Dynamic Light Scattering Data Research Articles

Effect of solvent-controlled aggregation on the intrinsic emission properties of PAMAM dendrimers

Solvent-induced aggregation and its effect on the intrinsic emission properties of amine, hydroxy and carboxylate terminated, poly(amidoamine) (PAMAM) dendrimers have been investigated in glycerol, ethylene glycol, methanol, ethylene diamine and water. Altering the solvent medium induces remarkable changes in the intrinsic emission properties of the PAMAM dendrimers at identical concentration. Upon excitation at 370 nm, amine terminated PAMAM dendrimer exhibits an intense emission at 470 nm in glycerol, ethylene glycol as well as glycerol–water mixtures. Conversely, weak luminescence is observed for hydroxy and carboxylate terminated PAMAM dendrimers in the same solvent systems. When the solvent is changed to ethylene diamine, hydroxy terminated PAMAM exhibits intense blue emission at 425 nm. While the emission intensity is varied when the solvent milieu is changed, excited state lifetime values of PAMAM dendrimers remain independent of the solvent used. UV–visible absorption and dynamic light scattering (DLS) experiments confirm the formation of solvent-controlled dendrimer aggregates in the systems. Comparison of the fluorescence and DLS data reveals that the size distribution of the dendrimer aggregates in each solvent system is distinct, which control the intrinsic emission intensity from PAMAM dendrimers. The experimental results suggest that intrinsic emission intensity from PAMAM dendrimers can be regulated by proper selection of solvents at neutral conditions and room temperature.

Unfolding and Refolding of Aspergillus niger PhyB Phytase: Role of Disulfide Bridges

The role of disulfide bridges in the folding of Aspergillus niger phytase pH 2.5-optimum (PhyB) was investigated using dynamic light scattering (DLS). Guanidinium chloride (GuCl) at 1.0 M unfolded phytase; however, its removal by dialysis refolded the protein. The thiol reagent tris(2-carboxyethyl)phosphine (TCEP) reduces the refolding activity by 68%. The hydrodynamic radius (R(H)) of PhyB phytase decreased from 5.5 to 4.14 nm when the protein was subjected to 1.0 M GuCl concentration. The active homodimer, 183 kDa, was reduced to a 92 kDa monomer. The DLS data taken together with activity measurements could indicate whether refolding took place or not in PhyB phytase. The correlation between molecular mass and the state of unfolding and refolding is a very strong one in fungal phytase belonging to histidine acid phosphatase (HAP). Unlike PhyA phytase, for which sodium chloride treatment boosted the activity at 0.5 M salt concentration, PhyB phytase activity was severely inhibited under identical condition. Thus, PhyA and PhyB phytases are structurally very different, and their chemical environment in the active site and substrate-binding domain may be different to elicit such an opposite reaction to monovalent cations.

Synthesis and aqueous solution properties of PAMAM dendron surfactants bearing a quaternary ammonium focal group and sugar terminal groups

Poly(amidoamine) (PAMAM) dendron surfactants bearing a focal quaternary alkyldimethylammonium group and terminal sugar groups (C m qb-G nLac; m = 12, 18, 22; n = 0, 1) have been synthesized. Solution properties of these dendron surfactants were investigated by means of static surface tension, electric conductivity, fluorescence probing with pyrene, dynamic light scattering (DLS) and static light scattering (SLS). In the surface tension profiles all C m qb-G nLac systems indicate a clear break point corresponding to the critical micelle concentration (cmc). The cmc decreases with increasing length of alkyl chain, from 8.2 × 10 −3 (C 12) to 4.5 × 10 −6 mol dm −3 (C 22) for G0Lac, from 1.0 × 10 −2 (C 12) to 3.7 × 10 −5 mol dm −3 (C 22) for G1Lac systems. Unlike conventional cationic surfactants, the surface tension at cmc (γ cmc) significantly increases with increasing alkyl chain length, associated with a slight increase in the molecular occupied area. Degree of counter ion (Br −) binding to the micelles is found to be very low due to an effective charge shielding by bulky non-ionic headgroups. In all C m qb-G nLac systems the micellar size decreases above a certain concentration. In the higher concentration regime, formation of micelles with a very small number of (at most a few) molecules is suggested from DLS data.

