Temperature-responding physical hydrogels are promising materials as injectable drug delivery carriers which could hold useful bioactive materials inside the polymer networks for further controlled releases. Aimed at desired qualities at body temperature, those gel characteristics need to be adjusted carefully. In this point of view, surfactant is one of the useful molecules to be used by simple formulations without harmful chemical reactions. In this study, thermothickening of amphiphilic nonionic polyphosphazene solution is modified by anionic and cationic surfactants with different alkyl chains and counter-ions. Specified in the thermothickening system, a maximum viscosity (ηmax) and a temperature at that point (Tmax) are changed independently reflecting unique intermolecular interactions. At low concentration (1–9 mM) of the added surfactant, the ηmax is maximized at 3 mM surfactant regardless of the surfactant type while the Tmax is increased continuously along with the surfactant concentration. From a kinetic point of view, this 3 mM surfactant at the maximized ηmax reflects a polymer-dominating interaction and highly favorable polymer–surfactant interaction with a low selectivity in the surfactant type. However, the magnitude of the maximum viscosity (ηmax) is dependent on the surfactant tail, which reflects the lifetime and the strength of the hydrophobic domains of the polymer network affected by the surfactants. Meanwhile, the magnitude of the Tmax depended on the surfactant head group, which means the interfacial tension of the polymer solutions changed by the surfactants. At high concentration (10 and 30 mM) of the cationic surfactants added to the polymer solutions with two different viscosities, the cationic surfactants are supposed to interact either with the hydrophobic parts of the aggregated polymer with high viscosity or on the backbone of the less- or non-aggregated polymer with low viscosity.Ionic surfactants change the thermothickening of the amphiphilic nonionic polyphosphazene solution in a unique tail- or head-dependent way. Moreover, the concentration of the added surfactants and the association pattern of the pure polymer solutions are also crucial for the thermothickening phase behaviors. Temperature-responsive polyphosphazenes in this work exhibit unique and controllable interactions with ionic surfactants. 相似文献
This article deals with the influence of micelles of the anionic surfactant sodium dodecyl benzene sulfonate (SDBS) on the Belousov? Zhabotinsky (B? Z) oscillating reaction catalyzed by a tetraazamacrocyclic copper(II) complex [CuL](ClO4)2, an enzyme‐like catalyst (L=5,7,7,12,14,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradeca‐4,11‐diene). Unlike the classical B? Z oscillator in which malonic acid is usually used as a substrate, malic acid (an intermediate in the Krebs cycle) is involved in this oscillating system. Experiments reveal that formation of the SDBS micelles markedly affects the behavior of the oscillating reaction. It is found that there is a linear relationship between the change in the oscillation amplitude (ΔA) and the concentration of SDBS, whereas the change in the oscillation period (ΔT) is linearly proportional to the SDBS concentration. The most likely mechanism that involves the formation of the SDBS micelles and the effects of the micelles on the oscillating chemical system can be rationalized by assuming that the SDBS micelles are so negatively charged that they attract more [CuL]3+ than [CuL]2+. This hypothesis was confirmed by UV/VIS spectrophotometric measurements of a constant concentration of [CuL](ClO4)2 in different concentrations of SDBS; as the SDBS concentration increased, the absorbance of [CuL](ClO4)2 increased, while the maximum absorption wavelength for [CuL](ClO4)2 remained at 502 nm. 相似文献
Shear viscosity deviations Δη have been investigated by using density (ρ) and kinematic viscosity (ν) measurements for isobutyric acid + water (IBA + W) mixtures over the entire range of mole fractions at atmospheric pressure
and at two temperatures (301.15 and 315.15 K). This study extends the temperature range from the five other temperatures investigated
in a previous work, 1.055 K≤(T−Tc)≤14.055 K, both far from and close to the critical temperature. This system exhibits very large positive values of Δη due to increased hydrogen bonding interactions and the correlation length between unlike molecules in the critical region,
and to very large differences between the molar volumes of the pure components at low temperatures. The results were also
fitted with the Redlich–Kister polynomial equations and the recently proposed Herráez correlation equation. Comparisons between
the two models at different temperatures and number of parameters are discussed. We note that, in this system where the shear
viscosity η as a function of mole fraction (x1) of IBA presents a maximum, experimental data are in agreement with the two correlation models when more than three parameters
are employed, especially for temperatures far from the critical temperature. 相似文献
