptidases (CpCPs) have presented several potential biotechnological applications. Here, these enzymes were immobilized on glyoxyl-agarose (glyoxyl-CpCPs) with yields of 90–95 % and the recovered activities ranged from 10 % to 15 %, according to enzyme loadings (5, 10, 20, 40, and 50 mgBSAeq/g). Spectrophotometric assays and SDS-PAGE showed that the casein hydrolysis by glyoxyl-CpCPs was similar to soluble CpCPs. In addition, glyoxyl-CpCPs exhibited similar ratio of milk-clotting activity to proteolytic activity in comparison with soluble CpCPs and chymosin. Even after being stored for six months at 8 °C, the residual proteolytic activity of glyoxyl-CpCPs remained close to 100 %. Atomic force microscopy and dynamic light scattering techniques showed that the process of casein micelle aggregation after treatment with glyoxyl-CpCPs was very similar to its soluble form and chymosin. Glyoxyl-CpCPs performed well after five reaction cycles, producing cheeses with yield, moisture, protein, and fat similar to those produced with chymosin.

Hydrogelation of TPGS for locoregional combination therapy of cancer

D-ɑ-tocopheryl poly(ethylene glycol)1000 succinate (TPGS) has been extensively applied in drug delivery systems for its amphiphilic property and inherent bioactivity. But TPGS has not always been utilized solely for the unstability of TPGS micelle. Inspired by the hydrogels made from other amphiphilic molecules, thermosensitive TPGS hydrogels were firstly discovered and developed in the presence of specific anions, which self-assembled from the aggregation of TPGS micelles stimulated by heating and salting-out effect. Subsequently, hydrophobic doxorubicin (DOX) loaded TPGS micelles were likewise prepared and converted into DOX loaded hydrogel with the help of β-Glycerol phosphate disodium (β-GP). It was found that the amount of TPGS and β-GP in the solution considerably affected the gelation time and critical temperature. One of the formulations containing 4 wt% TPGS and 15 wt% β-GP was selected due to its appropriate gelation time and temperature for subcutaneously injection. Pristine and drug-loaded TPGS hydrogels were explored for their potential values in clinic applications. Derived from the bioactivity of TPGS, the pristine TPGS hydrogel exhibited a certain tumor inhibiting efficiency comparable to the DOX-containing formulations. And the efficiency of DOX-loaded TPGS hydrogels were dosage-dependent and superior to systemically administrated free DOX, which demonstrated a synergistic effect between DOX and TPGS hydrogel. In short, this study developed a multifunctional injectable hydrogel and provided a new synergetic strategy for tumor therapy.

Micellization, aggregation, and gelation of polystyrene-block-poly(ethylene oxide) in cosolvents added with hydrochloric acid

The micellization, aggregation, and gelation of the polystyrene-block-poly(ethylene oxide) block copolymer in solutions were quantitatively analyzed by small-angle X-ray scattering. The content and concentration of added hydrochloric acid influence the micellization, aggregation, and gelation of a polystyrene-block-poly(ethylene oxide) block copolymer in tetrahydrofuran/water and dimethylformamide/water cosolvents added with hydrochloric acid. The polystyrene-block-poly(ethylene oxide) block copolymer forms spherical micelles with screened Coulomb repulsions when dispersed in tetrahydrofuran/water cosolvents added with hydrochloric acid. The screened Coulomb repulsion arises from the poly(ethylene oxide) shells bound with protonated water and surrounded by unbalanced negative charges. If excessive water is introduced from hydrochloric acid, the non-solvent quality of tetrahydrofuran/water cosolvent predominantly causes aggregation of spherical micelles. Such screened Coulomb repulsions do not form for core-shell cylinders dispersed in dimethylformamide/water added with hydrochloric acid. Hydrochloric acid tends to form complexes with dimethylformamide. The length of core-shell cylinders can increase with the increased content of hydrochloric acid. Long core-shell cylinders favorably form three-dimensional networks through inter-cylinder entanglement. Furthermore, the absence of screened Coulomb repulsions makes entangled cylinders more compact to strongly trap the liquid phase. Thus, gels occurred in dimethylformamide/water cosolvents with added hydrochloric acid. Nevertheless, the content of added hydrochloric acid should be finely controlled. Adding a large amount of hydrochloric acid prohibits network formation and instead favors kinetically trapped rigid cylinders. This study has demonstrated that finely controlling solvent quality by additives provides a physical design strategy for fabricating cylindrical micelles with tunable properties in solutions. This should offer the fundamental understanding of self-assembly for potential applications of block copolymer micelles.