Nanoemulsions Prepared by a Two-Step Low-Energy Process

A simple low-energy two-step dilution process has been applied in oil/surfactant/water systems with pentaoxyethylene lauryl ether (C12E5), dodecyldimethylammonium bromide, sodium bis(2-ethylhexyl)sulfosuccinate, sodium n-dodecyl sulfate-pentanol, and hexadecyltrimethylammonium bromide-pentanol. Appropriate formulations were chosen for the concentrate to be diluted with water to generate oil-in-water (O/W) emulsions or nanoemulsions. For the system of decane/C12E5/water, bluish, transparent nanoemulsions having droplet radii of the order of 15 nm were formed, only when the initial concentrate was a bicontinuous microemulsion, whereas opaque emulsions were generated if the concentrate began in an emulsion-phase region. Nanoemulsions generated in the system decane/C12E5/water have been investigated both by dynamic light scattering (DLS) and contrast-variation small-angle neutron scattering (SANS). The SANS profiles show that nanodroplets exist as spherical core-shell (decane-C12E5) particles, which suffer essentially no structural change on dilution with water, at least for volume fractions phi down to 0.060. These results suggest that the nanoemulsion droplet structure is mainly controlled by the phase behavior of the initial concentrate and is largely independent of dilution. A discrepancy between apparent nanoemulsion droplet sizes was observed by comparing DLS and SANS data, which is consistent with long-range droplet interactions occurring outside of the SANS sensitivity range. These combined phase behavior, SANS, and DLS results suggest a different reason for the stability/instability of nanoemulsions compared with earlier studies, and here it is proposed that a general mechanism for nanoemulsion formation is homogeneous nucleation of oil droplets during the emulsification.

Studies on the interaction of gallic acid with human serum albumin in membrane mimetic environments

In this study the interaction between gallic acid and human serum albumin (HSA) in AOT/isooctane/water microemulsions was characterized for the first time using fluorescence quenching technique in combination with UV absorption spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, circular dichroism (CD) spectroscopy and dynamic light scattering (DLS) technique. In water–surfactant molar ratio ( ω o) = 20 microemulsions fluorescence data revealed the presence of one binding site of gallic acid on HSA and its binding constants ( K) were (1.18 ± 0.02) × 10 4, (1.13 ± 0.02) × 10 4, (1.03 ± 0.02) × 10 4, (0.95 ± 0.02) × 10 4, (0.87 ± 0.02) × 10 4 and (0.82 ± 0.03) × 10 4 M −1 at 282, 289, 296, 303, 310 and 317 K, respectively. The affinities in microemulsions were much higher than that in buffer solution. FT-IR and CD data suggested that the protein conformations were altered with the reductions of α-helices from 54–56% for free HSA in buffer to 40–41% for free HSA in microemulsion. After binding with gallic acid, the α-helices of HSA in microemulsion increased 2–7% for different drug–protein molar ratio. The thermodynamic functions standard enthalpy (Δ H 0) and standard entropy (Δ S 0) for the reaction were calculated to be −8.10 kJ mol −1 and 49.42 J mol −1 K −1. These results indicated that gallic acid bound to HSA mainly by hydrophobic interaction and electrostatic interaction in microemulsions. In addition, the displacement experiments confirmed that gallic acid could bind to the site I of HSA, which was approved by the molecular modeling study. Furthermore, the DLS data suggested that HSA may locate at the interface of the microemulsion and gallic acid could interact with them.

Characterization of Interaction Between Bergenin and Human Serum Albumin in Membrane Mimetic Environments

The interaction between bergenin and human serum albumin (HSA) in AOT/isooctane/water microemulsions was studied by fluorescence quenching technique in combination with UV absorption spectroscopy, circular dichroism (CD) spectroscopy and dynamic light scattering (DLS) technique. Fluorescence data in omega (o) 20 microemulsions revealed the presence of a binding site of bergenin on HSA and its binding constants (K) were 1.64 x 10(4), 1.44 x 10(4), 1.26 x 10(4) and 1.09 x 10(4) M(-1) at 289, 296, 303, and 310 K, respectively. The binding of bergenin with HSA in microemulsions was stronger than that in buffer solution. The alterations of protein secondary structure in the microemulsions in the absence and presence of bergenin compared with the free form of HSA in buffer were qualitatively and quantitatively analyzed by the evidence from CD spectra. Enthalpy and entropy changes for the reaction were calculated to be -14.45 kJ mol(-1) and 30.76 J mol(-1) K(-1). These results indicated that bergenin bound to HSA mainly by a hydrophobic interaction in microemulsions which was in agreement with the result of the molecular modeling study. The DLS data suggested that HSA may locate at the interface of the microemulsion and bergenin could interact with them.