AbstractThe surface properties of the mixtures of zwitterionic surfactants derived from olive oil (carboxylbetaine-OCB and sulfobetaine-OSB) and anionic surfactant-sodium dodecylbenzene sulfonate (SDBS) at different mole fractions were investigated by surface tension measurement. The influences of the addition of inorganic salts (NaCl, MgCl2) on the surface activities in OCB/SDBS and OSB/SDBS systems were also studied. The result shows that the two mixed systems possess lower CMC values and higher surface activities over all mole fractions studied than their individual components. Meanwhile, the noticeable synergistic interactions of OCB/SDBS and OSB/SDBS were determined by the micelle interaction parameter (βm) according to regular solution theory. It is observed that the mixed OCB/SDBS system at αOCB?=?0.6 and the mixed OSB/SDBS system at αOSB?=?0.6 exhibit the strongest synergism. In addition, the binary surfactant mixtures performed better surface activities upon addition of inorganic salts and the different valence state of mental ions of the inorganic salts had different surface ability effect on the mixed system: Mg2+?>?Na+. 相似文献
Summary: Quartz crystal microbalance with dissipation monitoring (QCM‐D) is employed to determine the effect of salt on the volume phase transition of thermoresponsive polymer brushes. Changes in mass and viscoelasticity of poly(N‐isopropylacrylamide) (PNIPAM) layers grafted from a QCM‐D crystal are measured as a function of temperature, upon contact with aqueous solutions of varying salt concentrations. The phase‐transition temperature of PNIPAM brushes, TC,graft, quantified from the QCM‐D measurements is found to decrease as the concentration of salt is increased. This phenomenon is explained by the tendency of salt ions to affect the structure of water molecules (Hofmeister effect). However, in contrast to the linear decrease in phase‐transition temperature upon increasing salt concentration observed for free PNIPAM, the trend in TC,graft for PNIPAM brushes is distinctively non‐linear.
Schematic representation of the effect of salt concentration on the phase transition behavior of thermoresponsive polymer brushes. 相似文献
The purpose of this study was to conduct a thermal analysis of the hydrolysis and degradation behavior of biodegradable polymers
and bio-composites at 50°C and 90% relative humidity (RH). With increasing hydrolysis time, the thermal stability and degradation
temperature of polybutylene succinate (PBS) slightly decreased. The glass transition temperature (Tg) and melting temperature (Tm) of PBS and the anti-hydrolysis agent treated PBS did not vary significantly with increasing hydrolysis time, whereas those
of the trimethylolpropane triacrylate (TMPTA)-treated PBS slightly increased. With increasing hydrolysis time, the storage
modulus (E’) values of the bio-composites decreased, whereas those of the TMPTA treated bio-composites slightly increased. Also, the
tan values of the anti-hydrolysis agent and TMPTA treated PBS-BF bio-composites were slightly lower than those of the non-treated
bio-composites, due to the reduction in their degree of hydrolysis. The tanδmax peak temperature (Tg) of the anti-hydrolysis agent treated bio-composites was not significantly changed, whereas that of the TMPTA treated bio-composites
was increased. 相似文献
In this study, the thermal properties of agro-flour-filled polybutylene succinate (PBS) bio-composites were investigated. PBS is one of the biodegradable polymers made from the condensation reaction of glycols and dicarboxylic acid and is naturally degraded by natural soil burial system. The thermal properties of the bio-composites were analyzed according to the agro-flour content and mesh size. On increasing agro-flour content, the thermal stability, degradation temperature and derivative thermogravimetric curve (DTGmax) temperature of the bio-composites decreased while the ash content increased. The thermal degradation of the bio-composites was not affected by agro-flour mesh size. The glass transition (Tg) and melting (Tm) temperatures of the bio-composites were not significantly changed. The storage modulus (E’) of the bio-composites was higher than that of neat PBS, because the incorporation of agro-flour increased the stiffness of the bio-composites. At higher temperatures, E’ of the bio-composites decreased due to the increasing viscosity and chain mobility of neat PBS. The thermal properties of bio-composites have an important effect on the manufacturing system and application methods. 相似文献
We have studied the temperature dependence of the viscosity of some polymeric materials by using both, the bond-strength-coordination
number fluctuation model and the random walk model. The results reveal that both models show an excellent agreement with the
experimental data. For the random walk model, two equations corresponding to two temperature regimes (low-T and high-T) separated by the critical temperature Tc, which is difficult to determine, are needed to describe the temperature dependence of the viscosity of a fragile system,
whereas for the bond-strength-coordination number fluctuation model, a single equation with clear physical meaning describes
the temperature dependence of the viscosity of both, the fragile and strong systems. We have also studied the relationship
between the normalized temperature range of cooperativity and the fragility index. A theoretical expression for the relationship
has been derived based on the bond-strength-coordination number fluctuation model. The comparison with the experimental data
shows a good agreement, leading to the conclusion that the kinetic properties of glass forming liquids and the cooperativity
of molecular relaxations are correlated. 相似文献