Influence of electrolytes on the structural and viscosity properties of mixed anionic–nonionic–zwitterionic surfactants in detergent formulations

AbstractCleaning products have a global market of around $33 billion in 2020 and play an essential role in daily life, providing consumers with important public health benefits. Surfactants are the main ingredients of cleaning products and they can effectively remove dirt, germs, and other contaminants from surfaces. Understanding the role of each surfactant class in a detergent formulation and their interaction with NaCl is of utmost importance for formulating efficient and sustainable cleaning products. This paper describes the study of ternary surfactant systems consisting of surfactants (sodium lauryl ether sulfate, alkyl polyglycoside, or betaine, three of the most commonly used surfactants in detergent formulations), water, and NaCl. The effects of concentration on critical micelle concentration, aggregate size, and rheological behavior were evaluated by dynamic light scattering and rheology techniques.

Analytical modeling of micelle growth. 5. Molecular thermodynamics of micelles from zwitterionic surfactants

HypothesisThe critical micelle concentration, aggregation number, shape and length of spherocylindrical micelles in solutions of zwitterionic surfactants can be predicted by knowing the molecular parameters and surfactant concentrations. This can be achieved by upgrading the quantitative molecular thermodynamic model with expressions for the electrostatic interaction energy between the zwitterionic dipoles and micellar hydrophobic cores of spherical and cylindrical shapes. TheoryThe correct prediction of the mean micellar aggregation numbers requires precise calculations of the free energy per molecule in the micelles. New analytical expressions for the dipole electrostatic interaction energy are derived based on the exact solutions of the electrostatic problem for a single charge close to a boundary of spherical and cylindrical dielectric media. The obtained general theory is valid for arbitrary ratios between dielectric constants, radii of spheres and cylinders, positions, and orientations of dipoles. FindingsThe detailed numerical results show quantitatively the effects of the micelle curvature and dielectric properties of the continuum media on the decrease of the dipole electrostatic interaction energy. Excellent agreement was achieved between the theoretical predictions and experimental data for the critical micelle concentration, size and aggregation number of zwitterionic surfactant micelles. This study can be extended to mixed micelles of zwitterionic and ionic surfactants in the presence of salt to interpret and predict the synergistic effect on the rheology of solutions.

Biochemical, microbiological, and structural evaluations to early detect age gelation of milk caused by proteolytic activity of Pseudomonas fluorescens

Heat–stable peptidase AprX, released by Pseudomonas species in raw milk during cold storage, can cause gelation of UHT milk since it is able to split caseinomacropeptides (CMPtot) from κ-casein, so inducing aggregation of casein micelles. Identifying raw milk susceptibility to gelation would allow UHT milk manufacturers to select appropriate processing conditions or give the milk a different destination. Two approaches, i.e., detection of free CMPtot and evidence of casein aggregates, were evaluated as possible indicators for early detecting milk destabilization. With this aim, microfiltered milk was inoculated with a P. fluorescence strain and incubated at either 4 or 25 °C. The presence of CMPtot was detected using capillary electrophoresis after 96 and 24 h at the two temperatures, respectively, when milk also became heat unstable and small flocks of protein appeared. Confocal laser scanning microscopy evidenced initial aggregates of casein micelles after 48 and 24 h at 4 and 25 °C, respectively. Keeping the milk at 25 °C/24 h could be a useful condition to accelerate milk destabilization. Despite the similar timing of instability detection, presence of CMPtot was the only trait specific for AprX activity.

Hybrid Arborescent Polypeptide-Based Unimolecular Micelles: Synthesis, Characterization, and Drug Encapsulation.