Characterization of interaction between esculin and human serum albumin in membrane mimetic environments

In this study the interaction between esculin and human serum albumin (HSA) in AOT/isooctane/water microemulsions was studied for the first time using fluorescence quenching technique in combination with UV absorption spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, circular dichroism (CD) spectroscopy and dynamic light scattering (DLS) technique. Fluorescence data in ω o 20 microemulsions revealed the presence of the binding site of esculin on HSA and its binding constants at four different temperatures were obtained. The affinities in microemulsions are similar to that in buffer solution. The alterations of protein secondary structure in the microemulsions in the absence and presence of esculin compared with the free form of HSA in buffer were qualitatively and quantitatively analyzed by the evidence from CD and FT-IR spectroscopes. The displacement experiments confirmed that esculin could bind to the site I of HSA, which was in agreement with the result of the molecular modeling study. Furthermore, the DLS data suggested that HSA may locate at the interface of the microemulsion and esculin could interact with them.

Preparation and characterization of nanoparticles formed by chitosan–caseinate interactions

Intermacromolecular complexation between chitosan and sodium caseinate in aqueous solutions was studied as a function of pH (3–6.5), using absorbance measurements (at 600 nm), dynamic light scattering (DLS), and transmission electron microscopy (TEM). The chitosan–caseinate complexes formed were stable and soluble in the pH range 4.8–6.0. In this pH range, the biopolymers had opposite charges. At higher concentrations of chitosan (0.15 wt%), the soluble complexes associated to form larger particles. DLS data showed that, between pH 4.8 and 6.0, the particles formed by the complexation of chitosan and caseinate had sizes between 250 and 350 nm and these nanoparticles were visualized using negative staining TEM. Above pH 6.0, the nanoparticles associated to form larger particles, causing phase separation. Addition of NaCl increased the particle size. The pH dependence of the zeta potential of the mixture solutions was appreciably different from that of the pure protein and pure chitosan solutions.

An observation of the coexistence of multimers and micelles in a nonionic surfactant C 10E 4 solution by dynamic light scattering

The bulk phase of nonionic surfactant C 10E 4 solution was monitored by a dynamic light scattering (DLS) system at 20 °C in a narrow range of concentration near the cmc. Two particle aggregations were observed. The DLS data show (i) there exist premicellar multimers (or called sub-micelles) and (ii) micelles coexist with multimers. The C 10E 4 sub-micelles have a narrow size distribution with an averaged hydrodynamic diameter ( D h) of 1.35 nm. The D h of the micelles is around 10.5 nm at 1.0 × 10 −6 mol/mL and increases slightly with C 10E 4 concentration. It is illustrated from the DLS data that (i) at C = 0.78–0.82 μmol/mL, monomers and premicellar multimers coexist and (ii) at C = 0.84–0.92 μmol/mL, monomers + submicellar multimers + micelles coexist. At more elevated concentrations, only the signals from the micelles are detected by DLS.

Studies on the interaction of caffeic acid with human serum albumin in membrane mimetic environments

In this work, fluorescence quenching technique, Fourier transform infrared (FT-IR) spectroscopy, circular dichroism (CD) spectroscopy and dynamic light scattering (DLS) technique were used to gain the binding information of caffeic acid and human serum albumin (HSA) in AOT/isooctane/water microemulsions. The interaction of HSA with caffeic acid at 296, 303, and 310 K in ω 0 20 microemulsions was characterized by one binding site with the affinity constant K at (3.23 ± 0.01) × 10 4, (3.06 ± 0.03) × 10 4 and (2.82 ± 0.05) × 10 4 M −1, respectively. The affinities in microemulsions are much higher than that in buffer solution. The CD spectra and FT-IR spectra with qualitative and quantitative results proved that the protein secondary structure changed in the microemulsions in the absence and presence of caffeic acid compared with the free form of HSA in buffer. The binding process was exothermic and spontaneous, as indicated by the thermodynamic analyses. These data indicated that hydrophobic interaction played a major role in the binding of caffeic acid to HSA in microemulsions and electrostatic interaction can not be excluded. The displacement experiments confirmed that caffeic acid could bind to the site I of HSA, which was in agreement with the result of the molecular modeling study. Furthermore, the DLS data suggested that HSA may locate at the interface of the microemulsion and caffeic acid could interact with them.

