共查询到11条相似文献,搜索用时 0 毫秒
1.
C. Holmberg 《Colloid and polymer science》1996,274(9):836-847
Two fractions of ethyl(hydroxy)ethyl cellulose, EHEC, and their interactions with sodium dodecyl sulphate, SDS, have been investigated. The effect of salt on these interactions was explored. The more hydrophobic fraction exhibits a cloud point (CP) of 30°C, and the more hydrophilic fraction has a CP around 65°C. The properties of the systems were studied by means of hydrodynamic (viscosity), equilibrium dialysis and cloud point measurements. Dye solubilization was used to obtain indications of cluster formation on the polymer backbone. The equilibrium dialysis shows a steep binding beginning at a critical surfactant concentration indicating a cooperative effect in the EHEC/SDS/water system. It is found that when the degree of binding is moderate and only 10–20% of the value at saturation, the specific viscosity effects occur and solutions containing high polymer concentrations pass a marked maximum in viscosity. It is shown that the maximum in viscosity and the collcoil interaction, expressed as Huggins constant,k
H, appear a composition with the same fractional amount of SDS adsorbed to both EHEC fractions. It was found that the onset of redistribution and increase in viscosity were shifted to higher SDS concentrations, although still below the normal CMC, for the EHEC fraction with a high CP. When small amounts of salt are present in the EHEC/SDS/water solutions, the CP curves develop a pronounced minimum at low SDS concentrations. The redistribution of SDS to the polymers starts immediately in the presence of salt, but the viscosity of the solutions is affected only in a very narrow composition interval. 相似文献
2.
The present investigation proves that in the interaction between an uncharged polymer and a negatively charged amphiphilic ion (surfactant) clusters are actually formed and it provides data for the cluster concentration and the cluster size and their variation with composition. The polymer bound cluster size increases after a certain critical surfactant concentration and passes through a maximum. This maximum cluster size decreases with decreasing polymer concentration and attains a limiting value at infinite dilution. For the highest polymer concentration the cluster size is close to the size of normal surfactant micelles. The cluster concentration was determined by a fluorescence quenching technique and the amount surfactant adsorbed to the polymer by dialysis equilibrium measurements. Combining these independent sets of data permits the cluster aggregation number to be unambiguously determined. Solubilization experiments indicate the possibility to regulate the amount solubilized by varying the polymer concentration. The molecular properties of the system are sensitively monitored by the variation in two vibronic peaks in the pyrene fluorescence emission spectrum which defines a hydrophobic index. Very good agreement is found between all three experimental methods. Finally, the model suggested is analyzed in terms of coil size and cluster-cluster distance. Depending upon the degree of adsorption saturation and the density of polymer segments in solution the interaction may switch from being intramolecular to becoming intermolecular. 相似文献
3.
The properties of the system EHEC/SDS/water in solution show considerable time dependence during several hours after preparation. The paper discusses various reasons for this time dependence. Similar time dependence in polymer solutions has been observed elsewhere. It is found that although the system properties vary, a true equilibrium is finally attained for all compositions. The most pronounced time dependence is shown in a region close to and above the CMC of a pure surfactant solution and for polymer concentrations at least equal to the critical overlap concentration. It is proposed that part of the explanation resides in the fact that in the solution preparation there appears intermediate states corresponding to high local polymer concentrations. Some quantitative aspects of the time dependence are also discussed. 相似文献
4.
The interaction between the nonionic water soluble polysaccharide hydroxypropylmethyl cellulose (HPMC) and the low molecular weight amphiphile sodiumdodecyl sulphate (SDS) has been studied by NMR1H-chemical shift measurements and by self-diffusion NMR measurements. The polymer concentration has been kept sufficiently dilute to avoid coil overlap and the SDS composition range goes from zero up to well above the normal CMC point. Although a different fraction was used, the present results agree well with previous results for the same system obtained by techniques other than NMR and show very clear break points that can be related to the polymer surfactant interaction. Furthermore, it can be inferred from the chemical shift measurements that the structure of the micellar clusters are similar whether polymer is present or not. From a combination of chemical shift and self diffusion measurements it is also found that neither the size nor the shape of the clusters seem to change significantly in the composition interval investigated. 相似文献
5.
V. Sovilj 《Colloid and polymer science》1998,276(4):328-334
The interaction between gelatin and ionic surfactant is relevant to many biological and industrial processes. Therefore,
knowledge of the mechanism of ionic surfactant–gelatin interaction is an important factor influencing practical application
of such systems.