This paper reports novel hybrid arborescent polypeptides based on poly(γ-benzyl l-glutamate)-co-poly(γ-tert-butyl l-glutamate)-g-polysarcosine [P(BG-co-Glu(OtBu))-g-PSar]. The synthesis is launched by ring-opening polymerization (ROP) of N-carboxyanhydride of γ-benzyl l-glutamate (BG-NCA) and γ-tert-butyl l-glutamate (Glu(OtBu)-NCA) to synthesize a random copolymer P(BG-co-Glu(OtBu)) serving as a precursor for the arborescent system, followed by deprotection of the tert-butyl (tBu) groups to afford free COOH moieties serving as coupling sites. Two copolymerization reactions were carried out to afford the side chains. One type of side chain was a random copolymer P(BG-co-Glu(OtBu)), while the other type was a triblock copolymer PGlu(OtBu)-b-PBG-b-PGlu(OtBu). The peptide coupling reactions were conducted between the COOH moieties on the precursor and the terminus amine on the chain end of the P(BG-co-Glu(OtBu)) random copolymer or the PGlu(OtBu)-b-PBG-b-PGlu(OtBu) triblock copolymer to obtain G0 polymers. Afterward, hydrolyzing the tBu moieties of the G0 substrates yielded randomly functionalized G0 and end-functionalized G0. Randomly functionalized G0 was used as a substrate for the next generation G1 (randomly functionalized and end-functionalized G1 after deprotection) or coated with polysarcosine (PSar) to gain G0-g-PSar. The G0 substrate prepared with the triblock copolymer PGlu(OtBu)-b-PBG-b-PGlu(OtBu) was only grafted with PSar after deprotection, resulting in G0-eg-PSar. Depending on the functionality mode of the G1 substrate, the PSar coating yielded two different graft polymers, G1-g-PSar and G1-eg-PSar, for randomly functionalized and end-functionalized G1, respectively. The PSar hydrophilic shell was decorated with the sequence of (arginine, glycine, and aspartic acid) tripeptides (RGD) as a targeting ligand to improve the potentiality of the arborescent unimolecular micelles as drug carriers. Preparative size exclusion chromatography (SEC) was used to fractionate these complex macromolecular architectures. Nuclear magnetic resonance (NMR), Fourier-transform infrared (FTIR), Raman spectroscopy, and SEC were used for molecular characterization of all intermediate and final products and dynamic light scattering (DLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM) for micellar characterization. A comparison between randomly grafted (g) and end-grafted (eg) unimolecular micelles demonstrates that the former has an undefined core-shell structure, unlike its end-grafted analog. In addition, this study has proved that decoration of the shell with RGD contributed to avoiding micelle aggregation but limited chemotherapy agent encapsulation. However, more than their naked analog, the sustained release was noticeable in decorated micelles. Doxorubicin was utilized as a chemotherapy model, and loading was achieved successfully by physical entrapment.

Application of surfactants for better tomorrow

Surfactants are the important class of amphiphilic species, which consists of both hydrophilic as well as hydrophobic part. They are characterized by some important properties like critical micelle concentration (CMC), charge, hydrophile-lypophile balance (HLB), aggregation, and chemical structure, which make them good emulsifying, dispersing and foaming agents. Presently, the global demand of the surfactants is on the peak due to their increased applications in detergents, paints, food emulsion, biotechnological processes, biosciences, pharmaceuticals, cosmetic products, etc. In order to prevent Corona pandemic disease, WHO and other regulatory authorities have recommended frequent use of soaps and sanitizers that makes surfactants an important class of species to be explored more in terms of their applications.

Lateral growth of cylinders

The precise control of the shape, size and microstructure of nanomaterials is of high interest in chemistry and material sciences. However, living lateral growth of cylinders is still very challenging. Herein, we propose a crystallization-driven fusion-induced particle assembly (CD-FIPA) strategy to prepare cylinders with growing diameters by the controlled fusion of spherical micelles self-assembled from an amphiphilic homopolymer. The spherical micelles are heated upon glass transition temperature (Tg) to break the metastable state to induce the aggregation and fusion of the amorphous micelles to form crystalline cylinders. With the addition of extra spherical micelles, these micelles can attach onto and fuse with the cylinders, showing the living character of the lateral growth of cylinders. Computer simulations and mathematical calculations are preformed to reveal the total energy changes of the nanostructures during the self-assembly and CD-FIPA process. Overall, we demonstrated a CD-FIPA concept for preparing cylinders with growing diameters.