Lysozyme dimer association: Similarities and differences compared with lysozyme monomer association

The protein with a molecular weight of 28.6 kDa in lysozyme solution, which has been recognized as a lysozyme dimer, was purified and its association was observed using time-resolved static light scattering and dynamic light scattering under the same buffer condition as that used in lysozyme monomer association. The chromatography results and SDS–PAGE analysis showed that the bonding state of each molecule in a dimer unit was not uniform, i.e., there were at least two kinds of bonds, strong and weak. Some of the weak-bonded dimmers dissociated to monomers (molecular weight: 14.3 kDa) in the SDS–PAGE process. The relative amount of weak-bonded dimers greatly affected the association kinetics. With a 99% pure dimer solution (1% monomers in SDS–PAGE), association proceeded in the same manner as that of a monomer solution: the Zimm-square plot had a concave shape with a maximum at a particular q 2 for apparent protein concentrations, up to 2.4 mg/mL. The dynamic light-scattering data showed clear bimodal (dimer and aggregate), distributions. With a 95% pure dimer solution, the association behavior drastically changed when the apparent concentration exceeded 2.0 mg/mL. The Zimm-square plot had a bending point at a low q 2, and two discrete lines fitted the plot. The particles in the solution were either oligomers or large aggregates, both of which had polydispersity distributions, and an amorphous phase formed from the aggregates. This was not observed for monomer association.

Structural characterization and low-resolution model of BJ-48, a thrombin-like enzyme from Bothrops jararacussu venom

Thrombin-like enzymes (TLEs) are important components of snake venoms due to their involvement in coagulopathies occurring on envenoming. Structural characterization of this group of serine proteases is of utmost importance for better understanding their unique properties. However, the high carbohydrate content of some members of this group prevents successful crystallization for structural determination. Circumventing this difficulty, the structure of BJ-48, a highly glycosylated TLE from Bothrops jararacussu venom, was studied in solution. At pH 8.0, where the enzyme displays maximum activity, BJ-48 has a radius of gyration ( Rg) of 37 Å and a maximum dimension ( D max) of 130 Å as measured by small-angle X-ray scattering (SAXS) and a Stokes radius (SR) of 50 Å according to dynamic light scattering (DLS) data. At the naturally more acidic pH (6.0) of the B. jararacussu venom BJ-48 behaves as a more compact particle as evidenced by SAXS ( R g = 27.9 Å and D max = 82 Å) and DLS (SR = 30 Å) data. In addition, Kratky plot analysis indicates a rigid shape at pH 8.0 and a flexible shape at pH 6.0. On the other hand, the center of mass of intrinsic fluorescence was not changed while varying pH, possibly indicating the absence of fluorescent amino acids in the regions affected by pH variation. Circular dichroism experiments carried out with BJ-48 indicate a substantially random coiled secondary structure that is not affected by pH. Low-resolution model of BJ-48 presented a prolate elongated shape at pH 8.0 and a U-shape at 6.0. BJ-48 tertiary structure at pH 6.0 was maintained on heating up to 52 °C and was completely lost at 75 °C. The possible existence of two pH-induced folding states for BJ-48 and its importance for the biological role and stability of this enzyme was discussed.

Adsorption and micellization behavior of novel gluconamide-type gemini surfactants

The adsorption and micellization behavior of novel sugar-based gemini surfactants ( N , N ′ -dialkyl- N , N ′ -digluconamide ethylenediamine, Glu( n)-2-Glu( n), where n is the hydrocarbon chain length of 8, 10 and 12) has been studied on the basis of static/dynamic surface tension, fluorescence, dynamic light scattering (DLS) and cryogenic transmission electron microscope (cryo-TEM) data. The static surface tension of the aqueous Glu( n)-2-Glu( n) solutions measured at the critical micelle concentration (cmc) is observed to be significantly lower than that of the corresponding monomeric surfactants. This suggests that the gemini surfactants, newly synthesized in the current study, are able to form a closely packed monolayer film at the air/aqueous solution interface. The greater ability in the molecular association is supported by the remarkably (approximately 100–200 times) lower cmc of the gemini surfactants compared with the corresponding monomeric ones. With a combination of the fluorescence and DLS data, a structural transformation of the Glu( n)-2-Glu( n) micelles is suggested to occur with an increase in the concentration. The cryo-TEM measurements clearly confirm the formation of worm-like micelles of Glu(12)-2-Glu(12) at the concentration well above the cmc.