In this paper, conductometric and potentiometric titrations were used to study the interaction of sodium dodecyl sulfate as
an anionic and cetyltrimethylammonium bromide as a cationic surfactant with gelatin solutions of different concentrations.
Titrations were carried out at 40 °C by adding surfactant to the gelatin solutions. The titration course was followed by measuring
specific conductance and pH changes.
On the basis of the titration curves the prevailing mechanisms of surfactant–gelatin interaction, as well as the characteristic
concentrations at which they are changed, were determined. From the linear relationship established between the characteristic
surfactant concentrations and gelatin concentration, maximal amount of surfactant bonded per gram of gelatin was calculated.
Received: 22 July 1997 Accepted: 11 December 1997 相似文献
6.
The effect of the addition of n-butanol (BuOH) and n-hexanol (HexOH) on the micellization of sodium dodecylsulfate (SDS) has been investigated using fluorescence quenching methods.
The binding constants were calculated using an expression which relates the total concentration of alcohols and the micelle
concentration. The values of K were 4.67 and 17.6 M-1 for BuOH/SDS and HexOH/SDS, similar to values obtained by other methods. The cmc of SDS decreases on addition of alcohols
and goes through a minimum for the BuOH/SDS system. Micellar aggregation numbers (N) were determined from linear plots of Ln (I
0/I) against [Quencher] at low alcohol concentrations. For 15 mM SDS, in the presence of BuOH the N values decrease on addition of alcohol up to 0.2 M. For HexOH, N can be assumed to be constant up to 4.8 mM, after which N decreases. The polarity of the micellar core containing alcohol was evaluated from the I
1/I
3 ratio of monomeric pyrene. The effect of addition of the alcohol causes a decrease in the I
1/I
3, which corresponds to a decrease in the polarity of the pyrene solubilization site.
Received: 28 October 1996 Accepted: 10 January 1997 相似文献
7.
The effects of adding 0.1 molal 1-butanol to the aqueous SDS system at 298.1 K and the aqueous PEO–SDS system at 298.1 and
283.1 K have been studied. NMR NOESY experiments on the PEO– SDS–1-butanol system in D2O were obtained. NMR self-diffusion experiments and measurements of NMR chemical shifts and specific conductivity were carried
out on the samples, i.e. on samples with PEO and without PEO. The addition of 1-butanol to an aqueous SDS–PEO system decreases
the critical aggregation concentration (c.a.c). Determination of the second critical concentration (c
2) depends on the method of measurements, i.e. the molecular species monitored. Conductivity measurements will give c
2 as the SDS concentration where free micelles (micelles not bound to the polymer) are formed. PEO self-diffusion measurements,
on the other hand, determine c
2 as the SDS concentration where the polymer is saturated with SDS. Both the c.a.c and the c
2 decrease upon 1-butanol addition. However, the c
2 value exhibits a larger decrease than the c.a.c value. Thus, the amount of polymer bound surfactant molecules decreases upon
addition of 1-butanol. Micellar solubilization of 1-butanol starts at c.a.c., but the solubilization capacity is low until
the surfactant concentration reaches c
2, where the increase in solubilization is significant. Thus, solubilization data can be used to detect c
2, the concentration where free micelles form.
Received: 21 July 1997 Accepted: 9 February 1998 相似文献
8.
1H NMR chemical shifts of solutions of the following cationic surfactants in D2O were determined as a function of their concentrations: cetyltrimethylammonium chloride, CTACl, a 1 : 1 molar mixture of
CTACl and toluene, cetylpyridinium chloride, CPyCl, cetyldimethylphenylam-monium chloride, CDPhACl, cetyldimethylbenzylammonium
chloride, CDBzACl, cetyldimethyl-2-phenylethylammonium chloride, CDPhEtACl, and cetyldimethyl-3-phenylpropylammonium chloride,
CDPhPrACl. Plots of observed chemical shifts versus [surfactant] are sigmoidal, and were fitted to a model based on the mass-action
law. Satisfactory fitting was obtained for the discrete protons of all surfactants. From these fits, we calculated the equilibrium
constant for micelle formation, K, the critical micelle concentration, CMC and the chemical shifts of the monomer, δmon and the micelle δmic. 1H NMR-based CMC values are in excellent agreement with those which we determined by surface tension measurements of surfactant
solutions in H2O, allowing for the difference in structure between D2O and H2O. Values of K increase as a function of increasing the size of the hydrophilic group, but the free energy of transfer per CH2 group of the phenylalkyl moiety from bulk water to the micellar interface is approximately constant, 1.9±0.1 kJ mol-1. Values of (δmic–δmon) for the surfactant groups at the interface, e.g., CH3–(CH2)15–N+(CH3)2 and within the micellar core, e.g., CH3–(CH2)15–N+ were used to probe the (average) conformation of the phenyl group in the interfacial region. The picture that emerges is
that the aromatic ring is perpendicular to the interface in CDPhACl and is more or less parallel to it in CDBzACl, CDPhEtACl,
and CDPhPrACl.
