Effects of temperature, salt, and deuterium oxide on the self-aggregation of alkylglycosides in dilute solution. 2. n-Tetradecyl-beta-D-maltoside

The effects of salt, temperature, and deuterium oxide on the self-aggregation of n-tetradecyl-beta-d-maltoside (C(14)G(2)) in dilute solution have been investigated by static light scattering, dynamic light scattering (DLS), small-angle neutron scattering (SANS), tensiometry, and capillary viscometry. SANS data show that the micelles can be described as relatively flexible polymer-like micelles with an elliptical cross section, at least at temperatures between 35 and 50 degrees C. The micelles grow in one dimension with increasing temperature and concentration. DLS and viscometry data suggest that the micelle size reaches a maximum at 60-70 degrees C. Comparison of DLS data in D(2)O and H(2)O shows that the micelles are larger in the former case. The effect of salt on the micelle size was found to follow the Hofmeister series. Thus, at constant salt concentration, the micelle size decreases according to the sequence SO(4)(2)(-) > Cl(-) > NO(3)(-) > I(-) > SCN(-), where I(-) and SCN(-) act as salting-in anions. From tensiometric data, it can be concluded that the temperature effects on micelle morphology do not correlate directly with those on unimer solubility. Rather, the temperature effect on the hydrocarbon chain conformation seems to be decisive for the micelle morphology. At constant temperature, on the other hand, the effect of salt and deuterium isotope is attributable to changes in effective headgroup area, including intermolecular interactions and water of hydration.     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. V

Non-isothermal thermal studies of the dehydration of the double salt hydrates of the type M(I)₂SO₄·M(II)SO₄·6H₂O and their D₂O analogues were carried out where M(I) = TI(I) and M(II) = Mg(II), Co(II), Ni(II), Cu(II) or Zn(II). Thermal parameters like activation energy, order of reaction, enthalpy change, etc. were evaluated from the analysis of TG, DTA and DTG curves. These thermal parameters were compared with those of other series, like NH₄(I), K(I), Rb(I) and Cs(I) studied earlier. On deuteration the nature of dehydration altered in the case of Tl₂Zn(SO₄)₂·6H₂O only. The thermal stability of the salt hyd discussed in relation to the salt hydrates of other series. The role of divalent cation on the thermal properties of dehydration of salt hydrates is also discussed. The order of reaction was always found unity. The values of ΔH were within ≈12–≈16 kcal mol^?1.     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. III

Dehydration of double salt hydrates of the type M(I)₂SO₄·M(II)SO₄·6H₂O where M(I)Rb(I) and M(II)Mg(II), Mn(II), Co(II), Ni(II), Zn(II) and Cu(II) has been studied by derivatograph. Thermal parameters like activation energy, order of reaction, enthalpy change etc. for each step of dehydration have been evaluated from the analyses of TG, DTA and DTG curves and these parameters are compared with corresponding salt hydrates of the NH₄ and K(I) series. These double salt hydrates are deuterated and studied similarly. Activation energies for the first step of dehydration of these salt hydrates increase with the increase of second ionisation potential of the central metal except for Mg. The nature of dehydration changes in the cases of double salt hydrates of Mg(II) and Ni(II) on deuteration. The order of reaction for each case of dehydration has been found to be unity. The enthalpy change per mole of water varies from 11.4 to 17 kcal.     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. VI

Non-isothermal studies of the dehydration of double salt hydrates of the type K₂AB₄·M(II)SO₄·6H₂O where AB₄BeF^2?₄ or SeO^2?₄ and M(II)Mg(II), Co(II), Ni(II), Cu(II) or Zn(II) and their D₂O analogues were carried out. Thermal parameters like activation energy, order of reaction, enthalpy change, etc., for each step of dehydration were evaluated from the analysis of TG, DTA and DTG curves. These parameters were compared with the corresponding double sulphate, i.e., K₂SO₄·M(II)SO₄·6H₂O and their D₂O analogues. The role of divalent cation on the thermal properties of dehydration of the salt hydrates and also the effect on the thermal properties due to deuteration were discussed. The order of reaction was always found unity. The values of ΔH were within ～11-～19 kcal mol^?1     

Effect of block length, polydispersity, and salt concentration on PEO-PDEAMA block copolymer structures in dilute solution

A series of poly(ethylene oxide)-block-poly(N,N-diethylaminoethyl methacrylate) (PEO-PDEAMA) block copolymers with relatively high polydispersity (1.36 < PDI < 1.96) have been prepared to determine the effect that polydispersity has on the self-assembly of amphiphilic block copolymers in dilute solution. Because monodisperse macroinitiators were used for the ATRP reactions, the polydispersity resides within the hydrophobic block. By adjusting the relative block lengths, spherical micelles, wormlike micelles, vesicles, or a precipitate is formed. Here, we show that relatively high polydispersity in the block copolymer does not preclude efficient self-assembly. We also discuss the effect of increasing the concentration of NaCl in the systems and show that this can result in a shift from one morphology to another. These shifts are reversible in some cases, but for PEO12-PDEAMA39, this method allows access to giant vesicles of between 500 nm and 1 microm in diameter.     