DNA packaging in water solutions induced by polylysine and spermidine

The conformation properties of the DNA molecule complexed with polylysine (PLL) and spermidine (Spd) were studied by circular dichroism (CD), ultraviolet spectrophotometry, dynamic light scattering (DLS), viscosimetry, and dynamic birefringence. Experimental data suggest that when the concentration ratio of the monomer residues of polylysine and DNA (N/P) in moles is smaller than unity, the viscosity changes but slightly, whereas when N/P > 1, it abruptly drops to solvent viscosity. This is accompanied by changes in optical anisotropy and in the circular dichroism spectra of DNA. DLS data indicate that for N/P > 1, compact discrete particles are formed.

Combined NMR, SAXS, and DLS Study of Concentrated Clear Solutions Used in Silicalite-1 Zeolite Synthesis

Concentrated clear solutions, as used for the preparation of Silicalite-1 zeolite, were synthesized from tetrapropylammonium hydroxide, tetraethylorthosilicate, and water. The solutions were analyzed using three techniques: quantitative 29Si NMR, synchrotron small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS). 29Si NMR showed the coexistence of silicate oligomers and particles. For the first time, both fractions were analyzed simultaneously, providing a global, quantitative description of the clear solution microstructure. The SAXS patterns, typical of interacting particles, could be used together with the 29Si NMR deduced particle volume fraction to estimate a particle size. A careful analysis of DLS data of the dynamics of the suspensions revealed the occurrence of two diffusive processes. The faster process is a collective particle diffusion. The slower process corresponds to the particle self-diffusion and is present because of the presence of polydispersity in size, shape, and/or surface charge. The self-diffusion coefficient provides a means to estimate the equivalent hydrodynamic radius. The observations hence reveal a complex, polydisperse mixture of particles present at the onset of the Silicalite-1 zeolite formation. Implications on the proposed zeolite formation mechanisms are briefly discussed.

Compressibility, isothermal titration calorimetry and dynamic light scattering analysis of the aggregation of the amphiphilic phenothiazine drug thioridazine hydrochloride in water/ethanol mixed solvent

Thioridazine hydrochloride is a drug used in treatment of mental illness that shows side effects. Therefore, it is interesting to study the change of the physico-chemical properties of the drug in different environments to understand the mechanism of action of the drug. Thioridazine can be considered as a hydrotrope if we considered that the term comprise hydrophilic and hydrophobic moieties that form aggregates by a stacking mechanism as it is the case of all the phenothiazine tranquillizing drugs. The association properties of the amphiphilic phenothiazine drug thioridazine hydrochloride were investigated by density, ultrasound, isothermal titration calorimetry and dynamic light scattering (DLS), yielding values of the critical concentration, adiabatic apparent compressibilities and hydrodynamic radius. The DLS data were analyzed according to the treatment of the Derjaguin, Landau, Verwey and Overbeek (DLVO) theory to study the stability of the system. The aim of the study is to obtain information about the physico-chemical characterization of the drug in aqueous solution and the effect of ethanol on the aggregate stability of this amphiphilic drug. The phenothiazine tranquillizing drugs have interesting association characteristics that derive from their rigid, tricyclic hydrophobic groups.