Free energy calculations in associative polymers using molecular dynamics

ABSTRACT In this work, equilibrium molecular dynamics is used to predict the change in the Helmholtz free energy () for solutions of associative polymers of the telechelic type. is calculated using the thermodynamic integration method, wherein molecular chains are simulated in a coarse-grain scale within an NVT ensemble. Simulations take place in the concentration interval , such that aggregate formation is possible. The initial configuration is that of dispersed free chains; the increase of interactions among stickers signals the onset of the micelle formation process. The solution with high concentration experiences substantial micelle aggregation despite little conformation changes. Therein, transient networks among micellar flowers are formed. The decrease in free energy is related to the formation of aggregates to achieve stability. When solutions are thermodynamically stable, the free energy and configurational entropy decrease and increase non-linearly with concentration, respectively. Below critical micellar concentration, this behaviour is associated with a step-by-step process along which the sticker groups gather to form the first thermodynamically stable aggregate. Above critical micellar concentration, the most probable distribution increases with concentration, therefore, free energy decreases with increasing aggregates that form the network.

How Temperature Rise Can Induce Phase Separation in Aqueous Biphasic Solutions

Ionic-liquid-based acidic aqueous biphasic solutions (AcABSs) recently offered a breakthrough in the field of metal recycling. The particular mixture of tributyltetradecylphosphonium chloride ([P4,4,4,14]Cl), acid, and water presents the unusual characteristic of a lower solution critical temperature (LCST), leading to phase separation upon a temperature rise of typically a few tens of degrees. We address here the microscopic mechanisms driving the phase separation. Using small-angle neutron scattering, we characterized the spherical micelle formation in a binary ionic liquid/water solution and the micelle aggregation upon the addition of acid due to the screening of electrostatic repulsion. The increase in both the acid concentration and the temperature eventually leads to micelle flocculation and phase separation. This last step is achieved through chloride ion adsorption at the surface of the micelle. This exothermic adsorption compensates for the entropic cost, leading to a counterintuitive behavior, and may be generalized to a number of molecular systems with an LCST.

Reconstituted skim milk: effect of re-dilution after heating concentrated milk at different pH and temperatures

The change in particle size in milk is dependent on the concentration, pH and the temperature of heating. Many of the changes are attributed to a partial aggregation of the casein micelles during heating. κ-Casein dissociation and serum-phase whey protein levels increased with increasing milk concentration at each pH and temperature, whereas αS-casein/β-casein dissociation increased to a maximum at intermediate temperatures before decreasing and then increasing again. Small changes in non-sedimentable calcium and phosphate were observed. Casein micelle solvation decreased with increasing pH and milk concentration at temperatures above 80 °C. This decrease is related to the pH-dependent dissociation of κ-casein from the casein micelles and the extent of denatured whey protein in the serum phase. It is likely that the properties of milk could be manipulated by choosing appropriate milk concentrations pH and/or and heating conditions, even if the milk is subsequently diluted.

Surface mechanical behavior of water-spread poly(styrene)–poly(ethylene glycol) (PS–PEG) micelles at the air–water interface: Effect of micelle size and polymer end/linking group chemistry

Hypothesis:The surface mechanical properties of poly(styrene)-poly(ethylene glycol) (PS–PEG) micelles are influenced by the PEG corona structure. Changes in micelle aggregation number as well as changes in the PEG end group and linking group chemistry of the PS–PEG block copolymer are expected to alter PEG corona characteristics and therefore affect surface mechanical properties of the resulting micelle film. Experiments:Different sized micelles comprised of PS–PEG block copolymer chains were formulated by equilibrating micelles in different ratios of acetone/water mixtures and subsequently removing acetone using dialysis. Additionally, micelles of a similar size and PS–PEG molecular weight but slightly different chemistry were formulated. The micelles were characterized using dynamic light scattering (DLS), transmission electron microscopy (TEM), 1H NMR, surface pressure–area isotherms and Brewster angle microscopy (BAM). Findings:The reduction in micelle aggregation number results in the subsequent monolayer having higher compressibility moduli and bending stiffnesses and collapsing at lower surface pressures. Micelle hydrophobicity was shown to improve readsorption of micelles to interface after collapse. Analysis of Brewster angle microscopy images of out-of-plane wrinkle structures which formed upon monolayer collapse indicates the presence of continuous 1 nm thick PEG layer which allows micelle monolayers to bend under high compression.