Preparation,characterization, and dilute solution properties of four-branched cage-shaped poly(ethylene oxide)

A four-branched cage-shaped poly(ethylene oxide) (4C-PEO) was prepared by a coupling reaction at very dilute condition between two kinds of end-functional four-armed star-shaped PEOs having amino and N-hydroxysuccinimide groups on their four ends, followed by purification using α-cyclodextrin (α-CD). The raw coupling reaction product shows multiple peaks including various high molecular weight multimeric products in size-exclusion chromatography measurements, while the product after α-CD purification shows a single peak eluted slightly earlier than the precursor star PEOs. Moreover, the final product obtained has about twice higher molecular weight than the star precursors. These results suggest that the targeted 4C-PEO polymer was successfully isolated through the α-CD purification. Small-angle neutron scattering (SANS) measurements of the final product in dilute solution were conducted, and its chain conformation was evaluated from the scattering profile in comparison with linear and star polymers. It has been found that the cage-shaped sample exhibits a distinct peak at lower q-region in the Kratky plot, which is in strong contrast with the linear counterpart. This result must be originated from the characteristic cage-shaped architecture, that is, having branched and closed-loop configurations, and hence having higher segmental density than simple linear and star molecules. In fact, the present experimental result is consistent with the recent Monte Carlo simulation reported by Uehara and Deguchi.     

Effects of multivalent salt addition on effective charge of dilute colloidal solutions

The effective charge Z* is often invoked to account for the accumulation of counterions near the colloid with intrinsic charge Z. Although the ion concentrations c(i) are not uniform in the solution due to the presence of the charged particle, their chemical potentials are uniform everywhere. Thus, on the basis of ion chemical potential, effective ion concentrations c(i)*, which can be experimentally measured by potentiometry, are defined with the pure salt solution as the reference state. The effective charge associated with the charged particle can then be determined by the global electroneutrality condition. Monte Carlo simulations are performed in a spherical Wigner-Seitz cell to obtain the effective charge of the colloid. In terms of the charge ratio alpha=Z*/Z, the effects of added salt concentration, counterion valency, and particle charge are examined. The effective charge declines with increasing salt concentration and the multivalent salt is much more efficient in reducing the effective charge of the colloidal solution. Moreover, the extent of effective charge reduction is decreased with increasing intrinsic charge for a given concentration of added salt. Those results are qualitatively consistent with experimental observations by electrophoresis.     

Effects of salt on the protonation in aqueous solution of triethylenetetramine and tetraethylenepentamine

Protonation constants of triethylenetetramine (trien) and tetraethylenepentamine (tetren) were determined, in NaCl aqueous solutions, at different ionic strengths, at 25°C, using the the pH-metric technique. The behavior of protonation constants as a function of ionic strength can be explained by a model which takes into account the formation of the species AH _q Cl _p [A=amine; q=1...4, p=1,2 (trien); q=1...5, p=1.3 (tetren)].     

Light scattering characterization of thermodynamic interaction of polymers in dilute solution. Effect of experimental error and temperature

Interaction between non-identical polymer molecules in a dilute solution of a mixture of two polymers is quantitatively characterized by the interaction parameter A₂₄, which is the second virial coefficient for interaction of unlike species. The value of A₂₄ may be experimentally obtained by light scattering. The determination of A₂₄ is very sensitive to experimental error in the input data, particularly for mixtures in which one polymer is greatly in excess, and for mixtures of polymers having molecular weights differing by orders of magnitude. A slight rise in A₂₄ with temperature has been observed for solutions of mixtures of polystyrene and poly(methyl methacrylate) in diethyl malonate in the range 25–100 C. This change in A₂₄ reflects the increased mutual miscibility of the polymers in solution at elevated temperatures.     

Linear,branched and hyperbranched macromolecules in dilute solution

We report some theoretical results obtained for star polymers and dendrimers under different solvent conditions using the Gaussian self-consistent approach. The focus is mainly on the model assumptions and approximations, and on the results. We discuss the Θ state in terms of both the Θ temperature and the molecular size, and then we consider the good-solvent conditions also through the intramolecular dynamics.     

Properties of cellulose acetate in solution. I. Light scattering,osmometry, and viscometry on dilute solutions

Light-scattering, osmotic pressure, and viscometric studies on fractions of cellulose acetate (degree of substitution 2.45) in three solvents are described. The data yield the dependence of the mean-square radius of gyration 〈s²〉, the second virial coefficient Γ₂, and the intrinsic viscosity [η] on molecular weight M and temperature. The results are interpreted to show that excluded volume effects on 〈s²〉 are negligible, even though Γ₂ is large and dΓ₂/dT is positive. The large experimental value of d In [η]/d In M is interpreted in terms of partial draining effects. Data on 〈s₂〉 and [η] for other cellulose esters in the literature are similarly interpreted. Significant aggregation found in solutions of cellulose acetate in many solvents is discussed.     