Preparation and characterization of monocaprate nanostructured lipid carriers

Solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) are potential drug delivery systems based on solid lipids. Although both carrier types are based on solid lipids, SLN consist of pure solid lipids while NLC are made of a solid matrix entrapping liquid oil. In the present paper, aqueous dispersions of SLN and NLC were successfully prepared by an oil-in-water microemulsion technique using monocaprate (MC) as the solid lipid, medium chain triglyceride (MCT) as the liquid oil and polyethylene glycol sorbitan monooleate (Tween 80) as the emulsifier. The present work aimed to modify the inner structure of an SLN by inducing liquid oil into the system to form an NLC, and then to investigate these new carriers in detail. Several methods including dynamic light scattering (DLS), environmental scanning electron microscopy (ESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectra were applied to characterize the particle size, morphology and structure of the NLC and SLN. DLS data showed that the average diameters of the SLN were ∼42 nm and the diameters of the NLC ranged from ∼25 to ∼120 nm. All samples had polydispersity indexes about 0.27. Using ESEM and TEM, SLN and NLC were observed to be nearly spherical particles. XRD, DSC and FTIR measurements revealed that imperfect crystallization occurred in the inner core of the NLC particles. The results suggest that nanostructured lipid carriers can be produced by this microemulsion method, and incorporation of the liquid oil into the SLN may affect their encapsulation capacity.

Time evolution of crystallization phase of lysozyme protein in aqueous salt solution as studied by scattering techniques

Formation of protein crystallization in 1 wt% lysozyme in aqueous solution has been studied as a function of salt (KBr) concentration. The onset and the rate of crystallization in this protein solution strongly depend on the KBr concentration. It is found, while the presence of 0.4 M KBr starts producing crystals in 1 h, it takes about 120 h for 0.2 M KBr. The rate of protein crystallization has been studied by small-angle neutron scattering (SANS) and dynamic light scattering (DLS) in 1 wt% lysozyme solution in presence of three different KBr concentrations 0.3, 0.26 and 0.24 M, which show the start of crystallization at about 1.5, 3 and 5 h, respectively. Measurements have been performed for every half an hour from freshly prepared protein sample up to 72 h. Both time-evolved SANS and DLS data have been used to calculate the fraction of crystallization as a function of time. The variation of crystallization with time shows three distinguished regions: (i) prior to and the beginning of crystallization, which shows no significant change in the crystallization, (ii) growth region showing a significant increase in the crystallization with time and (iii) saturation region. These three regions have been found to be strongly depending on the start of the crystallization as controlled by the salt concentration.

Softening of the stiffness of bottle-brush polymers by mutual interaction

We study bottle-brush macromolecules in a good solvent by small-angle neutron scattering (SANS), static light scattering (SLS), and dynamic light scattering (DLS). These polymers consist of a linear backbone to which long side chains are chemically grafted. The backbone contains about 1600 monomer units (weight average) and every second monomer unit carries side chains with approximately 60 monomer units. The SLS and SANS data extrapolated to infinite dilution lead to the form factor of the polymer that can be described in terms of a wormlike chain with a contour length of 380 nm and a persistence length of 17.5 nm. An analysis of the DLS data confirms these model parameters. The scattering intensities taken at finite concentration can be modeled using the polymer reference interaction site model. It reveals a softening of the bottle-brush polymers caused by their mutual interaction. We demonstrate that the persistence decreases from 17.5 nm down to 5 nm upon increasing the concentration from dilute solution to the highest concentration (40.59 gl) under consideration. The observed softening of the chains is comparable to the theoretically predicted decrease of the electrostatic persistence length of linear polyelectrolyte chains at finite concentrations.

DLS and AFM Studies on the Cluster Evolution of Organically Modified Silica Gels Catalyzed by a Super Strong Acid

Time evolution of cross-linking clusters prepared by the sol−gel method was investigated by dynamic light scattering (DLS) and atomic force microscopy (AFM). The samples were prepared by the sol−gel synthesis of 1,8-bis(triethoxysilyl)octane (Tes-Oct) in the presence of phosphotungstic acid (PWA) as a super strong acid. The reaction batches were quenched at various reaction times, followed by dilution with a large amount of the solvent. DLS and AFM techniques simultaneously revealed that there exists a maximum cluster size, Rh and rAFM, respectively, for a specific PWA concentration. The information on the clusters density, ρcluster = (rAFM/Rh)3, generated during the reaction process was obtained by systematically comparing the DLS data obtained in the swollen state to the AFM data measured in the shrunken state of the cross-linked clusters. It was found that not only the cluster size but also ρcluster exhibited a maximum for [PWA]/[Tes-Oct] = 0.10 near the gel point of the Tes-Oct clusters. Since PWA is ...