Received: 23 February 1996 Accepted: 29 August 1996 相似文献
9.
T. Ogasawara A. Nara H. Okabayashi E. Nishio C. J. O'Connor 《Colloid and polymer science》2000,278(11):1070-1084
The polymerization behavior of 3-aminopropyltriethoxysilane, a process initiated by water molecules, has been examined using
time-resolved near-IR and 2D near-IR correlation spectra. By deconvolution of the time-resolved near-IR spectra, the existence
of the component bands at 5189, 5265 and 5300 cm−1, whose intensities decrease markedly as the reaction proceeds, has been confirmed in the 5000–5400 cm−1 region. The band at 5189 cm−1 has been assigned to water molecules, while those at 5265 and 5300 cm−1 have been assigned to the strongly and weakly associated silanol groups, respectively. The kinetics of the hydrolysis of
the ethoxy groups and of the formation of a siloxane bond have been analyzed using the time-dependent integral intensities
of these three bands and the mechanisms of the reactions have been discussed. Evidence for this polymerization process is
also clearly evident in the 2D near-IR correlation spectra.
Received: 14 March 2000/Accepted: 15 May 2000 相似文献
10.
S. Yamaguchi 《Colloid and polymer science》1998,276(8):715-722
Phase behavior of water/hexaethyleneglycol dodecyl ether (C12EO6)/propanol/heptane system was investigated in a composition–temperature space (25–30 °C) at atmospheric pressure. A cone-like three-phase body consisting of aqueous (W), surfactant (Dp), and oil (O) phases is
formed in the two-phase body of Wm (aqueous micellar phase)+O at 30.0 °C. With decreasing temperature the three-phase body becomes thinner and finally disappears at a critical double end point
(CDEP) where the two critical end points of W and Dp phases are merged. The CDEP exists at about 26.2 °C (T
CDEP). The hydrophile–lipophile balance (HLB) of the mixed amphiphile changes towards lipophilic on addition of propanol. As a
result, the Wm phase separates into two phases W+Dp above the T
CDEP. Further addition reduces the lipophobicity of aqueous media (or the solvophobicity of the mixed amphiphile), and the W and
Dp phases are merged again. Below T
CDEP, since C12EO6 becomes much hydrophilic, the change of HLB lurks and a middle phase (Dp) cannot be observed.
Received: 19 June 1997 Accepted: 20 March 1998 相似文献
11.
Pablo A. Molina R. Steven Sikorski Jan H. Jensen 《Theoretical chemistry accounts》2003,109(3):100-107
The relationship between hydrogen bonding and NMR chemical shifts in the catalytic triad of low-pH α-chymotrypsin is investigated
by combined use of the effective fragment potential [(2001) J Phys Chem A 105:293] and ONIOM–NMR [(2000) Chem Phys Lett 317:589] methods. Our study shows that while the His57 Nδ1−H bond is stretched by a relatively modest amount (to about 1.060 ?) this lengthening, combined with the polarization due
to the molecular environment, is sufficient to explain the experimentally observed chemical shifts of 18.2 ppm. Furthermore,
the unusual down-field shift of Hɛ1 (9.2 ppm) observed experimentally is reproduced and shown to be induced by interactions with the C=O group of Ser214 as previously
postulated. The free-energy cost of moving Hδ1 from His57 to Asp102 is predicted to be 5.5 kcal/mol.
Received: 26 September 2001 / Accepted: 6 September 2002 / Published online: 21 January 2003
Contribution to the Proceedings of the Symposium on Combined QM/MM Methods at the 222nd National Meeting of the American
Chemical Society, 2001
Correspondence to: J. H. Jensen e-mail: jan-jensen@uiowa.edu
Acknowledgements. This work was supported by a Research Innovation Award from the Research Corporation and a type G starter grant from the
Petroleum Research Fund. The calculations were performed on IBM RS/6000 workstations obtained through a CRIF grant from the
NSF (CHE-9974502) and on supercomputers at the National Center for Supercomputer Applications at Urbana-Champaign. The authors
are indebted to Visvaldas Kairys for help with the CHARMM program, and to Daniel Quinn for many helpful discussions. 相似文献