Kinetics and mechanism of hydration of ethylene oxide in dilute solution in the presence of Wofatit KPS catalyst

The kinetics of catalytic ethylene oxide hydration in dilute solution and in the presence of Wofatit KPS cation exchange resin has been studied. On the basis of kinetic studies it was found that the mechanism of catalytic action does not differ from homogeneous acid catalysis. Taking into consideration the kinetic isotope effect, an A-2 type mechanism of hydration in the presence of Wofatit KPS catalyst containing 8% divinylbenzene (DVB) was suggested.

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Wofatit KPS. , - . , A-2 Wofatit KPS, 8% ().

     

Effects of solvents on the crystallization of dilute poly(ethylene oxide) solutions

The crystallization kinetics of a poly(ethylene oxide) sample with molecular weight of 20 000 was studied in dilute solutions ofn-propanol,n-butanol andn-pentanol by dilatometric methods. The value of the Avrami exponent was observed to change with crystallization temperature in poorer solvents. The temperature coefficient of overall rate was analyzed according to the theory developed for polymer-diluent mixtures. Statistical analysis of data pertinent to overall rate temperature coefficient showed that the end surface free energy _en changes with the thermodynamic quality of the solvent. This is considered to be attributed to the loss in flexibility of polymer chains due to the intramolecular association displayed by poly(ethylene oxide) in its solutions of poor solvents.     

Chemical modification of polynorbornene. I. Sulfonation in dilute solution

The sulfonation of dilute solutions of polynorbornene (PN) in CCl₄ has been carried out using SO₃–triethylphosphate complexes of various stoichiometries dissolved in dichloroethane (DCE) or trifluoro-trichloro-ethane (TTE). This leads to an electrophilic substitution, with very few side reactions, yielding high sulfonation ratios (ca. 85%). The initial reaction is first order in both reactants (PN and SO₃) and has an activation energy of 17.5 kJ mol^?1. The reaction becomes diffusion-controlled after ca. 30 min at room temperature due to the precipitation of the partially sulfonated polymer. The initial rate is almost independent of the isomeric structure (cis or trans) and the molecular weight of the polymer, as well as on the stoichiometry of the SO₃–TEP complex; it is higher when TTE is used as solvent. The final sulfonation ratio is strongly dependent on the concentration of SO₃ and seems to be controlled by the conditions of diffusion inside the precipitated solid.     

The primary electroviscous effect,free solution electrophoretic mobility,and diffusion of dilute prolate ellipsoid particles (minor axis = 3 nm) in monovalent salt solution

The principal objective of the present work is the modeling of the primary electroviscous effect of charged prolate ellipsoid models of low axial ratio. Other transport properties examined include (free solution) electrophoretic mobilities and translational diffusion constants. A numerical boundary element method is employed to solve the coupled Poisson, low Reynolds number Navier-Stokes, and ion transport equations. The methodology is first applied to the primary electroviscous effect of spheres with a centrosymmetric charge distribution and excellent agreement with independent theory is obtained. Specific model studies are also carried out for prolate ellipsoid models with axial ratios less than 4 and a minor axis equal to 3 nm. Most studies are carried out in aqueous NaCl solution (2 to 50 mM) at 20 degrees C for a range of different particle charges, although limited results are also presented in LiCl and KCl solution. The primary electroviscous effect for weakly charged prolate ellipsoids is smaller than that of a sphere under similar conditions. These studies are also carried out at high absolute particle charge. A comparison is made between the primary electroviscous effect and electrophoretic mobilities of prolate ellipsoids and corresponding spherical models.     

The effect of pressure and temperature of self-diffusion coefficients in several concentrated deuterium oxide diamagnetic electrolyte solutions

The pressure dependences of the self-diffusion coefficients of deuterium oxide in 4.5m solutions of LiCl–D₂O and CsCl–D₂O (also 7m) and 3.06m CaCl₂–D₂O have been measured by the NMR spin-echo method at 30°C, 60°C, and 90°C. Shear viscosities and densities of these solutions have also been determined over the same range of experimental conditions. The experimental data show that the diffusion constantD decreases with the increasing structure-making ability of the electrolyte cation Ca⁺²>Li⁺. In contrast, the diffusion coefficient for D₂O in the 4.5 and 7m CsCl solutions is equal to that for pure D₂O at 30°C but lower at 60°C and 90°C. It has been found that the Stokes-Einstein equation relates well the diffusion coefficients to shear viscosity in these concentrated electrolyte solutions.     

Behaviour of cellulose tricarbanilate in dilute solution

Cotton linters were subjected to acid hydrolysis for various times and the products fully substituted to yield cellulose tricarbanilate samples ($\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{= 0·21 × 10}{}^6\text{to 1·1 × 10}{}^6$). Intrinsic viscosities were measured in dioxan and methyl ethyl ketone over a range of temperature. and also under θ-conditions. Mark-Houwink constants were found to be temperature dependent. Unperturbed dimensions and their temperature coefficient were derived by a number of procedures. The Flory-Huggins interaction parameter _%1 increased with temperature, thus indicating negative entropies and enthalpies of dilution. The results show that the environment is well displaced from the normal θ-state and is closer to the lower critical solution temperature, which was determined from cloud point measurements to be about 234° in dioxan.